CHARACTERIZATION OF THE MADH2 SMAD2 GENE, A HUMAN MAD HOMOLOG RESPONSIBLE FOR THE TRANSFORMING-GROWTH-FACTOR-BETA AND ACTIVIN SIGNAL-TRANSDUCTION PATHWAY/

The transforming growth factor beta (TGF-beta) super-family is a famil y of multifunctional cytokines that transduce signals via serine/threo nine kinase receptors. Recent studies revealed that Mothers against dp p (Mad) in Drosophila and its homologs play important roles in the int racellular signal transduction of the serine/threonine kinase receptor s. In mammals, one of the Mad homologs, MADH2 (also termed Smad2), was reported to be a mediator of TGF-beta and activin signaling and was f ound mutated in some of the colon and lung cancer cases. We describe h ere the genomic organization of the human MADH2 gene. The gene is comp osed of 12 exons; 2 exons 1, i.e., exon 1a and 1b, are used separately or in conjunction to form exon 1a-exon 1b-exon 2 alternatively splice d mRNA. The 2 exons 1 are closely located, and the MADH2 mRNAs are tra nscribed from two promoters in one CpG island. The promoter activity i n the 5' upstream sequence was confirmed by the luciferase assay. The 3' end of the mRNA is heterogenous, and we found several polyadenylati on signals. Northern blot analysis revealed high expression of the MAD H2 mRNA, e.g., in skeletal muscle, heart, and placenta. RT-PCR assay u sing primers in exons 2 and 4 and direct nucleotide sequencing proved that exon 3 is spliced out in about 10% of MADH2 in human placenta. Th ese data will be valuable for studying the MADH2 function in both norm al cells and cancer cells. (C) 1998 Academic Press.