DDA3 associates with microtubule plus ends and orchestrates microtubule dynamics and directional cell migration

Dermal Fibroblast Migration and Proliferation Upon Wounding or Lipopolysaccharide Exposure is Mediated by Stathmin

The dermal fibroblast is a crucial executor involved in wound healing, and lipopolysaccharide is a key factor in initiating the migration and proliferation of the dermal fibroblasts, followed by wound healing. However, the underlying molecular mechanism is still unknown. In this study, we demonstrated that stathmin increased concomitantly with p38/MAPK pathway activation by lipopolysaccharide stimulation of the human dermal fibroblast (HDF), which induced microtubule (MT) depolymerization followed by increased HDF migration and proliferation. In contrast, the application of taxol, the small interfering RNA transfection of stathmin, or the application of the p38/MAPK inhibitor SB203580 suppressed MT depolymerization and HDF migration and proliferation. Additionally, the overexpression of a MKK6(Glu) mutant, which constitutively activated p38/MAPK, resulted in MT depolymerization and, subsequently, promoted HDF migration and proliferation. Our data reveal a crucial role of stathmin in HDF migration and proliferation. These findings will provide new targets and strategies for clinical interventions in wound healing.

Damsel in distress calling on her knights: Illuminating the pioneering role of E3 ubiquitin ligases in guarding the genome integrity

The maintenance of genomic integrity is of utmost importance for the organisms to survive and to accurately inherit traits to their progenies. Any kind of DNA damage either due to defect in DNA duplication and/ or uncontrolled cell division or intracellular insults or environment radiation can result in gene mutation, chromosomal aberration and ultimately genomic instability, which may cause several diseases including cancers. Therefore, cells have evolved machineries for the surveillance of genomic integrity. Enormous exciting studies in the past indicate that ubiquitination (a posttranslational modification of proteins) plays a crucial role in maintaining the genomic integrity by diverse ways. In fact, various E3 ubiquitin ligases catalyse ubiquitination of key proteins to control their central role during cell cycle, DNA damage response (DDR) and DNA repair. Some E3 ligases promote genomic instability while others prevent it, deregulation of both of which leads to several malignancies. In this review, we consolidate the recent findings wherein the role of ubiquitination in conferring genome integrity is highlighted. We also discuss the latest discoveries on the mechanisms utilized by various E3 ligases to preserve genomic stability, with a focus on their actions during cell cycle progression and different types of DNA damage response as well as repair pathways.

Acetylation of ezrin regulates membrane-cytoskeleton interaction underlying CCL18-elicited cell migration

Ezrin, a membrane–cytoskeleton linker protein, plays an essential role in cell polarity establishment, cell migration, and division. Recent studies show that ezrin phosphorylation regulates breast cancer metastasis by promoting cancer cell survivor and promotes intrahepatic metastasis via cell migration. However, it was less characterized whether there are additional post-translational modifications and/or post-translational crosstalks on ezrin underlying context-dependent breast cancer cell migration and invasion. Here we show that ezrin is acetylated by p300/CBP-associated factor (PCAF) in breast cancer cells in response to CCL18 stimulation. Ezrin physically interacts with PCAF and is a cognate substrate of PCAF. The acetylation site of ezrin was mapped by mass spectrometric analyses, and dynamic acetylation of ezrin is essential for CCL18-induced breast cancer cell migration and invasion. Mechanistically, the acetylation reduced the lipid-binding activity of ezrin to ensure a robust and dynamic cycling between the plasma membrane and cytosol in response to CCL18 stimulation. Biochemical analyses show that ezrin acetylation prevents the phosphorylation of Thr567. Using atomic force microscopic measurements, our study revealed that acetylation of ezrin induced its unfolding into a dominant structure, which prevents ezrin phosphorylation at Thr567. Thus, these results present a previously undefined mechanism by which CCL18-elicited crosstalks between the acetylation and phosphorylation on ezrin control breast cancer cell migration and invasion. This suggests that targeting PCAF signaling could be a potential therapeutic strategy for combating hyperactive ezrin-driven cancer progression.

