AKT induces transcriptional activity of PU.1 through phosphorylation-mediated modifications within its transactivation domain.
Signal transduction by the antigen receptor complexes is critical for developmental progression of B-lymphocytes, which are defined by assembly and sequential expression of immunoglobulin genes, which in turn are regulated by the enhancer elements. Although proximal antigen-receptor signal transduction pathways are well defined, the precise nuclear factors targeted by these signals remained unknown. Previous studies have demonstrated that tissue-restricted transcription factors including PU.1 and PU.1 interaction partner (PIP) function synergistically with c-Fos plus c-Jun to stimulate the kappaE3'-enhancer in 3T3 cells. In this study, we demonstrate that the functional synergy between these factors is enhanced in response to mitogen-activated protein kinase kinase kinase, in 3T3 cells, where the enhancer is inactive. However in S194 plasmacytoma cells, mitogen-activated protein kinase kinase kinase was able to stimulate the activity of PU.1 but unable to induce the kappaE3'-enhancer activity. We have found that Ras-phosphoinositide 3-kinase-dependent externally regulated kinase, AKT, induces kappaE3'-enhancer activity in both pre-B and plasmacytoma cells. AKT stimulation of the kappaE3'-enhancer is primarily due to PU.1 induction and is independent of PU.1 interaction with PIP. Activation of AKT had no effect on the expression levels of PU.1 or its protein-protein interaction with PIP. Using a series of deletion constructs, we have determined that the PU.1 acid-rich (amino acids 33-74) transactivation domain is necessary for AKT-mediated induction. Substitution analyses within this region indicate that phosphorylation of Ser(41) is necessary to respond to AKT. Consistent with these studies, ligation of antigen receptors in A20 B cells mimics AKT activation of PU.1. Taken together, these results provide evidence that PU.1 is induced by AKT signal in a phosphoinositide 3-kinase-dependent manner, leading to inducible or constitutive activation of its target genes.
Rieske
P
P
Department of Biochemistry, MCP Hahnemann University School of Medicine, Philadelphia, Pennsylvania 19102, USA.
Pongubala
J M
JM
D016475:3T3 Cells; D000818:Animals; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000502:physiology; D004742:Enhancer Elements, Genetic; D050835:Interferon Regulatory Factors; D048728:MAP Kinase Kinase Kinase 1; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D016760:Proto-Oncogene Proteins c-fos / Q000502:physiology; D016755:Proto-Oncogene Proteins c-jun / Q000502:physiology; D011947:Receptors, Antigen, B-Cell / Q000502:physiology; D015534:Trans-Activators / Q000502:physiology*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D000099232:Proto-Oncogene Protein Spi-1; D000099218:Interferon Regulatory Factor-4
D004247:DNA; D004268:DNA-Binding Proteins; D050835:Interferon Regulatory Factors; D048728:MAP Kinase Kinase Kinase 1; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D011947:Receptors, Antigen, B-Cell; D015534:Trans-Activators; D000099232:Proto-Oncogene Protein Spi-1; D000099218:Interferon Regulatory Factor-4; C482578:Map3k1 protein, mouse