Journal of Biological Chemistry
Volume 282, Issue 37, 14 September 2007, Pages 26971-26980
Journal home page for Journal of Biological Chemistry

Enzyme Catalysis and Regulation
Selection of Protein Phosphatase 2A Regulatory Subunits Is Mediated by the C Terminus of the Catalytic Subunit*

https://doi.org/10.1074/jbc.M704059200Get rights and content
Under a Creative Commons license
open access

Protein phosphatase 2A (PP2A) is a family of multifunctional serine/threonine phosphatases all composed of a catalytic C, a structural A, and a regulatory B subunit. Assembly of the complex with the appropriate B subunit forms the key to the functional specificity and regulation of PP2A. Emerging evidence suggests a crucial role for methylation and phosphorylation of the PP2A C subunit in this process. In this study, we show that PP2A C subunit methylation was not absolutely required for binding the PR61/B′ and PR72/B″ subunit families, whereas binding of the PR55/B subunit family was determined by methylation and the nature of the C-terminal amino acid side chain. Moreover mutation of the phosphorylatable Tyr307 or Thr304 residues differentially affected binding of distinct B subunit family members. Down-regulation of the PP2A methyltransferase LCMT1 by RNA interference gradually reduced the cellular amount of methylated C subunit and induced a dynamic redistribution of the remaining methylated PP2AC between different PP2A trimers consistent with their methylation requirements. Persistent knockdown of LCMT1 eventually resulted in specific degradation of the PR55/B subunit and apoptotic cell death. Together these results establish a crucial foundation for understanding PP2A regulatory subunit selection.

Cited by (0)

Note Added in Proof—When this work was finished and submitted for review, we became aware of the work by E. Sontag and co-workers (42). The authors basically came to the same conclusions that C-terminal methylation of PP2AC and phosphorylation of Tyr307 and Thr304 are differentially important for formation of the different holoenzyme forms. There are some apparent discrepancies, though, that might be explained by the different experimental approaches. Whereas in our study the pulldowns of the individual GST fusions with the “third” subunits would reveal rather the intrinsic affinity of a specific subunit for the mutant forms of PP2AC, the use of an IP approach with the mutant catalytic subunits would largely reflect the presence of the relative amounts and affinities of the different subunits in the cellular conditions used. As discussed, we cannot explain the conflicting data of the methylation deficiency of Y307F in our work and in Ref. 4 as opposed to the results in Ref. 3 and 19, and now also 42, which might originate from the use of one and the same construct in the latter studies.

*

This work was supported by grants from the “Geconcerteerde Onderzoeks-Acties” (Flemish government), IUAP “Interuniversity Attraction Poles” (Belgian Science Policy), and F.W.O.-Vlaanderen. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.