Cellular logistics最新文献

Exosomes, small secreted microvesicles, are implicated in intercellular communication in diverse cell types, transporting protein, lipid and nucleic acid cargo that impact the physiology of recipient cells. Besides the signaling function of exosomes they also serve as a mechanism to dispose obsolete cellular material.¹ Particularly exciting is the involvement of exosomal communication in the nervous system, as this has important implications for brain development and function. The properties of exosomes are also beginning to entice the biomedical community since they represent potentially novel avenues for the targeted delivery of customized exosome cargo, such as miRNAs, during disease. Our findings implicating exosomes in trans-synaptic communication emerged from the serendipitous observation that at the Drosophila larval neuromuscular junction (NMJ) the release of a signaling molecule, Wnt1/Wingless (Wg) and its binding partner Evenness Interrupted (Evi)/Wntless (Wls)/Sprint (Srt), were released by motorneurons in association with vesicles, which we postulated to be exosomes.² In our most recent paper³ using in vivo analysis at the Drosophila NMJ as well as in cultured insect cells we formally demonstrate that Evi rides in exosomes that are released to the extracellular space and identify some of the players involved in their release. In addition, a proteomic analysis of exosomes highlights novel potential function of exosomes.

Regulatory GTPases are often portrayed as binary molecular switches that control a wide range of cellular processes, including, but not limited to, the generation of second messengers (e.g., cAMP and inositol phosphates), intracellular traffic, cytoskeleton organization and cell proliferation. GEF stimulators and GAP inhibitors regulate the nucleotide-bound state of these proteins. Because of the relevance of GTPases and their regulators to human diseases, they comprise a major therapeutic target. Currently, most of the information about GTPase regulators comes from structure analyses. Such structural information is limited to certain conditions and does not necessarily reflect specificity or physiological activity. To address questions about specificity and mechanisms of action, kinetic and cell-based analyses of GTPase regulators is necessary. Here, we compare these two approaches in the context of regulators of Arf and heterotrimeric G-proteins.

The p21-activated kinase (PAK) family plays a versatile role in cell signaling by forming a hub of interactions. PAKs bind the GTPases like RAC and CDC42. Their proline-rich motifs bind SH3 adaptor proteins such as PIX and NCK. PAKs display nuclear localization signal sites and a potential Integrin binding site. No fully complete structure of the PAKs has been published; partial 3D structures of the PAK family kinases include portions of the auto-inhibited PAK1, GTPase bound to small peptides from PAKs, and the kinase domains from PAK1 and PAK4-6 (with small ligands in a few cases). This review focuses on exploring the intermolecular interaction regions in these 3D structures and we offer insights on the missing regions in crystal structure of the auto-inhibited PAK1. Understanding and modulation of PAK intermolecular interactions can pave the way for PAK blockers and biosensors.

PAKs 4, 5 and 6 are members of the group B family of p21-activated kinases. Among this group, PAK4 has been most extensively studied. While it has essential roles in embryonic development, in adults high levels of PAK4 are frequently associated with cancer. PAK4 is overexpressed in a variety of cancers, and the Pak4 gene is amplified in some cancers. PAK4 overexpression is sufficient to cause oncogenic transformation in cells and in mouse models. The tight connection between PAK4 and cancer make it a promising diagnostic tool as well as a potential drug target. The group B PAKs also have important developmental functions. PAK4 is important for many early developmental processes, while PAK5 and PAK6 play roles in learning and memory in mice. This chapter provides an overview of the roles of the group B PAKs in cancer as well as development, and includes a discussion of PAK mediated signaling pathways and cellular functions.

PAK1 kinase is a crucial regulator of a variety of cellular processes, such as motility, cell division, gene transcription and apoptosis. Its deregulation is involved in several pathologies, including cancer, viral infection and neurodegenerative diseases. Due to this strong implication in human health, the complex network of signaling pathways centered on PAK1 is a subject of intensive investigations. This review summarizes the present knowledge on the multiple PAK1 intracellular localizations and on its shuttling between different compartments. The dynamics of PAK1 localization and activation are finely tuned by the cell and it is this tight control that underlies the capacity of PAK1 to participate in the regulation of many fundamental cell functions. Recently, PAK1 biosensors have been developed to visualize PAK1 activation in live cells. These new imaging tools should be of great help to better understand PAK1 biology and to conceive strategies for efficient and specific PAK1 inhibitors.

