Transcriptional regulation of the human interleukin 1 beta gene by fibronectin: Role of protein kinase C and activator protein 1 (AP-1)

Interleukin 1 beta (IL-1 beta) is a multifunctional polypeptide considered a key cytokine during inflammation. Fibronectin (FN), a matrix glycoprotein highly expressed in injured tissues, can induce expression of IL-1 beta in human blood monocytic cells. Herein, we explore the intracellular signals and transcriptional mechanisms responsible for IL-1 beta induction by FN us ing human promonocytic U937 cells transfected with the human IL-1 beta prom oter connected to a reporter gene. Exposure of transfected U937s to FN resu lted in increased expression of the full-length IL-1 beta promoter. This ef fect, mediated via the alpha5 beta1 integrin, was associated with activatio n of mitogen-activated protein kinases (MAPKs) and was abolished by pre-tre atment of cells with Calphostin C, a specific inhibitor of protein kinase C (PKC) activation. Deletion analysis and co-transfection studies using cons ensus activator protein 1 (AP-1) oligonucleotides suggested that an AP-1 si te present in the 5' end of the IL-1 beta promoter was involved in the FN-i nduced response. Finally, electrophoretic mobility shift assays showed that FN induced binding of AP-1, but not NF-kappaB, Together, these experiments demonstrate that FN binding to the alpha5 beta1 integrin activates MAPK-de pendent signal pathways, and results in the transcription of the IL-1 beta promoter in U937 cells by activating PKC and inducing AP-1, (C) 2000 Academ ic Press.