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Francis A Barr

Publications and source records attributed to Francis A Barr.

At least 19 recordsLinked to original sources
PubMed2006

Cooperation between mitotic kinesins controls the late stages of cytokinesis.

Cell division is regulated by protein kinases of the Cdk, Polo, and Aurora families. Although it has long been established that temporal control is central to the coordinated action of these kinases, the importance of spatial regulation has only recently been appreciated and is still poorly understood. The kinesin-6 family motor protein MKlp1 is a key regulator of cytokinesis and an ideal substrate for studying spatially regulated protein-phosphorylation events. MKlp1 is negatively regulated by Cdk1 phosphorylation during metaphase and becomes activated in anaphase when cleavage-furrow assembly commences. Aurora B phosphorylates MKlp1 during anaphase and is required for its function in cytokinesis. Another kinesin-6 family motor, MKlp2, mediates the relocation of Aurora B from the centromeres to the central spindle at the onset of anaphase. We now demonstrate that this process is required for the phosphorylation of MKlp1 at S911, an Aurora B consensus site overlapping a bipartite nuclear localization sequence (NLS). MKlp1(S911A) targets to the central spindle but is prematurely imported into the nucleus and fails to support cytokinesis. Spatial restriction of Aurora B to the central spindle by MKlp2 therefore regulates MKlp1 during cytokinesis in human cells.

Aurora Kinase B↗
PubMed2006

KIF14 and citron kinase act together to promote efficient cytokinesis.

Multiple mitotic kinesins and microtubule-associated proteins (MAPs) act in concert to direct cytokinesis (Glotzer, M. 2005. Science. 307:1735-1739). In anaphase cells, many of these proteins associate with an antiparallel array of microtubules termed the central spindle. The MAP and microtubule-bundling protein PRC1 (protein-regulating cytokinesis 1) is one of the key molecules required for the integrity of this structure (Jiang, W., G. Jimenez, N.J. Wells, T.J. Hope, G.M. Wahl, T. Hunter, and R. Fukunaga. 1998. Mol. Cell. 2:877-885; Mollinari, C., J.P. Kleman, W. Jiang, G. Schoehn, T. Hunter, and R.L. Margolis. 2002. J. Cell Biol. 157:1175-1186). In this study, we identify an interaction between endogenous PRC1 and the previously uncharacterized kinesin KIF14 as well as other mitotic kinesins (MKlp1/CHO1, MKlp2, and KIF4) with known functions in cytokinesis (Hill, E., M. Clarke, and F.A. Barr. 2000. EMBO J. 19:5711-5719; Matuliene, J., and R. Kuriyama. 2002. Mol. Biol. Cell. 13:1832-1845; Kurasawa, Y., W.C. Earnshaw, Y. Mochizuki, N. Dohmae, and K. Todokoro. 2004. EMBO J. 23:3237-3248). We find that KIF14 targets to the central spindle via its interaction with PRC1 and has an essential function in cytokinesis. In KIF14-depleted cells, citron kinase but not other components of the central spindle and cleavage furrow fail to localize. Furthermore, the localization of KIF14 and citron kinase to the central spindle and midbody is codependent, and they form a complex depending on the activation state of citron kinase. Contrary to a previous study (Di Cunto, F., S. Imarisio, E. Hirsch, V. Broccoli, A. Bulfone, A. Migheli, C. Atzori, E. Turco, R. Triolo, G.P. Dotto, et al. 2000. Neuron. 28:115-127), we find a general requirement for citron kinase in human cell division. Together, these findings identify a novel pathway required for efficient cytokinesis.

Binding Sites↗
PubMed2005

Phosphorylation of Nlp by Plk1 negatively regulates its dynein-dynactin-dependent targeting to the centrosome.

