Post Doctoral Research Fellow National Cancer Institute, NIH Frederick, Maryland, United States
Disclosure(s):
Amit Kumar Singh, PhD: No financial relationships to disclose
Introduction/Rationale: Pattern recognition receptors (PRRs) detect pathogen-associated molecular patterns (PAMPs) maintain epithelial immune balance. PRRs such as Toll-like receptor 4 (TLR4) are well studied in infection and inflammation, their roles in skin carcinogenesis and host–microbiota interactions are poorly defined. Analysis of TCGA revealed recurrent TLR4 mutations in human skin cancers, suggesting a tumor-suppressive function. We define how TLR4 deficiency and epithelial IKKα reduction cooperate with the microbiota to promote squamous cell carcinoma (SCC).
Methods: We used a mouse model carrying a keratin 5-driven hemizygous Ikka deletion (IkkaΔKC/+), which develops rare skin spontaneous SCCs. These were crossed with Tlr4–/– mice. Skin microbiotas were analyzed by 16S rRNA sequencing. 3D skin organoids derived from primary keratinocytes were exposed to tumor-associated microbial communities. DNA damage (γH2AX), cytokine expression, and lipid metabolism were assessed. Parallel experiments used IkkaΔKC/+ and IkkaΔKC/+; Il4R–/– mice derived organoids.
Results: IkkaΔKC/+; Tlr4–/– mice showed a marked increase in SCC incidence compared with controls. Tumors exhibited loss of the wild-type Ikka allele, consistent with a two-hit model. Microbial profiling revealed elevated total bacterial load with enrichment of Gram positive Firmicutes. Organoids exposed to tumor-associated microbiota displayed increased DNA damage, IL-1β induction, and lipid metabolic reprogramming, all significantly reduced in IkkaΔKC/+; Il4R–/– organoids. In vivo, IkkaΔKC/+; Il4R–/– mice were resistant to tumor formation. Antibiotic treatment suppressed tumor development, confirming a microbiota-dependent mechanism.
Conclusion: TLR4–microbiota–IL-4R signaling axis that fuels epithelial carcinogenesis in the context of reduced IKKα. Skin organoids provide a powerful ex vivo model to dissect host–microbiota–immune interactions. Targeting IL-4R signaling or microbial modulation may offer new therapeutic avenues for inflammation-driven skin cancers.
