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Hepatocyte Nuclear Factor-3 Binding at P Sequences of the Human Growth Hormone Locus Is Associated with Pituitary Repressor Function

Department of Physiology, University of Manitoba (X.Y., Y.J., K.A.D., P.A.C.), Winnipeg, Manitoba, Canada R3E 3J7; and Division of Endocrinology (L.D.N.), Children’s Hospital Boston, Harvard Medical School (L.D.N.), Boston, Massachusetts 02115

Address all correspondence and requests for reprints to: Dr. Peter A. Cattini, Department of Physiology, University of Manitoba, 730 William Avenue, Winnipeg, Manitoba, Canada R3E 3J7. E-mail: peter_cattini{at}umanitoba.ca.

The human GH family consists of five genes, including the placental chorionic somatomammotropins (CS), within a single locus on chromosome 17. Based on nuclease sensitivity, the entire GH/CS locus is accessible in pituitary chromatin, yet only GH-N is expressed. Previously, we reported a P sequence element (263P) capable of repressing placental CS-A promoter activity in transfected pituitary (GC) cells, and our data indicated a possible role for nuclear factor-1 (NF-1) and regulatory factor X1 in this repression. In this study we show the formation of two independent pituitary complexes in vitro: a repressor complex containing NF-1 and a nonfunctional complex containing regulatory factor X1. In vitro repressor function is stabilized by the presence of P sequence element C (PSE-C), downstream of the previously characterized PSE-A and PSE-B. Repressor function is also dependent on an intact Pit-1 binding site in the CS-A promoter. EMSAs with PSE-C reveal binding of the hepatocyte nuclear factor-3/forkhead (HNF-3/fkh) family of transcription factors in rat pituitary GC cells. This observation is extended to human pituitary tissue, where HNF-3’s association with P sequences is confirmed by chromatin immunoprecipitation. Furthermore, protein-protein interactions between HNF-3 and NF-1 family members are demonstrated. These results identify HNF-3 as an additional member of the pituitary P sequence regulatory complex, implicating it in tissue-specific expression of the human GH/CS family.