Expression of stathmin family genes in human tissues: non-neural-restricted expression for SCLIP

Tubulin Regulates the Stability and Localization of STMN2 by Binding Preferentially to Its Soluble Form

Loss of the tubulin-binding protein STMN2 is implicated in amyotrophic lateral sclerosis (ALS) but how it protects neurons is not known. STMN2 is known to turn over rapidly and accumulate at axotomy sites. We confirmed fast turnover of STMN2 in U2OS cells and iPSC-derived neurons and showed that degradation occurs mainly by the ubiquitin-proteasome system. The membrane targeting N-terminal domain of STMN2 promoted fast turnover, whereas its tubulin binding stathmin-like domain (SLD) promoted stabilization. Proximity labeling and imaging showed that STMN2 localizes to trans-Golgi network membranes and that tubulin binding reduces this localization. Pull-down assays showed that tubulin prefers to bind to soluble over membrane-bound STMN2. Our data suggest that STMN2 interconverts between a soluble form that is rapidly degraded unless bound to tubulin and a membrane-bound form that does not bind tubulin. We propose that STMN2 is sequestered and stabilized by tubulin binding, while its neuroprotective function depends on an unknown molecular activity of its membrane-bound form.

Multi-omics combined to investigate potential druggable therapeutic targets for stroke: A systematic Mendelian randomization study and transcriptome verification

OBJECTIVE

Stroke is a highly prevalent and disabling disease whose disease mechanisms are not fully understood. The discovery of disease-associated proteins with genetic evidence of pathogenicity provides an opportunity to identify new therapeutic targets.

METHOD

We examined the observed and causal associations of thousands of plasma and inflammatory proteins that were measured using affinity-based proteomic assays. First, we pooled >3000 relevant proteins using a fixed-effects meta-analysis of 2 population-based studies involving 48,383 participants, then investigated the causal effects of stroke and its subtype-associated proteins by forward Mendelian randomization using cis-protein quantitative locus genetic tools identified from genome-wide association studies of these >48,000 individuals. To improve the accuracy of causal estimation, we implemented a systematic Mendelian randomization model that accounts for cascading imbalances between instruments and tested the robustness of causal estimation through multi-method analyses. To further validate the hypothesis that ginsenoside Rg1 monomer acts on the five protein targets screened for drug-targeted regulation, we conducted a comparative analysis of the mRNA (gene) expression levels of a limited number of genes in the brain tissues of different groups of SD rats. The druggability of the candidate proteins was investigated and the mechanism of action and potential targeting side effects were explored by Phenome-wide MR.

RESULTS

Six circulating proteins were identified to have a significant genetic association with stroke (PFDR < 0.05). For example, in patients with cardioembolic stroke, higher genetically predicted APRT was associated with a lower risk of cardioembolic stroke (ORivw [95 % CI] = 0.641 [0.517, 0.795]; P = 5.25 × 10-5, ORSMR [95 % CI] = 0.572, [0.397, 0.825], PSMR = 0.003). Mediation analyses suggested that atrial fibrillation, angina pectoris, and heart failure may mediate the association of CD40L, LIFR, and UPA with stroke. Molecular docking revealed promising interactions between the identified proteins and glycosides. Transcriptomic sequencing in animal models indicated that ginsenoside Rg1 may act through APRT, IL15RA, and VSIR pathways, with APRT showing significant variability in mRNA sequencing expression. Phenome-wide MR of the six target proteins showed an overwhelming predominance of PFDR > 0.05, indicating less toxicity.

CONCLUSIONS

The present study provides genetic evidence to support the potential efficacy of targeting the three druggable protein targets for the treatment of stroke. This is achieved by triangulating population genomic and proteomic data. Furthermore, the study validates the pathway mechanisms by which APRT, IL15RA, and VSIR dock ginsenoside Rg1 in animal models. This will help to prioritize stroke drug development.

The role of stathmin expression in the differential diagnosis, prognosis, and potential treatment of ovarian sex cord-stromal tumors

BACKGROUND

Stathmin, a cytosolic microtubule-destabilizing phosphoprotein involved in the regulation of mitosis, is widely expressed in various malignancies and acts as an adverse prognostic factor. Our research analyzed its immunohistochemical expression on a large cohort of ovarian sex cord-stromal tumors, evaluating its potential utility in differential diagnosis, prognosis, and therapeutic application.

METHODS

We examined 390 cases of ovarian sex cord-stromal tumors including 281 adult granulosa cell tumors (AGCT), 5 juvenile granulosa cell tumors (JGCT), 33 Sertoli-Leydig cell tumors (SLCT), 50 fibromas/thecomas (F/T), 11 Leydig cell tumors/steroid cell tumors (LCT/SterCT), 5 sex-cord stromal tumors NOS (SCST-NOS), 3 Sertoli cell tumors (SCT), and 2 sclerosing stromal tumors (ScST). Immunohistochemical analysis was performed using TMAs.

RESULTS

Strong expression (> 50%) was observed in all cases of AGCT, JGCT, SLCT, SCST-NOS, SCT and 1 ScST. The other case of ScST exhibited mild expression (5-10%). The negative cases included exclusively F/T and LCT/SterCT, with F/T showing 24% of negative cases and LCT/SterCT comprising 64% of negative cases.

CONCLUSION

The results of our study indicate that stathmin is neither a prognostic marker nor suitable for the differential diagnosis of challenging cases of ovarian sex cord-stromal tumors. However, its predictive value may be theoretically significant, as a decrease in stathmin expression potentialy influences response to chemotherapy treatment.

TDP-43-regulated cryptic RNAs accumulate in Alzheimer's disease brains

BACKGROUND

Inclusions of TAR DNA-binding protein 43 kDa (TDP-43) has been designated limbic-predominant, age-related TDP-43 encephalopathy (LATE), with or without co-occurrence of Alzheimer's disease (AD). Approximately, 30-70% AD cases present TDP-43 proteinopathy (AD-TDP), and a greater disease severity compared to AD patients without TDP-43 pathology. However, it remains unclear to what extent TDP-43 dysfunction is involved in AD pathogenesis.

METHODS

To investigate whether TDP-43 dysfunction is a prominent feature in AD-TDP cases, we evaluated whether non-conserved cryptic exons, which serve as a marker of TDP-43 dysfunction in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD-TDP), accumulate in AD-TDP brains. We assessed a cohort of 192 post-mortem brains from three different brain regions: amygdala, hippocampus, and frontal cortex. Following RNA and protein extraction, qRT-PCR and immunoassays were performed to quantify the accumulation of cryptic RNA targets and phosphorylated TDP-43 pathology, respectively.

RESULTS

We detected the accumulation of misspliced cryptic or skiptic RNAs of STMN2, KCNQ2, UNC13A, CAMK2B, and SYT7 in the amygdala and hippocampus of AD-TDP cases. The topographic distribution of cryptic RNA accumulation mimicked that of phosphorylated TDP-43, regardless of TDP-43 subtype classification. Further, cryptic RNAs efficiently discriminated AD-TDP cases from controls.

CONCLUSIONS

Overall, our results indicate that cryptic RNAs may represent an intriguing new therapeutic and diagnostic target in AD, and that methods aimed at detecting and measuring these species in patient biofluids could be used as a reliable tool to assess TDP-43 pathology in AD. Our work also raises the possibility that TDP-43 dysfunction and related changes in cryptic splicing could represent a common molecular mechanism shared between AD-TDP and FTLD-TDP.

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.

STMN2 overexpression promotes cell proliferation and EMT in pancreatic cancer mediated by WNT/β-catenin signaling

STMN2, as a key regulator in microtubule disassembly and dynamics, has recently been shown to participate in cancer development. However, the corresponding role in pancreatic ductal adenocarcinoma (PC), to our knowledge, has not been reported yet. In the current study, we systematically investigate the potential role of STMN2 in the progression of PC in vitro and vivo. Overexpression of STMN2 was prevalently observed in 81 human cases of PC tissues compared with that in the paired adjacent pancreas (54.3% vs 18.5%, P < 0.01), which was positively associated with multiple advanced clinical stages of PC patients (tumor size, T stage, lymph-node metastasis and the poor prognosis). Meanwhile, a close correlation between high STMN2 and cytoplasmic/nuclear β-catenin expression (P = 0.007) was observed in PC tissues and cell lines. STMN2 overexpression induced EMT and cell proliferation in vitro via stimulating EMT-like cellular morphology, cell motility and proliferation, and the change of EMT (Snail1, E-cadherin and Vimentin) and Cyclin D1 signaling. However, XAV939 inhibited STMN2 overexpression-enhanced EMT and proliferation. Conversely, KY19382 reversed STMN2 silencing- inhibited EMT and cell proliferation in vitro. Furthermore, activated STMN2 and β-catenin were co-localized in cytoplasm/nuclear in vitro. β-catenin/TCF-mediated the transcription of STMN2 by the potential binding sites (TTCAAAG). Finally, STMN2 promoted subcutaneous tumor growth following the activation of EMT and Cyclin D1 signaling. STMN2 overexpression promotes the aggressive clinical stage of PC patients and promotes EMT and cell proliferation in vitro and vivo. β-catenin/TCF-mediated the transcription of STMN2.

