Non canonical functions of cellular transporter P-Glycoprotein

P-glycoprotein/ABCB1 (Pgp) is a well known protein of cell defense system. It is localized in cell membrane and pumps different drugs out of various cells using ATP energy. Its overexpression is associated with the development of multidrug resistance (MDR) in cancer cells. The data showing that Pgp has also another functions appeared recently, and this review surveys these data. In particular: 1) Pgp can protect cells from apop-tosis; it suppresses the endogenous protein TRAIL expression and decreases the activity of caspases 8 and 3; 2) Pgp is able to act as an outwardly directed flippase; 3) Pgp participates in a proper development of an innate immune response to intracellular pathogens and in the development of inflammation; 4) functionally active Pgp can be transferred from drug-resistant to drug-sensitive cells by microvesicles (M V). This is a new way of the Pgp-mediated MDR emergence in populations of tumor cells. Thus, Pgp functions as a regulator of some cellular processes. Molecular mechanisms of the Pgp influence on tumor cell viability are related not only with drug efflux but also with several other functions.