When cells enter mitosis the microtubule (MT) network undergoes a profound rearrangement, in part due to alterations in the MT nucleating and anchoring properties of the centrosome. Ninein and the ninein-like protein (Nlp) are centrosomal proteins involved in MT organisation in interphase cells. We show that the overexpression of these two proteins induces the fragmentation of the Golgi, and causes lysosomes to disperse toward the cell periphery. The ability of Nlp and ninein to perturb the cytoplasmic distribution of these organelles depends on their ability to interact with the dynein-dynactin motor complex. Our data also indicate that dynactin is required for the targeting of Nlp and ninein to the centrosome. Furthermore, phosphorylation of Nlp by the polo-like kinase 1 (Plk1) negatively regulates its association with dynactin. These findings uncover a mechanism through which Plk1 helps to coordinate changes in MT organisation with cell cycle progression, by controlling the dynein-dynactin-dependent transport of centrosomal proteins.

Cell Cycle Proteins↗
PubMed2005

Mitogen-inducible gene 6 is an endogenous inhibitor of HGF/Met-induced cell migration and neurite growth.

Hepatocyte growth factor (HGF)/Met signaling controls cell migration, growth and differentiation in several embryonic organs and is implicated in human cancer. The physiologic mechanisms that attenuate Met signaling are not well understood. Here we report a mechanism by which mitogen-inducible gene 6 (Mig6; also called Gene 33 and receptor-associated late transducer) negatively regulates HGF/Met-induced cell migration. The effect is observed by Mig6 overexpression and is reversed by Mig6 small interfering RNA knock-down experiments; this indicates that endogenous Mig6 is part of a mechanism that inhibits Met signaling. Mig6 functions in cells of hepatic origin and in neurons, which suggests a role for Mig6 in different cell lineages. Mechanistically, Mig6 requires an intact Cdc42/Rac interactive binding site to exert its inhibitory action, which suggests that Mig6 acts, at least in part, distally from Met, possibly by inhibiting Rho-like GTPases. Because Mig6 also is induced by HGF stimulation, our results suggest that Mig6 is part of a negative feedback loop that attenuates Met functions in different contexts and cell types.

Adaptor Proteins, Signal Transducing↗
PubMed2005

A GTPase-activating protein controls Rab5 function in endocytic trafficking.

Rab-family GTPases are conserved regulators of membrane trafficking that cycle between inactive GDP-bound and activated GTP-bound states. A key determinant of Rab function is the lifetime of the GTP-bound state. As Rabs have a low intrinsic rate of GTP hydrolysis, this process is under the control of GTP-hydrolysis-activating proteins (GAPs). Due to the large number of Rabs and GAPs that are encoded by the human genome, it has proven difficult to assign specific functional relationships to these proteins. Here, we identify a Rab5-specific GAP (RabGAP-5), and show that RN-Tre (previously described as a Rab5 GAP) acts on Rab41. RabGAP-5 overexpression triggers a loss of the Rab5 effector EEA1 from endosomes and blocks endocytic trafficking. By contrast, depletion of RabGAP-5 results in increased endosome size, more endosome-associated EEA1, and disrupts the trafficking of EGF and LAMP1. RabGAP-5 therefore limits the amount of activated Rab5, and thereby regulates trafficking through endosomes.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Convergence of cell cycle regulation and growth factor signals on GRASP65.

Together with other Golgi matrix components, GRASP65 contributes to the stacking of Golgi cisternae in interphase cells. During mitosis, GRASP65 is heavily phosphorylated, and in turn, cisternal stacking is inhibited leading to the breakdown of the Golgi apparatus. Here we show that GRASP65 is phosphorylated on serine 277 in interphase cells, and this is strongly enhanced in response to the addition of serum or epidermal growth factor. This is directly mediated by ERK suggesting that GRASP65 has some role in growth factor signal transduction. Phosphorylation of Ser-277 is also dramatically increased during mitosis, however this is mediated by Cdk1 and not by ERK. The microinjection of recombinant GRASP65 without N-terminal myristoylation or a peptide fragment containing Ser-277 into the cytosol of normal rat kidney cells inhibits passage through mitosis. This effect is abolished when Ser-277 is replaced with alanine suggesting the phosphorylation of Ser-277 plays an important role in cell cycle regulation. The convergence of cell cycle regulation and growth factor signals on GRASP65 Ser-277 suggests that GRASP65 may function as a signal integrator controlling the cell growth.

