The PP2A protein is a type of Serine/Threonine phosphatase with multiple functions in cellular physiology and signaling, mainly in apoptosis, cell cycle control and as a tumor suppressor. PP2A is a heterotrimer comprised of a catalytic subunit (C), a scaffolding subunit (A) and a variable regulatory subunit (B). The B subunit may belong to different families (B, B', B'' and B''') and each of these determines substrate specificity and subcellular localization of this phosphatase. It is known that regulatory proteins PME-1, LCMT-1, ±4, PTPA and TIPRL are involved in the phosphatase biogenesis process. This process consists of a series of steps involving the recognition of conserved sequence at C-terminal of the catalytic subunit and the sequential modification of the catalytic site that leads to active conformation. However, it is still unknown, how and when each of these proteins act in this process, especially in the case of TIPRL. TIPRL has a positive role in the development of liver cancer and possibly other cancers. Recently, our group has resolved the three-dimensional structure of the human TIPRL protein and demonstrated that this protein specifically binds to the conserved sequence present at the C-terminus of these phosphatases, which strongly suggests a role in the biogenesis process. Therefore, this project aims to study the biogenesis of PP2A phosphatase, elucidating the role of each of the regulatory proteins, mainly TIPRL, in the assembly and activity of the heterotrimer in normal and tumor cells. For the project development, site-directed mutagenesis techniques will be used, and the generated mutants will be expressed in human cells and their interactions and activity will be determined. The subcellular localization of regulatory proteins and mutants will be determined by confocal microscopy. The interactions profile and enzymatic activity of PP2A will be also analyzed by overexpression and silencing of TIPRL and ±4, under normal and nutritional stress conditions. Preliminary results of this project indicate that TIPRL can play an important role in the regulation of the assembly and activity of the holoenzyme PP2A.
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