Impaired autophagic flux and dedifferentiation in podocytes lacking Asah1 gene: Role of lysosomal TRPML1 channel.

Podocytopathy and associated nephrotic syndrome have been reported in a mouse strain (Asah1fl/fl/Podocre) with a podocyte-specific deletion of α subunit (the main catalytic subunit) of acid ceramidase (Ac). However, the pathogenesis of podocytopathy in these mice remains unclear. The present study tested whether Ac deficiency impairs autophagic flux in podocytes through blockade of transient receptor potential mucolipin 1 (TRPML1) channel as a potential pathogenic mechanism of podocytopathy in Asah1fl/fl/Podocre mice. We first demonstrated that impairment of autophagic flux occurred in podocytes lacking Asah1 gene, which was evidenced by autophagosome accumulation and reduced lysosome-autophagosome interaction. TRPML1 channel agonists recovered lysosome-autophagosome interaction and attenuated autophagosome accumulation in podocytes from Asah1fl/fl/Podocre mice, while TRPML1 channel inhibitors impaired autophagic flux in WT/WT podocytes and worsened autophagic deficiency in podocytes lacking Asah1 gene. The effects of TRPML1 channel agonist were blocked by dynein inhibitors, indicating a critical role of dynein activity in the control of lysosome movement due to TRPML1 channel-mediated Ca2+ release. It was also found that there is an enhanced phenotypic transition to dedifferentiation status in podocytes lacking Asah1 gene in vitro and in vivo. Such podocyte phenotypic transition was inhibited by TRPML1 channel agonists but enhanced by TRPML1 channel inhibitors. Moreover, we found that TRPML1 gene silencing induced autophagosome accumulation and dedifferentiation in podocytes. Based on these results, we conclude that Ac activity is essential for autophagic flux and maintenance of differentiated status of podocytes. Dysfunction or deficiency of Ac may impair autophagic flux and induce podocyte dedifferentiation, which may be an important pathogenic mechanism of podocytopathy and associated nephrotic syndrome.

The role of DYNLT3 in breast cancer proliferation, migration, and invasion via epithelial-to-mesenchymal transition.

PURPOSE: DYNLT3 is identified as an age-related gene. Nevertheless, the specific mechanism of its carcinogenesis in breast tumor has not been clarified. This research aims to elucidate the role and the underlying molecular pathways of DYNLT3 on breast cancer tumorigenesis. METHODS: The differential expression of DYNLT3 among breast cancer, breast fibroids, and normal tissues, as well as in various breast cancer cell lines were detected by immunohistochemical staining, real-time quantitative reverse transcription-PCR and Western blotting, respectively. Additionally, the role of DYNLT3 on cell viability and proliferation were observed through cell counting kit-8, bromodeoxyuridine, and colony formation experiments. Migratory and invasive abilities was envaulted by wound healing and Transwell methods. Apoptotic cells rate was examined by flow cytometry. Furthermore, nude mice xenograft models were established to confirm the role of DYNLT3 in tumor formation in vivo. RESULTS: DYNLT3 expression was highly rising in both breast cancer tissues and cells. DYNLT3 knockdown obviously suppressed cell growth, migration and invasion, and induced cell apoptosis in MDA-MB-231 and MCF-7 breast cancer cells. The overexpression of DYNLT3 exerted the opposite effect in MDA-MB-231 cells. Moreover, DYNLT3 knockdown inhibited tumor formation in vivo. Mechanistically, an elevation of N-cadherin and vimentin levels and a decline of E-cadherin were observed when DYNLT3 was upregulated, which was reversed when DYNLT3 knockdown was performed. CONCLUSION: DYNLT3 may function as a tumor-promotor of age-associated breast cancer, which is expected to provide experimental basis for new treatment options.

Dynein Coordinates ß2-Adrenoceptor-Mediated Relaxation in Normotensive and Hypertensive Rat Mesenteric Arteries.

