INCREASING THE RATIO OF PP2A CORE ENZYME TO HOLOENZYME INHIBITS TAT-STIMULATED HIV-1 TRANSCRIPTION AND VIRUS PRODUCTION

We demonstrated previously that PP2A exists in many cell types as two abundant forms: (1) holoenzyme composed of two regulatory subunits, A and B, and a catalytic subunit C; and (2) core enzyme consisting of th e A and C subunits. These two forms have different substrate specifici ties. Since published data suggested that HIV-I transcription may be r egulated by a cellular protein phosphatase, it was of interest to dete rmine whether changing the ratio between PP2A core and holoenzyme affe cts HIV-1 gene expression. This question was addressed by expression i n COS cells of an N-terminal mutant of the A subunit, A Delta 5, which binds the C but not the B subunit. This resulted in an increase in th e amount of core enzyme and a decrease in the amount of holoenzyme con comitant with the expected change in phosphatase activity. Tat-stimula ted transcription from the HIV-I LTR was inhibited 5-fold by mutant A Delta 5, whereas mRNA synthesis directed by the actin promoter was not affected. Furthermore, virus production in COS, HeLa, and Jurkat T ce lls was inhibited 45-, 5-, and 3-fold, respectively, by mutant A Delta 5. These results demonstrate that the balance between PP2A holoenzyme and core enzyme is important for HIV-I gene expression and virus prod uction. (C) 1997 academic Press.