Regulator of cullins-1 (ROC1) negatively regulates the Gli2 regulator SUFU to activate the hedgehog pathway in bladder cancer

W Wang,L Li,J Qiu,J Lan,H Chen,P Qu,M Gu

doi:10.1186/s12935-021-01775-5

Abstract

BackgroundThe regulator of cullins-1 (ROC1) is an essential subunit in the cullin-RING ligase (CRL) protein complex and has been shown to be critical in bladder cancer cell survival and progression. This study aimed to explore the molecular mechanism of ROC1 action in the malignant progression of bladder cancer.MethodsThis study utilized ex vivo, in vitro, and in vivo nude mouse experiments to assess the underlying mechanisms of ROC1 in bladder cancer cells. The expression of the components of the sonic hedgehog (SHH) pathway was determined by western blot analysis. ROC1 expression in human tumors was evaluated by immunohistochemistry.ResultsROC1 overexpression promoted the growth of bladder cancer cells, whereas knockdown of ROC1 expression had the opposite effect in bladder cancer cells. Mechanistically, ROC1 was able to target suppressor of fused homolog (SUFU) for ubiquitin-dependent degradation, allowing Gli2 release from the SUFU complex to activate the SHH pathway. Furthermore, knockdown of SUFU expression partially rescued the ROC1 knockdown-suppressed SHH activity as well as cancer cell growth inhibition. In ex vivo experiments, tissue microarray analysis of human bladder cancer specimens revealed a positive association of ROC1 expression with the SHH pathway activity.ConclusionThis study demonstrated that dysregulation of the ROC1–SUFU–GLI2 axis plays an important role in bladder cancer progression and that targeting ROC1 expression is warranted in further investigations as a novel strategy for the future control of bladder cancer.

Highlights

The regulator of cullins-1 (ROC1) is an essential subunit in the cullin-RING ligase (CRL) protein complex and has been shown to be critical in bladder cancer cell survival and progression
ROC1 induces bladder cancer cell growth in vitro and in vivo To evaluate the role of ROC1 in bladder cancer proliferation, we first assessed the oncogenic activity of ROC1 in bladder cancer 5637 and T24 cells by stable transfection of ROC1 cDNA (p-ROC1) or small interfering RNA, while the empty vector (p-CONT) and the negative control siRNA were used as controls, respectively (Additional file 1: Fig. S1)
Our in vivo orthotopic bladder cancer cell xenograft model in nude mice showed that overexpression of ROC1 resulted in a significant acceleration of tumor cell xenograft growth (Fig. 1e, f ), while our western blot analysis of the tumor cell xenografts confirmed ROC1 upregulation in the pROC1 group of mice compared with the vector-control group of mice (Fig. 1g)

Summary

Introduction

The regulator of cullins-1 (ROC1) is an essential subunit in the cullin-RING ligase (CRL) protein complex and has been shown to be critical in bladder cancer cell survival and progression. Our previous studies have demonstrated that ROC1 protein is overexpressed in bladder cancer tissues and that knockdown of ROC1 expression reduces the CRL activity, triggering the accumulation of its specific substrates (such as p21, p27, and DEPTOR) and leading to tumor growth suppression [13, 14]. As accumulating evidence suggests an essential role of hedgehog signaling in tumor cell proliferation [15], in this study, we explored the underlying molecular mechanisms by which ROC1 regulates the sonic hedgehog (SHH) pathway in bladder cancer using in vitro and in vivo experiments. The results of this study will form the molecular basis for the future development of a novel ROC1-based targeted therapy against bladder cancer

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