Caffeine Positively Modulates Ferritin Heavy Chain Expression in H460 Cells: Effects on Cell Proliferation.

Both the methylxanthine caffeine and the heavy subunit of ferritin molecule (FHC) are able to control the proliferation rate of several cancer cell lines. While caffeine acts exclusively as a negative modulator of cell proliferation, FHC might reduce or enhance cell viability depending upon the different cell type. In this work we have demonstrated that physiological concentrations of caffeine reduce the proliferation rate of H460 cells: along with the modulation of p53, pAKT and Cyclin D1, caffeine also determines a significant FHC up-regulation through the activation of its transcriptional efficiency. FHC plays a central role in the molecular pathways modulated by caffeine, ending in a reduced cell growth, since its specific silencing by siRNA almost completely abolishes caffeine effects on H460 cell proliferation. These results allow the inclusion of ferritin heavy subunits among the multiple molecular targets of caffeine and open the way for studying the relationship between caffeine and intracellular iron metabolism.

Introduction

The methylxanthine caffeine is a natural alkaloid present in significant amounts in various common beverages such as tea, cocoa, coffee and coke. The caffeine pharmacological actions have long been known, in particular its ability to increase the rate of metabolism [1]. The long list of effects induced by caffeine includes, among others: i) inhibition of alkaline phosphatase [2] and phosphodiesterase activities [3, 4], ii) antagonistic effects on adenosine receptors [5], iii) modification of intracellular calcium levels [6] iv) inhibition of phosphatidylinositol-3kinase (PI3K) activity [7]. Moreover, pharmaceutical companies are currently exploiting caffeine analgesic activity as an additive in various drugs.

In vitro, caffeine is known to strongly reduce cell proliferation activity: the inhibition of cell growth is associated in pancreatic cancer cells and in neuroblastoma cells with cell cycle arrest and induction of apoptosis [8, 9]. Caffeine can also modulate cell proliferation without inducing apoptosis, as it happens in JB6 C141 mouse epidermal cells [10].The anti-proliferative activity of caffeine has been extensively investigated in cancer cell lines and some key caffeine-target molecules have been identified [11]. On the other hand, some discrepancies still remain among various reports that might be attributed to the utilization of different experimental cellular models or to the wide range of drug concentrations utilised, ranging from micro- to milli-molar.

In the cell, iron availability is essential for virtually all metabolic activities, from respiration and macromolecule biosynthesis to DNA replication and cell growth [12].At the same time, free iron is toxic due to its ability to induce the formation of reactive oxygen species (ROS) [13].The task of keeping intracellular iron in a non-toxic and bioavailable form is carried out by ferritin, a450 kDa globular protein localized, in eukaryotes, in cytoplasm, nucleus and mitochondria [14].

In the cytoplasmic ferritin, 24 subunits of heavy (FHC, FTH) and light (FLC, FTL) type co-assemble to form a nano-cage structure with a central cavity where the iron atoms are stored [15].

The two subunits play different and critical roles towards intracellular iron metabolism: FHC performs a ferroxidase activity, indispensable to convert iron in a non-toxic form, while FLC is devoted to the long-term iron storage [16]. FHC and FLC are encoded by two different genes, whose expression is controlled at multiple levels, from the transcription to the translational efficiency [17].Along with its role in iron metabolism, it has been shown that FHC might be involved in other non-iron mediated cellular pathways [18, 19]. In our previous work, we demonstrated that FHC-silencing is accompanied, in K562 cells, by an increased expression of a repertoire of miRNAs and by a reduced proliferation rate [20]; in human metastatic melanoma cells FHC-knockdown determines, in vitro, decreased cell growth and adhesion activity and, in vivo, a consistent reduction of tumour growth [21].

In this study, using the human lung cancer cell line H460, we identified a previously undiscovered effect of caffeine as a positive modulator of FHC gene expression. Moreover, it appears that the anti-proliferative effects of caffeine on H460 cells are largely mediated by the FHC intracellular amounts.