HMGA1 positively regulates the microtubule-destabilizing protein stathmin promoting motility in TNBC cells and decreasing tumour sensitivity to paclitaxel

High Mobility Group A1 (HMGA1) is an architectural chromatin factor involved in the regulation of gene expression and a master regulator in Triple Negative Breast Cancer (TNBC). In TNBC, HMGA1 is overexpressed and coordinates a gene network that controls cellular processes involved in tumour development, progression, and metastasis formation. Here, we find that the expression of HMGA1 and of the microtubule-destabilizing protein stathmin correlates in breast cancer (BC) patients. We demonstrate that HMGA1 depletion leads to a downregulation of stathmin expression and activity on microtubules resulting in decreased TNBC cell motility. We show that this pathway is mediated by the cyclin-dependent kinase inhibitor p27^kip1 (p27). Indeed, the silencing of HMGA1 expression in TNBC cells results both in an increased p27 protein stability and p27-stathmin binding. When the expression of both HMGA1 and p27 is silenced, we observe a significant rescue in cell motility. These data, obtained in cellular models, were validated in BC patients. In fact, we find that patients with high levels of both HMGA1 and stathmin and low levels of p27 have a statistically significant lower survival probability in terms of relapse-free survival (RFS) and distant metastasis-free survival (DMFS) with respect to the patient group with low HMGA1, low stathmin, and high p27 expression levels. Finally, we show in an in vivo xenograft model that depletion of HMGA1 chemo-sensitizes tumour cells to paclitaxel, a drug that is commonly used in TNBC treatments. This study unveils a new interaction among HMGA1, p27, and stathmin that is critical in BC cell migration. Moreover, our data suggest that taxol-based treatments may be more effective in reducing the tumour burden when tumour cells express low levels of HMGA1.

The molecular phenotypes of injury, steatohepatitis, and fibrosis in liver transplant biopsies in the INTERLIVER study

To extend previous molecular analyses of rejection in liver transplant biopsies in the INTERLIVER study (ClinicalTrials.gov #NCT03193151), the present study aimed to define the gene expression selective for parenchymal injury, fibrosis, and steatohepatitis. We analyzed genome-wide microarray measurements from 337 liver transplant biopsies from 13 centers. We examined expression of genes previously annotated as increased in injury and fibrosis using principal component analysis (PCA). PC1 reflected parenchymal injury and related inflammation in the early posttransplant period, slowly regressing over many months. PC2 separated early injury from late fibrosis. Positive PC3 identified a distinct mildly inflamed state correlating with histologic steatohepatitis. Injury PCs correlated with liver function and histologic abnormalities. A classifier trained on histologic steatohepatitis predicted histologic steatohepatitis with cross-validated AUC = 0.83, and was associated with pathways reflecting metabolic abnormalities distinct from fibrosis. PC2 predicted histologic fibrosis (AUC = 0.80), as did a molecular fibrosis classifier (AUC = 0.74). The fibrosis classifier correlated with matrix remodeling pathways with minimal overlap with those selective for steatohepatitis, although some biopsies had both. Genome-wide assessment of liver transplant biopsies can not only detect molecular changes induced by rejection but also those correlating with parenchymal injury, steatohepatitis, and fibrosis, offering potential insights into disease mechanisms for primary diseases.

Transcriptomic Profiling of Skeletal Muscle Reveals Candidate Genes Influencing Muscle Growth and Associated Lipid Composition in Portuguese Local Pig Breeds

Simple Summary

Screening and interpretation of differentially expressed genes and associated biological pathways was conducted among experimental groups with divergent phenotypes providing valuable information about the metabolic events occurring and identification of candidate genes with major regulation roles. This comparative transcriptomic analysis includes the first RNA-seq analysis of the Longissimus lumborum muscle tissue from two Portuguese autochthonous pig breeds with different genetic backgrounds, Alentejano and Bísaro. Moreover, a complementary candidate gene approach was employed to analyse, by real time qPCR, the expression profile of relevant genes involved in lipid metabolism, and therefore with potential impacts on meat composition. This study contributes to explaining the biological basis of phenotypical differences occurring between breeds, particularly the ones related to meat quality traits that affect consumer interest.

Abstract

Gene expression is one of the main factors to influence meat quality by modulating fatty acid metabolism, composition, and deposition rates in muscle tissue. This study aimed to explore the transcriptomics of the Longissimus lumborum muscle in two local pig breeds with distinct genetic background using next-generation sequencing technology and Real-Time qPCR. RNA-seq yielded 49 differentially expressed genes between breeds, 34 overexpressed in the Alentejano (AL) and 15 in the Bísaro (BI) breed. Specific slow type myosin heavy chain components were associated with AL (MYH7) and BI (MYH3) pigs, while an overexpression of MAP3K14 in AL may be associated with their lower loin proportion, induced insulin resistance, and increased inflammatory response via NFkB activation. Overexpression of RUFY1 in AL pigs may explain the higher intramuscular (IMF) content via higher GLUT4 recruitment and consequently higher glucose uptake that can be stored as fat. Several candidate genes for lipid metabolism, excluded in the RNA-seq analysis due to low counts, such as ACLY, ADIPOQ, ELOVL6, LEP and ME1 were identified by qPCR as main gene factors defining the processes that influence meat composition and quality. These results agree with the fatter profile of the AL pig breed and adiponectin resistance can be postulated as responsible for the overexpression of MAP3K14′s coding product NIK, failing to restore insulin sensitivity.

STMN2 mediates nuclear translocation of Smad2/3 and enhances TGFβ signaling by destabilizing microtubules to promote epithelial-mesenchymal transition in hepatocellular carcinoma

Metastasis remains the major obstacle of improving the survival of patients with hepatocellular carcinoma (HCC). Epithelial-mesenchymal transition (EMT) is critical to cancer metastasis. Successful induction of EMT requires dramatic cytoskeleton rearrangement. However, the significance of microtubule (MT), one of the core components of cell cytoskeleton, in this process remains largely unknown. Here we revealed that STMN2, an important MT dynamics regulator, is barely expressed in normal live tissues but markedly up-regulated in HCCs, especially in those with early recurrence. High STMN2 expression correlates with aggressive clinicopathological features and predicts poor prognosis of HCC patients. STMN2 overexpression in HCC cells promotes EMT, invasion and metastasis in vitro and in vivo, whereas STMN2 knockdown has opposite results. Mechanistically, STMN2 modulates MTs disassembly, disrupts MT-Smad complex, and facilitates release from MT network, phosphorylation and nuclear translocation of Smad2/3 even independent of TGFβ stimulation, thereby enhancing TGFβ signaling. Collectively, STMN2 orchestrates MT disassembly to facilitate EMT via TGF-β signaling, providing a novel insight into the mechanisms underlying cancer metastasis. STMN2 is a promising prognostic biomarker and potential therapeutic target for HCC.

ALS-implicated protein TDP-43 sustains levels of STMN2, a mediator of motor neuron growth and repair

The findings that amyotrophic lateral sclerosis (ALS) patients almost universally display pathological mislocalization of the RNA-binding protein TDP-43 and that mutations in its gene cause familial ALS have nominated altered RNA metabolism as a disease mechanism. However, the RNAs regulated by TDP-43 in motor neurons and their connection to neuropathy remain to be identified. Here we report transcripts whose abundances in human motor neurons are sensitive to TDP-43 depletion. Notably, expression of STMN2, which encodes a microtubule regulator, declined after TDP-43 knockdown and TDP-43 mislocalization as well as in patient-specific motor neurons and postmortem patient spinal cord. STMN2 loss upon reduced TDP-43 function was due to altered splicing, which is functionally important, as we show STMN2 is necessary for normal axonal outgrowth and regeneration. Notably, post-translational stabilization of STMN2 rescued neurite outgrowth and axon regeneration deficits induced by TDP-43 depletion. We propose that restoring STMN2 expression warrants examination as a therapeutic strategy for ALS.

