The DYNLT3 light chain directly links cytoplasmic dynein to a spindle checkpoint protein, Bub3

A proteomics approach to isolating neuropilin-dependent α5 integrin trafficking pathways: neuropilin 1 and 2 co-traffic α5 integrin through endosomal p120RasGAP to promote polarised fibronectin fibrillogenesis in endothelial cells

Integrin trafficking to and from membrane adhesions is a crucial mechanism that dictates many aspects of a cell's behaviour, including motility, polarisation, and invasion. In endothelial cells (ECs), the intracellular traffic of α5 integrin is regulated by both neuropilin 1 (NRP1) and neuropilin 2 (NRP2), yet the redundancies in function between these co-receptors remain unclear. Moreover, the endocytic complexes that participate in NRP-directed traffic remain poorly annotated. Here we identify an important role for the GTPase-activating protein p120RasGAP in ECs, promoting the recycling of α5 integrin from early endosomes. Mechanistically, p120RasGAP enables transit of endocytosed α5 integrin-NRP1-NRP2 complexes to Rab11+ recycling endosomes, promoting cell polarisation and fibronectin (FN) fibrillogenesis. Silencing of both NRP receptors, or p120RasGAP, resulted in the accumulation of α5 integrin in early endosomes, a loss of α5 integrin from surface adhesions, and attenuated EC polarisation. Endothelial-specific deletion of both NRP1 and NRP2 in the postnatal retina recapitulated our in vitro findings, severely impairing FN fibrillogenesis and polarised sprouting. Our data assign an essential role for p120RasGAP during integrin traffic in ECs and support a hypothesis that NRP receptors co-traffic internalised cargoes. Importantly, we utilise comparative proteomics analyses to isolate a comprehensive map of NRP1-dependent and NRP2-dependent α5 integrin interactions in ECs.

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.

Common mechanisms underlying axonal transport deficits in neurodegenerative diseases: a mini review

Many neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis are characterized by the accumulation of pathogenic proteins and abnormal localization of organelles. These pathological features may be related to axonal transport deficits in neurons, which lead to failures in pathological protein targeting to specific sites for degradation and organelle transportation to designated areas needed for normal physiological functioning. Axonal transport deficits are most likely early pathological events in such diseases and gradually lead to the loss of axonal integrity and other degenerative changes. In this review, we investigated reports of mechanisms underlying the development of axonal transport deficits in a variety of common neurodegenerative diseases, such as Alzheimer's disease, amyotrophic lateral sclerosis, Parkinson's disease and Huntington's disease to provide new ideas for therapeutic targets that may be used early in the disease process. The mechanisms can be summarized as follows: (1) motor protein changes including expression levels and post-translational modification alteration; (2) changes in microtubules including reducing stability and disrupting tracks; (3) changes in cargoes including diminished binding to motor proteins. Future studies should determine which axonal transport defects are disease-specific and whether they are suitable therapeutic targets in neurodegenerative diseases.

DYNLT3 overexpression induces apoptosis and inhibits cell growth and migration via inhibition of the Wnt pathway and EMT in cervical cancer

The role of the dynein light chain Tctex-type 3 (DYNLT3) protein in the biological behavior of cervical cancer and its relative molecular mechanisms were investigated. Immunohistochemical staining was used to detect DYNLT3 protein expression in cervical cancer tissues. Cell proliferation and apoptosis rates and invasiveness and migratory capacities were determined by CCK-8 assays, BrdU staining assays and colony formation assays, fluorescence activated cell sorting (FACS), wound healing assays, and Transwell invasion assays of cervical cancer cells after DYNLT3 modulation. The expression levels of Wnt signaling pathway- and EMT-related proteins were examined by Western blotting. Furthermore, the effects of DYNLT3 on the tumorigenicity and metastasis of cervical cancer in nude mice were analyzed by performing immunohistochemistry, and we found that the expression level of the DYNLT3 protein was higher in human normal cervical tissues than in cervical cancer tissues. Overexpression of DYNLT3 obviously attenuated the proliferation, migration and invasion of CaSki and SiHa cells, and promoted cell apoptosis. Upregulation of DYNLT3 expression markedly decreased the expression of Wnt signaling pathway-related proteins (Dvl2, Dvl3, p-LRP6, Wnt3a, Wnt5a/b, Naked1, Naked2, β-catenin and C-Myc) and EMT-related proteins (N-cadherin, SOX2, OCT4, vimentin and Snail), and increased the expression of E-cadherin and Axin1. However, the opposite results were observed after down-regulation of DYNLT3 expression. Up-regulation of DYNLT3 expression significantly inhibited tumor growth in a nude mouse model, while downregulation of DYNLT3 showed the opposite results. In addition, the major metastatic site of cervical cancer cells in mice was the lung, and downregulation of DYNLT3 expression increased cancer metastasis in vivo. DYNLT3 exerted inhibitory effects on cervical cancer by inhibiting cell proliferation, migration and invasion, promoting cell apoptosis in vitro, and inhibiting tumor growth and metastasis in vivo, possibly by suppressing the Wnt signaling pathway and the EMT.

A Ran-binding protein facilitates nuclear import of human papillomavirus type 16

Human papillomaviruses (HPVs) utilize an atypical mode of nuclear import during cell entry. Residing in the Golgi apparatus until mitosis onset, a subviral complex composed of the minor capsid protein L2 and viral DNA (L2/vDNA) is imported into the nucleus after nuclear envelope breakdown by associating with mitotic chromatin. In this complex, L2 plays a crucial role in the interactions with cellular factors that enable delivery and ultimately tethering of the viral genome to mitotic chromatin. To date, the cellular proteins facilitating these steps remain unknown. Here, we addressed which cellular proteins may be required for this process. Using label-free mass spectrometry, biochemical assays, microscopy, and functional virological assays, we discovered that L2 engages a hitherto unknown protein complex of Ran-binding protein 10 (RanBP10), karyopherin alpha2 (KPNA2), and dynein light chain DYNLT3 to facilitate transport towards mitotic chromatin. Thus, our study not only identifies novel cellular interactors and mechanism that facilitate a poorly understood step in HPV entry, but also a novel cellular transport complex.

Human papillomaviruses (HPVs) cause proliferative lesions such as benign warts or malignant invasive cancers. Like other DNA viruses, HPV has to deliver its genome to the nucleus for viral genome transcription and replication. After initial attachment, HPVs are endocytosed to be eventually directed to the trans-Golgi-network (TGN) by intracellular trafficking, where they reside until cell division. Mitosis onset enables access of the virus to cellular chromatin after nuclear envelope breakdown. Tethering of the virus to mitotic chromatin ensures nuclear delivery upon reformation of the nuclear envelope after mitosis. Our previous work showed that the minor capsid protein L2 facilitates nuclear delivery. However, the detailed mechanism, namely, how HPV trafficks from cytosol to the nuclear space, is barely understood. Here, we identified for the first time cellular proteins that interacted with L2 for nuclear import. Mechanistically, the proteins formed a hitherto unknown cellular transport complex that interacted with L2 to direct the virus to mitotic chromosomes by microtubular transport. Our findings provided not only evidence for a transport mechanism of a poorly understood step of HPV entry, but also discovered a novel cellular transport complex.

