Regulation of mRNA caspase-8 levels by anti-nuclear autoantibodies

Apoptosis of the acinar and ductal epithelial cells of the salivary glands has been proposed as a mechanism possibly responsible for the impairment of the secretory function in Sjögren's syndrome, an organ-specific autoimmune disorder characterized by destruction of these glandular structures. The presence of serum autoantibodies (Abs) directed against the ribonucleoproteic antigens Ro and La is one of the classification criteria used to identify Sjögren patients, and there is increasing evidence of the direct involvement of Abs in tissue pathogenesis. Our recent report demonstrated that anti-Ro and anti-La Abs are able to trigger the extrinsic pathway of apoptosis in the human salivary gland cells. To better understand how the anti-Ro and anti-La Abs exert their apoptotic effect, human caspase-8 gene expression was examined in primary human salivary gland epithelial cell (SGEC) cultures established from biopsies of labial minor salivary glands. To measure mRNA expression changes of initiating caspase-8, the real-time polymerase chain reaction was employed. This was combined with western blot to study the activation of caspase-8 detecting the cleaved form of caspase-8 and the cleaved poly (ADP-ribose) polymerase, downstream consequences of caspases activation. Data obtained suggest that the anti-Ro and anti-La Abs determine a transcriptional up-regulation and activation of caspase-8. Study of the mRNA in SGEC experimental model may provide insight into the signal transduction pathway stimulated by anti-nuclear autoantibodies.