Steve Lipkin MD PhD
Associate Professor
University of California, Irvine
Departments of Biological Chemistry and Medicine
slipkin@uci.edu
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Research Interests:
DNA mismatch repair (MMR) is critical for maintaining both mitotic and meiotic genomic integrity. Defective MMR leads to carcinogenesis of the colorectum, endometrium, stomach, small bowel, ovary, brain and kidney Mutations in five MMR genes (MLH1, MSH2, MSH6, PMS2 and MLH3) cause cancer susceptibility. Germline MMR gene mutations underlie the most common cancer genetic syndrome, Hereditary Non-Polyposis Colon Cancer (HNPCC). Furthermore, somatic MMR defects are attributable for ~17,000 sporadic colorectal cancer (CRC) and ~10,000 endometrial cancer new diagnoses each year in the United
States.
MMR defects are thought to cause cancer through four distinct mechanisms, (A) Repair of single-basepair DNA mismatches, (B) Repair of frameshift mutations (commonly called microsatellite instability (MSI)), (C) Failure to repair damaged DNA, and (D) Failure to initiate apoptosis in response to DNA damage.
MMR is also critical for mammalian meiosis. Mice null for MMR genes Msh4, Msh5 or Mlh1 are infertile for both sexes. Similarly, male Pms2-/- mice are sterile.
Previously, my group cloned MLH3, the last uncharacterized mammalian MMR gene. MLH3 has higher amino-acid identity with homologues in S. cerevisiae, Arabidopsis, and C. elegans than to any other human protein. This conservation suggests it may perform unique functions in mammalian MMR.
My initial studies revealed a role for MLH3 in human and mouse CRC susceptibility. Subsequently, MLH3 mutations were found tounderlie HNPCC. I have recently created an Mlh3-/- mouse model that has revealed several provocative features:
(1) Mlh3-/- males and females are infertile due to meiotic chromosomal aneuploidy (see Nature Genetics August 2002 issue).
(2) A pilot Mlh3-/- mouse cohort develops multiple cancers, including stomach, large and small bowel adenomas, basal cell carcinomas and osteomas, compared to matched wild-type (wt) controls.
(3) Mlh3-/- mice develop greying of hair, which has not yet been described in MMR mouse models.
(4) While Mlh3p deficient yeast display MSI, Mlh3-/- fibroblasts do not display MSI.
If Mlh3-/- cells do not display an MSI mutator phenotype, by what mechanism does Mlh3 deficiency cause cancer? One hypothesis is that Mlh3 leads to carcinogenesis primarily through failure to initiate apoptosis in response to DNA damage. A second hypothesis is that, unlike its yeast homologue 8, Mlh3-/- cells have defects in single basepair DNA mismatches. A third hypothesis is that hair greying, infertility and cancer susceptibility phenotypes are all linked to defects in damaged and "aged" DNA repair. A fourth hypothesis is that Mlh3 deficiency cause MSI in cell types from which tumors arise, such as bowel epithelium, but not fibroblasts. Testing these hypotheses will yield data important for understanding the mechanisms of all MMR deficient tumors.
In addition, we are working to define whether MLH3 participates in meiotic checkpoint recognition and is a plausible candidate gene for mutation analyses in idiopathic human infertility or genetic aneuploidy disorders such as Down or Turner Syndromes.
Additionally, my lab has used a novel custom Affymetrix high-density array that resequences all MLH1, MSH2 and MSH6 exons and splice donor/acceptors (HNPCC DNA Chip) to examine whether MMR single nucleotide polymorphisms (SNPs) contribute to CRC susceptibility. Previously, an APC SNP (APC I1307K) was identified among CRC patients that is attributable for ~20% of CRC in Ashkenazi Jews with a CRC family history. Because of the association between MMR and HNPCC, we have performed in the past year successful studies for high-throughput SNP discovery for MLH1, MSH2 and MSH6 coding and splice-junction sequences in Molecular Epidemiology of Colon Cancer (MECC) Study CRC patients with an affected first degree relative using the HNPCC DNA Chip. SNPdiscovery is important at present in that recent studies suggest only ~2-12% of all human cSNPs are represented in public domain databases. This phase has largely been completed.
To perform a case-control study to determine if there exists any SNP(s) associated with altered CRC risk. This study is ongoing. We are using TaqMan, Mass spectroscopy and other methods for SNP genotyping.
To validate SNP association with CRC risk in a replication set of MECC matched CRC cases and controls distinct from those samples analyzed in (B). The discovery of MMR gene CRC susceptibility alleles as proposed in this study would help enable more precisely the identification of individuals at higher risk than the general population for targeted intensive screening before CRC initiation and/or metastasis. Furthermore, the ability to genotype CRC cases for the presence of different susceptibility alleles is anticipated in future randomized CRC therapeutic trials to allow stratification and identification of patient subpopulations with distinct tumor responses and clinical outcomes that might otherwise not be recognized without this type of patient stratification.
Future aims will include mouse models of MMR gene SNPs and intercrosses with bowel sensitizer mouse strains, such as Apc1638N.
Selected Publications:
Stella A, Wagner A, Shito K, Lipkin SM, Watson P, Guanti G, Lynch HT, Fodde R, Liu B. “A nonsense mutation in MLH1 causes exon skipping in three unrelated HNPCC families.” Cancer Research 2001 Oct 1;61(19):7020-4
Lipkin, SM, Moens PB,, Wang, V., Lenzi, M.,Shanmugarajah, D.,Gilgeous, A., Thomas, J. Cheng, J., Touchman, J. Green, E., Schwartzberg, P,.Collins, FS, & Paula E. Cohen “Meiotic arrest and aneuploidy in MLH3 deficient mice Nature Genetics 2002;31: 385-90.
