Ubiquitylation of the Paf oncoprotein and interaction with PCNA is essential for hematopoietic stem cell function and development.

Abstract

Abstract Hematopoietic stem cells (HSCs) are critical for the lifelong production and maintenance of all blood cell types. The molecular mechanisms that guide this process remain poorly understood. The 15kDa proliferating cell nuclear antigen (PCNA) associated factor (Paf) is a potent oncogene that is over-expressed in most cancers. We have previously shown that Paf is essential for HSC and progenitor function and development. Paf deficient mice (Paf−/−) are leukopenic due to reduced number of HSCs and committed progenitors. Paf−/− HSCs failed to maintain quiescence, to self-renew and to support long term hematopoietic reconstitution. To determine the in vivo molecular interactions and pathways by which Paf functions to mediate hematopoiesis, we introduced mutant versions of Paf into the Paf−/− mice. These unique mouse models allowed us to show that Paf-PCNA interactions and Paf ubiquitylation are both essential for hematopoiesis. Furthermore, biochemical analyses of cells from these mice showed that Paf interaction with PCNA was essential for nuclear localization and proper ubiquitylation of Paf. Collectively, therefore, our studies show that Paf function is dependent upon the ability to interact with PCNA and that the ubiquitylation of Paf regulates Paf’s function during hematopoiesis. Analyses are ongoing to further delineate the molecular mechanism by which Paf mediates HSC function and development.