PP2A regulates BCL-2 phosphorylation and proteasome-mediated degradation at the endoplasmic reticulum.
Anti-apoptotic activity of BCL-2 is mediated by phosphorylation at the endoplasmic reticulum (ER), but how this phosphorylation is regulated and the mechanism(s) by which it regulates apoptosis are unknown. We purified macromolecular complexes containing BCL-2 from ER membranes and found that BCL-2 co-purified with the main two subunits of the serine/threonine phosphatase, PP2A. The association of endogenous PP2A and BCL-2 at the ER was verified by co-immunoprecipitation and microcystin affinity purification. Knock down or pharmacological inhibition of PP2A caused degradation of phosphorylated BCL-2 and led to an overall reduction in BCL-2 levels. We found that this degradation was due to the action of the proteasome acting selectively at the ER. Conversely, overexpression of PP2A caused elevation in endogenous BCL-2. Most importantly, we found that PP2A knock down sensitized cells to several classes of death stimuli (including ER stress), but this effect was abolished in a genetic background featuring knock in of a non-phosphorylatable BCL-2 allele. These studies support the hypothesis that PP2A-mediated dephosphorylation of BCL-2 is required to protect BCL-2 from proteasome-dependent degradation, affecting resistance to ER stress.
Lin
Stephen S
SS
Howard Hughes Medical Institute, Department of Cancer Immunology and AIDS, Department of Medical Oncology, Dana-Farber Cancer Institute and Harvard Medical School, Boston, Massachusetts 02115, USA.
Bassik
Michael C
MC
Suh
Heikyung
H
Nishino
Mari
M
Arroyo
Jason D
JD
Hahn
William C
WC
Korsmeyer
Stanley J
SJ
Roberts
Thomas M
TM
D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D019169:Jurkat Cells; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D010749:Phosphoprotein Phosphatases / Q000378:metabolism / Q000502:physiology*; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
D019253:Proto-Oncogene Proteins c-bcl-2; D010749:Phosphoprotein Phosphatases; D046988:Proteasome Endopeptidase Complex