Evidence that protein kinase A activity is required for the basal and tax‐stimulated transcriptional activity of human T‐cell leukemia virus type‐I long terminal repeat

Abstract

The present study was undertaken to investigate the role of protein kinase A (PKA) in the control of human T-cell leukemia virus type-I (HTLV-I) long terminal repeat (LTR) expression, since this issue is still controversial. For this purpose we employed two human T-cell lines; the Jurkat cells in which long exposure to diBu-cAMP severely down-regulated the catalytic subunit of PKA (PKA-C), and H-9 cells in which such exposure markedly increased PKA-C level. Transient transfection assays revealed that addition of diBu-cAMP 1 h before or after transfection profoundly increased HTLV-I LTR directed CAT expression and synergistically enhanced its stimulation by the viral transactivator tax gene product in both cell lines. However longer exposure to diBu-cAMP before transfection reduced LTR-CAT expression to below its basal level and completely abolished its stimulation by tax in Jurkat cells, and this diBu-cAMP inhibitory effect could be abrogated by cotransfection of a PKA-C expressing vector. By contrast, in H-9 cells, this long exposure to diBu-cAMP continued enhancing LTR-CAT expression and its tax-mediated transactivation, and this stimulatory effect of diBu-cAMP could be diminished by the PKA-specific inhibitor N-[2-(p-bromocinnamylamine)ethyl]-5-isoquinolinsulfonamide (H-89). Notably, in the absence of diBu-cAMP treatment H-89 reduced LTR-CAT expression to below its basal level and prevented its stimulation by tax in both cell lines. Together these findings indicate not only that cAMPactivated PKA stimulates HTLV-I LTR expression and its transactivation by tax, but even in the absence of PKA activating signals the basal HTLV-I LTR expression as well as its stimulation by tax are both dependent on a basal PKA activity.z 1998 Federation of European Biochemical Societies.

Reciprocal Interactions between Human T-Lymphotropic Virus Type 1 and Prostaglandins: Implications for Viral Transmission

“…These results confirm a recent study demonstrating that PKA activity is required for HTLV-1 LTR activity (34) promoter for COX-2, a PG synthetase, leading to production of PGE 2 . Therefore, it is likely that such mutual aid helps accelerate viral transmission through seminal fluid or breast milk.…”

Co-requirement of Cyclic AMP- and Calcium-dependent Protein Kinases for Transcriptional Activation of Cholecystokinin Gene by Protein Hydrolysates

“…2A). Furthermore, extended exposure to agents that increase cAMP cell content has been shown to desensitize the cAMP-dependent pathway in cells of different origin, by down-regulating the PKA C (23)(24)(25). In STC-1 cells transfected with the Ϫ765-bp CCK gene promoter, pretreatment with 10 M forskolin for 24 h before a 16-h incubation period in the presence of forskolin/IBMX strongly decreased the stimulation of CCK gene promoter activity (Fig.…”

Molecular Characterization of the Tax-containing HTLV-1 Enhancer Complex Reveals a Prominent Role for CREB Phosphorylation in Tax Transactivation

“…Consonant with our hypotheses that Tax promotes CREB phosphorylation and utilizes pCREB for transactivation, kinase inhibitors have been shown to block Tax function (16,35). Another study (36) showed that Tax expression in mouse fibroblasts resulted in sustained CREB phosphorylation during serum starvation in both the absence and presence of forskolin, in agreement with our results.…”