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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-3alpha's association with P sequences is confirmed by chromatin immunoprecipitation. Furthermore, protein-protein interactions between HNF-3alpha and NF-1 family members are demonstrated. These results identify HNF-3alpha as an additional member of the pituitary P sequence regulatory complex, implicating it in tissue-specific expression of the human GH/CS family.

The prevalence of type 2 diabetes mellitus in the Oji-Cree of northwestern Ontario is the third highest in the world. A private mutation, G319S, in HNF1A , which encodes hepatic nuclear factor-1α (HNF-1α), was associated with Oji-Cree type 2 diabetes and was found in ≈40% of affected subjects. The G319S mutation reduced the in vitro ability of HNF-1α to activate transcription by ≈50%, with no effect on DNA binding or protein stability. There was no evidence of a dominant negative effect of the mutant protein. The impact of the G319S mutation at the population level was assessed by classifying subjects with type 2 diabetes according to HNF1A genotype and plotting the cumulative age of onset of diabetes. Disease onset was modeled satisfactorily by two-parameter sigmoidal functions for all diabetic subjects and all three HNF1A genotypes. Pairwise statistical comparisons showed significant between-genotype differences in t 50 (all P < 0.00001), corresponding to the age at which half the subjects had become diabetic. Each dose of G319S accelerated median disease onset by ≈7 years. Thus, the transactivation-deficient HNF1A G319S mutation affects the dynamics of disease onset. The demonstration of a functional consequence for HNF1A G319S provides a mechanistic basis for its strong association with Oji-Cree type 2 diabetes and its unparalleled specificity for diabetes prediction in these people, in whom diabetes presents a significant public health dilemma. The findings also show that HNF1A mutations can be associated with typical adult-onset insulin-resistant obesity-related diabetes in addition to maturity-onset diabetes of the young.

The human GH gene family is specifically expressed in somatotrophs of the anterior pituitary and placental syncytiotrophoblast. Two nuclease-hypersensitive sites, HS III and HS V, are associated with a region of chromatin located 28 and 30 kb upstream of the pituitary GH gene transcription initiation site (+1) in both pituitary and placenta nuclei. A role for this region in pituitary GH gene expression has been reported, but the potential relevance to placental gene expression has not been determined. Deletion analysis of a 5.2-kb region (nucleotides - 27,568/-32,746) containing HS III to V-related sequences localized significant enhancer activity to a 574-bp HS III fragment (nucleotides -27,676/-28,249) in multiple transfected cell lines. Four nuclease-protected regions [footprints (FP) 1-4] were identified in the 574-bp fragment. FP2 and FP3 were detected with placenta cell nuclear protein, whereas FP1 and FP4 were observed with placental and nonplacental cell nuclear extract. Disruption of FP1 had no effect on heterologous promoter activity in transfected pituitary and placental cells, whereas loss of FP2 and FP3 resulted in modest increases in placental cells, reflecting the presence of repressor activity associated with these regions in vitro. In contrast, disruption of the FP4 region by mutation or deletion significantly reduced enhancer activity. As a result, 30-fold enhancer activity was localized to a 41-bp region in transfected placental tumor cells. Binding of candidate proteins, activator protein (AP)-2 (FP3) and Elk-1 (FP4), was confirmed using competition assays with specific oligonucleotides and antibodies. Moreover, these factors were associated with the hyperacetylated HS III region in human pituitary [activator protein 2 (AP-2) and Elk-1] and term placenta (AP-2) chromatin. These data implicate AP-2 and ETS-domain family members in the regulation of the GH/CS locus and raise the possibility that different complexes form in the HS III region in placenta and pituitary cells.

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 promoter activity in transfected pituitary (GC) cells. Regions of protein binding within 263P include P sequence elements A and B (PSE-A and PSE-B), and we reported nuclear factor-1 (NF-1) recognition of PSE-B. We now provide evidence for multiple interactions on PSE-A, including binding of the regulatory factor X (RFX) family. Disruption of the RFX site within 263P blunts repressor activity in transfected GC cells; however, repression is only abolished when both PSE-A/RFX and PSE-B/NF-1 sites are mutated. The capacity of RFX and NF-1 to participate in a novel common complex is further suggested by coimmunoprecipitation of RFX1 and epitope-tagged NF-1 family members. Finally, we confirm the association of NF-1 and RFX1 with P sequences in human pituitary tissue by chromatin immunoprecipitation. Taken together, our data suggest that an inverse relationship exists between 263P and CS promoter histone hyperacetylation and the association of these factors in vivo.