Role of the PTEN protein in the multidrug resistance of prostate cancer cells

At present, there is no doubt that the signal transduction pathway P13K/Akt/PTEN/mTOR, controlled by phosphatidylinositol-3-kinase, is involved in tumor cell resistance to a number of drugs. Another well-known mechanism determining drug resistance in tumors is associated with the activity of drug transporters of the ABC superfamily (first of all, P-glycoprotein (Pgp), MRP1, BCRP, and LRP). Several mechanisms of cell defense can simultaneously operate in one cell. The interplay of different mechanisms involved in drug resistance is poorly understood. The PC3 and DU145 human prostate cell lines were used to show that the PTEN functional status determined the cell resistance to some drugs and that correlated with the levels of MRP1 and BCRP. Pgp was not involved in drug resistance of these cells. Introduction of PTEN into PTEN-deficient PC3 cells, as well as rapamycin treatment, inhibited Akt and mTOR and sensitized cells to doxorubicin and vinblastine. Exogenous PTEN altered the MRP1 and BCRP expression. The results indicate that at least two mechanisms of drug resistance operate in prostate cancer cells: the PI3K/Akt/PTEN/mTOR pathway and an elevated MRP1 expression. The mechanisms are interconnected: PTEN and mTOR signaling is involved in MRP1 and BCRP expression regulation.