Toll-Like Receptor 4 Deletion Increases Bacterial Burden and Tumorigenesis in Mice

Toll-like receptor 4 (TLR4) is an extracellular pathogen recognition receptor (PRR) that identifies a variety of pathogens and damage-associated molecular patterns. Analysis of human TCGA database reveals many mutations of the Toll-Like Receptor 4 (TLR4) gene in human skin cancers. The exact function of PRRs in response to elevated ambient and commensal bacteria for carcinogenesis is still unknown. Recently, we found a low number of spontaneous skin squamous cell carcinomas (SCCs) in 1-year-old Ikkaf/+K5 Cre mice with specific Ikka reduction in keratinocytes. Interestingly, ablation of Tlr4 enhanced SCC numbers and sizes but reduced the latency of SCC development in IkkαΔKC /+; Tlr4-/- mice compared to IkkaΔKC/+ mice. Both spontaneous skin SCCs obtained from IkkaΔKC/+ and IkkaΔKC/+; Tlr4-/- mice showed loss of wild-type (WT) Ikka allele. Thus, we hypothesize that Ikka reduction in keratinocytes alters skin microbes and Tlr4 deletion promote this condition, which lead to increased spontaneous skin SCCs. Indeed, the bacterial burden were increased in the skin of IkkaΔKC/+ and IkkaΔKC/+; Tlr4-/- mice compared to the skin of WT and Tlr4-/- mice predominately Gram (+) firmicutes. Further, we explore the interactions between bacteria and their hosts using skin organoids derived from these mice. Organoids are three dimensional structures recapitulating the organ’s epithelial layer, linking the gap between in vitro and in vivo models. Skin organoids infected with heat killed gram positive bacteria reveals more DNA damage in the IkkaΔKC/+; Tlr4-/- along with impaired bacteria clearance in these mice. Together, these findings suggest that increased bacteria cause genomic instability which leads to DNA damage. Additionally, we are investigating which bacterial pathways compromise the integrity of the skin genome through Ikka reduction or Ikka reduction/Tlr4 deletion, as well as whether Tlr4 deletion affects immune cell function in combat against bacterial infections. Citation Format: Deep Kumari Yadav, Amit Kumar Singh, Debra Tross, Yinling Hu, . Toll-like receptor 4 deletion promotes bacterial burden and cutaneous tumorigenesis in mice lacking one Ikkα allele in keratinocytes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 2875.