Materials and Methods

Cell culture

H460 cells, a human cell line established from the pleural effusion of a 53-year-old female with large cell lung cancer (ATCC number:HTB-177) and SKOV3 human ovarian cancer cells (ATCC number: HTB-77) were cultured in RPMI 1640 medium supplemented with 10% fetal bovine serum and antibiotics (Sigma Aldrich, St. Louis, Missouri, USA) at 37°C in an atmosphere of humidified air containing 5% CO2.

Western Blotting Analysis

Protein extractions were peformed on H460 wild-type, H460siRNA, H460siFHC, H460pcDNA or H460pcFHC treated or not with 20, 40 and 80μM caffeine (Sigma Aldrich) and SKOV3siRNA, SKOV3siFHC, SKOV3pcDNA or SKOV3pcFHC treated or not with 80μM caffeine. Methods for protein extraction and blots preparation have been previously published [20]. Briefly, H460 cells were lysed in ice-cold radioimmunoprecipitation assay (RIPA) buffer containing protease inhibitors (20 mmol/L Tris, 150 mmol/L NaCl, 1% Igepal, 0.5% sodium deoxycholate, 1 mmol/L EDTA, 0.1% SDS, 1 mmol/L phenylmethylsulfonyl fluoride, 0.15 units/mL aprotinin, and 10 μmol/L leupeptin) (Sigma Aldrich) and after removal of the cell debris by centrifugation (12,000×g, 30 min), the protein content was determined by the Bio-Rad protein assay according to the manufacturer's instructions (Bio-Rad Laboratories, Hercules, California, USA). The nitrocellulose membranes were incubated overnight at 4°C with the following antibodies: (a) rabbit polyclonal anti-Cyclin D1 (H-295) (sc-753,1:1000; Santa Cruz Biotechnology, Texas, USA), (b) anti-phospho-AKT (Ser473) (#4058, 1:500; Cell Signaling Technology, Danvers, MA, USA), (c) rabbit polyclonal anti-AKT (#9272, 1:500; Cell Signaling Technology), (d) mouse monoclonalanti-p53(sc-263, 1:1000; Santa Cruz Biotechnology), (e) rabbit polyclonal anti-FHC (H-53)(1:200; sc-25617, Santa Cruz Biotechnology).

Membranes were incubated with horseradish peroxidase (HRP)-conjugated secondary antibodies (1:3000 Cell Signaling) and immunoreactive bands were visualized with the ECL Western blotting detection system (Santa Cruz Biotechnology). To ensure equal loading of proteins was used a goat polyclonal anti-γ-Tubulin antibody (C-20) (1:3000; sc-7396, Santa Cruz Biotechnology).

RNA extraction and semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR)

Total RNA was extracted from H460 and SKOV3 cells with the TRizol RNA isolation system (Thermo Fisher Scientific, Waltham, Massachusetts, USA). All the RNA samples were DNase-1 treated (Thermo Fisher Scientific), and purity and integrity of the RNA was checked spectroscopically and by gel electrophoresis before use. One microgram of RNA from each sample was used for RT-PCR with a reverse transcriptase system kit (Thermo Fisher Scientific). Quantitative PCR was performed using SYBR Green universal PCR master mix (Bio-Rad Laboratories) using the following specific primers: FHC forward, 5’-cat caa ccg cca gat caa c-3’; FHC reverse, 5’-gat ggc ttt cac ctg ctc at-3’. Each sample was normalized to its glyceraldehyde 3-phosphate dehydrogenase (GAPDH) content. Relative gene expression for FHC mRNA was normalized to a calibrator that was chosen to be the basal condition. Results were calculated with the ΔΔCt method and expressed as n-fold differences in FHC gene expression relative to GAPDH and calibrator and were determined as follows: where the parameter Ct (threshold cycle) is defined as the fractional cycle number at which the PCR reporter signal passes a fixed threshold. ΔCt values of the sample and calibrator are determined by subtracting the average Ct value of the transcript under investigation from the average Ct value of the GAPDH gene, for each sample.

