No abstract

Cytoplasmic dyneins, the principal microtubule minus-end-directed motor proteins of the cell, are involved in many essential cellular processes. The major form of this enzyme is a complex of at least six protein subunits, and in mammals all but one of the subunits are encoded by at least two genes. Here we review current knowledge concerning the subunits, their interactions, and their functional roles as derived from biochemical and genetic analyses. We also carried out extensive database searches to look for new genes and to clarify anomalies in the databases. Our analysis documents evolutionary relationships among the dynein subunits of mammals and other model organisms, and sheds new light on the role of this diverse group of proteins, highlighting the existence of two cytoplasmic dynein complexes with distinct cellular roles.

In migrating adherent cells such as fibroblasts and endothelial cells, the microtubule-organizing center (MTOC) reorients toward the leading edge [1-3]. MTOC reorientation repositions the Golgi toward the front of the cell [1] and contributes to directional migration [4]. The mechanism of MTOC reorientation and its relation to the formation of stabilized microtubules (MTs) in the leading edge, which occurs concomitantly with MTOC reorientation [3], is unknown. We show that serum and the serum lipid, lysophosphatidic acid (LPA), increased Cdc42 GTP levels and triggered MTOC reorientation in serum-starved wounded monolayers of 3T3 fibroblasts. Cdc42, but not Rho or Rac, was both sufficient and necessary for LPA-stimulated MTOC reorientation. MTOC reorientation was independent of Cdc42-induced changes in actin and was not blocked by cytochalasin D. Inhibition of dynein or dynactin blocked LPA- and Cdc42-stimulated MTOC reorientation. LPA also stimulates a Rho/mDia pathway that selectively stabilizes MTs in the leading edge [5, 6]; however, activators and inhibitors of MTOC reorientation and MT stabilization showed that each response was regulated independently. These results establish an LPA/Cdc42 signaling pathway that regulates MTOC reorientation in a dynein-dependent manner. MTOC reorientation and MT stabilization both act to polarize the MT array in migrating cells, yet these processes act independently and are regulated by separate Rho family GTPase-signaling pathways.

Peri-operative SARS-CoV-2 infection increases postoperative mortality. The aim of this study was to determine the optimal duration of planned delay before surgery in patients who have had SARS-CoV-2 infection. This international, multicentre, prospective cohort study included patients undergoing elective or emergency surgery during October 2020. Surgical patients with pre-operative SARS-CoV-2 infection were compared with those without previous SARS-CoV-2 infection. The primary outcome measure was 30-day postoperative mortality. Logistic regression models were used to calculate adjusted 30-day mortality rates stratified by time from diagnosis of SARS-CoV-2 infection to surgery. Among 140,231 patients (116 countries), 3127 patients (2.2%) had a pre-operative SARS-CoV-2 diagnosis. Adjusted 30-day mortality in patients without SARS-CoV-2 infection was 1.5% (95%CI 1.4-1.5). In patients with a pre-operative SARS-CoV-2 diagnosis, mortality was increased in patients having surgery within 0-2 weeks, 3-4 weeks and 5-6 weeks of the diagnosis (odds ratio (95%CI) 4.1 (3.3-4.8), 3.9 (2.6-5.1) and 3.6 (2.0-5.2), respectively). Surgery performed ≥ 7 weeks after SARS-CoV-2 diagnosis was associated with a similar mortality risk to baseline (odds ratio (95%CI) 1.5 (0.9-2.1)). After a ≥ 7 week delay in undertaking surgery following SARS-CoV-2 infection, patients with ongoing symptoms had a higher mortality than patients whose symptoms had resolved or who had been asymptomatic (6.0% (95%CI 3.2-8.7) vs. 2.4% (95%CI 1.4-3.4) vs. 1.3% (95%CI 0.6-2.0), respectively). Where possible, surgery should be delayed for at least 7 weeks following SARS-CoV-2 infection. Patients with ongoing symptoms ≥ 7 weeks from diagnosis may benefit from further delay.

