Esophageal squamous carcinoma (ESCC) is the major subtype of esophageal cancer in China, accounting for 90% of cases. Recent studies revealed that abnormalities in the Hippo/YAP axis are pervasive in ESCC and are recognized as the important driver of ESCC progression. Since the activity of Hippo signaling is controlled by phosphorylation cascade, it is a mystery why the major effector YAP is still over-activated when the cascade is inhibited. Several studies suggested that in addition to phosphorylation, other protein modifications such as ubiquitination also play important roles in manipulating Hippo/YAP signaling activity. Since YAP protein stability is controlled via an appropriate balance between E3 ubiquitin ligases and deubiquitinases, we performed deubiquitinase siRNA screening and identified USP36 as a deubiquitinase significantly related to Hippo/YAP signaling activity and ESCC progression. USP36 expression was elevated in ESCC samples and correlated with poor differentiation. USP36 expression was correlated with YAP protein levels in ESCC samples. Molecular studies demonstrated that USP36 associated with the YAP protein and enhanced YAP protein stability by blocking the K48-linked polyubiquitination of YAP. In conclusion, our study revealed a novel deubiquitinase in regulating Hippo signaling in ESCC, which could be an encouraging drug target for Hippo-driven ESCC.

Increasing evidence has shown that circular RNAs (circRNAs) interact with RNA‐binding proteins (RBPs) and promote cancer progression. However, the function and mechanism of the circRNA/RBP complex in esophageal squamous cell carcinoma (ESCC) are still largely unknown. Herein, we first characterized a novel oncogenic circRNA, circ‐FIRRE, by RNA sequencing (Ribo‐free) profiling of ESCC samples. Furthermore, we observed marked circ‐FIRRE overexpression in ESCC patients with high TNM stage and poor overall survival. Mechanistic studies indicated that circ‐FIRRE, as a platform, interacts with the heterogeneous nuclear ribonucleoprotein C (HNRNPC) protein to stabilize GLI2 mRNA by directly binding to its 3’‐UTR in the cytoplasm, thereby resulting in elevated GLI2 protein expression and subsequent transcription of its target genes MYC, CCNE1, and CCNE2, ultimately contributing to ESCC progression. Moreover, HNRNPC overexpression in circ‐FIRRE knockdown cells notably abolished circ‐FIRRE knockdown‐mediated Hedgehog pathway inhibition and ESCC progression impairment in vitro and in vivo. Clinical specimen results showed that circ‐FIRRE and HNRNPC expression was positively correlated with GLI2 expression, which reveals the clear significance of the circ‐FIRRE/HNRNPC‐GLI2 axis in ESCC. In summary, our results indicate that circ‐FIRRE could serve as a valuable biomarker and potential therapeutic target for ESCC and highlight a novel mechanism of the circ‐FIRRE/HNRNPC complex in ESCC progression regulation.