The stat3 signaling pathway mediates sunitinib resistance in the renal cell carcinoma cell line

Abstract

Sunitinib is a first line treatment modality for patients with metastatic clear cell renal cell carcinoma. However, the development of resistance to sunitinib has emerged as an important clinical problem for molecular-targeted therapy in metastatic renal cell carcinoma. In this study, we have established the sunitinib-resistant renal cell carcinoma sub-lines (designated as OR) by culturing 786-O cells (O) with increasing concentrations of sunitinib for 6 months. Interestingly, exposure of OR cells to sunitinib failed to show the decline of Stat3 phosphorylation and upstream JAK2 phosphorylation. Subsequent experiments showed activated Stat3 promotes cell proliferation and prevents apoptosis in sunitinib resistant cell line by regulating cell cycle associated proteins (skp2, p21, p27, Cyclin E and Cdk2) and apoptosis associated proteins (p53, Bax and Bcl-2) in protein levels. Parental cells acquired sunitinib resistance and reduced apoptosis after forced expression of Stat3, and knock-down of Stat3 in OR cells markedly increased the sensitivity to sunitinib to similar level of parental cells. These findings indicate that activation of JAK2/Stat3 signaling plays critical role in sunitinib resistance. OR cells exhibited increased expression of IL-6, by which JAK2/Stat3 is stimulated. And this IL-6/JAK2/Stat3 pathway is less sensitive to sunitinib and is thought to be relevant for the escape pathway of inhibitory effect of sunitinib.In addition, we showed a series of processes of JAK2 activation, PKM2 phosphorylation, nuclear translocation of PKM2 and concomitant Stat3 phosphorylation by IL-6 stimulation and JAK2/Stat3 signaling were severely attenuated by PKM2 knock-down, leading to increased sunitinib-sensitivity. These results indicate that nuclear PKM2 has an important role in JAK2/Stat3 signaling activation by sustaining Stat3 phosphorylation.In summary, our findings suggest that Stat3 activation by IL-6/JAK2 activation is a key modulation in sunitinib resistant mechanism against direct anti-cancer cell effect in renal cell carcinoma cell lines. Increased nuclear level of PKM2 which enhances transcriptional activity of Stat3 also does an important role in sunitinib resistance. With further investigations of in vivo experiment and linkage of the clinical data, our results may be improve the information we have for overcoming sunitinib resistance in metastatic renal cell carcinoma patients