ENHANCEMENT OF TNF-ALPHA SYNTHESIS BY OVEREXPRESSION OF G(ALPHA-Z) INA MAST-CELL LINE

Ag stimulation of mast cells via the IgE receptor (Fc epsilon RI) elic its production and release of numerous cytokines. This activation of F c epsilon RI initiates various tyrosine kinase-dependent signaling cas cades, which ultimately result in the de novo synthesis of cytokines, To date, no heterotrimeric G proteins have been implicated in this pro cess, Here we report that the alpha subunit of the heterotrimeric G pr otein, G(2), can regulate production of the cytokine, TNF-alpha. The a lpha subunit was overexpressed in a cultured mast cell line (RBL-2H3) known to contain G(alpha z). In stimulated cells, overexpression of G( alpha z) significantly enhanced the production of TNF-alpha. This effe ct of G(alpha z) appeared to be restricted in that constitutive synthe sis of the cytokine, TGF-beta, and Ag-stimulation of the phosphoinosit ide-dependent secretory pathway were not significantly affected, Thus, G(alpha z), a heterotrimeric G protein, appeared to modulate the stim ulatory pathways for induction of TNF-alpha synthesis in RBL-2H3 cells .