Biomedical subjects

Ivan Dikic

Publications and source records attributed to Ivan Dikic.

At least 37 records · Page 2Linked to original sources

PubMed2005

Ubiquitylation and cell signaling.

Ubiquitylation is an emerging mechanism implicated in a variety of nonproteolytic cellular functions. The attachment of a single ubiquitin (Ub) or poly-Ub (lysine 63) chains to proteins control gene transcription, DNA repair and replication, intracellular trafficking and virus budding. In these processes, protein ubiquitylation exhibits inducibility, reversibility and recognition by specialized domains, features similar to protein phosphorylation, which enable Ub to act as a signaling device. Here, we highlight several recent examples on how Ub regulates signaling and how signaling regulates ubiquitylation during physiological and pathological cellular processes.

Cell Nucleus↗

PubMed2005

Polo-like kinase 1-mediated phosphorylation stabilizes Pin1 by inhibiting its ubiquitination in human cells.

The Polo-like kinase 1 (Plk1) is a key regulator of mitosis. It is reported that the human peptidyl-prolyl cis/trans-isomerase Pin1 binds to Plk1 from mitotic cell extracts in vitro. Here we demonstrate that Ser-65 in Pin1 is the major site for Plk1-specific phosphorylation, and the polo-box domain of Plk1 is required for this phosphorylation. Interestingly, the phosphorylation of Pin1 by Plk1 does not affect its isomerase activity but rather is linked to its protein stability. Pin1 is ubiquitinated in HeLa S3 cells, and substitution of Glu for Ser-65 reduces the ubiquitination of Pin1. Furthermore, inhibition of Plk1 activity by expression of a dominant negative form of Plk1 or by transfection of small interfering RNA targeted to Plk1 enhances the ubiquitination of Pin1 and subsequently reduces the amount of Pin1 in human cancer cells. Since previous reports suggested that Plk1 is a substrate of Pin1, our work adds a new dimension to this interaction of two important mitotic regulators.

Blotting, Western↗

PubMed2005

Oncogenic breakdowns in endocytic adaptor proteins.

Endocytosis is a versatile tool to regulate the intensity, localization, half-life and function of signaling complexes (signalosomes) that form in cells upon binding of growth factors, cytokines and morphogens to their cognate receptors. Endocytic adaptors are non-catalytic proteins that assemble effectors and structural components of the endocytic machinery around the trafficking cargo and serve as scaffolds for signalosomes, which in turn modify their location and activity by various post-translational modifications. We discuss how breakdowns in the function of endocytic adaptors might facilitate impairment of tissue homeostasis and consequent tumor development.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Implication of phospholipase D2 in oxidant-induced phosphoinositide 3-kinase signaling via Pyk2 activation in PC12 cells.

The role of phospholipase D (PLD) activation in hydrogen peroxide (H(2)O(2))-induced signal transduction and cellular responses is not completely understood. Here we present evidence that Ca(2+)-dependent tyrosine kinase, Pyk2, requires PLD activation to mediate survival pathways in rat pheochromocytoma PC12 cells under oxidative stress. The H(2)O(2)-induced phosphorylation of two Pyk2 sites (Tyr(580), and Tyr(881)) was suppressed by 1-butanol, an inhibitor of transphosphatidylation by PLD, and also by transfection of catalytically negative mouse PLD2K758R (PLD2KR). Furthermore, we found that PLD2 was associated with Pyk2 and Src, and that activation of PLD2 was required for H(2)O(2)-enhanced association of Src with Pyk2 leading to full activation of Pyk2. H(2)O(2)-induced phosphorylation of Akt and p70S6K was dependent on phosphatidylinositol 3-kinase (PI3K) activity and was abolished by 1-butanol but not t-butanol. Furthermore, the PI3K/Akt activation in response to H(2)O(2) was reduced by transfection of either PLD2KR or the dominant negative Pyk2DN. This study is the first demonstration that PLD2 activation is implicated in Src-dependent phosphorylation of Pyk2 (Tyr(580) and Tyr(881)) by promoting the complex formation between Pyk2 and activated Src in PC12 cells exposed to H(2)O(2), thereby resulting in activation of the survival signaling pathway PI3K/Akt/p70S6K.

Animals↗

PubMed2005

Compartmentalization of growth factor receptor signalling.

Spatial and temporal separation of signal transduction pathways often determines the specificity in cellular responses. Recent advances have improved our understanding of how growth factor signalling is influenced by the formation of molecular complexes (signalosomes) in distinct cellular compartments. There has also been new insight into the mechanisms that determine the signalling competence of these complexes and their role in receptor endocytosis, retrograde trafficking in neurons and restricted protein biosynthesis, and many examples have been found where signalosome deregulation leads to disease.

