Talk abstracts

Talk on Saturday 12:00-12:20pm submitted by Michael Markey

Human MDM4 is post-transcriptionally regulated by hsa-miR34a

Pooja Mandke (Department of Biochemistry and Molecular Biology, Wright State University), Nicholas Wyatt (Department of Biochemistry and Molecular Biology, Wright State University), Steven Berberich (Department of Biochemistry and Molecular Biology, Wright State University), Michael Markey (Department of Biochemistry and Molecular Biology, Wright State University)

Abstract:
MDM4, also called MDMX or HDMX in humans, is an important negative regulator of the p53 tumor suppressor. MDM4 is known to be post-translationally regulated by MDM2-mediated ubiquitination to decrease its protein levels in response to genotoxic stress, resulting in accumulation and activation of p53. Recently, MDM4 mRNA was also observed to be down-regulated in response to DNA damage, contributing to p53 activation. Here we report that MDM4 mRNA is a target of hsa-mir-34a. MDM4 mRNA contains a lengthy 3’ untranslated region; however, we find that it is a miR-34a site in the ORF of the last exon that is responsible for the repression. Overexpression of miR34a, but not a mutant miR34a, is sufficient to decrease MDM4 mRNA levels to an extent identical to those of known miR34a target genes. Likewise, MDM4 protein levels are decreased by miR34a overexpression, independent of HDM2 activity. A luciferase reporter gene fused to a portion of exon 11 of MDM4 containing a miR34a site is sufficient to decrease reporter expression, and is inhibited by additional expression of exogenous mir34a. These data establish a mechanism for the recently observed negative regulation of MDM4 and provide a means to manipulate MDM4 expression without introducing DNA damage.

Keywords: MDM4, microRNA, p53