The role of polymorphisms of glutathione S-transferase pi in redox regulation through protein S-glutathionylation

Abstract #2: Session: Resistance to Antitubulin Drugs, Resistance to Platinums, and Glutathione Metabolism

Glutathione S-transferase P1-1 (GSTP) is a prominent and ubiquitously expressed enzyme protein in many human cancers. Its expression is increased in response to a variety of apparently unrelated stress conditions and high levels (sometimes ~1-2% of cytosolic protein) are frequently linked to drug resistance phenotypes, even when the selecting drug is not a substrate for the enzyme. While recent results have shown that GSTP interacts non-covalently with kinases, it has always seemed probable that a more prevalent cellular function may be ascribed to such a common protein. Recently, we have demonstrated by in vitro and in vivo approaches that the catalytic properties of GSTP are critical to the post-translational S-glutathionylation of cysteine residues in a number of different target proteins (Townsend et al, JBC 2009). Genetic polymorphisms of GSTP have differing catalytic constants for some small molecule substrates. In the present studies, we evaluated the role of GSTP polymorphisms in regulating S-glutathionylation reactions. We generated stably transfected HEK293 cells expressing the four human GSTP*A-D alleles (Ile105/Ala114; Val105/Ala114; Val105/Val114; and Ile105/Val114) and a catalytically inactive mutant. In response to two drugs, NOV-002, a glutathione disulfide mimetic and PABA/NO, a nitric oxide releasing prodrug, cells mount a rapid S-glutathionylation of specific target proteins. The rate of protein S-glutathionylation is significantly enhanced by the presence of a catalytically active (intact tyr7 residue) GSTP and is also is greater for the GSTP*A and *D alleles. A role for GSTP in the catalytic formation of a disulfide between the thiolate of GSH and a low pK cysteine thiol in a target protein is a novel property for GSTP. The differential susceptibility to cancer initiation and drug response associated with some GSTP polymorphisms may be attributable to the their capacity to respond to oxidative and nitrosative stress through protein S-glutathionylation.