SNRPD1 inhibition suppresses the proliferation of hepatocellular carcinoma and promotes autophagy through the PI3K/AKT/mTOR/4EBP1 pathway

Small nuclear ribonucleoprotein Sm D1 (SNRPD1) has been reported as an oncogene in some solid cancers. Our previous study suggested that SNRPD1 has diagnostic and prognostic value in hepatocellular carcinoma (HCC), but its role in tumor growth and biological behavior remains unknown. In this study, we aimed to unravel the role and mechanism of SNRPD1 in HCC. We investigated the SNRPD1 mRNA level in adjacent normal liver tissues and HCC tissues with different tumor stages in the UALCAN database. The associations between SNRPD1 mRNA expression and HCC prognosis were investigated in TCGA database. Then, 52 pairs of frozen HCC tissues and corresponding adjacent normal liver tissues were collected to perform qPCR and immunohistochemistry assay. Next, we carried out a series of experiments in vitro and in vivo to investigate the effects of SNRPD1 expression on cell invasion, migration, proliferation, autophagy, and the PI3K/AKT/mTOR pathway. The bioinformatics analysis and qPCR in our patient cohort demonstrated that the SNRPD1 mRNA level in HCC tissues was higher than in adjacent normal tissues. In addition, the immunohistochemistry assay exhibited an increased SNRPD1 protein level with the tumor stage increase. Survival analysis suggested that higher expression of SNRPD1 was significantly associated with unfavorable prognosis of patients with HCC. The functional experiments in vitro indicated that SNRPD1 knockdown suppressed the cellular proliferation, migration, and invasion capacities. Furthermore, SNRPD1 inhibition induced cellular apoptosis and arrested the HCC cells at the G0/G1 phase of the cell cycle. Mechanistic analyses demonstrated that SNRPD1 knockdown induced the increase of autophagic vacuoles and the expression of autophagy-related genes (ATG5, ATG7, and ATG12) and blocked the PI3K/AKT/mTOR/4EBP1 pathway in vitro. Moreover, SNRPD1 inhibition suppressed tumor growth and expression of the Ki67 protein in vivo. SNRPD1 may serve as an oncogene in HCC and promote tumor proliferation via inhibiting autophagy induced through the PI3K/Akt/mTOR/4EBP1 pathway.