Increased MKK4 abundance with replicative senescence is linked to the joint reduction of multiple microRNAs.

MKK4 (mitogen-activated protein kinase kinase 4) is a pivotal upstream activator of c-Jun N-terminal kinase and p38. Here, we report that the abundance of MKK4 increases in senescent human diploid fibroblasts through enhanced translation. We identified four microRNAs (miR-15b, miR-24, miR-25, and miR-141) that target the MKK4 messenger RNA (mRNA); the abundance of these microRNAs decreased during replicative senescence. Individually modulating the amount of each microRNA did not modify MKK4 abundance, but their concomitant overexpression decreased and their joint reduction increased MKK4 abundance. Reporter analyses indicated that these microRNAs acted through the MKK4 5' and 3' untranslated regions. Elevated MKK4 abundance inhibited cell proliferation and increased the phosphorylation and activity of p38 and PRAK (p38-regulated/activated protein kinase). Thus, multiple microRNAs acting on a single target, the MKK4 mRNA, collectively influence MKK4 abundance during replicative senescence.