STAT3 interacts with Skp2/p27/p21 pathway to regulate the motility and invasion of gastric cancer cells.

The interleukin-6 (IL-6)/Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) pathway mediates cell proliferation and migration. S-phase kinase-associated protein-2 (Skp2) catalyzes the ubiquitylation of p27 and p21. Here we investigated that the cross-talk of the two pathways regulates motility and invasion of gastric cancer SGC7901 and MGC803 cells. Both cell lines endogenously secret IL-6, and blockage of IL-6 or JAK2 inhibited the activation of JAK2 and STAT3. Depletion of STAT3 downregulated Skp2 expression, and thereby increased the expression of p27 and p21. The depletion of STAT3 inhibited the ability of cells to migrate and invade, and impaired the cellular cytoskeleton mainly microtubules; while the depletion of p27 partially restored the impaired ability to migrate, and reversed the impaired microfilaments, further inhibited the ability to invade, but had little effect on microtubules and cellular adhering ability of STAT3-depleted cells. STAT3 depletion inhibited the activity of RhoA and the interaction with stathmin, downregulated the expression of pFAK (phosphorylated focal adhesion kinase), acetylated-tubulin, RECK (reversion-inducing-cysteine-rich protein with kazal motifs) and Sp1, upregulated E-cadherin, and reduced the activities of MMP (matrix metalloproteinase)-2 and -9. The depletion of p27 increased RhoA (Ras homolog family member A) activity, upregulated RECK, and downregulated E-cadherin and Sp1 in STAT3-depleted cells. The results indicate that the interaction between STAT3 and Skp2/p27/p21 pathway plays an important role in mediating the motility, migration and invasion of gastric cancer cells, and inhibition of STAT3 may be a useful therapeutic approach for metastasis of gastric cancer, but caution needs to be taken for its effects on Skp2/p27/p21 pathway.