Synergistic regulation of human cystathionine-beta-synthase-1b promoter by transcription factors NF-YA isoforms and Sp1.
Cystathionine-beta-synthase (CBS) catalyzes the condensation of serine and homocysteine to form cystathionine, an intermediate step in the synthesis of cysteine. We previously described essential transactivating roles for specificity protein 1 (Sp1), Sp3, nuclear factor Y (NF-Y), and USF-1 in the regulation of the CBS-1b promoter. Differential binding of Sp1/Sp3 to the CBS-1b promoter due to differences in Sp1/Sp3 phosphorylation, and Sp1/Sp3 synergism with NF-Y might, in part, explain cell-specific patterns of CBS expression. In this report, the roles of various NF-YA isoforms in influencing cell-specific differences in CBS gene expression were determined in HT1080 and HepG2 cells. Seven unique NF-YA isoforms were detected in HT1080 by reverse transcriptase-PCR (RT-PCR) and DNA sequencing, characterized by deletions in the glutamine-rich and/or serine/threonine-rich domains. Only four of the seven NF-YA isoforms were found in HepG2 cells. The six alternatively spliced NF-YA isoforms all showed significantly less synergistic transactivation of the CBS-1b promoter with Sp1 than wild-type NF-YA, as determined by cotransfections in Drosophila SL2 cells with NF-YB and NF-YC. Further, all six alternatively spliced NF-YA isoforms inhibited the synergistic transactivation of the CBS-1b promoter by wild-type NF-Y and Sp1. Thus, the cellular distributions of these alternatively spliced NF-YA isoforms could impart an important cell-specific component to CBS transcriptional regulation, by virtue of their abilities to directly synergize with Sp1/Sp3 and interfere with transactivation of the CBS-1b promoter by wild-type NF-Y. Characterization of CBS promoter structure and function should clarify the molecular bases for variations in CBS gene expression in genetic diseases and the relationship between CBS and Down's syndrome (DS).
Ge
Yubin
Y
Experimental and Clinical Therapeutics Program, Barbara Ann Karmanos Cancer Institute, Wayne State University School of Medicine, Detroit, MI, USA.
Jensen
Tanya L
TL
Matherly
Larry H
LH
Taub
Jeffrey W
JW
D001483:Base Sequence; D023081:CCAAT-Binding Factor / Q000737:chemistry / Q000494:pharmacology / Q000502:physiology*; D003541:Cystathionine beta-Synthase / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D004274:DNA, Recombinant; D004357:Drug Synergism; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006801:Humans; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms / Q000032:analysis / Q000737:chemistry / Q000502:physiology; D012313:RNA / Q000032:analysis; D016329:Sp1 Transcription Factor / Q000494:pharmacology / Q000502:physiology*; D014157:Transcription Factors / Q000737:chemistry / Q000494:pharmacology / Q000502:physiology*; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
D023081:CCAAT-Binding Factor; D004274:DNA, Recombinant; C492061:NFYA protein, human; D020033:Protein Isoforms; D016329:Sp1 Transcription Factor; D014157:Transcription Factors; D012313:RNA; D003541:Cystathionine beta-Synthase