MAP4 as a New Candidate in Cardiovascular Disease

Microtubule and mitochondrial dysfunction have been implicated in the pathogenesis of cardiovascular diseases (CVDs), including cardiac hypertrophy, fibrosis, heart failure, and hypoxic/ischemic related heart dysfunction. Microtubule dynamics instability leads to disrupted cell homeostasis and cell shape, decreased cell survival, and aberrant cell division and cell cycle, while mitochondrial dysfunction contributes to abnormal metabolism and calcium flux, increased cell death, oxidative stress, and inflammation, both of which causing cell and tissue dysfunction followed by CVDs. A cytosolic skeleton protein, microtubule-associated protein 4 (MAP4), belonging to the family of microtubule-associated proteins (MAPs), is widely expressed in non-neural cells and possesses an important role in microtubule dynamics. Increased MAP4 phosphorylation results in microtubule instability. In addition, MAP4 also expresses in mitochondria and reveals a crucial role in maintaining mitochondrial homeostasis. Phosphorylated MAP4 promotes mitochondrial apoptosis, followed by cardiac injury. The aim of the present review is to highlight the novel role of MAP4 as a potential candidate in multiple cardiovascular pathologies.

Celastrol inhibits ezrin-mediated migration of hepatocellular carcinoma cells

Progression of hepatocellular carcinoma involves multiple genetic and epigenetic alterations that promote cancer invasion and metastasis. Our recent study revealed that hyperphosphorylation of ezrin promotes intrahepatic metastasis in vivo and cell migration in vitro. Celastrol is a natural product from traditional Chinese medicine which has been used in treating liver cancer. However, the mechanism of action underlying celastrol treatment was less clear. Here we show that ROCK2 is a novel target of celastrol and inhibition of ROCK2 suppresses elicited ezrin activation and liver cancer cell migration. Using cell monolayer wound healing, we carried out a phenotype-based screen of natural products and discovered the efficacy of celastrol in inhibiting cell migration. The molecular target of celastrol was identified as ROCK2 using celastrol affinity pull-down assay. Our molecular docking analyses indicated celastrol binds to the active site of ROCK2 kinase. Mechanistically, celastrol inhibits the ROCK2-mediated phosphorylation of ezrin at Thr567 which harnesses liver cancer cell migration. Our findings suggest that targeting ROCK2-ezrin signaling is a potential therapeutic niche for celastrol-based intervention of cancer progression in hepatocellular carcinoma.

Nonhistone targets of KAT2A and KAT2B implicated in cancer biology 1

Lysine acetylation is a critical post-translation modification that can impact a protein's localization, stability, and function. Originally thought to only occur on histones, we now know thousands of nonhistone proteins are also acetylated. In conjunction with many other proteins, lysine acetyltransferases (KATs) are incorporated into large protein complexes that carry out these modifications. In this review we focus on the contribution of two KATs, KAT2A and KAT2B, and their potential roles in the development and progression of cancer. Systems biology demands that we take a broad look at protein function rather than focusing on individual pathways or targets. As such, in this review we examine KAT2A/2B-directed nonhistone protein acetylations in cancer in the context of the 10 "Hallmarks of Cancer", as defined by Hanahan and Weinberg. By focusing on specific examples of KAT2A/2B-directed acetylations with well-defined mechanisms or strong links to a cancer phenotype, we aim to reinforce the complex role that these enzymes play in cancer biology.

Microtubules-associated Rac regulation of endothelial barrier: a role of Asef in acute lung injury

The endothelial barrier function regulated by the cytoskeletal reorganizations has been implicated in the pathogenesis of multiple lung diseases including asthma, sepsis, edema, and acute respiratory distress syndrome. The extensive studies have established that activation of small GTPase Rac is a key mechanism in endothelial barrier protection but the role of microtubules-associated Rac in the endothelial functions remains poorly understood. With the emerging evidences that microtubules disassembly also plays a critical role in actin cytoskeleton remodeling leading to endothelial permeability, the knowledge on microtubules-mediated regulation of endothelial barrier is imperative to better understand the etiology of lung injuries as well as to develop novel therapeutics against these disorders. In this regard, our recent studies have revealed some novel aspects of microtubules-mediated regulation of endothelial barrier functions and unraveled a putative role of Rac-specific guanine nucleotide exchange factor Asef in mediating the barrier protective effects of hepatocyte growth factor. In this review, we will discuss the role of this novel Rac activator Asef in endothelial barrier protection and its regulation by microtubules.

Regulation of end-binding protein EB1 in the control of microtubule dynamics

The regulation of microtubule dynamics is critical to ensure essential cell functions, such as proper segregation of chromosomes during mitosis or cell polarity and migration. End-binding protein 1 (EB1) is a plus-end-tracking protein (+TIP) that accumulates at growing microtubule ends and plays a pivotal role in the regulation of microtubule dynamics. EB1 autonomously binds an extended tubulin-GTP/GDP-Pi structure at growing microtubule ends and acts as a molecular scaffold that recruits a large number of regulatory +TIPs through interaction with CAP-Gly or SxIP motifs. While extensive studies have focused on the structure of EB1-interacting site at microtubule ends and its role as a molecular platform, the mechanisms involved in the negative regulation of EB1 have only started to emerge and remain poorly understood. In this review, we summarize recent studies showing that EB1 association with MT ends is regulated by post-translational modifications and affected by microtubule-targeting agents. We also present recent findings that structural MAPs, that have no tip-tracking activity, physically interact with EB1 to prevent its accumulation at microtubule plus ends. These observations point out a novel concept of "endogenous EB1 antagonists" and emphasize the importance of finely regulating EB1 function at growing microtubule ends.

