Oncoprotein 18 is a phosphorylation-responsive regulator of microtubule dynamics

STMND1 is a phylogenetically ancient stathmin which localizes to motile cilia and exhibits nuclear translocation that is inhibited when soluble tubulin concentration increases

Stathmins are small, unstructured proteins that bind tubulin dimers and are implicated in several human diseases, but whose function remains unknown. We characterized a new stathmin, STMND1 (Stathmin Domain Containing 1) as the human representative of an ancient subfamily. STMND1 features a N-terminal myristoylated and palmitoylated motif which directs it to membranes and a tubulin-binding stathmin-like domain (SLD) that contains an internal nuclear localization signal. Biochemistry and proximity labeling showed that STMND1 binds tubulin, and live imaging showed that tubulin binding inhibits translocation from cellular membranes to the nucleus. STMND1 is highly expressed in multiciliated epithelial cells, where it localizes to motile cilia. Overexpression in a model system increased the length of primary cilia. Our study suggests that the most ancient stathmins have cilium-related functions that involve sensing soluble tubulin.

Survivin as a Therapeutic Target for the Treatment of Human Cancer

Survivin was initially identified as a member of the inhibitor apoptosis (IAP) protein family and has been shown to play a critical role in the regulation of apoptosis. More recent studies showed that survivin is a component of the chromosome passenger complex and acts as an essential mediator of mitotic progression. Other potential functions of survivin, such as mitochondrial function and autophagy, have also been proposed. Survivin has emerged as an attractive target for cancer therapy because its overexpression has been found in most human cancers and is frequently associated with chemotherapy resistance, recurrence, and poor survival rates in cancer patients. In this review, we discuss our current understanding of how survivin mediates various aspects of malignant transformation and drug resistance, as well as the efforts that have been made to develop therapeutics targeting survivin for the treatment of cancer.

Stathmin-2 loss leads to neurofilament-dependent axonal collapse driving motor and sensory denervation

The mRNA transcript of the human STMN2 gene, encoding for stathmin-2 protein (also called SCG10), is profoundly impacted by TAR DNA-binding protein 43 (TDP-43) loss of function. The latter is a hallmark of several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Using a combination of approaches, including transient antisense oligonucleotide-mediated suppression, sustained shRNA-induced depletion in aging mice, and germline deletion, we show that stathmin-2 has an important role in the establishment and maintenance of neurofilament-dependent axoplasmic organization that is critical for preserving the caliber and conduction velocity of myelinated large-diameter axons. Persistent stathmin-2 loss in adult mice results in pathologies found in ALS, including reduced interneurofilament spacing, axonal caliber collapse that drives tearing within outer myelin layers, diminished conduction velocity, progressive motor and sensory deficits, and muscle denervation. These findings reinforce restoration of stathmin-2 as an attractive therapeutic approach for ALS and other TDP-43-dependent neurodegenerative diseases.

Landscape of NcRNAs involved in drug resistance of breast cancer

Breast cancer (BC) leads to the most amounts of deaths among women. Chemo-, endocrine-, and targeted therapies are the mainstay drug treatments for BC in the clinic. However, drug resistance is a major obstacle for BC patients, and it leads to poor prognosis. Accumulating evidences suggested that noncoding RNAs (ncRNAs) are intricately linked to a wide range of pathological processes, including drug resistance. Till date, the correlation between drug resistance and ncRNAs is not completely understood in BC. Herein, we comprehensively summarized a dysregulated ncRNAs landscape that promotes or inhibits drug resistance in chemo-, endocrine-, and targeted BC therapies. Our review will pave way for the effective management of drug resistance by targeting oncogenic ncRNAs, which, in turn will promote drug sensitivity of BC in the future.

STNM1 in human cancers: role, function and potential therapy sensitizer

STMN1 belongs to the stathmin gene family, it encodes a cytoplasmic phosphorylated protein, stathmin1, which is commonly observed in vertebrate cells. STMN1 is a structural microtubule-associated protein (MAP) that binds to microtubule protein dimers rather than microtubules, with each STMN1 binding two microtubule protein dimers and preventing their aggregation, leading to microtubule instability. STMN1 expression is elevated in a number of malignancies, and inhibition of its expression can interfere with tumor cell division. Its expression can change the division of tumor cells, thereby arresting cell growth in the G2/M phase. Moreover, STMN1 expression affects tumor cell sensitivity to anti-microtubule drug analogs, including vincristine and paclitaxel. The research on MAPs is limited, and new insights on the mechanism of STMN1 in different cancers are emerging. The effective application of STMN1 in cancer prognosis and treatment requires further understanding of this protein. Here, we summarize the general characteristics of STMN1 and outline how STMN1 plays a role in cancer development, targeting multiple signaling networks and acting as a downstream target for multiple microRNAs, circRNAs, and lincRNAs. We also summarize recent findings on the function role of STMN1 in tumor resistance and as a therapeutic target for cancer.

The landscape of exosomal non-coding RNAs in breast cancer drug resistance, focusing on underlying molecular mechanisms

Breast cancer (BC) is the most common malignancy among women worldwide. Like many other cancers, BC therapy is challenging and sometimes frustrating. In spite of the various therapeutic modalities applied to treat the cancer, drug resistance, also known as, chemoresistance, is very common in almost all BCs. Undesirably, a breast tumor might be resistant to different curative approaches (e.g., chemo- and immunotherapy) at the same period of time. Exosomes, as double membrane-bound extracellular vesicles 1) secreted from different cell species, can considerably transfer cell products and components through the bloodstream. In this context, non-coding RNAs (ncRNAs), including miRNAs, long ncRNAs (lncRNAs), and circular RNAs (circRNAs), are a chief group of exosomal constituents with amazing abilities to regulate the underlying pathogenic mechanisms of BC, such as cell proliferation, angiogenesis, invasion, metastasis, migration, and particularly drug resistance. Thereby, exosomal ncRNAs can be considered potential mediators of BC progression and drug resistance. Moreover, as the corresponding exosomal ncRNAs circulate in the bloodstream and are found in different body fluids, they can serve as foremost prognostic/diagnostic biomarkers. The current study aims to comprehensively review the most recent findings on BC-related molecular mechanisms and signaling pathways affected by exosomal miRNAs, lncRNAs, and circRNAs, with a focus on drug resistance. Also, the potential of the same exosomal ncRNAs in the diagnosis and prognosis of BC will be discussed in detail.

Simvastatin Downregulates Cofilin and Stathmin to Inhibit Skeletal Muscle Cells Migration

Statins are the most effective therapeutic agents for reducing cholesterol synthesis. Given their widespread use, many adverse effects from statins have been reported; of these, musculoskeletal complications occurred in 15% of patients after receiving statins for 6 months, and simvastatin was the most commonly administered statin among these cases. This study investigated the negative effects of simvastatin on skeletal muscle cells. We performed RNA sequencing analysis to determine gene expression in simvastatin-treated cells. Cell proliferation and migration were examined through cell cycle analysis and the transwell filter migration assay, respectively. Cytoskeleton rearrangement was examined through F-actin and tubulin staining. Western blot analysis was performed to determine the expression of cell cycle-regulated and cytoskeleton-related proteins. Transfection of small interfering RNAs (siRNAs) was performed to validate the role of cofilin and stathmin in the simvastatin-mediated inhibition of cell migration. The results revealed that simvastatin inhibited the proliferation and migration of skeletal muscle cells and affected the rearrangement of F-actin and tubulin. Simvastatin reduced the expression of cofilin and stathmin. The knockdown of both cofilin and stathmin by specific siRNA synergistically impaired cell migration. In conclusion, our results indicated that simvastatin inhibited skeletal muscle cell migration by reducing the expressions of cofilin and stathmin.

