CircPRUNE inhibits the proliferation and metastasis of oral squamous cell carcinoma through PTBP3/NOTCH3 signaling axis

The five-year survival rate for patients with oral squamous cell carcinoma (OSCC) remains relatively low. Hence, there is an urgent need to explore more effective therapeutic strategies for this disease. CircRNAs are a class of circular non-coding RNAs which are reported playing key roles in tumorigenesis, development and progression of OSCC. But the biological function of most part of circRNAs are unknown. Our previous study had characterized a down-regulated circRNA-CircPRUNE in OSCC tissues. This study aims to investigate the role of circPRUNE in OSCC progression and its molecular interaction with PTBP3 and downstream effect on NOTCH3 signaling pathway. Our in vitro RNA pulldown combined mass spectroscopy assay and RNA binding protein immunoprecipitation (RIP) results suggested that CircPRUNE-PTBP3 interaction inhibits the proliferation and metastasis of OSCC cells. It was further found that CircPRUNE binding the RRM8 protein domain enhanced PTBP3 degradation by ubiquitination modification way. CircPRUNE knockdown transcriptome sequencing and the PTBP3 RIP-seq data revealed that NOTCH3 was a downstream mRNA affected by circPRUNE-PTBP3 interaction. PTBP3 overexpression could reverse circPRUNE's inhibition effects on OSCC cell proliferation, migration, invasion, and NOTCH3 expression level in vitro and in vivo. In summary, we found circPRUNE suppressed the proliferation and metastasis of OSCC cells by binding to PTBP3 RRM8 domain, inducing PTBP3 ubiquitination degradation, which weakened the NOTCH3 mRNA stability. Our study highlights the potential of circPRUNE as a prospective biomarker for the diagnosis of OSCC and as therapy target to inhibit cell proliferation and metastasis through modulation of PTBP3/NOTCH3 signaling axis for OSCC patients.