Pathogenesis of a transcription factor disease, combined pituitary hormone defficiency

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A pituitary-specific transcription factor, Pit-1 activates growth hormone (GH), prolactin (PRL), TSHb gene expressions. Mutant Pit-1 may lead to the deficiency of the three hormones (combined pituitary hormone deficiency), and several Pit-1 mutants, indeed, were reported as a cause of combined pituitary hormone deficiency. We analyzed the function of two mutant Pit-1s (P24L and R271W), both of which have been reported as a cause of combined pituitary hormone deficiency. In P24L, proline at 24 is replaced with lysine, and arginine at 271 is replaced with tryptophan in R271W. The P24L had normal binding activity to Pit-1 binding element, but lost the binding to CBP. Deletion construct and two hybrid assay revealed that both transactivation and POU domains were required for the binding of Pit-1 to CBP and that CH1 and CH3 domains were needed for the binding of CBP to Pit-1. Furthermore, P24L, unlike wild type Pit-1, did not activate cAMP-induced expression of a reporter plasmid containing Pit-1 binding elements. Adenovirus E1a, which inhibit CBP, lowered Pit-1 and cAMP-induced expression of the reporter plasmid. These findings suggested that CBP plays a role in Pit-1 and cAMP-induced gene expression. It Is reported that another Pit-1 mutant R271W is responsible for combined pituitary hormone deficiency. However, R271W and wild type Pit-1 increased expression of GH, PRL reporter plasmids to similar extent in various cells and experimental conditions in our study. Consistent with our data, there is a report showing that a subject with R271W did nof have any phenotypes of combined pituitary hormone deficiency. Further analysis will be required for concluding that R271W is a causative mutant for combined pituitary hormone deficiency.