Interactions of the DNA mismatch repair proteins MLH1 and MSH2 with c-MYC and MAX.
MSH2 and MLH1 have a central role in correcting mismatches in DNA occurring during DNA replication and have been implicated in the engagement of apoptosis induced by a number of cytotoxic anticancer agents. The function of MLH1 is not clearly defined, although it is required for mismatch repair (MMR) and engagement of apoptosis after certain types of DNA damage. In order to identify other partners of MLH1 that may be involved in signalling MMR or apoptosis, we used human MLH1 in yeast two-hybrid screens of normal human breast and ovarian cDNA libraries. As well as known partners of MLH1 such as PMS1, MLH3 and MBD4, we identified the carboxy terminus of the human c-MYC proto-oncogene as an interacting sequence. We demonstrate, both in vitro by yeast two-hybrid and GST-fusion pull-down experiments, as well as in vivo by coimmunoprecipitation from human tumour cell extracts, that MLH1 interacts with the c-MYC protein. We further demonstrate that the heterodimeric partner of c-MYC, MAX, interacts with a different MMR protein, MSH2, both in vitro and in vivo. Using an inducible c-MYC-ER fusion gene, we show that elevated c-MYC expression leads to an increased HGPRT mutation rate of Rat1 cells and an increase in the number of frameshift mutants at the HGPRT locus. The effect on HGPRT mutation rate is small (2-3-fold), but is consistent with deregulated c-MYC expression partially inhibiting MMR activity.
Mac Partlin
Mary
M
Department of Medical Oncology, Glasgow University, UK.
Homer
Elizabeth
E
Robinson
Helen
H
McCormick
Carol J
CJ
Crouch
Dorothy H
DH
Durant
Stephen T
ST
Matheson
Elizabeth C
EC
Hall
Andrew G
AG
Gillespie
David A F
DA
Brown
Robert
R
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D020137:Base Pair Mismatch; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D002352:Carrier Proteins; D004260:DNA Repair / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D016296:Mutagenesis / Q000502:physiology; D009363:Neoplasm Proteins / Q000378:metabolism*; D009687:Nuclear Proteins; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D014157:Transcription Factors; D014407:Tumor Cells, Cultured; D020798:Two-Hybrid System Techniques
D048868:Adaptor Proteins, Signal Transducing; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C000715470:MAS1 protein, human; C499330:MAX protein, human; C501486:MLH1 protein, human; C499329:Max protein, rat; C501484:Mlh1 protein, rat; C067850:Myc associated factor X; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D016271:Proto-Oncogene Proteins c-myc; D014157:Transcription Factors; D007041:Hypoxanthine Phosphoribosyltransferase; C497172:MSH2 protein, human; C497174:Msh2 protein, rat; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein