Function of Protein Phosphatase 2A in Control of Proliferation: Isolation and Analysis of Dominant-Defective Mutants

摘要

Reversible protein phosphorylation plays a crucial role in the circuitry controlling diverse cellular processes, and the activities of phosphorylating and dephosphorylating enzymes must be carefully balanced in normal cells. It is well documented that many of these enzymes are constitutively expressed, but their activities are tightly regulated by a variety of post translational mechanisms. In the case of the serine/threonine- specific protein phosphatase 2A (PP2A), a catalytic subunit is bound by two regulatory subunits designated A and B. Previously, we established a functional complementation assay for PP2A-C in the yeast S. cerevisiae and used this system to isolate two dominant-defective mutants in the human PP2A-Ca gene. We generated epitope-tagged forms of the wild-type and mutant alleles and showed that the epitope-tagged alleles retain biological function in our yeast system. The mutant alleles show reduced binding of the A regulatory subunit in yeast and mammalian cells. Stable fibroblastic cell lines expressing mutant and wild-type proteins have been isolated These studies will thus increase our understanding of PP2A function in the regulation of proliferation and malignant transformation, and will yield important information about structure-function relationships in the PP2A catalytic and regulatory subunit proteins.