Background N 7 ‐methylguanosine (m 7 G) modification is one of the most common transfer RNA (tRNA) modifications in humans. The precise function and molecular mechanism of m 7 G tRNA modification in hepatocellular carcinoma (HCC) remain poorly understood. Methods The prognostic value and expression level of m 7 G tRNA methyltransferase complex components methyltransferase‐like protein‐1 (METTL1) and WD repeat domain 4 (WDR4) in HCC were evaluated using clinical samples and TCGA data. The biological functions and mechanisms of m 7 G tRNA modification in HCC progression were studied in vitro and in vivo using cell culture, xenograft model, knockin and knockout mouse models. The m 7 G reduction and cleavage sequencing (TRAC‐seq), polysome profiling and polyribosome‐associated mRNA sequencing methods were used to study the levels of m 7 G tRNA modification, tRNA expression and mRNA translation efficiency. Results The levels of METTL1 and WDR4 are elevated in HCC and associated with advanced tumour stages and poor patient survival. Functionally, silencing METTL1 or WDR4 inhibits HCC cell proliferation, migration and invasion, while forced expression of wild‐type METTL1 but not its catalytic dead mutant promotes HCC progression. Knockdown of METTL1 reduces m 7 G tRNA modification and decreases m 7 G‐modified tRNA expression in HCC cells. Mechanistically, METTL1‐mediated tRNA m 7 G modification promotes the translation of target mRNAs with higher frequencies of m 7 G‐related codons. Furthermore, in vivo studies with Mettl1 knockin and conditional knockout mice reveal the essential physiological function of Mettl1 in hepatocarcinogenesis using hydrodynamics transfection HCC model. Conclusions Our work reveals new insights into the role of the misregulated tRNA modifications in liver cancer and provides molecular basis for HCC diagnosis and treatment.
BaCKgRoUND aND aIMS:The dynamic N6methyladenosine (m 6 A) mRNA modification is essential for acute stress response and cancer progression. Sublethal heat stress from insufficient radiofrequency ablation (IRFA) has been confirmed to promote HCC progression; however, whether m 6 A machinery is involved in IRFA-induced HCC recurrence remains open for study. appRoaCH aND ReSUltS: Using an IRFA HCC orthotopic mouse model, we detected a higher level of m 6 A reader YTH N6-methyladenosine RNA binding protein 1-3 (YTHDF1) in the sublethal-heat-exposed transitional zone close to the ablation center than that in the farther area. In addition, we validated the increased m 6 A modification and elevated YTHDF1 protein level in sublethal-heat-treated HCC cell lines, HCC patient-derived xenograft (PDX) mouse model, and patients' HCC tissues. Functionally, gain-of-function/lossof-function assays showed that YTHDF1 promotes HCC cell viability and metastasis. Knockdown of YTHDF1 drastically restrains the tumor metastasis evoked by sublethal heat treatment in tail vein injection lung metastasis and orthotopic HCC mouse models. Mechanistically, we found that sublethal heat treatment increases epidermal factor growth receptor (EGFR) m 6 A modification in the vicinity of the 5′ untranslated region and promotes its binding with YTHDF1, which enhances the translation of EGFR mRNA. The sublethalheat-induced up-regulation of EGFR level was further confirmed in the IRFA HCC PDX mouse model and patients' tissues. Combination of YTHDF1 silencing and EGFR inhibition suppressed the malignancies of HCC cells synergically. CoNClUSIoNS:The m 6 A-YTHDF1-EGFR axis promotes HCC progression after IRFA, supporting the rationale for targeting m 6 A machinery combined with EGFR inhibitors to suppress HCC metastasis after RFA. (Hepatology 2021;74:1339-1356). R adiofrequency ablation (RFA) is now recommended as one of the curative therapies for early-stage HCC by guidelines of the American Association for the Study of Liver
Recent studies indicated that insufficient radiofrequency ablation (RFA) could endow hepatocellular carcinoma (HCC) with higher aggressive potential. Stress-induced phosphoprotein 1 (STIP1), which was found highly expressed in HCC, is a chaperone molecule mediating cell homeostasis under thermal stress. We aimed to explore the role of STIP1 on the metastasis of residual HCC after RFA. Mice model with orthotopic HCC implants or caudal vein injection were employed to assess potential of lung metastasis and/or intrahepatic metastasis (IHM) of HCC cells. Cell culture model was used to determine cell invasion, mesenchymal marker genes expression, and underlying molecular mechanisms. Clinical specimens were collected to analyze the relationship between STIP1 and clinical outcome. We found that insufficient RFA elicited more IHM of HCCLM3 tumors, which could be reduced by silencing STIP1. Knockdown of STIP1 also significantly decreased lung metastatic potential of HCCLM3 cells. In vitro, HCCLM3 and HepG2 displayed a spindle-shaped morphology with upregulation of STIP1 and mesenchymal markers after sublethal heat exposure. Mechanistically, heat exposure induced the formation of STIP1-heat shock protein 90 (HSP90) complex, which could shuttle epithelial transcription repressor Snail1 into nucleus and regulate mesenchymal gene transcription. Blocking the HSP90-STIP1 complex reduced the invasive potential of HCC cells after heat exposure. Using clinical specimen, we found that STIP1 was expressed significantly higher in metastatic tumor tissues and in sera from metastatic HCC patients (p < 0.05). The high expression of STIP1 was significantly linked to shorter recurrence-free survival (p < 0.05). To sum up, our study found that STIP1 is positively associated with the sublethal heat-induced cancer cell metastasis through mediating the mesenchymal gene transcription. Blocking STIP1 activity may suppress HCC cell metastatic potential after RFA.
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