Endotoxin stress-response in cardiomyocytes: NF-kappa B activation and tumor necrosis factor-alpha expression

1 Department of Biochemistry and Molecular Biology and 2 Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland 21201 Although tumor necrosis factor (TNF)- is implicated in numerous cardiac pathologies, the intracellular events leading to its production by heart cells are largely unknown. The goal of the present study was to identify the role of the transcription factor nuclear factor (NF)- B in this process. Among the many inducers of TNF- expression in myeloid cells, only lipopolysaccharide (LPS) led to its induction in cultured neonatal myocytes. LPS also activated the NF- B pathway, as evidenced by the degradation of the inhibitory protein I B and the appearance of NF- B-binding complexes in nuclear extracts. Furthermore, inhibitors of NF- B activation, such as lactacystin, MG132, and pyrrolidine dithiocarbamate, were found to completely block the production of TNF- in response to LPS stimulation, indicating a requirement of NF- B for TNF- expression. However, interleukin-1 and phorbol 12-myristate 13-acetate also activated NF- B but did not evoke TNF- expression, revealing that this factor is not sufficient for cytokine production. Detailed examination of the NF- B cascade revealed that cardiac cells displayed a unique pattern of I B degradation in response to LPS, with I B but not I B being degraded upon stimulation. Additionally, two specific p65-containing DNA-binding complexes were observed in the nuclear extracts of neonatal cardiomyocytes: an inducible complex that is necessary for TNF- expression and a constitutive species. Taken together, these results reveal that NF- B is not only involved in cytokine production but also may be linked to other pathways that subserve a constitutive, protective mechanism for the heart cell. lipopolysaccharide; nuclear factor- b; interleukin-1 ; cytokine production