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PubMed1999

Expression and localisation of dynamin and syntaxin during neural development and neuromuscular synapse formation.

The expression and subcellular localisation of dynamin and syntaxin were examined during the periods of motor neuron development and neuromuscular synaptogenesis in the mouse embryo. Both dynamin and syntaxin could be detected by immunoblotting in the spinal cord at embryonic day 10 (E10; 2 days before axon outgrowth) and at all subsequent ages examined. Reverse transcription and polymerase chain reaction (RT-PCR) identified low levels of all three carboxy-terminal splicing forms of dynamin I in spinal cord from as early as E10. During the period of maturation of spinal neurons, from E10 to the first postnatal day (P0), the short carboxy-terminal splicing form of dynamin I (dynamin I*b) was up-regulated, as was dynamin III, relative to dynamin II mRNA. Syntaxin immunostaining became colocalized with the synaptic vesicle protein, SV2, at neuromuscular synapses within 12 hours of the commencement of synapse formation and throughout subsequent development. In contrast, dynamin, which is important for activity-dependent synaptic vesicle recycling and, thus, sustained neurotransmission, could not be detected at most newly formed synapses until several days after synapse formation. The delayed appearance of dynamin at the synapse, thus, heralds the neonatal development of robust synaptic transmission at the neuromuscular junction.

Animals↗

PubMed1996

Three dynamin-encoding genes are differentially expressed in developing rat brain.

Dynamin proteins are members of a recently described family of GTPases involved in receptor-mediated processes. To date, three different dynamin-encoding genes have been identified in mammalian tissues. Dynamin I is expressed only in neurons, whereas dynamin II is ubiquitously expressed. A third isoform, dynamin III, was originally isolated from a rat testis cDNA library and shown to be testis-specific. However, here we report the cloning and characterization of dynamin III from brain and lung, demonstrating a more extended pattern of expression for this isoform. In addition, we have investigated the temporal pattern of expression of these three genes during brain development. We find that both dynamin I and dynamin III mRNA levels are up-regulated during embryogenesis, whereas dynamin II mRNA levels remain unchanged. From these results, we conclude that dynamin III is not a testis-specific isoform and, furthermore, that rat brain expresses three different dynamin-encoding genes that are differentially regulated during development. Therefore, this large isoform diversity of dynamin proteins in brain predicts a significant complexity in the understanding of dynamin-based processes in this tissue.

Alternative Splicing↗

PubMed1999

Dynamin II is involved in endocytosis but not in the formation of transport vesicles from the trans-Golgi network.

Dynamins are a family of approximately 100-kDa GTPases that are thought to play a pivotal role in the formation of endocytic coated vesicles. There are three dynamin genes in mammals: dynamin I is neuron-specific, dynamin II shows ubiquitous expression, and dynamin III is expressed in testis, brain, and lung. However, most studies on the functions of dynamins to date have been restricted to dynamin I. In the present study, we show that, like dynamin I, dynamin II is involved in receptor-mediated endocytosis. While this study was in progress, Jones et al. [Jones, S.M., Howell, K.E., Henley, J.R., Cao, H., and McNiven, M.A. (1998) Science 279, 573-577] reported that dynamin II is localized in the trans-Golgi network (TGN) and involved in the formation of constitutive transport vesicles and clathrin-coated vesicles from this compartment. However, immunofluorescence analyses and experiments using cells transfected with dominant-negative dynamin II failed to show any evidence for localization of dynamin II in the TGN or for its involvement in vesicle formation from this compartment. Our data thus indicate that dynamin II is involved in endocytosis but not in the formation of transport vesicles from the TGN.

Animals↗

PubMed1998

Differential distribution of dynamin isoforms in mammalian cells.

Dynamins are 100-kDa GTPases that are essential for clathrin-coated vesicle formation during receptor-mediated endocytosis. To date, three different dynamin genes have been identified, with each gene expressing at least four different alternatively spliced forms. Currently, it is unclear whether these different dynamin gene products perform distinct or redundant cellular functions. Therefore, the focus of this study was to identify additional spliced variants of dynamin from rat tissues and to define the distribution of the dynamin family members in a cultured rat epithelial cell model (Clone 9 cells). After long-distance reverse transcription (RT)-PCR of mRNA from different rat tissues, the full-length cDNAs encoding the different dynamin isoforms were sequenced and revealed four additional spliced variants for dynamin I and nine for dynamin III. Thus, in rat tissues there are a total of at least 25 different mRNAs produced from the three dynamin genes. Subsequently, we generated stably transfected Clone 9 cells expressing full-length cDNAs of six different spliced forms tagged with green fluorescent protein. Confocal or fluorescence microscopy of these transfected cells revealed that many of the dynamin proteins associate with distinct membrane compartments, which include clathrin-coated pits at the plasma membrane and the Golgi apparatus, and several undefined vesicle populations. These results indicate that the dynamin family is more extensive than was originally predicted and suggest that the different dynamin proteins are localized to distinct cytoplasmic or membrane compartments.

Amino Acid Sequence↗

PubMed1997

Identification and subcellular localization of a novel mammalian dynamin-related protein homologous to yeast Vps1p and Dnm1p.

The dynamin family of GTP-binding proteins are implicated in vesicular transport. These include mammalian dynamins I, II, III, and yeast Vps1p and Dnm1p. Dynamin is involved in the formation of clathrin-coated vesicles at the plasma membrane. On the other hand, Vps1p and Dnm1p appear to be involved in transport from the late Golgi compartment to vacuoles and in an endocytic process, respectively. In this study, we identified a novel human protein, named Dnm1p/Vps1p-like protein (DVLP). It resembled more closely Dnm1p and Vps1p than dynamins not only in the primary structure but also in the domain organization. DVLP mRNA was expressed ubiquitously, suggesting that this protein plays a fundamental role in cellular function. Immunofluorescence analysis of cells expressing epitope-tagged DVLP revealed that it showed a diffused perinuclear staining pattern that was not superimposed on that of the marker protein for the Golgi apparatus, trans-Golgi network, lysosomes, endosomes, or endoplasmic reticulum. These data suggest that DVLP is not involved in the formation of known coated vesicles.

