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

Abstract

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 damageinducible 45 (Gadd45β) and Cdk5 and ABL enzyme substrate 1 (Cables1) mRNA levels were increased in response to the drug. Gadd45β or Cables1 knockdown partially inhibited the DUBs-IN-2-induced decrease in cell proliferation, but not Pomc mRNA levels. Both GADD45β 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.

Ubiquitin-specific protease 8 (USP8/UBPy): a prototypic multidomain deubiquitinating enzyme with pleiotropic functions

“…Inhibitor treatment revealed that USP8 is required for growth of glioblastoma stem cells [111], multiple myeloma cells [112] and gefitinib-resistant non-small cell lung cancer cells [113] and demonstrated the existence of a therapeutic window in comparison with growth inhibition of control cells. Using mouse corticotroph tumor AtT20 cells DUBs-IN-2 also suppressed ACTH production and cell proliferation [114,115]. However, representing an essential gene, USP8 does not meet ideal requirements to serve as a druggable target and toxicity aspects will need to be tightly controlled.…”

Genetic Basis of ACTH-Secreting Adenomas

“…In AtT-20 cells, CABLES1 levels normally increase in response to glucocorticoids, together with many other molecular responses involving c-Myc, GADD45, and other proteins, contributing to the glucocorticoid-mediated negative feedback mechanisms on cell proliferation [ 53 ]. Moreover, the administration of a USP8-inhibitor in AtT-20 cells led to a suppression in proliferation and an increase in the CABLES1 levels and GADD45, possibly demonstrating a role for CABLES1 in the suppression of pathologic proliferation [ 55 ]. In fact, CABLES1 levels have been shown to decrease in ACTH-secreting adenomas [ 53 , 55 ].…”

“…Moreover, the administration of a USP8-inhibitor in AtT-20 cells led to a suppression in proliferation and an increase in the CABLES1 levels and GADD45, possibly demonstrating a role for CABLES1 in the suppression of pathologic proliferation [ 55 ]. In fact, CABLES1 levels have been shown to decrease in ACTH-secreting adenomas [ 53 , 55 ]. The role of CABLES1, however, may be overestimated in AtT-20 cells; in fact, CABLES1-knockout mice showed normal pituitary development up to one year, suggesting that other mechanisms may be required for corticotrope adenoma formation [ 53 ].…”

Ubiquitin-specific peptidase 8 regulates the trafficking and stability of the human organic anion transporter 1

“…USP8 plays critical roles in various pathological developments and USP8 inhibitors are the potential treatments for those diseases including lung cancer, Cushing's disease and Alzheimer disease. Some USP8-specific inhibitors are developed in pre-clinical stage and will be progressed into clinical therapies in the near future [42][43][44][45][46]. Downexpression of USP8 decreased OAT1 transport activity and OAT1 expression.…”