MTT assay and direct cell counting

3-[4,5-Dimethylthiaoly]-2,5-diphenyltetrazolium bromide (MTT) (Sigma Aldrich) assay was performed to detect proliferation of H460 and SKOV3 cells untreated or treated with caffeine at different doses or transiently silenced (H460siFHC and SKOV3siFHC) or overexpressed for FHC (H460pcFHC and SKOV3pcFHC) for 48 h. Cell proliferation analysis after treatment with caffeine was performed on starved cells that were obtained culturing proliferating cells with RPMI 1640 without FBS for 24h. A total of 4.5x103 cells/well were seeded into 96-well plate and let to grow for 48h in RPMI medium. There were octuplicates for each cell type. Fresh MTT (Sigma Aldrich), re-suspended in PBS was added to each well. After 4h incubation, culture medium was discarded and replaced with 200μL of isopropanol. Optical density was measured at 490 nm in a spectrophotometer. Each experiment was performed in triplicate. For direct cell counting, cells were seeded at 200x103 cells/well; during the exponential phase of growth, cells were trypsinized and then washed in 10 mL of 1X PBS by centrifugation at 1000 rpm x 5 min. Subsequently, cell pellets were resuspended in 5 mL of fresh PBS and pipetted vigorously to disperse any clumps. 50 μL of sample was mixed with 50 μL of 0.4% trypan blue by gently pipetting, and then 20 μL of the mix were loaded into the Bürker chamber. Counts were performed by triplicate under a 10× objective according to the standard methodology.

Determination of DNA fragmentation

To determine the occurrence of DNA fragmentation, total DNA was extracted from control and caffeine treated (20, 40, 80, 120μM) (48h)H460 cells and DNA laddering assay was performed as previously described [22]. Equal amounts (4 μg) of DNA were analyzed by electrophoresis on a 2% agarose gel stained with Ethidium Bromide (Sigma Aldrich).

Transfections and transductions of H460 and SKOV3 cells

H460 and SKOV3 cells were plated into 60-mm dishes, at 5 × 105 cells, for protein extraction and into 96-well plates, at 2 × 104 cells, for proliferation assay, and used for transfection 24h later. In particular FHC silencing was performed using two different small interfering RNA: a pre-cast siFHC (Thermo Fisher) and a home-made siFHC provided by Professor Sonia Levi from the Vita-Salute San Raffaele University Milano (Italy) while over-expression of FHC was performed using the expression vector containing the full length of human FHC cDNA (pcFHC). Transfections were performed using the Lipofectamine 2000 reagent accordingly to the manufacturer's recommendations (Thermo Fisher Scientific). H460 cells were also stably transduced with a lentiviral DNA containing either an shRNA that targets the 196–210 region of the FHC mRNA (sh29432) (H460shFHC) or a control shRNA without significant homology to known human mRNAs (H460shRNA). FHC-specific knockdown and over-expression was checked by Western analysis, RT-PCR and qPCR of proteins and mRNAs extracted from cells stably transduced or transiently transfected for 48h.

Luciferase activity assay

Plasmids were used at the concentration of 4,5μg/well for the FHC promoter-luciferase reporter plasmid (5’HPM/pLUC) and of 0.2μg/well for PRLSV40 Renilla luciferase control reporter vector (Promega Italia S.r.l., Milano, Italy) and transfected using Lipofectamine2000 reagent.

5’HPM/pLUC was generated by cloning a 170 bp DNA fragment containing a cis element responsive to cAMP into the mammal pGL3-Basic expression vector (Promega Italia S.r.l.). DNA fragments were generated from the 5’HPM/CAT previously described [23] using the restriction enzymes Sac1 and HindIII (BioLabs, Ipswich, Massachusetts, USA).

