Function of the N-terminus of zizimin1: autoinhibition and membrane targeting

Roles Played by DOCK11, a Guanine Nucleotide Exchange Factor, in HBV Entry and Persistence in Hepatocytes

HBV infection is challenging to cure due to the persistence of viral covalently closed circular viral DNA (cccDNA). The dedicator of cytokinesis 11 (DOCK11) is recognized as a guanine nucleotide exchange factor (GEF) for CDC42 that has been reported to be required for HBV persistence. DOCK11 is expressed in both the cytoplasm and nucleus of human hepatocytes and is functionally associated with retrograde trafficking proteins Arf-GAP with GTPase domain, ankyrin repeat, and pleckstrin homology domain-containing protein 2 (AGAP2), and ADP-ribosylation factor 1 (ARF1), together with the HBV capsid, in the trans-Golgi network (TGN). This opens an alternative retrograde trafficking route for HBV from early endosomes (EEs) to the TGN and then to the endoplasmic reticulum (ER), thereby avoiding lysosomal degradation. DOCK11 also facilitates the association of cccDNA with H3K4me3 and RNA Pol II for activating cccDNA transcription. In addition, DOCK11 plays a crucial role in the host DNA repair system, being essential for cccDNA synthesis. This function can be inhibited by 10M-D42AN, a novel DOCK11-binding peptide, leading to the suppression of HBV replication both in vitro and in vivo. Treatment with a combination of 10M-D42AN and entecavir may represent a promising therapeutic strategy for patients with chronic hepatitis B (CHB). Consequently, DOCK11 may be seen as a potential candidate molecule in the development of molecularly targeted drugs against CHB.

Structural basis for the dual GTPase specificity of the DOCK10 guanine nucleotide exchange factor

Dedicator of cytokinesis 10 (DOCK10), an evolutionarily conserved guanine nucleotide exchange factor (GEF) for Rho GTPases, has the unique specificity within the DOCK-D subfamily to activate both Cdc42 and Rac, but the structural bases for these activities remained unknown. Here we present the crystal structures of the catalytic DHR2 domain of mouse DOCK10, complexed with either Cdc42 or Rac1. The structures revealed that DOCK10DHR2 binds to Cdc42 or Rac1 by slightly changing the arrangement of its two catalytic lobes. DOCK10 also has a flexible binding pocket for the 56th GTPase residue, allowing a novel interaction with Trp56Rac1. The conserved residues in switch 1 of Cdc42 and Rac1 showed common interactions with the unique Lys-His sequence in the β5/β6 loop of DOCK10DHR2. However, the interaction of switch 1 in Rac1 was less stable than that of switch 1 in Cdc42, due to amino acid differences at positions 27 and 30. Structure-based mutagenesis identified the DOCK10 residues that determine the Cdc42/Rac1 dual specificity.

Structural biology of DOCK-family guanine nucleotide exchange factors

DOCK proteins are a family of multi-domain guanine nucleotide exchange factors (GEFs) that activate the RHO GTPases CDC42 and RAC1, thereby regulating several RHO GTPase-dependent cellular processes. DOCK proteins are characterized by the catalytic DHR2 domain (DOCKDHR2 ), and a phosphatidylinositol(3,4,5)P3 -binding DHR1 domain (DOCKDHR1 ) that targets DOCK proteins to plasma membranes. DOCK-family GEFs are divided into four subfamilies (A to D) differing in their specificities for CDC42 and RAC1, and the composition of accessory signalling domains. Additionally, the DOCK-A and DOCK-B subfamilies are constitutively associated with ELMO proteins that auto-inhibit DOCK GEF activity. We review structural studies that have provided mechanistic insights into DOCK-protein functions. These studies revealed how a conserved nucleotide sensor in DOCKDHR2 catalyses nucleotide exchange, the basis for how different DOCK proteins activate specifically CDC42 and RAC1, and sometimes both, and how up-stream regulators relieve the ELMO-mediated auto-inhibition. We conclude by presenting a model for full-length DOCK9 of the DOCK-D subfamily. The involvement of DOCK GEFs in a range of diseases highlights the importance of gaining structural insights into these proteins to better understand and specifically target them.

