Synergy between signal transduction pathways is obligatory for expression of c-fos in B and T cell lines: implication for c-fos control via surface immunoglobulin and T cell antigen receptors.
Expression of the protooncogene c-fos is controlled by three main regulatory pathways involving kinase C, cAMP, and calcium. Kinase C mediates its effects via phosphorylation of serum response factor (SRF) which interacts with the serum response element (SRE); cAMP and calcium mediate their effects via phosphorylation of CREB (cAMP regulatory element binding protein) presumably by activation of a protein kinase A or calmodulin-regulated kinase. We have examined the function of these elements in Burkitt's lymphoma cells (Ramos and Daudi) as well as a T lymphocytic cell line (Jurkat). We have found that stimulation of any one of these pathways alone has little or no effect on c-fos induction. However, kinase C activation (PMA stimulation) combined with either cAMP (forskolin plus MIX) or calcium stimulation (ionophore) leads to greatly enhanced c-fos induction. By contrast, cAMP in the presence of calcium shows no synergy in c-fos induction. Okadaic acid augments PMA- as well as calcium-mediated activation of c-fos, and has little or no effect when combined with cAMP. The main difference between Ramos (B cells) and Jurkat (T cells) in the regulation of c-fos is that cAMP plus calcium is strongly synergistic in Jurkat and is without effect in Ramos. Analysis of AP-1 activity using gel mobility shift assays confirms that the requirements for synergy in c-fos mRNA induction are paralleled by requirements for synergy in induction of AP-1 activity. Signaling in B cells due to anti-Ig stimulation involves both kinase C activation and release of intracellular calcium, and results in c-fos mRNA induction. Our results indicate that synergy between the kinase C activation and calcium is needed for efficient c-fos induction since neither of these two alone induces c-fos well. That synergy of signaling pathways is relevant for the anti-Ig induction of c-fos is supported by the fact that cAMP-inducing agents and okadaic acid further enhance anti-Ig induction of c-fos. These results suggest that cell-specific patterns of synergy are an essential feature for c-fos induction and may be relevant for c-fos control through B and T cell antigen receptors.
Regional Research Laboratory, Kaiser Permanente Medical Center, Los Angeles, CA, USA.
J S
JS
Kaptein
C L
CL
Yang
C K
CK
Lin
T T
TT
Nguyen
F S
FS
Chen
P M
PM
Lad
D000888:Antibodies, Anti-Idiotypic / Q000494:pharmacology; D001402:B-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D001483:Base Sequence; D002051:Burkitt Lymphoma / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000276:immunology*; D016762:Genes, fos / Q000276:immunology*; D006801:Humans; D008969:Molecular Sequence Data; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors; D012333:RNA, Messenger / Q000096:biosynthesis; D011947:Receptors, Antigen, B-Cell / Q000502:physiology*; D011948:Receptors, Antigen, T-Cell / Q000502:physiology*; D015398:Signal Transduction / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000096:biosynthesis; D014407:Tumor Cells, Cultured
D000888:Antibodies, Anti-Idiotypic; D012333:RNA, Messenger; D011947:Receptors, Antigen, B-Cell; D011948:Receptors, Antigen, T-Cell; D018808:Transcription Factor AP-1; D010744:Phosphoric Monoester Hydrolases