Six hours after transfection, the medium was removed and replaced with serum free medium supplemented with the indicated concentrations of caffeine. Cells were lysed using the passive lysis buffer (Promega Italia S.r.l.) and enzymatic activities were assayed using the Dual-Luciferase Reporter Assay system (Promega Italia S.r.l.) following the manufacturer's instructions. Firefly luciferase values of each sample were normalized by renilla activity and data were reported as relative light units (RLU) values.

ROS detection

ROS were determined by incubating H460siRNA and H460siFHC with the redox-sensitive probe 2’-7’-DCF (CM-H2CFDA; Molecular Probes). In detail, 1 × 106 H460 cells were plated in 96-well plates and incubated with Hanks balanced saline solution (HBSS), 10 mm glucose and 20μm DCF for 15 min at 37°C. After two cyclewashes, cells were maintained in HBSS supplemented with 10 mm glucose. Fluorescence was revealed, after 60 min incubation, using the Victor3 Multilabel Counter (Wallac, Perkin Elmer) at 485 nm and 535 nm for excitation and emission, respectively. Results were normalized on protein concentration evaluated by the bicinchoninic acid (BCA) method (Thermo Fisher Scientific).

Data analysis and statistical methods

All experiments were conducted at least two times, and the results were from representative experiments. Data were expressed as mean values +/- SD. The Student’s t-test was used to compare the groups. p≤0.05 were considered statistically significant.

Results

Caffeine reduces H460 cell proliferation

Among the various effects induced by caffeine, its inhibitory role on cell proliferation has been known for a long time, although with variable results [11]. We analysed the effects of a 48 hours caffeine treatment at 20, 40 and 80μM concentration on the proliferation of the human lung cancer H460 cell line. The results of the MTT assay, reported in Panel A of Fig 1, show that the proliferation rate of H460 cells was reduced in a dose-dependent manner by caffeine treatment up to 60% at 80μM concentration. The reduction of H460 proliferation rate upon 80μMcaffeine treatment was also confirmed with direct cell counting (Panel B of Fig 1). Next, we evaluated the expression of key proteins involved in the control of cell proliferation. Panel C of Fig 1 shows a reduced cyclinD1 (CCND1) protein content with a concomitant increase of p53 in the 24h-treated H460 cells. Caffeine treatment also severely impaired AKT phosphorylation, as shown in Panel D of Fig 1. These effects were dose-dependent, again reaching the maximum effect at 80μM concentration. None of the utilized concentrations of caffeine was able to induce terminal apoptosis (i.e. fragmentation of genomic DNA), as shown by the assay reported in Panel E of Fig 1.

Fig 1

Caffeine reduces H460 cell proliferation.

(A) Cell proliferation was assessed using the MTT method as indicated in the Materials and Methods section. Final results represent mean ± SD of three independent experiments each performed in triplicate (*p < 0.05 of each caffeine concentration compared with NT-untreated cells). (B) Direct cell counting of NT-untreated and 80μM caffeine-treated cells. The results are the mean of two independent experiments (*p < 0.05 compared with NT-untreated cells). (C) and (D)Western blot analysis for CCND1, p53 and pAKT were performed on 50μg of total proteins. Blots are representative of three independent experiments. γ-Tubulin and AKT were used as loading controls. (E) DNA was extracted from cells and analyzed on a 2% agarose gel as described in Materials and Methods. The image is a representative experiment.

FHC intracellular amounts modulate H460 cell proliferation

We have recently demonstrated that FHC intracellular amounts are able to modulate cell proliferation in the transformed cell lines K562, MM07 and SKOV3 [20, 21, 24]. Here, we either overexpressed or silenced FHC to evaluate the effects on H460 cell proliferation. Transient transfection with an FHC expression vector (H460pcFHC) gave rise to an approximately 8-fold increase of FHC both at mRNA and protein levels, as shown in Panels A and B of Fig 2. The increased amount of FHC was associated with an approximately 50% reduction in cell proliferation activity, as demonstrated by the MTT assay reported in Panel C of Fig 2. This reduction was accompanied by a decrease in CCND1 protein content, by a reduced AKT phosphorylation and by a significant increase in p53 expression levels in comparison with that of control cells (H460pcDNA) (Panel D of Fig 2).