Structural insights into the small GTPase specificity of the DOCK guanine nucleotide exchange factors

The dedicator of cytokinesis (DOCK) family of guanine nucleotide exchange factors (GEFs) regulates cytoskeletal dynamics by activating the GTPases Rac and/or Cdc42. Eleven human DOCK proteins play various important roles in developmental processes and the immune system. Of these, DOCK1-5 proteins bind to engulfment and cell motility (ELMO) proteins to perform their physiological functions. Recent structural studies have greatly enhanced our understanding of the complex and diverse mechanisms of DOCK GEF activity and GTPase recognition and its regulation by ELMO. This review is focused on gaining structural insights into the substrate specificity of the DOCK GEFs, and discuss how Rac and Cdc42 are specifically recognized by the catalytic DHR-2 and surrounding domains of DOCK or binding partners.

LKB1-MARK2 signalling mediates lipopolysaccharide-induced production of cytokines in mouse macrophages

Lipopolysaccharide (LPS) is an endotoxin involved in a number of acute and chronic inflammatory syndromes. Although LPS-induced signalling has been extensively studied, there are still mysteries remaining to be revealed. In the current study, we used high-throughput phosphoproteomics to profile LPS-initiated signalling and aimed to find novel mediators. A total of 448 phosphoproteins with 765 phosphorylation sites were identified, and we further validated that the phosphorylation of MARK2 on T208 was important for the regulation on LPS-induced CXCL15 (human IL-8 homolog), IL-1β, IL-6 and TNF-α release, in which LKB1 had a significant contribution. In summary, induction of cytokines by LPS in mouse macrophage is regulated by LKB1-MARK2 signals. Our study provides new clues for further exploring the underlying mechanisms of LPS-induced diseases, and new therapeutic approaches concerning bacterial infection may be derived from these findings.

Allosteric inhibition of the guanine nucleotide exchange factor DOCK5 by a small molecule

Rac small GTPases and their GEFs of the DOCK family are pivotal checkpoints in development, autoimmunity and bone homeostasis, and their abnormal regulation is associated to diverse pathologies. Small molecules that inhibit their activities are therefore needed to investigate their functions. Here, we characterized the mechanism of inhibition of human DOCK5 by C21, a small molecule that inhibits mouse Dock5 in cells and blocks bone degradation in mice models of osteoporosis. We showed that the catalytic DHR2 domain of DOCK5 has a high basal GEF activity in the absence of membranes which is not regulated by a simple feedback loop. C21 blocks this activity in a non-competitive manner and is specific for DOCK5. In contrast, another Dock inhibitor, CPYPP, inhibits both DOCK5 and an unrelated GEF, Trio. To gain insight into structural features of the inhibitory mechanism of C21, we used SAXS analysis of DOCK5^DHR2 and crystallographic analysis of unbound Rac1-GDP. Together, these data suggest that C21 takes advantage of intramolecular dynamics of DOCK5 and Rac1 to remodel the complex into an unproductive conformation. Based on this allosteric mechanism, we propose that diversion of intramolecular dynamics is a potent mechanism for the inhibition of multidomain regulators of small GTPases.

ELMO proteins transduce G protein-coupled receptor signal to control reorganization of actin cytoskeleton in chemotaxis of eukaryotic cells

Chemotaxis, which is chemoattractant-guided directional cell migration, plays major roles in recruitment of neutrophils, the metastasis of cancer cells, and the development of the model organism Dictyostelium discoideum. These cells share remarkable similarities in the signaling pathways by which they control chemotaxis. They all use a G protein-coupled receptor (GPCR)-mediated signal transduction pathway to sense the chemotactic gradient to guide cell migration. Diverse chemokines activate Rac through conserved GPCR signaling pathways. ELMO proteins are an evolutionarily conserved, essential component of the ELMO/Dock complex, which functions as a guanine nucleotide exchange factor (GEF) for small G protein Rac activation. The linkages between the GPCR-initiated gradient sensing compass and the Rac-mediated migrating machinery have long been missing. Here, we summarize recent findings on ELMO proteins that directly interact with G protein and transduce GPCR signaling to control the reorganization of actin-based cytoskeleton through regulating Rac activation during chemotaxis, first in D. discoideum and then in mammalian cancer cells. This represents an evolutionarily conserved signaling shortcut from GPCR to the actin cytoskeleton.

LRCH1 interferes with DOCK8-Cdc42-induced T cell migration and ameliorates experimental autoimmune encephalomyelitis

Xu et al. show that LRCH1 interferes with the GEF activity of DOCK8 to inhibit Cdc42 activation. Upon chemokine stimulation, DOCK8 is phosphorylated and released from LRCH1 to drive cell migration. LRCH1 overexpression reduces CD4⁺ T cell migration to the CNS and ameliorates experimental autoimmune encephalomyelitis.

