Protein Kinase A Regulatory Subunit Type IIβ Directly Interacts with and Suppresses CREB Transcriptional Activity in Activated T Cells

Abstract

Levels of the type IIβ regulatory subunit (RIIβ) of protein kinase A are abnormally high in the nuclei of T cells of some subjects with the autoimmune disorder systemic lupus erythematosus (SLE). However, the role of nuclear RIIβ in the regulation of T cell function is unknown. Based on previous studies demonstrating that nuclear protein kinase A-RII subunits can modify cAMP response element (CRE)-dependent transcription, we tested the hypothesis that nuclear RIIβ can alter CRE-directed gene expression in T cells through interaction with the nuclear transcription factor CRE-binding protein CREB. To test this hypothesis, we used the RIIβ-deficient S49 and the Jurkat T cell lines. In both cell lines, transient transfection of RIIβ resulted in nuclear localization of a portion of the ectopically expressed RIIβ. In vitro and in vivo analyses revealed a novel, specific interaction between RIIβ and CREB that mapped to the N-terminal 135 aa of RIIβ. In functional studies, RIIβ inhibited the transcriptional activity of a GAL4-CREB fusion protein by 67% in Jurkat T cells following activation with anti-CD3 and anti-CD28 mAbs. Importantly, deletion of the CREB-binding region of RIIβ completely abrogated inhibition. Additionally, RIIβ suppressed CRE-directed reporter gene expression and substantially reduced induction of promoter activity and endogenous protein levels of the CREB-dependent gene, c-fos, in activated T cells. We conclude that nuclear RIIβ can act as a repressor of CREB transcriptional activity in T cells, providing a potential functional significance for aberrant levels of nuclear RIIβ in systemic lupus erythematosus T cells.