A role for Dynlt3 in melanosome movement, distribution, acidity and transfer

Skin pigmentation is dependent on cellular processes including melanosome biogenesis, transport, maturation and transfer to keratinocytes. However, how the cells finely control these processes in space and time to ensure proper pigmentation remains unclear. Here, we show that a component of the cytoplasmic dynein complex, Dynlt3, is required for efficient melanosome transport, acidity and transfer. In Mus musculus melanocytes with decreased levels of Dynlt3, pigmented melanosomes undergo a more directional motion, leading to their peripheral location in the cell. Stage IV melanosomes are more acidic, but still heavily pigmented, resulting in a less efficient melanosome transfer. Finally, the level of Dynlt3 is dependent on β-catenin activity, revealing a function of the Wnt/β-catenin signalling pathway during melanocyte and skin pigmentation, by coupling the transport, positioning and acidity of melanosomes required for their transfer.

Age-associated genes in human mammary gland drive human breast cancer progression

Background

Aging is a comorbidity of breast cancer suggesting that aging-associated transcriptome changes may promote breast cancer progression. However, the mechanism underlying the age effect on breast cancer remains poorly understood.

Method

We analyzed transcriptomics of the matched normal breast tissues from the 82 breast cancer patients in The Cancer Genome Atlas (TCGA) dataset with linear regression for genes with age-associated expression that are not associated with menopause. We also analyzed differentially expressed genes between the paired tumor and non-tumor breast tissues in TCGA for the identification of age and breast cancer (ABC)-associated genes. A few of these genes were selected for further investigation of their malignancy-regulating activities with in vitro and in vivo assays.

Results

We identified 148 upregulated and 189 downregulated genes during aging. Overlapping of tumor-associated genes between normal and tumor tissues with age-dependent genes resulted in 14 upregulated and 24 downregulated genes that were both age and breast cancer associated. These genes are predictive in relapse-free survival, indicative of their potential tumor promoting or suppressive functions, respectively. Knockdown of two upregulated genes (DYNLT3 and P4HA3) or overexpression of the downregulated ALX4 significantly reduced breast cancer cell proliferation, migration, and clonogenicity. Moreover, knockdown of P4HA3 reduced growth and metastasis whereas overexpression of ALX4 inhibited the growth of xenografted breast cancer cells in mice.

Conclusion

Our study suggests that transcriptome alterations during aging may contribute to breast tumorigenesis. DYNLT3, P4HA3, and ALX4 play significant roles in breast cancer progression.

Replicative and radiation-induced aging: a comparison of gene expression profiles

All living organisms are subject to the aging process and experience the effect of ionizing radiation throughout their life. There have been a number of studies that linked ionizing radiation process to accelerated aging, but comprehensive signalome analysis of both processes was rarely conducted. Here we present a comparative signaling pathway based analysis of the transcriptomes of fibroblasts irradiated with different doses of ionizing radiation, replicatively aged fibroblasts and fibroblasts collected from young, middle age and old patients. We demonstrate a significant concordance between irradiation-induced and replicative senescence signalome signatures of fibroblasts. Additionally, significant differences in transcriptional response were also observed between fibroblasts irradiated with high and low dose. Our data shows that the transcriptome of replicatively aged fibroblasts is more similar to the transcriptome of the cells irradiated with 2 Gy, than with 5 сGy.This work revealed a number of signaling pathways that are shared between senescence and irradiation processes and can potentially be targeted by the new generation of gero- and radioprotectors.

Effects of dynein light chain Tctex-type 3 on the biological behavior of ovarian cancer

OBJECTIVE

To investigate dynein light chain Tctex-type 3 (DYNLT3) protein expression in ovarian epithelial lesions and explore the effects and related mechanisms of DYNLT3 in terms of the biological behavior of ovarian cancer.

MATERIALS AND METHODS

Initially, expression of the DYNLT3 protein in ovarian epithelial lesions was detected by immunohistochemical staining, and the prognostic value of DYNLT3 mRNA expression in ovarian cancer patients was assessed using the Kaplan-Meier plotter database. Then, the mRNA and protein expression of DYNLT3 in IOSE80 normal ovarian epithelial cells and SKOV3 ovarian cancer cells was evaluated by quantitative real-time polymerase chain reaction and Western blotting respectively, and the proliferation, apoptosis, migration and invasion of SKOV3 cells after DYNLT3 over-expression and under-expression were investigated by CCK-8 assays and immunofluorescence staining, flow cytometry, wound healing assays and Transwell invasion assays, respectively. Furthermore, the expression of the proliferation-related proteins PCNA and Ki-67 and the invasion- and migration-related proteins Ezrin, Fascin, MMP2 and MMP9 in cells was examined by Western blotting.

RESULTS

The protein expression of DYNLT3 gradually increased during the progression of ovarian epithelial lesions, and was related to the development of ovarian cancer. High expression of DYNLT3 mRNA was related to poor overall survival and progression free survival, especially in serous ovarian cancer patients. In addition, overexpression of DYNLT3 promoted SKOV3 cell proliferation, invasion and migration. The corresponding results were also verified by a DYNLT3 knockdown assay. Moreover, DYNLT3 increased cell proliferation, which was related to Ki-67 expression. Besides, DYNLT3 enhanced cell invasion and migration through regulating Ezrin, but not Fascin, MMP2 or MMP9.

CONCLUSION

DYNLT3 exerts pro-tumoral effects on ovarian cancer through promoting cell proliferation, migration and invasion, possibly via regulating the protein expression of Ki-67 and Ezrin. DYNLT3 may be a potential prognostic predictor in ovarian cancer.

Proteome and behavioral alterations in phosphorylation-deficient mutant Collapsin Response Mediator Protein2 knock-in mice