Directional autoreactive CD4⁺ T cell migration into the central nervous system plays a critical role in multiple sclerosis. Recently, DOCK8 was identified as a guanine-nucleotide exchange factor (GEF) for Cdc42 activation and has been associated with human mental retardation. Little is known about whether DOCK8 is related to multiple sclerosis (MS) and how to restrict its GEF activity. Using two screening systems, we found that LRCH1 competes with Cdc42 for interaction with DOCK8 and restrains T cell migration. In response to chemokine stimulation, PKCα phosphorylates DOCK8 at its three serine sites, promoting DOCK8 separation from LRCH1 and translocation to the leading edge to guide T cell migration. Point mutations at the DOCK8 serine sites block chemokine- and PKCα-induced T cell migration. Importantly, Dock8 mutant mice or Lrch1 transgenic mice were protected from MOG (35–55) peptide–induced experimental autoimmune encephalomyelitis (EAE), whereas Lrch1-deficient mice displayed a more severe phenotype. Notably, DOCK8 expression was markedly increased in PBMCs from the acute phase of MS patients. Together, our study demonstrates LRCH1 as a novel effector to restrain PKCα–DOCK8–Cdc42 module–induced T cell migration and ameliorate EAE.

Membrane and Protein Interactions of the Pleckstrin Homology Domain Superfamily

The human genome encodes about 285 proteins that contain at least one annotated pleckstrin homology (PH) domain. As the first phosphoinositide binding module domain to be discovered, the PH domain recruits diverse protein architectures to cellular membranes. PH domains constitute one of the largest protein superfamilies, and have diverged to regulate many different signaling proteins and modules such as Dbl homology (DH) and Tec homology (TH) domains. The ligands of approximately 70 PH domains have been validated by binding assays and complexed structures, allowing meaningful extrapolation across the entire superfamily. Here the Membrane Optimal Docking Area (MODA) program is used at a genome-wide level to identify all membrane docking PH structures and map their lipid-binding determinants. In addition to the linear sequence motifs which are employed for phosphoinositide recognition, the three dimensional structural features that allow peripheral membrane domains to approach and insert into the bilayer are pinpointed and can be predicted ab initio. The analysis shows that conserved structural surfaces distinguish which PH domains associate with membrane from those that do not. Moreover, the results indicate that lipid-binding PH domains can be classified into different functional subgroups based on the type of membrane insertion elements they project towards the bilayer.

Dock4 forms a complex with SH3YL1 and regulates cancer cell migration

Dock4 is a member of the Dock180 family of proteins that mediates cancer cell migration through activation of Rac. However, the regulatory mechanism of Dock4 remains unclear. In this study, we show that the C-terminal proline-rich region of Dock4 is essential for the Dock4 mediated promotion of cell migration in MDA-MB-231 breast cancer cells. We found that a phosphoinositide-binding protein SH3YL1 interacted with the C-terminal proline-rich region of Dock4. Interaction of SH3YL1 with Dock4 promoted Dock4-mediated Rac1 activation and cell migration. Mutations in the phosphoinositide-binding domain disrupted the ability of SH3YL1 to promote Dock4-mediated cell migration. In addition, depletion of SH3YL1 in MDA-MB-231 cells suppressed cell migration. Taken together, these results provide evidence for a novel and functionally important interaction between Dock4 and SH3YL1 to promote cancer cell migration by regulating Rac1 activity.

Dock protein family in brain development and neurological disease

The family of dedicator of cytokinesis (Dock), a protein family that belongs to the atypical Rho guanine nucleotide exchange factors (GEFs) for Rac and/or Cdc42 GTPases, plays pivotal roles in various processes of brain development. To date, 11 members of Docks have been identified in the mammalian system. Emerging evidence has suggested that members of the Dock family are associated with several neurodegenerative and neuropsychiatric diseases, including Alzheimer disease and autism spectrum disorders. This review summarizes recent advances on the understanding of the roles of the Dock protein family in normal and diseased processes in the nervous system. Furthermore, interacting proteins and the molecular regulation of Docks are discussed.