Amino Acid Sequence↗
PubMed2005

Golgi positioning: are we looking at the right MAP?

One of the characteristics of the mammalian Golgi is its position adjacent to the nucleus. This characteristic is maintained through the action of the microtubule (MT) minus end-directed motor dynein and MT-associated proteins (MAPs). Recent findings suggest that GMAP-210, a member of the golgin family of proteins, may help to link Golgi membranes and vesicles with the MT cytoskeleton. However, there are good grounds to doubt that either GMAP-210 or its yeast homologue Rud3p is a MAP. Instead, they appear to function in vesicle trafficking events at the Golgi together with the GTPase ARF1 and a small membrane protein, Erv14. As such, the interesting question of how the Golgi interacts with MTs may well remain open to further investigation.

ADP-Ribosylation Factor 1↗
PubMed2005

Golgins and GTPases, giving identity and structure to the Golgi apparatus.

In this review we will focus on the recent advances in how coiled-coil proteins of the golgin family give identity and structure to the Golgi apparatus in animal cells. A number of recent studies reveal a common theme for the targeting of golgins containing the ARL-binding GRIP domain, and the related ARF-binding GRAB domain. Similarly, other golgins such as the vesicle tethering factor p115 and Bicaudal-D are targeted by the Rab GTPases, Rab1 and Rab6, respectively. Together golgins and their regulatory GTPases form a complex network, commonly known as the Golgi matrix, which organizes Golgi membranes and regulates membrane trafficking.

Animals↗
PubMed2005

Plk1 docking to GRASP65 phosphorylated by Cdk1 suggests a mechanism for Golgi checkpoint signalling.

GRASP65, a structural protein of the Golgi apparatus, has been linked to the sensing of Golgi structure and the integration of this information with the control of mitotic entry in the form of a Golgi checkpoint. We show that Cdk1-cyclin B is the major kinase phosphorylating GRASP65 in mitosis, and that phosphorylated GRASP65 interacts with the polo box domain of the polo-like kinase Plk1. GRASP65 is phosphorylated in its C-terminal domain at four consensus sites by Cdk1-cyclin B, and mutation of these residues to alanine essentially abolishes both mitotic phosphorylation and Plk1 binding. Expression of the wild-type GRASP65 C-terminus but not the phosphorylation defective mutant in normal rat kidney cells causes a delay but not the block in mitotic entry expected if this were a true cell cycle checkpoint. These findings identify a Plk1-dependent signalling mechanism potentially linking Golgi structure and cell cycle control, but suggest that this may not be a cell cycle checkpoint in the classical sense.

Amino Acid Sequence↗
PubMed2005

Purification and functional interactions of GRASP55 with Rab2.

GRASP55 is a member of the GRASP family of peripheral membrane proteins thought to contribute to the organization of the Golgi apparatus. GRASPs are typically found in complex with coiled-coil protein, termed golgins, which interact with specific GTPases of the RAB family. Here I will describe the purification of native GRASP55 complexes from Golgi membranes, and the comparison with the related GRASP65 complex, standard methods for the analysis of interactions between GRASPs, golgins, and Rab GTPases using yeast two-hybrid analysis and protein biochemistry with native and recombinant proteins are also described.

Animals↗
PubMed2005

Assay and properties of rab6 interaction with dynein-dynactin complexes.

RAB GTPases help to maintain the fidelity of membrane trafficking events by recruiting cytosolic tethering and motility factors to vesicle and organelle membranes. In the case of Rab6, it recruits the dynein-dynaction complex to Golgi-associated vesicles via an adaptor protein of the Bicaudal-D family. Here we describe methods for the identification of Rab6-binding partners in cell extracts. We then focus on the biochemical analysis of interactions with the dynein-dynactin complex and the adaptor proteins Bicaudal-D1 and -D2. Standard protocols for yeast two-hybrid analysis, and biochemical assays for the analysis of the interactions between Rab6, Bicaudal-D, and the subunits of the dynein-dynactin complex are outlined.

Dynactin Complex↗
PubMed2005

Assay and functional properties of Rabkinesin-6/Rab6-KIFL/MKlp2 in cytokinesis.

