Bone morphogenetic protein (BMP) 7 expression is regulated by the E3 ligase UBE4A in diabetic nephropathy

Mesangial cells played a central role in the pathophysiology of diabetic nephropathy (DN). Our goal was to evaluate the molecular mechanism that regulates loss of BMP7 protein expression in DN. The mRNA and protein levels of BMP7 or UBE4A were detected using qRT-PCR and Western blot respectively. Mass spectrometry and co-immunoprecipitation were used to explore the E3 ligase which regulated BMP7 post-translationally. We initially confirmed that BMP7 protein, but not mRNA, is downregulated when cultured under high glucose mimicking DN conditions, which was rescued by MG-132 treatment. Proteomic analysis of NRK-52E cells +/- MG-132 revealed a list of ubiquitin ligases associated with BMP7. Knockdown of the ubiquitin ligase UBE4A stabilized BMP7 expression in NRK-52E cells grown under high glucose conditions. Concurrent overexpression experiments confirmed that UBE4A is the ubiquitin ligase that degrades BMP7. Co-immunoprecipitation analysis confirmed that BMP7 and UBE4A interact. BMP7 expression in DN is regulated by post-translational mechanism.