Stathmin is a potential therapeutic target but not a prognostic marker in melanoma: an immunohistochemical study of 323 melanocytic lesions

In several solid tumors, an increased stathmin expression is associated with both poor prognosis and resistance to certain chemotherapy types. However, the data regarding melanocytic lesions are very limited. The goals of our study are as follows: the assessment of stathmin expression in benign and malignant melanocytic lesions, and the significance of its expression for the differential diagnostics between benign and malignant lesions; the analysis of the prognostic significance of stathmin expression in melanoma; and the evaluation of stathmin expression in melanoma and melanoma metastases with respect to possible therapeutic targeting. Immunohistochemical analysis of stathmin expression was done in 323 melanocytic lesions, including 205 primary cutaneous melanomas, 60 melanoma metastases, and 58 melanocytic nevi. Stathmin expression was found in all analyzed groups of melanocytic lesions. Using the H-scoring system, the observed intensity of expression was as follows: melanocytic nevi: 146.1 (mean) and 150 (median); melanomas: 116.7 (mean) and 110 (median); and melanoma metastases: 136.8 (mean) and 140 (median). The stathmin expression was significantly lower in the cohort of primary melanomas when compared with metastases and nevi (P=0.001). The stathmin expression showed no prognostic significance. The high stathmin expression in melanoma suggests that stathmin might be a promising marker for therapeutic targeting in ongoing clinical trials. Compared with several other solid tumors, stathmin expression in melanoma showed no prognostic significance. The potential use of stathmin expression in differential diagnostics is limited by its common expression, and despite the statistically significant differences between nevi and melanoma, it may not be used in this setting.

Involvement of the FOXO6 transcriptional factor in breast carcinogenesis

In mammals, FOXO transcriptional factors form a family of four members (FOXO1, 3, 4, and 6) involved in the modulation proliferation, apoptosis, and carcinogenesis. The role of the FOXO family in breast cancer remains poorly elucidated. According to the cellular context and the stage of the disease, FOXOs can have opposite effects on carcinogenesis. To study the role of FOXOs in breast carcinogenesis in more detail, we examined their expression in normal tissues, breast cell lines, and a large series of breast tumours of human origin. We found a very low physiological level of FOXO6 expression in normal adult tissues and high levels of expression in foetal brain. FOXO gene expressions fluctuate specifically in breast cancer cells compared to normal cells, suggesting that these genes may have different roles in breast carcinogenesis. For the first time, we have shown that, among the various FOXO genes, only FOXO6 was frequently highly overexpressed in breast cell lines and tumours. We also found that inhibition of the endogenous expression of FOXO6 by a specific siRNA inhibited the growth of the human breast cell lines MDA-MB-468 and HCC-38. FACS and Western blot analysis showed that inhibition of endogenous expression of FOXO6 induced accumulation of cells in G0/G1 phase of the cell cycle, but not apoptosis. These results tend to demonstrate that the overexpression of the human FOXO6 gene that we highlighted in the breast tumors stimulates breast carcinogenesis by activating breast cancer cell proliferation.

Evidence for contribution of common genetic variants within chromosome 8p21.2-8p21.1 to restricted and repetitive behaviors in autism spectrum disorders

BACKGROUND

Restricted and Repetitive Behaviors (RRB), one of the core symptom categories for Autism Spectrum Disorders (ASD), comprises heterogeneous groups of behaviors. Previous research indicates that there are two or more factors (subcategories) within the RRB domain. In an effort to identify common variants associated with RRB, we have carried out a genome-wide association study (GWAS) using the Autism Genetic Resource Exchange (AGRE) dataset (n = 1,335, all ASD probands of European ancestry) for each identified RRB subcategory, while allowing for comparisons of associated single nucleotide polymorphisms (SNPs) with associated SNPs in the same set of probands analyzed using all the RRB subcategories as phenotypes in a multivariate linear mixed model. The top ranked SNPs were then explored in an independent dataset.

RESULTS

Using principal component analysis of item scores obtained from Autism Diagnostic Interview-Revised (ADI-R), two distinct subcategories within Restricted and Repetitive Behaviors were identified: Repetitive Sensory Motor (RSM) and Insistence on Sameness (IS). Quantitative RSM and IS scores were subsequently used as phenotypes in a GWAS using the AGRE ASD cohort. Although no associated SNPs with genome-wide significance (P < 5.0E-08) were detected when RSM or IS were analyzed independently, three SNPs approached genome-wide significance when RSM and IS were considered together using multivariate association analysis. These included the top IS-associated SNP, rs62503729 (P-value = 6.48E-08), which is located within chromosome 8p21.2-8p21.1, a locus previously linked to schizophrenia. Notably, all of the most significantly associated SNPs are located in close proximity to STMN4 and PTK2B, genes previously shown to function in neuron development. In addition, several of the top-ranked SNPs showed correlations with STMN4 mRNA expression in adult CEU (Caucasian and European descent) human prefrontal cortex. However, the association signals within chromosome 8p21.2-8p21.1 failed to replicate in an independent sample of 2,588 ASD probands; the insufficient sample size and between-study heterogeneity are possible explanations for the non-replication.

CONCLUSIONS

Our analysis indicates that RRB in ASD can be represented by two distinct subcategories: RSM and IS. Subsequent univariate and multivariate genome-wide association studies of these RRB subcategories enabled the detection of associated SNPs at 8p21.2-8p21.1. Although these results did not replicate in an independent ASD dataset, genomic features of this region and pathway analysis suggest that common variants in 8p21.2-8p21.1 may contribute to RRB, particularly IS. Together, these observations warrant future studies to elucidate the possible contributions of common variants in 8p21.2-8p21.1 to the etiology of RSM and IS in ASD.

Loss of miR-223 and JNK Signaling Contribute to Elevated Stathmin in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is often fatal, and studies have revealed that aberrant miRNAs contribute to MPM development and aggressiveness. Here, a screen of miRNAs identified reduced levels of miR-223 in MPM patient specimens. Interestingly, miR-223 targets Stathmin (STMN1), a microtubule regulator that has been associated with MPM. However, whether miR-223 regulates STMN1 in MPM and the functions of miR-223 and STMN1 in this disease are yet to be determined. STMN1 is also regulated by c-Jun N-terminal kinase (JNK) signaling, but whether this occurs in MPM and whether miR-223 plays a role are unknown. The relationship between STMN1, miR-223, and JNK was assessed using MPM cell lines, cells from pleural effusions, and MPM tissue. Evidence indicates that miR-223 is decreased in all MPM tissue compared with normal/healthy tissue. Conversely, STMN1 expression was higher in MPM cell lines when compared with primary mesothelial cell controls. Following overexpression of miR-223 in MPM cell lines, STMN1 levels were reduced, cell motility was inhibited, and tubulin acetylation induced. Knockdown of STMN1 using siRNAs led to inhibition of MPM cell proliferation and motility. Finally, miR-223 levels increased while STMN1 was reduced following the re-expression of the JNK isoforms in JNK-null murine embryonic fibroblasts, and STMN1 was reduced in MPM cell lines following the activation of JNK signaling.

IMPLICATIONS

miR-223 regulates STMN1 in MPM, and both are in turn regulated by the JNK signaling pathway. As such, miR-223 and STMN1 play an important role in regulating MPM cell motility and may be therapeutic targets.