CRMP2, alternatively designated as DPYSL2, was the first CRMP family member to be identified as an intracellular molecule mediating the signaling of the axon guidance molecule Semaphorin 3A (Sema3A). In Sema3A signaling, cyclin-dependent kinase 5 (Cdk5) primarily phosphorylates CRMP2 at Ser522. Glycogen synthase kinase-3β (GSK-3β) subsequently phosphorylates the residues of Thr509 and Thr514 of CRMP2. Previous studies showed that CRMP2 is involved in pathogenesis of neurological disorders such as Alzheimer's disease. In Alzheimer's disease, hyper-phosphorylated forms of CRMP2 are accumulated in the paired helical filaments. To get insight into the possible involvement of the phosphorylation of CRMP2 in pathogenesis of neurological disorders, we previously created CRMP2 S522A knock-in (crmp2^ki/ki) mice and demonstrated that the phosphorylation of CRMP2 at Ser522 is involved in normal dendrite patterning in cortical neurons. However, the behavioral impact and in vivo signaling network of the CRMP2 phosphorylation are not fully understood. In this study, we performed behavioral and proteomics analysis of crmp2^ki/ki mice. The crmp2^ki/ki mice appeared healthy and showed no obvious differences in physical characteristics compared to wild-type mice, but they showed impaired emotional behavior, reduced sociality, and low sensitivity to pain stimulation. Through mass-spectrometry-based proteomic analysis, we found that 59 proteins were increased and 77 proteins were decreased in the prefrontal cortex of crmp2^ki/ki mice. Notably, CRMP3, CRMP4, and CRMP5, the other CRMP family proteins, were increased in crmp2^ki/ki mice. KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analyses identified 14 pathways in increased total proteins and 13 pathways in decreased total proteins which are associated with the pathogenesis of Parkinson's, Alzheimer's, and Huntington's diseases. We also detected 20 pathways in increased phosphopeptides and 16 pathways in decreased phosphopeptides including "inflammatory mediator regulation of TRP channels" in crmp2^ki/ki mice. Our study suggests that the phosphorylation of CRMP2 at Ser522 is involved in the signaling pathways that may be related to neuropsychiatric and neurodegenerative diseases and pain.

Impacts of virus-mediated manipulation of host Dynein

In general viruses' modus operandi to propagate is achieved by the co-opting host cell components, membranes, proteins, and machineries to their advantage. This is true for virtually every aspect of a virus' replication cycle from virus entry to the budding or release of progeny virus particles. In this chapter, we will discuss new information on the impacts of virus-mediated manipulation of Dynein motor complexes and associated machineries and factors. We will highlight how these host cell components impact on pathogenicity and immune responses, as many of the virus-mediated hijacked components also play pivotal roles in immune responses to pathogen insult. There are several comprehensive reviews that define virus–Dynein interactions including the first edition of this book that describes how viruses manipulate the host cell machineries their advantage. An updated table is included to summarize these virus–host interactions. Notably, barriers to intracellular translocation represent major hurdles to viral components during de novo infection and during active replication and the generation of progeny virus particles. Clearly, the subversion of host cell molecular motor protein activities takes advantage of constitutive and regulated membrane trafficking events and will target virus components to intracytoplasmic locales and membrane assembly. Broadening our understanding of the interplay between viruses, Dynein and the cytoskeleton will likely inform on new types of therapies. Continual enhancement of the breadth of new information on how viruses manipulate host cell biology will inevitably aid in the identification of new targets that can be poisoned to block old, new, and emerging viruses alike in their tracks.

A dynein independent role of Tctex-1 at the kinetochore

Dynein light chains are accessory subunits of the cytoplasmic dynein complex, a minus-end directed microtubule motor. Here, we demonstrate that the dynein light chain Tctex-1 associates with unattached kinetochores and is essential for accurate chromosome segregation. Tctex-1 knockdown in cells does not affect the localization and function of dynein at the kinetochore, but produces a prolonged mitotic arrest with a few misaligned chromosomes, which are subsequently missegregated during anaphase. This function is independent of Tctex-1's association with dynein. The kinetochore localization of Tctex-1 is independent of the ZW10-dynein pathway, but requires the Ndc80 complex. Thus, our findings reveal a dynein independent role of Tctex-1 at the kinetochore to enhance the stability of kinetochore-microtubule attachment.

Co-silencing of human Bub3 and dynein highlights an antagonistic relationship in regulating kinetochore-microtubule attachments

We previously reported that the spindle assembly checkpoint protein Bub3 is involved in regulating kinetochore-microtubule (KT-MT) attachments. Also, Bub3 was reported to interact with the microtubule motor protein dynein. Here we examined how this interaction contributes to KT-MT attachments. Depletion of Bub3 or dynein induced misaligned chromosomes, consistent with their role in KT-MT attachments. Unexpectedly, co-silencing of both proteins partially suppressed the misalignment phenotype and restored chromosome congression. Consistent with these observations, KT-MT attachments in co-depleted cells were stable, able to drive chromosome congression, and produce inter- and intra-kinetochore stretch, indicating they are functional. We suggest that a mutual antagonism exists between Bub3 and dynein to ensure optimal KT-MT attachments.

Human immunodeficiency virus type 1 employs the cellular dynein light chain 1 protein for reverse transcription through interaction with its integrase protein

In this study, we examined the requirement for host dynein adapter proteins such as dynein light chain 1 (DYNLL1), dynein light chain Tctex-type 1 (DYNLT1), and p150(Glued) in early steps of human immunodeficiency virus type 1 (HIV-1) replication. We found that the knockdown (KD) of DYNLL1, but not DYNLT1 or p150(Glued), resulted in significantly lower levels of HIV-1 reverse transcription in cells. Following an attempt to determine how DYNLL1 could impact HIV-1 reverse transcription, we detected the DYNLL1 interaction with HIV-1 integrase (IN) but not with capsid (CA), matrix (MA), or reverse transcriptase (RT) protein. Furthermore, by mutational analysis of putative DYNLL1 interaction motifs in IN, we identified the motifs (52)GQVD and (250)VIQD in IN as essential for DYNLL1 interaction. The DYNLL1 interaction-defective IN mutant HIV-1 (HIV-1IN(Q53A/Q252A)) exhibited impaired reverse transcription. Through further investigations, we have also detected relatively smaller amounts of particulate CA in DYNLL1-KD cells or in infections with HIV-1IN(Q53A/Q252A) mutant virus. Overall, our study demonstrates the novel interaction between HIV-1 IN and cellular DYNLL1 proteins and suggests the requirement of this virus-cell interaction for proper uncoating and efficient reverse transcription of HIV-1.

IMPORTANCE

Host cellular DYNLL1, DYNLT1, and p150(Glued) proteins have been implicated in the replication of several viruses. However, their roles in HIV-1 replication have not been investigated. For the first time, we demonstrated that during viral infection, HIV-1 IN interacts with DYNLL1, and their interaction was found to have a role in proper uncoating and efficient reverse transcription of HIV-1. Thus, interaction of IN and DYNLL1 may be a potential target for future anti-HIV therapy. Moreover, while our study has evaluated the involvement of IN in HIV-1 uncoating and reverse transcription, it also predicts a possible mechanism by which IN contributes to these early viral replication steps.

hsa-mir-30c promotes the invasive phenotype of metastatic breast cancer cells by targeting NOV/CCN3

Background

For treatment and prevention of metastatic disease, one of the premier challenges is the identification of pathways and proteins to target for clinical intervention. Micro RNAs (miRNAs) are short, non-coding RNAs, which regulate cellular activities by either mRNA degradation or translational inhibition. Our studies focused on the invasive properties of hsa-mir30c based on its high expression in MDA-MB-231 metastatic cells and our bioinformatic analysis of the Cancer Genome Atlas that identified aberrant hsa-mir-30c to be associated with poor survival.

