The invention is based in part on the discovery that uncoupling proteins (UCPs) are expressed in the plasma membrane of rapidly dividing cells but not of growth arrested, chemotherapy resistant cells. It has also been found according to the invention that UCP is expressed in the lysosomal membrane under certain metabolic conditions. Thus the invention is methods, products, screening assays and kits relating to the manipulation of UCP expression within cellular and intracellular membranes.