MECHANISM OF INTERFERON BETA-INDUCED SQUAMOUS DIFFERENTIATION AND PROGRAMMED CELL-DEATH IN HUMAN NON-SMALL-CELL LUNG-CANCER CELL-LINES

Background: Non-small-cell lung cancer (NSCLC) is one of the leading c auses of cancer-related mortality due largely to the failure of system ic chemotherapy, Thus, new therapeutic paradigms involving the manipul ation of normal physiologic growth-regulatory mechanisms, such as term inal cellular differentiation or programmed cell death, are being expl ored, Interferons may function as antineoplastic agents, in part becau se of their effects on cell proliferation and differentiation. We have previously demonstrated the antiproliferative and differentiating eff ects of interferon beta (IFN beta). Purpose: The present investigation was designed to study the mechanism of IFN beta on squamous different iation and/or programmed cell death in cultured NSCLC cells. Methods: Crosslinked envelope competence and transglutaminase expression and ac tivity were measured in three NSCLC cell lines (NCI-H226, NCI-H358, an d NCI-H596) as common markers for squamous differentiation and program med cell death. DNA fragmentation, as determined by gel electrophoreti c analysis, served as a marker for programmed cell death, In addition, the expression of several regulatory and differentiation-related gene s (measured by Northern blot analysis of messenger RNA levels) as well as protein kinase C activity was measured to begin to explore possibl e mechanisms of IFN beta activity, Results: IFN beta-induced crosslink ed envelope competence occurred in cell lines with squamous features ( NCI-H226 and NCI-H596); conversely, DNA fragmentation occurred in cell lines with glandular features (NCI-H358 and NCI-H596). Stimulation of cross-linked envelope competence by IFN beta was associated with the induction of tissue transglutaminase activity, Both of these parameter s were protein-synthesis independent, As previously observed for NCI-H 596, IFN beta suppressed the growth of the other two cell lines, Total protein kinase C activity was not altered, Expression of a variety of possibly relevant oncogenes and other genes was variably altered by I FN beta. Conclusions: IFN beta induces programmed cell death in NSCLC cell lines in a phenotype-specific manner, The programmed cell death p athway represented by cross-linked envelope competence is dependent on the expression of the squamous phenotype and is protein-synthesis ind ependent, suggesting post-translational mechanisms. In addition, squam ous differentiation itself mag be induced. Changes in gene expression, while not necessary for induction of cross-linked envelope competence , may be involved in other aspects of cellular homeostasis, such as gr owth suppression, Implications: By inducing terminal cellular differen tiation or programmed cell death, IFN beta may be therapeutically usef ul in NSCLC. The post-translational nature of IFN beta-induced effects suggests that it will be best used in combination with other agents t hat can regulate these cellular pathways at the pretranslational level , increasing the proportion of cells capable of being driven to a term inal state by this biotherapeutic agent.