BACKGROUND: The voltage-gated potassium channel (Kv)7.4 and Kv7.5 channels contribute to the ß-adrenoceptor-mediated vasodilatation. In arteries from hypertensive rodents, the Kv7.4 channel is downregulated and function attenuated, which contributes to the reduced ß-adrenoceptor-mediated vasodilatation observed in these arteries. Recently, we showed that disruption of the microtubule network, with colchicine, or inhibition of the microtubule motor protein, dynein, with ciliobrevin D, enhanced the membrane abundance and function of Kv7.4 channels in rat mesenteric arteries. This study aimed to determine whether these pharmacological compounds can improve Kv7.4 function in third-order mesenteric arteries from the spontaneously hypertensive rat, thereby restoring the ß-adrenoceptor-mediated vasodilatation. METHODS: Wire and intravital myography was performed on normotensive and hypertensive male rat mesenteric arteries and immunostaining was performed on isolated smooth muscle cells from the same arteries. RESULTS: Using wire and intravital microscopy, we show that ciliobrevin D enhanced the ß-adrenoceptor-mediated vasodilatation by isoprenaline. This effect was inhibited partially by the Kv7 channel blocker linopirdine and was dependent on an increased functional contribution of the ß2-adrenoceptor to the isoprenaline-mediated relaxation. In mesenteric arteries from the spontaneously hypertensive rat, ciliobrevin D and colchicine both improved the isoprenaline-mediated vasorelaxation and relaxation to the Kv7.2 -7.5 activator, ML213. Immunostaining confirmed ciliobrevin D enhanced the membrane abundance of Kv7.4. As well as an increase in the function of Kv7.4, the functional changes were associated with an increase in the contribution of ß2-adrenoceptor following isoprenaline treatment. Immunostaining experiments showed ciliobrevin D prevented isoprenaline-mediated internalizationof the ß2-adrenoceptor. CONCLUSIONS: Overall, these data show that colchicine and ciliobrevin D can induce a ß2-adrenoceptor-mediated vasodilatation in arteries from the spontaneously hypertensive rat as well as reinstating Kv7.4 channel function.

Molecular motors: the driving force behind mammalian left-right development.

The molecular motors dynein and kinesin are large protein complexes that convert the energy generated by ATP hydrolysis into directional movement along the microtubule cytoskeleton. They are required for a myriad of cellular processes, including mitotic spindle movement, axonal and vesicular transport, and ciliary beating. Recently, it has been shown that, in addition, they have a unique role during embryonic patterning: they are required to orient and establish the left-right axis in early vertebrate development.

Directional instability of microtubule transport in the presence of kinesin and dynein, two opposite polarity motor proteins.

Kinesin and dynein are motor proteins that move in opposite directions along microtubules. In this study, we examine the consequences of having kinesin and dynein (ciliary outer arm or cytoplasmic) bound to glass surfaces interacting with the same microtubule in vitro. Although one might expect a balance of opposing forces to produce little or no net movement, we find instead that microtubules move unidirectionally for several microns (corresponding to hundreds of ATPase cycles by a motor) but continually switch between kinesin-directed and dynein-directed transport. The velocities in the plus-end (0.2-0.3 microns/s) and minus-end (3.5-4 microns/s) directions were approximately half those produced by kinesin (0.5 microns/s) and ciliary dynein (6.7 microns/s) alone, indicating that the motors not contributing to movement can interact with and impose a drag upon the microtubule. By comparing two dyneins with different duty ratios (percentage of time spent in a strongly bound state during the ATPase cycle) and varying the nucleotide conditions, we show that the microtubule attachment times of the two opposing motors as well as their relative numbers determine which motor predominates in this assay. Together, these findings are consistent with a model in which kinesin-induced movement of a microtubule induces a negative strain in attached dyneins which causes them to dissociate before entering a force-generating state (and vice versa); reversals in the direction of transport may require the temporary dissociation of the transporting motor from the microtubule. The bidirectional movements described here are also remarkably similar to the back-and-forth movements of chromosomes during mitosis and membrane vesicles in fibroblasts. These results suggest that the underlying mechanical properties of motor proteins, at least in part, may be responsible for reversals in microtubule-based transport observed in cells.

Cytoplasmic dynein and dynactin are required for the transport of microtubules into the axon.

