Short Communication Glutathione Transferase P1 Interacts Strongly with the Inner Leaflet of the Plasma Membrane

GSH transferases (GSTs) are a superfamily of proteins best known for detoxifying harmful electrophilic compounds by catalyzing their conjugation with GSH. GSTP1 is the most prevalent and widely distributed GST in human tissues, helping to detoxify a diverse array of carcinogens and drugs. In contrast with its protective role, overexpression of GSTP1 in a variety of malignancies is associated with a poor prognosis due to failure of chemotherapy. Although GSTP1 is classified as a cytosolic GST, we discovered previously that it is associated with the plasma membrane of the small cell lung cancer cell lines, H69 and H69AR. In the current study, en-dogenous and overexpressed GSTP1 in human embryonic kidney (HEK) 293 and MCF-7 cell lines, respectively, were found also to associate with the plasma membrane, indicating that this interac-tion is not unique to H69 and H69AR cells. GSTP1 immunostaining in HEK293 and MCF7-GSTP1 cells only occurred under permeabil-ized conditions, suggesting that GSTP1 is associated with the intracellular surface of the plasma membrane. Cell surface bioti-nylation studies confirmed this finding. Immunogold electron mi-croscopy revealed the presence of GSTP1 in close proximity to the plasma membrane. GSTP1 was not dissociated from plasma mem-brane sheets by high salt [potassium iodide (KI; 1 M) or KI/EDTA (1 M/2 mM)] or alkaline Na2CO3 (100 mM, pH 11.4), conditions known to strip peripherally associated membrane proteins. Thus, we re-port for the first time that GSTP1 is associated with the inner leaflet of the plasma membrane through a remarkably strong interaction