The role of KLF6 and KLF6-SV1 in the development and progression of epithelial ovarian cancer: Identification of a novel pro-survival protein that regulates apoptosis

Epithelial ovarian cancer (EOC) is one of the most lethal gynaecologic cancers nationwide and the fifth most frequent cause of cancer deaths in women 1. While five-year survival rates have slightly increased over the past several decades to approximately 40%, overall mortality rates remain relatively constant1,2. Thus, if advances are to be made in diagnosis, prevention and treatment of this disease, it will be critical to characterize the genetic defects that underlie key steps in the development and spread of ovarian cancer. We and others have demonstrated that inactivation of the tumor suppressor KLF6 is present in a number of human cancers including prostate5,6, colorectal7, lung cancer 8,9, gastric10, astrocytic glioma11,12, nasopharyngeal13, hepatocellular carcinomas14,15,16 head and neck squamous cell carcinomas17 and Barrett's-related adenocarcinomas18. We have also shown that KLF6 is alternatively spliced into biologically active isoforms KLF6-SV1, -SV2, and -SV3, in both normal and cancerous tissues19. Most notably, KLF6-SV1 expression is upregulated in prostate cancer tumors compared to normal prostate tissue 19 and its activity directly opposes KLF6 effects on cell proliferation, colony formation, invasion, and in vivo tumor growth 20.;Here, we demonstrate a number of important associations between KLF6 and KLF6-SV1 and the molecular basis of ovarian carcinogenesis. Briefly, (1) KLF6 inactivation is present in the majority of epithelial ovarian cancer (EOC) patient samples, (2) KLF6-SV1 is overexpressed approximately 5-fold in nearly all EOC and the degree of overexpression is associated with increased tumor grade, (3) E-cadherin is transcriptionally regulated by KLF6 and KLF6-SV1, (4) KLF6-SV1 functions an anti-apoptotic protein, binding the pro-apoptotic protein Noxa and targeting them both for HDM2 dependent degradation (5) siRNA-mediated inhibition of KLF6-SV1 results in decreased tumor cell proliferation, invasion, angiogenic capacity, and restores chemosensitivity, and finally, (6) systemic, in vivo delivery of a novel class of siRNA molecules targeting KLF6-SV1 inhibits tumor growth and significantly prolongs median and overall survival of tumor-bearing mice beyond 1 year of tumor implantation. Taken together, these findings demonstrate the importance of KLF6 and KLF6-SV1 in the progression of EOC, identify a number of cancer-relevant mechanisms through which they function, including a previously unrecognized control point in BH3-only mediated apoptosis, and finally, demonstrate the proof-of-principle concept that siRNA-mediated inhibition of KLF6-SV1 may represent a novel therapeutic target for ovarian cancer.