Differential gene expression profile of SCC13 tumor cells after TLR4 overexpression and LPS treatment

BACKGROUND & AIMS: TLR4 is an innate immune receptor with expression in human skin, keratinocytes as well as squamous cell carcinoma (SCC) of the skin. In the present study we investigate the role of TLR4 as a negative regulator of keratinocyte proliferation. We present here that the expression of TLR4 increased with the differentiation of cultured keratinocytes in a passage-dependent manner or under calcium-rich conditions. Moreover, the down-regulation of TLR4 by specific knockdown increased the proliferation of primary normal, SCC-derived and HaCaT keratinocytes in vitro. In addition, subcutaneously injected HaCaT keratinocytes with shTLR4 formed growing tumors in nude mice. In contrast, we observed lower proliferation and increased migration in vitro of the SCC13 cell line stably overexpressing TLR4 in comparison to SCC13 TLR4 negative cells. In vivo, SCC13 TLR4-overexpressing tumors showed delayed growth in comparison to TLR4 negative tumors. The overexpression of TLR4 in SCC13 tumor cells was followed by phosphorylation of ERK1/2 and JNK and increased expression of ATF3. In gene expression arrays, the overexpression of TLR4 in tumor cells correlated with gene expression of ATF-3, IL-6, CDH13, CXCL-1, and TFPI. In summary, TLR4 negatively regulates the proliferation of primary keratinocytes and its overexpression reduces tumor growth of SCC cells. SCC13 tumor cells were stably transfected with pUNOTLR4 and pUNO (control) plasmids. SCC13 TLR4 cells and SCC13 pUNO were seeded in tetraplicates and treated with 10μg/ml ultrapure LPS for 24 hours. As controls untreated SCC13TLR4 and SCC13 pUNO cells were used.Gene expression comparison was performed between untreated SCC13TLR4 and control cells as well as between LPS treated cells.