Cul4-Ddb1 ubiquitin ligases facilitate DNA replication-coupled sister chromatid cohesion through regulation of cohesin acetyltransferase Esco2

Cohesin acetyltransferases ESCO1 and ESCO2 play a vital role in establishing sister chromatid cohesion. How ESCO1 and ESCO2 are controlled in a DNA replication-coupled manner remains unclear in higher eukaryotes. Here we show a critical role of CUL4-RING ligases (CRL4s) in cohesion establishment via regulating ESCO2 in human cells. Depletion of CUL4A, CUL4B or DDB1 subunits substantially reduces the normal cohesion efficiency. We also show that MMS22L, a vertebrate ortholog of yeast Mms22, is one of DDB1 and CUL4-associated factors (DCAFs) involved in cohesion. Several lines of evidence show selective interaction of CRL4s with ESCO2 through LxG motif, which is lost in ESCO1. Depletion of either CRL4s or ESCO2 causes a defect in SMC3 acetylation, which can be rescued by HDAC8 inhibition. More importantly, both CRL4s and PCNA act as mediators for efficiently stabilizing ESCO2 on chromatin and catalyzing SMC3 acetylation. Taken together, we propose an evolutionarily conserved mechanism in which CRL4s and PCNA promote ESCO2-dependent establishment of sister chromatid cohesion. Author summary During the cycle of cell division and proliferation, each chromosome is copied into twin sister chromatids. To make sure a complete set of chromosomes are correctly passed on from generation to generation, the twins must be tethered together by a multi-protein ring called cohesin. ESCO1 and ESCO2 have been known to catalyze the acetylation of a cohesin subunit SMC3, which triggers the establishment of sister chromatid cohesion. Here, we have shown that CUL4-DDB1 ubiquitin ligases (CRL4(MMS22L)), in collaboration with PCNA, promote this key reaction. CRL4s selectively bind and stabilize ESCO2 on chromatin through a particular motif, which is lost in its cousin ESCO1. This explains the functional divergence and division of labor between these two paralogs. Both CRL4(MMS22L) and PCNA are known components of the moving DNA replication machines. So, our results help us to understand how twin sister chromatids become cohesive concomitantly with chromosome duplication process in human cells.