Methods

Contributions of hsa-mir-30c to breast cancer cell invasion were examined by Matrigel invasion transwell assays following modulation of hsa-mir-30c or hsa-mir-30c* levels in MDA-MB-231 cells. hsa-mir-30c in silico predicted targets linked to cell invasion were screened for targeting by hsa-mir-30c in metastatic breast cancer cells by RT-qPCR. The contribution to invasion by a target of hsa-mir-30c, Nephroblastoma overexpressed (NOV), was characterized by siRNA and invasion assays. Significant effects were determined using Student’s T-tests with Welch’s correction for unequal variance.

Results

MCF-7 and MDA-MB-231 cells were used as models of poorly invasive and late-stage metastatic disease, respectively. By modulating the levels of hsa-mir-30c in these cells, we observed concomitant changes in breast cancer cell invasiveness. From predicted targets of hsa-mir-30c that were related to cellular migration and invasion, NOV/CCN3 was identified as a novel target of hsa-mir-30c. Depleting NOV by siRNA caused a significant increase in the invasiveness of MDA-MB-231 cells is a regulatory protein associated with the extracellular matrix.

Conclusions

NOV/CCN3 expression, which protects cells from invasion, is known in patient tumors to inversely correlate with advanced breast cancer and metastasis. This study has identified a novel target of hsa-mir-30c, NOV, which is an inhibitor of the invasiveness of metastatic breast cancer cells. Thus, hsa-mir-30c-mediated inhibition of NOV levels promotes the invasive phenotype of MDA-MB-231 cells and significantly, the miR-30/NOV pathways is independent of RUNX2, a known target of hsa-mir-30c that promotes osteolytic disease in metastatic breast cancer cells. Our findings allow for mechanistic insight into the clinical observation of poor survival of patients with elevated hsa-mir-30c levels, which can be considered for miRNA-based translational studies.

Live cell imaging reveals differential modifications to cytoplasmic dynein properties by phospho- and dephosphomimic mutations of the intermediate chain 2C S84

Cytoplasmic dynein is a multisubunit motor protein responsible for intracellular cargo transport toward microtubule minus ends. There are multiple isoforms of the dynein intermediate chain (DYNC1I, IC), which is encoded by two genes. One way to regulate cytoplasmic dynein is by IC phosphorylation. The IC-2C isoform is expressed in all cells, and the functional significance of phosphorylation on IC-2C serine 84 was investigated by using live cell imaging of fluorescent protein-tagged IC-2C wild type (WT) and phospho- and dephosphomimic mutant isoforms in axonal transport model systems. Both mutations modulated dynein functional properties. The dephosphomimic mutant IC-2C S84A had greater colocalization with mitochondria than the IC-2C WT or the phosphomimic mutant IC-2C S84D. The dephosphomimic mutant IC-2C S84A was also more likely to be motile than the phosphomimic mutant IC-2C S84D or the IC-2C WT. In contrast, the phosphomimic mutant IC-2C S84D mutant was more likely to move in the retrograde direction than was the IC-2C S84A mutant. The phosphomimic IC-2C S84D was also as likely as the IC-2C WT to colocalize with mitochondria. Both the S84D phospho- and the S84A dephosphomimic mutants were found to be capable of microtubule minus-end-directed (retrograde) movement in axons. They were also observed to be passively transported in the anterograde direction. These data suggest that the IC-2C S84 has a role in modulating dynein properties.

A microtubule-associated zinc finger protein, BuGZ, regulates mitotic chromosome alignment by ensuring Bub3 stability and kinetochore targeting

Equal chromosome segregation requires proper assembly of many proteins, including Bub3, onto kinetochores to promote kinetochore-microtubule interactions. By screening for mitotic regulators in the spindle envelope and matrix (Spemix), we identify a conserved Bub3 interacting and GLE-2-binding sequence (GLEBS) containing ZNF207 (BuGZ) that associates with spindle microtubules and regulates chromosome alignment. Using its conserved GLEBS, BuGZ directly binds and stabilizes Bub3. BuGZ also uses its microtubule-binding domain to enhance the loading of Bub3 to kinetochores that have assumed initial interactions with microtubules in prometaphase. This enhanced Bub3 loading is required for proper chromosome alignment and metaphase to anaphase progression. Interestingly, we show that microtubules are required for the highest kinetochore loading of Bub3, BubR1, and CENP-E during prometaphase. These findings suggest that BuGZ not only serves as a molecular chaperone for Bub3 but also enhances its loading onto kinetochores during prometaphase in a microtubule-dependent manner to promote chromosome alignment.

Alteration of dynein function affects α-synuclein degradation via the autophagosome-lysosome pathway

Growing evidence suggests that dynein dysfunction may be implicated in the pathogenesis of neurodegeneration. It plays a central role in aggresome formation, the delivery of autophagosome to lysosome for fusion and degradation, which is a pro-survival mechanism essential for the bulk degradation of misfolded proteins and damaged organells. Previous studies reported that dynein dysfuntion was associated with aberrant aggregation of α-synuclein, which is a major component of inclusion bodies in Parkinson's disease (PD). However, it remains unclear what roles dynein plays in α-synuclein degradation. Our study demonstrated a decrease of dynein expression in neurotoxin-induced PD models in vitro and in vivo, accompanied by an increase of α-synuclein protein level. Dynein down-regulation induced by siRNA resulted in a prolonged half-life of α-synuclein and its over-accumulation in A53T overexpressing PC12 cells. Dynein knockdown also prompted the increase of microtubule-associated protein 1 light chain 3 (LC3-II) and sequestosome 1 (SQSTM1, p62) expression, and the accumulation of autophagic vacuoles. Moreover, dynein suppression impaired the autophagosome fusion with lysosome. In summary, our findings indicate that dynein is critical for the clearance of aberrant α-synuclein via autophagosome-lysosome pathway.

An intriguing shift occurs in the novel protein phosphatase 1 binding partner, TCTEX1D4: evidence of positive selection in a pika model

T-complex testis expressed protein 1 domain containing 4 (TCTEX1D4) contains the canonical phosphoprotein phosphatase 1 (PPP1) binding motif, composed by the amino acid sequence RVSF. We identified and validated the binding of TCTEX1D4 to PPP1 and demonstrated that indeed this protein is a novel PPP1 interacting protein. Analyses of twenty-one mammalian species available in public databases and seven Lagomorpha sequences obtained in this work showed that the PPP1 binding motif ₉₀RVSF₉₃ is present in all of them and is flanked by a palindromic sequence, PLGS, except in three species of pikas (Ochotona princeps, O. dauurica and O. pusilla). Furthermore, for the Ochotona species an extra glycosylation site, motif ₉₆NLS₉₈, and the loss of the palindromic sequence were observed. Comparison with other lagomorphs suggests that this event happened before the Ochotona radiation. The d_N/d_S for the sequence region comprising the PPP1 binding motif and the flanking palindrome highly supports the hypothesis that for Ochotona species this region has been evolving under positive selection. In addition, mutational screening shows that the ability of pikas TCTEX1D4 to bind to PPP1 is maintained, although the PPP1 binding motif is disrupted, and the N- and C-terminal surrounding residues are also abrogated. These observations suggest pika as an ideal model to study novel PPP1 complexes regulatory mechanisms.