Animals↗

PubMed2005

Molecular responses to acidosis of central chemosensitive neurons in brain.

Significant advances have been made in understanding how neurons sense and respond to acidosis at the cellular level. Decrease in pH of the cerebrospinal fluid followed by hypercapnia (increased arterial CO2) is monitored by the chemosensory neurons of the medulla oblongata. Then the intracellular signalling pathways are activated to regulate specific gene expression, which leads to a hyperventilatory response. However, little is known about molecular details of such cellular responses. Recent studies have identified several transcription factors such as c-Jun, Fos and small Maf proteins that may play critical roles in the brain adaptation to hypercapnia. Hypercapnic stimulation also activates c-Jun NH2-terminal kinase (JNK) cascade via influx of extracellular Ca2+ through voltage-gated Ca2+ channels. In addition, several transmembrane proteins including Rhombex-29 (rhombencephalic expression protein-29 kDa) and Past-A (proton-associated sugar transporter-A) have been implicated in regulation of H+ sensitivity and brain acidosis-mediated energy metabolism, respectively. This review discusses current knowledge on the signalling mechanisms and molecular basis of neuronal adaptation during acidosis.

Acidosis↗

PubMed2005

The Cbl interactome and its functions.

Cbl proteins are ubiquitin ligases and multifunctional adaptor proteins that are implicated in the regulation of signal transduction in various cell types and in response to different stimuli. Cbl-associated proteins can assemble together at a given time or space inside the cell, and such an interactome can form signal competent networks that control many physiological processes. Dysregulation of spatial or temporal constraints in the Cbl interactome results in the development of human pathologies such as immune diseases, diabetes and cancer.

Actins↗

PubMed2005

Cbl promotes clustering of endocytic adaptor proteins.

The ubiquitin ligases c-Cbl and Cbl-b play a crucial role in receptor downregulation by mediating multiple monoubiquitination of receptors and promoting their sorting for lysosomal degradation. Their function is modulated through interactions with regulatory proteins including CIN85 and PIX, which recognize a proline-arginine motif in Cbl and thus promote or inhibit receptor endocytosis. We report the structures of SH3 domains of CIN85 and beta-PIX in complex with a proline-arginine peptide from Cbl-b. Both structures reveal a heterotrimeric complex containing two SH3 domains held together by a single peptide. Trimerization also occurs in solution and is facilitated by the pseudo-symmetrical peptide sequence. Moreover, ternary complexes of CIN85 and Cbl are formed in vivo and are important for the ability of Cbl to promote epidermal growth factor receptor (EGFR) downregulation. These results provide molecular explanations for a novel mechanism by which Cbl controls receptor downregulation.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Sprouty2 acts at the Cbl/CIN85 interface to inhibit epidermal growth factor receptor downregulation.

The ubiquitin ligase Cbl mediates ubiquitination of activated receptor tyrosine kinases (RTKs) and interacts with endocytic scaffold complexes, including CIN85/endophilins, to facilitate RTK endocytosis and degradation. Several mechanisms regulate the functions of Cbl to ensure the fine-tuning of RTK signalling and cellular homeostasis. One regulatory mechanism involves the binding of Cbl to Sprouty2, which sequesters Cbl away from activated epidermal growth factor receptors (EGFRs). Here, we show that Sprouty2 associates with CIN85 and acts at the interface between Cbl and CIN85 to inhibit EGFR downregulation. The CIN85 SH3 domains A and C bind specifically to proline-arginine motifs present in Sprouty2. Intact association between Sprouty2, Cbl and CIN85 is required for inhibition of EGFR endocytosis as well as EGF-induced differentiation of PC12 cells. Moreover, Sprouty4, which lacks CIN85-binding sites, does not inhibit EGFR downregulation, providing a molecular explanation for functional differences between Sprouty isoforms. Sprouty2 therefore acts as an inducible inhibitor of EGFR downregulation by targeting both the Cbl and CIN85 pathways.

Adaptor Proteins, Signal Transducing↗

PubMed2004

Src phosphorylation of Alix/AIP1 modulates its interaction with binding partners and antagonizes its activities.