PAK4 kinase-mediated SCG10 phosphorylation involved in gastric cancer metastasis

Superior cervical ganglia 10 (SCG10), as a microtubule (MT) destabilizer, maintains MT homeostasis and has a critical role in neuronal development, but its function in tumorigenesis has not been characterized. In the present study, we demonstrated that p21-activated kinase 4 (PAK4)-mediated SCG10 phosphorylation regulates MT homeostasis in metastatic gastric cancer. Our results indicate that SCG10 is a physiological substrate of PAK4, which is phosphorylated on serine 50 (Ser50) in a PAK4-dependent manner. Phosphorylated SCG10 regulated MT dynamics to promote gastric cancer cell migration and invasion in vitro and metastasis in a xenograft mouse models. Inhibiting PAK4, either by LCH-7749944 or RNA interference, resulted in the inhibition of Ser50 phosphorylation and a blockade to cell invasion, suggesting that PAK4-SCG10 signaling occurs in gastric cancer cell invasion. Moreover, we demonstrated a strong positive correlation between PAK4 and phospho-Ser50 SCG10 expression in gastric cancer samples. We also showed that high expression of SCG10 phospho-Ser50 is highly correlated to an aggressive phenotype of clinical gastric cancer. These findings revealed a novel function of SCG10 in promoting invasive potential of gastric cancer cells, suggesting that blocking PAK4-mediated SCG10 phosphorylation might be a potential therapeutic strategy for metastasis of gastric cancer.

Proteomic analysis of colorectal cancer metastasis: stathmin-1 revealed as a player in cancer cell migration and prognostic marker

Metastasis accounts largely for the high mortality rate of colorectal cancer (CRC) patients. In this study, we performed comparative proteome analysis of primary CRC cell lines HCT-116 and its metastatic derivative E1 using 2-D DIGE. We identified 74 differentially expressed proteins, many of which function in transcription, translation, angiogenesis signal transduction, or cytoskeletal remodeling pathways, which are indispensable cellular processes involved in the metastatic cascade. Among these proteins, stathmin-1 (STMN1) was found to be highly up-regulated in E1 as compared to HCT-116 and was thus selected for further functional studies. Our results showed that perturbations in STMN1 levels resulted in significant changes in cell migration, invasion, adhesion, and colony formation. We further showed that the differential expression of STMN1 correlated with the cells' metastatic potential in other paradigms of CRC models. Using immunohistochemistry, we also showed that STMN1 was highly expressed in colorectal primary tumors and metastatic tissues as compared to the adjacent normal colorectal tissues. Furthermore, we also showed via tissue microarray analyses of 324 CRC tissues and Kaplan-Meier survival plot that CRC patients with higher expression of STMN1 have poorer prognosis.

Stathmin: a protein with many tasks. New biomarker and potential target in cancer

INTRODUCTION

Stathmin is a microtubule-destabilizing phosphoprotein, firstly identified as the downstream target of many signal transduction pathways. Several studies then indicated that stathmin is overexpressed in many types of human malignancies, thus deserving the name of Oncoprotein 18 (Op18). At molecular level, stathmin depolymerizes microtubules by either sequestering free tubulin dimers or directly inducing microtubule-catastrophe. A crucial role for stathmin in the control of mitosis has been proposed, since both its overexpression and its downregulation induce failure in the correct completion of cell division. Accordingly, stathmin is an important target of the main regulator of M phase, cyclin-dependent kinase 1.

AREAS COVERED

Recent evidences support a role for stathmin in the regulation of cell growth and motility, both in vitro and in vivo, and indicate its involvement in advanced, invasive and metastatic cancer more than in primary tumors.

EXPERT OPINION

Many studies suggest that high stathmin expression levels in cancer negatively influence the response to microtubule-targeting drugs. These notions together with the fact that stathmin is expressed at very low levels in most adult tissues strongly support the use of stathmin as marker of prognosis and as target for novel anti-tumoral and anti-metastatic therapies.

Mediators of the Jak/STAT signaling pathway in human spermatozoa

In their journey to acquire the ability to fertilize the egg, numerous intracellular signaling systems are activated in spermatozoa, leading to an increase in protein tyrosine phosphorylation. Although the JAK/STAT signaling pathway is usually associated with the activation of transcription of specific genes, our laboratory previously demonstrated the presence of the IL6 receptor (IL6R) and the Janus kinase 1 (JAK1) in human spermatozoa, a cell that is mostly transcriptionally inactive. In order to determine the importance of the JAK/STAT signaling pathway, our objectives were to identify and characterize the mediators of this system in human sperm. Cell fractionation and surface biotinylation assays clearly demonstrated that IL6R is expressed at the sperm membrane surface. The kinase JAK1 is enriched in membrane fractions and is activated during human sperm capacitation as suggested by its increase in phosphotyrosine content. Many signal transducer and activator of transcription (STAT) proteins are expressed in human sperm, including STAT1, STAT3, STAT4, STAT5, and STAT6. Among them, only STAT1 and STAT5 were detected in the cytosolic fraction. All the detected STAT proteins were enriched in the cytoskeletal structures. STAT4 was present in the perinuclear theca, whereas JAK1, STAT1, and STAT5 were detected in the fibrous sheath. Indirect immunofluorescence studies showed that JAK1 and STAT1 colocalized in the neck region and that STAT4 is present at the equatorial segment and flagella. The presence of STAT proteins in sperm structural components suggests that their role is different from their well-known transcription factor activity in somatic cells, but further investigations are required to determine their role in sperm function.

Calmyrin1 binds to SCG10 protein (stathmin2) to modulate neurite outgrowth

Calmyrin1 (CaMy1) is an EF-hand Ca(2+)-binding protein expressed in several cell types, including brain neurons. Using a yeast two-hybrid screen of a human fetal brain cDNA library, we identified SCG10 protein (stathmin2) as a CaMy1 partner. SCG10 is a microtubule-destabilizing factor involved in neuronal growth during brain development. We found increased mRNA and protein levels of CaMy1 during neuronal development, which paralleled the changes in SCG10 levels. In developing primary rat hippocampal neurons in culture, CaMy1 and SCG10 colocalized in cell soma, neurites, and growth cones. Pull-down, coimmunoprecipitation, and proximity ligation assays demonstrated that the interaction between CaMy1 and SCG10 is direct and Ca(2+)-dependent in vivo and requires the C-terminal domain of CaMy1 (residues 99-192) and the N-terminal domain of SCG10 (residues 1-35). CaMy1 did not interact with stathmin1, a protein that is homologous with SCG10 but lacks the N-terminal domain characteristic of SCG10. CaMy1 interfered with SCG10 inhibitory activity in a microtubule polymerization assay. Moreover, CaMy1 overexpression inhibited SCG10-mediated neurite outgrowth in nerve growth factor (NGF)-stimulated PC12 cells. This CaMy1 activity did not occur when an N-terminally truncated SCG10 mutant unable to interact with CaMy1 was expressed. Altogether, these data suggest that CaMy1 via SCG10 couples Ca(2+) signals with the dynamics of microtubules during neuronal outgrowth in the developing brain. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.

SCG10 expression on activation of hepatic stellate cells promotes cell motility through interference with microtubules

During liver fibrogenesis, quiescent hepatic stellate cells switch their phenotype toward a myofibroblastic-like pattern with a gain in motility. Here, we show that SCG10 (superior cervical ganglia 10) mRNA expression, a microtubule-destabilizing protein that favors cell growth and motility in neurons, both increases and correlates with the stage of fibrosis in patients with chronic hepatitis C. We also show the de novo expression of SCG10 mRNA in two rat models of liver fibrosis. We demonstrate that activated hepatic stellate cells appear to be the major cellular sources of SCG10 in the liver. Tracking of the SCG10 pathway in hepatic stellate cells shows that SCG10 initially accumulates in the perinuclear Golgi area then migrates in small vesicle-like structures along individual microtubules. Moreover, SCG10 vesicles cluster at the distal ends of microtubules in areas where tubules are spread and decompacted, suggesting their preferential association with destabilized and dynamic microtubules. Inhibition of SCG10 expression by gene-specific short interfering RNA in primary rat hepatic stellate cells is associated with a significant reduction in microtubule-dependent cellular functions, such as proliferation and migration. In conclusion, the de novo expression of SCG10 by hepatic stellate cells may play a major role in cellular mechanisms associated with HSC activation, namely cell motility and division, through interference with microtubules. SCG10 may represent a potential molecular target for anti-fibrosis therapies.

The microtubule regulator stathmin is an endogenous protein agonist for TLR3

TLR3 recognizes dsRNAs and is considered of key importance to antiviral host-defense responses. TLR3 also triggers neuroprotective responses in astrocytes and controls the growth of axons and neuronal progenitor cells, suggesting additional roles for TLR3-mediated signaling in the CNS. This prompted us to search for alternative, CNS-borne protein agonists for TLR3. A genome-scale functional screening of a transcript library from brain tumors revealed that the microtubule regulator stathmin is an activator of TLR3-dependent signaling in astrocytes, inducing the same set of neuroprotective factors as the known TLR3 agonist polyinosinic:polycytidylic acid. This activity of stathmin crucially depends on a long, negatively charged alpha helix in the protein. Colocalization of stathmin with TLR3 on astrocytes, microglia, and neurons in multiple sclerosis-affected human brain indicates that as an endogenous TLR3 agonist, stathmin may fulfill previously unsuspected regulatory roles during inflammation and repair in the adult CNS.

