RESUMO
There is evidence that the insulin-like growth factor-I (IGF-I) receptor is required for transformation by a variety of viral and cellular oncogenes in a mouse embryo fibroblast model. To further investigate the IGF-I receptor signaling pathways that are required for the permissive effect of the receptor on transformation by SV40 T antigen, we established three independent fibroblast cell lines each from wild-type and IGF-I receptor null embryos (R-). We transfected the wild-type and R- cell lines with an SV40 T antigen plasmid and selected three clones from each cell line that expressed T antigen. As in previous reports, none of the cloned R- cell lines expressing T antigen were transformed as measured by the ability to form large colonies in soft agar. However, with further passage, all three T antigen-expressing clones from one of the R- cell lines (R(-)3) formed large colonies in soft agar and the transformation of these T antigen-expressing clones was confirmed by tumorigenesis experiments in immunodeficient mice. DNA microarray analysis comparing gene expression between early passage and late passage R(-)3/T antigen clones showed, among other changes, an increase in the expression of ErbB-3 mRNA in the late passage clones. Also, the expression of ErbB-3 protein was dramatically increased in the late passage R(-)3/T antigen clones. We conclude that late passage IGF-I receptor null mouse embryo fibroblasts can be transformed by SV40 T antigen, and that ErbB-3 may play a role in permitting transformation by T antigen.
Assuntos
Antígenos Transformantes de Poliomavirus/fisiologia , Transformação Celular Neoplásica/metabolismo , Fibroblastos/fisiologia , Receptor IGF Tipo 1/deficiência , Animais , Antígenos Transformantes de Poliomavirus/genética , Processos de Crescimento Celular/fisiologia , Transformação Celular Neoplásica/genética , Transformação Celular Neoplásica/patologia , DNA/biossíntese , Embrião de Mamíferos , Fibroblastos/metabolismo , Fibroblastos/patologia , Quinase 1 de Adesão Focal/metabolismo , Proteína Adaptadora GRB2/biossíntese , Proteína Adaptadora GRB2/genética , Genótipo , Proteínas Substratos do Receptor de Insulina , Ligantes , Camundongos , Camundongos Knockout , Fosfoproteínas/biossíntese , Fosfoproteínas/genética , Fosforilação , RNA Mensageiro/biossíntese , RNA Mensageiro/genética , Receptor ErbB-3/biossíntese , Receptor ErbB-3/genética , Receptor IGF Tipo 1/genética , Receptor IGF Tipo 1/metabolismo , TransfecçãoRESUMO
The growth hormone/IGF-1-signaling (GH/IGF-1-signaling) system is involved in numerous physiological processes during normal growth and development and also in the aging process. Understanding the regulation of this system is therefore of importance to the biologist. Studies conducted over the past decade have shown that the JAK/STAT pathways are involved in GH signaling to the nucleus. More recently, evidence has been presented that a member of the SOCS family, SOCS2, is a negative regulator of GH signaling. This story began several years ago with the dramatic demonstration of gigantism in the SOCS2-knockout mouse. A more specific definition of the role of SOCS2 in GH signaling is provided in this issue of the JCI by the demonstration that the overgrowth phenotype of the SOCS2-/- mouse is dependent upon the presence of endogenous GH and that administration of GH to mice lacking both endogenous GH and SOCS2 produced excessive growth.
Assuntos
Envelhecimento/fisiologia , Proteínas de Ligação a DNA/metabolismo , Hormônio do Crescimento/fisiologia , Crescimento/fisiologia , Proteínas Repressoras/metabolismo , Transdução de Sinais/fisiologia , Transativadores/metabolismo , Envelhecimento/genética , Animais , Proteínas de Ligação a DNA/genética , Gigantismo/genética , Gigantismo/metabolismo , Gigantismo/patologia , Crescimento/genética , Fator de Crescimento Insulin-Like I/fisiologia , Camundongos , Proteínas Repressoras/genética , Proteínas Supressoras da Sinalização de Citocina , Transativadores/genéticaRESUMO
We have extended our previous yeast two-hybrid findings to show that 14-3-3beta also interacts with the insulin-like growth factor I receptor (IGFIR) in mammalian cells overexpressing both proteins and that the interaction involves serine 1283 and is dependent on receptor activation. Treatment of cells with the phorbol ester PMA stimulates the interaction of 14-3-3beta with the IGFIR in the absence of receptor tyrosine phosphorylation, suggesting that receptor activation leads to activation of an endogenous protein kinase that catalyzes the phosphorylation of serine 1283. To investigate the role of 14-3-3 proteins in IGF signal transduction, IGFIR structure-function studies were performed. Mutation of serine 1283 alone (S1283A) (a mutation that decreases but does not abolish the interaction of the IGFIR with 14-3-3) did not affect anchorage-independent growth of NIH 3T3 fibroblasts overexpressing the mutant receptor. However, the simultaneous mutation of this residue and the truncation of the C-terminal 27 residues of the receptor (Delta1310/S1283A) abolished the interaction of the receptor with 14-3-3 and reversed the enhanced colony formation observed with the IGFIR truncation mutation alone (Delta1310). The difference between the Delta1310 and Delta1310/S1283A transfectants in the soft agar assay was confirmed by tumorigenesis experiments. These findings suggest that 14-3-3 proteins interact with the IGFIR in vivo and that this interaction may play a role in a transformation pathway signaled by the IGFIR.
