Induction of deubiquitinating enzyme USP50 during erythropoiesis and its potential role in the regulation of Ku70 stability.

Anemia is a very common blood disorder that affects the lives of billions of people worldwide. Anemia is caused by the loss of blood, increased destruction of red blood cells (RBCs), or reduced production of RBCs. Erythropoiesis is the complex process of RBC differentiation and maturation, in which protein degradation plays a crucial role. Protein ubiquitination regulates programmed protein degradation, which can be reversed by deubiquitinating enzymes (DUBs); however, the role of DUBs in erythropoiesis has not been well studied. We examined the expression of DUBs during erythropoiesis using an ex vivo human CD34+ hematopoietic progenitor cell culture system. Here we show that ubiquitin-specific protease 50 (USP50) levels are increased during erythropoiesis. USP50 mRNA levels are significantly increased on day 3 and protein levels are elevated on day 9 of erythroid differentiation. Coimmunoprecipitation and proteomics analyses reveal that Ku70, a DNA-binding protein, is associated with USP50. Overexpression of USP50 has no effect on Ku70 mRNA levels, while it reduces Ku70 protein levels by promoting Ku70 degradation, suggesting that USP50 may indirectly regulate Ku70 protein stability. USP50 protein is also not stable. USP50 protein degradation is independent of the proteasomal and the lysosomal degradation systems. This study suggests that DUBs like USP50 may regulate protein stability during erythropoiesis; however, more investigation is warranted.