PPM1M regulates EP300 protein levels to suppress EMT in renal proximal tubular epithelial cells.

Renal fibrosis is a final common pathological outcome of chronic kidney disease, and EP300 has been implicated in fibrogenic responses. However, the mechanism that regulates EP300 protein levels in renal proximal tubule epithelial cells remains unclear. Here, we investigated whether PPM1M regulates EP300 protein levels and modulates TGF-β-induced fibrogenic responses. In HK-2 cells, TGF-β increased protein levels of EP300, and PPM1M overexpression reduced TGF-β-induced EP300 accumulation. The interaction between EP300 and PPM1M was assessed by proximity ligation assays, and the results showed that this interaction was diminished following TGF-β treatment. Furthermore, immunoprecipitation assays using in vitro-translated proteins supported a direct interaction between EP300 and PPM1M. Overexpression of PPM1M in HK-2 cells reduced the TGF-β-induced increases in EP300 phosphorylation at Ser1834 and total EP300 protein levels. Functionally, PPM1M attenuated TGF-β-induced EMT and fibrosis-associated transcriptional changes in HK-2 cells. Consistent with these findings, protein levels of EMT- and fibrosis-related markers were decreased by PPM1M overexpression, and TGF-β-induced spindle-like morphological changes were significantly attenuated. Analysis of a human chronic kidney disease dataset showed that PPM1M transcript levels were reduced, and PPM1M expression was decreased in the unilateral ureteral obstruction model, where EP300 expression was increased. Together, these findings suggest that PPM1M may act as a negative regulator of EP300 phosphorylation and protein levels, thereby modulating TGF-β-induced EMT and fibrogenic responses in proximal tubular epithelial cells.