Fidgetin regulates cultured astrocyte migration by severing tyrosinated microtubules at the leading edge

Fign regulates cultured astrocyte migration by severing tyrosinated microtubules (MTs). Inhibition of cellular migration induced by Fign knockdown can be rescued with concomitant knockdown of kinesin-12. A working model is given for the MT reconfiguration underlying cellular migration elicited by the cooperation of two distinct MT-related proteins.

Microtubule (MT) organization is essential for many cellular events, including mitosis, migration, and cell polarity. Fidgetin (Fign), an ATP-dependent, MT-severing protein, contributes to the regulation of MT configuration by cutting and trimming MT polymers. Functions of Fign have been indicated in neurite outgrowth, mitosis, meiosis, and cellular migration. Here we focus on migration of astrocytes. We find that Fign plays an essential role in cultured astrocyte migration by preferentially targeting MTs (or regions of MTs) that are rich in tyrosinated tubulin, a marker for especially dynamic MTs or especially dynamic regions of MTs. Inhibition of cellular migration induced by Fign knockdown can be rescued with concomitant knockdown of kinesin-12, a motor protein best known for its role in mitosis. We propose a novel working model for MT reconfiguration underlying cellular migration elicited by the functional cooperation of two distinct MT-related proteins.

The Microtubule Plus End Tracking Protein TIP150 Interacts with Cortactin to Steer Directional Cell Migration

Cell migration is orchestrated by dynamic interactions of microtubules with the plasma membrane cortex. How these interactions facilitate these dynamic processes is still being actively investigated. TIP150 is a newly characterized microtubule plus end tracking protein essential for mitosis and entosis (Ward, T., Wang, M., Liu, X., Wang, Z., Xia, P., Chu, Y., Wang, X., Liu, L., Jiang, K., Yu, H., Yan, M., Wang, J., Hill, D. L., Huang, Y., Zhu, T., and Yao, X. (2013) Regulation of a dynamic interaction between two microtubule-binding proteins, EB1 and TIP150, by the mitotic p300/CBP-associated factor (PCAF) orchestrates kinetochore microtubule plasticity and chromosome stability during mitosis. J. Biol. Chem. 288, 15771-15785; Xia, P., Zhou, J., Song, X., Wu, B., Liu, X., Li, D., Zhang, S., Wang, Z., Yu, H., Ward, T., Zhang, J., Li, Y., Wang, X., Chen, Y., Guo, Z., and Yao, X. (2014) Aurora A orchestrates entosis by regulating a dynamic MCAK-TIP150 interaction. J. Mol. Cell Biol. 6, 240-254). Here we show that TIP150 links dynamic microtubules to steer cell migration by interacting with cortactin. Mechanistically, TIP150 binds to cortactin via its C-terminal tail. Interestingly, the C-terminal TIP150 proline-rich region (CT150) binds to the Src homology 3 domain of cortactin specifically, and such an interaction is negatively regulated by EGF-elicited tyrosine phosphorylation of cortactin. Importantly, suppression of TIP150 or overexpression of phospho-mimicking cortactin inhibits polarized cell migration. In addition, CT150 disrupts the biochemical interaction between TIP150 and cortactin in vitro, and perturbation of the TIP150-cortactin interaction in vivo using a membrane-permeable TAT-CT150 peptide results in an inhibition of directional cell migration. We reason that a dynamic TIP150-cortactin interaction orchestrates directional cell migration via coupling dynamic microtubule plus ends to the cortical cytoskeleton.

Microtubule plus-end tracking proteins in neuronal development

Regulation of the microtubule cytoskeleton is of pivotal importance for neuronal development and function. One such regulatory mechanism centers on microtubule plus-end tracking proteins (+TIPs): structurally and functionally diverse regulatory factors, which can form complex macromolecular assemblies at the growing microtubule plus-ends. +TIPs modulate important properties of microtubules including their dynamics and their ability to control cell polarity, membrane transport and signaling. Several neurodevelopmental and neurodegenerative diseases are associated with mutations in +TIPs or with misregulation of these proteins. In this review, we focus on the role and regulation of +TIPs in neuronal development and associated disorders.

