Rapid and reversible tubulin tyrosination in human neutrophils stimulated by the chemotactic peptide, fMet-Leu-Phe

A novel myeloid cell marker genes related signature can indicate immune infiltration and predict prognosis of hepatocellular carcinoma: Integrated analysis of bulk and single-cell RNA sequencing

Myeloid cells are physiologically related to innate immunity and inflammation. Tumor-associated myeloid cells gained increasing interest because of their critical roles in tumor progression and anticancer immune responses in human malignancies. However, the associations between tumor-associated myeloid cell-related genes and hepatocellular carcinoma have yet to be revealed. Here, through the integrating analysis of bulk and single-cell RNA (scRNA) sequencing of public HCC samples, we developed a gene signature to investigate the role of HCC-specific myeloid signature genes in HCC patients. We firstly defined 317 myeloid cell marker genes through analyzing scRNA data of HCC from the GEO dataset. After selecting the differentially expressed genes, eleven genes were also proved prognostic. Then we built a gene signature from the TCGA cohort and verified further with the ICGC dataset by applying the LASSO Cox method. An eight genes signature (FABP5, C15orf48, PABPC1, TUBA1B, AKR1C3, NQO1, AKR1B10, SPP1) was achieved finally. Patients in the high risk group correlated with higher tumor stages and poor survival than those in the low-risk group. The risk score was proved to be an independent risk factor for prognosis. The high risk group had higher infiltrations of dendritic cells, macrophages and Tregs. And the APC co-inhibition, T cell co-inhibition pathways were also activated. Besides, the risk score positively correlated with multidrug resistance proteins. In conclusion, our myeloid cell marker genes related signature can predict patients' survival and may also indicate the levels of immune infiltration and drug resistance.

Tubulin tail sequences and post-translational modifications regulate closure of mitochondrial voltage-dependent anion channel (VDAC)

It was previously shown that tubulin dimer interaction with the mitochondrial outer membrane protein voltage-dependent anion channel (VDAC) blocks traffic through the channel and reduces oxidative metabolism and that this requires the unstructured anionic C-terminal tail peptides found on both α- and β-tubulin subunits. It was unclear whether the α- and β-tubulin tails contribute equally to VDAC blockade and what effects might be due to sequence variations in these tail peptides or to tubulin post-translational modifications, which mostly occur on the tails. The nature of the contribution of the tubulin body beyond acting as an anchor for the tails had not been clarified either. Here we present peptide-protein chimeras to address these questions. These constructs allow us to easily combine a tail peptide with different proteins or combine different tail peptides with a particular protein. The results show that a single tail grafted to an inert protein is sufficient to produce channel closure similar to that observed with tubulin. We show that the β-tail is more than an order of magnitude more potent than the α-tail and that the lower α-tail activity is largely due to the presence of a terminal tyrosine. Detyrosination activates the α-tail, and activation is reversed by the removal of the glutamic acid penultimate to the tyrosine. Nitration of tyrosine reverses the tyrosine inhibition of binding and even induces prolonged VDAC closures. Our results demonstrate that small changes in sequence or post-translational modification of the unstructured tails of tubulin result in substantial changes in VDAC closure.

Detection of the centriole tyr- or acet-tubulin changes in endothelial cells treated with thrombin using microscopic immunocytochemistry

We used electron microscopic immunocytochemistry to examine the pattern of centriolar staining for tyrosinated or acetylated alpha-tubulin in endothelial cells during short-term incubation with thrombin. Endothelial cells isolated from human aorta (HAEC) and those isolated from umbilical vein (HUVEC) displayed an increase in the intensity of centriolar staining for acet-tubulin within 1 min after thrombin addition. A decrease in the intensity of centriolar staining for tyr-tubulin was detected in HUVEC within 1 min after thrombin addition, while in HAEC centriolar staining for tyr-tubulin became less intense only 5 min later. Mother and daughter centrioles of HUVEC cells displayed different intensity of immunostaining for acet-tubulin and showed no significant variation in the number of subdistal appendages after thrombin addition. Differently, HAEC cells had the same staining pattern of mother and daughter centrioles in both thrombin-untreated and thrombin-treated cultures. A sharp increase in the number of subdistal appendages of mother centriole occurred in HAEC within 5 min of incubation with thrombin. Our findings provided the direct evidence for centrosome involvement in the ligand-mediated signaling events and showed for the first time that ligand-dependent centrosome reorganization includes the centriole per se. Furthermore, based on our observations we would like to propose that MT-nucleating/anchoring properties of the centrosome are subject to rapid regulation by external signals such as thrombin.

