Identification and characterization of the cell type-specific and developmentally regulated alpha7 integrin gene promoter.
Expression of alpha7 is mainly confined to skeletal and cardiac muscle in which it appears to be the major laminin-binding integrin. When myoblasts differentiate to myotubes, alpha7 mRNA and protein expression is up-regulated. To explore the mechanisms involved in the tissue-specific and developmentally regulated expression of alpha7, we isolated and characterized a genomic clone containing approximately 2.8 kilobase pairs (kb) of the 5'-flanking region of the murine alpha7 gene. The 5'-flanking region lacks both TATA and CCAAT boxes but contains five putative Sp1 binding sites located in a CpG island. Two transcription start sites, located near an initiator-like sequence, are 176 and 170 base pairs upstream of the translation start site. There are numerous binding sites for developmental and cell type-specific transcription factors, including AP-1, AP-2, GATA, and several AT-rich sites. There are also eight consensus E-boxes that bind the basic helix-loop-helix family of muscle-specific transcription factors. The approximately 2.8-kb 5'-flanking region was an active promoter in C2C12 skeletal myoblasts and exhibited increased expression upon conversion to myotubes but was inactive in HtLM2 cells, a mouse breast carcinoma epithelial cell line that does not express alpha7. Deletion analysis identified both positive and negative regulatory elements within the approximately 2.8-kb fragment. In 10T1/2 fibroblasts the approximately 2.8-kb alpha7 promoter was trans-activated by the myogenic basic helix-loop-helix proteins myogenin and MyoD but not by MRF4 and myf5. These results suggest that muscle-specific transcription factors play a role in regulating the cell-type expression of the alpha7 gene during development.
Ziober
B L
BL
Department of Stomatology, University of California, San Francisco, California 94143-0512, USA.
Kramer
R H
RH
D000818:Animals; D015703:Antigens, CD / Q000235:genetics*; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins / Q000235:genetics; D010064:Embryo Implantation; D005260:Female; D017353:Gene Deletion; D018507:Gene Expression Regulation, Developmental; D039001:Integrin alpha Chains; D051379:Mice; D008969:Molecular Sequence Data; D009132:Muscles / Q000196:embryology; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D015183:Restriction Mapping; D015719:Single-Strand Specific DNA and RNA Endonucleases / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic
D015703:Antigens, CD; D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D039001:Integrin alpha Chains; D012333:RNA, Messenger; D015719:Single-Strand Specific DNA and RNA Endonucleases; D014157:Transcription Factors; C085725:integrin alpha7