title: Aberrant expression and modification of silencing mediator of retinoic acid and thyroid hormone receptors involved in the pathogenesis of tumoral cortisol resistance.
abstract: Ectopic ACTH syndrome (EAS) accounts for 10-15% of cases of Cushing's syndrome and is mostly caused by small cell lung cancers or thymic carcinoids. EAS is characterized by tumoral cortisol resistance, whose underlying mechanism remains unknown. In this study, we reported that silencing mediator of retinoic acid and thyroid hormone receptors (SMRT), a major nuclear corepressor, was aberrantly expressed in ACTH-secreting thymic carcinoids. Overexpression and knockdown of SMRT in the ACTH-secreting AtT-20 cell line demonstrated that SMRT participated in the negative feedback of dexamethasone-mediated suppression of proopiomelanocortin. Posttranslational modification by the small ubiquitin-like modifiers (SUMO), i.e. SUMOylation plays an important role in fine-tuning transcriptional activities. SUMOylation of SMRT was observed in dexamethasone-resistant cell lines. Moreover, overexpression of the deSUMOylation enzyme enhanced the suppression of proopiomelanocortin by dexamethasone in AtT-20 cells. An evolutionarily conserved consensus SUMOylation site was identified close to the histone deacetylase 3 recruiting domain of SMRT, which might interfere with the recruiting process. These results suggested that aberrant expression and modification of SMRT might be involved in the pathogenesis of tumoral cortisol resistance. A therapeutic approach targeting SMRT SUMOylation might be developed for EAS patients.
authors.affiliation: Shanghai Clinical Center for Endocrine and Metabolic Diseases, Shanghai Institute of Endocrinology and Metabolism, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China.
authors.forename: Jingjing
authors.initials: J
authors.lastname: Jiang
authors.forename: Na
authors.initials: N
authors.lastname: Li
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Wang
authors.forename: Yan
authors.initials: Y
authors.lastname: Lu
authors.forename: Yufang
authors.initials: Y
authors.lastname: Bi
authors.forename: Weiqing
authors.initials: W
authors.lastname: Wang
authors.forename: Xiaoying
authors.initials: X
authors.lastname: Li
authors.forename: Guang
authors.initials: G
authors.lastname: Ning
mesh_terms: D000182:ACTH Syndrome, Ectopic / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D000818:Animals; D002276:Carcinoid Tumor / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002478:Cells, Cultured; D004351:Drug Resistance / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000502:physiology; D006655:Histone Deacetylases / Q000378:metabolism / Q000502:physiology; D006801:Humans; D006854:Hydrocortisone / Q000494:pharmacology; D051379:Mice; D056985:Nuclear Receptor Co-Repressor 2 / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D011333:Pro-Opiomelanocortin / Q000235:genetics / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000502:physiology; D034741:RNA, Small Interfering / Q000494:pharmacology; D025842:SUMO-1 Protein / Q000378:metabolism; D013953:Thymus Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D014162:Transfection; D000099186:Histone Deacetylase 3
chemical_list: D006655:Histone Deacetylases; D006854:Hydrocortisone; D056985:Nuclear Receptor Co-Repressor 2; D011333:Pro-Opiomelanocortin; D034741:RNA, Small Interfering; D025842:SUMO-1 Protein; D000099186:Histone Deacetylase 3