Aphidicolin-induced proliferative arrest of murine mast cells: morphological and biochemical changes are not accompanied by alterations in cytokine gene induction

Abstract

Investigations of mast cell biology have often used immortalized cultured cells which are continuously proliferating. In vivo, however, only 2% or fewer tissue mast cells are actively dividing. We used aphidicolin, an inhibitor of DNA polymerase to induce a proliferative arrest of murine mast cells characterized by an inhibition of cell division and thymidine incorporation, with accumulation of cells in G1 and early S phase of the cell cycle. Uridine incorporation and cell viability were not significantly impaired. DNA synthesis and cell division both resumed rapidly upon removal of the drug. Morphometric analysis demonstrated that cell size, granule size, and number of granules per cell were all increased in aphidicolin-treated cells. Proliferative arrest also produced a 14-fold increase in cellular histamine content, but did not alter the proteoglycans synthesized by the cell. The level of c-myc mRNA was reduced in aphidicolin-arrested cells, but returned to the level observed in untreated cells within 1 hr of removal of the drug. In contrast, the constitutive steady-state RNA levels of tumour necrosis factor-alpha (TNF-alpha), B2-microglobulin, actin, and the c-Ha-ras and c-fes protooncogenes were not altered. Aphidicolin-induced proliferative arrest did not prevent the induction of TNF-alpha, interleukin-6 (IL-6) and c-fos genes in response to calcium ionophore. Both the magnitude and induction kinetics of these messages were similar in aphidicolin-treated and untreated cells. We conclude that proliferative arrest results in morphological and biochemical changes suggestive of cellular maturation, but inhibition of cell division alone is not sufficient to alter mast cell phenotype. Although optimal c-myc expression appears to require active proliferation, cytokine gene induction can occur in non-dividing cells. These data suggest that the proliferative quiescence of in vivo mast cells should not preclude their involvement in biological events via elaboration of multi-functional cytokines.