ALKBH5‐mediated m⁶A demethylation of TIRAP mRNA promotes radiation‐induced liver fibrosis and decreases radiosensitivity of hepatocellular carcinoma

Abstract

Background Radiation‐induced hepatic stellate cell (HSC) activation promotes radiation‐induced liver fibrosis (RILF), a complication for hepatocellular carcinoma (HCC) radiotherapy. The demethylase alpha‐ketoglutarate‐dependent dioxygenase alkB homolog 5 (ALKBH5) decreases N6‐methyladenylate methylation (m 6 A) modification of RNA, while its role in regulating RILF pathogenesis and HCC radiosensitivity remains unknown. Methods Methylated RNA immunoprecipitation sequencing (MeRIP‐seq) and RNA‐sequencing (RNA‐seq) were used to screen target genes regulated by ALKBH5. HSC with altered ALKBH5 expression was used to assess irradiation‐induced HSC activation and the effect of HSC on recruitment and polarisation of monocytes. Key cytokines in medium from irradiated HSC‐educated monocytes were identified by cytokine array detection. The effects of blocking ALKBH5 and key cytokines on RILF and HCC radiosensitivity were also evaluated. Results Radiation‐induced ALKBH5 expression in HSC mediated m 6 A demethylation of toll‐interleukin 1 receptor domain containing adaptor protein (TIRAP) mRNA and activated its downstream NF‐κB and JNK/Smad2 pathways to promote HSC activation. Additionally, ALKBH5 regulated CCL5 secretion by irradiated HSC to promote monocyte recruitment and M2 macrophage polarisation. Notably, polarised monocytes secreted CCL20 to up‐regulate ALKBH5 expression in HSC, and reduce HCC radiosensitivity by activating ALKBH5/TIRAP axis in HCC cells. ALKBH5 knockdown‐combined CCR6 (CCL20 receptor) inhibitor significantly alleviated RILF and improved HCC radiosensitivity in mice. HCC patients with high ALKBH5 and TIRAP expression were prone to radiation‐induced liver injury and poor tumour response to radiotherapy. Conclusions Collectively, irradiation up‐regulates ALKBH5 in HSC to mediate monocyte recruitment and M2 polarisation and form positive feedback to promote RILF and reduce HCC radiosensitivity. The dual roles of ALKBH5 as a microenvironmental regulator and radiosensitisation target provide new ideas for RILF prevention and radiosensitisation of HCC.

Epigenetic modification in liver fibrosis: Promising therapeutic direction with significant challenges ahead

“…Therefore, IOX1 upregulated T reg recruitment and inhibited inflammatory cells via increasing CCl28 expression, which alleviated Ischemia–reperfusion injury-stimulated renal fibrosis mouse model 177 . It is noteworthy that radiation-induced ALKBH5 could inhibit toll-interleukin 1 receptor domain containing adaptor protein (TIRAP) m 6 A methylation and thus activate NF- κ B–Smad2 pathway to activate HSCs 178 . It may attract interest whether ALKBH5 inhibitors could disturb TIRAP–NF- κ B–Smad2 pathway to suppress HSC activation and liver fibrosis for further studies.…”

Clinical significance of RNA methylation in hepatocellular carcinoma

“…By modulating the expression of cancer-related genes, RNA methylation drives the regulation of a wide range of processes in HCC progression, such as cell proliferation, invasion, resistance to therapy, tumor growth, and metastasis. Several studies have explored the interaction between RNA methylation and HCC progression and confirmed the great potential of targeted RNA methylation in vitro and in animal models (Table 2 ) [ 71 , 73 , 79 , 80 ]. Thus, a thorough understanding of molecular pathology of RNA methylation in HCC is essential for the improvement of treatment landscape and clinical outcomes in HCC.…”

“…Moreover, ALKBH5 directly downregulates LINC02551, which slows down the growth and metastasis of HCC cells by weakening the stability of DEAD box protein 24 (DDX24) [ 72 ]. During radiation therapy for HCC, radiation-induced hepatic stellate cells upregulate ALKBH5 to mediate the methylation modification of tollinterleukin 1 receptor domain containing adaptor protein (TIRAP), resulting in reduced apoptosis and radiosensitivity of HCC cells [ 71 ]. In HCC HepG2 and Hep3B cells, circGPR137B has been identified as a sponge for miR-4739 and FTO as a direct target of miR-4739, forming a positive feedback loop.…”

“…Furthermore, promising strategies such as inhibiting METTL3 with the compound STM2457 have shown potential in enhancing the sensitivity of lenvatinib in preclinical settings [ 79 ]. In patients with HCC resistant to radiation therapy, ALKBH5 upregulation serves as a marker for evaluating the efficacy of radiotherapy [ 71 ]. Additionally, AC115619, a liver-specific lncRNA encoding a micropeptide AC115619-22aa, reduces m6A levels.…”

Editorial: The role of tumor microenvironment in the development, treatment and prognosis of hepatocellular carcinoma

“…The interaction between TME and cancer cells can enhance the malignant properties of tumors, including proliferation, metastasis, and therapy resistance ( Hosaka et al, 2020 ; Tian et al, 2021 ). In addition, TME can also lead to abnormal angiogenesis and promote immunosuppression ( Chen et al, 2023 ). Therefore, further study of TME of HCC may be helpful for the development of therapeutic methods for HCC.…”