Early development of hyperparathyroidism due to loss of PTH transcriptional repression in patients with HNF1β mutations?

CONTEXT

Heterozygous mutations or deletions of the transcription factor hepatocyte nuclear factor 1β (HNF1β) result in a heterogeneous syndrome characterized by renal cysts and diabetes, together with a variety of other extrarenal and renal manifestations. Interestingly, in several patients with HNF1β abnormalities, we observed early hyperparathyroidism and PTH levels that we judged inappropriately high compared with the degree of renal function decline.

OBJECTIVE

Based on the above clinical observations, we tested the hypothesis of a direct role of HNF1β in the transcriptional regulation of the human PTH gene in the parathyroid gland.

DESIGN, SETTING, AND PATIENTS: Immunostaining of human parathyroid sections, RT-PCR, chromatin immunoprecipitation (ChIP), and luciferase reporter assays in human embryonic kidney cells (HEK293) were performed. We eventually report clinical data from all 11 HNF1β patients known at our institute, 9 with heterozygous HNF1β whole-gene deletions and 2 with heterozygous HNF1β mutations.

RESULTS

PTH levels were high in 8 patients. In 2 of these patients, the hyperparathyroidism was clearly appropriate for the level of kidney function, whereas PTH might be discrepant in the others. We demonstrated HNF1β expression in PTH-positive cells of human parathyroid gland. Chromatin immunoprecipitation analysis showed that HNF1β directly binds responsive elements within the human PTH promoter. Cotransfection of a PTH promoter- luciferase construct with a wild-type HNF1β construct resulted in a maximal reduction of 30% of PTH promoter activity. Importantly, HNF1β mutants lacked this inhibitory property. Serial deletions in the PTH promoter construct revealed that the inhibitory effect of HNF1β resides between -200 and -70 bp from the transcription initiation site.

CONCLUSIONS

Our data demonstrate that HNF1β is a novel repressor of human PTH gene transcription, which could contribute to the development of hyperparathyroidism in patients with HNF1β mutations or deletions.