Previous work from our laboratory suggested that microtubules are released from the neuronal centrosome and then transported into the axon (Ahmad, F.J., and P.W. Baas. 1995. J. Cell Sci. 108: 2761-2769). In these studies, cultured sympathetic neurons were treated with nocodazole to depolymerize most of their microtubule polymer, rinsed free of the drug for a few minutes to permit a burst of microtubule assembly from the centrosome, and then exposed to nanomolar levels of vinblastine to suppress further microtubule assembly from occurring. Over time, the microtubules appeared first near the centrosome, then dispersed throughout the cytoplasm, and finally concentrated beneath the periphery of the cell body and within developing axons. In the present study, we microinjected fluorescent tubulin into the neurons at the time of the vinblastine treatment. Fluorescent tubulin was not detected in the microtubules over the time frame of the experiment, confirming that the redistribution of microtubules observed with the experimental regime reflects microtubule transport rather than microtubule assembly. To determine whether cytoplasmic dynein is the motor protein that drives this transport, we experimentally increased the levels of the dynamitin subunit of dynactin within the neurons. Dynactin, a complex of proteins that mediates the interaction of cytoplasmic dynein and its cargo, dissociates under these conditions, resulting in a cessation of all functions of the motor tested to date (Echeverri, C.J., B.M. Paschal, K.T. Vaughan, and R.B. Vallee. 1996. J. Cell Biol. 132: 617-633). In the presence of excess dynamitin, the microtubules did not show the outward progression but instead remained near the centrosome or dispersed throughout the cytoplasm. On the basis of these results, we conclude that cytoplasmic dynein and dynactin are essential for the transport of microtubules from the centrosome into the axon.

Apoptotic cleavage of cytoplasmic dynein intermediate chain and p150(Glued) stops dynein-dependent membrane motility.

Cytoplasmic dynein is the major minus end-directed microtubule motor in animal cells, and associates with many of its cargoes in conjunction with the dynactin complex. Interaction between cytoplasmic dynein and dynactin is mediated by the binding of cytoplasmic dynein intermediate chains (CD-IC) to the dynactin subunit, p150(Glued). We have found that both CD-IC and p150(Glued) are cleaved by caspases during apoptosis in cultured mammalian cells and in Xenopus egg extracts. Xenopus CD-IC is rapidly cleaved at a conserved aspartic acid residue adjacent to its NH(2)-terminal p150(Glued) binding domain, resulting in loss of the otherwise intact cytoplasmic dynein complex from membranes. Cleavage of CD-IC and p150(Glued) in apoptotic Xenopus egg extracts causes the cessation of cytoplasmic dynein--driven endoplasmic reticulum movement. Motility of apoptotic membranes is restored by recruitment of intact cytoplasmic dynein and dynactin from control cytosol, or from apoptotic cytosol supplemented with purified cytoplasmic dynein--dynactin, demonstrating the dynamic nature of the association of cytoplasmic dynein and dynactin with their membrane cargo.

Calcium signaling is involved in dynein-dependent microtubule organization.

The microtubule cytoskeleton supports cellular morphogenesis and polar growth, but the underlying mechanisms are not understood. In a screen for morphology mutants defective in microtubule organization in the fungus Ustilago maydis, we identified eca1 that encodes a sarcoplasmic/endoplasmic calcium ATPase. Eca1 resides in the endoplasmic reticulum and restores growth of a yeast mutant defective in calcium homeostasis. Deletion of eca1 resulted in elevated cytosolic calcium levels and a severe growth and morphology defect. While F-actin and myosin V distribution is unaffected, Deltaeca1 mutants contain longer and disorganized microtubules that show increased rescue and reduced catastrophe frequencies. Morphology can be restored by inhibition of Ca(2+)/calmodulin-dependent kinases or destabilizing microtubules, indicating that calcium-dependent alterations in dynamic instability are a major cause of the growth defect. Interestingly, dynein mutants show virtually identical changes in microtubule dynamics and dynein-dependent ER motility was drastically decreased in Deltaeca1. This indicates a connection between calcium signaling, dynein, and microtubule organization in morphogenesis of U. maydis.

The effect of acrylamide and other sulfhydryl alkylators on the ability of dynein and kinesin to translocate microtubules in vitro.