Transcriptomic indices of fast and slow disease progression in two mouse models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is heterogeneous with high variability in the speed of progression even in cases with a defined genetic cause such as superoxide dismutase 1 (SOD1) mutations. We reported that SOD1(G93A) mice on distinct genetic backgrounds (C57 and 129Sv) show consistent phenotypic differences in speed of disease progression and life-span that are not explained by differences in human SOD1 transgene copy number or the burden of mutant SOD1 protein within the nervous system. We aimed to compare the gene expression profiles of motor neurons from these two SOD1(G93A) mouse strains to discover the molecular mechanisms contributing to the distinct phenotypes and to identify factors underlying fast and slow disease progression. Lumbar spinal motor neurons from the two SOD1(G93A) mouse strains were isolated by laser capture microdissection and transcriptome analysis was conducted at four stages of disease. We identified marked differences in the motor neuron transcriptome between the two mice strains at disease onset, with a dramatic reduction of gene expression in the rapidly progressive (129Sv-SOD1(G93A)) compared with the slowly progressing mutant SOD1 mice (C57-SOD1(G93A)) (1276 versus 346; Q-value ≤ 0.01). Gene ontology pathway analysis of the transcriptional profile from 129Sv-SOD1(G93A) mice showed marked downregulation of specific pathways involved in mitochondrial function, as well as predicted deficiencies in protein degradation and axonal transport mechanisms. In contrast, the transcriptional profile from C57-SOD1(G93A) mice with the more benign disease course, revealed strong gene enrichment relating to immune system processes compared with 129Sv-SOD1(G93A) mice. Motor neurons from the more benign mutant strain demonstrated striking complement activation, over-expressing genes normally involved in immune cell function. We validated through immunohistochemistry increased expression of the C3 complement subunit and major histocompatibility complex I within motor neurons. In addition, we demonstrated that motor neurons from the slowly progressing mice activate a series of genes with neuroprotective properties such as angiogenin and the nuclear factor (erythroid-derived 2)-like 2 transcriptional regulator. In contrast, the faster progressing mice show dramatically reduced expression at disease onset of cell pathways involved in neuroprotection. This study highlights a set of key gene and molecular pathway indices of fast or slow disease progression which may prove useful in identifying potential disease modifiers responsible for the heterogeneity of human amyotrophic lateral sclerosis and which may represent valid therapeutic targets for ameliorating the disease course in humans.

TCTEX1D4, a novel protein phosphatase 1 interactor: connecting the phosphatase to the microtubule network

Reversible phosphorylation plays an important role as a mechanism of intracellular control in eukaryotes. PPP1, a major eukaryotic Ser/Thr-protein phosphatase, acquires its specificity by interacting with different protein regulators, also known as PPP1 interacting proteins (PIPs). In the present work we characterized a physiologically relevant PIP in testis. Using a yeast two-hybrid screen with a human testis cDNA library, we identified a novel PIP of PPP1CC2 isoform, the T-complex testis expressed protein 1 domain containing 4 (TCTEX1D4) that has recently been described as a Tctex1 dynein light chain family member. The overlay assays confirm that TCTEX1D4 interacts with the different spliced isoforms of PPP1CC. Also, the binding domain occurs in the N-terminus, where a consensus PPP1 binding motif (PPP1BM) RVSF is present. The distribution of TCTEX1D4 in testis suggests its involvement in distinct functions, such as TGFβ signaling at the blood–testis barrier and acrosome cap formation. Immunofluorescence in human ejaculated sperm shows that TCTEX1D4 is present in the flagellum and in the acrosome region of the head. Moreover, TCTEX1D4 and PPP1 co-localize in the microtubule organizing center (MTOC) and microtubules in cell cultures. Importantly, the TCTEX1D4 PPP1BM seems to be relevant for complex formation, for PPP1 retention in the MTOC and movement along microtubules.

These novel results open new avenues to possible roles of this dynein, together with PPP1. In essence TCTEX1D4/PPP1C complex appears to be involved in microtubule dynamics, sperm motility, acrosome reaction and in the regulation of the blood–testis barrier.

Novel genes underlying beta cell survival in metabolic stress

Relative insulin deficiency, in response to increased metabolic demand (obesity, genetic insulin resistance, pregnancy and aging) lead to Type2 diabetes. Susceptibility of the type 2 diabetes has a genetic basis, as a subset of people with risk factors (obesity, Insulin Resistance, pregnancy), develop Type2 Diabetes. We aimed to identify 'cluster' of overexpressed genes, underlying increased beta cell survival in diabetes resistant C57BL/6J ob/ob mice (compared to diabetes susceptible BTBR ob/ob mice). We used 'consensus' overexpression status to identify 'cluster' of 11 genes consisting of Aldh18a1, Rfc4, Dynlt3, Prom1, H13, Psen1, Ssr4, Dad1, Anpep, Fam111a and Plk1. Information (biological processes, molecular functions, cellular components, protein-protein interactions/associations, gene deletion/knockout/inhibition studies) of all the genes in 'cluster' were collected by text mining using different literature search tools, gene information databases and protein-protein interaction databases. Beta cell specific function of these genes were also inferred using meta analysis tool of Beta Cell Biology Consortium, by studying the expression pattern of these genes in microarray studies related to beta-cell stimulation/injury, pancreas development and growth and cell differentiation. In the 'clusters', 6 genes (Dad1, Psen1, Ssr4, Rfc4, H13, Plk1) have a role in cell survival. Only Psen1 was previously identified to have role in successful beta cell compensation. We advocate these genes to be potentially involved in successful beta cell compensation and prevent T2D in humans, by conferring protection against diabetogenic insults.

Transcriptional activation of prostate specific homeobox gene NKX3-1 in subsets of T-cell lymphoblastic leukemia (T-ALL)

Homeobox genes encode transcription factors impacting key developmental processes including embryogenesis, organogenesis, and cell differentiation. Reflecting their tight transcriptional control, homeobox genes are often embedded in large non-coding, cis-regulatory regions, containing tissue specific elements. In T-cell acute lymphoblastic leukemia (T-ALL) homeobox genes are frequently deregulated by chromosomal aberrations, notably translocations adding T-cell specific activatory elements. NKX3-1 is a prostate specific homeobox gene activated in T-ALL patients expressing oncogenic TAL1 or displaying immature T-cell characteristics. After investigating regulation of NKX3-1 in primary cells and cell lines, we report its ectopic expression in T-ALL cells independent of chromosomal rearrangements. Using siRNAs and expression profiling, we exploited NKX3-1 positive T-ALL cell lines as tools to investigate aberrant activatory mechanisms. Our data confirmed NKX3-1 activation by TAL1/GATA3/LMO and identified LYL1 as an alternative activator in immature T-ALL cells devoid of GATA3. Moreover, we showed that NKX3-1 is directly activated by early T-cell homeodomain factor MSX2. These activators were regulated by MLL and/or by IL7-, BMP4- and IGF2-signalling. Finally, we demonstrated homeobox gene SIX6 as a direct leukemic target of NKX3-1 in T-ALL. In conclusion, we identified three major mechanisms of NKX3-1 regulation in T-ALL cell lines which are represented by activators TAL1, LYL1 and MSX2, corresponding to particular T-ALL subtypes described in patients. These results may contribute to the understanding of leukemic transcriptional networks underlying disturbed T-cell differentiation in T-ALL.

