Differential Activation of Viral and Cellular Promoters by Human T-cell Lymphotropic Virus-1 Tax and cAMP-responsive Element Modulator Isoforms

Megan E Laurance,Roland P.S Kwok,Mary S Huang,Jane P Richards,James R Lundblad,Richard H Goodman

doi:10.1074/jbc.272.5.2646

Abstract

We have previously proposed that cAMP-responsive element-binding protein (CREB) activity is stimulated by human T-cell lymphotropic virus-1 (HTLV-1) Tax through two mechanisms that are differentially dependent upon CREB phosphorylation. We have tested this model by examining how Tax affects transcriptional activation mediated by the cAMP-responsive element (CRE) modulator (CREM). The CREM proteins are highly homologous to CREB, particularly in their DNA-binding domains and the kinase-inducible domain (KID), a region that interacts with the coactivator CREB-binding protein (CBP) in a phosphorylation-dependent manner. Despite this similarity, most CREM isoforms are transcriptional repressors. CREMalpha lacks the glutamine-rich domains found in CREB that are essential for transcriptional activation. We show that the normally repressive CREMalpha activates the HTLV-1 and cellular CREs in the presence of Tax; activation of the viral element is phosphorylation-independent, and activation of the cellular CRE is phosphorylation-dependent. CREMDelta(C-G) lacks both the KID and the glutamine-rich regions. This isoform activates the HTLV-1 long terminal repeat in a phosphorylation-independent manner, but does not activate the cellular CRE. This study suggests that Tax, interacting with the basic/zipper region of CREM, recruits CBP to the viral promoter. Tax activation of the cellular CRE depends on the KID and its ability to interact with CBP in a phosphorylation-dependent manner.

Highlights

Human T-cell lymphotropic virus-1 (HTLV-1)1 is the causative agent in adult T-cell leukemia (1)
We showed that the ability of Tax to function in this manner depends upon cAMP-responsive element-binding protein (CREB) phosphorylation, as the augmentation is prevented when protein kinase A (PKA) is omitted and is significantly decreased when the consensus PKA site in the kinase-inducible domain (KID) of CREB is mutated (8)
Our model for Tax activation of cAMP-responsive element (CRE)-containing genes (8) suggested that CREM␣ should be converted into a PKA-dependent activator by the addition of Tax

Summary

Introduction

Human T-cell lymphotropic virus-1 (HTLV-1)1 is the causative agent in adult T-cell leukemia (1). By using a combination of in vivo transfection and in vitro fluorescence polarization binding assays, we show that the Tax activation of cellular and viral CRE-containing genes is mediated through different functional domains of the bZIP proteins in a manner that is differentially dependent upon phosphorylation.

Results

Conclusion