Chronic exposure to acrylamide leads to a dying-back axonopathy afflicting the longest axons of all tested mammalian and avian species. Prior to the onset of acrylamide-induced axonal degeneration, alterations in axonal fast transport have been consistently reported to be more severe for the retrograde than the anterograde direction. The putative retrograde motor protein, dynein, is compromised by exposure to the sulfhydryl-alkylating agent N-ethylmaleimide (NEM) at concentrations far below those required to inactivate kinesin, the putative anterograde motor protein. Since acrylamide is capable of alkylating protein sulfhydryl moieties, we tested whether a direct exposure of purified kinesin or dynein to acrylamide would result in an impairment of either enzyme's ability to translocate microtubules. Motor activity was assayed by sequentially adsorbing either kinesin or dynein to acid-washed coverslips, treating with an alkylating agent or control solution, adding microtubules and ATP, and finally imaging and quantifying the binding and gliding of microtubules using video-enhanced differential interference contrast (VE-DIC) microscopy. In comparison to controls, incubation of dynein with NEM, ethacrynic acid, or iodoacetic acid resulted in dose-dependent decreases in the amount and rate of microtubule gliding, but increases in irreversible high-affinity microtubule binding. In contrast, exposure of dynein to 1-100 mM solutions of acrylamide did not significantly alter either the binding or gliding of microtubules (a molar/hour exposure to acrylamide equivalent to 50 times that which causes retrograde transport deficits in vivo). Likewise, kinesin motility parameters were not significantly affected by acrylamide concentrations up to 100 mM while NEM solutions > 100 microM led to significant losses in the ability of kinesin to bind MT. These data indicate that acrylamide does not significantly interact with bound (adsorbed) kinesin or dynein, implying that the mechanism by which acrylamide interferes with fast axonal transport in vivo is by interaction with other factor(s) that govern the movement of vesicles.

Modification of flagellar waveform and adenosine triphosphatase activity in reactivated sea-urchin sperm treated with N-ethylmaleimide.

Treatment of demembranated sea-urchin sperm for 1-2 min with 10 microM-N-ethylmaleimide (Mal-NEt) at pH 8.0 prior to reactivation with 1 mM-ATP causes the asymmetry of the flagellar waveform to become desensitized to the presence or absence of Ca2+ in the reactivating medium. In such sperm, changes in concentration of free Ca2+ between 10(-7) M and 10(-3) M have no effect on the asymmetry of the waveforms as measured by the turning rate of the sperm in radians per beat cycle, while the beat frequency and the propulsive efficiency of the waves remain unchanged from the values observed in control preparations not treated with MalNEt. A somewhat more prolonged treatment with MalNEt causes a progressive decrease in the bend angles of the flagellar waves, while the beat frequency and the wavelength still remain largely unchanged. Further extension of the treatment with MalNEt causes complete loss of motility. Little ATP-induced sliding of the doublet tubules is observed upon treatment with trypsin of sperm flagella that have been rendered non-motile with MalNEt. However, the preparations of solubilized dynein 1 obtained by 0.6 M-NaCl extraction of axonemes treated with MalNEt appear almost identical to those obtained from untreated axonemes, both in terms of the amount solubilized and in the specific ATPase activities of their latent and Triton-activated forms. These preparations also appear capable of restoring much of the beat frequency of dynein-1-depleted flagella. These results suggest that the observed desensitization to Ca2+ and decrease in bend angle result from the reaction of MalNEt with axonemal polypeptides that are not part of the dynein 1 particle extracted with 0.6 M-NaCl. The rate of ATP hydrolysis by demembranated sperm rendered non-motile with MalNEt remains relatively high, and it decreases about 50% when the flagella are broken by brief homogenization. This 'homogenizer-sensitive' ATPase activity appears to be derived from some flagellar regulatory mechanism, which controls the ATPase activity of intact non-motile axonemes.

Reactivation of outer-arm-depleted lung axonemes: evidence for functional differences between inner and outer dynein arms in situ.