PICT1 is critical for regulating the Rps27a-Mdm2-p53 pathway by microtubule polymerization inhibitor against cervical cancer

In our previous study, it showed that P-3F, a podophyllotoxin derivative, causes the increased level of p53 expression by enhancing p53 stability, resulting from blockage of the Mdm2-p53 feedback loop via nucleolus-to-nucleoplasm translocation of Rps27a in human cervical cancer HeLa cell line. However, the mechanism of regulating Rps27a localization remains to be studied. In the current study, it has been demonstrated that the level of protein interacting with carboxyl terminus 1 (PICT1), originally identified as a tumor suppressor, was decreased in a concentration-dependent manner in response to P-3F, leading to inhibition of human cervical cancer cell lines proliferation. Also remarkably, reduction of serine phosphorylation of STMN1 at position 16 induced by P-3F was required in the downregulation of PICT1, in which p53 activity was likely to be directly involved. Note as well that, PICT1 also played an important role in p53 stability enhancement by inhibiting Mdm2-mediated p53 ubiquitination due to Rps27a translocation from the nucleolus to the nucleoplasm to interact with Mdm2 following treatment with P-3F. Collectively, these findings indicated that P-3F, a microtubule polymerization inhibitor, promotes the decreased level of PICT1 expression, which is critical for regulating the Rps27a-Mdm2-p53 pathway against cervical cancer.

TRP Channels Interactome as a Novel Therapeutic Target in Breast Cancer

Breast cancer is one of the most frequent cancer types worldwide and the first cause of cancer-related deaths in women. Although significant therapeutic advances have been achieved with drugs such as tamoxifen and trastuzumab, breast cancer still caused 627,000 deaths in 2018. Since cancer is a multifactorial disease, it has become necessary to develop new molecular therapies that can target several relevant cellular processes at once. Ion channels are versatile regulators of several physiological- and pathophysiological-related mechanisms, including cancer-relevant processes such as tumor progression, apoptosis inhibition, proliferation, migration, invasion, and chemoresistance. Ion channels are the main regulators of cellular functions, conducting ions selectively through a pore-forming structure located in the plasma membrane, protein–protein interactions one of their main regulatory mechanisms. Among the different ion channel families, the Transient Receptor Potential (TRP) family stands out in the context of breast cancer since several members have been proposed as prognostic markers in this pathology. However, only a few approaches exist to block their specific activity during tumoral progress. In this article, we describe several TRP channels that have been involved in breast cancer progress with a particular focus on their binding partners that have also been described as drivers of breast cancer progression. Here, we propose disrupting these interactions as attractive and potential new therapeutic targets for treating this neoplastic disease.

MicroRNAs as the critical regulators of Doxorubicin resistance in breast tumor cells

BACKGROUND

Chemotherapy is one of the most common treatment options for breast cancer (BC) patients. However, about half of the BC patients are chemotherapeutic resistant. Doxorubicin (DOX) is considered as one of the first line drugs in the treatment of BC patients whose function is negatively affected by multi drug resistance. Due to the severe side effects of DOX, it is very important to diagnose the DOX resistant BC patients. Therefore, assessment of molecular mechanisms involved in DOX resistance can improve the clinical outcomes in BC patients by introducing the novel therapeutic and diagnostic molecular markers. MicroRNAs (miRNAs) as members of the non-coding RNAs family have pivotal roles in various cellular processes including cell proliferation and apoptosis. Therefore, aberrant miRNAs functions and expressions can be associated with tumor progression, metastasis, and drug resistance. Moreover, due to miRNAs stability in body fluids, they can be considered as non-invasive diagnostic markers for the DOX response in BC patients.

MAIN BODY

In the present review, we have summarized all of the miRNAs that have been reported to be associated with DOX resistance in BC for the first time in the world.

CONCLUSIONS

Since, DOX has severe side effects; it is required to distinguish the non DOX-responders from responders to improve the clinical outcomes of BC patients. This review highlights the miRNAs as pivotal regulators of DOX resistance in breast tumor cells. Moreover, the present review paves the way of introducing a non-invasive panel of prediction markers for DOX response among BC patients.

The microRNA-210-Stathmin1 Axis Decreases Cell Stiffness to Facilitate the Invasiveness of Colorectal Cancer Stem Cells

Simple Summary

Metastasis of tumor cells is the leading cause of death in cancer patients. Concurrent therapy with surgical removal of primary and metastatic lesions is the main approach for cancer therapy. Currently, therapeutic resistant properties of cancer stem cells (CSCs) are known to drive malignant cancer progression, including metastasis. Our study aimed to identify molecular tools dedicated to the detection and treatment of CSCs. We confirmed that microRNA-210-3p (miR-210) was upregulated in colorectal stem-like cancer cells, which targeted stathmin1 (STMN1), to decrease cell elasticity for increasing mobility. We envision that strategies for softening cellular elasticity will reduce the onset of CSC-orientated metastasis.

Abstract

Cell migration is critical for regional dissemination and distal metastasis of cancer cells, which remain the major causes of poor prognosis and death in patients with colorectal cancer (CRC). Although cytoskeletal dynamics and cellular deformability contribute to the migration of cancer cells and metastasis, the mechanisms governing the migratory ability of cancer stem cells (CSCs), a nongenetic source of tumor heterogeneity, are unclear. Here, we expanded colorectal CSCs (CRCSCs) as colonospheres and showed that CRCSCs exhibited higher cell motility in transwell migration assays and 3D invasion assays and greater deformability in particle tracking microrheology than did their parental CRC cells. Mechanistically, in CRCSCs, microRNA-210-3p (miR-210) targeted stathmin1 (STMN1), which is known for inducing microtubule destabilization, to decrease cell elasticity in order to facilitate cell motility without affecting the epithelial–mesenchymal transition (EMT) status. Clinically, the miR-210-STMN1 axis was activated in CRC patients with liver metastasis and correlated with a worse clinical outcome. This study elucidates a miRNA-oriented mechanism regulating the deformability of CRCSCs beyond the EMT process.

HIV-1 exposure promotes PKG1-mediated phosphorylation and degradation of stathmin to increase epithelial barrier permeability

Exposure of mucosal epithelial cells to the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein gp120 is known to disrupt epithelial cell junctions by impairing stathmin-mediated microtubule depolymerization. However, the pathological significance of this process and its underlying molecular mechanism remain unclear. Here we show that treatment of epithelial cells with pseudotyped HIV-1 viral particles or recombinant gp120 protein results in the activation of protein kinase G 1 (PKG1). Examination of epithelial cells by immunofluorescence microscopy reveals that PKG1 activation mediates the epithelial barrier damage upon HIV-1 exposure. Immunoprecipitation experiments show that PKG1 interacts with stathmin and phosphorylates stathmin at serine 63 in the presence of gp120. Immunoprecipitation and immunofluorescence microscopy further demonstrate that PKG1-mediated phosphorylation of stathmin promotes its autophagic degradation by enhancing the interaction between stathmin and the autophagy adaptor protein p62. Collectively, these results suggest that HIV-1 exposure exploits the PKG1/stathmin axis to affect the microtubule cytoskeleton and thereby perturbs epithelial cell junctions. Our findings reveal a novel molecular mechanism by which exposure to HIV-1 increases epithelial permeability, which has implications for the development of effective strategies to prevent mucosal HIV-1 transmission.

Synthetic lethality of RB1 and aurora A is driven by stathmin-mediated disruption of microtubule dynamics

RB1 mutational inactivation is a cancer driver in various types of cancer including lung cancer, making it an important target for therapeutic exploitation. We performed chemical and genetic vulnerability screens in RB1-isogenic lung cancer pair and herein report that aurora kinase A (AURKA) inhibition is synthetic lethal in RB1-deficient lung cancer. Mechanistically, RB1^−/− cells show unbalanced microtubule dynamics through E2F-mediated upregulation of the microtubule destabilizer stathmin and are hypersensitive to agents targeting microtubule stability. Inhibition of AURKA activity activates stathmin function via reduced phosphorylation and facilitates microtubule destabilization in RB1^−/− cells, heavily impacting the bipolar spindle formation and inducing mitotic cell death selectively in RB1^−/− cells. This study shows that stathmin-mediated disruption of microtubule dynamics is critical to induce synthetic lethality in RB1-deficient cancer and suggests that upstream factors regulating microtubule dynamics, such as AURKA, can be potential therapeutic targets in RB1-deficient cancer.

Retinoblastoma susceptibility gene (RB1) is frequently mutated in lung cancers. Here the authors perform chemical and genetic vulnerability screens and identify aurora A kinase (AURKA) as a synthetic lethal candidate for RB1-deficient lung cancer cells and that AURKA inhibition sensitizes these cells to mitotic cell death.

