MAPK (mitogen-activated protein kinase) kinase 4 (MKK4) is a pivotal upstream activator of c-Jun-N-terminal kinase (JNK) and p38MAPK. Here, we report that MKK4 is increased in senescent human diploid fibroblasts (HDFs) through enhanced translation. We identified four microRNAs (miR-15b, miR-24, miR-25, and miR-141) that target the MKK4 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 MKK4, whereas their joint reduction increased MKK4. Reporter analyses indicated that these microRNAs acted through the MKK4 5′ and 3′ untranslated regions. Elevated MKK4 inhibited cell proliferation and increased the phosphorylation of p38 and PRAK (p38-regulated/activated protein kinase), thereby contributing to the senescent phenotype of HDFs. Thus, multiple microRNAs acting on a single target, the MKK4 mRNA, collectively influence MKK4 abundance during replicative senescence.