Altered gene expression in cerulein-stimulated pancreatic acinar cells: pathologic mechanism of acute pancreatitis

Acute pancreatitis is a multifactorial disease associated with the premature activation of digestive enzymes. The genes expressed in pancreatic acinar cells determine the severity of the disease. The present study determined the differentially expressed genes in pancreatic acinar cells treated with cerulein as an in vitro model of acute pancreatitis. Pancreatic acinar AR42J cells were stimulated with 10(-8) M cerulein for 4 h, and genes with altered expression were identified using a cDNA microarray for 4,000 rat genes and validated by real-time PCR. These genes showed a 2.5-fold or higher increase with cerulein: lithostatin, guanylate cyclase, myosin light chain kinase 2, cathepsin C, progestin-induced protein, and pancreatic trypsin 2. Stathin 1 and ribosomal protein S13 showed a 2.5-fold or higher decreases in expression. Real-time PCR analysis showed time-dependent alterations of these genes. Using commercially available antibodies specific for guanylate cyclase, myosin light chain kinase 2, and cathepsin C, a time-dependent increase in these proteins were observed by Western blotting. Thus, disturbances in proliferation, differentiation, cytoskeleton arrangement, enzyme activity, and secretion may be underlying mechanisms of acute pancreatitis.

SCG10-like protein (SCLIP) is a STAT3-interacting protein involved in maintaining epithelial morphology in MCF-7 breast cancer cells

STAT (signal transducer and activator of transcription) 3 is a key contributor to cancer cell migration and invasion, with excessive STAT3 activity promoting growth arrest, cell-cell dissociation and increased migration of breast cancer epithelial cells. The STAT3-regulated mechanisms involved in this process, however, are not fully defined. Previously, we had revealed SCLIP [SCG10 (superior cervical ganglia protein 10)-like protein] as a novel STAT3-interacting protein. In the present study, we show that STAT3 binds the C-terminal tubulin-associating region of SCLIP. In a search for a function of SCLIP, we show that SCLIP was down-regulated during OSM (oncostatin M) treatment in MCF-7 cells, which also stimulates epithelial morphology loss. SCLIP knockdown likewise triggered a loss of epithelial morphology which included reduced E-cadherin expression. We found that STAT3 was required to maintain SCLIP stability. Furthermore, inhibition of OSM-induced STAT3 activity preserved SCLIP expression and MCF-7 epithelial monolayers. Taken together, we propose that a STAT3-SCLIP interaction is required to preserve SCLIP stability and contributes to the maintenance of normal epithelial morphology. Disruption of the STAT3-SCLIP interaction with OSM may contribute to cytokine-mediated loss in cell-cell attachment and morphology transition in MCF-7 cells.

Predominant regulators of tubulin monomer-polymer partitioning and their implication for cell polarization

The microtubule-system organizes the cytoplasm during interphase and segregates condensed chromosomes during mitosis. Four unrelated conserved proteins, XMAP215/Dis1/TOGp, MCAK, MAP4 and Op18/stathmin, have all been implicated as predominant regulators of tubulin monomer-polymer partitioning in animal cells. However, while studies employing the Xenopus egg extract model system indicate that the partitioning is largely governed by the counteractive activities of XMAP215 and MCAK, studies of human cell lines indicate that MAP4 and Op18 are the predominant regulators of the interphase microtubule-array. Here, we review functional interplay of these proteins during interphase and mitosis in various cell model systems. We also review the evidence that MAP4 and Op18 have interphase-specific, counteractive and phosphorylation-inactivated activities that govern tubulin subunit partitioning in many mammalian cell types. Finally, we discuss evidence indicating that partitioning regulation by MAP4 and Op18 may be of significance to establish cell polarity.

Stathmin, a microtubule regulatory protein, is associated with hypoxia-inducible factor-1alpha levels in human endometrial and endothelial cells

Local hypoxia that occurs during menstruation triggers angiogenesis that is crucial for cyclical remodeling of the endometrium during the menstrual cycle. Hypoxia is thought to be important for the expression of vascular endothelial growth factor (VEGF) via its transcriptional factor, hypoxia inducible factor (HIF)-1alpha, in the endometrium. The activation of the phosphatidylinositol-3-kinase (PI3K)/Akt signaling pathway may modulate HIF-1alpha protein levels. Stathmin, a microtubule regulatory protein, was expressed in the stroma, glandular epithelium, and vascular endothelium in human endometrium. In this study, we examined a possible role of stathmin in hypoxia-induced HIF-1alpha and VEGF expression in primary isolated and immortalized human endometrial stromal cells, glandular epithelial cells, and human umbilical venous endothelial cells (HUVEC). Knocking down stathmin expression using small interfering RNA caused microtubule stabilization and inhibited hypoxia-induced VEGF mRNA expression via the reduction of HIF-1alpha protein levels in endometrial cells and HUVEC. Treatment of the cells with a PI3K inhibitor, wortmannin, inhibited the expression of VEGF mRNA and the accumulation of HIF-1alpha protein. Silencing of stathmin expression repressed the activation (phosphorylation) of Akt in endometrial cells and HUVEC. These results suggest that endometrial stathmin is linked to HIF-1alpha protein accumulation and VEGF expression through the PI3K/Akt signaling pathway and may be involved in regeneration of the endometrium during the menstrual cycle in human uterine cells.

Coordinated expression of stathmin family members by far upstream sequence element-binding protein-1 increases motility in non-small cell lung cancer

Dynamic instability of the microtubule network modulates processes such as cell division and motility, as well as cellular morphology. Overexpression of the microtubule-destabilizing phosphoprotein stathmin is frequent in human malignancies and represents a promising therapeutic target. Although stathmin inhibition gives rise to antineoplastic effects, additional and functionally redundant microtubule-interacting proteins may attenuate the efficiency of this therapeutic approach. We have systematically analyzed the expression and potential protumorigenic effects of stathmin family members in human non-small cell lung cancer (NSCLC). Both stathmin and stathmin-like 3 (SCLIP) were overexpressed in adenocarcinoma as well as squamous cell carcinoma (SCC) tissues and induced tumor cell proliferation, migration, and matrix invasion in respective cell lines. Accordingly, reduced stathmin and SCLIP levels affected cell morphology and were associated with a less malignant phenotype. Combined inhibition of both factors caused additive effects on tumor cell motility, indicating partial functional redundancy. Because stathmin and SCLIP expression significantly correlated in NSCLC tissues, we searched for common upstream regulators and identified the far upstream sequence element-binding protein-1 (FBP-1) as a pivotal inducer of several stathmin family members. Our results indicate that the coordinated overexpression of microtubule-destabilizing factors by FBP-1 is a critical step to facilitate microtubule dynamics and subsequently increases proliferation and motility of tumor cells.

Identifying compartment-specific non-HLA targets after renal transplantation by integrating transcriptome and "antibodyome" measures

We have conducted an integrative genomics analysis of serological responses to non-HLA targets after renal transplantation, with the aim of identifying the tissue specificity and types of immunogenic non-HLA antigenic targets after transplantation. Posttransplant antibody responses were measured by paired comparative analysis of pretransplant and posttransplant serum samples from 18 pediatric renal transplant recipients, measured against 5,056 unique protein targets on the ProtoArray platform. The specificity of antibody responses were measured against gene expression levels specific to the kidney, and 2 other randomly selected organs (heart and pancreas), by integrated genomics, employing the mapping of transcription and ProtoArray platform measures, using AILUN. The likelihood of posttransplant non-HLA targets being recognized preferentially in any of 7 microdissected kidney compartments was also examined. In addition to HLA targets, non-HLA immune responses, including anti-MICA antibodies, were detected against kidney compartment-specific antigens, with highest posttransplant recognition for renal pelvis and cortex specific antigens. The compartment specificity of selected antibodies was confirmed by IHC. In conclusion, this study provides an immunogenic and anatomic roadmap of the most likely non-HLA antigens that can generate serological responses after renal transplantation. Correlation of the most significant non-HLA antibody responses with transplant health and dysfunction are currently underway.

