Serum-dependent and independent regulation of PARP2

PARP2 belongs to a family of proteins involved in cell differentiation, DNA damage repair, cellular energy expenditure, chromatin modeling and cell differentiation. In addition to these overlapping functions with PARP1, PARP2 participates in spermatogenesis, T-cell maturation, extraembryonic endoderm formation and adipogenesis. The function(s) of PARP2 is far from complete, and the mechanism(s) by which the gene and protein are regulated are unknown. In this study, we found that two different mechanisms are used in vitro to regulate PARP2 levels. In the presence of serum, PARP2 is degraded through the ubiquitin-proteasome pathway, however, when serum is removed, PARP2 is rapidly sequestered into an SDS- and urea-insoluble fraction. This sequestration is relieved by serum in a dose-dependent manner, and again PARP2 is detected by immunoblotting. Furthermore, and despite the presence of a putative serum response element in the PARP2 gene, transcription is not affected by serum deprivation. These observations that PARP2 is tightly regulated by distinct pathways highlights the critical roles PARP2 plays under different physiological conditions.