Fig 2

FHC over-expression reduces cell proliferation.

(A) Western blot analysis for FHC was performed on 50μg of total proteins extracted from H460 over-expressing FHC (H460pcFHC) and H460 control cells (H460pcDNA). γ-Tubulin was used as a loading control. Blots are representative of three independent experiments. The graph representsthe mean of the optical densities (*p < 0.001 compared with control cells). (B) Real-time PCR analysis of FHC mRNA levels was performed on total RNA from H460pcFHC and H460pcDNA. Results are representative of three different experiments (* p<0.05 compared with H460pcDNA). (C) Cell proliferation was assessed using the MTT method as indicated in the Materials and Methods section. Final results represent mean ± SD of three independent experiments each performed in octuplicate (*p< 0.05 compared with H460pcDNA). (D) Western blot analysis for CCND1, p53 and pAKT were performed on 50 μg of total proteins extracted from H460pcFHC and H460pcDNA. Blots are representative of three independent experiments. γ-Tubulin and AKT were used as loading controls.

To further strengthen these findings, cell proliferation rate and CCND1, p53 and pAKT expression levels were studied in H460 cells in which FHC has been transiently silenced with a home-made FHC siRNA kindly provided by Prof. Sonia Levi (H460siFHC) and compared with control cells transfected with a siRNA without any significant homology to known human RNA (H460siRNA). siRNA interference reduced FHC protein and mRNA amounts by about 60% (Panels A and B of Fig 3) and was accompanied by a slight increase in ROS content as determined by a quantitative analysis performed with 2’-7’-DCF (Panel C of Fig 3). Under these conditions, the proliferation rate of H460siFHC cells was increased by about 50%, as shown in Panel D of Fig 3. Accordingly, CCND1 and pAKT were up-regulated, while p53 was consistently down-modulated (Panel Eof Fig 3). We also transiently silenced the cells with a pre-cast siRNA, achieving an increased cell proliferation comparable to that obtained with the home-made siRNA (S1 Fig). Moreover, to definitively rule out any off-target effect of the siRNA, we analysed the proliferation rate of stably FHC-silenced H460 cells (H460shFHC) (FHC protein levels in silenced and control cells are shown in Panel F). Panel G shows that the stable knock-down of FHC is accompanied by a 50% increase in the proliferation rate.

Fig 3

FHC silencing increases cell proliferation.

(A) Western blot analysis for FHC was performed on 50μg of total proteins extracted from FHC-silenced H460 (H460siFHC) or from H460 control cells (H460siRNA). Blots are representative of three independent experiments. γ-Tubulin was used as a loading control. The graph represents the mean of the optical densities (*p < 0.05 compared with H460siRNA). (B) Real-time PCR analysis of FHC mRNA amounts performed on total RNA from H460siFHC and H460siRNAcells. Results are representative of three different experiments (*p<0,05 compared with H460siRNA). (C) H460siRNAand H460siFHCcells were incubated for 15 min with 20 μM of 2’-7’-DCF and washed with HBSS solution. Fluorescence was measured at 485 nm and 535 nm after60 min. (D) Cell proliferation was assessed using the MTT method as indicated in the Materials and Methods section. Final results represent mean ± SD of three independent experiments each performed in octuplicate (*p< 0.05 compared with H460siRNA). (E) Western blot analysis for CCND1, p53 and pAKT were performed on 50μg of total proteins extracted from H460siFHC and H460siRNA. Blots are representative of three independent experiments. γ-Tubulin and AKT were used as loading controls.(F) Western blot analysis for FHC was performed on 50μg of total proteins extracted from FHC-stably silenced H460 (H460shFHC) or from H460 control cells (H460shRNA). Blots are representative of three independent experiments. γ-Tubulin was used as a loading control. The graph represents the mean of the optical densities (*p < 0.05 compared with H460shRNA). (G) Cell proliferation of stably silenced cells was assessed using the MTT method. Final results represent mean ± SD of three independent experiments each performed in octuplicate (*p< 0.05 compared with H460shRNA).

