ESPE Abstracts (2015) 84 FC-LB6

PROP1 Mutations Cause Hypopituitarism by Disrupting the Transition of Pituitary Stem Cells to Differentiation

Maria Ines Perez Millan, Amanda Mortensen, Michelle Brinkmeier & Sally Camper

University of Michigan, Ann Arbor, Michigan, USA

Background: 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.

Objective and hypotheses: Our objective is to understand the role of PROP1 in the generation of this disease and to improve molecular diagnosis of MPHD. Our hypothesis is that PROP1 promotes the transition of progenitors into differentiating cells and that new PROP1 target genes can be MPHD candidates.

Method: We performed stem cell colony formation assays, RNA-Seq, immunohistochemistry and qPCR using Prop1 mutant mice and their controls. We created a Prop1-expressing pituitary cell line to perform ChIP-Seq experiments for PROP1.

Results: 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 pathway and cell cycle regulation. We identified novel PROP1 binding sites near Gli2, which is mutated in some cases of MPHD. PROP1 also bound at genes associated with 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.

Conclusion: Prop1 promotes the transition of progenitors into differentiating cells by driving an EMT-like process. Our results advanced our understanding of the mechanism of PROP1 action and MPHD pathophysiology.

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