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

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• Mitogen-activated protein kinase kinase 4 (MKK4) is a key regulator of stress-induced signaling pathways, including those involving c-Jun N-terminal kinase and p38.
• Cellular senescence is a state of irreversible growth arrest associated with aging and disease, characterized by complex molecular changes.
• MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression post-transcriptionally, playing critical roles in various cellular processes.

Purpose of the Study:

• To investigate the regulation of MKK4 abundance during replicative senescence in human diploid fibroblasts.
• To identify specific microRNAs involved in controlling MKK4 levels.
• To elucidate the functional consequences of altered MKK4 abundance on cell proliferation and downstream signaling.

Main Methods:

• Quantitative analysis of MKK4 protein and mRNA levels in senescent fibroblasts.
• Identification and validation of microRNA targets using reporter assays and manipulation of miRNA abundance.
• Assessment of cell proliferation rates and phosphorylation status of downstream kinases (p38, PRAK).

Main Results:

• MKK4 protein abundance was found to increase in senescent human diploid fibroblasts, primarily through enhanced translation.
• Four specific microRNAs (miR-15b, miR-24, miR-25, and miR-141) were identified as targeting MKK4 mRNA.
• The abundance of these regulatory microRNAs decreased during replicative senescence, and their collective modulation significantly impacted MKK4 levels.
• Overexpression of these miRNAs reduced MKK4 abundance, while their joint inhibition increased it, acting via MKK4's 5' and 3' untranslated regions.
• Elevated MKK4 levels led to inhibited cell proliferation and increased p38 and PRAK activity.

Conclusions:

• Multiple microRNAs collectively regulate MKK4 mRNA abundance during replicative senescence.
• This coordinated miRNA regulation of MKK4 influences cellular processes such as proliferation and stress response signaling.
• The findings reveal a novel layer of post-transcriptional control governing MKK4 levels in the context of cellular aging.