Interplay Of MVA And Hippo Pathways Regulates YAP-RHAMM Transcription To Control Cancer Metastasis

RHAMM, as a novel breast cancer susceptibility gene, has positive correlationwith higher risk of breast cancer. Over-expression of RHAMM could activate ERK andpromote migration and invasion of breast cancer cells. Here, we found RHAMM isregulated by the mevalonate pathway, which produces isoprenoids that are vital for anumber of cellular functions. Simvastatin, a potent inhibitor of HMG–CoA reductase,the rate controlling enzyme of the mevalonate pathway, significantly attenuated thetranscription of RHAMM while adding the mevalonate reverse this effect. Bothsimvastatin and lentivirus mediated shRNA down-regulation of RHAMM expressionreduced the phosphorylation level of ERK and suppressed breast cancer cell migrationand invasion. Yes-associated protein (YAP), the key transcriptional co-activator in theHippo signaling pathway, is essential for organ size control, tissue regeneration andcancer development in mammals. Activated YAP could bind its target transcriptionfactor TEAD to activate YAP-dependent gene expression. To study the mechanism ofRHAMM transcription regulation by the mevalonate pathway, we identified twoputative YAP-TEAD binding sites in the RHAMM promoter sequence and foundlentivirus mediated shRNA inhibition of YAP or TEAD expression down-regulatedRHAMM transcription, leading to a decrease in ERK phosphorylation and the migrationand invasion of breast cancer cells. Moreover, the phosphorylation level of YAP and itscytoplasmic localization is dramatic increased by simvastatin, while addition ofmevalonate decrease the phosphorylation level of YAP and relocalizes YAP into thenucleus. We further demonstrated that geranylgeranylation in the downstream ofmevalonate pathway are required to regulate YAP activity, RHAMM transcription andERK activity, and this regulation is through Rho GTPase activity modulation andcytoskeleton arrangement affected by the mevalonate pathway. Together, our resultsdemonstrated that mevalonate pathway can regulate the activity of YAP, a keycomponent in the Hippo signaling pathway, which control the transcriptional expressionof RHAMM, and eventually modulate the activity of ERK and the migration andinvasion of breast cancer cells. Our results for the first time linked mevalonate andHippo pathways with RHAMM as a downstream effector, a YAP-transcription and simvastatin-inhibition target, and a cancer metastasis mediator; uncover a mechanismregulating RHAMM expression and cancer metastases; and reveal a mode wherebysimvastatin exerts anticancer effects; providing potential targets for cancer therapeuticagents.