A homozygous mutation in HESX1 is associated with evolving hypopituitarism due to impaired repressor-corepressor interaction
Luciani R. Carvalho, … , Ivo J.P. Arnhold, Mehul T. Dattani
Luciani R. Carvalho, … , Ivo J.P. Arnhold, Mehul T. Dattani
Published October 15, 2003
Citation Information: J Clin Invest. 2003;112(8):1192-1201. https://doi.org/10.1172/JCI18589.
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A homozygous mutation in HESX1 is associated with evolving hypopituitarism due to impaired repressor-corepressor interaction

Abstract

The paired-like homeobox gene expressed in embryonic stem cells Hesx1/HESX1 encodes a developmental repressor and is expressed in early development in a region fated to form the forebrain, with subsequent localization to Rathke’s pouch, the primordium of the anterior pituitary gland. Mutations within the gene have been associated with septo-optic dysplasia, a constellation of phenotypes including eye, forebrain, and pituitary abnormalities, or milder degrees of hypopituitarism. We identified a novel homozygous nonconservative missense mutation (I26T) in the critical Engrailed homology repressor domain (eh1) of HESX1, the first, to our knowledge, to be described in humans, in a girl with evolving combined pituitary hormone deficiency born to consanguineous parents. Neuroimaging revealed a thin pituitary stalk with anterior pituitary hypoplasia and an ectopic posterior pituitary, but no midline or optic nerve abnormalities. This I26T mutation did not affect the DNA-binding ability of HESX1 but led to an impaired ability to recruit the mammalian Groucho homolog/Transducin-like enhancer of split-1 (Gro/TLE1), a crucial corepressor for HESX1, thereby leading to partial loss of repression. Thus, the novel pituitary phenotype highlighted here appears to be a specific consequence of the inability of HESX1 to recruit Groucho-related corepressors, suggesting that other molecular mechanisms govern HESX1 function in the forebrain.

Authors

Luciani R. Carvalho, Kathryn S. Woods, Berenice B. Mendonca, Nathalie Marcal, Andrea L. Zamparini, Stefano Stifani, Joshua M. Brickman, Ivo J.P. Arnhold, Mehul T. Dattani

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(a) HESX1(I26T) leads to impaired repression at the SV40 promoter. Incre...
(a) HESX1(I26T) leads to impaired repression at the SV40 promoter. Increasing concentrations of GAL4-HESX1, GAL4-HESX1(I26T), and GAL4-HESX1(50–185) (10 ng, 100 ng, 250 ng, and 500 ng) were cotransfected with the SV40 promoter reporter construct. GAL4-HESX1 led to a dose-dependent repression of the SV40 promoter (67.5% at the highest concentration tested), whereas GAL4-HESX1(I26T) was associated with impaired repression (35.2% at the highest concentration tested) (P = 0.02). GAL4-HESX1(50–185) was associated with 24.4% repression, which did not achieve statistical significance (P = 0.19). The results represent the means of three independent experiments, each performed in triplicate. (b) HESX1(I26T) leads to impaired repression of Bix activation. Two different concentrations (10 ng and 250 ng) of GAL4-HESX1, GAL4-HESX1(I26T), GAL4-HESX1(50–185), GAL4-HESX1(R160C), GAL4-HESX1(I26T)(R160C), and GAL4-HESX1(50–185)(R160C) were cotransfected with a reporter containing six paired-class binding sites upstream of the E4 promoter that drives luciferase expression [(P3)6E4], and with the paired-class activator Bix. GAL4-HESX1 was associated with a tenfold repression of Bix activation at the highest concentration tested, whereas both GAL4-HESX1(I26T) and GAL4-HESX1(50–185) led to a threefold repression of Bix activation at the (P3)6E4 promoter. GAL4-HESX1(R160C) was associated with a fourfold repression of Bix activation, whereas the introduction of the I26T mutation [GAL4-HESX1(I26T)(R160C)] or the removal of the N-terminal AAs [GAL4-HESX1(50–185)(R160C)] led to a twofold repression and no repression of Bix activation, respectively. A constant concentration of Bix was used in all experiments (250 ng). The results represent the means of three independent experiments, each performed in triplicate.