leupeptins and Acquired-Immunodeficiency-Syndrome

The human multidrug resistance P-glycoprotein (P-gp) contributes to the phenomenon of multidrug resistance during cancer and AIDS chemotherapy. A potential novel strategy to circumvent the effects of P-gp during chemotherapy is to prevent maturation of P-gp during biosynthesis so that the transporter does not reach the cell surface. Here we report that immature, core-glycosylated P-gp that is prevented from reaching the cell surface by processing mutations or by proteasome inhibitors such as lactacystin or MG-132 exhibited no detectable drug-stimulated ATPase activity. Disulfide cross-linking analysis also showed that the immature P-gp did not exhibit ATP-induced conformational changes as found in the mature enzyme. In addition, the immature P-gp was more sensitive to trypsin than the mature enzyme. These results suggest that P-gp is unlikely to be functional immediately after synthesis. These differences in the structural and enzymatic properties of the mature and core-glycosylated, immature P-gp could potentially be used during chemotherapy, and should result in the search for compounds that can specifically inhibit the maturation of P-gp.

Topics: Acetylcysteine; Acquired Immunodeficiency Syndrome; Adenosine Triphosphatases; Adenosine Triphosphate; ATP Binding Cassette Transporter, Subfamily B, Member 1; Biological Transport; Cell Membrane; Cysteine Endopeptidases; Cysteine Proteinase Inhibitors; Drug Resistance, Multiple; Glycosylation; Humans; Leupeptins; Multienzyme Complexes; Neoplasms; Proteasome Endopeptidase Complex; Protein Conformation; Protein Folding; Protein Precursors; Protein Processing, Post-Translational