Overall, these data indicate that in H460 cells the heavy ferritin subunit negatively regulates cell growth.

Caffeine increases FHC expression in H460 cells

Both caffeine and FHC-overexpression inhibit H460 cell growth. We wondered whether the two observed phenomena might be related; to this, we first evaluated if caffeine treatment is able to modify FHC expression. Western blot, RT-PCR and qPCR were performed in triplicate on independent protein extracts and RNAs from caffeine-treated and untreated cells. The results, reported in Panels A, B and C of Fig 4, highlighted a dose-dependent increase in FHC expression following caffeine treatment.

Fig 4

Caffeine increases FHC expression.

(A) Western blot analysis for FHC was performed on 50μg of total proteins extracted from H460 untreated or treated with caffeine at the indicated concentrations. The blot is representative of three independent experiments. γ-Tubulin was used as a loading control. The graph represents the mean of the optical densities. (*p < 0.05of each caffeine concentration compared with NT-untreated cells). (B-C) RT-PCR and Real-time PCR analysis of FHC mRNA amounts performed on total RNA from H460 untreated or treated with caffeine at the indicated concentrations. Results are representative of three different experiments (*p < 0.05 of each caffeine concentration compared with NT-untreated cells). (D) H460 cells were transiently transfected using 4,5μg/well of the FHC promoter-luciferase reporter plasmid (5’HPM/pLUC) and treated with the indicated doses of caffeine. Data were normalized to the co-expressed PRLSV40 Renilla luciferase control reporter vector and expressed as RLU. Results represent the mean ± SD of data from three independent experiments, each performed in triplicate. (*p < 0.05 of each caffeine concentration compared with NT-untreated cells).

FHC expression is controlled at multiple levels, both in cell nucleus and cytoplasm [12]. To evaluate if caffeine acts at transcriptional level, the-170 bp FHC proximal promoter region was cloned into the pGL3-Basic vector (5’HPM/pLUC). The results of three independent transient transfection assays indicate that caffeine induced an increased transcriptional activity driven by the FHC promoter, as shown in Panel D of Fig 4.

Remarkably, the 80μM concentration was able to induce FHC transcription to a level even greater than that induced by c-Jun, a known positive trans-acting factor of the FHC promoter [25].

FHC is required for caffeine modulation of H460 proliferation

In order to evaluate the role of FHC in caffeine inhibitory effect on cell proliferation,H460 cells transiently silenced for FHC were exposed to increasing doses of caffeine. Panel A of Fig 5 shows that the FHC-siRNA was indeed able to abolish caffeine-induced FHC expression on a wide range of drug concentrations. Next, we analysed by MTT assay and by direct cell counting cell viability of FHC silenced and unsilenced cells after caffeine treatment. The results of two different experiments, shown in Panels B and C of Fig 5, indicate that in FHC-silenced cells caffeine was no longer able to down-regulate the proliferation rate; accordingly, CCND1, p53 and pAKT were unchanged in the H460siFHC cells upon the drug treatment (Panel D). These findings strongly suggesta central role for FHC in mediating the anti-proliferative effects of caffeine in H460 cells.

Fig 5

FHC is required for caffeine modulation of H460 proliferation.

