title: Interdependence of DNA mismatch repair proteins MLH1 and MSH2 in apoptosis in human colorectal carcinoma cell lines.
abstract: The mammalian DNA mismatch repair (MMR) system consists of a number of proteins that play important roles in repair of base pair mismatch mutations and in maintenance of genomic integrity. A defect in this system can cause genetic instability, which can lead to carcinogenesis. For instance, a germline mutation in one of the mismatch repair proteins, especially MLH1 or MSH2, is responsible for hereditary non-polyposis colorectal cancer. These MMR proteins also play an important role in the induction of apoptosis. Accordingly, altered expression of or a defect in MLH1 or MSH2 may confer resistance to anti-cancer drugs used in chemotherapy. We hypothesized that the ability of these two MMR proteins to regulate apoptosis are interdependent. Moreover, a defect in either one may confer resistance to chemotherapy by an inability to trigger apoptosis. To this end, we studied three cell lines-SW480, LoVo, and HTC116. These cell lines were selected based on their differential expression of MLH1 and MSH2 proteins. SW480 expresses both MLH1 and MSH2; LoVo expresses only MLH1 but not MSH2; HCT116 expresses only MSH2 but not MLH1 protein. MTT assays, a measure of cytotoxicity, showed that there were different cytotoxic effects of an anti-cancer drug, etoposide, on these cell lines, effects that were correlated with the MMR status of the cells. Cells that are deficient in MLH1 protein (HCT116 cells) were resistant to the drug. Cells that express both MLH1 and MSH2 proteins (SW480 cells) showed caspase-3 cleavage, an indicator of apoptosis. Cells that lack MLH1 (HCT116 cells) did not show any caspase-3 cleavage. Expression of full-length MLH1 protein was decreased in MMR proficient (SW480) cells during apoptosis; it remained unchanged in cells that lack MSH2 (LoVo cells). The expression of MSH2 protein remained unchanged during apoptosis both in MMR proficient (SW480) and deficient (HCT116) cells. Studies on translocation of MLH1 protein from nucleus to cytosolic fraction, an indicator of apoptosis, showed that MLH1 translocation only occurred in MMR proficient (SW480) cells upon induction of apoptosis further suggested a MSH2 dependent role of MLH1 in apoptosis. These data suggest a role of MLH1 in mediation of apoptosis in a MSH2-dependent manner. Taken together, our data supported an interdependence of mismatch repair proteins, particularly MLH1 and MSH2, in the mediation of apoptosis in human colorectal carcinoma cell lines.
authors.affiliation: Department of Biology, College of Arts, Letters and Sciences, University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR, 72204, USA.
authors.forename: Samar
authors.initials: S
authors.lastname: Hassen
authors.affiliation: Department of Biology, College of Arts, Letters and Sciences, University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR, 72204, USA.|CATX Inc., Gladwyne, PA, 19035, USA.
authors.forename: Akhtar A
authors.initials: AA
authors.lastname: Ali
authors.affiliation: Department of Biology, College of Arts, Letters and Sciences, University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR, 72204, USA.
authors.forename: Surya P
authors.initials: SP
authors.lastname: Kilaparty
authors.affiliation: Department of Biology, College of Arts, Letters and Sciences, University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR, 72204, USA.
authors.forename: Qudes A
authors.initials: QA
authors.lastname: Al-Anbaky
authors.affiliation: Center for Integrative Nanotechnology Sciences, University of Arkansas at Little Rock, Little Rock, AR, 72204, USA.
authors.forename: Waqar
authors.initials: W
authors.lastname: Majeed
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, Thomas Jefferson University, Kimmel Cancer Center, Philadelphia, PA, 19107, USA.|Center for Translational Cancer Research, University of Delaware, Helen F Graham Cancer Center, Newark, DE, 19713, USA.|CATX Inc., Gladwyne, PA, 19035, USA.
authors.forename: Bruce M
authors.initials: BM
authors.lastname: Boman
authors.affiliation: CATX Inc., Gladwyne, PA, 19035, USA.
authors.forename: Jeremy Z
authors.initials: JZ
authors.lastname: Fields
authors.affiliation: Department of Biology, College of Arts, Letters and Sciences, University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR, 72204, USA. nali@ualr.edu.
authors.forename: Nawab
authors.initials: N
authors.lastname: Ali
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000502:physiology*; D000970:Antineoplastic Agents / Q000627:therapeutic use; D017209:Apoptosis / Q000502:physiology*; D053148:Caspase 3 / Q000378:metabolism; D015179:Colorectal Neoplasms / Q000188:drug therapy / Q000473:pathology*; D053843:DNA Mismatch Repair; D005047:Etoposide / Q000627:therapeutic use; D006801:Humans; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein / Q000502:physiology*; D009687:Nuclear Proteins / Q000502:physiology*; D059748:Proteolysis
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000970:Antineoplastic Agents; C501486:MLH1 protein, human; D009687:Nuclear Proteins; D005047:Etoposide; D053148:Caspase 3; C497172:MSH2 protein, human; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein
keywords: Apoptosis; Colorectal cancer; Cytotoxicity; HNPCC; MLH1; MSH2; Mismatch repair proteins