Pi-class glutathione S-transferase: regulation and function.

Our laboratory has been involved in the study of Glutathione S-transferase pi (GST pi) for many years, both in terms of regulation of gene expression and in trying to understand the endogenous function(s) of this enzyme and also what role it may play in the carcinogenic process [1]. Over-expression of GST pi has been associated with carcinogenesis and the development of many different human tumours, for example testis [2], ovarian [3] and colorectal [4] and is often inversely correlated with prognosis or patient survival [5,6]. In addition, GST Pi has been implicated in the acquisition of antineoplastic drug resistance [7-9]. In order to study the transcriptional regulation of this gene, we have utilised a multi-drug resistant derivative (VCREMS) of the human mammary carcinoma cell line, MCF7, in which GST P1 mRNA and protein are significantly elevated in the absence of gene amplification [10-13]. Interestingly, we have recently reported the discovery of polymorphisms at the GSTP1 locus, resulting in two alleles GSTP1a and GSTP1b. In the study, the GSTP1b allele was found with increased frequency in bladder and testicular cancer, while the GSTP1a allele was significantly decreased in cases of prostate cancer [14]. In an attempt to elucidate the endogenous role(s) of GST pi, we have used homologous recombination in embryonic stem (ES) cells to inactivate both murine GST Pi genes and create a mouse strain completely deficient in the expression of this enzyme. This provides us with a unique animal model with which to study the effects of the absence of GST pi expression on the metabolism and pharmacokinetics of xenobiotics.