Thr 163 phosphorylation causes Mcl-1 stabilization when degradation is independent of the adjacent GSK3-targeted phosphodegron, promoting drug resistance in cancer.
The antiapoptotic Bcl-2 family member Mcl-1 is a PEST protein (containing sequences enriched in proline, glutamic acid, serine, and threonine) and is subject to rapid degradation via multiple pathways. Impaired degradation leading to the maintenance of Mcl-1 expression is an important determinant of drug resistance in cancer. Phosphorylation at Thr 163 in the PEST region, stimulated by 12-O-tetradecanoylphorbol acetic acid (TPA)-induced activation of extracellular signal-regulated kinase (ERK), is associated with Mcl-1 stabilization in BL41-3 Burkitt lymphoma cells. This contrasts with the observation that Thr 163 phosphorylation in normal fibroblasts primes glycogen synthase kinase (GSK3)-induced phosphorylation at Ser 159, producing a phosphodegron that targets Mcl-1 for degradation. In the present follow-up studies in BL41-3 cells, Mcl-1 degradation was found to be independent of the GSK3-mediated pathway, providing a parallel to emerging findings showing that Mcl-1 degradation through this pathway is lost in many different types of cancer. Findings in Mcl-1-transfected CHO cells corroborated those in BL41-3 cells in that the GSK3-targeted phosphodegron did not play a major role in Mcl-1 degradation, and a phosphomimetic T163E mutation resulted in marked Mcl-1 stabilization. TPA-treated BL41-3 cells, in addition to exhibiting Thr 163 phosphorylation and Mcl-1 stabilization, exhibited an ∼10-fold increase in resistance to multiple chemotherapeutic agents, including Ara-C, etoposide, vinblastine, or cisplatin. In these cancer cells in which Mcl-1 degradation is not dependent on the GSK3/phosphodegron-targeted pathway, ERK activation and Thr 163 phosphorylation are associated with pronounced Mcl-1 stabilization and drug resistance - effects that can be suppressed by inhibition of ERK activation.
Department of Pharmacology and Toxicology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, United States of America.
Shanna K
SK
Nifoussi
Julie A
JA
Vrana
Aaron M
AM
Domina
Alfredo
A
De Biasio
Jingang
J
Gui
Mark A
MA
Gregory
Stephen R
SR
Hann
Ruth W
RW
Craig
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D015153:Blotting, Western; D016466:CHO Cells; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology; D006224:Cricetinae; D003561:Cytarabine / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D005047:Etoposide / Q000494:pharmacology; D005434:Flow Cytometry; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D010766:Phosphorylation; D055550:Protein Stability; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D013912:Threonine / Q000378:metabolism*; D014747:Vinblastine / Q000494:pharmacology
D000970:Antineoplastic Agents; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D019253:Proto-Oncogene Proteins c-bcl-2; D003561:Cytarabine; D013912:Threonine; D014747:Vinblastine; D005047:Etoposide; D038362:Glycogen Synthase Kinase 3; D002945:Cisplatin