RESUMO
The current model of innate immune recognition of Gram-positive bacteria suggests that the bacterial cell wall interacts with host recognition proteins such as TLRs and Nod proteins. We describe an additional recognition system mediated by the platelet-activating factor receptor (PAFr) and directed to the pathogen-associated molecular pattern phosphorylcholine that results in the uptake of bacterial components into host cells. Intravascular choline-containing cell walls bound to endothelial cells and caused rapid lethality in wild-type, Tlr2(-/-), and Nod2(-/-) mice but not in Pafr(-/-) mice. The cell wall exited the vasculature into the heart and brain, accumulating within endothelial cells, cardiomyocytes, and neurons in a PAFr-dependent way. Physiological consequences of the cell wall/PAFr interaction were cell specific, being noninflammatory in endothelial cells and neurons but causing a rapid loss of cardiomyocyte contractility that contributed to death. Thus, PAFr shepherds phosphorylcholine-containing bacterial components such as the cell wall into host cells from where the response ranges from quiescence to severe pathophysiology.
Assuntos
Parede Celular/metabolismo , Imunidade Inata , Glicoproteínas da Membrana de Plaquetas/fisiologia , Infecções Pneumocócicas/imunologia , Receptores Acoplados a Proteínas G/fisiologia , Animais , Parede Celular/química , Endotélio Vascular/citologia , Endotélio Vascular/metabolismo , Endotélio Vascular/microbiologia , Bactérias Gram-Positivas/imunologia , Imunidade Inata/genética , Camundongos , Camundongos Mutantes , Miócitos Cardíacos/metabolismo , Neurônios/metabolismo , Proteína Adaptadora de Sinalização NOD2/genética , Proteína Adaptadora de Sinalização NOD2/fisiologia , Fosforilcolina/análise , Glicoproteínas da Membrana de Plaquetas/genética , Infecções Pneumocócicas/microbiologia , Infecções Pneumocócicas/fisiopatologia , Ratos , Receptores Acoplados a Proteínas G/genética , Streptococcus pneumoniae/imunologia , Receptor 2 Toll-Like/genética , Receptor 2 Toll-Like/fisiologiaRESUMO
The human papillomavirus type 18 (HPV-18) E7 protein promotes S-phase reentry in postmitotic, differentiated keratinocytes in squamous epithelium to facilitate vegetative viral DNA amplification. To examine the nature and fate of the differentiated cells that reenter S phase, organotypic cultures of primary human keratinocytes transduced with HPV-18 E7 were pulse-chase-pulse-labeled with (3)H-thymidine ((3)H-TdR) and bromodeoxyuridine (BrdU). The kinetics of the appearance of doubly labeled suprabasal cells demonstrate that E7 expression did not promote prolonged S phase. Rather, there was a considerable lag before a small percentage of the cells reentered another round of S phase. Fluorescence in situ hybridization analysis, indeed, revealed a small fraction of the cells with more than 4n chromosomes in the differentiated strata. Differentiated cells positive for (3)H-TdR, BrdU, or both often had enlarged nuclei or were binucleated. These results suggest that S phase is not followed by cell division, although nuclear division may occur. Interestingly, a significant fraction of differentiated cells that entered S phase subsequently accumulated p27kip1 protein with a kinetics preceding the accumulation of cyclin E. We conclude that E7-transduced, differentiated keratinocytes that enter S phase have two alternative fates: (i) a low percentage of cells undergoes endoreduplication, achieving higher than 4n ploidy, and (ii) a high percentage of cells accumulates the p27kip1, cyclin E, and p21cip1 proteins, resulting in arrest and preventing further S-phase reentry.
