our study also suggests that uvb might reduce ythdf2 phosphorylation at s39 by promoting the interaction between ythdf2 and mypt1, which could be involved in the autophagic degradation of ythdf2. previous studies have shown that chk1, a kinase activated by dna damage and uv radiation, binds and phosphorylates mypt1, leading to the recruitment of protein phosphatase 1β ( pp1cβ ) to dephosphorylate its substrate. it remains to be investigated whether uv radiation - induced chk1 activation mediates mypt1 phosphorylation, thus leading to increased mypt1 binding to ythdf2. in addition, ythdf2 s39 / t381 phosphorylation by egfr / src / erk signaling has previously been shown to promote ythdf2 protein stability. it is possible that uvb - induced ythdf2 dephosphorylation mediates ythdf2 down - regulation by autophagy. in addition, we show that ythdf2 s39 phosphorylation is critical for its interaction with cnot1, u6 decay, and its endosomal trafficking, suggesting that ythdf2 ’ s function in promoting rna decay and endosomal localization is regulated by its phosphorylation at s39. future investigation is needed to determine whether phosphorylation at other sites regulates ythdf2 activity. in addition to stabilizing u6 by inhibiting ythdf2, uvb further increases u6 snrna levels in ythdf2 - depleted cells ( fig. 2i - j ), suggesting that uvb also induces u6 snrna transcription, leading to tlr3 activation independent of ythdf2. these ythdf2 - dependent and - independent mechanisms may serve as a multilayer defense mechanism to ensure the induction of a robust inflammatory and innate immune response in the skin under uvb stress to prevent microbe infection and maintain barrier function. future investigation is warranted to fully map the molecular machinery that regulates u6 ma methylation, decay, and trafficking under baseline conditions, uvb stress, and other stresses. taken together, our studies establish a critical role for ythdf2 in recognizing ma methylation of u6 snrna, thus increasing u6 decay and competing with ma u6 binding to tlr3 to suppress tlr3 activation in inflammation and tumorigenesis under baseline and uvb stress conditions. these findings may also open promising opportunities for targeting the ythdf2 / ma u6 axis in the intervention and treatment of epithelial cancers and autoimmune diseases, such as sle. all research complied with relevant ethical regulations. human tissue samples were obtained from us biomax under protocols approved by institutional review boards, with informed consent obtained from the donors, as documented by the vendor. all animal experiments were conducted in accordance with institutional guidelines and were approved by the institutional animal care and use committee ( iacuc ) of the university of chicago. human tissue microarrays were obtained from us biomax ( derwood, md ). according to the vendor ’ s documentation, all human tissues were collected under protocols approved by institutional review boards, with informed consent obtained from the donors. the samples were provided in a fully de - identified form, ensuring that no personally identifiable information was accessible to the investigators. all research involving human - derived samples was conducted in accordance with the ethical principles set forth in the declaration of helsinki. primary normal human epidermal keratinocytes ( nhek ) were purchased from invitrogen ( invitrogen, c - 001 - 5 c ) and lonza ( 00192907 ). nhek cells from invitrogen were maintained in nhek complete medium ( invitrogen, s - 001 - 5 ) according to the manufacturer ’ s instructions, and nhek cells from lonza maintained in kgm gold keratinocyte growth basal medium ( lonza, # 00192151 ) and kgm gold keratinocyte growth medium supplements and growth factors ( lonza, # 00192152 ). hacat cells ( human keratinocyte, kindly provided by dr. fusenig ), a431 cells ( human squamous carcinoma cells, atcc, crl - 1555 ), hek - 293t cells ( human embryonic kidney cells, atcc, crl - 3216 ), hela cells ( wt and ythdf2 knockout [ ko ] cells, kindly provided by dr. chuan he ), and chl - 1 cells ( melanoma cells, provided by the comprehensive cancer center core facilities at the university of chicago ) were maintained in dulbecco ’ s modified eagle ’ s medium ( invitrogen, carlsbad, ca ) supplemented with 10 % fetal bovine serum ( gibco ), 100u / ml penicillin, and 100 µg / ml streptomycin ( invitrogen, carlsbad, ca ). cells were treated with the following agents: dynasore ( 80 μm, 16 h. sigma, d7693 ), human cgas inhibitor g140 ( 5 µm, 24 h. invivogen ), pla dien olide b ( 500 nm, 3 h. medchemexpress, hy - 16399 ), followed by sham or uvb irradiation ( 20 mj / cm, 6 h, unless indicated otherwise ), or actinomycin d ( 2 μm. sigma, sbr00013 ) post - sham or uvb irradiation. cells were irradiated with sham or uvb irradiation ( 20 mj / cm for hacat cells and 30 mj / cm for other cell lines that exbibit decreased sensitivity to uvb stress ) and then collected for analysis at 6 h or 24 h for the delayed uvb stress response such as inflammatory gene expression and ythdf2 protein down - regulation, or 1 h for the early or direct uvb stress response such as ythdf2 - interacting proteins and ythdf2 phosphorylation, unless indicated otherwise. all animal procedures were approved by the university of chicago institutional animal care and use committee ( iacuc ). athymic nude mice were obtained from harlan sprague - dawley ( now envigo ). for xenograft experiments, one million cells were injected subcutaneously into the right flanks of 6 - week - old female nude mice. tumor growth was monitored and measured weekly by a caliper, and tumor volume was calculated using the formula, tumor volume ( mm ) = d x d / 2, where d and d are the shortest and the longest diameters, respectively. mice with wild type ( wt, ythdf2 ) & conditional skin - specific ythdf2 homozygous knockout ( df2 cko, k14cre; ythdf2 ), wt & atg5 cko ( k14cre; atg5 ), wt & atg7 cko ( k14cre; atg7 ), and wt & p62 cko ( k14cre; p62 ) were generated and maintained on an skh - 1 hairless background, both male and female mice ( 6 – 8 weeks old ) were used for uvb irradiation experiments. the initial dose of uvb was 80 mj / cm for the first week, followed by a weekly 10 % increase until it reached 100 mj / cm. wt and cko were irradiated with uvb every other day 3 times a week, and tumor formation was recorded. for short uvb treatment, mice were irradiated with uvb irradiation ( 100 mj / cm ) 3 times every other day and skin samples were collected 24 h after the final uvb irradiation. all mice were housed in the university of chicago animal resources center ( arc ) under specific pathogen - free conditions. arc follows standard operating conditions, including a 12 - h light / 12 - h dark cycle, ambient temperature of 21 – 23 °c, and relative humidity of 40 – 60 %, with food and water provided ad libitum. primary keratinocytes were isolated from neonatal mice as described previously in ref.. briefly, wt ( ythdf2 ) and df2 chet ( k14cre; ythdf2 ) neonatal mice were euthanized and rinsed briefly with sterile pbs containing penicillin - streptomycin, followed by a quick rinse with 70 % ethanol and then submerging in fresh 70 % ethanol for 10 minutes to allow thorough surface sterilization. mice were then rinsed again with sterile pbs ( with penicillin - streptomycin ) and kept in fresh pbs on ice. skin was collected on a 60 mm tissue culture dish containing 5 ml of cold sterile ca - free 0. 25 % trypsin solution without edta ( invitrogen, cat # 15090 - 046, 10x stock, use pbs to dilute ), with dermis facing down, and incubated at 4 °c for 15 to 24 h. skin was then transferred to a dry, sterile tissue culture plate and epidermis was separated from dermis using a sterile pasteur pipette.