The Global Phosphorylation Landscape of SARS-CoV-2 Infection

The causative agent of the coronavirus disease 2019 (COVID-19) pandemic, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has infected millions and killed hundreds of thousands of people worldwide, highlighting an urgent need to develop antiviral therapies. Here we present a quantitative mass spectrometry-based phosphoproteomics survey of SARS-CoV-2 infection in Vero E6 cells, revealing dramatic rewiring of phosphorylation on host and viral proteins. SARS-CoV-2 infection promoted casein kinase II (CK2) and p38 MAPK activation, production of diverse cytokines, and shutdown of mitotic kinases, resulting in cell cycle arrest. Infection also stimulated a marked induction of CK2-containing filopodial protrusions possessing budding viral particles. Eighty-seven drugs and compounds were identified by mapping global phosphorylation profiles to dysregulated kinases and pathways. We found pharmacologic inhibition of the p38, CK2, CDK, AXL, and PIKFYVE kinases to possess antiviral efficacy, representing potential COVID-19 therapies.

Oncoprotein 18 is necessary for malignant cell proliferation in bladder cancer cells and serves as a G3-specific non-invasive diagnostic marker candidate in urinary RNA

Background

Urine-based diagnostics indicated involvement of oncoprotein 18 (OP18) in bladder cancer. In cell culture models we investigated the role of OP18 for malignant cell growth.

Methods

We analyzed 113 urine samples and investigated two human BCa cell lines as a dual model: RT-4 and ECV-304, which represented differentiated (G1) and poorly differentiated (G3) BCa. We designed specific siRNA for down-regulation of OP18 in both cell lines. Phenotypes were characterized by cell viability, proliferation, and expression of apoptosis-related genes. Besides, sensitivity to cisplatin treatment was evaluated.

Results

Analysis of urine samples from patients with urothelial BCa revealed a significant correlation of the RNA-ratio OP18:uroplakin 1A with bladder cancer. High urinary ratios were mainly found in moderately to poorly differentiated tumors (grade G2-3) that were muscle invasive (stage T2-3), whereas samples from patients with more differentiated non-invasive BCa (G1) showed low OP18:UPK1A RNA ratios. Down-regulation of OP18 expression in ECV-304 shifted its phenotype towards G1 state. Further, OP18-directed siRNA induced apoptosis and increased chemo-sensitivity to cisplatin.

Conclusions

This study provides conclusive experimental evidence for the link between OP18-derived RNA as a diagnostic marker for molecular staging of BCa in non-invasive urine-based diagnostics and the patho-mechanistic role of OP18 suggesting this gene as a therapeutic target.

Stathmin expression associates with vascular and immune responses in aggressive breast cancer subgroups

Studies indicate that stathmin expression associates with PI3K activation in breast cancer, suggesting stathmin as a marker for targetable patient subgroups. Here we assessed stathmin in relation to tumour proliferation, vascular and immune responses, BRCA1 germline status, basal-like differentiation, clinico-pathologic features, and survival. Immunohistochemical staining was performed on breast cancers from two series (cohort 1, n = 187; cohort 2, n = 198), and mass spectrometry data from 24 cases and 12 breast cancer cell lines was examined for proteomic profiles. Open databases were also explored (TCGA, METABRIC, Oslo2 Landscape cohort, Cancer Cell Line Encyclopedia). High stathmin expression associated with tumour proliferation, p53 status, basal-like differentiation, BRCA1 genotype, and high-grade histology. These patterns were confirmed using mRNA data. Stathmin mRNA further associated with tumour angiogenesis, immune responses and reduced survival. By logistic regression, stathmin protein independently predicted a BRCA1 genotype (OR 10.0, p = 0.015) among ER negative tumours. Cell line analysis (Connectivity Map) implied PI3K inhibition in tumours with high stathmin. Altogether, our findings indicate that stathmin might be involved in the regulation of tumour angiogenesis and immune responses in breast cancer, in addition to tumour proliferation. Cell data point to potential effects of PI3K inhibition in tumours with high stathmin expression.

Stathmin Regulates Spatiotemporal Variation in the Memory Loop in Single-Prolonged Stress Rats

Posttraumatic stress disorder (PTSD) is closely related to brain structures of the memory loop such as the hippocampus, amygdala, and medial prefrontal cortex (mPFC). The fear gene stathmin plays an important role in regulating fear memory. However, whether the fear gene stathmin is related to fear memory loop anomalies caused by PTSD is unclear. A single-prolonged stress (SPS) rat model of PTSD was constructed. Wistar rats were randomly divided into 5 groups: the control group, SPS 1-day group, SPS 4-day group, SPS 7-day group, and SPS 14-day group. Then, we measured the protein and mRNA expression of stathmin, p-stathmin (Ser16, Ser25, Ser38, and Ser63), β-tubulin, and MAP-1B in the hippocampus, amygdala, and mPFC in the 5 groups by immunohistochemistry, Western blotting, and qRT-PCR. The expression of the stathmin protein in the hippocampus, mPFC, and amygdala of the rat memory loop decreased gradually in the SPS 1-day group, the SPS 4-day group, and the SPS 7-day group, in which it was the lowest, and then increased. The trend of the expression of stathmin mRNA in the three areas of the memory loop was consistent with the trend of the expression of the stathmin protein. The trend of the protein expression of p-stathmin (Ser25 and Ser38) was opposite of that of stathmin; it reached a peak on the 7th day, and then decreased in the hippocampus. The protein expression of p-stathmin (Ser63) showed the same trend in the mPFC. The protein and mRNA expression of β-tubulin and MAP-1B was consistent with that of p-stathmin; it reached a peak on the 7th day, and then decreased in the rat hippocampus, mPFC, and amygdala. Stathmin in the memory loop, especially in the hippocampus, regulates microtubule structure through its phosphorylation at Ser25 and Ser38 and thereby participates in the mediation of fear memory abnormalities in PTSD.

Stathmin 1 Induces Murine Hepatocyte Proliferation and Increased Liver Mass

The endogenous cellular signals that initiate the transition of hepatocytes from quiescence to proliferation remain unclear. The protein stathmin 1 (STMN1) is highly expressed in dividing cells, including hepatocytes, and functions to promote cell mitosis through physical interactions with tubulin and microtubules that regulate mitotic spindle formation. The recent finding that STMN1 mediates the resistance of cultured hepatocytes to oxidant stress led to an examination of the expression and function of this protein in the liver in vivo. STMN1 messenger RNA (mRNA) and protein were essentially undetectable in normal mouse liver but increased markedly in response to oxidant injury from carbon tetrachloride. Similarly, levels of STMN1 mRNA and protein were increased in human livers from patients with acute fulminant hepatic failure. To determine STMN1 function in the liver in vivo, mice were infected with a control or Stmn1-expressing adenovirus. Stmn1 expression induced spontaneous liver enlargement with a doubling of the liver to body weight ratio. The increase in liver mass resulted, in part, from hepatocellular hypertrophy but mainly from an induction of hepatocyte proliferation. STMN1 expression led to marked increases in the numbers of 5-bromo-2'-deoxyuridine-positive and mitotic hepatocytes and hepatic nuclear levels of cyclins and cyclin-dependent kinases. STMN1-induced hepatocyte proliferation was followed by an apoptotic response and a return of the liver to its normal mass. Conclusion: STMN1 promotes entry of quiescent hepatocytes into the cell cycle. STMN1 expression by itself in the absence of any reduction in liver mass is sufficient to stimulate a hepatic proliferative response that significantly increases liver mass.

Efa6 protects axons and regulates their growth and branching by inhibiting microtubule polymerisation at the cortex

Cortical collapse factors affect microtubule (MT) dynamics at the plasma membrane. They play important roles in neurons, as suggested by inhibition of axon growth and regeneration through the ARF activator Efa6 in C. elegans, and by neurodevelopmental disorders linked to the mammalian kinesin Kif21A. How cortical collapse factors influence axon growth is little understood. Here we studied them, focussing on the function of Drosophila Efa6 in experimentally and genetically amenable fly neurons. First, we show that Drosophila Efa6 can inhibit MTs directly without interacting molecules via an N-terminal 18 amino acid motif (MT elimination domain/MTED) that binds tubulin and inhibits microtubule growth in vitro and cells. If N-terminal MTED-containing fragments are in the cytoplasm they abolish entire microtubule networks of mouse fibroblasts and whole axons of fly neurons. Full-length Efa6 is membrane-attached, hence primarily blocks MTs in the periphery of fibroblasts, and explorative MTs that have left axonal bundles in neurons. Accordingly, loss of Efa6 causes an increase of explorative MTs: in growth cones they enhance axon growth, in axon shafts they cause excessive branching, as well as atrophy through perturbations of MT bundles. Efa6 over-expression causes the opposite phenotypes. Taken together, our work conceptually links molecular and sub-cellular functions of cortical collapse factors to axon growth regulation and reveals new roles in axon branching and in the prevention of axonal atrophy. Furthermore, the MTED delivers a promising tool that can be used to inhibit MTs in a compartmentalised fashion when fusing it to specifically localising protein domains.

