Activation of phospholipase C beta4 by heterotrimeric GTP-binding proteins

Transient transfection assays were used to determine how the activity of phospholipase C beta 4, which is preferentially expressed in retina, was regulated. An expression vector carrying the full-length cDNA corresponding to phospholipase C beta 4 was constructed and co- transfected into COS-7 cells together with cDNA encoding the alpha subunits of the Gq class and various beta and gamma subunits corresponding to the heterotrimeric GTP-binding proteins. We found that all the alpha subunits of the Gq class, including G alpha q, G alpha 11, G alpha 14, G alpha 15, and G alpha 16 could activate PLC beta 4 and that none of the G beta gamma subunits that we tested including G beta 1 gamma 1, G beta 1 gamma 2, G beta 1 gamma 3, or G beta 2 gamma 2 activated phospholipase C beta 4. In control experiments, cotransfection with cDNA encoding the alpha subunit of transducin or Gi2 gave no activation of PLC beta 4. These results indicate that phospholipase C beta 4 is activated by G alpha subunits that are members of the Gq class, and, like the phospholipase C beta 1 isoform, it is refractory to activation in the transfection assay by many of the combinations of beta and gamma subunits found in the heterotrimeric G- proteins

Spectrum Sensing Framework based on Blind Source Separation for Cognitive Radio Environments

El uso eficiente del espectro se ha convertido en un área de investigación activa, debido a la escasez de este recurso y a su subutilización. En un escenario en el que el espectro es un recurso compartido como en la radio cognitiva (CR), los espacios sin uso dentro de las bandas de frecuencias con licencia podrían ser detectados y posteriormente utilizados por un usuario secundario a través de técnicas de detección y sensado del espectro. Generalmente, estas técnicas de detección se utilizan a partir de un conocimiento previo de las características de canal. En el presente trabajo se propone un enfoque de detección ciega del espectro basado en análisis de componentes independientes (ICA) y análisis de espectro singular (SSA). La técnica de detección se valida a través de simulación, y su desempeño se compara con metodologías propuestas por otros autores en la literatura. Los resultados muestran que el sistema propuesto es capaz de detectar la mayoría de las fuentes con bajo consumo de tiempo, un aspecto que cabe resaltar para aplicaciones en línea con exigencias de tiempo.The efficient use of spectrum has become an active research area, due to its scarcity and underutilization. In a spectrum sharing scenario as Cognitive Radio (CR), the vacancy of licensed frequency bands could be detected by a secondary user through spectrum sensing techniques. Usually, this sensing approaches are performed with a priori knowledge of the channel features. In the present work, a blind spectrum sensing approach based on Independent Component Analysis and Singular Spectrum Analysis is proposed. The approach is tested and compared with other outcomes. Results show that the proposed scheme is capable of detect most of the sources with low time consumption, which is a remarkable aspect for online applications with demanding time issues

Pertussis Toxin-sensitive Activation of Phospholipase C by the C5a and fMet-Leu-Phe Receptors

Signal transduction pathways that mediate C5a and fMet-Leu-Phe (fMLP)-induced pertussis toxin (PTx)-sensitive activation of phospholipase C (PLC) have been investigated using a cotransfection assay system in COS-7 cells. The abilities of the receptors for C5a and fMLP to activate PLC beta 2 and PLC beta 3 through the Gbeta gamma subunits of endogenous Gi proteins in COS-7 cells were tested because both PLC beta 2 and PLC beta 3 were shown to be activated by the beta gamma subunits of G proteins in in vitro reconstitution assays. Neither of the receptors can activate endogenous PLC beta 3 or recombinant PLC beta 3 in transfected COS-7 cells. However, both receptors can clearly activate PLC beta 2 in a PTx-sensitive manner, suggesting that the receptors may interact with endogenous PTx-sensitive G proteins and activate PLC beta 2 probably through the Gbeta gamma subunits. These findings were further corroborated by the results that PLC beta 3 could only be slightly activated by Gbeta 1gamma 1 or Gbeta 1gamma 5 in the cotransfection assay, whereas the Gbeta gamma subunits strongly activated PLC beta 2 under the same conditions. PLC beta 3 can be activated by Galpha q, Galpha 11, and Galpha 16 in the cotransfection assay. In addition, the Ggamma 2 and Ggamma 3 mutants with substitution of the C-terminal Cys residue by a Ser residue, which can inhibit wild type Gbeta gamma -mediated activation of PLC beta 2, were able to inhibit C5a or fMLP-mediated activation of PLC beta 2. These Ggamma mutants, however, showed little effect on m1-muscarinic receptor-mediated PLC activation, which is mediated by the Gq class of G proteins. These results all confirm that the Gbeta gamma subunits are involved in PLC beta 2 activation by the two chemoattractant receptors and suggest that in COS-7 cells activation of PLC beta 3 by Gbeta gamma may not be the primary pathway for the receptors