The Effect Of Rktg, A RAS/RAF/ERK Signaling Antagonist, In Breast Cancer Cells And Its Related Regulative Mechanism

Breast cancer is a serious health problem for women and remains themost common malignancy in females around the world. Numerousconstitutively activated signaling pathways have been identified as essentialfor the carcinogenesis and cancer development, including RAS/RAF/ERK.Raf kinase trapping to Golgi (RKTG), a seven transmembrane proteinlocalized to the Golgi apparatus, is considered a novel inhibitor of theRAS/RAF/ERK signaling pathway. RKTG can bind to and translocateRAF-1from the cytoplasm to the Golgi apparatus, a process that inhibitsRAF-1activation and blocks its interaction with RAS and MEK, thusinactivating the ERK signaling pathway.Breast cancer growth is highly dependent on the ERK signalingpathway activation, therefore, RKTG is considered to possess asuppressive role in breast cancer. We found the ectopic expression ofRKTG significantly inhibited colony formation, metastasis, and invasioncapabilities of breast cancer cells. We also found that the proliferation ofcancer cells was inhibited in vivo and vitro, accompanied by the induction of G0/G1arrest, an increase in the P27KIP1level, decrease in thephosphorylation of ERK and JNK, Cyclin D1, and CDK4. Conversely, thesmall interfering RNA mediated downregulation of RKTG decreasedP27KIP1, increased Cyclin D1, CDK4and phosphorylation of ERK and JNK.Furthermore, RKTG overexpression inhibited epithelial mesenchymalTransition (EMT), with decreaseded mesenchymal markers fibronectin andvimentin, location of β-catenin to cell-cell junctions. Also, we found thattreatment with Trastuzumab, a monoclonal antibody targeting HER2,increased the RKTG levels in cultures of SK-BR-3cells, the effect ofHerceptin on RKTG expression was both time and concentration dependent,which indicates us the influence of HER2function on RKTG expression.Collectively, our results provide the first evidence that RKTGsuppresses breast cancer development and that RKTG can be influenced byHER2function, which enable the targeted therapy for breast cancer.