title: Inhibition of protein phosphatase 2A (PP2A) prevents Mcl-1 protein dephosphorylation at the Thr-163/Ser-159 phosphodegron, dramatically reducing expression in Mcl-1-amplified lymphoma cells.
abstract: Abundant, sustained expression of prosurvival Mcl-1 is an important determinant of viability and drug resistance in cancer cells. The Mcl-1 protein contains PEST sequences (enriched in proline, glutamic acid, serine, and threonine) and is normally subject to rapid turnover via multiple different pathways. One of these pathways involves a phosphodegron in the PEST region, where Thr-163 phosphorylation primes for Ser-159 phosphorylation by glycogen synthase kinase-3. Turnover via this phosphodegron-targeted pathway is reduced in Mcl-1-overexpressing BL41-3 Burkitt lymphoma and other cancer cells; turnover is further slowed in the presence of phorbol ester-induced ERK activation, resulting in Mcl-1 stabilization and an exacerbation of chemoresistance. The present studies focused on Mcl-1 dephosphorylation, which was also found to profoundly influence turnover. Exposure of BL41-3 cells to an inhibitor of protein phosphatase 2A (PP2A), okadaic acid, resulted in a rapid increase in phosphorylation at Thr-163 and Ser-159, along with a precipitous decrease in Mcl-1 expression. The decline in Mcl-1 expression preceded the appearance of cell death markers and was not slowed in the presence of phorbol ester. Upon exposure to calyculin A, which also potently inhibits PP2A, versus tautomycin, which does not, only the former increased Thr-163/Ser-159 phosphorylation and decreased Mcl-1 expression. Mcl-1 co-immunoprecipitated with PP2A upon transfection into CHO cells, and PP2A/Aα knockdown recapitulated the increase in Mcl-1 phosphorylation and decrease in expression. In sum, inhibition of PP2A prevents Mcl-1 dephosphorylation and results in rapid loss of this prosurvival protein in chemoresistant cancer cells.
authors.affiliation: From the Departments of Pharmacology and Toxicology and the Norris Cotton Cancer Center, Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire 03766.
authors.forename: Shanna K
authors.initials: SK
authors.lastname: Nifoussi
authors.affiliation: Pathology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire 03755, the Veterans Affairs Medical Center, White River Junction, Vermont 05001.
authors.forename: Nora R
authors.initials: NR
authors.lastname: Ratcliffe
authors.affiliation: Pathology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire 03755.
authors.forename: Deborah L
authors.initials: DL
authors.lastname: Ornstein
authors.affiliation: Cell Signaling Technology, Danvers, Massachusetts 01923, and.
authors.forename: Gary
authors.initials: G
authors.lastname: Kasof
authors.affiliation: Department of Pharmacology, The University of Iowa, Iowa City, Iowa 52242.
authors.forename: Stefan
authors.initials: S
authors.lastname: Strack
authors.affiliation: From the Departments of Pharmacology and Toxicology and the Norris Cotton Cancer Center, Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire 03766, Ruth.W.Craig@Dartmouth.edu.
authors.forename: Ruth W
authors.initials: RW
authors.lastname: Craig
mesh_terms: D001665:Binding Sites; D002051:Burkitt Lymphoma / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression; D055785:Gene Knockdown Techniques; D006801:Humans; D020935:MAP Kinase Signaling System; D008387:Marine Toxins; D064549:Myeloid Cell Leukemia Sequence 1 Protein / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019319:Okadaic Acid / Q000494:pharmacology; D010080:Oxazoles / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors* / Q000235:genetics; D059748:Proteolysis; D012694:Serine / Q000737:chemistry; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013912:Threonine / Q000737:chemistry
chemical_list: D004791:Enzyme Inhibitors; C579095:MCL1 protein, human; D008387:Marine Toxins; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D010080:Oxazoles; D019319:Okadaic Acid; D013912:Threonine; D012694:Serine; C059041:calyculin A; D054648:Protein Phosphatase 2; D013755:Tetradecanoylphorbol Acetate
keywords: B-cell Lymphoma 2 (Bcl-2) Family; Cancer; Cell Death; Extracellular Signal-regulated Kinase (ERK); Mcl-1; Protein Phosphatase 2 (PP2A)