Genetic evidence that stress-activated p38 MAP kinase is necessary but notsufficient for UV activation of HIV gene expression

We have examined the role of stress-activated p38 MAP kinase in regulating human immunodeficiency virus (HIV) gene expression in response to ultraviol et light (UV). We found that UV activated p38 in HeLa cells harboring stabl y integrated copies of an HIVcat plasmid to levels similar to those obtaine d by hyperosmotic shock. However, hyperosmotic shock resulted in one order of magnitude smaller increase in CAT activity than treatment with UV. The s pecific p38 inhibitor SB203580 significantly decreased (> 80%) UV activatio n of HIV gene expression whereas PD98059, a specific MEK-1 inhibitor did no t, suggesting that p38 is specifically involved an the HIV UV response and little to no contribution is provided by MEK-1 and the p42/p44 MAP kinase p athway. Whereas increased binding of NF-kappa B to an oligonucleotide spann ing the HIV enhancer was, observed after UV, as expected, this binding was not affected by SB203580. Furthermore, UV activation of HIV gene expression in cells having the cat reporter gene under control of an HIV promoter del eted of the enhancer (-69/+80) produced results indistinguishable from thos e using HIVcat/HeLa cells with an intact HIV promoter (-485/+80), suggestin g that SB203580 acts through the basal transcription machinery. Northern bl ot analysis of steady-state RNA from HIVcat/HeLa cells revealed an almost c omplete inhibition of UV activation with SB203580 at the RNA level. Similar ly, the UV response was almost completely obliterated at the CAT and RNA le vels in HIVcat/HeLa cells stably transfected with a plasmid expressing a ki nase-inactive mutant of p38 (isoform alpha), without affecting NF-kappa B a ctivation, providing strong genetic evidence that p38, at least the alpha i soform, is necessary for UV activation of HIV gene expression and that NF-k appa B activation alone is insufficient. These results firmly establish p38 MAP kinase as a key modulator of HIV gene expression in response to UV tha t acts independently of NF-kappa B.