RESUMEN
Protein kinase D2 (PKD2) is a member of the PKD family of serine/threonine kinases, a subfamily of the CAMK super-family. PKDs have a critical role in cell motility, migration and invasion of cancer cells. Expression of PKD isoforms is deregulated in various tumours and PKDs, in particular PKD2, have been implicated in the regulation of tumour angiogenesis. In order to further elucidate the role of PKD2 in tumours, we investigated the signalling context of this kinase by performing an extensive substrate screen by in vitro expression cloning (IVEC). We identified a novel splice variant of calcium and integrin-binding protein 1, termed CIB1a, as a potential substrate of PKD2. CIB1 is a widely expressed protein that has been implicated in angiogenesis, cell migration and proliferation, all important hallmarks of cancer, and CIB1a was found to be highly expressed in various cancer cell lines. We identify Ser(118) as the major PKD2 phosphorylation site in CIB1a and show that PKD2 interacts with CIB1a via its alanine and proline-rich domain. Furthermore, we confirm that CIB1a is indeed a substrate of PKD2 also in intact cells using a phosphorylation-specific antibody against CIB1a-Ser(118). Functional analysis of PKD2-mediated CIB1a phosphorylation revealed that on phosphorylation, CIB1a mediates tumour cell invasion, tumour growth and angiogenesis by mediating PKD-induced vascular endothelial growth factor secretion by the tumour cells. Thus, CIB1a is a novel mediator of PKD2-driven carcinogenesis and a potentially interesting therapeutic target.
Asunto(s)
Proteínas de Unión al Calcio/genética , Proteínas de Unión al Calcio/metabolismo , Neovascularización Patológica/genética , Empalme del ARN/genética , Canales Catiónicos TRPP/genética , Canales Catiónicos TRPP/metabolismo , Factor A de Crecimiento Endotelial Vascular/genética , Línea Celular Tumoral , Movimiento Celular/genética , Membrana Corioalantoides/metabolismo , Células HeLa , Humanos , Fosforilación/genética , Factor A de Crecimiento Endotelial Vascular/metabolismoRESUMEN
A common characteristic of neurodegenerative diseases like Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD) is the accumulation of protein aggregates. This reflects a severe disturbance of protein homeostasis, the proteostasis. Here, we review the involvement of the two major proteolytic machineries, the ubiquitin proteasome system (UPS) and the autophagy/lysosomal system, in the pathogenesis of neurodegenerative diseases. These proteolytic systems cooperate to maintain the proteostasis, as is indicated by intricate cross talk. In addition, the UPS and autophagy are regulated by stress pathways that are activated by disturbed proteostasis, like the unfolded protein response (UPR). We will specifically discuss how these proteolytic pathways are affected in neurodegenerative diseases. We will show that there is a differential involvement of the UPS and autophagy in different neurodegenerative disorders. In addition, the proteolytic impairment may be primary or secondary to the pathology. These differences have important implications for the design of therapeutic strategies. The opportunities and caveats of targeting the UPS and autophagy/lysosomal system as a therapeutic strategy in neurodegeneration will be discussed.
Asunto(s)
Degeneración Nerviosa/metabolismo , Enfermedades Neurodegenerativas/metabolismo , Proteínas/metabolismo , Animales , Autofagia , Humanos , Complejo de la Endopetidasa Proteasomal/metabolismo , Procesamiento Proteico-Postraduccional , Ubiquitina/metabolismoRESUMEN
Amyloid beta (Abeta) is the main component of one of the major pathological hallmarks of Alzheimer's disease and is generally considered as one of the earliest factors that induce the pathogenic cascade. Abeta is produced from a larger precursor protein through proteolytic cleavage by secretase activities, which results in fragments that differ in size depending on the cleavage site used to create the C-terminus. In addition, heterogeneity at the N-terminus is created by proteases/peptidases. Moreover, various amino acid modifications further enhance the heterogeneity of Abeta that accumulates in Alzheimer brain. All these species with their different N-and C termini, with or without modifications have different aggregation properties. Abeta requires an aggregated state to be pathogenic and the exact aggregation state is a major determinant of the cellular effects of Abeta: smaller oligomeric aggregates are more neurotoxic, whereas large fibrillar aggregates are generally more associated with a glial response. It is therefore increasingly clear that Abeta is not a single entity, but a peptide with multiple molecular appearances. In this review we will discuss the mechanisms leading to the generation of the different Abeta species and their involvement in Alzheimer pathogenesis. This will be discussed in the framework of therapeutic approaches that target one of the steps in the biogenesis of toxic Abeta species: inhibition of the formation of Abeta, inhibition of aggregation and stimulation of its degradation or clearance.