Down-regulated microRNA-124 expression as predictive biomarker and its prognostic significance with clinicopathological features in breast cancer patients.

BACKGROUND: MicroRNAs (miRNAs) have been documented as playing important roles in cancer development. In this study, we investigated to clarify the clinicopathological significance and prognostic value of miR-124 in breast cancer.
METHODS: Quantitative Real-time PCR method was used to assess the expression levels of miR-124 in breast cancer patients and the association of miR-124 expression levels with the clinicopathological characteristics in breast cancer patients. Survival and Multivariate Cox proportional hazards model analysis was used to evaluate whether the miR-124 expression level and various clinicopathological characteristics were independent prognostic marker for breast cancer patients.
RESULTS: We found that the lower expression of miR-124 in breast cancer specimens compared with corresponding adjacent normal breast tissues P < 0.05. Results showed that decreased expression of miR-124 was significantly related to advanced clinical stage (stage III and IV) (P = 0.021) and positive lymph node-metastasis (P = 0.011). Patients with low expression of miR-124 had significantly shorter overall survival (70.2 %) than patients who had cancers with high miR-124 expression (29.8), (logrank test P = 0.021). Moreover, Multivariate Cox proportional hazards model analysis indicated that lowr miR-124 expression was found to be independently linked to poor survival of patients with breast cancer and other factors were not significantly associated with survival of patients.
CONCLUSION: Our data suggested that decreased expression of miR-124 has prognostic value in breast cancer and may serve as a prognostic marker for breast cancer, and also downregulation of miR-124 was inversely associated with the lymph node metastasis in breast cancer.

Background

Breast cancer is cause of cancer related mortality among women worldwide [1, 2]. Results of molecular research in breast cancer patients may be useful in order to improve the management of patients and also it can help to identify the therapeutic effect of these mechanisms. MicroRNAs (miRNAs) are small, non-coding RNA molecules that are involved in post-transcriptional gene regulation,and functions in RNA silencing and post-transcriptional regulation of gene expression [3-6]. As matter of fact, these small RNAs regulate gene expression by directing their target mRNAs for degradation or translational repression [7]. Thereby, controlling a wide range of biological functions such as cellular proliferation, differentiation, and apoptosis. With the advent of miRNA expression profiles, significant efforts have been done to evaluate the correlation of miRNAs expression with tumor prognosis [8, 9]. It is worth noting that alteration in microRNA expression may play a critical role in tumorigenesis and cancer progression [10]. These differences in expression of miRNAs can be useful (as biomarkers) for breast cancer progression and clinical course, as well as may play a critical role in the transformation process [10-12].

Previous studies have suggested that miR-124 was epigenetically silenced in various types of cancers [13, 14]. These studies highlighted an important role of miR-124 in the regulation of invasion and metastasis in breast cancer cells, and suggest a potential application of miR-124 in prognosis prediction and cancer treatment. Li et al. [3] demonstrated that miR-124 was downregulated in breast cancer and might act as a tumor suppressor in breast cancer via the regulation of FLOT1.

In the present study, we investigated the role of miR-124 in breast cancer and the clinicopathological significance and prognostic value of miR-124.

Methods

Patients

A total of 100 breast cancer tissues and adjacent normal tissues were evaluated after taking the informed consents in current study. All patients underwent breast surgical resection at Tehran between March 2010 and March 2014. None of these patients had received radiotherapy or chemotherapy prior to surgery. The carcinomas and the adjacent normal tissues were snap frozen in liquid and then stored at −80 °C until use. All the specimens were diagnosed by pathologists. None of the patients recruited in current study had undergone preoperative chemotherapy or radiotherapy. Patients’ clinical information stored in a database and was summarized in Table 1.

