title: Suppression of autophagy sensitizes multidrug resistant cells towards Src tyrosine kinase specific inhibitor PP2.
abstract: Upregulated Src activity has been implicated in a variety of cancers. Thus, Src family tyrosine kinase (SFK) inhibitors are often effective cancer treatments. Here, we employed 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2), a selective SFK inhibitor, to determine the possible involvement of tyrosine phosphorylation in the modulation of autophagy, for overcoming multidrug resistance. We found that multidrug-resistant v-Ha-ras-transformed NIH 3T3 cells (Ras-NIH 3T3/Mdr) were more susceptible to PP2 treatment than were their parental cells (Ras-NIH 3T3). The antiproliferative activity of PP2 appeared to be due to cell-cycle arrest at G1/S without induction of apoptosis. Interestingly, PP2 preferentially induced autophagy in Ras-NIH 3T3 cells but not in Ras-NIH 3T3/Mdr cells, which implies that a high level of autophagy may protect PP2-treated cells from undergoing cell death. PP2-induced autophagy in Ras-NIH 3T3 cells is accompanied by an inhibition of the mTOR signaling pathway. However, we found that in Ras-NIH 3T3/Mdr cells, PP2-induced mTOR inhibition was uncoupled from the induction of autophagy-likely due to the hyperactivation of AMPK by delayed Raf activation. We also found that PP2-induced dissociation of Beclin 1 from Bcl-2 leads to autophagy in Ras-NIH 3T3 cells. Taken together, these results suggest that functional autophagy in response to PP2 may lead to cell survival in Ras-NIH 3T3 cells, while defective autophagy may contribute to inhibition of growth in Ras-NIH 3T3/Mdr cells. Thus, modulators of autophagy may be used beneficially as adjunctive therapeutic agents during the treatment of cancers with SFK inhibitors.
authors.affiliation: Division of Life Sciences, College of Natural Sciences, University of Incheon, Incheon 406-772, Republic of Korea.
authors.forename: Jun-Ho
authors.initials: JH
authors.lastname: Ahn
authors.forename: Michael
authors.initials: M
authors.lastname: Lee
mesh_terms: D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D001343:Autophagy / Q000187:drug effects* / Q000235:genetics; D000071186:Beclin-1; D048708:Cell Growth Processes / Q000187:drug effects; D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000096:biosynthesis; D015536:Down-Regulation / Q000187:drug effects; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D016193:G1 Phase / Q000187:drug effects; D051379:Mice; D041681:NIH 3T3 Cells; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011743:Pyrimidines / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D014162:Transfection; D019061:src-Family Kinases / Q000037:antagonists & inhibitors*
chemical_list: C412373:AG 1879; D051017:Apoptosis Regulatory Proteins; D000071186:Beclin-1; C115010:Becn1 protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D047428:Protein Kinase Inhibitors; D011743:Pyrimidines; C546843:mTOR protein, mouse; D019061:src-Family Kinases; D058570:TOR Serine-Threonine Kinases