Developmental cognitive deficits including X-linked mental retardation (XLMR) can be caused by mutations in P21-activated kinase 3 (PAK3) that disrupt actin dynamics in dendritic spines. Neurodegenerative diseases such as Alzheimer disease (AD), where both PAK1 and PAK3 are dysregulated, may share final common pathways with XLMR. Independent of familial mutation, cognitive deficits emerging with aging, notably AD, begin after decades of normal function. This prolonged prodromal period involves the buildup of amyloid-β (Aβ) extracellular plaques and intraneuronal neurofibrillary tangles (NFT). Subsequently region dependent deficits in synapses, dendritic spines and cognition coincide with dysregulation in PAK1 and PAK. Specifically proximal to decline, cytoplasmic levels of actin-regulating Rho GTPase and PAK1 kinase are decreased in moderate to severe AD, while aberrant activation and translocation of PAK1 appears around the onset of cognitive deficits. Downstream to PAK1, LIM kinase inactivates cofilin, contributing to cofilin pathology, while the activation of Rho-dependent kinase ROCK increases Aβ production. Aβ activation of fyn disrupts neuronal PAK1 and ROCK-mediated signaling, resulting in synaptic deficits. Reductions in PAK1 by the anti-amyloid compound curcumin suppress synaptotoxicity. Similarly other neurological disorders, including Huntington disease (HD) show dysregulation of PAKs. PAK1 modulates mutant huntingtin toxicity by enhancing huntingtin aggregation, and inhibition of PAK activity protects HD as well as fragile X syndrome (FXS) symptoms. Since PAK plays critical roles in learning and memory and is disrupted in many cognitive disorders, targeting PAK signaling in AD, HD and XLMR may be a novel common therapeutic target for AD, HD and XLMR.

The p21-activated kinases (PAKs) are a family of Ser/Thr protein kinases that are represented by six genes in humans (PAK 1-6), and are found in all eukaryotes sequenced to date. Genetic and knockdown experiments in frogs, fish and mice indicate group I PAKs are widely expressed, required for multiple tissue development, and particularly important for immune and nervous system function in the adult. The group II PAKs (human PAKs 4-6) are more enigmatic, but their restriction to metazoans and presence at cell-cell junctions suggests these kinases emerged to regulate junctional signaling. Studies of protozoa and fungal PAKs show that they regulate cell shape and polarity through phosphorylation of multiple cytoskeletal proteins, including microtubule binding proteins, myosins and septins. This chapter discusses what we know about the regulation of PAKs and their physiological role in different model organisms, based primarily on gene knockout studies.

Our work and others' over the past few years have led to the identification of new roles of PAK1 in cardiac physiology, such as the regulation of cardiac ion channel and actomyosin function. More recent studies have revealed that PAK1-deficient mice were vulnerable to cardiac hypertrophy and readily progress to failure under sustained pressure overload and susceptible to ischemia/reperfusion injury. Our further study indicated that the PAK1 activator FTY720 was able to prevent this pressure overload-induced hypertrophy in wild-type mice without compromising their cardiac functions. A cardiac protective effect against ischemia/reperfusion injury by FTY720 was also observed in both rat and mouse models by us and others. Thus, these studies suggest that PAK1 is more important in the heart than previously thought, in particular a therapeutic potential of PAK1 activators. In the future, in-depth investigations are required to further substantiate our hypotheses on mechanisms for PAK1 function in the heart and to explore a therapeutic potential of FTY720 and other PAK1 activators in heart disease conditions.

Eukaryotic, prokaryotic and viral pathogens are known to interfere with signaling pathways of their host to promote their own survival and proliferation. Here, we present selected examples of modulation of PAK activity in human cells by both intracellular and extracellular pathogens, focusing on one eukaryotic pathogen, the human malaria parasite Plasmodium falciparum, two Gram-negative bacteria (Helicobacter pylori and Pseudomonas aeruginosa), and two viruses belonging to distinct groups, the lentivirus HIV and the orthomyxovirus Influenza virus A.