The KBTBD6/7-DRD2 axis regulates pituitary adenoma sensitivity to dopamine agonist treatment

• Published in: Acta neuropathologica 2020-09, Vol.140 (3), p.377-396
• Main Authors: Liu, Yan Ting, Liu, Fang, Cao, Lei, Xue, Li, Gu, Wei Ting, Zheng, Yong Zhi, Tang, Hao, Wang, Yu, Yao, Hong, Zhang, Yong, Xie, Wan Qun, Ren, Bo Han, Xiao, Zhuo Hui, Nie, Ying Jie, Hu, Ronggui, Wu, Zhe Bao
• Format: Article
• Language: English
• Subjects: Adenoma; Agonists; AKT protein; Biodegradation; Brain cancer; Brain tumors; CRISPR; Dopamine; Dopamine D2 receptors; Internalization; Medicine; Medicine & Public Health; Molecular modelling; Neurosciences; Original Paper; Pathology; Pituitary; Pituitary gland; Prolactin; Proteasomes; Proteins; Thalamus; TOR protein; Tumor cells; Tumors; Ubiquitin; Ubiquitin-protein ligase; Ubiquitination
• ISSN: 0001-6322; 1432-0533
• DOI: 10.1007/s00401-020-02180-4

Pituitary adenoma (PA) is one of the most common intracranial tumors, and approximately 40% of all PAs are prolactinomas. Dopamine agonists (DAs), such as cabergoline (CAB), have been successfully used in the treatment of prolactinomas. The expression of dopamine type 2 receptor (DRD2) determines the therapeutic effect of DAs, but the molecular mechanisms of DRD2 regulation are not fully understood. In this study, we first demonstrated that DRD2 underwent proteasome-mediated degradation. We further employed the yeast two-hybrid system and identified kelch repeat and BTB (POZ) domain containing 7 (KBTBD7), a substrate adaptor for the CUL3-RING ubiquitin (Ub) ligase complex, as a DRD2-interacting protein. KBTBD6/7 directly interacted with, and ubiquitinated DRD2 at five ubiquitination sites (K221, K226, K241, K251, and K258). CAB, a high-affinity DRD2 agonist, induced DRD2 internalization, and cytoplasmic DRD2 was degraded via ubiquitination under the control of KBTBD6/7, the activity of which attenuated CAB-mediated inhibition of the AKT/mTOR pathway. KBTBD7 knockout (KO) mice were generated using the CRISPR-Cas9 technique, in which the static level of DRD2 protein was elevated in the pituitary gland, thalamus, and heart, compared to that of WT mice. Consistently, the expression of KBTBD6/7 was negatively correlated with that of DRD2 in human pituitary tumors. Moreover, KBTBD7 was highly expressed in dopamine-resistant prolactinomas, but at low levels in dopamine-sensitive prolactinomas. Knockdown of KBTBD6/7 sensitized MMQ cells and primary pituitary tumor cells to CAB treatment. Conversely, KBTBD7 overexpression increased CAB resistance of estrogen-induced in situ rat prolactinoma model. Together, our findings have uncovered the novel mechanism of DRD2 protein degradation and shown that the KBTBD6/7-DRD2 axis regulates PA sensitivity to DA treatment. KBTBD6/7 may thus become a promising therapeutic target for pituitary tumors.