Topology and Function of Human p-Glycoprotein in Multidrug Resistant Breast Cancer Cells.

摘要

Overexpression of P-glycoprotein (Pgp) in breast and other cancers is thought to be largely involved in the development of multidrug resistance to chemotherapy. Pgp has been reported to have multiple topologies and multiple functions. The goal of our research is to investigate the relationship between Pgp structure and its multiple functions. Here, we examined in detail the topologies of the C-terminal half of Pgp. We found that transmembrane (TM) 8 may be important in the generation of multiple topological orientations. In addition, when TM8 initiated membrane insertion, TM9 was found to stop the translocation event and anchor into the membrane. Based on our findings, a model for the C-half topology is proposed. Previously, we were able to manipulate the generation of C-half topologies by altering the charge distribution flanking TM8. Here, we transfected Pgp constructs that contained these alterations in charge distribution into the mouse fibroblast cell line, BALB/c-3T3. Expression of Pgp was determined by quantitative western blot analysis and both drug transport and regulation of swelling-activated chloride currents were examined. To date our results are incomplete to draw any conclusions about the relationship between Pgp topology and function. An update of our progress is discussed.