OR26-6 The Histone Modifying Enzyme, Lysine-Specific Demethylase 1 (LSD1), is Implicated in the Pathogenesis of Human Pituitary Adenomas

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: OR26-Pituitary Tumorigenesis: Advances in Mechanism & Treatment
Sunday, June 16, 2013: 11:15 AM-12:45 PM
Presentation Start Time: 12:30 PM
Room 130 (Moscone Center)
Iain Robert Thompson*1, Erin A Clark1, Shuyun Xu1, Dan Tang1, Edward Raymond Laws Jr.2, Yujiang Shi1, Rona S. Carroll1 and Ursula B Kaiser1
1Brigham and Women's Hospital/Harvard Medical School, Boston, MA, 2BWH Neurosurgery, Boston, MA
The pathogenesis of pituitary adenomas is poorly understood. In a subset of cases, genetic mutations have been identified, providing some insight into pathogenetic mechanisms. One of the first genetic abnormalities identified in association with pituitary adenomas occurs in patients with multiple endocrine neoplasia type 1 syndrome (MEN-1), due to mutations in the MEN1 gene, encoding menin. A tumor suppressor, menin associates with histone methyltransferase complexes to regulate modulators of cell cycle progression. We hypothesized that the histone methylation status of specific cyclin-dependent kinase (CDK) and CDK inhibitor genes might serve as an underlying epigenetic mechanism important in pituitary tumor pathogenesis. LSD1 and LSD2 are flavin-dependent monoamine oxidases, functioning to demethylate histone H3K4. We studied the expression levels of LSD1, LSD2 and menin in pituitary adenoma tissue specimens (n=11) plus normal pituitary control tissue acquired at autopsy (n=6). By RT-qPCR, the mRNA expression of all three genes was significantly higher in the adenomas, compared to the control samples. Western blot analysis demonstrated significant increases in LSD1 and menin protein levels in the adenomas compared to controls, whereas LSD2 protein levels were not elevated. The increased menin protein levels found in the adenomas may be a consequence of increased proliferation compared to normal pituitary cells, since menin expression is known to peak in the S-phase of the cell cycle. To further characterize the potential roles of these histone demethylases in pituitary tumorigenesis, the effect of a LSD inhibitor, tranylcypromine, on the proliferation of pituitary cell lines was investigated. Tranylcypromine significantly reduced the proliferation rates of GH3 somatolactotrope- and LβT2 gonadotrope-derived cells. Specific, lentiviral-delivered shRNA against LSD1 or LSD2 reduced mRNA levels of the respective demethylase by at least 70% in LβT2 cells, compared to scramble shRNA infected control cells. LSD1, but not LSD2, knock-down significantly reduced the LβT2 cell proliferation rate, compared to scramble shRNA controls. Candidate cell cycle genes regulated by LSD1 were identified from a microarray analyzing relative gene expression in A549 lung adenocarcinoma cells infected with LSD1 or scramble shRNA. We found that CDK 1, 4 and 19 mRNA levels were significantly reduced, and mRNA levels of a CDK inhibitor, CDKN1C, were significantly increased in LβT2 cells infected with LSD1 shRNA compared to controls. Taken together, these findings suggest a role for LSD1 in pituitary tumorigenesis through effects on cellular proliferation, likely mediated through effects on histone methylation at the promoters of genes encoding cell cycle regulators.

Nothing to Disclose: IRT, EAC, SX, DT, ERL Jr., YS, RSC, UBK

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

Sources of Research Support: Brain Science Foundation awarded to UBK
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