No abstract

Melanoma is one of the most deadly and therapy-resistant cancers. Here we show that N 6 -methyladenosine (m 6 A) mRNA demethylation by fat mass and obesity-associated protein (FTO) increases melanoma growth and decreases response to anti-PD-1 blockade immunotherapy. FTO level is increased in human melanoma and enhances melanoma tumorigenesis in mice. FTO is induced by metabolic starvation stress through the autophagy and NF-κB pathway. Knockdown of FTO increases m 6 A methylation in the critical protumorigenic melanoma cell-intrinsic genes including PD-1 (PDCD1), CXCR4, and SOX10, leading to increased RNA decay through the m 6 A reader YTHDF2. Knockdown of FTO sensitizes melanoma cells to interferon gamma (IFNγ) and sensitizes melanoma to anti-PD-1 treatment in mice, depending on adaptive immunity. Our findings demonstrate a crucial role of FTO as an m 6 A demethylase in promoting melanoma tumorigenesis and anti-PD-1 resistance, and suggest that the combination of FTO inhibition with anti-PD-1 blockade may reduce the resistance to immunotherapy in melanoma.

Macroautophagy (hereafter autophagy) is a cellular catabolic process that is essential for maintaining tissue homeostasis and regulating various normal and pathologic processes in human diseases including cancer. One cancer-driving process is accumulation of genetic mutations due to impaired DNA damage repair, including nucleotide excision repair. Here we show that autophagy positively regulates nucleotide excision repair through enhancing DNA damage recognition by the DNA damage sensor proteins XPC and DDB2 via 2 pathways. First, autophagy deficiency downregulates the transcription of XPC through TWIST1-dependent activation of the transcription repressor complex E2F4-RBL2. Second, autophagy deficiency impairs the recruitment of DDB2 to ultraviolet radiation (UV)-induced DNA damage sites through TWIST1-mediated inhibition of EP300. In mice, the pharmacological autophagy inhibitor Spautin-1 promotes UVB-induced tumorigenesis, whereas the autophagy inducer rapamycin reduces UVB-induced tumorigenesis. These findings demonstrate the crucial role of autophagy in maintaining proper nucleotide excision repair in mammalian cells and suggest a previously unrecognized tumor-suppressive mechanism of autophagy in cancer.

Macroautophagy/autophagy is a cellular catabolic process that is implicated in several physiological and pathological processes. However, the role of epidermal autophagy in wound healing remains unknown.Here, using mice with genetic ablation of the essential Atg5 (autophagy related 5) or Atg7 (autophagy related 7) in their epidermis to inhibit autophagy, we show that keratinocyte autophagy regulates wound healing in mice. Wounding induces the expression of autophagy genes in mouse skin. Epidermisspecific autophagy deficiency inhibits wound closure, re-epithelialization, keratinocyte proliferation and differentiation, dermal granulation tissue formation, and infiltration of immune cells including macrophages, neutrophils, and mast cells, while it does not affect angiogenesis. Using cytokine array screening, we found that autophagy deficiency inhibits the transcription and production of the cytokine CCL2/ MCP-1 by TNF. At the molecular level, TNF induces autophagic flux and the expression of autophagy genes through NFKB in epidermal keratinocytes. TNF promotes CCL2 transcription through the autophagy-AMPK-BRAF-MAPK1/3/ERK-activator protein 1 (AP1) pathway. Indeed, treating mice with recombinant CCL2 can reverse the effect of autophagy deficiency in keratinocytes. At the cellular level, we found that CCL2 induction via autophagy in keratinocytes is required not only for keratinocyte migration and proliferation but also for dermal fibroblast activation. Our findings demonstrate a critical role of epidermal autophagy in wound healing in vivo and elucidate a critical molecular machinery coordinating keratinocyte-fibroblast interaction in skin repair.

No abstract

Here we show that FTO as an N6-methyladenosine (m6A) RNA demethylase is degraded by selective autophagy, which is impaired by low-level arsenic exposure to promote tumorigenesis. We found that in arsenic-associated human skin lesions, FTO is upregulated, while m6A RNA methylation is downregulated. In keratinocytes, chronic relevant low-level arsenic exposure upregulated FTO, downregulated m6A RNA methylation, and induced malignant transformation and tumorigenesis. FTO deletion inhibited arsenic-induced tumorigenesis. Moreover, in mice, epidermis-specific FTO deletion prevented skin tumorigenesis induced by arsenic and UVB irradiation. Targeting FTO genetically or pharmacologically inhibits the tumorigenicity of arsenic-transformed tumor cells. We identified NEDD4L as the m6A-modified gene target of FTO. Finally, arsenic stabilizes FTO protein through inhibiting p62-mediated selective autophagy. FTO upregulation can in turn inhibit autophagy, leading to a positive feedback loop to maintain FTO accumulation. Our study reveals FTO-mediated dysregulation of mRNA m6A methylation as an epitranscriptomic mechanism to promote arsenic tumorigenicity.

No abstract

Global genome repair (GGR), a subpathway of nucleotide excision repair, corrects bulky helix-distorting DNA lesions across the whole genome and is essential for preventing mutagenesis and skin cancer. Here, we show that METTL14 (methyltransferase-like 14), a critical component of the N6-methyladenosine (m6A) RNA methyltransferase complex, promotes GGR through regulating m6A mRNA methylation–mediated DDB2 translation and suppresses ultraviolet B (UVB) radiation-induced skin tumorigenesis. UVB irradiation down-regulates METTL14 protein through NBR1-dependent selective autophagy. METTL14 knockdown decreases GGR and DDB2 abundance. Conversely, overexpression of wild-type METTL14 but not its enzymatically inactive mutant increases GGR and DDB2 abundance. METTL14 knockdown decreases m6A methylation and translation of the DDB2 transcripts. Adding DDB2 reverses the GGR repair defect in METTL14 knockdown cells, indicating that METTL14 facilitates GGR through regulating DDB2 m6A methylation and translation. Similarly, knockdown of YTHDF1, an m6A reader promoting translation of m6A-modified transcripts, decreases DDB2 protein levels. Both METTL14 and YTHDF1 bind to the DDB2 transcript. In mice, skin-specific heterozygous METTL14 deletion increases UVB-induced skin tumorigenesis. Furthermore, METTL14 as well as DDB2 is down-regulated in human and mouse skin tumors and by chronic UVB irradiation in mouse skin, and METTL14 level is associated with the DDB2 level, suggesting a tumor-suppressive role of METTL14 in UVB-associated skin tumorigenesis in association with DDB2 regulation. Taken together, these findings demonstrate that METTL14 is a target for selective autophagy and acts as a critical epitranscriptomic mechanism to regulate GGR and suppress UVB-induced skin tumorigenesis.