Ferroptosis is governed by differential regulation of transcription in liver cancer

Ferroptosis is an outcome of metabolic disorders and closely linked to liver cancer. However, the mechanism underlying the fine regulation of ferroptosis in liver cancer remains unclear. Here, we have identified two categories of genes: ferroptosis up-regulated factors (FUF) and ferroptosis down-regulated factors (FDF), which stimulate and suppress ferroptosis by affecting the synthesis of GSH. Furthermore, FUF are controlled by one transcription factor HIC1, while FDF controlled by another transcription factor HNF4A. Occurrence of ferroptosis might depend on the histone acetyltransferase KAT2B. Upon stimulation of ferroptosis, dissociation of KAT2B prevents HNF4A from binding to the FDF promoter. This effect happens prior to the recruitment of KAT2B to the FUF promoter, which facilitates HIC1 binding to transcribe FUF. Clinically, HIC1 and HNF4A conversely correlate with tumor stage in liver cancer. Patients with lower HIC1 and higher HNF4A exhibit poorer prognostic outcomes. Disrupting the balance between HIC1 and HNF4A might be helpful in treating liver cancer.

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Opposite gene expression profiles trigged by ferroptosis are identified.

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Reduction of GSH is the major cause of inducing ferroptosis in liver cancer cells.

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Genes related to ferroptosis are controlled by transcription factors HIC1 and HNF4A.

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Stimulation of ferroptosis breaks the balance between HIC1 and HNF4A.

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Lower HIC1 with higher HNF4A has poorer clinical outcomes in liver cancer patients.

A Nucleolar Stress-Specific p53-miR-101 Molecular Circuit Functions as an Intrinsic Tumor-Suppressor Network

Background

Activation of intrinsic p53 tumor-suppressor (TS) pathways is an important principle underlying cancer chemotherapy. It is necessary to elucidate the precise regulatory mechanisms of these networks to create new treatment strategies.

Methods

Comprehensive analyses were carried out by microarray. Expression of miR-101 was analyzed by clinical samples of lung adenocarcinomas.

Findings

We discovered a functional link between p53 and miR-101, which form a molecular circuit in response to nucleolar stress. Inhibition of RNA polymerase I (Pol I) transcription resulted in the post-transcriptional activation of miR-101 in a p53-dependent manner. miR-101 induced G2 phase–specific feedback regulation of p53 through direct repression of its target, EG5, resulting in elevated phosphorylation of ATM. In lung cancer patients, low expression of miR-101 was associated with significantly poorer prognosis exclusively in p53 WT cases. miR-101 sensitized cancer cells to Pol I transcription inhibitors and strongly repressed xenograft growth in mice. Interestingly, the most downstream targets of this circuit included the inhibitor of apoptosis proteins (IAPs). Repression of cIAP1 by a selective inhibitor, birinapant, promoted activation of the apoptosis induced by Pol I transcription inhibitor in p53 WT cancer cells.

Interpretation

Our findings indicate that the p53–miR-101 circuit is a component of an intrinsic TS network formed by nucleolar stress, and that mimicking activation of this circuit represents a promising strategy for cancer therapy.

Fund

National Institute of Biomedical Innovation, Ministry of Education, Culture, Sports & Technology of Japan, Japan Agency for Medical Research and Development.

Activation of β- and α2-adrenergic receptors stimulate tubulin polymerization and promote the association of Gβγ with microtubules in cultured NIH3T3 cells

Microtubules (MTs) constitute a crucial part of the cytoskeleton and are essential for cell division and differentiation, cell motility, intracellular transport, and cell morphology. Precise regulation of MT assembly and dynamics is essential for the performance of these functions. Although much progress has been made in identifying and characterizing the cellular factors that regulate MT assembly and dynamics, signaling events in this process is not well understood. Gβγ, an important component of the G protein-coupled receptor (GPCR) signaling pathway, has been shown to promote MT assembly in vitro and in cultured NIH3T3 and PC12 cells. Using the MT depolymerizing agent nocodazole, it has been demonstrated that the association of Gβγ with polymerized tubulin is critical for MT assembly. More recently, Gβγ has been shown to play a key role in NGF-induced neuronal differentiation of PC12 cells through its interaction with tubulin/MTs and modulation of MT assembly. Although NGF is known to exert its effect through tyrosine kinase receptor TrkA, the result suggests a possible involvement of GPCRs in this process. The present study was undertaken to determine whether agonist activation of GPCR utilizes Gβγ to promote MT assembly. We used isoproterenol and UK 14,304, agonists for two different GPCRs (β- and α2-adrenergic receptors, respectively) known to activate Gs and Gi respectively, with an opposing effect on production of cAMP. The results demonstrate that the agonist activation of β- and α2-adrenergic receptors promotes the association of Gβγ with MTs and stimulates MT assembly in NIH3T3 cells. Interestingly, the effects of these two agonists were more prominent when the cellular level of MT assembly was low (30% or less). In contrast to MT assembly, actin polymerization was not affected by isoproterenol or UK 14, 304 indicating that the effects of these agonists are limited to MTs. Thus, it appears that, upon cellular demand, GPCRs may utilize Gβγ to promote MT assembly. Stimulation of MT assembly appears to be a novel function of G protein-mediated signaling.

MiR-770 suppresses the chemo-resistance and metastasis of triple negative breast cancer via direct targeting of STMN1

Chemo-resistance and metastasis of triple negative breast cancer (TNBC) contributed the most of treatment failure in the clinic. MicroRNAs (miRNAs) have been proved to be involved in many biological processes and diseases. In this study, we aimed to determine the role of miR-770 in the regulation of chemo-resistance and metastasis of TNBC. Clinically, miR-770 was highly expressed in chemo-sensitive tissues and predicted a better prognosis of TNBC. Functionally, ectopic expression of miR-770 suppressed the doxorubicin-resistance of TNBC cell lines via regulation of apoptosis and tumor microenvironment, which was mediated by exosomes. Moreover, miR-770 overexpression inhibited the migration and invasion. Rescue of STMN1 could partly reverse the effect of miR-770 in TNBC behaviors. Furthermore, we also demonstrated that overexpression of miR-770 inhibited DOX resistance and metastasis in vivo. Taken together, our results proved that miR-770 could suppress the doxorubicin-resistance and metastasis of TNBC cells, which broaden our insights into the underlying mechanisms in chemo-resistance and metastasis, and provided a new prognostic marker for TNBC cells.

High STMN1 level is associated with chemo-resistance and poor prognosis in gastric cancer patients

Background:

Stathmin1 (STMN1) is a cytosolic phosphoprotein that regulates cellular microtubule dynamics and is known to have oncogenic activity. Despite several reports, its roles in gastric cancer (GC) remain unclear owing to a lack of analyses of highly metastatic cases. This study aimed to investigate STMN1 as a prognostic and predictive indicator of response to paclitaxel therapy in patients with GC, including inoperable cases.

Methods:

Immunohistochemical analysis of STMN1 was performed on both operable (n=95) and inoperable GC (n=61) samples. The roles of STMN1 in cancer cell proliferation and sensitivity to a microtubule-targeting drug, paclitaxel, were confirmed by knockdown experiments using GC cell lines.

Results:

Multivariate and Kaplan–Meier analyses demonstrated that high STMN1 was predictive of poor prognosis in both the groups. In the operable cohort, STMN1 expression correlated with cancer curability, recurrence, and resistance to adjuvant therapy. A correlation with paclitaxel resistance was observed in inoperable cases. Knockdown of STMN1 in GC cell lines inhibited proliferation and sensitised the cells to paclitaxel by enhancing apoptosis.

