Role of pds5 proteins in cohesin dynamics

Resumen

Cohesin is a ring-shaped complex that entraps DNA to mediate sister chromatid cohesion. In recent years, it has also been described as a major organizer of interphase chromatin, being essential for processes that include transcriptional regulation or the organization of replication factories. In order to perform its functions, the association of cohesin to chromatin needs to be tightly regulated. In this work, we have characterized the central role of the cohesin cofactor Pds5 in the regulation of cohesin dynamics and cohesin distribution along the genome, as well as the consequences of its ablation for cell proliferation and gene regulation. Vertebrate cells have two versions of Pds5, Pds5A and Pds5B, whose functional specificity remains unclear. Using Mouse Embryonic Fibroblasts (MEFs) deficient in Pds5A, Pds5B or both, we have demonstrated that Pds5 proteins play a dual role in cohesin dynamics: they allow Smc3 acetylation and Sororin binding during DNA replication to stabilize the fraction of “cohesive” cohesin while, at the same time they cooperate with Wapl to promote cohesin release throughout the cell cycle. The dynamic association of cohesin with chromatin is significantly decreased in cells lacking both Pds5A and Pds5B, leading to aberrant localization of cohesin in axial structures known as vermicelli. Cells lacking only Pds5A or Pds5B show mild defects, which suggests an overlapping contribution of both Pds5 proteins to bulk cohesin unloading throughout the genome. We have also found that Pds5 proteins do not dictate cohesin localization at particular genomic locations. However, simultaneous elimination of Pds5A and Pds5B changes genome wide distribution of cohesin in a manner that is different from Wapl depletion. We speculate that this difference might be due to the lack of Smc3 acetylation in Pds5 depleted cells which would restrict cohesin translocation along DNA after loading. The defects in cohesin dynamics and distribution result in transcriptional deregulation. Moreover, cells lacking Pds5 proteins have trouble entering S phase after release from a G0 arrest due to transcriptional alterations and even those that initiate DNA replication display a significant reduction in the replication fork rate, suggesting that cohesin unloading is required to allow replication fork progression. Taken together, our results reveal the importance of Pds5 proteins for cohesin dynamics beyond Wapl-mediated unloading and suggest a clear redundancy of Pds5A and Pds5B for most cohesin functions analysed here.