Alix/AIP1 is an adaptor protein involved in regulating the function of receptor and cytoskeleton-associated tyrosine kinases. Here, we investigated its interaction with and regulation by Src. Tyr319 of Alix bound the isolated Src homology-2 (SH2) domain and was necessary for interaction with intact Src. A proline-rich region in the C terminus of Alix bound the Src SH3 domain, but this interaction was dependent on the release of the Src SH2 domain from its Src internal ligand either by interaction with Alix Tyr319 or by mutation of Src Tyr527. Src phosphorylated Alix at a C-terminal region rich in tyrosines, an activity that was stimulated by the presence of the Alix binding partner SETA/CIN85. Phosphorylation of Alix by Src caused it to translocate from the membrane and cytoskeleton to the cytoplasm and reduced its interaction with binding partners SETA/CIN85, epidermal growth factor receptor, and Pyk2. As a consequence of this, Src antagonized the negative regulation of receptor tyrosine kinase internalization and cell adhesion by Alix. We propose a model whereby Src antagonizes the effects of Alix by phosphorylation of its C terminus, leading to the disruption of interactions with target proteins.

Animals↗

PubMed2004

Cargo- and compartment-selective endocytic scaffold proteins.

The endocytosis of membrane receptors is a complex and tightly controlled process that is essential for maintaining cellular homoeostasis. The removal of receptors from the cell surface can be constitutive or ligand-induced, and occurs in a clathrin-dependent or -independent manner. The recruitment of receptors into specialized membrane domains, the formation of vesicles and the trafficking of receptors together with their ligands within endocytic compartments are regulated by reversible protein modifications, and multiple protein-protein and protein-lipid interactions. Recent reports describe a variety of multidomain molecules that facilitate receptor endocytosis and function as platforms for the assembly of protein complexes. These scaffold proteins typically act in a cargo-specific manner, recognizing one or more receptor types, or function at the level of endocytic cellular microcompartments by controlling the movement of cargo molecules and linking endocytic machineries to signalling pathways. In the present review we summarize present knowledge on endocytic scaffold molecules and discuss their functions.

Adaptor Proteins, Signal Transducing↗

PubMed2004

Suppressors of T-cell receptor signaling Sts-1 and Sts-2 bind to Cbl and inhibit endocytosis of receptor tyrosine kinases.

The ubiquitin (Ub) ligase Cbl plays a critical role in attenuation of receptor tyrosine kinase (RTK) signaling by inducing ubiquitination of RTKs and promoting their sorting for endosomal degradation. Herein, we describe the identification of two novel Cbl-interacting proteins, p70 and Clip4 (recently assigned the names Sts-1 and Sts-2, respectively), that inhibit endocytosis of epidermal growth factor receptor (EGFR) and platelet-derived growth factor receptor. Sts-1 and Sts-2 contain SH3 domains that interacted with Cbl, Ub-associated domains, which bound directly to mono-Ub or to the EGFR/Ub chimera as well as phosphoglycerate mutase domains that mediated oligomerization of Sts-1/2. Ligand-induced recruitment of Sts-1/Sts-2 into activated EGFR complexes led to inhibition of receptor internalization, reduction in the number of EGFR-containing endocytic vesicles, and subsequent block of receptor degradation followed by prolonged activation of mitogenic signaling pathways. On the other hand, interference with Sts-1/Sts-2 functions diminished ligand-induced receptor degradation, cell proliferation, and oncogenic transformation in cultured fibroblasts. We suggest that Sts-1 and Sts-2 represent a novel class of Ub-binding proteins that regulate RTK endocytosis and control growth factor-induced cellular functions.

Amino Acid Sequence↗

PubMed2004

SH3P2 in complex with Cbl and Src.

In this report, we describe SH3P2, an SH3-domain containing protein, as a novel Cbl-interacting molecule that is a substrate of tyrosine kinase Src. We identified a specific polyproline motif of Cbl responsible for binding of SH3P2 and Src, and observed mutual sequestration of Src and SH3P2 from monomer Cbl molecules. In adherent cells, SH3P2 associated with Cbl and fibrilar actin and was localized at focal contacts in fibroblasts as well as at the apical part of podosome rings in differentiated osteoclasts. Our data implicate that SH3P2, a novel component of adhesion sites, is involved in Cbl and Src-mediated pathways.

Actins↗

PubMed2004

Recruitment of Pyk2 and Cbl to lipid rafts mediates signals important for actin reorganization in growing neurites.

Protein tyrosine kinase Pyk2 and multifunctional adaptor protein Cbl are implicated in the regulation of the cytoskeleton in several cell types. We report that Pyk2 and Cbl form a signaling complex that is translocated to lipid rafts and is enriched in growth cones of differentiating PC12 cells following growth factor stimulation. We found that Pyk2 and Cbl interacted with the adaptor protein ArgBP2, which also bound to flotillin-1, a component of lipid raft microdomains. These interactions contributed to recruitment of the Pyk2/Cbl complex to lipid raft compartments. In addition, Pyk2, Cbl and ArgBP2 were found co-localized with actin in axons and growth cones of differentiated PC12 cells. Moreover, co-expression of Pyk2, ArgBP2 and Cbl facilitated growth factor-induced formation of lamellipodia at the tip of neurites. Formation of these growth cone lamellipodia was dependent on intact lipid rafts and the Cbl-associated effectors Crk and phosphatidylinositol 3 (PI 3)-kinase. Our results indicate that recruitment of Pyk2/Cbl complexes to lipid rafts participates in growth factor-induced regulation of the actin cytoskeleton in growing neurites.