Characterization of spatial and temporal expression pattern of SCG10 during zebrafish development

SCG10 (Superior Cervical Ganglia 10, STMN2) is a member of the stathmin family of proteins. Stathmins regulate microtubule dynamics by inhibiting polymerization and promoting their depolymerization. SCG10 is believed to be a neuronal-specific stathmin that is enriched in the growth cones of developing neurons and plays a role in regulating neurite outgrowth. In all species examined so far, SCG10 is expressed in both the CNS and PNS. We have cloned two zebrafish SCG10 homologues and have determined the temporal and spatial expression pattern of both of these genes by RT-PCR and in situ hybridization. RT-PCR shows that both transcripts are expressed maternally and zygotically through at least 5 days. In situ hybridization analysis reveals that both SCG10 orthologues have dynamic, spatial expression patterns that are nearly identical to each other. Initially, these orthologues are expressed in discrete areas of the forebrain, midbrain, and hindbrain, as well as in the anterior and posterior lateral line ganglia and transiently in the spinal cord Rohon-Beard neurons. From 48hpf onwards, the level of expression of both genes increases and becomes mainly restricted to the anterior CNS (the forebrain region, retina, optic tectum, and hindbrain), and to the cranial ganglia. From 72 to 96hpf, SCG10 genes are also expressed in the developing neurons in the gut and in the surrounding intestinal mesenchyme. Our results provide a starting point for future studies that will investigate the in vivo function of SCG10 orthologues in zebrafish neural development.

Expression of cyclophilin B is associated with malignant progression and regulation of genes implicated in the pathogenesis of breast cancer

Cyclophilin B (CypB) is a 21-kDa protein with peptidyl-prolyl cis-trans isomerase activity that functions as a transcriptional inducer for Stat5 and as a ligand for CD147. To better understand the global function of CypB in breast cancer, T47D cells with a small interfering RNA-mediated knockdown of CypB were generated. Subsequent expression profiling analysis showed that 663 transcripts were regulated by CypB knockdown, and that many of these gene products contributed to cell proliferation, cell motility, and tumorigenesis. Real-time PCR confirmed that STMN3, S100A4, S100A6, c-Myb, estrogen receptor alpha, growth hormone receptor, and progesterone receptor were all down-regulated in si-CypB cells. A linkage analysis of these array data to protein networks resulted in the identification of 27 different protein networks that were impacted by CypB knockdown. Functional assays demonstrated that CypB knockdown also decreased cell growth, proliferation, and motility. Immunohistochemical and immunofluorescent analyses of a matched breast cancer progression tissue microarray that was labeled with an anti-CypB antibody demonstrated a highly significant increase in CypB protein levels as a function of breast cancer progression. Taken together, these results suggest that the enhanced expression of CypB in malignant breast epithelium may contribute to the pathogenesis of this disease through its regulation of the expression of hormone receptors and gene products that are involved in cell proliferation and motility.

[Role of implantation-related factors, stathmin and insulin-like growth factor-binding protein 7 in reproductive endocrinology]

Successful implantation and placentation require that trophoblasts adhere to the uterine epithelium and penetrate the decidualized endometrium. However, the biochemical mechanisms of the establishment of pregnancy including these phenomena have not yet to be definitively elucidated. We have found that stathmin, a cytosolic phosphoprotein that regulates microtubule dynamics, and insulin-like growth factor-binding protein (IGFBP)-related protein 1 (IGFBP-rP1, now called IGF-binding protein 7) were highly expressed in the endometrium around the time of implantation and decidualization. In this article, we review our recent findings of the research regarding the functions of these implantation-associated proteins in endocrine physiology and pharmacology. Analysis of the expression of both factors in rodent and human uterus has revealed that both factors are crucial for the process of endometrial stromal cell differentiation.

Stathmin expression during newt retina regeneration

Japanese common newts (Cynops pyrrhogaster) have high ability to regenerate their injured organs including neural tissues, for example, the neural retina belonging to central nervous system. We attempted to clarify the molecular mechanism underlying the formation of a neural network during newt retina regeneration, and focused on the microtubule dynamics controlled by stathmin family proteins. Stathmin is a small cytoplasmic phosphoprotein known to be a microtubule regulator. We isolated a clone encoding stathmin from the newt. The expression level of stathmin is higher in lung and spleen than in the adult intact retina where stathmin was localized on plexiform layers, the ganglion layer and in photoreceptor inner segments. However, in a regenerating process of the retina, stathmin was upregulated from an early regenerating stage until the retinal layered structure was formed. Immunohistochemical analyses revealed that stathmin existed all around the regenerating retina consisting of retinal progenitor cells. These results suggest that stathmin plays important roles in the construction and maintenance of retinal structure and its neural network, by controlling the proliferation of retinal progenitor cells and the microtubule dynamics of retinal neurons. Moreover, stathmin may function in the dedifferentiating process of retinal pigment epithelium cells.

Involvement of stathmin in proliferation and differentiation of immortalized human endometrial stromal cells

Uterine endometrial stromal cells differentiate into decidual cells during the late secretory phase of the menstrual cycle and pregnancy. However, the biochemical mechanisms of decidualization have yet to be definitively elucidated. In the present study, we transfected primary human endometrial stromal cell with a temperature-sensitive mutant of simian virus 40 large T antigen and thereby established an immortalized stromal cell line (EtsT) in order to examine the role of stathmin, a cytosolic phosphoprotein that regulates microtubule dynamics, in stromal cell differentiation. When treated with the decidual stimulus dibutyryl-cAMP (db-cAMP) or forskolin, the fibroblastic cell-shaped EtsT cells transformed into large- and round-shaped cells and secreted large amounts of the decidual markers prolactin (PRL) and insulin-like growth factor binding protein-1 (IGFBP-1). Analysis of the stathmin protein levels in the db-cAMP- and forskolin-treated EtsT cells revealed that the total and phosphorylated protein levels dropped as decidualization progressed. Suppression of stathmin expression by transfection with small interfering RNA (siRNA) suppressed EtsT cell proliferation. It also abolished db-cAMP-induced PRL and IGFBP-1 mRNA expression and protein secretion. Thus, stathmin expression can be considered an integral factor regulating the initial stage of the process of human endometrial stromal cell differentiation.

SCLIP, a Microtubule-destabilizing Factor, Interacts with RasGRF1 and Inhibits Its Ability to Promote Rac Activation and Neurite Outgrowth

RasGRF1 is a neuron-specific guanine nucleotide exchange factor for the small GTPases Ras and Rac. It is implicated in the regulation of memory formation and in the development of tolerance to drug abuse, although the mechanisms have been elucidated only in part. Here we report the isolation, by the yeast two-hybrid screen, of the microtubule-destabilizing factor SCLIP (SCG10-like protein) as a novel RasGRF1-interacting protein. This interaction requires the region spanning the Dbl-homology domain of RasGRF1, endowed with catalytic activity on Rac. In search for a possible function we found by biochemical means that SCLIP influences the signaling properties of RasGRF1, greatly reducing its ability to activate the Rac/p38 MAPK pathway, while the Ras/Erk one remains unaffected. Moreover, a potential role is suggested by transfection studies in neuronal PC12 cells in which RasGRF1 induces neurite outgrowth, and coexpression of SCLIP counteracts this effect, causing a dramatic decrease in the percentage of cells bearing neurites, which also appear significantly shortened. This study unveils a physical and functional interaction between RasGRF1 and SCLIP. We suggest that this novel interplay may have possible implications in mechanisms that regulate neuronal morphology and structural plasticity.

