The CD8 antiviral factor (CAF) can suppress HIV-1 transcription from the long terminal repeat (LTR) promoter in the absence of elements upstream of the CATATAA box.

Varsha Shridhar,Yue Chen,Phalguni Gupta

doi:10.1186/1743-422x-11-130

Abstract

BackgroundThe CD8 Antiviral Factor (CAF) suppresses viral transcription from the HIV-1 Long Terminal Repeat (LTR) promoter in a non-cytolytic manner. However, the region on the LTR upon which CAF acts is unknown. Our objective was to determine the region on the LTR upon which CAF acts to suppress HIV-1 transcription.MethodsSerial deletions of the LTR from the 5’ end and inactivating point mutations were made.ResultsSerial deletions of the LTR from the 5’ end indicated the importance of a short ~120 bp segment, containing the 3 SpI sites, CATA box (used by HIV-1 instead of the TATA box) and TAR region, in the suppressive process. Introduction of deletions or inactivating point mutations in the SpI sites or deletion of the TAR region did not abolish CAF-mediated transcriptional suppression. Yet, CAF-mediated transcriptional suppression was still retained in the HIV-1 CATA-TAR segment.ConclusionCAF is able to suppress transcription from the LTR lacking all the elements upstream of the CATA box. Our results suggest that the HIV-1 CATA box may be responsible for CAF-mediated suppression of transcription from the HIV-1 LTR.

Highlights

CD8+ T cells can control HIV-1 replication by noncytolytic mechanisms [1,2]
When 293 T cells, treated with CD8 Antiviral Factor (CAF) from the CD8+ T cells of an HIV-1 infected individual or with media control, were transfected with CMV-CAT (CAT = chloramphenicol acetyltransferase, a reporter gene), SV40-luciferase or HIV Long Terminal Repeat (LTR)-CAT constructs, we found that CAF was able to completely suppress reporter protein production in cell transfected with the full length HIV-1 LTR construct (referred to as “wt (FL)” in the figure) (Figure 1A)
Their results showed that the replication of full-length HIV-1 molecular clones bearing mutations and deletions in individual transcription factor binding sites could still be suppressed in the presence of CAF

Summary

Introduction

CD8+ T cells can control HIV-1 replication by noncytolytic mechanisms [1,2]. The first non-cytolytic antiviral CD8+ T cell response was described in Long Term Non-Progressers of HIV-1 infection [1] and the factor mediating it was termed “CD8 Antiviral Factor” (CAF) [3]. We focused on determining the region in viral promoter that was crucial for the suppressive effect of CAF. We performed serial progressive deletions on the LTR at 5’ end to identify the minimal region required for CAF-mediated transcriptional suppression. The CD8 Antiviral Factor (CAF) suppresses viral transcription from the HIV-1 Long Terminal Repeat (LTR) promoter in a non-cytolytic manner. Results: Serial deletions of the LTR from the 5’ end indicated the importance of a short ~120 bp segment, containing the 3 SpI sites, CATA box (used by HIV-1 instead of the TATA box) and TAR region, in the suppressive process. Introduction of deletions or inactivating point mutations in the SpI sites or deletion of the TAR region did not abolish CAF-mediated transcriptional suppression. CAF-mediated transcriptional suppression was still retained in the HIV-1 CATA-TAR segment

Objectives

Methods

Results