Truncation of PITX2 differentially affects its activity on physiological targets.
The bicoid-like transcription factor PITX2 has been previously described to interact with the pituitary-specific POU homeodomain factor POU1F1 (human ortholog of PIT-1) to achieve cell-specific expression of prolactin (PRL) and GH in pituitary somatolactotroph cells. In this work, we have investigated the functional properties of three PITX2 mutants reported in Axenfeld-Rieger syndrome patients relative to the regulation of these genes, using reporter genes under the control of human PRL (hPRL), hGH, or POU1F1 promoters transfected in nonpituitary and pituitary cell lines. Among the three mutations studied, Y167X and E101X introduce a premature stop codon, and F104L leads to an amino acid substitution. While PITX2(E101X) is not expressed in the cells following transfection, and PITX2(F104L) is functionally inactive, the PITX2(Y167X) mutant keeps its DNA-binding capacity and displays a markedly enhanced activation of the hPRL and POU1F1 promoters, but not of the hGH promoter. Y167X is the first mutation of PITX2 described to result in a differential effect on the activation of its different physiological targets, hPRL and POU1F1 on one hand and hGH on the other hand. The differential effect of the Y167X mutation might be linked to an interaction of PITX2 with different transcription factors or cofactors when bound to the hPRL and POU1F1 or the hGH promoters. These results might form the basis for the identification of the PITX2 protein complex necessary for the differential GH or PRL expression.
Faculté de Médecine Secteur Nord, Université de la Méditerranée, Centre de Recherche en Neurobiologie et Neurophysiologie de Marseille, UMR6231, CS 80011, 13344 Marseille Cedex 15, France.
Marie-Hélène
MH
Quentien
Véronique
V
Vieira
Maurice
M
Menasche
Jean-Louis
JL
Dufier
Jean-Paul
JP
Herman
Alain
A
Enjalbert
Marc
M
Abitbol
Thierry
T
Brue
D000818:Animals; D000869:Anterior Eye Segment / Q000002:abnormalities; D015153:Blotting, Western; D002460:Cell Line; D024202:Electrophoretic Mobility Shift Assay; D005124:Eye Abnormalities / Q000235:genetics; D015785:Eye Diseases, Hereditary; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism*; D019382:Human Growth Hormone / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D009154:Mutation; D010902:Pituitary Gland / Q000378:metabolism; D011388:Prolactin / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D050817:Transcription Factor Pit-1 / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism*; D015533:Transcriptional Activation; D000097577:Homeobox Protein PITX2
D018398:Homeodomain Proteins; D019382:Human Growth Hormone; D011388:Prolactin; D050817:Transcription Factor Pit-1; D014157:Transcription Factors; D000097577:Homeobox Protein PITX2