Alterations in axonal transport motor proteins in sporadic and experimental Parkinson's disease

The progressive loss of the nigrostriatal pathway is a distinguishing feature of Parkinson's disease. As terminal field loss seems to precede cell body loss, we tested whether alterations of axonal transport motor proteins would be early features in Parkinson's disease. There was a decline in axonal transport motor proteins in sporadic Parkinson's disease that preceded other well-known nigral cell-related pathology such as phenotypic downregulation of dopamine. Reductions in conventional kinesin levels precede the alterations in dopaminergic phenotypic markers (tyrosine hydroxylase) in the early stages of Parkinson's disease. This reduction was significantly greater in nigral neurons containing α-synuclein inclusions. Unlike conventional kinesin, reductions in the levels of the cytoplasmic dynein light chain Tctex type 3 subunit were only observed at late Parkinson's disease stages. Reductions in levels of conventional kinesin and cytoplasmic dynein subunits were recapitulated in a rat genetic Parkinson's disease model based on over-expression of human mutant α-synuclein (A30P). Together, our data suggest that α-synuclein aggregation is a key feature associated with reductions of axonal transport motor proteins in Parkinson's disease and support the hypothesis that dopaminergic neurodegeneration following a 'dying-back' pattern involving axonal transport disruption.

Identification of a single amino acid residue which is critical for the interaction between HSV-1 inner tegument proteins pUL36 and pUL37

The herpes simplex virus type 1 (HSV-1) structural tegument proteins pUL36 and pUL37 are essential for secondary envelopment during the egress of viral particles. For this study, scanning alanine mutagenesis of HSV-1 pUL37, in combination with yeast two-hybrid, identified pUL37 residue D631 as a major determinant for binding of pUL36. Further analysis of the binding of this pUL37 mutant to pUL36 by coimmunoprecipitation assay confirmed the role of pUL37 D631 in mediating binding of pUL36. A trans-complementation assay using pUL37 deletion virus FRΔUL37 was then carried out, where pUL37 wild type or D631A were provided in trans. For pUL37 D631A, a significant reduction in virus titer was observed compared to that seen when pUL37 wild type was present. The results presented here underline the crucial role of the pUL36/pUL37 interaction in replication of HSV-1 and indicate a critical role for pUL37 D631 in mediating this interaction.

Dynein light chain Tctex-type 1 modulates orexin signaling through its interaction with orexin 1 receptor

Orexins (OX-A, OX-B) are neuropeptides involved in the regulation of the sleep-wake cycle, feeding and reward, via activation of orexin receptors 1 and 2 (OX1R, OX2R). The loss of orexin peptides or functional OX2R has been shown to cause the sleep disorder, narcolepsy. Since the regulation of orexin receptors remains largely undefined, we searched for novel protein partners of the intracellular tail of orexin receptors. Using a yeast two-hybrid screening strategy in combination with co-immunoprecipitation experiments, we found interactions between OX1R and the dynein light chains Tctex-type 1 and 3 (Dynlt1, Dynlt3). These interactions were mapped to the C-terminal region of the dynein light chains and to specific residues within the last 10 amino acids of OX1R. Hence, we hypothesized that dynein light chains could regulate orexin signaling. In HEK293 cells expressing OX1R, stimulation with OX-A produced a less sustained extracellular signal-regulated kinases 1/2 (ERK1/2) activation when Dynlt1 was co-expressed, while it was prolonged under reduced Dynlt1 expression. The amount of OX1R located at the plasma membrane as well as the kinetics and extent of OX-A-induced internalization of OX1R (disappearance from membrane) were not altered by Dynlt1. However, Dynlt1 reduced the localization of OX1R in early endosomes following initial internalization. Taken together, these data suggest that Dynlt1 modulates orexin signaling by regulating OX1R, namely its intracellular localization following ligand-induced internalization.

Global proteomics analysis of testis and ovary in adult zebrafish (Danio rerio)

The molecular mechanisms controlling sex determination and differentiation in zebrafish (Danio rerio) are largely unknown. A genome-wide analysis may provide comprehensive insights into the processes involved. The mRNA expression in zebrafish gonads has been fairly well studied, but much less data on the corresponding protein expression are available, although the proteins are considered to be more relevant markers of gene function. Because mRNA and protein abundances rarely correlate well, mRNA profiles need to be complemented with the information on protein expression. The work presented here analyzed the proteomes of adult zebrafish gonads by a multidimensional protein identification technology, generating the to-date most populated lists of proteins expressed in mature zebrafish gonads. The acquired proteomics data partially confirmed existing transcriptomics information for several genes, including several novel transcripts. However, disagreements between mRNA and protein abundances were often observed, further stressing the necessity to assess the expression on different levels before drawing conclusions on a certain gene's expression and function. Several gene groups expressed in a sexually dimorphic way in zebrafish gonads were identified. Their potential importance for gonad development and function is discussed. The data gained in the current study provide a basis for further work on elucidating processes occurring during zebrafish development with use of high-throughput proteomics.

DYNLT3 is required for chromosome alignment during mouse oocyte meiotic maturation

Dynein light chain, Tctex-type 3 (DYNLT3), is a member of the cytoplasmic dynein DYNLT light chain family and has been reported to have a potential role in chromosome congression in human mitosis. However, its role in mammalian meiosis is unclear. In this study, we examined its localization, expression, and functions in mouse oocyte meiosis. Immunofluorescent staining showed that DYNLT3 was restricted to the germinal vesicle and associated with kinetochores at the germinal vesicle breakdown stage, metaphase I and metaphase II. The expression level of DYNLT3 was similar at all meiotic stages. Depletion of DYNLT3 by antibody injection resulted in chromosome misalignment and decrease of the polar body extrusion rate. We further found that DYNLT3-depleted oocytes displayed kinetochore-microtubule detachments. Chromosome-spread experiments showed that depletion of DYNLT3 inhibited the metaphase-anaphase transition by preventing homologous chromosome segregation in meiosis I. Our data suggest that DYNLT3 is required for chromosome alignment and homologous chromosome segregation during mouse oocyte meiosis.