Lynch HT, Weisenburger, D., Quinn-Laquer, B. Snyder, C., Lynch JF, D., Lipkin, SM, and Sanger, W.G.“Family with acute myelogenous leukemia, breast, ovarian and gastrointestinal cancer. Cancer Genetics and Cytogenetics, 2002 Aug; 137(1):8-14
Kudryavtseva, E., Sugihara, T., Wang, N., Lasso, R., Gudnason,
J., Lipkin, SM and Andersen, B.A.
“Identification and characterization of Grainyhead-like Epithelial
Transactivator (GET-1), a novel mammalian grainyhead-like
factor.” Developmental Dynamics 2002 226(4):604-17.
Lipkin SM, Chen, J., Hacia, J., Fodor, S., Rennert, G. and Gruber, S. “Novel DNA Mismatch Repair Gene Variants Associated With Microsatellite Stable Population Based Colorectal Cancer.” Nature Genetics 2004 36: 694-9.
Lipkin SM. “Cancer Genetics in Patients of Jewish Ethnicity.” Familial Cancer 2004 Nov 3: 175.16. 16. 16. Domcheck, S., Rebbeck, T., Lipkin S.M and Tucker, M. “Risk Modifiers in Hereditary Cancer Syndromes.” Journal of Clinical Oncology Supplement 89-97, 2005.
Shin, BY, Rozek, L., Paxton, L., Peel, D., Anton-Culver, H., Rennert, G., Goodfellow, P., Gruber, S., Lipkin SM. “Low Allele Frequency of MLH1 D132H in American Colorectal and Endometrial Cancer Patients” Dis. of the Colon and Rectum 2005 48: 1723-7.
Rozek, L., Lipkin, SM, Fearon E., Hanash, S., Giordano T., Greenson J., Kuick R., Misek, D., Taylor J., Douglas, J., Rennert, G., and Gruber S. “CDX2 Polymorphisms, RNA Expression, and Risk of Colorectal Cancer” Cancer Research 2005 65(13):5488-92.
Chen, J., Kuriaguchi, M., Reichow, D., Dudley, S., Arnheim. N., Liskay, RM and Lipkin SM. “Contributions by MutL Homologues Mlh3 and Pms2 to DNA Mismatch Repair and Tumor Suppression in the Mouse.” Cancer Research 2005 65(19):8662-7065.
Kolas, N., Svetlanov, A, Lenzi, M., Macaluso, F., Lipkin, S.M., Liskay, R.M, Greally, J., Edelmann, W. and Cohen, P. “Localization of MMR proteins on meiotic chromosomes in mice indicates distinct functions during prophase I.” J. Cell Biology 2005 171(3):447-58
J. L. Velasquez and S. M. Lipkin" "What Are SNPs and Haplotypes and How Will They Help Us Manage the Prevention of Adult Cancer?" Curr Oncol Rep 2005 7(6) 475-9.
Cannavo, E., Marra, G., Sabatés-Bellver, J., Menigatti, M., Lipkin, S.M. Fischer, S., Cejka, P., and Jiricny, J. “Expression of the MutL homologue hMLH3 in human cells and its role in DNA mismatch repair.” Cancer Research 2005 65(23):10759-66.
Wu, X., Tsai, C., Patam, M., Zan, H., Chen, J., Lipkin, S.M. and Casali, P. “A role for the MutL mismatch repair Mlh3 protein in immunoglobulin class switch DNA recombination and somatic hypermutation.” Journal of Immunology 176: 5426-37.
S.A. Frank, Chen, J., and Lipkin, S.M. “Kinetics of cancer: a method to test hypotheses of genetic causation” BMC Cancer 2005 Dec 21;5:163 .
Chao, L. and Lipkin, SM. “Molecular Models for the Tissue Specificity of DNA Mismatch Repair Deficient Carcinogenesis.” Nucleic Acids Research 2006 Feb 6;34(3):840-52.
Lipkin, SM, Boman, B. and Offit, K. “Hereditary Colorectal Cancer: New Advances and the Integration of Molecular Testing into Clinical Practice.” Journal of Clinical Oncology Supplement 2006 42:64-66
Zell, JA, Rhee,JM, Ziogas, A, Lipkin,SM and Anton-Culver, H. “Race, Socioeconomic Status, Treatment, and Survival Time among Pancreatic Cancer Cases in California.” Cancer Epidemiol Biomarkers Prev 2007;16(3). March 2007
Zishu, P., Sikandar, S., Witherspoon, M., Dizon, D., Bernischke,
K., Vrana, P., and Lipkin, SM.
Impaired Placental Trophoblast Lineage Differentiation in Alkbh1-/-
mice. Developmental
Dynamics February 2008.
Le, H, Ziogas, A, Lipkin,SM and Zell, J. “Race, Socioeconomic Status, Treatment, and Survival among Colorectal Cancer Cases in California.” Cancer Epidemiol Biomarkers Prev 2007;16(3). In press
Chao, E, Velasquez, J, Ng, P, Peel, D, Anton-Culver, H, Gruber,
SB and Lipkin, SM. “MAPP-MMR:
A Novel in silico Approach to Distinguish Deleterious MLH1/MSH2
Missense Mutations from Benign Polymorphisms.” Human Mutation March
27 2008 Epub.
Chen, P., Kuraguchi, M., Velasquez, J., Wang, Y., Yang, K., Edwards, R., Gillen, D., Edelmann, W. Kucherlapati, R.,and Steven M. Lipkin”Novel Roles for MLH3 Deficiency and TLE6-like Amplification in DNA Mismatch Repair-Deficient Gastrointestinal Tumorgenesis and Progression.”PLoS Genetics (in press).
