Transforming growth factor-beta 1 induces expression of statin during differentiation of human promonocytic leukemia cells.

Transforming growth factor-Beta (TGF-beta) is a potent growth inhibitor for several cell types including epithelial cells and hematopoietic progenitor cells. Using a human promonocytic leukemia cell line, THP-1, we have shown that TGF-beta inhibits their proliferation and promotes differentiation into cells exhibiting macrophage-like properties. Therefore, a key question is whether TGF-beta influences the expression of genes associated with proliferation and/or growth inhibition. TGF-beta treatment of THP-1 cells results in downregulation of expression of c-myc. We also observe that TGF-beta 1-treated cells express reduced levels of the cell cycle regulated histone, H2B, but express elevated levels of an RNA splicing variant of this histone that has been observed to be upregulated in growth inhibited and terminally differentiated cells. In addition, a nuclear protein associated with senescence and withdrawal of cells from the cell cycle, statin, is also expressed by THP-1 cells in response to TGF-beta 1 treatment. These results suggest that TGF-beta 1 is capable of inducing expression of specific nuclear proteins associated with differentiation and/or cessation of proliferation that may result in changes in nuclear organization and altered gene expression. Such changes in nuclear organization may be incompatible with continued proliferation of the cells.