Amino Acid Sequence↗

PubMed1998

Limited entry of adenovirus vectors into well-differentiated airway epithelium is responsible for inefficient gene transfer.

Investigations of the efficiency and safety of human adenovirus vector (AdV)-mediated gene transfer in the airways of patients with cystic fibrosis (CF) in vivo have demonstrated little success in correcting the CF bioelectrical functional defect, reflecting the inefficiency of AdV-mediated gene transfer to the epithelial cells that line the airway luminal surface. In this study, we demonstrate that low AdV-mediated gene transfer efficiency to well-differentiated (WD) cultured airway epithelial cells is due to three distinct steps in the apical membrane of the airway epithelial cells: (i) the absence of specific adenovirus fiber-knob protein attachment receptors; (ii) the absence of alphavbeta3/5 integrins, reported to partially mediate the internalization of AdV into the cell cytoplasm; and (iii) the low rate of apical plasma membrane uptake pathways of WD airway epithelial cells. Attempts to increase gene transfer efficiency by increasing nonspecific attachment of AdV were unsuccessful, reflecting the inability of the attached vector to enter (penetrate) WD cells via nonspecific entry paths. Strategies to improve the efficiency of AdV for the treatment of CF lung disease will require methods to increase the attachment of AdV to and promote its internalization into the WD respiratory epithelium.

Adenoviridae↗

PubMed1995

Isolation of an ubiquitously expressed cDNA encoding human dynamin II, a member of the large GTP-binding protein family.

Dynamin (Dyn) is a member of a novel group of GTPases which was initially identified as a microtubule-binding protein with a role in vectorial movement. Three distinct Dyn-encoding genes (DYN I, II and III), with a neuronal-, ubiquitous or testis-specific expression, respectively, have been identified in rat. In man, only DYN I has so far been characterized. We have previously isolated a genomic DNA fragment implicated in the correction of mitomycin C hypersensitivity of cells from a Fanconi anemia patient belonging to genetic complementation group D (FA(D)). Using this probe, we have cloned a human complementary DNA designated hDYN II encoding a ubiquitous Dyn isoform. The predicted protein consists of 866 amino acids (97.5 kDa). Dyn proteins exhibit a high degree of evolutionary conservation: hDyn II is 98% identical to rat Dyn II and 73% identical to hDyn I. A unique 3.6-kb transcript is found in all human tissues examined and it is more abundant in skeletal muscle and heart. This transcript is also expressed in tissue-culture cells. The hDYN II message is present and not mutated in the FA(D) patient studied. In addition to the GTP-binding domain and motifs associated with regulatory function, the hDyn II protein contains a noticeable number of concensus motifs for p34Cdc2 kinase phosphorylation which may indicate a potential role at the G2/mitosis transition. The sequence reported here should allow a more complete analysis of Dyn function(s) in man.

Amino Acid Sequence↗

PubMed2026

High-fat diet-responsive DNM1 promotes hepatocellular carcinoma progression and predicts poor prognosis in viral-associated patients.

Hepatocellular carcinoma (HCC) arises from diverse etiologies, among which metabolic dysfunction-associated liver disease and chronic viral hepatitis are the two major drivers worldwide. However, the molecular mechanisms linking metabolic stress to HCC progression remain incompletely understood. Dynamin-1 (DNM1), primarily known for its role in vesicular trafficking, has emerged as a potential oncogene, yet its prognostic and functional significance in HCC remains largely unexplored. Here, we investigated the role of DNM1 in high-fat diet (HFD)-associated hepatocarcinogenesis. Transcriptomic profiling was conducted to identify differentially expressed genes between normal and high-fat diet murine models, with human orthologs mapped. Clinical relevance was validated using The Cancer Genome Atlas (TCGA-LIHC) dataset. Survival analysis, GSEA (Gene Set Enrichment Analysis), and subgroup stratifications based on viral hepatitis status were performed. In vitro, loss-of-function assays (shRNA knockdown) were executed in HepG2 and SK-Hep1 cell lines to assess cell viability and migration. DNM1 was significantly upregulated in high-fat diet models. In the TCGA-LIHC cohort, high DNM1 expression was an independent risk factor for poor overall survival (HR=1.44, P=0.039) and correlated with advanced tumor stages (Stage III+IV, P=0.010). In vitro knockdown of DNM1 profoundly impaired cell proliferation and migration in HCC cell lines. Strikingly, DNM1 expression was further elevated in patients with concurrent viral hepatitis (P=0.009). GSEA revealed that high DNM1 expression was positively associated with viral infection pathways and negatively correlated with critical immune responses, including interferon-alpha/gamma responses and host immune cytolysis. Survival analysis stratified by four subgroups demonstrated that patients with both viral infection and high DNM1 expression exhibited the worst prognosis (Overall Log-rank P < 0.001). Our findings identify DNM1 as a high-fat diet-responsive regulator that links metabolic stress to hepatocellular carcinoma progression. Elevated DNM1 expression promotes malignant phenotypes in HCC and identifies a subgroup of viral-associated patients with particularly poor prognosis, highlighting DNM1 as a potential prognostic biomarker and therapeutic target.

Hepatocellular carcinoma (HCC)↗