Stathmin overexpression cooperates with p53 mutation and osteopontin overexpression, and is associated with tumour progression, early recurrence, and poor prognosis in hepatocellular carcinoma

Stathmin, a major microtubule-depolymerizing protein, is involved in cell cycle progression and cell motility. This study aimed to elucidate its role in the progression, early tumour recurrence (ETR), and prognosis of hepatocellular carcinoma (HCC). Stathmin mRNA was overexpressed in 88/156 (56%) resected, unifocal, primary HCCs, while p53 mutation was present in 72 (46%) and osteopontin mRNA overexpression in 79 (51%). Stathmin mRNA expression exhibited high concordance (93%) with protein expression in 107 cases examined by immunohistochemistry. Stathmin overexpression correlated with high alpha-fetoprotein (>200 ng/ml, p = 0.02), larger tumour size (>5 cm, p = 0.012), high tumour grade (p < 0.0002), high tumour stage (stage IIIA-IV) with vascular invasion and various degrees of intrahepatic metastasis (p < 1 x 10(-8)), ETR (p = 0.003), and lower 5-year survival (p = 0.0007). Stathmin protein expression was often more intense in the peripheral regions of tumour trabeculae, tumour borders, and portal vein tumour thrombi. Stathmin overexpression correlated with p53 mutation (p = 0.017) and osteopontin overexpression (p = 1 x 10(-8)), both of which were associated with vascular invasion (both p < 0.0001) and poorer prognosis (p < 0.0004 and p = 0.0004, respectively). Regardless of the status of p53 mutation or osteopontin expression, stathmin overexpression was associated with higher vascular invasion (all p < 0.0001). Approximately 90% of HCCs harbouring stathmin overexpression with concomitant p53 mutation or osteopontin overexpression exhibited vascular invasion, and hence the lowest 5-year survival, p = 0.00018 and p = 0.0009, respectively. However, we did not find that stathmin overexpression exerted prognostic impact independent of tumour stage. In conclusion, stathmin expression correlates with metastatic potential, is an important prognostic factor for HCC, and may serve as a useful marker to predict ETR.

Anti-TNF Effects on Destructive Fibroblasts Depend on Mechanical Stress

Joint destruction in rheumatoid arthritis (RA) starts typically at sites of mechanically stressed inserts of the synovial membrane near the cartilage/bone border. In the therapy of RA, tumour necrosis factor (TNF) antagonists have rapidly emerged as a valuable class of anti-rheumatic agents that reduce joint destruction. The aim of this study was to investigate and profile genes involved in the interaction between articular movement and anti-TNF therapy in an in vitro model. Murine LS48 cells, an established substitute for invasive RA synovial fibroblasts, were cultured, stretched and/or treated with anti-TNF-alpha antibody for 24 h. RNA was isolated and gene transcript levels were determined using U74Av2 Affymetrix GeneChips to identify transcriptional events. Positive findings were verified by polymerase chain reaction (PCR). We identified 170 differentially regulated genes, including 44 of particular interest. Gene expression fell into different functional groups that can be explained by RA pathogenesis and experimental conditions. For 21 genes of the 44 of particular interest, regulation could be confirmed by real-time PCR. Remarkably, we found structural as well as functional genes differently regulated between stretched cells, anti-TNF-treated cells, and stretched cells treated with anti-TNF antibody. Additionally, we also found a large number of genes that are apparently not related to the experimental conditions. Mechanical exertion modulates gene expression and subsequently cellular response to anti-TNF therapy. Results in exerted cells correspond to current knowledge regarding RA pathogenesis and underline the relevance of our experimental approach. Finally, the central function of the interleukin-18 system in joint destruction could be confirmed by our findings.

Expression of stathmin in human uterus and decidualizing endometrial stromal cells

The cytosolic phosphoprotein stathmin is upregulated at the site of embryo implantation in the rodents. However, stathmin expression in the human uterus has not yet been investigated. The distribution of uterine and placental stathmin was analyzed by immunohistochemistry, while stathmin mRNA expression was detected in endometrial tissues by the reverse transcriptase-PCR. Cultured endometrial stromal cells were used to investigate whether stathmin plays a role in decidualization. Stathmin is expressed specifically in the glandular epithelium and the stromal cells of human endometrial tissue. It is also expressed by cytotrophoblasts and extravillous trophoblasts, but not by syncytiotrophoblasts or decidual tissues during the first trimester of pregnancy. When stromal cells isolated from normal endometrial tissues were cultured and stimulated to decidualize by progesterone (P4) plus estrogen or dibutyryl cyclic 3′,5′-AMP, their total and phosphorylated stathmin levels decreased. Knocking down stathmin expression in the cultured stromal cells using small interfering RNA, before the cells were exposed to the decidualizing agents, significantly suppressed decidualization, as indicated by the decreased expression of IGF-binding protein-1 and prolactin. Stathmin is differently expressed in human endometrial and placental cells and may participate in the decidualization of endometrial stromal cells.

Structural organization and expression of human MTUS1, a candidate 8p22 tumor suppressor gene encoding a family of angiotensin II AT2 receptor-interacting proteins, ATIP

The Mitochondrial Tumor suppressor 1 (MTUS1) gene is a newly identified candidate tumor suppressor gene at chromosomal position 8p22. We report here that MTUS1 encodes a family of proteins whose leader member (ATIP1) was previously isolated in our laboratory as a novel interacting partner of the angiotensin II AT2 receptor involved in growth inhibition (Nouet, JBC 279: 28989-97, 2004). The MTUS1 gene contains 17 coding exons distributed over 112 kb of genomic DNA. Alternative exon usage generates three major transcripts (ATIP1, ATIP3 and ATIP4), each showing different tissue distribution. ATIP polypeptides are identical in their carboxy-terminal region carrying four coiled-coil domains. In their amino-terminal portion, ATIP polypeptides exhibit distinct motifs for localisation in the cytosol, nucleus or cell membrane, suggesting that MTUS1 gene products may be involved in a variety of intracellular functions in an AT2-dependent and independent manner. ATIP1 is ubiquitous and highly expressed in the brain. ATIP3 is the major transcript in tissues (prostate, bladder, breast, ovary, colon) corresponding to cancer types with frequent loss of heterozygosity at 8p22. Interestingly, ATIP4 is a brain-specific transcript highly abundant in the cerebellum and fetal brain. High evolutionary conservation of ATIP amino-acid sequences suggests important biological roles for this new family of proteins in tumor suppression and/or brain function.

Expression of stathmin family genes in the murine uterus during early pregnancy

Stathmin, a cytosolic phosphoprotein that regulates microtubule dynamics during cell-cycle progression, is abundantly expressed at embryo implantation sites in rats. Here, we characterized the expression of stathmin and its family genes in the murine uterus during the peri-implantation period. Stathmin protein was expressed in the glandular and luminal epithelium, blood vessels, and stromal cells on day 3 of pregnancy. On the day of implantation (day 5), stathmin was mainly localized in blood vessels in the endometrium. On day 7, intense stathmin expression was limited to capillary vessels and secondary decidual cells. Stathmin expression was higher at implantation sites than at uterine segments between implantation sites and increased during oil-induced decidualization. Although the artificially-induced deciduoma weights and number of implantation sites were similar between stathmin-knockout (KO) and wild-type (WT) mice, the stathmin-KO mice had fewer newborn pups (reduced by 30%). The expression of alkaline phosphatase, desmin, and cyclin D3 was attenuated in decidual zones of stathmin-KO mice. Messenger RNA level of the stathmin family gene, SCG10, was high at the time of decidualization in WT and stathmin-KO mice. In contrast, the others of stathmin family members, SCLIP and RB3 were highly expressed in stathmin-KO mice compared to WT mice. These results suggest that stathmin and stathmin family genes are expressed in the murine endometrium with enhanced expression in the implantation or the decidualization process.

Stathmin Strongly Increases the Minus End Catastrophe Frequency and Induces Rapid Treadmilling of Bovine Brain Microtubules at Steady State in Vitro

Stathmin is a ubiquitous microtubule destabilizing protein that is believed to play an important role linking cell signaling to the regulation of microtubule dynamics. Here we show that stathmin strongly destabilizes microtubule minus ends in vitro at steady state, conditions in which the soluble tubulin and microtubule levels remain constant. Stathmin increased the minus end catastrophe frequency approximately 13-fold at a stathmin:tubulin molar ratio of 1:5. Stathmin steady-state catastrophe-promoting activity was considerably stronger at the minus ends than at the plus ends. Consistent with its ability to destabilize minus ends, stathmin strongly increased the treadmilling rate of bovine brain microtubules. By immunofluorescence microscopy, we also found that stathmin binds to purified microtubules along their lengths in vitro. Co-sedimentation of purified microtubules polymerized in the presence of a 1:5 initial molar ratio of stathmin to tubulin yielded a binding stoichiometry of 1 mol of stathmin per approximately 14.7 mol of tubulin in the microtubules. The results firmly establish that stathmin can increase the steady-state catastrophe frequency by a direct action on microtubules, and furthermore, they indicate that an important regulatory action of stathmin in cells may be to destabilize microtubule minus ends.

