Abstract 124: Effect of RKIP on MMP expression and regulation of breast cancer metastasis

Raf Kinase Inhibitory Protein or RKIP was initially identified as a Raf-1 binding protein using the yeast 2-hybrid screen. RKIP inhibits the activation phosphorylation of MEK by Raf-1 by competitively inhibiting the binding of MEK to Raf-1 and thus exerting an inhibitory effect on the Raf-MEK-ERK pathway. RKIP has been identified as a metastasis suppressor gene. Metastasis is a complex multiple-step process. Expression of RKIP is low in cancer metastases. Although primary tumor growth was unaffected, re-expression of RKIP inhibits cancer metastasis. Mechanistically, RKIP constrains metastasis by inhibiting angiogenesis, local invasion, intravasation, and colonization. The molecular mechanism of how RKIP inhibits these individual steps remains undefined. Using an unbiased PCR based screening and by analyzing DNA microarray expression datasets we observed that the expression of multiple metalloproteases (MMP) including MMP1, MMP3, MMP10 and MMP13 were negatively correlated with RKIP expression in breast cancer cell lines and clinical samples. Since expression of MMPs by cancer cells is important for cancer metastasis, we hypothesize that RKIP may mediate suppression of breast cancer metastasis by inhibiting multiple MMPs. In this study we show that the expression signature of RKIP and MMPs is better at predicting high metastatic risk than the individual gene. Using a combination of loss- and gain-of-function approaches, we found that MMP13 is the cause of RKIP-mediated inhibition of local cancer invasion. Interestingly expression of MMP13 alone was not sufficient to reverse the inhibition of breast cancer cells metastasis to the lung due to the expression of RKIP. We found that RKIP negatively regulated MMP13 through the Erk2-Fra1 transcriptional axis and the repression of MMP13 by RKIP requires the presence of the a TPA-responsive element in the MMP13 proximal promoter. Together, our findings indicate that RKIP inhibits cancer cell invasion, in part, via MMP13 inhibition. These data also implicate RKIP in the regulation of MMPs transcription, suggesting a potential mechanism by which RKIP inhibits tumor progression and metastasis. Citation Format: Ila J. Datar, Jingwei Feng, Gang Ren, Zehui Li, Xiaoliang Qiu, Fahd Al-Mulla, Milad S. Bitar, Miranda Yeung, Kam Yeung. Effect of RKIP on MMP expression and regulation of breast cancer metastasis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 124. doi:10.1158/1538-7445.AM2014-124