Conclusions:

STMN1 is a possible biomarker for paclitaxel sensitivity and poor prognosis in GC and could be a novel therapeutic target in metastatic GC.

Targeted proteomics driven verification of biomarker candidates associated with breast cancer aggressiveness

Breast cancer is the most common and molecularly relatively well characterized malignant disease in women, however, its progression to metastatic cancer remains lethal for 78% of patients 5years after diagnosis. Novel markers could identify the high risk patients and their verification using quantitative methods is essential to overcome genetic, inter-tumor and intra-tumor variability and translate novel findings into cancer diagnosis and treatment. We recently identified 13 proteins associated with estrogen receptor, tumor grade and lymph node status, the key factors of breast cancer aggressiveness, using untargeted proteomics. Here we verified these findings in the same set of 96 tumors using targeted proteomics based on selected reaction monitoring with mTRAQ labeling (mTRAQ-SRM), transcriptomics and immunohistochemistry and validated in 5 independent sets of 715 patients using transcriptomics. We confirmed: (i) positive association of anterior gradient protein 2 homolog (AGR2) and periostin (POSTN) and negative association of annexin A1 (ANXA1) with estrogen receptor status; (ii) positive association of stathmin (STMN1), cofilin-1 (COF1), plasminogen activator inhibitor 1 RNA-binding protein (PAIRBP1) and negative associations of thrombospondin-2 (TSP2) and POSTN levels with tumor grade; and (iii) positive association of POSTN, alpha-actinin-4 (ACTN4) and STMN1 with lymph node status. This study highlights a panel of gene products that can contribute to breast cancer aggressiveness and metastasis, the understanding of which is important for development of more precise breast cancer treatment.

Mechanism of paclitaxel resistance in a human prostate cancer cell line, PC3-PR, and its sensitization by cabazitaxel

Paclitaxel (PTX) is a microtubule-targeting drug widely used for the treatment of a variety of cancers. However, drug resistance can emerge after a series of treatments, and this can seriously affect the patient's prognosis. Here, we analyzed the mechanism of PTX resistance using a human prostate cancer cell line, PC3, and its PTX-resistant subline, PC3-PR. Compared with PC3, PC3-PR exhibited some unique phenotypes that might be associated with PTX resistance, including decreased expression of acetylated α-tubulin and the cell cycle regulator p21, and increased expression of βIII tubulin, histone deacetylase 6 (HDAC6), and the anti-apoptotic protein Bcl2. The drug exporters MDR1 and MRP1 were not involved in PTX resistance. Although cabazitaxel (CTX), a novel taxoid, has been reported to overcome PTX resistance, its mechanism of action is unknown. We found that treatment of PC3-PR cells with CTX induced expression of acetylated α-tubulin and p21, but not the related regulators p27, p15, and p16 or the Bcl2 family proteins. The pan-HDAC inhibitors trichostatin A and suberanilohydroxamic acid and the HDAC6-specific inhibitor tubacin inhibited PC3-PR proliferation and increased expression of p21 and acetylated α-tubulin in a manner similar to CTX. Our data shed light on the cellular response to PTX and CTX.

Neurofilament depletion improves microtubule dynamics via modulation of Stat3/stathmin signaling

In neurons, microtubules form a dense array within axons, and the stability and function of this microtubule network is modulated by neurofilaments. Accumulation of neurofilaments has been observed in several forms of neurodegenerative diseases, but the mechanisms how elevated neurofilament levels destabilize axons are unknown so far. Here, we show that increased neurofilament expression in motor nerves of pmn mutant mice, a model of motoneuron disease, causes disturbed microtubule dynamics. The disease is caused by a point mutation in the tubulin-specific chaperone E (Tbce) gene, leading to an exchange of the most C-terminal amino acid tryptophan to glycine. As a consequence, the TBCE protein becomes instable which then results in destabilization of axonal microtubules and defects in axonal transport, in particular in motoneurons. Depletion of neurofilament increases the number and regrowth of microtubules in pmn mutant motoneurons and restores axon elongation. This effect is mediated by interaction of neurofilament with the stathmin complex. Accumulating neurofilaments associate with stathmin in axons of pmn mutant motoneurons. Depletion of neurofilament by Nefl knockout increases Stat3–stathmin interaction and stabilizes the microtubules in pmn mutant motoneurons. Consequently, counteracting enhanced neurofilament expression improves axonal maintenance and prolongs survival of pmn mutant mice. We propose that this mechanism could also be relevant for other neurodegenerative diseases in which neurofilament accumulation and loss of microtubules are prominent features.

Novel indolyl-chalcones target stathmin to induce cancer cell death

Efficacy of current therapies for advanced and metastatic cancers remains a challenge in clinical practice. We investigated the anti-cancer potency of 3 novel indoly-chalcones (CITs). Our results indicated the lead molecule CIT-026 (Formula = C20H16FNO) induced cell death in prostate and lung cancer cell lines at sub-micromolar concentration. CITs (CIT-026, CIT-214, CIT-223) lead to microtubule destabilization, cell death and low cell proliferation, which in part was dependent on stathmin (STMN1) expression. Knockdown of STMN1 with siRNA against STMN1 in part restored viability of cancer cells in response to CITs. Further, CIT-026 and CIT-223 blocked cancer cell invasion through matrigel-coated chambers. Mechanistically, CITs inhibited phosphorylation of STMN1 leading to STMN1 accumulation and mitotic catastrophe. In summary, we have synthetized novel anti-cancer CIT molecules and defined their mechanism of action in vitro.

A mass spectrometric insight into the origins of benign gynecological disorders

Applications of mass spectrometry (MS) are rapidly expanding and encompass molecular and cellular biology. MS aids in the analysis of in vivo global molecular alterations, identifying potential biomarkers which may improve diagnosis and treatment of various pathologies. MS has added new dimensionality to medical research. Pioneering gynecologists now study molecular mechanisms underlying female reproductive pathology with MS-based tools. Although benign gynecologic disorders including endometriosis, adenomyosis, leiomyoma, and polycystic ovarian syndrome (PCOS) carry low mortality rates, they cause significant physical, mental, and social detriments. Additionally, some benign disorders are unfortunately associated with malignancies. MS-based technology can detect malignant changes in formerly benign proteomes and metabolomes with distinct advantages of speed, sensitivity, and specificity. We present the use of MS in proteomics and metabolomics, and summarize the current understanding of the molecular pathways concerning female reproductive anatomy. Highlight discoveries of novel protein and metabolite biomarkers via MS-based technology, we underscore the clinical application of these techniques in the diagnosis and management of benign gynecological disorders. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 36:450-470, 2017.

Microtubule Dynamics in Neuronal Development, Plasticity, and Neurodegeneration

Neurons are the basic information-processing units of the nervous system. In fulfilling their task, they establish a structural polarity with an axon that can be over a meter long and dendrites with a complex arbor, which can harbor ten-thousands of spines. Microtubules and their associated proteins play important roles during the development of neuronal morphology, the plasticity of neurons, and neurodegenerative processes. They are dynamic structures, which can quickly adapt to changes in the environment and establish a structural scaffold with high local variations in composition and stability. This review presents a comprehensive overview about the role of microtubules and their dynamic behavior during the formation and maturation of processes and spines in the healthy brain, during aging and under neurodegenerative conditions. The review ends with a discussion of microtubule-targeted therapies as a perspective for the supportive treatment of neurodegenerative disorders.

The Fanconi Anemia C Protein Binds to and Regulates Stathmin-1 Phosphorylation

The Fanconi anemia (FA) proteins are involved in a signaling network that assures the safeguard of chromosomes. To understand the function of FA proteins in cellular division events, we investigated the interaction between Stathmin-1 (STMN1) and the FA group C (FANCC) protein. STMN1 is a ubiquitous cytosolic protein that regulates microtubule dynamics. STMN1 activities are regulated through phosphorylation-dephosphorylation mechanisms that control assembly of the mitotic spindle, and dysregulation of STMN1 phosphorylation is associated with mitotic aberrancies leading to chromosome instability and cancer progression. Using different biochemical approaches, we showed that FANCC interacts and co-localizes with STMN1 at centrosomes during mitosis. We also showed that FANCC is required for STMN1 phosphorylation, as mutations in FANCC reduced serine 16- and 38-phosphorylated forms of STMN1. Phosphorylation of STMN1 at serine 16 is likely an event dependent on a functional FA pathway, as it is reduced in FANCA- and FANCD2-mutant cells. Furthermore, FA-mutant cells exhibited mitotic spindle anomalies such as supernumerary centrosomes and shorter mitotic spindles. These results suggest that FA proteins participate in the regulation of cellular division via the microtubule-associated protein STMN1.

