RESUMO
Precursor B lymphocytes expand upon expression of a pre-B cell receptor (pre-BCR), but then transit into a resting state in which immunoglobulin light chain gene recombination is initiated. This bi-phasic sequence is orchestrated by the IL-7 receptor (IL-7R) and pre-BCR signaling, respectively, but little is known about microRNAs fine-tuning these events. Here, we show that pre-B cells lacking miR-15 family functions exhibit prolonged proliferation due to aberrant expression of the target genes cyclin E1 and D3. As a consequence, they fail to trigger the transcriptional reprogramming normally accompanying their differentiation, resulting in a developmental block at the pre-B cell stage. Intriguingly, our data indicate that the miR-15 family is suppressed by both IL-7R and pre-BCR signaling, suggesting it is actively integrated into the regulatory circuits of developing B cells. These findings identify the miR-15 family as a novel element required to promote the switch from pre-B cell proliferation to differentiation.
Assuntos
Diferenciação Celular , Proliferação de Células , MicroRNAs/imunologia , MicroRNAs/metabolismo , Células Precursoras de Linfócitos B/fisiologia , Animais , Linfócitos B/imunologia , Ciclina D3/genética , Ciclina E/genética , Ativação Linfocitária , Linfopoese , Camundongos , MicroRNAs/genética , Proteínas Oncogênicas/genética , Receptores de Antígenos de Linfócitos B/genética , Receptores de Interleucina-7/genética , Transdução de SinaisRESUMO
The Escherichia coli Cytotoxic Necrotizing Factors, CNF1, CNF2, CNF3 and CNFY from Yersinia pseudotuberculosis belong to a family of deamidating toxins. CNFs deamidate glutamine 63/61 in the switch II region of Rho GTPases that is essential for GTP hydrolysing activity. Deamidation leads to constitutive activation of Rho GTPases. However, cellular mechanisms like proteasomal degradation of the activated Rho proteins restrict the action of the GTPases. This review describes the differences between the toxin family members concerning expression, cellular entry and substrate specificity.
Assuntos
Proteínas de Escherichia coli , Escherichia coli , Toxinas Bacterianas/metabolismo , Citotoxinas/metabolismo , Escherichia coli/metabolismo , Proteínas de Escherichia coli/metabolismo , Yersinia pseudotuberculosis , Proteínas rho de Ligação ao GTP/metabolismoRESUMO
Cytotoxic necrotizing factor 1 (CNF1) is a protein toxin produced by pathogenic Escherichia coli strains. CNF1 constitutively activates small GTPases of the Rho family by deamidation of a glutamine, which is crucial for GTP hydrolysis. The toxin is taken up into mammalian cells by receptor-mediated endocytosis and is delivered from late endosomes into the cytosol. Here, we show that an approximately 55-kDa fragment of CNF1, which contains the catalytic domain and an additional part of the toxin, is present in the cytosol. The processing of this fragment requires an acidic pH and insertion of the toxin into the endosomal membrane. We define the cleavage site region as the region located between amino acids 532 and 544 of CNF1. The data provide insight into the complex mechanism of uptake of bacterial toxins into mammalian cells.
