Abstract
Simple SummaryUltraviolet B (UVB) radiation is largely responsible for the development of skin cancer. When UVB-induced DNA damage in cells is not repaired, it can lead to the initiation of non-melanoma skin cancers. Xeroderma pigmentosum (XP) disease is caused by a defect in the repair of damaged DNA. Toll-like receptor-4 (TLR4) and NLR family pyrin domain containing 3 (NLRP3) belong to the family of innate immune receptors and are highly expressed in skin tumors. In this study, we determined the mechanism through which TLR4 inhibitor TAK-242 regulates inflammation and prevents skin cancer.Ultraviolet (UV) irradiation of the skin is related to the development of skin cancer. UVB also causes DNA damage in the form of cyclobutane pyrimidine dimers (CPDs), which can result in stable mutations. Toll-like receptor 4 (TLR4), a component of innate immunity, plays a key role in cancer. Previous studies from our laboratory have observed that TLR4 deficiency resulted in the repair of UVB-induced DNA damage, inhibition of UVB-induced immune suppression, and carcinogenesis. In this study, we determined the efficacy of TLR4 antagonist TAK-242 in regulation of UVB-induced DNA damage, inflammation, and tumor development. Our results indicate that TAK-242 treatment increased the expression of xeroderma pigmentosum group A (XPA) mRNA, resulting in the repair of UVB-induced CPDs in skin of SKH-1 mice. Treatment with TAK-242 also inhibited the activation of NLR family pyrin domain containing 3 (NLRP3) in UVB-exposed skin of SKH-1 mice. Cutaneous carcinogenesis was significantly reduced in mice treated with TAK-242 in comparison to vehicle-treated mice. The proinflammatory cytokines IL-1β, IL-6, and TNF-α were also found to be significantly greater in vehicle-treated mice than TAK-242-treated mice. Finally, treatment with TAK-242 augmented anti-tumor immune responses in mice. Our data provide further evidence that activation of the TLR4 pathway promotes the development of UV-induced non-melanoma skin cancer mediated at least in part on its negative effects on DNA damage. Moreover, treatment with the TLR4 inhibitor TAK-242 may be effective for prevention of skin cancer.
Highlights
Ultraviolet (UV) B radiation is an important contributor to the growth and development of keratinocyte carcinoma [1,2,3]
We have shown that Toll-like receptor 4 (TLR4) deficiency inhibited UVB-induced chronic inflammation and reduced immune suppression in tumor microenvironment, resulting in enhanced tumor development [20]
We determined the role of TLR4 inhibitor, TAK-242, in the repair of DNA damage, inhibition of inflammation, and augmentation of cutaneous immune responses all of which contribute to prevention of photocarcinogenesis in mice
Summary
Ultraviolet (UV) B radiation is an important contributor to the growth and development of keratinocyte carcinoma (basal and squamous cell carcinoma) [1,2,3]. In an animal model of UV carcinogenesis, we observed that TLR4 deficiency enhanced the repair of UVB-induced DNA damage in the form of cyclobutane pyrimidine dimers (CPD) in mouse and bone marrow dendritic cells (BMDC). We have shown that loss of TLR4 resulted in prevention of UVB-induced suppression of immune responses by inhibiting development of regulatory T-cells [19]. We have shown that TLR4 deficiency inhibited UVB-induced chronic inflammation and reduced immune suppression in tumor microenvironment, resulting in enhanced tumor development [20]. We determined the role of TLR4 inhibitor, TAK-242, in the repair of DNA damage, inhibition of inflammation, and augmentation of cutaneous immune responses all of which contribute to prevention of photocarcinogenesis in mice
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