Pdx1 level defines pancreatic gene expression pattern and cell lineage differentiation.
The absence of Pdx1 and the expression of brain-4 distinguish alpha-cells from other pancreatic endocrine cell lineages. To define the transcription factor responsible for pancreatic cell differentiation, we employed the reverse tetracycline-dependent transactivator system in INS-I cell-derived subclones INSralphabeta and INSrbeta to achieve tightly controlled and conditional expression of wild type Pdx1 or its dominant-negative mutant, as well as brain-4. INSralphabeta cells express not only insulin but also glucagon and brain-4, while INSrbeta cells express only insulin. Overexpression of Pdx1 eliminated glucagon mRNA and protein in INSralphabeta cells and promoted the expression of beta-cell-specific genes in INSrbeta cells. Induction of dominant-negative Pdx1 in INSralphabeta cells resulted in differentiation of insulin-producing beta-cells into glucagon-containing alpha-cells without altering brain4 expression. Loss of Pdx1 function alone in INSrbeta cells, which do not express endogenous brain-4 and glucagon, was also sufficient to abolish the expression of genes restricted to beta-cells and to cause alpha-cell differentiation. In contrast, induction of brain-4 in INSrbeta cells initiated detectable expression of glucagon but did not affect beta-cell-specific gene expression. In conclusion, Pdx1 confers the expression of pancreatic beta-cell-specific genes, such as genes encoding insulin, islet amyloid polypeptide, Glut2, and Nkx6.1. Pdx1 defines pancreatic cell lineage differentiation. Loss of Pdx1 function rather than expression of brain4 is a prerequisite for alpha-cell differentiation.
Wang
H
H
Division of Clinical Biochemistry, Department of Internal Medicine, Geneva University Medical Center, CH-1211 Geneva 4, Switzerland.
Maechler
P
P
Ritz-Laser
B
B
Hagenfeldt
K A
KA
Ishihara
H
H
Philippe
J
J
Wollheim
C B
CB
D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D005786:Gene Expression Regulation; D005934:Glucagon / Q000096:biosynthesis; D018398:Homeodomain Proteins; D007340:Insulinoma / Q000737:chemistry; D007515:Islets of Langerhans / Q000378:metabolism; D008970:Molecular Weight; D010179:Pancreas / Q000166:cytology*; D010190:Pancreatic Neoplasms / Q000737:chemistry; D051381:Rats; D015534:Trans-Activators / Q000235:genetics*; D014407:Tumor Cells, Cultured
D018398:Homeodomain Proteins; D015534:Trans-Activators; C084010:pancreatic and duodenal homeobox 1 protein; D005934:Glucagon