C-fos and c-myc gene activation, ionic signals, and DNA synthesis in thymocytes.

J P Moore,J A Todd,T R Hesketh,J C Metcalfe

doi:10.1016/s0021-9258(19)83890-5

Abstract

Among the earliest responses to mitogens that have been detected in normal quiescent cells are ionic changes: we have described rapid increases in the cytosolic free Ca2+ concentration ([Ca]i) and in the intracellular pH (pHi) in mitogen-stimulated thymocytes and fibroblasts (Hesketh, T. R., Moore, J. P., Morris, J. D. H., Taylor, M. V., Rogers, J., Smith, G. A., and Metcalfe, J. C. (1985) Nature 313, 482-484). Here we investigate the relationship between these ionic signals and the subsequent expression of the c-fos and c-myc proto-oncogenes in murine thymocytes. We show that the plant lectin concanavalin A (ConA), the phorbol ester 12-O-tetradecanoyl phorbol 13-acetate (TPA) and the Ca2+-ionophore A23187 each causes a rapid increase in both c-fos and c-myc mRNAs. The activation of both genes is completely dependent on the extracellular Ca2+ concentration ([Ca]o) for A23187 and independent of [Ca]o for TPA. Activation of c-myc, but not c-fos, by ConA is partially dependent on [Ca]o. The pHi increases generated by ConA or TPA are not necessary for expression of mRNA from either gene in response to these mitogens. Exogenous 8-bromo-cyclic AMP (but not 8-bromo-cyclic GMP) inhibits the c-myc responses to ConA and TPA. The data also show that neither early c-fos nor c-myc expression is sufficient to commit the cells to DNA synthesis.

Highlights

PHi increases generated byConA or tetradecanoyl phorbol 13-acetate (TPA) are not nec- The c-myc and c-fos genes are the cellular counterparts of essary for expression of mRNAfrom either gene in the transforming genes of the avian myelocytomatosis and response to these mitogens
C-fos proteins are located in the nucleus [21, 22], but their functions have not been defined. Both genes are activated in quiescent cells by mitogens within 1 h: the c-mycgene is expressed in T and B lymphocytes stimulated by ConA or lipopolysaccharide,respectively [11];in peripheral blood lymphocytes and A431 carcinoma cells in response to TPA or Quiescent mouse T cells in the nonproliferating Go state respond to mitogens with rapid changes in cytoplasmic cationconcentrations [1,2,3]
From these data the optimal mitogenic concentrations were taken as 0.8-1.0 pg/ml for ConA, 10 nM for TPA, and25-50 nM for A23187

Summary

Introduction

PHi increases generated byConA or TPA are not nec- The c-myc and c-fos genes are the cellular counterparts of essary for expression of mRNAfrom either gene in the transforming genes of the avian myelocytomatosis and response to these mitogens. Itself (Fig. l),but each caused an increase in c-myc mRNA comparable to or greater than the response to the optimal mitogenic concentration of ConA.

Results

Conclusion