Regulation of the Human MAT2A Gene Encoding the Catalytic α2 Subunit of Methionine Adenosyltransferase, MAT II

• Published in: The Journal of biological chemistry 2001-03, Vol.276 (13), p.9784-9791
• Main Authors: Halim, Abdel-Baset, LeGros, Leighton, Chamberlin, Margaret E., Geller, Arthur, Kotb, Malak
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M002347200

Mammalian methionine adenosyltransferase II (MAT II) consists of a catalytic α2/α2′ and a regulatory β subunit. Up-regulation of α2 subunit expression is associated with increased intracellular levels of S-adenosylmethionine, the major methyl group donor and a key compound in cell metabolism and polyamine synthesis. Previous studies have shown that expression of the α2 subunit is differentially regulated in normal and malignant cells. To delineate the molecular basis for the differential regulation of α2 subunit expression, we cloned and characterized the humanMAT2A gene 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 Sp1 sites (Sp1-1 at −14, Sp1-2 at −47, and Sp1-3 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 complex formation. Furthermore, mutation of the Sp1-3 site, but not the Sp1-1 or Sp1-2 sites, inhibited the in vivopromoter activity by ∼85%. Supershift assays showed that the transcription factors Sp2 and Sp3 are part of the complexes formed at the Sp1-3 site, and that Sp1 does not appear to be directly involved. The data indicate that complex formation is initiated at site Sp1-3, which appears to be essential for promoter activity. However, other regions of the proximal promoter may also contribute to the regulation of MAT2A gene expression. These studies may lead to the delineation of the molecular basis for the differential regulation ofMAT2A expression in normal and leukemic T cells.