Polypyrimidine tract-binding protein 3 (PTBP3) is an essential RNA-binding protein with roles in RNA splicing, 3′ end processing and translation. Although increasing evidence implicates PTBP3 in several cancers, its role in gastric cancer metastasis remains poorly explored. In this study, we found that PTBP3 was upregulated in the gastric cancer tissues of patients with lymph node metastasis. Patients with high PTBP3 expression levels had significantly shorter survival than those with low PTBP3 expression. Overexpression/knockdown of PTBP3 expression had no effect on proliferation, whereas it regulated migration and invasion in vitro. In addition, when a mouse xenotransplant model of MKN45 was established, knockdown of PTBP3 in MKN45 cells caused the formation of tumours that were smaller in size than their counterparts, with suppression of tumour lymphangiogenesis and metastasis to regional lymph nodes. Furthermore, we identified caveolin 1 (CAV1) as a downstream target of PTBP3. RNA immunoprecipitation (RIP) assays and dual-luciferase reporter gene assays indicated that PTBP3 interacted with the CU-rich region of the CAV1 gene to downregulate CAV1α expression. Knockdown of CAV1α abrogated the reduction of FAK and Src induced by PTBP3 knockdown. In summary, our findings provide experimental evidence that PTBP3 may function as a metastatic gene in gastric cancer by regulating CAV1 through alternative splicing.

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Background:Human polypyrimidine tract binding protein 3 (PTBP3) was first discovered in 1999 and has been well characterised as a differentiation regulator. However, its role in human cancer has rarely been reported. Our previous study revealed increased PTBP3 protein level in gastric cancer tissues. Downregulation of PTBP3 suppressed the proliferation and differentiation of gastric cancer cells in vivo.Methods:PTBP3 mRNA levels in human gastric cancer and adjuvant non-tumour tissues were detected. Apoptosis and 5-FU effect were determined in PTBP3-silenced gastric cancer cells. Underlying molecular mechanisms were investigated.Results:MRNA expression of PTBP3 was upregulated in gastric cancer tissues, especially in those at an advanced stage. PTBP3 silencing led to apoptosis, under which modulation of PTB and thereby switch of Bcl-x pre-mRNA splicing pattern might be an important mechanism. Further research found that inhibition of PTBP3 expression enhanced the chemosensitivity of gastric cancer cells towards 5-FU treatment. This was mediated by reduced expression of histone deacetylase 6 (HDAC6), which further inhibited the phosphorylation of Akt and the expression of thymidylate synthase (TYMS), the critical determinant of 5-FU cytotoxicity.Conclusions:PTBP3 might serve as a biomarker of gastric cancer or potential target for anti-cancer therapy.