Rarity of PIT1 involvement in children from Russia with combined pituitary hormone deficiency

Abstract

To ascertain the molecular background of combined pituitary hormone deficiency, screening for mutations in the pituitary-specific transcription factor (Pit-1/GHF-1) gene (PIT1) was performed on a cohort of 15 children from Russia with combined growth hormone (GH)/prolactin (Prl)/thyroid-stimulating hormone (TSH) deficiency. The group of patients, suspected of PIT1 mutations, consisted of four familial cases (seven patients) and eight sporadic cases. All had complete GH deficiency and complete or partial Prl and TSH deficiency. Direct sequencing of all six exons of PIT1 and its promoter region showed a C to T transition mutation at codon 14 of exon 1 in a 3 8/12-year-old girl. This novel PIT1 mutation results in a proline to leucine substitution (P14L). The patient was heterozygous for mutant and normal alleles. The heterozygous P14L mutation was also present in her mother as well as in her maternal aunt and grandmother, all of whom were phenotypically normal. There was no mutation in the father's DNA, suggesting the need for reevaluation of genomic imprinting. In other children of our series, no mutation in PIT1 or in its promotor region was identified. This is the first report on the analysis of PIT1 and its promoter region in Russian children with GH/Prl/TSH deficiency. However, as the involvement of PIT1 mutation is rare in Russia, the other negative cases need to be analyzed for another candidate gene responsible for combined GH/Pr/TSH deficiency.

Novel Function of the Transactivation Domain of a Pituitary-specific Transcription Factor, Pit-1

“…This is the first functional analysis of Pit-1 with mutations in the transactivation domain found in patients with CPHD (19,20). The case reported by Fofanova et al (19) was a 3-year-old girl who showed total GH/PRL and partial TSH deficiency without mental retardation.…”

“…Neither P14L nor P24L Dominantly Inhibited the Transcriptional Activity of Wild Type Pit-1-Because both of the probands with P14L or P24L were found to be heterozygous for these mutations (19,20), it has been hypothesized that P14L and P24L might inhibit the activity of the wild type Pit-1 (21)(22)(23). To test the ability of these mutants to interfere with the transactivation of Pit-1-targeted gene expression by wild type Pit-1, the expression vector for P14L or P24L was transfected into COS7 cells together with the PRL-Luc and wild type Pit-1 expression vector.…”

“…Because both of the probands with P14L or P24L showed heterozygous for these mutations (19,20), we examined whether P14L and P24L function dominant negatively. A, 0.3 g of pcDNA3.1-wild type-Pit-1, pcDNA3.1-P14L, or pcDNA3.1-P24L were transfected with 0.3 g of pcDNA3.1-wild typePit-1 and 2 g of PRL-Luc.…”

“…To date, at least 16 different mutations of the human Pit-1 gene related to combined pituitary hormone deficiency (CPHD) have been reported (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24). Most mutations are seen in the POU domain of Pit-1, which is important for its ability to dimerize and bind to DNA (25).…”

“…One is a C to T mutation in codon 14 of the Pit-1 gene, resulting in an amino acid change from proline (P) to leucine (L) (P14L) (19) and the other is a Cys to Thr mutation in codon 24 leading to a corresponding change from Pro to Leu (P24L) (20). Because the patients with these mutations were both heterozygous for the mutation, it is believed that P14L and P24L may dominantly inhibit the transcriptional activity of the wild type Pit-1 (21)(22)(23).…”