Table 1

Relationship between miR-124 expression and clinicopathological characteristics of patients

Variables	Number of cases	miR-124expression		P value
		Low	High
Age (years)
<60	58	22	36	0.231
≥60	42	25	17
TNM stage
I + II	68	24	44	0.021
III	32	23	9
Lymph node metastasis
Yes	34	26	8	0.011
No	66	18	48
ER status
Positive	40	24	16	0.41
Negative	60	19	21
PR status
Positive	55	25	30	0.13
Negative	45	26	19
HER2 status
Positive	42	16	26	0.12
Negative	58	34	24

Quantitative real-time PCR

Total RNA and enrichment of small RNA was isolated from fresh samples using the miRVana™ microRNA. Isolation Kit (Applied Biosystems/Ambion, Austin, TX,. USA) according to the manufacturer’s protocol and stored at −80 °C until use. Total RNA from fresh cultured cells was extracted with TRIzol reagent (Invitrogen, Carlsbad, California, USA). Real-time.

Real-time PCR was carried out using an Express SYBR® GreenER qPCRs supermix Universal kit (Invitrogen) on a Rotor-gene 6000 system (Qiagen, Valencia, CA, USA). USA). The relative amount of miR-124was normalized against U6 RNA. In current study, we calculated a ΔCt (target-reference) that is equal to the difference between threshold cycles for miR-124 (target) and those for U6 RNA.

The fold-change between cancer tissues and normal breast tissue control for miR-124 was calculated by the 2ΔΔCt method, in which ΔΔCt = ΔCt (target-reference in tumor samples) - ΔCt (target-reference in normal samples). The relative expression levels of miRNAs in cancer compared to their non-tumorous controls were calculated using the method of 2-ΔΔCt. The primers for miR-124 were used as follows: forward: 5′-GATACTCATAAGGCACGCGG-3′ and reverse: 5′-GTGCAGGGTCCGAGGT-3′.

Statistical analysis

The software, SPSS Version 16.0 for Windows (SPSS Inc., Chicago, IL, USA), was used for analysis. Differences in miR-124 expression between the tumor and normal tissues were analyzed using the Student’s t-test. Moreover, the chi-square test and Fisher’s exact test were used to evaluate the relationships between miR-124 expression level and the clinicopathological characteristics. Differences were considered significant when P < 0.05. Survival curves were plotted by the Kaplan-Meier method and compared by the log-rank test. The survival data were evaluated by multivariate Cox regression analyses.

Ethical approval

All parts of the study were approved by the Institutional Ethical Committee of the First Affiliated Hospital of Tehran Province, and informed consent according to the Declaration of Helsinki was obtained from all participants or their families/surrogates.

Results

To compare the miR-124 expression levels in breast cancer specimens and normal breast tissues, real-time analysis performed. The results have showed that lower expression of miR-124 in breast cancer specimens when compared with corresponding adjacent normal breast tissues P < 0.05.

According to the median level of miR-124, breast cancer patients were classified in to low and high expression groups. 53 cases were assigned to the low miR-14-8b expression group, while 47 cases were classified to the high expression group.

Association of miR-124 expression levels with the clinicopathological outcome

Association of miR-124 expression levels with the clinicopathological characteristics patients with breast cancer are summarized in Table 1. Results showed that decreased expression of miR-124 was significantly related to advanced clinical stage (stage III and IV) (P = 0.021) and positive lymph node-metastasis (P = 0.011).

However, miR-124 expression was not found to be associated with other clinicopathological characteristics including, age (P = 0.231), ER status (P = 0.41), PR status (P = 0.13), and HER2 status (P = 0.12).

Survival analysis in two groups based on their miR-148b expression level

Kaplan-Meier survival analysis and log-rank test demonstrated that patients with low expression of miR-124 had significantly shorter overall survival (70.2 %) than patients who had cancers with high miR-124 expression (29.8), (logrank test P = 0.021).

Multivariate Cox proportional hazards model analysis

Multivariate Cox proportional hazards model analysis was used to evaluate whether the miR-124 expression level and various clinicopathological characteristics were independent prognostic marker for breast cancer patient. The result indicated that lower expression level of miR-124 was independently linked to poor survival of patients with breast cancer and other factors were not significantly associated with survival of patients (Table 2).