Stathmin is enriched in the developing corticospinal tract

Understanding the intra- and extracellular proteins involved in the development of the corticospinal tract (CST) may offer insights into how the pathway could be regenerated following traumatic spinal cord injury. Currently, however, little is known about the proteome of the developing corticospinal system. The present study, therefore, has used quantitative proteomics and bioinformatics to detail the protein profile of the rat CST during its formation in the spinal cord. This analysis identified increased expression of 65 proteins during the early ingrowth of corticospinal axons into the spinal cord, and 36 proteins at the period of heightened CST growth. A majority of these proteins were involved in cellular assembly and organization, with annotations being most highly associated with cytoskeletal organization, microtubule dynamics, neurite outgrowth, and the formation, polymerization and quantity of microtubules. In addition, 22 proteins were more highly expressed within the developing CST in comparison to other developing white matter tracts of the spinal cord of age-matched animals. Of these differentially expressed proteins, only one, stathmin 1 (a protein known to be involved in microtubule dynamics), was both highly enriched in the developing CST and relatively sparse in other developing descending and ascending spinal tracts. Immunohistochemical analyses of the developing rat spinal cord and fetal human brain stem confirmed the enriched pattern of stathmin expression along the developing CST, and in vitro growth assays of rat corticospinal neurons showed a reduced length of neurite processes in response to pharmacological perturbation of stathmin activity. Combined, these findings suggest that stathmin activity may modulate axonal growth during development of the corticospinal projection, and reinforces the notion that microtubule dynamics could play an important role in the generation and regeneration of the CST.

Microtubule-Binding Proteins as Promising Biomarkers of Paclitaxel Sensitivity in Cancer Chemotherapy

Microtubules, tirelessly animated and highly dynamic structures, are vital for most cellular processes and their intricacies are still being revealed even after a century since their discovery. The importance of microtubules as chemotherapeutic targets cannot be overstated, and their clinical role is unlikely to abate in the near future. Indeed, improved understanding of microtubule biology could herald a new epoch of anticancer drug design by permitting fine-tuning of microtubule-targeting agents, the clinical utility of which is presently often limited by primary or acquired resistance. Paclitaxel, one such agent belonging to the taxane family, has proven a resoundingly successful treatment for many cancer patients; however, for too many others with paclitaxel-refractory tumors, the drug has offered nothing but side effects. Accumulating evidence suggests that microtubule-binding proteins (MBPs) can regulate paclitaxel sensitivity in a wide range of cancer types. Improved understanding of how these proteins can be assayed to predict treatment responses or manipulated pharmacologically to improve clinical outcomes could transform modern chemotherapy and is urgently awaited.

Stathmin 1 in normal and malignant hematopoiesis

Stathmin 1 is a microtubule destabilizer that plays an important role in cell cycle progression, segregation of chromosomes, clonogenicity, cell motility and survival. Stathmin 1 overexpression has been reported in malignant hematopoietic cells and Stathmin 1 inhibition reduces the highly proliferative potential of leukemia cell lines. However, during the differentiation of primary hematopoietic cells, Stathmin 1 expression decreases in parallel to decreases in the proliferative potential of early hematopoietic progenitors. The scope of the present review is to survey the current knowledge and highlight future perspectives for Stathmin 1 in normal and malignant hematopoiesis, with regard to the expression, function and clinical implications of this protein. [BMB Reports 2014; 47(12): 660-665]

Exploitation of the Androgen Receptor to Overcome Taxane Resistance in Advanced Prostate Cancer

Prostate cancer is a tumor addicted to androgen receptor (AR) signaling, even in its castration resistant state, and recently developed antiandrogen therapies including Abiraterone acetate and enzalutamide effectively target the androgen signaling axis, but there is ultimately recurrence to lethal disease. Development of advanced castration-resistant prostate cancer (CRPC) is a biological consequence of lack of an apoptotic response of prostate tumor cells to androgen ablation. Taxanes represent the major clinically relevant chemotherapy for the treatment of patients with metastatic CRPC; unfortunately, they do not deliver a cure but an extension of overall survival. First-generation taxane chemotherapies, Docetaxel (Taxotere), effectively target the cytoskeleton by stabilizing the interaction of β-tubulin subunits of microtubules preventing depolymerization, inducing G2M arrest and apoptosis. Shifting the current paradigm is a growing evidence to indicate that Docetaxel can effectively target the AR signaling axis by blocking its nuclear translocation and transcriptional activity in androgen-sensitive and castration-resistant prostate cancer cells, implicating a new mechanism of cross-resistance between microtubule-targeting chemotherapy and antiandrogen therapies. More recently, Cabazitaxel has emerged as a second-line taxane chemotherapy capable of conferring additional survival benefit to patients with CRPC previously treated with Docetaxel or in combination with antiandrogens. Similar to Docetaxel, Cabazitaxel induces apoptosis and G2M arrest; in contrast to Docetaxel, it sustains AR nuclear accumulation although it reduces the overall AR levels and FOXO1 expression. Cabazitaxel treatment also leads to downregulation of the microtubule-depolymerizing mitotic kinesins, MCAK, and HSET, preventing their ability to depolymerize microtubules and thus enhancing sensitivity to taxane treatment. The molecular mechanisms underlying taxane resistance involve mutational alterations in the tubulin subunits, microtubule dynamics, phenotyping programming of the epithelial-to-mesenchymal transition landscape, and the status of AR activity. This chapter discusses the mechanisms driving the therapeutic resistance of taxanes and antiandrogen therapies in CRPC, and the role of AR in potential interventions toward overcoming such resistance in patients with advanced metastatic disease.

Nerve growth factor induces neurite outgrowth of PC12 cells by promoting Gβγ-microtubule interaction

BACKGROUND

Assembly and disassembly of microtubules (MTs) is critical for neurite outgrowth and differentiation. Evidence suggests that nerve growth factor (NGF) induces neurite outgrowth from PC12 cells by activating the receptor tyrosine kinase, TrkA. G protein-coupled receptors (GPCRs) as well as heterotrimeric G proteins are also involved in regulating neurite outgrowth. However, the possible connection between these pathways and how they might ultimately converge to regulate the assembly and organization of MTs during neurite outgrowth is not well understood.

RESULTS

Here, we report that Gβγ, an important component of the GPCR pathway, is critical for NGF-induced neuronal differentiation of PC12 cells. We have found that NGF promoted the interaction of Gβγ with MTs and stimulated MT assembly. While Gβγ-sequestering peptide GRK2i inhibited neurite formation, disrupted MTs, and induced neurite damage, the Gβγ activator mSIRK stimulated neurite outgrowth, which indicates the involvement of Gβγ in this process. Because we have shown earlier that prenylation and subsequent methylation/demethylation of γ subunits are required for the Gβγ-MTs interaction in vitro, small-molecule inhibitors (L-28 and L-23) targeting prenylated methylated protein methyl esterase (PMPMEase) were tested in the current study. We found that these inhibitors disrupted Gβγ and ΜΤ organization and affected cellular morphology and neurite outgrowth. In further support of a role of Gβγ-MT interaction in neuronal differentiation, it was observed that overexpression of Gβγ in PC12 cells induced neurite outgrowth in the absence of added NGF. Moreover, overexpressed Gβγ exhibited a pattern of association with MTs similar to that observed in NGF-differentiated cells.

CONCLUSIONS

Altogether, our results demonstrate that βγ subunit of heterotrimeric G proteins play a critical role in neurite outgrowth and differentiation by interacting with MTs and modulating MT rearrangement.