Spatiotemporal dynamics of Aurora B-PLK1-MCAK signaling axis orchestrates kinetochore bi-orientation and faithful chromosome segregation

Chromosome segregation in mitosis is orchestrated by the dynamic interactions between the kinetochore and spindle microtubules. The microtubule depolymerase mitotic centromere-associated kinesin (MCAK) is a key regulator for an accurate kinetochore-microtubule attachment. However, the regulatory mechanism underlying precise MCAK depolymerase activity control during mitosis remains elusive. Here, we describe a novel pathway involving an Aurora B-PLK1 axis for regulation of MCAK activity in mitosis. Aurora B phosphorylates PLK1 on Thr210 to activate its kinase activity at the kinetochores during mitosis. Aurora B-orchestrated PLK1 kinase activity was examined in real-time mitosis using a fluorescence resonance energy transfer-based reporter and quantitative analysis of native PLK1 substrate phosphorylation. Active PLK1, in turn, phosphorylates MCAK at Ser715 which promotes its microtubule depolymerase activity essential for faithful chromosome segregation. Importantly, inhibition of PLK1 kinase activity or expression of a non-phosphorylatable MCAK mutant prevents correct kinetochore-microtubule attachment, resulting in abnormal anaphase with chromosome bridges. We reason that the Aurora B-PLK1 signaling at the kinetochore orchestrates MCAK activity, which is essential for timely correction of aberrant kinetochore attachment to ensure accurate chromosome segregation during mitosis.

P38/MAPK contributes to endothelial barrier dysfunction via MAP4 phosphorylation-dependent microtubule disassembly in inflammation-induced acute lung injury

Excessive activation of inflammation and the accompanying lung vascular endothelial barrier disruption are primary pathogenic features of acute lung injury (ALI). Microtubule-associated protein 4 (MAP4), a tubulin assembly-promoting protein, is important for maintaining the microtubule (MT) cytoskeleton and cell-cell junctional structures. However, both the involvement and exact mechanism of MAP4 in the development of endothelial barrier disruption in ALI remains unknown. In this study, lipopolysaccharide (LPS) and tumour necrosis factor-α (TNF-α) were applied to human pulmonary microvascular endothelial cells (HPMECs) to mimic the endothelial damage during inflammation in vitro. We demonstrated that the MAP4 (Ser696 and Ser787) phosphorylation increased concomitantly with the p38/MAPK pathway activation by the LPS and TNF-α stimulation of HPMECs, which induced MT disassembly followed by hyperpermeability. Moreover, the application of taxol, the overexpression of a MAP4 (Ala) mutant, or the application of the p38/MAPK inhibitor SB203580 inhibited the MT disruption and the intracellular junction dysfunction. In contrast, MKK6 (Glu), which constitutively activated p38/MAPK, resulted in microtubule depolymerisation and, subsequently, hyperpermeability. Our findings reveal a novel role of MAP4 in endothelial barrier dysfunction.

Targeting LUNX inhibits non-small cell lung cancer growth and metastasis

There remains a great need for effective therapies for lung cancer, the majority of which are non-small cell lung cancers (NSCLC). Here, we report the identification of a novel candidate therapeutic target, LUNX, as a molecule overexpressed in primary NSCLC and lymph node metastases that is associated with reduced postoperative survival. Functional studies demonstrated that LUNX overexpression promoted lung cancer cell migration and proliferation by interactions with the chaperone protein 14-3-3. Conversely, LUNX silencing disrupted primary tumor growth, local invasion, and metastatic colonization. The finding that LUNX was expressed on cell membranes prompted us to generate and characterize LUNX antibodies as a candidate therapeutic. Anti-LUNX could downregulate LUNX and reduce lung cancer cell proliferation and migration in vitro. Administered in vivo to mice bearing lung cancer xenografts, anti-LUNX could slow tumor growth and metastasis and improve mouse survival. Together, our work provides a preclinical proof of concept for LUNX as a novel candidate target for immunotherapy in lung cancer.