Overexpression of the dynein light chain km23-1 in human ovarian carcinoma cells inhibits tumor formation in vivo and causes mitotic delay at prometaphase/metaphase

km23-1 is a dynein light chain that was identified as a TGFβ receptor-interacting protein. To investigate whether km23-1 controls human ovarian carcinoma cell (HOCC) growth, we established a tet-off inducible expression system in SKOV-3 cells in which the expression of km23-1 is induced upon doxycycline removal. We found that forced expression of km23-1 inhibited both anchorage-dependent and anchorage-independent growth of SKOV-3 cells. More importantly, induction of km23-1 expression substantially reduced the tumorigenicity of SKOV-3 cells in a xenograft model in vivo. Fluorescence-activated cell sorting analysis of SKOV-3 and IGROV-1 HOCCs demonstrated that the cells were accumulating at G2/M. Phospho-MEK, phospho-ERK and cyclin B1 were elevated, as was the mitotic index, suggesting that km23-1 suppresses HOCCs growth by inducing a mitotic delay. Immunofluorescence analyses demonstrated that the cells were accumulating at prometaphase/metaphase with increases in multipolar and multinucleated cells. Further, although the mitotic spindle assembly checkpoint protein BubR1 was present at the prometaphase kinetochore in Dox+/- cells, it was inappropriately retained at the metaphase kinetochore in Dox- cells. Thus, the mechanism by which high levels of km23-1 suppress ovarian carcinoma growth in vitro and inhibit ovary tumor formation in vivo appears to involve a BubR1-related mitotic delay.

Recruitment of dynein to late endosomes and lysosomes through light intermediate chains

Cytoplasmic dynein is involved in a wide range of cellular processes, but how it is regulated and how it recognizes an extremely wide range of cargo are incompletely understood. The dynein light intermediate chains, LIC1 and LIC2 (DYNC1LI1 and DYNC1LI2, respectively), have been implicated in cargo binding, but their full range of functions is unknown. Using LIC isoform-specific antibodies, we report the first characterization of their subcellular distribution and identify a specific association with elements of the late endocytic pathway, but not other vesicular compartments. LIC1 and LIC2 RNA interference (RNAi) each specifically disrupts the distribution of lysosomes and late endosomes. Stimulation of dynein-mediated late-endosomal transport by the Rab7-interacting lysosomal protein (RILP) is reversed by LIC1 RNAi, which displaces dynein, but not dynactin, from these structures. Conversely, expression of ΔN-RILP or the dynactin subunit dynamitin each fails to displace dynein, but not dynactin. Thus, using a variety of complementary approaches, our results indicate a novel specific role for the LICs in dynein recruitment to components of the late endocytic pathway.

Requirement of a dynein light chain in TGFbeta/Smad3 signaling

We have previously reported that the dynein light chain (DLC) km23-1 is required for Smad2-dependent TGFbeta signaling. Here we describe another member of the km23/DYNLRB/LC7/robl family of DLCs, termed km23-2, which is also involved in TGFbeta signaling. We show not only that TGFbeta stimulates the interaction of km23-2 (DYNLRB2) with TGFbeta receptor II (TbetaRII) but also that TGFbeta regulates the interaction between km23-2 and endogenous TbetaRII in vivo. In addition, TGFbeta treatment causes km23-2 phosphorylation, whereas a kinase-deficient form of TbetaRII prevents km23-2 phosphorylation. In contrast to the km23-1 isoform, blockade of km23-2 expression using small interfering RNAs (siRNAs) decreased key TGFbeta/Smad3-specific responses, including the induction of both plasminogen activator inhibitor-1 (PAI-1) gene expression and p21 protein expression. Blockade of km23-1 expression had no effect on these two major TGFbeta/Smad3 responses under similar conditions. Further, km23-2 was required for TGFbeta stimulation of Smad3-dependent Smad-binding element (SBE)2-Luc transcriptional activity, but not for TGFbeta stimulation of Smad2-dependent activin responsive element (ARE)-Lux transcriptional activity. In order to assess the mechanisms underlying the preferential stimulation of Smad3- versus Smad2-specific TGFbeta responses, immunoprecipitation (IP)/blot analyses were performed, which demonstrate that TGFbeta stimulated preferential complex formation of km23-2 with Smad3, relative to Smad2. Collectively, our findings indicate that km23-2 is required for Smad3-dependent TGFbeta signaling. More importantly, we demonstrate that km23-2 has functions in TGFbeta signaling that are distinct from those for km23-1. This is the first report to describe a differential requirement for unique isoforms of a specific DLC family in Smad-specific TGFbeta signaling.

Bub3 is a spindle assembly checkpoint protein regulating chromosome segregation during mouse oocyte meiosis

In mitosis, the spindle assembly checkpoint (SAC) prevents anaphase onset until all chromosomes have been attached to the spindle microtubules and aligned correctly at the equatorial metaphase plate. The major checkpoint proteins in mitosis consist of mitotic arrest-deficient (Mad)1–3, budding uninhibited by benzimidazole (Bub)1, Bub3, and monopolar spindle 1(Mps1). During meiosis, for the formation of a haploid gamete, two consecutive rounds of chromosome segregation occur with only one round of DNA replication. To pull homologous chromosomes to opposite spindle poles during meiosis I, both sister kinetochores of a homologue must face toward the same pole which is very different from mitosis and meiosis II. As a core member of checkpoint proteins, the individual role of Bub3 in mammalian oocyte meiosis is unclear. In this study, using overexpression and RNA interference (RNAi) approaches, we analyzed the role of Bub3 in mouse oocyte meiosis. Our data showed that overexpressed Bub3 inhibited meiotic metaphase-anaphase transition by preventing homologous chromosome and sister chromatid segregations in meiosis I and II, respectively. Misaligned chromosomes, abnormal polar body and double polar bodies were observed in Bub3 knock-down oocytes, causing aneuploidy. Furthermore, through cold treatment combined with Bub3 overexpression, we found that overexpressed Bub3 affected the attachments of microtubules and kinetochores during metaphase-anaphase transition. We propose that as a member of SAC, Bub3 is required for regulation of both meiosis I and II, and is potentially involved in kinetochore-microtubule attachment in mammalian oocytes.

Bub1 and Bub3 promote the conversion from monopolar to bipolar chromosome attachment independently of shugoshin

The eukaryotic spindle assembly checkpoint (SAC) delays anaphase in the presence of chromosome attachment errors. Bub3 has been reported to be required for SAC activity in all eukaryotes examined so far. We find that Bub3, unlike its binding partner Bub1, is not essential for the SAC in fission yeast. As Bub3 is needed for the efficient kinetochore localization of Bub1, and of Mad1, Mad2 and Mad3, this implies that most SAC proteins do not need to be enriched at the kinetochores for the SAC to function. We find that Bub3 is also dispensable for shugoshin localization to the centromeres, which is the second known function of Bub1. Instead, Bub3, together with Bub1, has a specific function in promoting the conversion from chromosome mono-orientation to bi-orientation.

