Regulation of apoptotic cell death by cytokines in a human salivary gland cell line: Distinct and synergistic mechanisms in apoptosis induced by tumor necrosis factor α and interferon γ

Abstract

We examined the mechanisms of apoptosis in a human salivary gland (HSG) cell line induced by tumor necrosis factor (TNF) α and interferon (IFN) γ. DNA fragmentation and the activation of caspase-3 were determined in HSG cells cultured with TNF-α or IFN-γ. Mitochondrial dysfunction also appeared to be involved in the process because a disruption of mitochondrial transmembrane potential with the activation of caspase-9 was demonstrated in TNF-α– and IFN-γ–stimulated HSG cells. Activation of caspase-8 was thought to be essential in TNF-α–induced apoptosis of HSG cells; however, the activation of caspase-8 was not involved in IFN-γ–induced apoptosis of HSG cells. In contrast, Bcl-2 appeared to be an indispensable regulatory molecule in IFN-γ–induced, but not in TNF-α–induced, apoptosis of HSG cells because its expression was inhibited in IFN-γ–stimulated, but not in TNF-α–stimulated, cells. The inhibitory effect of IFN-γ in Bcl-2 expression was enhanced by coadministration of TNF-α and, interestingly, apoptosis of HSG cells, as assessed by DNA fragmentation and the activation of caspase-9 and caspase-3, and disruption of mitochondrial transmembrane potential was also synergistically augmented by TNF-α and IFN-γ. Our results suggest that cytokines expressed in the salivary glands of patients with Sjögren syndrome play an important role in regulating apoptosis of acinar-ductal epithelial cells through distinct and synergistic mechanisms, thereby modulating salivary gland function in patients with Sjögren syndrome. (J Lab Clin Med 2002;139:13-9)