Cyclin E-Mediated Human Proopiomelanocortin Regulation as a Therapeutic Target for Cushing Disease.

Abstract

CONTEXT:

Cushing disease, due to pituitary corticotroph tumor ACTH hypersecretion, drives excess adrenal cortisol production with adverse morbidity and mortality. Loss of glucocorticoid negative feedback on the hypothalamic-pituitary-adrenal axis leads to autonomous transcription of the corticotroph precursor hormone proopiomelanocortin (POMC), consequent ACTH overproduction, and adrenal hypercortisolism. We previously reported that R-roscovitine (CYC202, seliciclib), a 2,6,9-trisubstituted purine analog, suppresses cyclin-dependent-kinase 2/cyclin E and inhibits ACTH in mice and zebrafish. We hypothesized that intrapituitary cyclin E signaling regulates corticotroph tumor POMC transcription independently of cell cycle progression. The aim was to investigate whether R-roscovitine inhibits human ACTH in corticotroph tumors by targeting the cyclin-dependent kinase 2/cyclin E signaling pathway.

METHODS:

Primary cell cultures of surgically resected human corticotroph tumors were treated with or without R-roscovitine, ACTH measured by RIA and quantitative PCR, and/or Western blot analysis performed to investigate ACTH and lineage-specific transcription factors. Cyclin E and E2F transcription factor 1 (E2F1) small interfering RNA (siRNA) transfection was performed in murine corticotroph tumor AtT20 cells to elucidate mechanisms for drug action. POMC gene promoter activity in response to R-roscovitine treatment was analyzed using luciferase reporter and chromatin immunoprecipitation assays.

RESULTS:

R-roscovitine inhibits human corticotroph tumor POMC and Tpit/Tbx19 transcription with decreased ACTH expression. Cyclin E and E2F1 exhibit reciprocal positive regulation in corticotroph tumors. R-roscovitine disrupts E2F1 binding to the POMC gene promoter and suppresses Tpit/Tbx19 and other lineage-specific POMC transcription cofactors via E2F1-dependent and -independent pathways.

CONCLUSION:

R-roscovitine inhibits human pituitary corticotroph tumor ACTH by targeting the cyclin E/E2F1 pathway. Pituitary cyclin E/E2F1 signaling is a previously unappreciated molecular mechanism underlying neuroendocrine regulation of the hypothalamic-pituitary-adrenal axis, providing a subcellular therapeutic target for small molecule cyclin-dependent kinase 2 inhibitors of pituitary ACTH-dependent hypercortisolism, ie, Cushing disease.

• Authors: Ning-Ai Liu, Takako Araki, Daniel Cuevas-Ramos, Jiang Hong, Anat Ben-Shlomo, Yukiko Tone, Masahide Tone, Shlomo Melmed
• Journal: The Journal of clinical endocrinology and metabolism (J Clin Endocrinol Metab) Vol. 100 Issue 7 Pg. 2557-64 (Jul 2015) ISSN: 1945-7197 [Electronic] United States
• PMID: 25942479 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• Antineoplastic Agents
• Cyclin E
• Purines
• Roscovitine
• Pro-Opiomelanocortin

Topics

• ACTH-Secreting Pituitary Adenoma (complications, drug therapy, genetics, pathology)
• Adenoma (complications, drug therapy, genetics, pathology)
• Adolescent
• Adult
• Aged
• Antineoplastic Agents (therapeutic use)
• Cyclin E (antagonists & inhibitors, physiology)
• Female
• Gene Expression Regulation, Neoplastic (drug effects)
• Humans
• Male
• Molecular Targeted Therapy (methods)
• Pituitary ACTH Hypersecretion (drug therapy, pathology)
• Primary Cell Culture
• Pro-Opiomelanocortin (genetics, metabolism)
• Purines (therapeutic use)
• Roscovitine
• Tumor Cells, Cultured
• Young Adult