Autocrine stimulation of TNF-alpha mRNA expression in HL-60 cells.

We have employed a human promyelocytic leukemic cell line, HL-60, to investigate the conditions that regulate TNF-alpha gene expression in vitro. Using a cloned TNF-alpha specific cDNA probe, we show by Northern blot analysis that TNF-alpha mRNA rapidly accumulates in HL-60 cells following treatment with phorbol myristate acetate (PMA). TNF-alpha mRNA levels peak at 1-2 hours and then decline to base-line levels within 8 hours. TNF-alpha protein levels as detected in the supernatants of PMA-stimulated HL-60 cells peak at 2 hours and decline within 24 hours. Cytokines of recombinant source like interferon-alpha and -gamma, and, more intruigingly, TNF-beta as well as TNF-alpha itself are also able to induce transient TNF-alpha mRNA expression in HL-60 cells. In the presence of a protein kinase inhibitor, neither PMA nor any of the cytokines used are able to induce TNF-alpha mRNA accumulation, indicating that protein kinases may be crucially involved in signal transduction leading to activation of the TNF-alpha gene. The data presented provide new insights into the control of TNF-alpha gene expression suggesting regulatory functions of T- and B-cell derived lymphokines as well as a TNF-alpha-mediated positive feedback mechanism.