(A) Real-time PCR analysis of FHC mRNA amounts was performed on total RNA from H460siFHC and H460siRNA cells treated with the indicated doses of caffeine. Results are representative of two different experiments (*p < 0.05 of each caffeine concentration compared with untreated cells; NS not significant). (B) Cell proliferation was assessed using the MTT method on H460siFHC and H460siRNAcells treated with caffeine at the indicated doses. Final results represent mean ± SD of three independent experiments each performed in triplicate (*p < 0.05 of each caffeine concentration compared withuntreated cells; NS not significant). (C) Direct cell counting of H460siFHC and H460siRNAcells treated with caffeine at the indicated doses. Final results represent mean ± SD of two independent experiments (*p < 0.05 of each caffeine concentration compared with untreated cells; NS not significant). (D) Western blot analysis forCCND1, p53 and pAKT were performed on 50μg of total proteins extracted from H460siFHC and H460siRNA treated with 80μM caffeine or untreated. γ-Tubulin and AKT were used as loading controls.

Finally, we asked if the relationship between FHC and caffeine was restricted to a specific cell-type or it might represent a more general phenomenon. To this, we transiently overexpressed FHC in the human ovarian cancer cells SKOV3 and analysed the effects on cell proliferation. The results highlight that a five-fold increase in FHC intracellular amounts (Panels A and B of Fig 6) was accompanied by an approximately 30% reduction of SKOV3 cell proliferation rate (Panel C). Conversely, down-regulation of FHC in SKOV3 cells is accompanied by an enhancement of the proliferative activity [24]. Moreover, as it occurs in H460 cells, 80μM caffeine treatment for 48h induced a consistent accumulation of FHC protein exclusively in the control cells, while leaving unaltered the FHC levels in the FHC-silenced cells (Panel D of Fig 6). MTT assay (Panel E) and direct cell counting (Panel F) demonstrated that caffeine decreases the proliferation rate in the control cells, albeit less dramatically than in H460 cells, while FHC silencing almost totally counteracted the drug effect.

Fig 6

FHC is required for caffeine modulation of SKOV3 cells proliferation.

(A) Real-time PCR analysis of FHC mRNA amounts was performed on total RNA from SKOV3pcDNA and from SKOV3pcFHCcells. Results are representative of two different experiments (*p < 0.05compared with control cells. (B) Western blot analysis for FHC was performed on 50μg of total proteins extracted from SKOV3pcDNA and from SKOV3pcFHC cells. γ-Tubulin was used as a loading control. (C) Cell proliferation was assessed using the MTT method on SKOV3pcDNA and SKOV3pcFHCcells. The results represent mean ± SD of two independent experiments (*p < 0.05 compared with control cells). (D) Western blot analysis for FHC was performed on 50 μg of total proteins extracted from SKOV3siRNA and from SKOV3siFHC cells treated with 80μM caffeine or untreated. γ-Tubulin was used as a loading control. (E) Cell proliferation was assessed using the MTT method on SKOV3siFHC and SKOV3siRNAcells treated with caffeine at the indicated doses. Final results represent mean ± SD of two independent experiments each performed in triplicate (*p < 0.05 of each caffeine concentration compared with untreated cells; NS not significant). (F) Direct cell counting of SKOV3siFHC and SKOV3siRNA cells treated with caffeine at the indicated doses. Final results represent mean ± SD of two independent experiments (*p < 0.05 of each caffeine concentration compared with untreated cells; NS not significant).

Discussion

Both caffeine and FHC play critical functions in the control of cell proliferation [11, 20, 21]. The negative regulation of proliferation achieved by caffeine has a long history and is confirmed by a number of studies performed in various cell culture and in vivo models [26, 27]. The molecular bases of this phenomenon have been deeply investigated, leading to the identification of several key target molecules regulated by caffeine. For instance, Alao et al. have demonstrated that a 5mM treatment suppresses CCND1 expression and reduces proliferation in several cell lines [28]; Al-Ansari et al. investigated the modulation of p53 and pAKT expression levels in cells exposed to 200μM caffeine [29], while the effects on PI3Ks have been exploited by Foukas et al [30]. Caffeine might induce cell cycle arrest with or without inducing apoptosis [31]. To our knowledge, caffeine effects on the human lung cancer H460 cells have not yet been investigated: our results allow their inclusion to the long list of transformed cells whose proliferation can be modulated by caffeine.

