Supplementary Material for: Resistance to Fas-Mediated Apoptosis Does Not Correlate to Structural Alterations or Expression Changes of the Death Receptor in Papillary Thyroid Carcinomas

<b><i>Background:</i></b> Malignant cells exhibit significant resistance to FAS-mediated cell death, through different processes, including <i>FAS</i> mutations, soluble <i>FAS</i> expression, or FAS transcriptional dysregulation by P53, eventually escaping from immune surveillance. Since thyroid carcinomas were shown to be resistant to FAS-mediated apoptosis, we investigated the above mechanisms in thyroid carcinoma samples. <b><i>Methods:</i></b> Thirty-seven thyroid carcinoma samples were analyzed for mutations in <i>FAS</i> exon 9 and <i>TP53</i> exons 5–8 and protein expression by means of immunohistochemistry. Moreover, thyroid carcinoma mRNA samples were subjected to reverse transcription – PCR, to evaluate the relative expression of transmembrane FAS versus its soluble form. <b><i>Results:</i></b> Analysis revealed indications for <i>TP53</i> mutations in the anaplastic carcinomas, but not in the other thyroid specimens examined for <i>TP53</i> or <i>FAS</i> exon 9 mutations. FAS receptor expression was observed in almost all thyroid specimens (97%) with significant up-regulation in papillary carcinomas. P53 nuclear staining was observed only in anaplastic carcinomas. Full-length <i>FAS</i> mRNA was detected in all specimens examined, with soluble <i>FAS</i> mRNA being either absent or present in very low amounts. <b><i>Conclusions:</i></b> Our results denote that <i>FAS</i> death domain or <i>TP53</i> DNA-binding domain mutations, down-regulation of FAS receptor expression, or expression of <i>FAS</i> soluble isoform are not responsible for the seeming inhibition of FAS-mediated apoptosis in papillary thyroid carcinoma cells.