Distinct patterns of protein binding to the MAT2A promoter in normal and leukemic T cells.

The metabolism of S-adenosylmethionine (AdoMet), a key molecule in regulating T cell differentiation and proliferation, is different in normal and leukemic T cells. To delineate the basis for these differences we studied the transcriptional regulation of human methionine adenosyltransferase II (MAT II), which catalyzes AdoMet synthesis in these cells. Recently, we identified an Sp1 site in the proximal promoter of the MAT2A gene, which encodes the alpha2 catalytic subunit of MAT II, that is essential for the in vitro and in vivo promoter activity in Jurkat leukemic T cells, and that involves binding of the nuclear factors Sp2 and Sp3, but not Sp1. Here, the in vitro and in vivo activity of the proximal MAT2A promoter in normal resting, PHA-stimulated, and leukemic human T cells was compared. Significantly different patterns of protein factor interaction in the proximal region of the MAT2A promoter were found. Normal resting and activated T cells produced complexes of significantly lower molecular weight than those formed in leukemic T cells. Supershift studies coupled with analysis of proteins bound to the proximal promoter suggest that low levels of expression of Sp2 and Sp3 in normal T cells may be responsible for the difference in the in vitro promoter activity between normal and leukemic cells. Mutation of the key Sp1 site equally reduced the in vivo promoter activity in normal and malignant T cells; by contrast, it had significantly different effects on protein-DNA interactions in normal and leukemic T cells. Together, the data support the idea that differences in protein-DNA interactions may contribute to significant differences in MAT2A regulation in normal and malignant cells.