Identifying the Mechanism(s) Responsible for the Translational Regulation of the Stress Signaling Kinase MKK4.

摘要

Dysregulation of MKK4 has been associated with cancer progression in a variety of disease states. While the preponderance of data implicate a role for MKK4 and its signaling pathway in disease, the mechanism(s) that regulate its expression have been incompletely studied. We sought to determine the mechanism by which MKK4 protein levels are modulated using high- and low- MKK4- expressing prostate and ovarian cancer cell lines as a model system. Using a variety of complementary approaches we showed that MKK4 protein is highly stable in all cell lines tested and displays no differential sensitivity to protease inhibitors. The compartmentalization of the MKK4 mRNA is also unchanged when comparing high- and low- expressing cells, which all show a highly stable transcript with a predominantly nuclear localization. However, within the cytoplasmic MKK4 mRNA subset, there is a distinct increase in the association of the MKK4 mRNA with the translational machinery in high- MKK4- expressing cells compared to low- MKK4- expressing cells. Together, these observations suggested that MKK4 protein levels could be subject to translational regulation. This mechanism of control endows cells with the ability to rapidly fine- tune levels of specific proteins in response to temporal and spatial signals. Our findings, and the evolving literature on translational regulation, prompted the possibility that microRNAs (miRs) could play a key role in regulating cellular levels of MKK4 in prostate cancer model systems. miRNAs are small noncoding RNAs which have been shown to regulate diverse biological processes in a wide variety of organisms. Over the past few years significant progress has been made in delineating the biogenesis of these approximately 22 nt non- coding RNAs, their involvement in human disease, and tools for their study. Of specific relevance to our data on MKK4 is the role that miRNAs can play in the translational repression of target mRNAs.