Inhibition of CD95-mediated apoptosis through beta 1 integrin in the HSG epithelial cell line.

The HSG cell line serves as a model for salivary gland epithelial progenitor cell differentiation. In order for a progenitor cell to differentiate, the cell must maintain viability within its niche. Studies were designed to elucidate the mechanism for integrin-mediated HSG cell survival. HSG cells, grown on Matrigel, were resistant to CD95-mediated apoptosis. Western blot analysis showed that Matrigel induced the expression of bcl-2, bcl-xL, p63, and DeltaNp63. This induction occurred by as early as 2 hrs and remained for 24 hrs. CD95-mediated apoptosis resistance was dependent, however, upon the expression of the bcl-2 family. Furthermore, Matrigel induced bcl-2 family expression was dependent on the transactivation of the EGF receptor pathway since PD98059 and AG1478 inhibited Matrigel induced bcl-2 family expression and caused HSG cells to be sensitive to CD95-mediated apoptosis. Activation of the EGF receptor pathway, by itself, however, was not sufficient to inhibit apoptosis. Blocking antibody showed that bcl-2 family expression was mediated through beta1 integrin. These studies show that salivary progenitor epithelial cell survival is integrin dependent and involves the transactivation of the EGF receptor pathway.