Implications of Rho GTPase Signaling in Glioma Cell Invasion and Tumor Progression

Glioblastoma (GB) is the most malignant of primary adult brain tumors, characterized by a highly locally invasive cell population, as well as abundant proliferative cells, neoangiogenesis, and necrosis. Clinical intervention with chemotherapy or radiation may either promote or establish an environment for manifestation of invasive behavior. Understanding the molecular drivers of invasion in the context of glioma progression may be insightful in directing new treatments for patients with GB. Here, we review current knowledge on Rho family GTPases, their aberrant regulation in GB, and their effect on GB cell invasion and tumor progression. Rho GTPases are modulators of cell migration through effects on actin cytoskeleton rearrangement; in non-neoplastic tissue, expression and activation of Rho GTPases are normally under tight regulation. In GB, Rho GTPases are deregulated, often via hyperactivity or overexpression of their activators, Rho GEFs. Downstream effectors of Rho GTPases have been shown to promote invasiveness and, importantly, glioma cell survival. The study of aberrant Rho GTPase signaling in GB is thus an important investigation of cell invasion as well as treatment resistance and disease progression.

A shortcut from GPCR signaling to Rac-mediated actin cytoskeleton through an ELMO/DOCK complex

Chemotaxis, chemoattractant-guided directional cell migration, plays major roles in human innate immunity and in development of a model organism Dictyostelium discoideum. Human leukocytes and D. disscoideum share remarkable similarities in the molecular mechanisms that control chemotaxis. These cells use G-Protein-Coupled Receptors (GPCRs), such as chemokine receptors, to control a signaling network that carries out chemotactic gradient sensing and directs cell migration. Diverse chemokines bind to their receptors to activate small G protein Rac through an evolutionarily conserved mechanism. Elmo and Dock180 proteins form ELMO/Dock180 complexes functioning as guanine nucleotide exchange factors (GEFs) for Rac activation. However, the linkage between GPCR to Elmo/Dock180 for Rac activation that controls F-actin dynamics remained unclear. Recently, we discovered a novel function of an ELMO protein in Dictyostelium discoideum linking GPCR signaling from Gβ to actin dynamics through regulating Rac activation during chemotaxis.

Age-related guanine nucleotide exchange factor, mouse Zizimin2, induces filopodia in bone marrow-derived dendritic cells

Background

We recently isolated and identified Zizimin2 as a functional factor that is highly expressed in murine splenic germinal center B cells after immunization with T-cell-dependent antigen. Zizimin2 was revealed to be a new family member of Dock (dedicator of cytokinesis), Dock11, which is the guanine nucleotide exchange factor for Cdc42, a low-molecular-weight GTPase. However, the molecular function of Zizimin2 in acquired immunity has not been elucidated.

Results

In this study, we show that the protein expression of Zizimin2, which is also restricted to lymphoid tissues and lymphocytes, is reduced in aged mice. Over-expression of full-length Zizimin2 induced filopodial formation in 293T cells, whereas expression of CZH2 domain inhibited it. Stimulation of Fcγ receptor and Toll-like receptor 4 triggered Zizimin2 up-regulation and Cdc42 activation in bone marrow-derived dendritic cells.

Conclusions

These data suggest that Zizimin2 is an immune-related and age-regulated guanine nucleotide exchange factor, which facilitates filopodial formation through activation of Cdc42, which results in activation of cell migration.

Deconstructing signal transduction pathways that regulate the actin cytoskeleton in dendritic spines

Dendritic spines are the sites of most excitatory synapses in the central nervous system. Recent studies have shown that spines function independently of each other, and they are currently the smallest known processing units in the brain. Spines exist in an array of morphologies, and spine structure helps dictate synaptic function. Dendritic spines are rich in actin, and actin rearrangements are critical regulators of spine morphology and density. In this review, we discuss the importance of actin in regulating dendritic spine morphogenesis, and discuss the upstream signal transduction pathways that either foster or inhibit actin polymerization. The understanding of actin regulatory pathways is best conceptualized as a hierarchical network in which molecules function in discrete levels defined by their molecular distance to actin. To this end, we focus on several classes of molecules, including guanine nucleotide exchange factors, small GTPases, small GTPase effectors, and actin binding proteins. We discuss how individual proteins in these molecular classes impact spine morphogenesis, and reveal the biochemical interactions in these networks that are responsible for shaping actin polymerization. Finally, we discuss the importance of these actin regulatory pathways in neuropsychiatric disorders.

