Functional Analysis of HIV-1 subtypes B and C HIV-1 Tat exons and RGD/QGD motifs with respect to Tatmediated transactivation and Apoptosis

Abstract

HIV-1 Tat is known to influence several intracellular functions including its ability to activate long terminal repeat (LTR) promoter-mediated transactivation and cause apoptosis [1–3]. Although a number of studies have been performed with subtype B gene products, relatively little information is available for subtype C, which is responsible for causing more than 50% infections worldwide, including India where it is the major subtype. In the present study, we constructed several recombinant clones of Tat-B (derived from pNL4-3) [4] and Tat-C (derived from an Indian isolate which is 95% similar to the consensus subtype C based on its amino acid sequence [5] (clone 93IN905, GenBank Accession no. AF067158) [6] with respect to the two exons for fine functional domain analysis. It is worth noting that most subtype C isolates possess QGD compared with RGD in the second exon of Tat gene in the same position (78–80 amino acids) (a known cell adhesion motif), which is associated with integrin-mediated signaling and cell adhesion, etc., besides other changes throughout the gene. We reasoned that these changes might modulate its ability to transactivate LTR promoters and apoptosis. Therefore, we made constructs of subtypes B and C Tat that consisted of either the RGD or QGD motif and also swapped the first and second exons of the Tat gene. Precise gene fusion technologywas used to generate such chimeric constructs as described by one of us earlier [7] and confirmed by sequencing. The various constructs made are indicated at the bottom of Fig. 1a with Tat-B and Tat-C with RGD/QGD domains. An internal reporter gene control (pSV-b-gal; Promega, Madison, Wisconsin, USA) was always included to ensure uniform transfection efficiency.