Demembranated axonemes isolated from newt lung ciliated cells show a complex beat frequency response to varying [MgATP] and temperature [Hard and Cypher, 1992, Cell Motil. Cytoskeleton 21:187-198]. The present study was undertaken to ascertain whether the beat frequency of outer-arm-depleted newt lung axonemes is controlled in a manner similar to that of intact axonemes. Populations of demembranated ciliary axonemes were isolated by Triton X-100 extraction of lungs from the newt, Taricha granulosa. Aliquots of the demembranated axonemes were further treated with solutions containing high salt (0.375 M KC1) and 1.25 mM MgATP. This treatment resulted in the selective removal of outer dynein arms and a concomitant decrease in beat frequency to a stable level, 33-35% of control values. The effects of pH, salt concentration, nucleotides, and temperature on the beat frequency of reactivated outer-arm-depleted axonemes were ascertained and compared with those of intact axonemes. Some reactivation properties, such as nucleotide specificity, the effect of pH on beat frequency and the threshold [MgATP] required for reactivation (approximately 5 microM) were similar to those observed for intact axonemes. Other properties, such as the relationship between beat frequency and varying [MgATP] or salt concentration, differed both qualitatively and quantitatively from those of control axonemes, as did their response to temperature over the range, 5 degrees-32 degrees C. The nature of the results obtained with temperature and MgATP suggests that inner and outer dynein arms are not functionally equivalent in situ.

Inhibition of gliding movement by calcium in doublet microtubules on Tetrahymena ciliary dyneins in vitro.

We examined the effects of Ca ions on the gliding movement of Tetrahymena ciliary doublet microtubules induced by 14S or 22S dyneins in an in vitro motility assay system. The doublet microtubule appeared as circular-arc in solution, about 5 to 6 microns in length [1]. The doublet microtubules glided distal-end first on a 14S or 22S dynein-coated glass surface either clockwise or counterclockwise following the addition of ATP. The diameter of the circular path changed according to Ca concentration in the solution. Gliding velocity was from 1 to 5 microns/s. The addition of 0.1% Nonidet P-40 was necessary to induce the gliding movement on 22S dynein. This movement on 22S dynein was strongly inhibited above 0.5 mM ATP in the presence of 10(-9) M Ca, and at 0.05 to 1 mM ATP in the presence of 10(-3) M Ca. Many studies have indicated that Ca ions regulate ciliary movement [2-8] in which dyneins and doublet microtubule in the axoneme may play an essential role. The inhibition of the gliding movement of doublet microtubule on dyneins at appropriate concentrations of Ca and ATP as observed in this study may be the key for understanding Ca regulation of ciliary motility.

African swine fever virus protein p54 interacts with the microtubular motor complex through direct binding to light-chain dynein.

Dynein is a minus-end-directed microtubule-associated motor protein involved in cargo transport in the cytoplasm. African swine fever virus (ASFV), a large DNA virus, hijacks the microtubule motor complex cellular transport machinery during virus infection of the cell through direct binding of virus protein p54 to the light chain of cytoplasmic dynein (LC8). Interaction of p54 and LC8 occurs both in vitro and in cells, and the two proteins colocalize at the microtubular organizing center during viral infection. p50/dynamitin, a dominant-negative inhibitor of dynein-dynactin function, impeded ASFV infection, suggesting an essential role for dynein during virus infection. A 13-amino-acid domain of p54 was sufficient for binding to LC8, an SQT motif within this domain being critical for this binding. Direct binding of a viral structural protein to LC8, a small molecule of the dynein motor complex, could constitute a molecular mechanism for microtubule-mediated virus transport.

Enhancement of peptide antigen presentation by a second peptide.

The influence of nonstimulatory "competitor" peptides on the binding of an antigenic peptide to a major histocompatibility complex (MHC) class II molecule was investigated. Using high-performance size-exclusion chromatography and fluorescein-labeled peptides, we show that the presence of the peptides dynorphin A-(1-13) and poly(L-lysine) results in enhancement rather than inhibition of the binding of hen egg lysozyme peptide-(107-116) [HEL-(107-116)] to the detergent-solubilized mouse class II molecule IEd. In parallel, dynorphin A-(1-13) and poly(L-lysine) were found to enhance the specific activation of an IEd-restricted T-cell hybridoma by HEL-(107-116). A molecular mechanism involving an intermediate two peptide-MHC class II protein complex is proposed to explain the enhancement of peptide binding to class II molecules by an irrelevant second peptide.

Movement of nuclei.

This unit describes the first assay that reconstructs the movement of the female pronucleus in the newly fertilized frog egg. Nuclei are assembled in frog egg extracts and translocated along microtubules using the microtubule motor dynein.