PROP1 mutations cause hypopituitarism by disrupting the transition of pituitary stem cells to differentiation

MARÍA INÉS PÉREZ MILLÁN; MORTENSEN AH; BRINKMEIER ML; CAMPER SA

Barcelona

Congreso; ESPE 2015; 2015

Congenital multiple pituitary hormone deficiency (MPHD) arises from defects in pituitary development and is sometimes associated with craniofacial abnormalities. Mutations in the transcription factor PROP1 are the most common known genetic cause of the disorder. In this case the course of disease is progressive, and can lead to life threatening adrenal insufficiency. Our objectives are to understand this disease pathophysiology and to improve molecular diagnosis and treatment of MPHD. We discovered that Prop1 deficiency in mice causes elevated expression of the stem cell marker SOX2, and altered stem cell colony forming behavior including increased growth rate, abnormal cellular morphology, and misexpression of genes associated with the Notch signaling pathway and cell cycle regulation. This suggests that PROP1 regulates stem cell function. To understand the underlying molecular mechanism, we sought to identify downstream targets of PROP1 by creating a Prop1-expressing pituitary cell line and conducting ChIP-Seq. We identified novel PROP1 binding sites near Gli2, which encodes a mediator of SHH signaling is mutated in some cases of MPHD. PROP1 also bound at genes associated with two major biological pathways: cell junction signaling and regulation of epithelial-mesenchymal transition (EMT). We validated representative putative Prop1 target genes by comparing expression in pituitaries of developing normal and Prop1 mutant mice. Prop1 mutants exhibit elevated expression of claudins, indicating that Prop1 may normally suppress tight junction maintenance, promoting progenitor release from the stem cell niche. Genes that can induce EMT, like Notch2 and Zeb2, had reduced expression in Prop1 mutants, while the epithelial marker E-cadherin was increased. This suggests that Prop1 promotes the transition of progenitors into differentiating cells by driving an EMT-like process. In conclusion, we have advanced our understanding of the mechanism of PROP1 action and MPHD pathophysiology.