RESUMO
Son of Sevenless 1 (SOS1) is a dual guanine nucleotide exchange factor (GEF) that activates the small GTPases RAC and RAS. Although the molecular mechanisms of RAS GEF catalysis have been unveiled, how SOS1 acquires RAC GEF activity and what is the physio-pathological relevance of this activity is much less understood. Here we show that SOS1 is tyrosine phosphorylated on Y1196 by ABL. Phosphorylation of Y1196 controls SOS1 inter-molecular interaction, is required to promote the exchange of nucleotides on RAC in vitro and for platelet-derived growth factor (PDGF) activation of RAC- and RAC-dependent actin remodeling and cell migration. SOS1 is also phosphorylated on Y1196 by BCR-ABL in chronic myelogenous leukemic cells. Importantly, in these cells, SOS1 is required for BCR-ABL-mediated activation of RAC, cell proliferation and transformation in vitro and in a xenograft mouse model. Finally, genetic removal of Sos1 in the bone marrow-derived cells (BMDCs) from Sos1fl/fl mice and infected with BCR-ABL causes a significant delay in the onset of leukemogenesis once BMDCs are injected into recipient, lethally irradiated mice. Thus, SOS1 is required for full transformation and critically contribute to the leukemogenic potential of BCR-ABL.
Assuntos
Transformação Celular Neoplásica/genética , Transformação Celular Neoplásica/metabolismo , Proteínas de Fusão bcr-abl/genética , Fatores de Troca do Nucleotídeo Guanina/metabolismo , Proteína SOS1/metabolismo , Animais , Linhagem Celular Tumoral , Movimento Celular , Proliferação de Células , Modelos Animais de Doenças , Proteínas de Fusão bcr-abl/metabolismo , Humanos , Leucemia/genética , Leucemia/metabolismo , Camundongos , Fosforilação , Fator de Crescimento Derivado de Plaquetas/metabolismo , Proteínas Proto-Oncogênicas p21(ras)/metabolismo , Tirosina/metabolismo , Proteínas rac de Ligação ao GTP , Proteínas rac1 de Ligação ao GTP/metabolismoRESUMO
The vulnerability of motor neurons in transgenic SOD1G93A mice, a model of familial amyotrophic lateral sclerosis (ALS), may depend on the failure of these cells to activate survival mechanisms in response to the toxic mutant SOD1. To test this we investigated whether defects in the PI3K/Akt pathway, a survival signal, and of its neuron-specific activator, Rai, were important for motor neuron degeneration in these mice. No substantial changes were found in the levels of Rai, PI3K(p85) or phosphorylated Akt (P-Akt) in the ventral horn of spinal cord of SOD1G93A mice during disease progression. P-Akt immunoreactivity was the same in degenerating and healthy motor neurons. Rai ablation in SOD1G93A mice slightly accelerated the motor dysfunction without affecting their life span. Thus, motor neurons in SOD1G93A mice do not lose the pro-survival PI3K/Akt signal nor increase it in order to suppress the cell death mechanisms.
Assuntos
Esclerose Lateral Amiotrófica/metabolismo , Neurônios Motores/metabolismo , Fosfatidilinositol 3-Quinases/metabolismo , Proteínas Proto-Oncogênicas c-akt/metabolismo , Transdução de Sinais/fisiologia , Medula Espinal/metabolismo , Esclerose Lateral Amiotrófica/patologia , Animais , Western Blotting , Sobrevivência Celular/fisiologia , Modelos Animais de Doenças , Progressão da Doença , Feminino , Humanos , Processamento de Imagem Assistida por Computador , Imuno-Histoquímica , Camundongos , Camundongos Transgênicos , Microscopia Confocal , Neurônios Motores/patologia , Degeneração Neural/metabolismo , Degeneração Neural/patologia , Medula Espinal/patologia , Superóxido Dismutase/genéticaRESUMO
SEL1L, highly similar to the C elegans sel-1 gene, is a recently cloned human gene whose function is under investigation. SEL1L is differentially expressed in tumors and normal tissues and seems to play a role in tumor growth and aggressiveness. We used the recombinant N-terminus of the SEL1L protein to immunize a Balb/c mouse and produce a monoclonal antibody. A hybridoma secreting an antibody specifically reacting on the SEL1L recombinant fragment was selected. This monoclonal antibody, named MSel1, recognizes the SEL1L protein by Western blotting, immunofluorescence and immunohistochemistry on normal and tumor cells. MSel1 is able to recognize SEL1L even on archival tumor specimens and is therefore particularly appropriate to study SEL1L involvement in tumor progression.