Unbiased proteomic and transcript analyses reveal that stathmin-1 silencing inhibits colorectal cancer metastasis and sensitizes to 5-fluorouracil treatment

Colorectal cancer metastasis is a major cause of mortality worldwide, which may only be controlled with novel methods limiting tumor dissemination and chemoresistance. High stathmin-1 (STMN1) expression was previously established as a hallmark of colorectal cancer progression and predictor of poor survival; however, the mechanism of action is less clear. This work demonstrates that STMN1 silencing arrests tumor-disseminative cascades by inhibiting multiple metastatic drivers, and repressing oncogenic and mesenchymal transcription. Using a sensitive iTRAQ labeling proteomic approach that quantified differential abundance of 4562 proteins, targeting STMN1 expression was shown to reinstate the default cellular program of metastatic inhibition, and promote cellular adhesion via amplification of hemidesmosomal junctions and intermediate filament tethering. Silencing STMN1 also significantly improved chemoresponse to the classical colorectal cancer therapeutic agent, 5FU, via a novel caspase-6 (CASP6)-dependent mechanism. Interestingly, the prometastatic function of STMN1 was independent of p53 but required phosphorylations at S25 or S38; abrogating phosphorylative events may constitute an alternative route to achieving metastatic inhibition. These findings establish STMN1 as a potential target in antimetastatic therapy, and demonstrate the power of an approach coupling proteomics and transcript analyses in the global assessment of treatment benefits and potential side-effects.

IMPLICATIONS

Stathmin-1 is a potential candidate in colorectal cancer therapy that targets simultaneously the twin problems of metastatic spread and chemoresistance.

Stathmin destabilizing microtubule dynamics promotes malignant potential in cancer cells by epithelial-mesenchymal transition

BACKGROUND

Stathmin is a ubiquitous cytosolic regulatory phosphoprotein and is overexpressed in different human malignancies. The main physiological function of stathmin is to interfere with microtubule dynamics by promoting depolymerization of microtubules or by preventing polymerization of tubulin heterodimers. Stathmin plays important roles in regulating many cellular functions as a result of its microtubule-destabilizing activity. Currently, the critical roles of stathmin in cancer cells, as well as in lymphocytes have been valued. This review discusses stathmin and microtubule dynamics in cancer development, and hypothesizes their possible relationship with epithelial-mesenchymal transition (EMT).

DATA SOURCES

A PubMed search using such terms as "stathmin", "microtubule dynamics", "epithelial-mesenchymal transition", "EMT", "malignant potential" and "cancer" was performed to identify relevant studies published in English. More than 100 related articles were reviewed.

RESULTS

The literature clearly documented the relationship between stathmin and its microtubule-destabilizing activity of cancer development. However, the particular mechanism is poorly understood. Microtubule disruption is essential for EMT, which is a crucial process during cancer development. As a microtubule-destabilizing protein, stathmin may promote malignant potential in cancer cells by initiating EMT.

CONCLUSIONS

We propose that there is a stathmin-microtubule dynamics-EMT (S-M-E) axis during cancer development. By this axis, stathmin together with its microtubule-destabilizing activity contributes to EMT, which stimulates the malignant potential in cancer cells.

Autophagy and microRNA dysregulation in liver diseases

Autophagy is a catabolic process through which organelles and cellular components are sequestered into autophagosomes and degraded via fusion with lysosomes. Autophagy plays a role in many physiological processes, including stress responses, energy homeostasis, elimination of cellular organelles, and tissue remodeling. In addition, autophagy capacity changes in various disease states. A series of studies have shown that autophagy is strictly controlled to maintain homeostatic balance of energy metabolism and cellular organelle and protein turnover. These studies have also shown that this process is post-transcriptionally controlled by small noncoding microRNAs that regulate gene expression through complementary base pairing with mRNAs. Conversely, autophagy regulates the expression of microRNAs. Therefore, dysregulation of the link between autophagy and microRNA expression exacerbates the pathogenesis of various diseases. In this review, we summarize the roles of autophagy and microRNA dysregulation in the course of liver diseases, with the aim of understanding how microRNAs modify key autophagic effector molecules, and we discuss how this dysregulation affects both physiological and pathological conditions. This article may advance our understanding of the cellular and molecular bases of liver disease progression and promote the development of strategies for pharmacological intervention.

Learning-induced and stathmin-dependent changes in microtubule stability are critical for memory and disrupted in ageing

Changes in the stability of microtubules regulate many biological processes, but their role in memory remains unclear. Here we show that learning causes biphasic changes in the microtubule-associated network in the hippocampus. In the early phase, stathmin is dephosphorylated, enhancing its microtubule-destabilizing activity by promoting stathmin-tubulin binding, whereas in the late phase these processes are reversed leading to an increase in microtubule/KIF5-mediated localization of the GluA2 subunit of AMPA receptors at synaptic sites. A microtubule stabilizer paclitaxel decreases or increases memory when applied at the early or late phases, respectively. Stathmin mutations disrupt changes in microtubule stability, GluA2 localization, synaptic plasticity and memory. Aged wild-type mice show impairments in stathmin levels, changes in microtubule stability, and GluA2 localization. Blocking GluA2 endocytosis rescues memory deficits in stathmin mutant and aged wild-type mice. These findings demonstrate a role for microtubules in memory in young adult and aged individuals.

Stathmin protein level, a potential predictive marker for taxane treatment response in endometrial cancer

Stathmin is a prognostic marker in many cancers, including endometrial cancer. Preclinical studies, predominantly in breast cancer, have suggested that stathmin may additionally be a predictive marker for response to paclitaxel. We first evaluated the response to paclitaxel in endometrial cancer cell lines before and after stathmin knock-down. Subsequently we investigated the clinical response to paclitaxel containing chemotherapy in metastatic endometrial cancer in relation to stathmin protein level in tumors. Stathmin level was also determined in metastatic lesions, analyzing changes in biomarker status on disease progression. Knock-down of stathmin improved sensitivity to paclitaxel in endometrial carcinoma cell lines with both naturally higher and lower sensitivity to paclitaxel. In clinical samples, high stathmin level was demonstrated to be associated with poor response to paclitaxel containing chemotherapy and to reduced disease specific survival only in patients treated with such combination. Stathmin level increased significantly from primary to metastatic lesions. This study suggests, supported by both preclinical and clinical data, that stathmin could be a predictive biomarker for response to paclitaxel treatment in endometrial cancer. Re-assessment of stathmin level in metastatic lesions prior to treatment start may be relevant. Also, validation in a randomized clinical trial will be important.

Molecular determinants of outcome with mammalian target of rapamycin inhibition in endometrial cancer

BACKGROUND

Targeting the phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway is of increasing interest as a therapeutic strategy in many tumors. The aim of this study was to identify molecular markers associated with mTOR inhibitor activity in women with metastatic endometrial cancer.

METHODS

Archival tumor samples were collected from 94 women with recurrent or metastatic endometrial cancer who participated in 3 National Cancer Insitute of Canada Clinical Trials Group phase 2 trials investigating single-agent mTOR inhibitors: IND160A and IND160B (temsirolimus) and IND192 (ridaforolimus). Analyses included mutational profiling using the OncoCarta Panel version 1.0 and immunohistochemical expression of the tumor suppressor gene PTEN (phosphatase and tensin homologue) and stathmin, a marker of PI3K activation. Associations between biomarker results and clinical outcomes were assessed.

RESULTS

Mutations were found in 32 of 73 analyzed tumors, PIK3CA (21 patients) was the most common mutated gene. Co-mutations were seen in 8 tumors, most frequently KRAS and PIK3CA (4 cases). PTEN loss was observed in 46 of 85 samples analyzed and increased stathmin expression was observed in 15 of 65 analyzed samples. No correlation was observed between biomarkers and response or progression. In patients taking concurrent metformin, there was a trend toward lower progression, of 11.8% versus 32.5% (P = .14).

CONCLUSIONS

No predictive biomarker or combination of biomarkers for mTOR inhibitor activity were identified in this study. Restriction and enrichment of study entry, especially based on archival tumor tissue, should be undertaken with caution in trials using these agents.