Epigenome-guided analysis of the transcriptome of plaque macrophages during atherosclerosis regression reveals activation of the Wnt signaling pathway

We report the first systems biology investigation of regulators controlling arterial plaque macrophage transcriptional changes in response to lipid lowering in vivo in two distinct mouse models of atherosclerosis regression. Transcriptome measurements from plaque macrophages from the Reversa mouse were integrated with measurements from an aortic transplant-based mouse model of plaque regression. Functional relevance of the genes detected as differentially expressed in plaque macrophages in response to lipid lowering in vivo was assessed through analysis of gene functional annotations, overlap with in vitro foam cell studies, and overlap of associated eQTLs with human atherosclerosis/CAD risk SNPs. To identify transcription factors that control plaque macrophage responses to lipid lowering in vivo, we used an integrative strategy – leveraging macrophage epigenomic measurements – to detect enrichment of transcription factor binding sites upstream of genes that are differentially expressed in plaque macrophages during regression. The integrated analysis uncovered eight transcription factor binding site elements that were statistically overrepresented within the 5′ regulatory regions of genes that were upregulated in plaque macrophages in the Reversa model under maximal regression conditions and within the 5′ regulatory regions of genes that were upregulated in the aortic transplant model during regression. Of these, the TCF/LEF binding site was present in promoters of upregulated genes related to cell motility, suggesting that the canonical Wnt signaling pathway may be activated in plaque macrophages during regression. We validated this network-based prediction by demonstrating that β-catenin expression is higher in regressing (vs. control group) plaques in both regression models, and we further demonstrated that stimulation of canonical Wnt signaling increases macrophage migration in vitro. These results suggest involvement of canonical Wnt signaling in macrophage emigration from the plaque during lipid lowering-induced regression, and they illustrate the discovery potential of an epigenome-guided, systems approach to understanding atherosclerosis regression.

Atherosclerosis, a progressive accumulation of lipid-rich plaque within arteries, is an inflammatory disease in which the response of macrophages (a key cell type of the innate immune system) to plasma lipoproteins plays a central role. In humans, the goal of significantly reducing already-established plaque through drug treatments, including statins, remains elusive. In mice, atherosclerosis can be reversed by experimental manipulations that lower circulating lipid levels. A common feature of many regression models is that macrophages transition to a less inflammatory state and emigrate from the plaque. While the molecular regulators that control these responses are largely unknown, we hypothesized that by integrating global measurements of macrophage gene expression in regressing plaques with measurements of the macrophage chromatin landscape, we could identify key molecules that control macrophage responses to the lowering of circulating lipid levels. Our systems biology analysis of plaque macrophages yielded a network in which the Wnt signaling pathway emerged as a candidate upstream regulator. Wnt signaling is known to affect both inflammation and the ability of macrophages to migrate from one location to another, and our targeted validation studies provide evidence that Wnt signaling is increased in plaque macrophages during regression. Our findings both demonstrate the power of a systems approach to uncover candidate regulators of regression and to identify a potential new therapeutic target.

Superresolution imaging reveals structural features of EB1 in microtubule plus-end tracking

A method is introduced for optically imaging intracellular protein interactions at nanometer spatial resolution in live cells using photoactivatable complementary fluorescent (PACF) proteins. The PACF approach established here will enable the simultaneous visualization of homo- and heterodimeric interactions at the single live-cell level.

Visualization of specific molecules and their interactions in real time and space is essential to delineate how cellular dynamics and the signaling circuit are orchestrated. Spatial regulation of conformational dynamics and structural plasticity of protein interactions is required to rewire signaling circuitry in response to extracellular cues. We introduce a method for optically imaging intracellular protein interactions at nanometer spatial resolution in live cells, using photoactivatable complementary fluorescent (PACF) proteins. Subsets of complementary fluorescent protein molecules were activated, localized, and then bleached; this was followed by the assembly of superresolution images from aggregate position of sum interactive molecules. Using PACF, we obtained precise localization of dynamic microtubule plus-end hub protein EB1 dimers and their distinct distributions at the leading edges and in the cell bodies of migrating cells. We further delineated the structure–function relationship of EB1 by generating EB1-PACF dimers (EB1^wt:EB1^wt, EB1^wt:EB1^mt, and EB1^mt:EB1^mt) and imaging their precise localizations in culture cells. Surprisingly, our analyses revealed critical role of a previously uncharacterized EB1 linker region in tracking microtubule plus ends in live cells. Thus PACF provides a unique approach to delineating spatial dynamics of homo- or heterodimerized proteins at the nanometer scale and establishes a platform to report the precise regulation of protein interactions in space and time in live cells.

Microtubule plus-end tracking proteins and their roles in cell division

Microtubules are cellular components that are required for a variety of essential processes such as cell motility, mitosis, and intracellular transport. This is possible because of the inherent dynamic properties of microtubules. Many of these properties are tightly regulated by a number of microtubule plus-end-binding proteins or +TIPs. These proteins recognize the distal end of microtubules and are thus in the right context to control microtubule dynamics. In this review, we address how microtubule dynamics are regulated by different +TIP families, focusing on how functionally diverse +TIPs spatially and temporally regulate microtubule dynamics during animal cell division.