Selective inhibition of mitogen-induced transactivation of the HIV long terminal repeat by carboxyamidotriazole. Calcium influx blockade represses HIV-1 transcriptional activation.

Carboxyamidotriazole (CAI) is a calcium influx inhibitor that has both antiproliferative and antimetastatic activities. Pretreatment of human T-cells with micromolar concentrations of CAI causes a near complete inhibition of calcium-regulated mitogen-induced transcription from the human immunodeficiency virus (HIV) long terminal repeat (LTR). This inhibition is selective since other mitogen-activated gene regulatory elements, such as the 12-O-tetradecanoylphorbol-13-acetate response element, are not influenced by the drug. HIV LTR transcription inhibition is maximal at 1.0 microM CAI, requires a pretreatment interval of at least 8 h for optimum inhibition, and shows no acute interference with the growth properties of the cells. Moreover, the inhibition is rapidly reversible upon removal of the drug from the medium. Studies to identify enhancer elements within the HIV LTR that are functionally sensitive to low-dose long-term pretreatment with CAI indicate that the NF-kappaB-binding sites are among the major targets of drug action. In vitro DNA binding studies with nuclear extracts prepared from mitogen-induced T-cells stimulated in the presence of CAI indicate that the drug differentially influences the calcium-regulated downstream signal transduction pathways necessary for specific NF-kappaB DNA binding activity at the two kappaB sites within the HIV LTR. Studies with ionomycin and thapsigargin show that repression is specific for selected modes of inducible calcium entry and indicate that, in T-cells, a major mechanism of CAI action is to modulate calcium influx at a level that is proximal to the regulated release of calcium from intracellular stores. Measurement of calcium influx in CAI-treated cells reveals a dramatic and reversible inhibition of mitogen-induced calcium influx. These results indicate that CAI can be an important and effective pharmacological tool for analysis of the calcium-dependent modulation of HIV LTR transcription.