In the majority of the in vitro studies, caffeine is used at milli-molar concentration to control proliferation of transformed cells. However, treatment with these concentrations may not be physiologically applicable to clinical settings [32]. Our data indicate that H460 cells are strongly responsive to physiological doses of caffeine corresponding to the average daily consumption of coffee (up to 4 cups) [33].

In the recent years, the body of data concerning FHC and cell growth is steadily increasing and demonstrates that FHC, unlike caffeine, might act either as positive or negative modulator of cell proliferation, most probably depending on the different cell types. In HeLa cells, two different groups have reported that FHC over-expression strongly reduces cell growth [34, 35], while in human metastatic melanoma and in K562 cells this effect was linked to FHC-knockdown [21, 20]. Here we demonstrate that FHC over-expression in H460 cells mimics the effects of caffeine, acting as negative regulator of cell proliferation via modulation of p53, AKT and CCND1 proteins. Interestingly, transient FHC knockdown by siRNA almost completely abolishes the anti-proliferative effects of caffeine in H460 cells, and prevents the caffeine-mediated effects on the key molecules CCND1, p53 and pAKT. These data suggest that FHC is a central hub in the molecular events triggered by caffeine leading to modulation of cell growth. Moreover, the role of FHC is not restricted to the H460 cells, since comparable results were also reproduced in SKOV3 ovarian cancer cells, suggesting the existence of a more general phenomenon.

These findings prompted us to investigate the existence of a possible relationship between FHC and caffeine. Indeed, increasing doses of caffeine induce a parallel enhancement of FHC mRNA and protein amounts in H460 cells. This so far undiscovered caffeine effect on FHC gene expression is largely due to higher transcription efficiency, driven by the proximal promoter region. A massive wealth of data, both in vivo and in vitro, demonstrates that many of the caffeine effects on different metabolic pathways are mediated by its ability to inhibit cyclic nucleotide phosphodiesterase, the enzyme responsible for the conversion of cyclic AMP to AMP [3, 4]. cAMP is a positive modulator of FHC gene transcription in a variety of cell types [36-38], acting on a promoter cis-element called B-box [39]. The B-box is included in our luciferase construct, strongly suggesting that cAMP levels in H460 caffeine-treated cells might mediate the FHC transcriptional activation.

A number of studies have shown that the heavy chain of ferritin is a multifunctional protein implicated in several cellular pathways, including differentiation [40], neoplastic transformation [41], chemokine signalling [18], control of proper protein folding [42] and cell proliferation [20, 21]. On the other hand, the FHC main role is still represented by its capacity to buffer intracellular free iron through its ferroxidase activity. The dual nature of the molecule makes it difficult to dissect the molecular events brought on by FHC overexpression or silencing, that is if and how they are exclusively related to perturbations of the intracellular iron metabolism ultimately leading to an altered redox status. In H460 cells, Chauvorachote and Luanpitpong demonstrated that subchronic treatment with FeSO4induced an accumulation of hROS and promoted the cell growth [43]. According with these results, we found a slight increase in ROS content in the H460 cells silenced for FHC where the cell proliferation rate is enhanced. We believe that this finding further confirms that the role FHC plays in modulating cell growth is, at least partially, mediated by perturbation of iron/redox status of the cell. Further and more focused analyses are needed to definitively address this point.

Taken all together, our results allow the inclusion of ferritin heavy chain among the caffeine target molecules and open new perspectives on the caffeine effects on intracellular iron metabolism.

FHC silencing, through a pre-cast siRNA, increases cell proliferation of H460 cells.

Cell proliferation was assessed using the MTT method on H460precast-siFHC and H460cntr cells treated with caffeine at the indicated doses.

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