Role of topbp1 msh2 interaction in atr chk1 pathway

Abstract

The cell cycle checkpoint signaling cascade maintains integrity of the eukaryotic genome It is activated upon DNA damage and it responds to a variety of genetic lesions like single or double strand breaks and damage caused by UV or chemicals Two canonical DNA damage signaling pathways operate namely the ATR Ataxia Telangiectasia Rad3 related and ATM Ataxia Telangiectasia mutated pathways In these pathways the key sensor kinases detect stalled replication forks or strand breaks and signal the effector kinases Chk1 or Chk2 respectively thus delaying the cell cycle until the DNA is repaired DNA damage initiates a signaling cascade that involves a number of protein interactions We focused on the interaction between Topoisomerase II 946 binding protein TopBP1 and MutS homolog 2 Msh2 Though TopBP1 was identified earlier as a binding partner of Msh2 the functional relevance of this interaction is still not well understood TopBP1 is an important scaffolding protein that detects single stranded breaks and activates ATR kinase upon DNA damage Human TopBP1 protein contains nine BRCT domains that are capable of multiple protein protein interactions which in turn regulate processes like DNA replication initiation and checkpoint activation Msh2 is a key player in the mismatch repair MMR signaling and is commonly mutated in colorectal cancers HNPCCs Msh2 along with Msh6 scan the DNA in search of any mismatch that may have occurred during replication Msh2 has recently been implicated in checkpoint activation following methylation damage and has been shown to interact with ATR following Cisplatin as well as N Methyl N Nitro N Nitrosoguanidine MNNG damage In the current study we elucidate the functional relevance of TopBP1 Msh2 interaction in the ATR Chk1 pathway following methylation damage Employing in vitro studies we show that BRCT domains 7 and 8 of TopBP1 interact with the Mutsd and Mutsac domain of Msh2 Our studies show that TopBP1 and Msh2 8211 Msh6 complex exists in vivo and is possibly recruited on newline