Interleukin-1b Regulation of the Human Brain Natriuretic Peptide Promoter Involves Ras-, Rac-, and p38 Kinase–Dependent Pathways in Cardiac Myocytes

Because both the brain natriuretic peptide (BNP) gene and the cytokine interleukin-1b (IL-1b) are induced in the infarcted myocardium, localized production of IL-1b may regulate the BNP gene. We tested whether (1) IL-1b regulates the human BNP promoter, (2) cis elements in the proximal promoter respond to IL-1b, and (3) mitogenactivated protein kinase (MAPK) signaling pathways [p42/44, c-jun (JNK) and p38 kinase] are involved. We transferred the hBNP promoter coupled to a luciferase reporter gene or constructs with mutations in the proximal promoter GATA and M-CAT elements into neonatal rat ventricular myocytes and treated the cells with IL-1b for 24 hours. IL-1b–stimulated hBNP luciferase activity was eliminated by pretreatment with the transcription inhibitor actinomycin D. Both the p38 kinase inhibitor SB205380 (SB) and cotransfection of a dominant-negative mutant of p38 kinase reduced IL-1b stimulation of the hBNP promoter. Dominant-negative mutants of Ras and Rac inhibited IL-1b– stimulated hBNP luciferase activity by 64% and 90%, respectively. Constitutively active forms of Rac and MKK6, the immediate upstream activator of p38, were stimulatory; however, only the effect of MKK6 was inhibited by SB. Neither the p42/44 nor the JNK pathway was involved in the action of IL-1b. Both IL-1b and MKK6 activation of the hBNP promoter were partially reduced when the promoter contained a mutated M-CAT element. In summary, (1) IL-1b is a transcriptional activator of the hBNP promoter; (2) IL-1b acts through a Ras-dependent pathway not coupled to activation of p42/44 MAPK or JNK; (3) IL-1b acts through a Rac-dependent pathway, but the downstream effector is not known; and (4) IL-1b activation of p38 kinase is partially involved in regulation of the hBNP promoter, targeting the proximal M-CAT element. (Hypertension. 1999;33[part II]:283-289.)