PI(3,4,5)P3 and PI(4,5)P2 lipids target proteins with polybasic clusters to the plasma membrane.
01 Dec 2006-Science (American Association for the Advancement of Science)-Vol. 314, Iss: 5804, pp 1458-1461
TL;DR: This work surveyed PM-targeting mechanisms by imaging the subcellular localization of 125 fluorescent protein–conjugated Ras, Rab, Arf, and Rho proteins and found that proteins with polybasic clusters dissociated from the PM only when both PI(4,5)P2 and phosphatidylinositol 3,4, 5-trisphosphate were depleted.
Abstract: Many signaling, cytoskeletal, and transport proteins have to be localized to the plasma membrane (PM) in order to carry out their function. We surveyed PM-targeting mechanisms by imaging the subcellular localization of 125 fluorescent protein–conjugated Ras, Rab, Arf, and Rho proteins. Out of 48 proteins that were PM-localized, 37 contained clusters of positively charged amino acids. To test whether these polybasic clusters bind negatively charged phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] lipids, we developed a chemical phosphatase activation method to deplete PM PI(4,5)P2. Unexpectedly, proteins with polybasic clusters dissociated from the PM only when both PI(4,5)P2 and phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P3] were depleted, arguing that both lipid second messengers jointly regulate PM targeting.
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TL;DR: This review is an attempt to give an overview of this enormous research field focusing on major developments in diverse areas of basic science linked to cellular physiology and disease.
Abstract: Phosphoinositides (PIs) make up only a small fraction of cellular phospholipids, yet they control almost all aspects of a cell's life and death. These lipids gained tremendous research interest as plasma membrane signaling molecules when discovered in the 1970s and 1980s. Research in the last 15 years has added a wide range of biological processes regulated by PIs, turning these lipids into one of the most universal signaling entities in eukaryotic cells. PIs control organelle biology by regulating vesicular trafficking, but they also modulate lipid distribution and metabolism via their close relationship with lipid transfer proteins. PIs regulate ion channels, pumps, and transporters and control both endocytic and exocytic processes. The nuclear phosphoinositides have grown from being an epiphenomenon to a research area of its own. As expected from such pleiotropic regulators, derangements of phosphoinositide metabolism are responsible for a number of human diseases ranging from rare genetic disorders to the most common ones such as cancer, obesity, and diabetes. Moreover, it is increasingly evident that a number of infectious agents hijack the PI regulatory systems of host cells for their intracellular movements, replication, and assembly. As a result, PI converting enzymes began to be noticed by pharmaceutical companies as potential therapeutic targets. This review is an attempt to give an overview of this enormous research field focusing on major developments in diverse areas of basic science linked to cellular physiology and disease.
1,239 citations
TL;DR: A biosensor developed to study the subcellular distribution of phosphatidylserine found that it binds the cytosolic leaflets of the plasma membrane, as well as endosomes and lysosomes.
Abstract: Electrostatic interactions with negatively charged membranes contribute to the subcellular targeting of proteins with polybasic clusters or cationic domains. Although the anionic phospholipid phosphatidylserine is comparatively abundant, its contribution to the surface charge of individual cellular membranes is unknown, partly because of the lack of reagents to analyze its distribution in intact cells. We developed a biosensor to study the subcellular distribution of phosphatidylserine and found that it binds the cytosolic leaflets of the plasma membrane, as well as endosomes and lysosomes. The negative charge associated with the presence of phosphatidylserine directed proteins with moderately positive charge to the endocytic pathway. More strongly cationic proteins, normally associated with the plasma membrane, relocalized to endocytic compartments when the plasma membrane surface charge decreased on calcium influx.
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Abstract: Genetically encodable optical reporters, such as green fluorescent protein, have revolutionized the observation and measurement of cellular states. However, the inverse challenge of using light to control precisely cellular behaviour has only recently begun to be addressed; semi-synthetic chromophore-tethered receptors and naturally occurring channel rhodopsins have been used to perturb directly neuronal networks. The difficulty of engineering light-sensitive proteins remains a significant impediment to the optical control of most cell-biological processes. Here we demonstrate the use of a new genetically encoded light-control system based on an optimized, reversible protein-protein interaction from the phytochrome signalling network of Arabidopsis thaliana. Because protein-protein interactions are one of the most general currencies of cellular information, this system can, in principle, be generically used to control diverse functions. Here we show that this system can be used to translocate target proteins precisely and reversibly to the membrane with micrometre spatial resolution and at the second timescale. We show that light-gated translocation of the upstream activators of Rho-family GTPases, which control the actin cytoskeleton, can be used to precisely reshape and direct the cell morphology of mammalian cells. The light-gated protein-protein interaction that has been optimized here should be useful for the design of diverse light-programmable reagents, potentially enabling a new generation of perturbative, quantitative experiments in cell biology.
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TL;DR: In this article, a review of Ca2+ signaling in cells of the immune system was presented, focusing on identifying modulators of store-operated Ca 2+ entry into Drosophila cells.
