Ubiquitin-specific protease 8 inhibitor suppresses adrenocorticotropic hormone production and corticotroph tumor cell proliferation.

Cushing's disease is primarily caused by autonomic hypersecretion of adrenocorticotropic hormone (ACTH) from a pituitary adenoma. In Cushing's disease, mutations in the ubiquitin-specific protease 8 (USP8) have been detected. These mutations are associated with hyperactivation of USP8 that prevent epidermal growth factor receptor (EGFR) degradation. This leads to increased EGFR stability and results in the maintenance of EGFR signaling in Cushing's disease. USP8 inhibitors can suppress the growth of various tumors. In this study, the effects of a potent USP8 inhibitor, DUBs-IN-2, on ACTH production and cell proliferation were examined in mouse corticotroph tumor (AtT-20) cells. Proopiomelanocortin (Pomc) mRNA levels and ACTH levels were decreased in AtT-20 cells by DUBs-IN-2. Further, cell proliferation was inhibited, and apoptosis was induced by DUBs-IN-2. Transcript levels of pituitary tumor-transforming gene 1 (Pttg1), a pituitary tumor growth marker, were increased; and transcript levels of stress response growth arrest and DNA damage-inducible 45 (Gadd45ß) and Cdk5 and ABL enzyme substrate 1 (Cables1) mRNA levels were increased in response to the drug. Gadd45ß or Cables1 knockdown partially inhibited the DUBs-IN-2-induced decrease in cell proliferation, but not Pomc mRNA levels. Both GADD45ß and CABLES1 may be responsible, at least in part, for the USP8-induced suppression of corticotroph tumor cell proliferation. USP-8 may be a new treatment target in Cushing's disease.

Pituitary tumor transforming gene: a novel therapeutic target for glioma treatment.

Glioma which has strong proliferation and angiogenesis ability is the most common and malignant primary tumor in central nervous system. Pituitary tumor transforming gene (PTTG) is found in pituitary tumor, and plays important role in cell proliferation, cell cycle, cell apoptosis, and angiogenesis. However, the role of PTTG in glioma is still incompletely investigated. Here, we explored the correlation between PTTG and glioma grade, as well as micro-vessel density (MVD). In addition, siRNA was used to silence PTTG expression in glioma cell lines including U87MG, U251, and SHG44. Cell proliferation, apoptosis, invasion, and angiogenesis were studied both in vitro and in vivo. Our results demonstrated that PTTG expression was significantly up-regulated in glioma, and had positive correlation with glioma grade and MVD. Silencing of PTTG inhibited glioma cell proliferation, migration/invasion, and angiogenesis, induced cell apoptosis, suppressed cell invasion, and arrested cell cycle at G0/G1 stage. Silencing of PTTG could also inhibit tumor growth, invasion, and angiogenesis in vivo. Our data indicated that PTTG might be a potential target for glioma treatment.

Inhibition of heat shock protein 90 decreases ACTH production and cell proliferation in AtT-20 cells.

PURPOSE: Cushing's disease is primarily caused by adrenocorticotropic hormone (ACTH)-producing pituitary adenomas. If excision of the tumor from the pituitary, which is the primary treatment for Cushing's disease, is unsuccessful, further medical therapy is needed to treat the resultant hypercortisolism. Some of the drugs used to treat this condition have shown potential therapeutic benefits, but a more effective treatment should be explored for the treatment of Cushing's disease. In the present study, we determined the effect of heat shock protein 90 inhibitors on ACTH production and cell proliferation of AtT-20 corticotroph tumor cells. METHODS: AtT-20 pituitary corticotroph tumor cells were cultured. The expression levels of mouse proopiomelanocortin (POMC) and pituitary tumor transforming gene 1 (PTTG1) mRNA were evaluated using quantitative real-time PCR. Cellular DNA content was analyzed with fluorescence-activated cell sorting (FACS) analysis. The protein levels were determined by Western blot analysis. RESULTS: Both 17-allylamino-17-demethoxygeldanamycin and CCT018159 decreased POMC mRNA levels in AtT-20 cells and ACTH levels in the culture medium of these cells, suggesting that both drugs suppress ACTH synthesis and secretion in corticotroph tumor cells. Both drugs also decreased cell proliferation and induced apoptosis. FACS analyses revealed that both agents increased the percentage of AtT-20 cells in the G2/M phase. These drugs decreased cell proliferation, presumably due to the induction of cell death and arrest of the cell cycle in AtT-20 cells. Tumor weight in mice xenografted with AtT-20 cells and treated with CCT018159 was lower than in AtT-20-xenografted control mice. CCT018159 also decreased plasma ACTH levels, and POMC and PTTG1 mRNA levels in the tumor cells. CONCLUSIONS: CCT018159 inhibits ACTH production and corticotroph tumor cell proliferation in vitro and in vivo.