Identification and characterization of an alternatively spliced isoform of the human protein phosphatase 2Aalpha catalytic subunit.
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Migueleti DL, Smetana JH, Nunes HF, Kobarg J, Zanchin NI
Identification and characterization of an alternatively spliced isoform of the human protein phosphatase 2Aalpha catalytic subunit.
J Biol Chem. 2012 Feb 10;287(7):4853-62. doi: 10.1074/jbc.M111.283341. Epub 2011 Dec 13.
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- 22167190 [ View in PubMed]
- Abstract
PP2A is the main serine/threonine-specific phosphatase in animal cells. The active phosphatase has been described as a holoenzyme consisting of a catalytic, a scaffolding, and a variable regulatory subunit, all encoded by multiple genes, allowing for the assembly of more than 70 different holoenzymes. The catalytic subunit can also interact with alpha4, TIPRL (TIP41, TOR signaling pathway regulator-like), the methyl-transferase LCMT-1, and the methyl-esterase PME-1. Here, we report that the gene encoding the catalytic subunit PP2Acalpha can generate two mRNA types, the standard mRNA and a shorter isoform, lacking exon 5, which we termed PP2Acalpha2. Higher levels of the PP2Acalpha2 mRNA, equivalent to the level of the longer PP2Acalpha mRNA, were detected in peripheral blood mononuclear cells that were left to rest for 24 h. After this time, the peripheral blood mononuclear cells are still viable and the PP2Acalpha2 mRNA decreases soon after they are transferred to culture medium, showing that generation of the shorter isoform depends on the incubation conditions. FLAG-tagged PP2Acalpha2 expressed in HEK293 is catalytically inactive. It displays a specific interaction profile with enhanced binding to the alpha4 regulatory subunit, but no binding to the scaffolding subunit and PME-1. Consistently, alpha4 out-competes PME-1 and LCMT-1 for binding to both PP2Acalpha isoforms in pulldown assays. Together with molecular modeling studies, this suggests that all three regulators share a common binding surface on the catalytic subunit. Our findings add important new insights into the complex mechanisms of PP2A regulation.