No abstract

Modified viruses are used as gene transfer vectors because of their ability to transfer genetic material efficiently to the nucleus of a target cell. To better understand intracellular translocation of adenovirus serotype 5 (Ad), fluorophores were covalently conjugated to Ad capsids, and movement of fluorescent Ad within the cytoplasm was observed during the first hour of infection of a human lung epithelial carcinoma cell line (A549). Ad translocation was characterized with respect to its ability to achieve nuclear envelope localization as well as directed movement in the cytoplasm. Whereas Ad achieved efficient nuclear localization 60 min after infection of A549 cells under control conditions, depolymerization of the microtubule cytoskeleton by addition of 25 microM nocodazole reversibly inhibited development of nuclear localization. In contrast, depolymerization of microfilaments by addition of 1 microM cytochalasin D had no effect on nuclear localization. Direct video observation of Ad motility showed that nocodazole, but not cytochalasin D, caused a reversible decrease in rapid linear translocations of Ad in the cytoplasm of A549 cells. Microinjection of function-blocking antibodies against the microtubule-dependent motor protein, cytoplasmic dynein, but not kinesin, blocked nuclear localization of Ad, consistent with net minus end-directed motility indicated by accumulation of Ad at mitotic spindles. Fluorescence ratio imaging revealed a neutral pH in the environment of translocating Ad, leading to a model in which the interaction of Ad with an intact microtubule cytoskeleton and functional cytoplasmic dynein occurs after escape from endosomes and is a necessary prerequisite to nuclear localization of adenovirus serotype 5.

Kinesin was extensively purified from bovine brain cytosol by a microtubule-binding step in the presence of 5'-adenylyl imidodiphosphate (AMP-PNP), followed by gel filtration chromatography and sucrose gradient ultracentrifugation. The products consistently contained 124,000 (124K) and 64,000 (64K) dalton polypeptides. These two polypeptides appear to represent heavy and light chains of kinesin, respectively, because they copurified on sucrose gradients to a constant and equimolar stoichiometry and bound stably to microtubules in the presence of AMP-PNP but not ATP. The mobilities of 124K and 64K in sodium dodecyl sulfate-polyacrylamide gels under reducing conditions were the same as under nonreducing conditions. A diffusion coefficient of (2.24 +/- 0.21) X 10(-7) cm2 s-1 and a sedimentation coefficient of (9.56 +/- 0.34) X 10(-13) s were determined for native kinesin by gel filtration and sucrose gradient ultracentrifugation, respectively. These values were used to calculate a native molecular weight of about 379,000 and suggest that kinesin has an axial ratio of approximately 20. Extensively purified kinesin exhibited microtubule-activated ATPase activity, and only the 124K subunit incorporated ATP in photoaffinity labeling experiments using [32P]ATP. Collectively, these data favor the interpretation that bovine brain kinesin is a highly elongated, microtubule-activated ATPase comprising two subunits each of 124,000 and 64,000 daltons, that the subunits are not linked to one another by disulfide bonds, and that the heavy chains are the ATP-binding subunits.

Abstract. Kinesin, a microtubule-activated ATPase and putative motor protein for the transport of membrane-bounded organelles along microtubules, was purified from bovine brain and used as an immunogen for the production of murine monoclonal antibodies. Hybridoma lines that secreted five distinct antikinesin IgGs were cloned. Three of the antibodies reacted on immunoblots with the 124-kD heavy chain of kinesin, while the other two antibodies recognized the 64-kD light chain. When used for immunofluorescence microscopy, the antibodies stained punctate, cytoplasmic structures in a variety of cultured mammalian cell types. Consistent with the identification of these structures as membrane-bounded organelles was the observation that cells which had been extracted with Triton X-100 before fixation contained little or no immunoreactive material. Staining of microtubules in the interphase cytoplasm or mitotic spindle was never observed, nor were associated structures, such as centrosomes and primary cilia, labeled by any of the antibodies, Nevertheless, in double-labeling experiments using antibodies to kinesin and tubulin, kinesincontaining particles were most abundant in regions where microtubules were most highly concentrated and the particles often appeared to be aligned on microtubules. These results constitute the first direct evidence for the association of kinesin with membrane-bounded organelles, and suggest a molecular mechanism for organelle motility based on transient interactions of organelle-bound kinesin with the microtubule surface.