Multiple factors confer specific Cdc42 and Rac protein activation by dedicator of cytokinesis (DOCK) nucleotide exchange factors

DOCK (dedicator of cytokinesis) guanine nucleotide exchange factors (GEFs) activate the Rho-family GTPases Rac and Cdc42 to control cell migration, morphogenesis, and phagocytosis. The DOCK A and B subfamilies activate Rac, whereas the DOCK D subfamily activates Cdc42. Nucleotide exchange is catalyzed by a conserved DHR2 domain (DOCK(DHR2)). Although the molecular basis for DOCK(DHR2)-mediated GTPase activation has been elucidated through structures of a DOCK9(DHR2)-Cdc42 complex, the factors determining recognition of specific GTPases are unknown. To understand the molecular basis for DOCK-GTPase specificity, we have determined the crystal structure of DOCK2(DHR2) in complex with Rac1. DOCK2(DHR2) and DOCK9(DHR2) exhibit similar tertiary structures and homodimer interfaces and share a conserved GTPase-activating mechanism. Multiple structural differences between DOCK2(DHR2) and DOCK9(DHR2) account for their selectivity toward Rac1 and Cdc42. Key determinants of selectivity of Cdc42 and Rac for their cognate DOCK(DHR2) are a Phe or Trp residue within β3 (residue 56) and the ability of DOCK proteins to exploit differences in the GEF-induced conformational changes of switch 1 dependent on a divergent residue at position 27. DOCK proteins, therefore, differ from DH-PH GEFs that select their cognate GTPases through recognition of structural differences within the β2/β3 strands.

Ephexin4 and EphA2 mediate cell migration through a RhoG-dependent mechanism

Ephexin4 is a RhoG-specific guanine nucleotide exchange factor that interacts with the EphA2 receptor in breast cancer cells.

EphA2, a member of the Eph receptor family, is frequently overexpressed in a variety of human cancers, including breast cancers, and promotes cancer cell motility and invasion independently of its ligand ephrin stimulation. In this study, we identify Ephexin4 as a guanine nucleotide exchange factor (GEF) for RhoG that interacts with EphA2 in breast cancer cells, and knockdown and rescue experiments show that Ephexin4 acts downstream of EphA2 to promote ligand-independent breast cancer cell migration and invasion toward epidermal growth factor through activation of RhoG. The activation of RhoG recruits its effector ELMO2 and a Rac GEF Dock4 to form a complex with EphA2 at the tips of cortactin-rich protrusions in migrating breast cancer cells. In addition, the Dock4-mediated Rac activation is required for breast cancer cell migration. Our findings reveal a novel link between EphA2 and Rac activation that contributes to the cell motility and invasiveness of breast cancer cells.

Structural basis of membrane targeting by the Dock180 family of Rho family guanine exchange factors (Rho-GEFs)

The Dock180 family of atypical Rho family guanine nucleotide exchange factors (Rho-GEFs) regulate a variety of processes involving cellular or subcellular polarization, including cell migration and phagocytosis. Each contains a Dock homology region-1 (DHR-1) domain that is required to localize its GEF activity to a specific membrane compartment where levels of phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P(3)) are up-regulated by the local activity of PtdIns 3-kinase. Here we define the structural and energetic bases of phosphoinositide specificity by the DHR-1 domain of Dock1 (a GEF for Rac1), and show that DHR-1 utilizes a C2 domain scaffold and surface loops to create a basic pocket on its upper surface for recognition of the PtdIns(3,4,5)P(3) head group. The pocket has many of the characteristics of those observed in pleckstrin homology domains. We show that point mutations in the pocket that abolish phospholipid binding in vitro ablate the ability of Dock1 to induce cell polarization, and propose a model that brings together recent mechanistic and structural studies to rationalize the central role of DHR-1 in dynamic membrane targeting of the Rho-GEF activity of Dock180.

Cellular signaling of Dock family proteins in neural function

Dock180-related proteins are genetically conserved from Drosophila and C. elegans to mammals and are atypical types of guanine-nucleotide exchange factors (GEFs) for Rac and/or Cdc42 of small GTPases of the Rho family. Eleven members of the family occur in mammalian cells, each playing key roles in many aspects of essential cellular functions such as regulation of cytoskeletal organization, phagocytosis, cell migration, polarity formation, and differentiation. This review will summarize the newly accumulated findings concerning the Dock180-related proteins' molecular and cellular functions, emphasizing the roles of these proteins in neuronal cells and glial cells as well as their interactions in the central and peripheral nervous systems.