Stathmin regulates keratinocyte proliferation and migration during cutaneous regeneration

Cutaneous regeneration utilizes paracrine feedback mechanisms to fine-tune the regulation of epidermal keratinocyte proliferation and migration. However, it is unknown how fibroblast-derived hepatocyte growth factor (HGF) affects these mutually exclusive processes in distinct cell populations. We here show that HGF stimulates the expression and phosphorylation of the microtubule-destabilizing factor stathmin in primary human keratinocytes. Quantitative single cell- and cell population-based analyses revealed that basal stathmin levels are important for the migratory ability of keratinocytes in vitro; however, its expression is moderately induced in the migration tongue of mouse skin or organotypic multi-layered keratinocyte 3D cultures after full-thickness wounding. In contrast, clearly elevated stathmin expression is detectable in hyperproliferative epidermal areas. In vitro, stathmin silencing significantly reduced keratinocyte proliferation. Automated quantitative and time-resolved analyses in organotypic cocultures demonstrated a high correlation between Stathmin/phospho-Stathmin and Ki67 positivity in epidermal regions with proliferative activity. Thus, activation of stathmin may stimulate keratinocyte proliferation, while basal stathmin levels are sufficient for keratinocyte migration during cutaneous regeneration.

The Microtubule Regulatory Protein Stathmin Is Required to Maintain the Integrity of Axonal Microtubules in Drosophila

Axonal transport, a form of long-distance, bi-directional intracellular transport that occurs between the cell body and synaptic terminal, is critical in maintaining the function and viability of neurons. We have identified a requirement for the stathmin (stai) gene in the maintenance of axonal microtubules and regulation of axonal transport in Drosophila. The stai gene encodes a cytosolic phosphoprotein that regulates microtubule dynamics by partitioning tubulin dimers between pools of soluble tubulin and polymerized microtubules, and by directly binding to microtubules and promoting depolymerization. Analysis of stai function in Drosophila, which has a single stai gene, circumvents potential complications with studies performed in vertebrate systems in which mutant phenotypes may be compensated by genetic redundancy of other members of the stai gene family. This has allowed us to identify an essential function for stai in the maintenance of the integrity of axonal microtubules. In addition to the severe disruption in the abundance and architecture of microtubules in the axons of stai mutant Drosophila, we also observe additional neurological phenotypes associated with loss of stai function including a posterior paralysis and tail-flip phenotype in third instar larvae, aberrant accumulation of transported membranous organelles in stai deficient axons, a progressive bang-sensitive response to mechanical stimulation reminiscent of the class of Drosophila mutants used to model human epileptic seizures, and a reduced adult lifespan. Reductions in the levels of Kinesin-1, the primary anterograde motor in axonal transport, enhance these phenotypes. Collectively, our results indicate that stai has an important role in neuronal function, likely through the maintenance of microtubule integrity in the axons of nerves of the peripheral nervous system necessary to support and sustain long-distance axonal transport.

Identification of dynamic changes in proteins associated with the cellular cytoskeleton after exposure to okadaic acid

Exposure of cells to the diarrhetic shellfish poison, okadaic acid, leads to a dramatic reorganization of cytoskeletal architecture and loss of cell-cell contact. When cells are exposed to high concentrations of okadaic acid (100–500 nM), the morphological rearrangement is followed by apoptotic cell death. Okadaic acid inhibits the broad acting Ser/Thr protein phosphatases 1 and 2A, which results in hyperphosphorylation of a large number of proteins. Some of these hyperphosphorylated proteins are most likely key players in the reorganization of the cell morphology induced by okadaic acid. We wanted to identify these phosphoproteins and searched for them in the cellular lipid rafts, which have been found to contain proteins that regulate cytoskeletal dynamics and cell adhesion. By using stable isotope labeling by amino acids in cell culture cells treated with okadaic acid (400 nM) could be combined with control cells before the isolation of lipid rafts. Protein phosphorylation events and translocations induced by okadaic acid were identified by mass spectrometry. Okadaic acid was shown to regulate the phosphorylation status and location of proteins associated with the actin cytoskeleton, microtubules and cell adhesion structures. A large number of these okadaic acid-regulated proteins have previously also been shown to be similarly regulated prior to cell proliferation and migration. Our results suggest that okadaic acid activates general cell signaling pathways that induce breakdown of the cortical actin cytoskeleton and cell detachment.

New paradigms in microtubule-mediated endocrine signaling in prostate cancer

Metastatic prostate cancer has limited therapeutic options and has remained a major clinical challenge. Historically, prostate cancer has been widely recognized as a chemotherapy-resistant disease. However, clinical studies with anti-microtubule agents over the past decade have shown important efficacy in improving survival in patients with advanced disease. The favorable outcomes with microtubule-targeted agents have thus rekindled interest in such therapies for the clinical management of prostate cancer. Microtubules are dynamic polymers of tubulin molecules that play diverse roles within the cell. The dynamic property of microtubules is responsible for forming the bipolar mitotic apparatus, the mitotic spindle, that functions to precisely segregate the chromosomes during cell division. Thus, owing to the pivotal role that they play in the orchestration of mitotic events, microtubules provide excellent targets for anti-cancer therapy. Recent evidence also suggests that microtubules play a crucial role in the regulation of endocrine signaling pathways. Interestingly, microtubule-targeted agents such as taxanes not only inhibit cell division but also impair endocrine receptor signaling in prostate cancer. Herein, we provide an overview of the current status of microtubule-targeted therapies that are used in the treatment of prostate cancer and discuss novel mechanisms by which such therapies modulate endocrine signaling in prostate cancer. We also address the emerging roles of microtubule regulatory proteins in prostate carcinogenesis that could serve as attractive targets for prostate cancer therapy and might also serve as predictive biomarkers to identify patients who may benefit from endocrine and/or chemotherapy. This may have important implications in designing mechanism-based and targeted-therapeutic strategies for prostate cancer.

Cell cycle inhibition therapy that targets stathmin in in vitro and in vivo models of breast cancer

Stathmin is the founding member of a family of microtubule-destabilizing proteins that have a critical role in the regulation of mitosis. Stathmin is expressed at high levels in breast cancer and its overexpression is linked to disease progression. Although there is a large body of evidence to support a role for stathmin in breast cancer progression, the validity of stathmin as a viable therapeutic target for breast cancer has not been investigated. Here, we used a bicistronic adenoviral vector that co-expresses green fluorescent protein and a ribozyme that targets stathmin messenger RNA in preclinical breast cancer models with different estrogen receptor (ER) status. We examined the effects of anti-stathmin ribozyme on the malignant phenotype of breast cancer cells in vitro and in xenograft models in vivo both as a single agent and in combination with chemotherapeutic agents. Adenovirus-mediated gene transfer of anti-stathmin ribozyme resulted in a dose-dependent inhibition of proliferation and clonogenicity associated with a G2/M arrest and increase in apoptosis in both ER-positive and ER-negative breast cancer cell lines. This inhibition was markedly enhanced when stathmin-inhibited breast cancer cells were exposed to low concentrations of taxol, which resulted in virtually complete loss of the malignant phenotype. Interestingly, breast cancer xenografts treated with low doses of anti-stathmin therapy and taxol showed regression in a majority of tumors, while some tumors stopped growing completely. In contrast, combination of anti-stathmin ribozyme and adriamycin resulted in only a modest inhibition of growth in vitro and in breast cancer xenografts in vivo. Although inhibition of tumor growth was observed in both the combination treatment groups compared with groups treated with single agent alone, combination of anti-stathmin therapy and taxol had a more profound inhibition of tumorigenicity, as both agents target the microtubule pathway. Clinically, these findings are highly relevant because taxol is one of the most active chemotherapeutic agents in breast cancer. These studies provide the proof-of-principle that stathmin provides an attractive molecular target, which could serve as a primary focus of novel approaches to breast cancer.

Expression and phosphorylation of stathmin correlate with cell migration in esophageal squamous cell carcinoma

Microtubules play extensive roles in cellular processes, including cell motility. Stathmin is an important protein which destabilizes microtubules. The essential function of stathmin is closely associated with its phosphorylation status. Stathmin is overexpressed in many human cancers and has a significant relationship with clinical characteristics such as grade, tumor size and prognosis. We demonstrated that stathmin was overexpressed in ESCC tissues using both 2-DE and immunohistochemistry analysis. In addition, overexpression of stathmin was significantly correlated with histological grade in ESCC. However, no correlation was found with age, gender and lymph node metastasis. Knockdown of stathmin with siRNA impaired cell migration in KYSE30 and KYSE410 cells. When EC0156 cells were treated with paclitaxel, stathmin was stably phosphorylated and migration was impaired. These observations suggest that stathmin may have a more important function in ESCC development and migration. The present study provides further understanding of the importance of stathmin in ESCC therapy or diagnosis.