Liver gene expression signature of mild fibrosis in patients with chronic hepatitis C

BACKGROUND & AIMS

The molecular mechanisms of hepatocellular carcinoma have been studied, but little is known of the changes in liver gene expression during the different stages of chronic hepatitis C virus (HCV) infection, in particular the transition from mild to moderate fibrosis.

METHODS

We used real-time quantitative RT PCR to study the messenger RNA expression of 240 selected genes in 2 pools of liver specimens according to the stages of fibrosis (Metavir score; mild fibrosis = F1 and septal fibrosis = F2). Genes whose expression differed between pools (F2 vs F1) by at least 2-fold were selected. In addition, the expression level of these selected genes then was assessed in each of the 62 individual samples (F4, n = 6; F3, n = 17; F2, n = 21; vs F1, n = 18).

RESULTS

The 22 genes that were up-regulated in the 21 F2 samples relative to the 18 F1 samples mainly encoded genes involved in cytoskeleton (KRT 19 and SCG 10), growth factors/cytokines (CXCL6, interleukin 8 [IL8], IL1A, IL2, and CXCL10), or growth factor receptors (CCR2, CXCR3, and CXCR4), or were involved in extracellular matrix production (COL1A1, CHI3L, and SPP1), in extracellular matrix remodeling (TIMP1, MMP7, and MMP9), and in cell junction (ITGA2 and CLDN 4). When hierarchically clustering the F2 and F1 samples according to the expression of the 11 most discriminatory genes (KRT 19, COL1A1, STMN2, CXCL6, CCR2, TIMP1, IL8, IL1A, ITGA2, CLDN 4, and IL2), the patient population was categorized into 2 subgroups: F1 and F2. Specifically, 15 of 18 F1 (83%) and 19 of 21 F2 (90%) were classified correctly (P < 10(-5)). We also studied the messenger RNA expression of these 240 selected genes in normal liver in comparison with F1. Genes dysregulated in the transition from normal liver to F1 mainly were interferon-inducible genes, and therefore were very different from those dysregulated in the transition from F1 to F2.

CONCLUSIONS

Genes involved in extracellular matrix turnover and immune response are implicated in the transition from mild to moderate fibrosis. Eleven of the genes could form the basis for the gene expression signature of mild versus moderate fibrosis in patients with chronic hepatitis C.

Functional mu opioid receptors are expressed in cholinergic interneurons of the rat dorsal striatum: territorial specificity and diurnal variation

Striatal cholinergic interneurons play a crucial role in the control of movement as well as in motivational and learning aspects of behaviour. Neuropeptides regulate striatal cholinergic transmission and particularly activation of mu opioid receptor (MOR) inhibits acetylcholine (ACh) release in the dorsal striatum. In the present study we investigated whether this cholinergic transmission could be modulated by an enkephalin/MOR direct process. We show that mRNA and protein of MORs are expressed by cholinergic interneurons in the limbic/prefrontal territory but not by those in the sensorimotor territory of the dorsal striatum. These MORs are functional because potassium-evoked release of ACh from striatal synaptosomes was dose-dependently reduced by a selective MOR agonist, this effect being suppressed by a MOR antagonist. The MOR regulation of cholinergic interneurons presented a diurnal variation. (i) The percentage of cholinergic interneurons containing MORs that was 32% at the beginning of the light period (morning) increased to 80% in the afternoon. (ii) The MOR-mediated inhibition of synaptosomal ACh release was higher in the afternoon than in the morning. (iii) While preproenkephalin mRNA levels remained stable, enkephalin tissue content was the lowest (-32%) in the afternoon when the spontaneous (+35%) and the N-methyl-d-aspartate-evoked (+140%) releases of enkephalin (from microsuperfused slices) were the highest. Therefore, by acting on MORs present on cholinergic interneurons, endogenously released enkephalin reduces ACh release. This direct enkephalin/MOR regulation of cholinergic transmission that operates only in the limbic/prefrontal territory of the dorsal striatum might contribute to information processing in fronto-cortico-basal ganglia circuits.

The role of stathmin in the regulation of the cell cycle

Stathmin is the founding member of a family of proteins that play critically important roles in the regulation of the microtubule cytoskeleton. Stathmin regulates microtubule dynamics by promoting depolymerization of microtubules and/or preventing polymerization of tubulin heterodimers. Upon entry into mitosis, microtubules polymerize to form the mitotic spindle, a cellular structure that is essential for accurate chromosome segregation and cell division. The microtubule-depolymerizing activity of stathmin is switched off at the onset of mitosis by phosphorylation to allow microtubule polymerization and assembly of the mitotic spindle. Phosphorylated stathmin has to be reactivated by dephosphorylation before cells exit mitosis and enter a new interphase. Interfering with stathmin function by forced expression or inhibition of expression results in reduced cellular proliferation and accumulation of cells in the G2/M phases of the cell cycle. Forced expression of stathmin leads to abnormalities in or a total lack of mitotic spindle assembly and arrest of cells in the early stages of mitosis. On the other hand, inhibition of stathmin expression leads to accumulation of cells in the G2/M phases and is associated with severe mitotic spindle abnormalities and difficulty in the exit from mitosis. Thus, stathmin is critically important not only for the formation of a normal mitotic spindle upon entry into mitosis but also for the regulation of the function of the mitotic spindle in the later stages of mitosis and for the timely exit from mitosis. In this review, we summarize the early studies that led to the identification of the important mitotic function of stathmin and discuss the present understanding of its role in the regulation of microtubules dynamics during cell-cycle progression. We also describe briefly other less mature avenues of investigation which suggest that stathmin may participate in other important biological functions and speculate about the future directions that research in this rapidly developing field may take.

Identification of genes regulating sensory neuron genesis and differentiation in the avian dorsal root ganglia

The dorsal root ganglia (DRG) derive from a population of migrating neural crest cells that coalesce laterally to the neural tube. As the DRG matures, discrete cell types emerge from a pool of differentiating progenitor cells. To identify genes that regulate sensory genesis and differentiation, we have designed screens to identify members from families of known regulatory molecules such as receptor tyrosine kinases, and generated full-length and subtractive cDNA libraries between immature and mature DRG for identifying novel genes not previously implicated in DRG development. Several genes were identified in these analyses that belong to important regulatory gene families. Quantitative PCR confirmed differential expression of candidate cDNAs identified from the subtraction/differential screening. In situ hybridization further validated dynamic expression of several cDNAs identified in our screens. Our results demonstrate the utility of combining specific and general screening approaches for isolating key regulatory genes involved in the genesis and differentiation of discrete cell types and tissues within the classic embryonic chick model system.

Modulation of the Stathmin-like Microtubule Destabilizing Activity of RB3, a Neuron-specific Member of the SCG10 Family, by Its N-terminal Domain

RB3 is a neuron-specific homologue of the SCG10/stathmin family proteins, possessing a unique N-terminal membrane-associated domain and the stathmin-like domain at the C terminus, which promotes microtubule (MT) catastrophe and/or tubulin sequestering. We examined herein the contribution of the N-terminal subdomain of RB3 to the regulation of MT dynamics. To begin with, we determined the effects of full-length (RB3-f) and short truncated (RB3-s) forms of RB3 on the polymerization of MT in vitro. RB3-s had a deletion of amino acids 1-75 from the N terminus, leaving the so-called stathmin-like domain, consisting of residues 76-217. Although both RB3-f and RB3-s exhibited MT-depolymerizing activity, RB3-f was less effective. The binding affinity for tubulin was also lower in RB3-f. Direct observation of the dynamics of individual MTs using dark field microscopy revealed that RB3-s slowed MT elongation velocity, increased catastrophes, and reduced rescues. This effect is almost identical to that by stathmin/oncoprotein 18. On the other hand, the MT elongation rate increased at lower concentrations of RB3-f. In addition, RB3-f, indicated higher rescue frequency than control as well as the catastrophe in a dose-dependent manner. The functionality of RB3-f indicated that full-length RB3 has not only stathmin-like MT destabilizing activity but also MT-associated protein-like MT stabilizing activity. Possibly, the balance of these activities is altered in a concentration-dependent manner in vitro. This interesting regulatory role of the unique N-terminal domain of RB3 in MT dynamics would contribute to the physiological regulation of neuronal morphogenesis.