Regulation of dendrite growth by the Cdc42 activator Zizimin1/Dock9 in hippocampal neurons

Rho family small GTPases are key regulators of morphological changes in neurons. Cdc42, one of the most characterized members of the Rho family of proteins, is involved in axon and dendrite outgrowth through cytoskeletal reorganization. Recent studies have identified Zizimin1, a member of the Dock180-related family of proteins [also called CDM (Ced-5/Dock180/Myoblast city)-zizimin homology (CZH) proteins], as a specific guanine-nucleotide exchange factor (GEF) for Cdc42. However, the physiological function of Zizimin1 is totally unknown. In this study, we investigated the role of Zizimin1 in dendrite development in rat hippocampal neurons. In situ hybridization and Western blot analysis showed that Zizimin1 is strongly expressed in the developing brain including in the hippocampus and cerebral cortex in late developmental stages. Overexpression of wild-type Zizimin1 promoted dendrite growth, whereas knockdown of Zizimin1 by short hairpin RNA or expression of a mutant Zizimin1 lacking Cdc42 GEF activity suppressed dendrite growth in primary cultured rat hippocampal neurons. Both the N-terminal CZH1 domain, which is conserved among CZH proteins, and the Pleckstrin homology domain of Zizimin1 are involved in membrane localization, Cdc42 activation, and regulation of dendrite growth. Thus, these results suggest that Zizimin1 plays an important role in dendrite growth in hippocampal neurons through activation of Cdc42.

An alpha-helical extension of the ELMO1 pleckstrin homology domain mediates direct interaction to DOCK180 and is critical in Rac signaling

The mammalian DOCK180 protein belongs to an evolutionarily conserved protein family, which together with ELMO proteins, is essential for activation of Rac GTPase-dependent biological processes. Here, we have analyzed the DOCK180-ELMO1 interaction, and map direct interaction interfaces to the N-terminal 200 amino acids of DOCK180, and to the C-terminal 200 amino acids of ELMO1, comprising the ELMO1 PH domain. Structural and biochemical analysis of this PH domain reveals that it is incapable of phospholipid binding, but instead structurally resembles FERM domains. Moreover, the structure revealed an N-terminal amphiphatic alpha-helix, and point mutants of invariant hydrophobic residues in this helix disrupt ELMO1-DOCK180 complex formation. A secondary interaction between ELMO1 and DOCK180 is conferred by the DOCK180 SH3 domain and proline-rich motifs at the ELMO1 C-terminus. Mutation of both DOCK180-interaction sites on ELMO1 is required to disrupt the DOCK180-ELMO1 complex. Significantly, although this does not affect DOCK180 GEF activity toward Rac in vivo, Rac signaling is impaired, implying additional roles for ELMO in mediating intracellular Rac signaling.

Dock10, a novel CZH protein selectively induced by interleukin-4 in human B lymphocytes

The Dock or CZH proteins are a family of activators for Rho GTPase proteins. The Zizimin subfamily is composed of three members: Dock9, Dock10, and Dock11. We have identified DOCK10 as an interleukin-4 (IL4)-inducible gene in chronic lymphocytic leukemias (CLLs). Subsequently, we have obtained the full-length cDNA sequence, which encodes a 2180 amino acid protein. Dock9 (2069 amino acids) and Dock11 (2073 amino acids) share more identity between them (58%) than with Dock10 (52% and 50%, respectively). Among normal human tissues, DOCK10 and DOCK11 mRNAs were mainly expressed in peripheral blood (PB) leukocytes. Dock10 protein was expressed at similar levels in normal PB-B and PB-T cells. Dock10 protein levels were heterogeneous in CLLs. IL4 consistently increased Dock10 mRNA and protein levels in CLL and normal PB-B cells. In contrast, IL4 did not affect the levels of Dock10 expression in normal PB-T cells. IL4 neither increased DOCK9 or DOCK11 mRNA levels in CLL cells. Dock10 protein distributed in the cytoplasm and nucleus of CLL cells, and IL4 increased its expression in both cellular compartments. The rapid and distinctive induction of Dock10 expression by IL4 in CLL and normal PB-B cells suggests a role for Dock10 in IL4-induced B-cell activation. Dock10 could represent a point of convergence for IL4 signalling and small Rho GTPase function in B cells.