The Influence of a Single Nucleotide Polymorphism In The MatrixMetalloproteinase-1 Promoter on Glioma Biology

Abstract

THE INFLUENCE OF A SINGLE NUCLEOTIDE POLYMORPHISM IN THE MATRIX METALLOPROTEINASE-1 PROMOTER ON GLIOMA BIOLOGY Jessica McCready A dissertation submitted in partial fulfillment of the requirements for ,the degree of Doctor of Philosophy at Virginia Commonwealth University Virginia Commonwealth University, 2006 Director: Helen L. Fillmore, Ph.D. Assistant Professor Department of Neurosurgery, Adjunct Assistant Professor Department of Anatomy and Neurobiology Glioblastomas are an incurable type of brain tumor with a mean survival time of 9-12 months following diagnosis. One of the reasons for this poor prognosis is the ability of tumor cells to invade the surrounding normal brain tissue. Enzymes responsible for this invasive nature include the matrix metalloproteinase family. MMP1 is a member of this family which has been well studied in many types of invasive ,tumors, with gliomas being an exception. We studied a single nucleotide polymorphism (SNP) in the MMP-1 promoter that may influence glioma biology. This SNP consists of the presence (2G) or absence (1G) of a guanine nucleotide at position -1607. The additional guanine nucleotide creates a binding site for ETS transcription factors and combined with the AP-1 binding site at position -1602 creates a Ras Responsive Element. We determined that the distribution of the MMP-1 genotype differed significantly between the healthy population and the glioblastoma patient population, with the 2G/2G genotype more prevalent in the glioblastoma patients. In addition, MMP-1 mRNA and protein examined in a select group of patient tissue had significantly higher levels when compared to normal brain controls, however, there was no correlation with genotype. Promoter reporter assays indicated that the 2G promoter was approximately three times more active than the 1G promoter in three different glioma cell lines. We investigated potential signaling mechanisms responsible for increases in MMP-1 transcription due to the presence of the RAS responsive element. Treatment of glioma cell lines with hepatocyte growth factorlscatter factor (HGFISF) led to significant increases in MMP-1 transcription, via the MAP kinase ERK pathway. AP-1 transcription factor proteins, cJun and cFos were increased in response to HGF treatment but not Ets-1 and ETV-1. HGFISF treatment of glioma cell lines differing in their MMP-1 genotype affected binding of ETS and AP-1 proteins to the endogenous MMP-1 distal promoter. Using chromatin immunoprecipitation assays, we identified these differentially DNA-bound AP-1 and ETS proteins. The data presented indicate that the MMP-1 SNP (-1607) is important in glioma biology and may contribute to tumor function and future investigations into its role in glioma biology is warranted. Chapter