Regulation of the human MAT2A gene encoding the catalytic alpha 2 subunit of methionine adenosyltransferase, MAT II - Gene organization, promoter characterization, and identification of a site in the proximal promoter that is essential for its activity

Mammalian methionine adenosyltransferase II (MAT II) consists of a catalyti c alpha2/alpha2 ' and a regulatory beta subunit. Up-regulation of alpha2 su bunit expression is associated with increased intracellular levels of S-ade nosylmethionine, the major methyl group donor and a key compound in cell me tabolism and polyamine synthesis. Previous studies have shown that expressi on of the alpha2 subunit is differentially regulated in normal and malignan t cells, To delineate the molecular basis for the differential regulation o f alpha2 subunit expression, we cloned and characterized the human MAT2A ge ne and its promoter and defined regions that contain enhancer and repressor elements, Detailed functional characterization of the proximal promoter of the MAT2A gene revealed the formation of three major protein-DNA complexes with probes containing three Spl sites (Spl-l at -14, Sp1-2 at -47, and Sp 1-3 at -69), Competition with a probe copying sequence between -76 and -54, which contains the Sp1-3 site only, or mutation of this site, abolished co mplex formation. Furthermore, mutation of the Sp1-3 site, but not the Spl-l or Sp1-2 sites, inhibited the in vivo promoter activity by similar to 85%, Supershift assays showed that the transcription factors Sp2 and Sp3 are pa rt of the complexes formed at the Sp1-3 site, and that Spl does not appear to be directly involved. The data indicate that complex formation is initia ted at site Sp1-3, which appears to be essential for promoter activity. How ever, other regions of the proximal promoter may also contribute to the reg ulation of MAT2A gene expression. These studies may lead to the delineation of the molecular basis for the differential regulation of MAT2A expression in normal and leukemic T cells.