Regulatory elements involved in human pdx-1 gene expression.
PDX-1 was shown to be expressed early during development in cells of both exocrine and endocrine origin; later it becomes restricted primarily to beta-cells where it regulates the expression of beta-cell-specific genes and mediates the glucose effect on insulin gene transcription. Therefore, it was important to identify the molecular mechanisms that specifically govern the expression of pdx-1 in the mature beta-cell. To address this question, we analyzed 7 kb of the 5' flanking region of the human pdx-1 gene. By transient transfections of beta- and non-beta-cell lines with different 5' and 3' deletions of that region, a strong beta-cell-specific enhancer element located between -3.71 and 3.46 kb was revealed. We also sequenced about 4.5 kb of the human 5' flanking region and compared it with that of the mouse pdx-1 gene. This comparison revealed three short conserved regions, designated PH1, PH2, and PH3. We showed that HNF-3beta can bind and stimulate the activity of the human PH1 and PH2 elements in non-beta-cells. Results reported by Wu et al. (7) and Sharma et al. (6) also indicate that expression of the mouse pdx-1 is controlled by an HNF-3-like element. Thus, it can be stated that at least some aspects of pdx-1 expression rely on the transcription factor HNF-3beta. Because HNF-3beta is not restricted to beta-cells, the selective transcription of pdx-1 is likely to rely on additional factors. Our findings that the PH1 enhancer element binds both HNF-3beta and PDX-1 and that mutations in each individual site dramatically impair its transcriptional activity suggest that these factors cooperate with one another. We therefore propose that a possible feedback mechanism might control the expression of pdx-1 at different stages during development.
Department of Endocrinology and Metabolism, Hadassah University Hospital, Jerusalem, Israel.
S
S
Marshak
E
E
Ben-Shushan
M
M
Shoshkes
L
L
Havin
E
E
Cerasi
D
D
Melloul
D000818:Animals; D017124:Conserved Sequence; D004247:DNA / Q000235:genetics; D018983:DNA Footprinting; D004268:DNA-Binding Proteins / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D018507:Gene Expression Regulation, Developmental; D051542:Hepatocyte Nuclear Factor 3-beta; D018398:Homeodomain Proteins; D006801:Humans; D007515:Islets of Langerhans / Q000254:growth & development / Q000378:metabolism*; D051379:Mice; D009687:Nuclear Proteins / Q000378:metabolism; D011485:Protein Binding; D012045:Regulatory Sequences, Nucleic Acid; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors; D014158:Transcription, Genetic
D004268:DNA-Binding Proteins; C496502:FOXA2 protein, human; C496503:Foxa2 protein, mouse; D018398:Homeodomain Proteins; D009687:Nuclear Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C084010:pancreatic and duodenal homeobox 1 protein; D051542:Hepatocyte Nuclear Factor 3-beta; D004247:DNA