Here we describe methods for the characterization of the kinesin-9 family motor protein Rabkinesin-6/Rab6-KIFL/MKlp2 in cytokinesis. Here we outline biochemical assays for studying the interaction of Rabkinesin-6/Rab6-KIFL/MKlp2 with microtubules, and its regulation and interaction with the mitotic polo-like kinase 1 using recombinant proteins expressed in and purified from insect cells. Protocols for the in vivo functional analysis of Rabkinesin-6/Rab6-KIFL/MKlp2 using depletion with small interfering RNA duplexes are described.

Animals↗
PubMed2005

Kinases regulating Golgi apparatus structure and function.

Protein kinases control Golgi function in both mitotic and interphase cells. In mitosis, phosphorylation of structural proteins by Cdk1 (cyclin-dependent kinase 1)-cyclin B, Polo-like and mitogen-activated protein kinases underlie changes in Golgi reorganization during cell division. While in interphase, signalling pathways that are associated with the Golgi control secretory function through a variety of mechanisms. Some of these, notably those involving protein kinase D and Ste20 family kinases, are also relevant for the establishment and maintenance of cell polarization and migration.

Animals↗
PubMed2004

Relocation of Aurora B from centromeres to the central spindle at the metaphase to anaphase transition requires MKlp2.

Mitotic kinases of the Polo and Aurora families are key regulators of chromosome segregation and cytokinesis. Here, we have investigated the role of MKlp1 and MKlp2, two vertebrate mitotic kinesins essential for cytokinesis, in the spatial regulation of the Aurora B kinase. Previously, we have demonstrated that MKlp2 recruits Polo-like kinase 1 (Plk1) to the central spindle in anaphase. We now find that in MKlp2 but not MKlp1-depleted cells the Aurora B-INCENP complex remains at the centromeres and fails to relocate to the central spindle. MKlp2 exerts dual control over Aurora B localization, because it is a binding partner for Aurora B, and furthermore for the phosphatase Cdc14A. Cdc14A can dephosphorylate INCENP and may contribute to its relocation to the central spindle in anaphase. We propose that MKlp2 is involved in the localization of Plk1, Aurora B, and Cdc14A to the central spindle during anaphase, and that the integration of signaling by these proteins is necessary for proper cytokinesis.

Anaphase↗
PubMed2004

Golgi inheritance: shaken but not stirred.

Our view of what happens to the Golgi and ER during mitosis in mammalian cells has been shaken once more. Rather than the Golgi contents being recycled through, or mixed with the ER, two recent studies taking complementary approaches, find that the contents of these organelles remain separate throughout mitosis.

Animals↗
PubMed2004

YSK1 is activated by the Golgi matrix protein GM130 and plays a role in cell migration through its substrate 14-3-3zeta.

The Golgi apparatus has long been suggested to be important for directing secretion to specific sites on the plasma membrane in response to extracellular signaling events. However, the mechanisms by which signaling events are coordinated with Golgi apparatus function remain poorly understood. Here, we identify a scaffolding function for the Golgi matrix protein GM130 that sheds light on how such signaling events may be regulated. We show that the mammalian Ste20 kinases YSK1 and MST4 target to the Golgi apparatus via the Golgi matrix protein GM130. In addition, GM130 binding activates these kinases by promoting autophosphorylation of a conserved threonine within the T-loop. Interference with YSK1 function perturbs perinuclear Golgi organization, cell migration, and invasion into type I collagen. A biochemical screen identifies 14-3-3zeta as a specific substrate for YSK1 that localizes to the Golgi apparatus, and potentially links YSK1 signaling at the Golgi apparatus with protein transport events, cell adhesion, and polarity complexes important for cell migration.

14-3-3 Proteins↗
PubMed2004

Membrane fusion: caught in a trap.

SNAREs are small coiled-coil proteins required for specific membrane fusion events in eukaryotic cells. Recent evidence points to the existence of an inhibitory class of SNAREs, i-SNAREs, which prevent incorrect fusions from occurring, adding a further layer of regulation to the process of membrane docking and fusion.

Golgi Apparatus↗