Inhibition of mitogen-induced DNA synthesis by bafilomycin A sub(1) in Swiss 3T3 fibroblasts

• Published in: Biochemical journal Vol. 313; no. 1; pp. 49 - 54
• Main Authors: Saurin, A J, Hamlett, J, Clague, MJ, Pennington, SR
• Format: Journal Article
• Language: English
• Published: 01.01.1996
• ISSN: 0264-6021

Quiescent cells (in G sub(0)) can be stimulated to enter the cell cycle and proceed to DNA synthesis in S-phase by a wide range of growth factors and mitogens. Activation of cell-surface growth factor receptors with intrinsic protein tyrosine kinase activity initiates autophosphorylation of the receptors and subsequent activation of signal transduction cascades. After activation the receptors undergo ligand-induced internalization to endosomes, which become acidified by the action of a vacuolar H super(+)-ATPase (V-ATPase). The extent to which vesicular acidification plays a role in mitogenic signalling by receptors with intrinsic tyrosine kinase activity remains unknown. Here we have shown that bafilomycin A sub(1), a specific inhibitor of V-ATPase, inhibits endosome acidification and mitogen-induced DNA synthesis in Swiss 3T3 fibroblasts. Addition of bafilomycin A sub(1) at successively later times during G sub(1) progressively decreased the inhibition of DNA synthesis such that no inhibition was observed when bafilomycin A sub(1) was added at the onset of S-phase. Bafilomycin A sub(1) also induced a dramatic but reversible change in the morphology of Swiss 3T3 cells. However, the rapid activation of c-fos mRNA accumulation by epidermal growth factor and insulin was unaffected by bafilomycin A sub(1). Together, the results suggest that activation of the V-ATPase plays an important role in the mitogenic signalling pathways that occur during the G sub(1) phase of the cell cycle but is not required for the initial epidermal growth factor and insulin-evoked signalling events that lead to c-fos mRNA expression.