RESUMEN
Translational regulation plays an important role in development. In terminally differentiating cells a decrease in translation rate is common, although the regulatory mechanisms are unknown. We utilized 32Dcl3 myeloblast cells to investigate translational regulation during granulocyte colony-stimulating factor (G-CSF)-induced differentiation. G-CSF causes a significant decrease in translation rate compared with interleukin-3, which is a mitogen for these cells. Although these two cytokines exhibit modest differences in their effect on translation factor phosphorylation, they exhibit dramatic differences in their effect on ribosomal abundance and ribosomal DNA transcription. However, because both cytokines stimulate cell cycling, G-CSF induces a dissociation of ribosomal biogenesis from cell cycle progression. This uncoupling of ribosomal biogenesis from cell cycle progression appears to be closely related to the transmission of a differentiation signal, because it is not observed in cells expressing a carboxyl-terminally truncated G-CSF receptor, which supports proliferation but not differentiation of these cells. Because a similar event occurs early in differentiation of murine erythroleukemic cells, this suggests that ribosomal content is a common target of differentiating agents.
Asunto(s)
Ciclo Celular/fisiología , Diferenciación Celular/fisiología , Factor Estimulante de Colonias de Granulocitos/farmacología , Células Mieloides/fisiología , Biosíntesis de Proteínas/fisiología , Receptores de Factor Estimulante de Colonias de Granulocito/química , Ribosomas/metabolismo , Animales , Línea Celular , Citometría de Flujo , Factor Estimulante de Colonias de Granulocitos/química , Humanos , Interleucina-3/farmacología , Células Mieloides/citología , Células Mieloides/efectos de los fármacos , Factores de Iniciación de Péptidos/metabolismo , Fosforilación , Estructura Terciaria de Proteína , ARN Ribosómico 18S/genética , ARN Ribosómico 18S/metabolismo , Receptores de Factor Estimulante de Colonias de Granulocito/metabolismo , Transcripción Genética/fisiologíaRESUMEN
Translation has an established role in the regulation of cell growth. Posttranslational modification of translation initiation and elongation factors or regulation of mRNA polyadenylation represent common means of regulating translation in response to mitogenic or developmental signals. Induced differentiation of Friend virus-transformed erythroleukemia cells is accompanied by a rapid decrease in the translation rate of these cells. Although inducers do not alter initiation factor modifications, characterization of their effect on mRNA translation provides evidence that this is mediated by the poly(A)-binding protein (PABP). Inducer exposure results in an increase in the amount of mRNA that sediments at 80 S and a decrease in the amount in polysomes. Although these 80 S ribosomes have characteristics previously attributed to "vacant ribosomal couples," including lability in 500 mM KCl and an inability to incorporate amino acids into protein, we provide evidence that these 80 S complexes are not vacant but contain mRNA that is stably bound to the 40 S subunit, whereas the 60 S subunit is dissociated from the complex by high salt. The absence of eukaryotic initiation factor 2 from these complexes suggests that translation has proceeded through subunit joining. Immunoblotting demonstrates that the mRNAs in these 80 S ribosomal complexes do not contain bound PABP and that this protein is found to be almost exclusively associated with translating polysomes. These data suggest that the PABP plays a role in the accumulation of these 80 S ribosomal.mRNA complexes and may facilitate the formation of translationally active salt-stable ribosomes.