These myofibroblasts have been shown in vitro to respond to TLR signals and may therefore contribute to tumor promotion by secreting trophic factors in response to bacterial ligands . One of the interesting findings among the platforms containing multiple TLR4 selleck inhibitor probes was a marked divergence of transcripts with clinical outcomes. In particular, the direction and magnitude of specific TLR4 transcript expression on survival was evident, where TLR4 probes fall into two distinct groups, each
of which targets a different transcript variant. There exist four recognized mRNA TLR4 products (Figure 1B) . Four probes from the commercial platform correspond to longer transcripts, while the remaining two probes are associated specifically with shorter GS-9973 datasheet mRNAs. The dichotomous relationship between RNA transcripts and clinical outcomes raises the possibility that different TLR4 transcripts or their relative ratios have different biological activities and consequences. The immunology literature supports
the notion that alternative splicing of genes involved in innate immunity regulates their function [42–44]. In particular, alternative splicing has been observed in TLR family members expressed in response to LPS . This splicing phenomenon may explain the opposing survival results observed herein. Epigenetic events, like hypermethylation of gene promoters which occur frequently in CRCs, may also AZD6738 datasheet play a cAMP role in the expression of varying transcripts . Other post-transcriptional regulatory events may also contribute; trafficking of transcripts by microRNAs offers
another plausible explanation. miR21, a microRNA present in many tumors, also has been shown to down-regulate TLR4 . We speculate that the type of TLR4 mRNA/protein product regulates biological events, as may non-coding TLR4 transcripts found in genome browsers (Figure 1C). Bench and animal experiments are required to interrogate the mechanism for the functional differences in TLR4 transcripts. The authors acknowledge the limitations of this study. Most notably, the TMA histologic scoring was based on cores; accordingly, TLR4 positivity may have been underestimated given the heterogeneous nature of CRCs and sampling error inherent in cores. We did not incubate TMA controls with only secondary antibody (TLR4) without the primary antibody; our controls consisted of unmatched, uninvolved colonic tissue. Finally, RNA expression and protein staining conclusions were drawn from unmatched samples in some instances. Conclusions TLR4 may play distinct roles in the transition from normal colon to adenoma and from a local to a more advanced tumor. In our animal models, the absence of TLR4 protects against developing dysplasia. In animals with colonic tumors, treatment with an anti-TLR4 antibody results in smaller tumors.