The Role Of NudC-like Protein 2 In Sister Chromatid Separation

During mitosis,the proper segregation of duplicated chromosomes into daughter cells is essential for maintaining genome integrity.Sister chromatid cohesion,which is mediated by the highly conserved protein complex—cohesin,plays an essential role during chromosome segregation.In mammals,the cohesin complex involved in mitosis is composed of four subunits.Two structural maintenance of chromosomes(SMC)proteins(Smela and Smc3)form a heterodimer by interacting their hinge regions.One a-kleisin subunit protein(Rad21)interacts with the head domains of Srmela and Smc3 and effectively closes the ring.One stromal antigen(SAI or SA2)directly interacts with Rad21 via its C-terminal region to stabilize the cohesin ring structure.The cohesin complex is dynamically regulated by a number of cohesin-assoeiated proteins during the cell cycle progression in mammalian cells.Defects in cohesin lead to a range of human disorders termed cohesinopathy,including Cornelia de Lange Syndrome(CdLS)and Roberts-SC phocomelia.Furthermore,cohesin mutations also contribute cancer development.However,little is known about the regulation of cohesin subunits stability.NudC(nuclear distribution gene C)is a highly conserved protein from yeasts to humans.In the filamentous fungus Aspergillus nidulans,NudC has been demonstrated as an upstream regulator of NudF(a homologue of human LISI,a key regulator of cytoplasmic dynein).Our group and others have found that vertebrate NudC has three principal homologs,NudC,NudCL(NudC-like protein)and NudCL2(NudC-like protein 2),all of which contain a p23 domain that regulates the ATPase activity and chaperoning function of Hsp90(heat shock protein 90).We cloned and characterized two mammalian homologues of NudC,NudCL and NudCL2.We found that NudC and NudCL participate in many biological processes,including cell cycle progression and cell migration,by regulating the stability of their client proteins.Recently,our group found that NudCL2 is able to stabilize LIS1 by enhancing the interaction between LIS1 and Hsp90.However,whether NudCL2 plays a role in the cell cycle regulation by regulating cohesin subunits stability is unknown.In this study,we show that NudCL2 is essential for the stability of cohesin subunits by regulating Hsp90 ATPase activity in mammalian cells.Depletion of NudCL2 induces mitotic defects and premature sister chromatid separation and destabilizes cohesin subunits that interact with NudCL2.Similar defects are also observed upon inhibition of Hsp90 ATPase activity.Interestingly,ectopic expression of Hsp90 efficiently rescues the protein instability and functional deficiency of cohesin induced by NudCL2 depletion,but not vice versa.Moreover,NudCL2 not only binds to Hsp90,but also significantly inhibits Hsp90 ATPase activity and promotes the chaperone function of Hsp90 to inhibit the heat-induced aggregation and enzymatic inactivation of Hsp90 substrates.Taken together,these data suggest that NudCL2 acts as an Hsp90 cochaperone to modulate sister chromatid cohesion by stabilizing cohesin subunits,providing a previously undescribed regulation of precise chromosome segregation during mitosis.