Transcription Factor ASCL1 Acts as a Novel Potential Therapeutic Target for the Treatment of the Cushing’s Disease
Authors: Chen Zhengyuan , Jia Qi , Zhao Zhaozhao , Zhang Qilin , Chen Yu , Qiao Nidan , Ye Zhao , Ji Chenxing , Zhang Yichao , He Wenqiang , Shi Chengzhang , Cai Yixin , Yao Boyuan , Han Rui , Wang Ye , Shou Xuefei , Shen Ming , Cao Xiaoyun , Zhou Xiang , Cheng Haixia , Zhu Jingjing , Hu Yao , Zhang Zhaoyun , Ye Hongying , Li Yiming , Li Shiqi , Wang Yongfei , Ma Zengyi , Ni Ting , Zhao Yao 
Published: May 2022

Abstract

Background
The pathogenesis of Cushing’s disease (CD) is still not adequately understood despite the identification of somatic driver mutations in USP8, BRAF, and USP48. In this multiomics study, we combined RNA sequencing (RNA-seq) with Sanger sequencing to depict transcriptional dysregulation under different gene mutation backgrounds. Furthermore, we evaluated the potential of achaete-scute complex homolog 1 (ASCL1), a pioneer transcription factor, as a novel therapeutic target for treatment of CD and its possible downstream pathway.

Methods
RNA-seq was adopted to investigate the gene expression profile of CD, and Sanger sequencing was adopted to detect gene mutations. Bioinformatics analysis was used to depict transcriptional dysregulation under different gene mutation backgrounds. The function of ASCL1 in hormone secretion, cell proliferation, and apoptosis were studied in vitro. The effectiveness of an ASCL1 inhibitor was evaluated in primary CD cells, and the clinical relevance of ASCL1 was examined in 68 patients with CD. RNA-seq in AtT-20 cells on Ascl1 knockdown combined with published chromatin immunoprecipitation sequencing data and dual luciferase assays were used to explore downstream pathways.

Results
ASCL1 was exclusively overexpressed in USP8-mutant and wild-type tumors. Ascl1 promoted adrenocorticotrophin hormone overproduction and tumorigenesis and directly regulated Pomc in AtT-20 cells. An ASCL1 inhibitor presented promising efficacy in both AtT-20 and primary CD cells. ASCL1 overexpression was associated with a larger tumor volume and higher adrenocorticotrophin secretion in patients with CD.

Conclusion
Our findings help to clarify the pathogenesis of CD and suggest that ASCL1 is a potential therapeutic target the treatment of CD.

Summary
The pathogenesis of Cushing’s disease (CD) is still not adequately understood despite the identification of somatic driver mutations in USP8, BRAF, and USP48. Moreover, few effective medical therapies are currently available for the treatment of CD. Here, using a multiomics approach, we first report the aberrant overexpression of the transcription factor gene ASCL1 in USP8-mutant and wild-type tumors of CD. Ascl1 promoted adrenocorticotrophin hormone overproduction and tumorigenesis and directly regulated Pomc in mouse AtT-20 cells. Notably, an ASCL1 inhibitor presented promising efficacy in both AtT-20 and primary CD cells. Importantly, ASCL1 overexpression was associated with a larger tumor volume and higher adrenocorticotrophin secretion in patients with CD. Thus, our findings improve understanding of CD pathogenesis and suggest that ASCL1 is a potential therapeutic target the treatment of CD.