Table 2

Multivariate analyses of clinicopathological characteristics by Cox regression model

Variable	Hazard ratio	95 % CI	P-value
Age	1.432	0.861–3.611	0.614
TNM stage	2.021	1.455–9.110	0.011
Lymph node metastasis	2.327	0.952–6.656	0.021
ER status	1.012	0.822–2.521	0.423
PR status	0.871	0.265–2.225	0.551
HER2 status	0.752	0.412–2.043	0.563
miR-124 level	3.753	1.623–10.421	0.021

Discussion

Results of molecular research may improve the management of patients, as well as it is essential to identify powerful prognostic indicator for breast cancer.

It was found that the deregulated miRNAs was correlated with substantial cell physiological and pathological processes and is ultimately involved in tumorigenesis and the tumor progression of many different human cancers. For instance, ectopical expression of miR-148b inhibits the invasion, survival to anoikis, extravasation in breast cancer, and lung metastasis formation of breast cancer cells [15]. In this study, we investigated the role of miR-124 in breast cancer and the clinicopathological significance and prognostic value of miR-124 in breast cancer. In current study, MiR-124 downregulation was significantly related to advanced clinical stage (stage III and IV) and positive lymph node-metastasis in breast cancer patients. Furthermore, the results showed that lower expression of miR-124 in breast cancer specimens when compared with corresponding adjacent normal breast tissues. These results indicated that miR-124 is downregulated in breast cancer, and decreased expression of miR-124 may be responsible for the progression and metastasis of breast cancer. The miR-124 has been reported that might be involved in epigenetic regulation of various tumors, including breast cancer [16, 17]. According to the recent studies, down regulated miR-124 can contribute to lymph node-metastasis and tumor progression in patients with breast cancer [13, 18] and in other cancers patients [14, 17, 19]. Previous studies have suggested that miR-124 was epigenetically silenced in various types of cancers [13, 17]. These studies highlighted an important role of miR-124 in the regulation of invasion and metastasis in breast cancer cells, and suggest a potential application of miR-124 in prognosis prediction and cancer treatment. Li et al., [3] demonstrated that miR-124 might be a tumor suppressor in breast cancer via the regulation of FLOT1. Luciferase assays confirmed that miR- FLOT1 was identified as a direct and functional target of miR-124 that bind to the 3′ untranslated region of FLOT1 and suppress translation. They identified that the FLOT1 gene is as a novel direct target of miR-124, and ectopic expression of miR-124 significantly inhibited FLOT1 [3]. Han et al. [13] found that miR-124 was downregulated in breast cancer and the ectopic expression of miR-124could suppress the invasion and metastatic ability, probably by directly targeting the CD151. It is worth noting that these results indicated an important role for miR-124 in the proliferation and metastasis of different cancers [13].

Kaplan-Meier survival analysis and log-rank test demonstrated that patients with low expression of miR-124 had significantly shorter overall survival than patients who had cancers with high miR-124 expression. Furthermore, multivariate Cox proportional hazards model analysis indicated that low miR-124 expression was independently linked to poor survival of patients with breast cancer and other factors were not significantly associated with survival of patients. Zhang et al. [20] have shown that decreased expression of miR-148b was linked to poor overall survival of patients with hepatocellular carcinoma, indicating the potential role of miR-148b as a prognostic marker in clinical practice. Furthermore, Zheng et al. showed that miR-124 levels were frequently reduced in hepatocellular carcinoma, and this expression level was significantly associated with the patients’ clinical stages and prognoses, as well as, regulated the invasion and migration of hepatocellular carcinoma [14]. In addition, Lv et al., Liang et al. and Han et al. also reported that miR-124 can suppress breast cancer growth and metastasis [13, 18, 21].

Conclusions

In summary, our data suggest that decreased expression of miR-124 has prognostic value in breast cancer and may serve as a prognostic marker for breast cancer, as well as our study indicates that miR-124 is downregulated and is inversely associated with the lymph node metastasis in breast cancer.