Actins↗

PubMed2004

CIN85 associates with multiple effectors controlling intracellular trafficking of epidermal growth factor receptors.

CIN85 is a multidomain adaptor protein involved in Cbl-mediated down-regulation of epidermal growth factor (EGF) receptors. CIN85 src homology 3 domains specifically bind to a proline-arginine (PxxxPR) motif in Cbl, and this association seems to be important for EGF receptor endocytosis. Here, we report identification of novel CIN85 effectors, all containing one or more PxxxPR motifs, that are indispensable for their mutual interactions. These effectors include phosphatidyl-inositol phosphatases SHIP-1 and synaptojanin 2B1, Arf GTPase-activating proteins ASAP1 and ARAP3, adaptor proteins Hip1R and STAP1, and a Rho exchange factor, p115Rho GEF. Acting as a molecular scaffold, CIN85 clusters its effectors and recruits them to high-molecular-weight complexes in cytosolic extracts of cells. Further characterization of CIN85 binding to ASAP1 revealed that formation of the complex is independent on cell stimulation. Overexpression of ASAP1 increased EGF receptor recycling, whereas ASAP1 containing mutated PxxxPR motif failed to promote this event. We propose that CIN85 functions as a scaffold molecule that binds to numerous endocytic accessory proteins, thus controlling distinct steps in trafficking of EGF receptors along the endocytic and recycling pathways.

Adaptor Proteins, Signal Transducing↗

PubMed2004

Receptor endocytosis via ubiquitin-dependent and -independent pathways.

The controlled termination of signaling pathways after their ligand-induced activation is an important mechanism to ensure appropriate signal intensity and the consequent cellular response. Most cell surface receptors are downregulated by receptor endocytosis and subsequent lysosomal degradation, processes accompanied by attachment of ubiquitin (Ub) molecules to activated receptors and associated proteins. A significant body of evidence supports the view that mono-Ub functions as an important internalization and degradation signal conserved from yeast to mammals. Yet, the mechanisms underlying ligand-dependent receptor endocytosis seem to be divergent and more complex in mammalian cells. This is not only a consequence of evolution-based expansion of endocytic proteins and protein-interaction domains, but is also caused by enhanced formation of networks and multi-molecular complexes linked to activated receptors in higher eukaryotes. Here, we discuss the current view on the role of Ub-dependent and -independent pathways in receptor internalization and endocytosis in mammalian cells.

Animals↗

PubMed2004

ALIX-ing phospholipids with endosome biogenesis.

Endosomes, which comprise a diverse population of membrane vesicles and tubules, sort proteins and lipids to various cellular destinations. The organization and functions of these pleiomorphic cellular organelles have been extensively studied. Matsuo et al.1 now provide new exciting evidence on the role of lysobiphosphatidic acid (LBPA), a resident phospholipid of internal vesicles of the late endosome, in the control of membrane invagination and endosome biogenesis. In vivo, LBPA functions are controlled by the adaptor protein Alix and depend on pH gradients along the endosomal compartments.

Animals↗

PubMed2004

Phosphorylation of JNK is involved in regulation of H(+)-induced c-Jun expression.

Cells respond to physical and chemical stimulations mediated by pH, osmolarity, and oxidative and mechanical stresses. Various signal transduction pathways cooperate and participate in these responses. Here we describe the role of c-Jun NH2-terminal kinase (JNK) in regulation of gene transcription after an increase in extracellular H+. When cells were incubated in low pH medium, the promotion of JNK phosphorylation and c-Jun expression was clearly observed in cells in an extracellular pH- and time-dependent manner. Activation of p38 and extracellular signal-regulated kinase 1/2 (ERK1/2) was extremely weak compared with that of JNK. An increase in extracellular H+ led to enhanced nuclear translocation of phosphorylated JNK leading to augmentation of the transcriptional activity of c-Jun. Nimodipine, a blocker of voltage-gated Ca2+ ion channels, prevented the phosphorylation of JNK and expression of c-Jun in a dose-dependent manner. These results suggest a novel intracellular signalling pathway for H+-induced c-Jun expression: an increase of extracellular H+ induces JNK phosphorylation and c-Jun expression via partly extracellular Ca2+ influx through voltage-gated Ca2+ channels.

Animals↗