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EGF activation of POMC gene transcription is mediated by STAT3

ABSTRACT: Classical activation of the hypothalamic-pituitary-adrenal axis (HPA) is exerted by stimulation of pituitary POMC gene transcription and ACTH release by the hypothalamic hormone CRH. In parallel, inflammatory cytokines such as IL6 and LIF also stimulate ACTH release and POMC transcription through the JAK/STAT pathway. In recent years, a particular interest in the role of the EGF pathway for POMC activation was sparked by the identification of causative mutations in the USP8 gene that have been implicated in formation of pituitary corticotrope adenomas that are the hallmark of Cushing’s disease. These mutations were associated with persistent upregulation of the EGF/EGFR pathway and its putative role in ACTH hypersecretion. In the present work, we reassessed the signalling pathways that are activated in response to ACTH in pituitary corticotrope cells using the AtT-20 cell model. We confirmed activation of the MAP kinase pathway by EGF but also show activation of the AKT/mTOR and JAK/STAT pathways. Whereas activation of all three pathways appears essential for stimulation of cell proliferation, only the JAK/STAT pathway and more specifically STAT3, enhances POMC gene transcription. This action is mapped to a single STAT binding element of the POMC promoter in contrast to activation by the other STAT-activating cytokines LIF and IL6. Further, EGF signalling is specifically enhanced by STAT3 but not STAT1 in contrast to LIF-dependent activation. All together, the data identified a unique STAT3-dependent target on the POMC promoter that mediates EGF activation of POMC gene transcription.

ORGANISM(S): Mus musculus

PROVIDER: GSE292424 | GEO | 2025/11/03

REPOSITORIES: GEO

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Project description:While the hypothalamo-pituitary-adrenal axis (HPA) activates a general stress response by increasing glucocorticoid (Gc) synthesis, biological stress resulting from infections triggers the inflammatory response through production of cytokines. The pituitary gland integrates some of these signals by responding to the pro-inflammatory cytokines IL6 and LIF and to a negative Gc feedback loop. The present work used whole-genome approaches to define the LIF/STAT3 regulatory network and to delineate cross-talk between this pathway and Gc action. Genome-wide ChIP-chip identified 3 449 STAT3 binding sites, whereas 2 396 genes regulated by LIF and/or Gc were found by expression profiling. Surprisingly, LIF on its own changed expression of only 85 genes but the joint action of LIF and Gc potentiated the expression of more than a thousand genes. Accordingly, activation of both LIF and Gc pathways also potentiated STAT3 and GR recruitment to many STAT3 targets. Our analyses revealed an unexpected gene cluster that requires both stimuli for delayed activation: 83% of the genes in this cluster are involved in different cell defense mechanisms. Thus, stressors that trigger both general stress and inflammatory responses lead to activation of a stereotypic innate cellular defense response. Experiment Overall Design: 1) Pituitary corticotrophs cell line (AtT-20) response to glucocorticoids and LIF: Experiment Overall Design: AtT-20 cells mRNA extracted after treatment with PBS as control, LIF for 18h, Dex+LIF for 3h and Dex+LIF for 18h. Each treatment were made in duplicate. [GSM471246-GSM471253] Experiment Overall Design: 2) Pituitary corticotrophs cell line (AtT-20) response to LIF after 3h treatment: Experiment Overall Design: AtT-20 cells mRNA extracted after treatment with PBS as control or LIF for 3h. Each treatment were made in duplicate. [GSM471254-GSM471257] Experiment Overall Design: 3) Pituitary corticotrophs cell line (AtT-20) response to Dex after 3h treatment: Experiment Overall Design: AtT-20 cells mRNA extracted after treatment with PBS as control or Dex for 3h. Each treatment were made in duplicate. [GSM471258-GSM471261] Experiment Overall Design: 4) Pituitary corticotrophs cell line (AtT-20) response to Dex after 18h treatment: Experiment Overall Design: AtT-20 cells mRNA extracted after treatment with PBS as control or Dex for 18h. Each treatment were made in duplicate. [GSM471262-GSM471269]

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EGF activation of POMC gene transcription is mediated by STAT3

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