Interferon-Mediated Block in Cell Cycle and Altered Integrin Expression in a Differentiated Salivary Gland Cell Line (HSG) Cultured on Matrigel

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Abstract
Sjögren's syndrome (SS), an idiopathic, autoimmune exocrinopathy, is partly characterized by diminished salivary flow, acinar cell atrophy, and increased expression of several cytokines. Several in vivo characteristics of the sialoadenitis are also evident in a human salivary gland ductal epithelial cell line (HSG) treated with cytokines. HSG cells differentiate to the acinar phenotype when cultured on Matrigel (Becton Dickinson, Bedford, MA), a basement membrane extract. To elucidate mechanisms of salivary gland pathology, the effects of interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) on cell cycle progression and integrin expression were evaluated in HSG acinarlike cells. Flow cytometry experiments showed that cytokine treatment for 2 days arrested cells in G1 phase of the cell cycle, and this preceded significant morphologic changes and decreased viability. Whereas only modest cytokine-mediated increases in protein expression for the α3 and β1 integrin subunits were seen by immunoprecipitation, a form of α3 integrin displaying enhanced electrophoretic mobility was evident after 6 days of cytokine treatment. To our knowledge, this is the first report demonstrating an IFN-mediated alteration in the electrophoretic mobility of integrin subunits. From this study, it was evident that the combination of IFN-γ and TNF-α resulted in a block in G1 phase for acinar cells before accumulation of the α3 integrin variant or significant degenerative cellular changes. Information from the present and previous studies suggests that cytokines may alter the patter of integrin expression and block cell cycle progression in salivary gland cells grown in three-dimensional acinarlike clusters. These experiments may provide a new cell culture model to study the effects of cytokines in normal and diseased salivary glands, including SS.