Correlation of Pit-1 gene expression and Pit-1 content with proliferation and differentiation in human myeloid leukemic cells

The transcription factor pituitary-l (Pit-l) is a homeodomain-containing pr otein that is expressed mainly in the pituitary, where it drives the expres sion of growth hormone, prolactin, and thyroid-stimulating hormone beta cha in genes. In addition, Pit-1 is required for adequate pituitary cell growth and may be involved in the pathogenesis of pituitary adenomas. Pit-1 expre ssion has been also reported in nonpituitary tissues, where it might be inv olved in the control of cell proliferation. In order to elucidate such a po ssibility, we have investigated the changes in both Pit-1 mRNA and Pit-1 im munoreactivity in HL-60 cells following the addition of several differentia ting agents. Our results show that while high Pit-1 levels are found in exp onentially growing HL-60 cells, a significant decrease occurs after inducti on of cells to differentiate along the macrophage lineage with 12-O-tetrade canoylphorbol-13-acetate (TPA). In contrast no changes were observed when c ells were treated with interferon-alpha, which also induces differentiation of HL-60 cells that, at odds with TPA, is not accompanied with growth arre st. In all, these findings suggest that Pit-1 expression is specifically as sociated with proliferation in HL-60 cells, thus supporting the idea that o ne of the functions of nonpituitary Pit-1 may be the control of cell prolif eration. (C) 1998 Academic Press.