Dynein light intermediate chain 1 is required for progress through the spindle assembly checkpoint

The spindle assembly checkpoint monitors microtubule attachment to kinetochores and tension across sister kinetochores to ensure accurate division of chromosomes between daughter cells. Cytoplasmic dynein functions in the checkpoint, apparently by moving critical checkpoint components off kinetochores. The dynein subunit required for this function is unknown. Here we show that human cells depleted of dynein light intermediate chain 1 (LIC1) delay in metaphase with increased interkinetochore distances; dynein remains intact, localised and functional. The checkpoint proteins Mad1/2 and Zw10 localise to kinetochores under full tension, whereas BubR1 is diminished at kinetochores. Metaphase delay and increased interkinetochore distances are suppressed by depletion of Mad1, Mad2 or BubR1 or by re-expression of wtLIC1 or a Cdk1 site phosphomimetic LIC1 mutant, but not Cdk1-phosphorylation-deficient LIC1. When the checkpoint is activated by microtubule depolymerisation, Mad1/2 and BubR1 localise to kinetochores. We conclude that a Cdk1 phosphorylated form of LIC1 is required to remove Mad1/2 and Zw10 but not BubR1 from kinetochores during spindle assembly checkpoint silencing.

Dynein light intermediate chain: an essential subunit that contributes to spindle checkpoint inactivation

The dynein light intermediate chain (LIC) is a subunit unique to the cytoplasmic form of dynein, but how it contributes to dynein function is not fully understood. Previous work has established that the LIC homodimer binds directly to the dynein heavy chain and may mediate the attachment of dynein to centrosomes and other cargoes. Here, we report our characterization of the LIC in Drosophila. Unlike vertebrates, in which two Lic genes encode multiple subunit isoforms, the Drosophila LIC is encoded by a single gene. We determined that the single LIC polypeptide is phosphorylated, and that different phosphoisoforms can assemble into the dynein motor complex. Our mutational analyses demonstrate that, similar to other dynein subunits, the Drosophila LIC is required for zygotic development, germline specification of the oocyte, and mitotic cell division. We show that RNA interference depletion of LIC in Drosophila S2 cells does not block the recruitment of a dynein complex to kinetochores, but it does delay inactivation of Mad2 signaling and mitotic progression. Our observations suggest the LIC contributes to a broad range of dynein functions.

A neuron-specific cytoplasmic dynein isoform preferentially transports TrkB signaling endosomes

Cytoplasmic dynein is the multisubunit motor protein for retrograde movement of diverse cargoes to microtubule minus ends. Here, we investigate the function of dynein variants, defined by different intermediate chain (IC) isoforms, by expressing fluorescent ICs in neuronal cells. Green fluorescent protein (GFP)-IC incorporates into functional dynein complexes that copurify with membranous organelles. In living PC12 cell neurites, GFP-dynein puncta travel in both the anterograde and retrograde directions. In cultured hippocampal neurons, neurotrophin receptor tyrosine kinase B (TrkB) signaling endosomes are transported by cytoplasmic dynein containing the neuron-specific IC-1B isoform and not by dynein containing the ubiquitous IC-2C isoform. Similarly, organelles containing TrkB isolated from brain by immunoaffinity purification also contain dynein with IC-1 but not IC-2 isoforms. These data demonstrate that the IC isoforms define dynein populations that are selectively recruited to transport distinct cargoes.

Transport and egress of herpes simplex virus in neurons

The mechanisms of axonal transport of the alphaherpesviruses, HSV and pseudorabies virus (PrV), in neuronal axons are of fundamental interest, particularly in comparison with other viruses, and offer potential sites for antiviral intervention or development of gene therapy vectors. These herpesviruses are transported rapidly along microtubules (MTs) in the retrograde direction from the axon terminus to the dorsal root ganglion and then anterogradely in the opposite direction. Retrograde transport follows fusion and deenvelopment of the viral capsid at the axonal membrane followed by loss of most of the tegument proteins and then binding of the capsid via one or more viral proteins (VPs) to the retrograde molecular motor dynein. The HSV capsid protein pUL35 has been shown to bind to the dynein light chain Tctex1 but is likely to be accompanied by additional dynein binding of an inner tegument protein. The mechanism of anterograde transport is much more controversial with different processes being claimed for PrV and HSV: separate transport of HSV capsid/tegument and glycoproteins versus PrV transport as an enveloped virion. The controversy has not been resolved despite application, in several laboratories, of confocal microscopy (CFM), real-time fluorescence with viruses dual labelled on capsid and glycoprotein, electron microscopy in situ and immuno-electron microscopy. Different processes for each virus seem counterintuitive although they are the most divergent in the alphaherpesvirus subfamily. Current hypotheses suggest that unenveloped HSV capsids complete assembly in the axonal growth cones and varicosities, whereas with PrV unenveloped capsids are only found travelling in a retrograde direction.

The human spindle assembly checkpoint protein Bub3 is required for the establishment of efficient kinetochore-microtubule attachments

The spindle assembly checkpoint monitors the status of kinetochore-microtubule (K-MT) attachments and delays anaphase onset until full metaphase alignment is achieved. Recently, the role of spindle assembly checkpoint proteins was expanded with the discovery that BubR1 and Bub1 are implicated in the regulation of K-MT attachments. One unsolved question is whether Bub3, known to form cell cycle constitutive complexes with both BubR1 and Bub1, is also required for proper chromosome-to-spindle attachments. Using RNA interference and high-resolution microscopy, we analyzed K-MT interactions in Bub3-depleted cells and compared them to those in Bub1- or BubR1-depleted cells. We found that Bub3 is essential for the establishment of correct K-MT attachments. In contrast to BubR1 depletion, which severely compromises chromosome attachment and alignment, we found Bub3 and Bub1 depletions to produce defective K-MT attachments that, however, still account for significant chromosome congression. After Aurora B inhibition, alignment defects become severer in Bub3- and Bub1-depleted cells, while partially rescued in BubR1-depleted cells, suggesting that Bub3 and Bub1 depletions perturb K-MT attachments distinctly from BubR1. Interestingly, misaligned chromosomes in Bub3- and Bub1-depleted cells were found to be predominantly bound in a side-on configuration. We propose that Bub3 promotes the formation of stable end-on bipolar attachments.

Interaction of the DYNLT (TCTEX1/RP3) light chains and the intermediate chains reveals novel intersubunit regulation during assembly of the dynein complex

The cytoplasmic dynein 1 cargo binding domain is formed by five subunits including the intermediate chain and the DYNLT, DYNLL, and DYNLRB light chain families. Six isoforms of the intermediate chain and two isoforms of each of the light chain families have been identified in mammals. There is evidence that different subunit isoforms are involved in regulating dynein function, in particular linking dynein to different cargoes. However, it is unclear how the subunit isoforms are assembled or if there is any specificity to their interactions. Co-immunoprecipitation using DYNLT-specific antibodies reveals that dynein complexes with DYNLT light chains also contain the DYNLL and DYNLRB light chains. The DYNLT light chains, but not DYNLL light chains, associate exclusively with the dynein complex. Yeast two-hybrid and co-immunoprecipitation assays demonstrate that both members of the DYNLT family are capable of forming homodimers and heterodimers. In addition, both homodimers of the DYNLT family bind all six intermediate chain isoforms. However, DYNLT heterodimers do not bind to the intermediate chain. Thus, whereas all combinations of DYNLT light chain dimers can be made, not all of the possible combinations of the isoforms are utilized during the assembly of the dynein complex.