Abstract: Objective To investigate the effect of SIRT4 on the proliferation and invasion of pancreatic cancer cells and the growth of transplanted tumor in nude mice by regulating MAPK signaling pathway and lipid metabolism pathway. Methods The cancer tissues and adjacent tissues samples of 5 patients with pancreatic ductal adenocarcinoma, who underwent surgical treatment in the Department of Hepatobiliary Surgery of the First Affiliated Hospital of Guangxi Medical University from June 1, 2021 to July 28, 2022, were collected. The Human normal pancreatic cell lines (HPDE6⁃C7) and pancreatic cancer cell lines (CFPAC⁃1, PANC⁃1, BXPC⁃3, ASPC⁃1) were selected, and the expression level of SIRT4 in pancreatic cancer tissues and cells were detected by RT⁃qPCR and Western blot. BXPC⁃3 and PANC⁃1 cell lines overexpressing SIRT4 were constructed by plasmid transfection, and cell proliferation was detected by CCK⁃8 assay and plate clone formation assay. Transwell assay was used to detect cell invasion ability. The BXPC⁃3 cell line stably overexpressing SIRT4 was constructed by lentiviral vector and inoculated into the armpits of nude mice, the effect of SIRT4 on tumor growth in vivo was observed by tumor formation experiment in nude mice. Immunohistochemistry was used to detect the expression of Ki67 in the transplanted tumor of nude mice. The expression of SIRT4 downstream molecules was detected by mRNA⁃seq, and the expression levels of MAPK signaling pathway and lipid metabolism related proteins were detected by Western blot. Results RT⁃qPCR and Western blot results showed that SIRT4 mRNA and protein expression levels in pancreatic cancer tissues were significantly lower than those in adjacent tissues (all P<0.05). The results of CCK⁃8 assay, colony formation assay and Transwell invasion assay showed that compared with the NC group, the proliferation and invasion ability of BXPC⁃3 and PANC⁃1 cells in the SIRT4⁃OE group were decreased (all P<0.05). The tumor formation experiment in nude mice showed that the volume and weight of transplanted tumors were significantly reduced after SIRT4 overexpression (all P<0.05). Immunohistochemistry showed that the number of Ki67 positive cells was significantly reduced in the SIRT4⁃OE group compared with the NC group (P=0.002). The results of mRNA⁃seq and enrichment analysis showed that the downstream differential genes of SIRT4 were significantly enriched in MAPK signaling pathway Western blot showed that the expression of p⁃ERK protein related to MAPK signaling pathway decreased after SIRT4 overexpression, while the protein expression levels of JNK, p⁃JNK, p38 and p⁃p38 changed insignificantly. The protein expression levels of ACC, FASN and SREBP1C, which were the key factors of lipid production, were decreased, while the protein expression levels of PPARα and CPT1a, which were the regulators of lipid metabolism, were increased. Conclusions SIRT4 may inhibit the proliferation and invasion of pancreatic cancer and the growth of transplanted tumor in nude mice by inhibiting the MAPK signaling pathway and lipid metabolism pathway.

Key words: Pancreatic cancer, SIRT4, Lipid metabolism, MAPK signaling pathway, Proliferation, Invasion