A novel regulator of the PI3K/AKT pathway encoded by circ-PDE5A inhibits esophageal squamous carcinoma progression by promoting USP14-mediated deubiquitination of PIK3IP1

Objective: Esophageal squamous carcinoma (ESCC) is one of the most common gastrointestinal tumors, and the PI3K/AKT signaling pathway plays a key role in the development of ESCC. circRNAs have been reported to be involved in the regulation of PI3K/AKT signaling, but the underlying mechanisms are unclear. This study aimed to identify protein-coding circRNAs and investigate their function in ESCC. Design: Differential expression of circRNAs between ESCC tissues and adjacent normal tissues was identified using circRNA microarray analysis. A novel protein encoded by circ-PDE5A was identified by LC-MS/MS. Molecular biological methods were used to explore the biological functions and regulatory mechanisms of circ-PDE5A and its encoded PDE5A-500aa novel protein in ESCC. Construction of a nanoplatform for the coupling of circRNAs to investigate the therapeutic translation value of circ-PDE5A. Results: We found that circ-PDE5A expression was downregulated in ESCC cells and tissues, and its low expression was associated with later clinicopathological staging and poorer prognosis. Functionally, circ-PDE5A inhibited ESCC proliferation and metastasis in vitro and in vivo by encoding the novel PDE5A-500aa protein, which was identified as a key player in regulating PI3K/AKT signaling activation in ESCC. Mechanistically, the novel PDE5A-500aa protein binds directly to PIK3IP1 and promotes USP14-mediated deubiquitination of the k48-linked polyubiquitin chain at residue K198 of PIK3IP1, thereby attenuating PI3K/AKT pathway in ESCC. In addition, the circ-PDE5A plasmid-coupled reduction-responsive nanoplatform successfully inhibited ESCC growth and metastasis. Conclusions: circ-PDE5A represents an epigenetic mechanism regulating PI3K/ATK signaling and serves as a novel and promising therapeutic target and prognostic marker for ESCC. To explore the specific mechanism by which circ-PDE5A affects the biological function of ESCC, we constructed KYSE30 cells with stable overexpression of circ-PDE5A and performed RNA-sequencing analysis.