Salivary epithelial cells from Sjogren's syndrome patients are highly sensitive to anoikis induced by TLR-3 ligation.

In certain types of cells, Toll-like receptor-3 (TLR-3) ligation by viral dsRNA induces apoptotic death, likely engaged into the elimination of virus-infected cells. We have previously shown that TLR-3 ligation on cultured non-neoplastic salivary gland epithelial cells (SGEC) with polyI:C (a synthetic analogue of viral dsRNA) results in the induction of surface immunoactive molecules, however, the pro-apoptotic effect of such signaling has not been addressed. In this study, polyI:C-treated SGEC were found to suffer severe detachment from substratum and subsequent apoptosis, a phenomenon suggestive of anoikis or anoikia (detachment-induced apoptosis). PolyI:C-induced anoikis in SGEC was associated with the upregulation of the pro-apoptotic Bmf, BimEL and Bax and the down-regulation of the pro-survival Bcl-2 (real-time PCR analyses). Finally, the comparative analysis of SGEC lines derived from primary Sjogren's syndrome (SS) patients (SS-SGEC) and non-SS controls had revealed that SS-SGEC are particularly susceptible to TLR-3-induced anoikis, as it was triggered by suboptimally low concentrations of polyI:C. This finding correlated with significantly higher constitutive surface TLR-3 expression by SS-SGEC, a feature indicative of their intrinsic activation status. In conclusion, TLR-3 signaling pathway in the salivary epithelium appears to extend beyond the induction of innate immune responses and to involve the activation of programmed-cell death via anoikis. In the same context, the increased vulnerability of SS-SGEC to the injurious effect of TLR-3 ligation is likely associated with the intrinsic activation processes that apparently operate in the epithelia of SS patients, and a feature of key pathogenetic importance for the disorder.

RNA interference of interferon regulatory factor-1 gene expression in THP-1 cell line leads to Toll-like receptor-4 overexpression/activation as well as up-modulation of annexin-II.

Interferon regulatory factor-1 (IRF-1) is a candidate transcription factor for the regulation of the Toll-like receptor-4 (TLR-4) gene. Using a small interfering RNA-based (siRNA) process to silence IRF-1 gene expression in the leukemic monocytic cell line THP-1, we investigated whether such a modulation would alter TLR-4 expression and activation status in these cells. The siIRF-1 cells expressed elevated levels of TLR-4 mRNA and protein compared to controls by 90% and 77%, respectively. ICAM.1 protein expression and apoptosis levels were increased by 8.35- and 4.25-fold, respectively. The siIRF-1 cells overexpressed Bax mRNA compared to controls. Proteomic analysis revealed upmodulation of the Annexin-II protein in siIRF-1 THP-1 cells. Myelodysplastic syndrome (MDS) patients with an absence of full-length IRF-1 mRNA also overexpressed Annexin-II. It is plausible that this overexpression may lead to the activation of TLR-4 contributing to the increased apoptosis characterizing MDS.