Secretion of TNF from a rat mast cell line is a brefeldin A-sensitive and a calcium/protein kinase C-regulated process.

Stimulated mast cells and cognate cultured cell lines produce and secrete a variety of cytokines including TNF. Because the mechanism by which cytokines are delivered to the external milieu is unknown, the release of TNF was studied in a rat mast cell line (RBL-2H3 cells). In these cells, TNF was not constitutively expressed nor incorporated into secretory granules but was generated de novo upon cell stimulation. It was then released by a process analogous to constitutive secretion in that brefeldin A, an agent known to disrupt Golgi membranes in these cells, inhibited this release without inhibiting release of secretory granules. Unlike constitutive secretion, however, the secretion of TNF was highly regulated by Ca2+ and protein kinase C. Studies with various stimulants and inhibitors indicated that simultaneous mobilization of Ca2+ and activation of protein kinase C were sufficient signals for secretion although optimal production of TNF may be dependent on additional synergistic signals. Because suppression of Ca2+ mobilization or inhibition of protein kinase C alone abrogated TNF secretion, the process may be amenable to therapeutic intervention.