Localized exocytosis of primary (lysosomal) granules during phagocytosis: role of Ca2+-dependent tyrosine phosphorylation and microtubules

The uptake and killing of bacteria by human neutrophils are dependent on the fusion of secretory granules with forming phagosomes. The earliest component of exocytosis was found to precede phagosome closure, so that granular membrane constituents were detectable on the plasmalemma. We show that during phagocytosis of IgG-opsonized particles, this early secretory response is highly polarized in the case of primary granules, but less so for specific granules. The vectorial discharge of primary granules was dependent on calcium, but no evidence was found that calcium is involved in determining the polarity of exocytosis. In particular, a redistribution of endomembrane calcium stores toward forming phagosomes could not be detected. Polarized granule exocytosis was accompanied by focal tyrosine phosphorylation and actin polymerization, although the latter was not required for the response. Instead, microtubules seemed to contribute to the vectorial nature of the response. During particle ingestion, the microtubule-organizing center relocated toward forming phagosomes, and colchicine treatment altered the pattern of exocytosis, reducing its directionality. We hypothesize that the focal activation of tyrosine kinases generates localized signals that induce exocytosis in a calcium-dependent manner, and that reorientation of microtubules facilitates preferential delivery of granules toward the forming phagosome.

Human neutrophil (PMN) oxygen radical production and the cytoskeleton

Electron paramagnetic resonance (EPR) studies were conducted to examine oxygen radical generation following PMN activation by N-formyl-1-methionyl-1-leucyl-1-phenylalanine (fMLP) in the presence or absence of phalloidin and cytochalasin B (CB), agents which stabilize or disrupt f-actin, or taxol and colchicine which stabilize and disrupt microtubule cytoskeletal structures respectively. PMN oxyradical production was monitored using the spin trap 5,5-dimethyl-1-pyrroline n-oxide (DMPO). PMN when unstimulated, treated with phalloidin (10(-6)-10(-8)M), CB (10(-6)-10(-8)M), taxol (10(-6)-10(-8)M), or colchicine (10(-6)-10(-8)M), did not produce a detectable DMPO signal. Stimulation with fMLP (10(-6)M), however, resulted in a significant hydroxyl radical signal which was augmented by PMN treatment with CB (10(-6)-10(-7)M, p < 0.05) and attenuated following PMN treatment with phalloidin (10(-6)-10(-7)M, p < 0.05). Interestingly, colchicine treatment (10(-6)-10(-8)M) significantly attenuated fMLP-mediated oxyradical production, whereas taxol (10(-6)-10(-7)M) significantly increased PMN oxyradical production. These data suggest that stabilization of f-actin and disruption of microtubules attenuates the PMN oxidative burst, whereas disruption of f-actin and stabilization of microtubules increases radical production. These findings suggest cytoskeletal domain-specific contributions to PMN oxidative activity.

Immunocytochemical comparison of posttranslationally modified forms of tubulin in the vestibular end-organs of the gerbil: tyrosinated, acetylated and polyglutamylated tubulin

Specific antibodies against alpha-tubulin, acetylated alpha-tubulin, tyrosinated alpha-tubulin and polyglutamylated alpha- and beta-tubulin were used to compare the distribution of posttranslationally modified tubulin in the vestibular end-organs of the gerbil. Antibodies to acetylated tubulin labeled a dense network of microtubules in the hair cells and bundles of microtubule in the supporting cells. Nerve fibers within and below the epithelium were weakly labeled. This localization paralleled that seen with antibodies to alpha-tubulin which labeled all microtubules present in the cells. Antibodies to tyrosinated tubulin labeled networks and bundles of microtubules in both hair cells and supporting cells and in addition gave intense, diffuse labeling in the cytoplasm of both cell types. It also labeled the nerve fibers. Antibodies to polyglutamylated tubulin were localized mainly in nerve fibers, and in the calyces the labeled microtubules were found running circumferentially around the type I sensory hair cells. Thus, tyrosinated tubulin was found in the fine networks of microtubules in both the sensory and supporting cells. Acetylated tubulin was found in the dense networks and bundles of microtubules in the sensory and supporting cells, but did not colocalize with polyglutamylated tubulin, which was found predominantly in the nerve fibers. The labeling patterns for the tyrosinated tubulin and posttranslationally modified tubulins in the sensory and supporting cells of the vestibular end organs differ from that seen in the organ of Corti and may reflect differences in the stability of the microtubules and the mechanical properties of the sensory epithelium.

Stimulus-dependent alterations in macrophage microtubules: increased tubulin polymerization and detyrosination

Murine macrophage microtubules are very dynamic. The majority of the microtubules (approximately 80%) exist in a rapidly depolymerizing pool (t1/2 approximately 30 seconds). The remaining 20% of the microtubules are in a more slowly depolymerizing pool (t1/2 approximately 7 minutes). Macrophage microtubules are responsive to cell stimulation with phorbol esters; upon cell stimulation there is a rapid increase in total microtubule polymer and number. In addition there is stimulus-induced detyrosination of alpha-tubulin in macrophage microtubules that is rapid and essentially complete, occurring in all microtubules rather than a subset of microtubules. Detyrosination of the macrophage microtubules in response to phorbol esters does not confer increased stability to these microtubules, since treated cells have nocodazole-induced depolymerization kinetics similar to that in non-stimulated macrophages. Regrowth of microtubules following washout of nocodazole is also rapid. Interestingly the regrown microtubules are initially in the tyrosinated form even in the presence of phorbol ester. These experiments provide in vivo support for the model that detyrosination of alpha-tubulin occurs in polymeric tubulin while retyrosination occurs in dimeric tubulin. Macrophage microtubules also demonstrate an unusually rapid response to extracellular stimuli and thus provide a unique model system in which to examine signal transduction events and modulation of microtubules.