Up-regulation of cytokine mRNA in human monocytes and myeloid cell lines by the differentiation/activation factor p48.

Polypeptide 48 is a 48,000 MW protein, originally isolated from conditioned media of some human leukaemic cell lines, that induces differentiation and cytolytic activity in HL-60 promyelocytic leukaemia cells and activates human peripheral blood monocytes to secrete interleukin-1 (IL-1) and tumour necrosis factor-alpha (TNF-alpha). In the present study we examined the effects of p48 on the accumulation of a series of monokine transcripts, including TNF-alpha, IL-1 alpha, IL-1 beta and IL-6, in human peripheral blood monocytes and the myeloid/monocyte cell lines HL-60 and U937. Using reverse transcriptase polymerase chain reaction (RT-PCR) and Northern blot analysis, p48 was found to induce accumulation of TNF-alpha, IL-1 alpha and IL-1 beta mRNA in peripheral blood monocytes, HL-60 and U937 cells. IL-6 mRNA was found to be increased in p48-stimulated peripheral blood monocytes but not HL-60 or U937. Thus, the secretion of IL-1 and TNF-alpha by p48-stimulated monocytic cells was associated with up-regulation of cytokine mRNA, suggesting that p48 leads to increased transcription or mRNA stability in these cells. As U937 and HL-60 are likely to represent premonocyte stages of haemopoietic differentiation, it is possible that the effect of p48 on IL-6 mRNA, in contrast to its effect on TNF and IL-1, requires cells to be at a later differentiation step.