Abstract: Ca2+ entry into cells of the peripheral immune system occurs through highly Ca2+-selective channels known as CRAC (calcium release-activated calcium) channels. CRAC channels are a very well-characterized example of store-operated Ca2+ channels, so designated because they open when the endoplasmic reticulum (ER) Ca2+ store becomes depleted. Physiologically, Ca2+ is released from the ER lumen into the cytoplasm when activated receptors couple to phospholipase C and trigger production of the second messenger inositol 1,4,5-trisphosphate (IP3). IP3 binds to IP3 receptors in the ER membrane and activates Ca2+ release. The proteins STIM and ORAI were discovered through limited and genome-wide RNAi screens, respectively, performed in Drosophila cells and focused on identifying modulators of store-operated Ca2+ entry. STIM1 and STIM2 sense the depletion of ER Ca2+ stores, whereas ORAI1 is a pore subunit of the CRAC channel. In this review, we discuss selected aspects of Ca2+ signaling in cells of the immune syste...
681 citations
TL;DR: This review discusses the dependence of ion channels on phosphoinositides and considers possible mechanisms by which PIP2 and analogues regulate ion channel activity.
Abstract: Phosphatidylinositol 4,5-bisphosphate (PIP2) is a minority phospholipid of the inner leaflet of plasma membranes. Many plasma membrane ion channels and ion transporters require PIP2 to function and can be turned off by signaling pathways that deplete PIP2. This review discusses the dependence of ion channels on phosphoinositides and considers possible mechanisms by which PIP2 and analogues regulate ion channel activity.
603 citations
Cites background from "PI(3,4,5)P3 and PI(4,5)P2 lipids ta..."
...The GTPases leave the plasma membrane when PIP2 is hydrolyzed—or if some of their basic or hydrophobic residues are mutated (26)....
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References
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TL;DR: Recent studies suggest that membrane proteins concentrate PIP2 and, in response to local increases in intracellular calcium concentration, release it to interact with other biologically important molecules.
Abstract: Phosphatidylinositol 4,5-bisphosphate (PIP2), which comprises only about 1% of the phospholipids in the cytoplasmic leaflet of the plasma membrane, is the source of three second messengers, activates many ion channels and enzymes, is involved in both endocytosis and exocytosis, anchors proteins to the membrane through several structured domains and has other roles. How can a single lipid in a fluid bilayer regulate so many distinct physiological processes? Spatial organization might be the key to this. Recent studies suggest that membrane proteins concentrate PIP2 and, in response to local increases in intracellular calcium concentration, release it to interact with other biologically important molecules.
856 citations
TL;DR: The hypothesis that proteins such as MARCKS bind a significant fraction of the PIP2 in a cell, helping to sequester it in lateral membrane domains, then release this lipid in response to local signals such as an increased concentration of Ca(++)/calmodulin or activation of protein kinase C is considered.
Abstract: ▪ Abstract We review the physical properties of phosphatidylinositol 4,5-bisphosphate (PIP2) that determine both its specific interactions with protein domains of known structure and its nonspecific electrostatic sequestration by unstructured domains. Several investigators have postulated the existence of distinct pools of PIP2 within the cell to account for the myriad functions of this lipid. Recent experimental work indicates certain regions of the plasma membrane—membrane ruffles and nascent phagosomes—do indeed concentrate PIP2. We consider two mechanisms that could account for this phenomenon: local synthesis and electrostatic sequestration. We conclude by considering the hypothesis that proteins such as MARCKS bind a significant fraction of the PIP2 in a cell, helping to sequester it in lateral membrane domains, then release this lipid in response to local signals such as an increased concentration of Ca++/calmodulin or activation of protein kinase C.
839 citations
TL;DR: It is shown that the specific subcellular distribution of H- and Nras guanosine triphosphate–binding proteins is generated by a constitutive de/reacylation cycle that operates on palmitoylated proteins, driving their rapid exchange between the plasma membrane (PM) and the Golgi apparatus.
Abstract: We show that the specific subcellular distribution of H- and Nras guanosine triphosphate-binding proteins is generated by a constitutive de/reacylation cycle that operates on palmitoylated proteins, driving their rapid exchange between the plasma membrane (PM) and the Golgi apparatus. Depalmitoylation redistributes farnesylated Ras in all membranes, followed by repalmitoylation and trapping of Ras at the Golgi, from where it is redirected to the PM via the secretory pathway. This continuous cycle prevents Ras from nonspecific residence on endomembranes, thereby maintaining the specific intracellular compartmentalization. The de/reacylation cycle also initiates Ras activation at the Golgi by transport of PM-localized Ras guanosine triphosphate. Different de/repalmitoylation kinetics account for isoform-specific activation responses to growth factors.
797 citations
TL;DR: It is shown that Nras is transiently localized in the Golgi prior to the plasma membrane (PM), and green fluorescent protein (GFP)-tagged Nras illuminated motile, peri-Golgi vesicles, and prolonged BFA treatment blocked PM expression.
756 citations
TL;DR: The studies show that PtdIns(4,5)P2 can have second messenger functions of its own, by mediating a transient dissociation of proteins anchored in the plasma membrane.
708 citations