Altered levels and regulation of stathmin in paclitaxel-resistant ovarian cancer cells

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.

Protein Phosphatase 1 Subunit PPP1R14B Stabilizes STMN1 to Promote Progression and Paclitaxel Resistance in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) represents the most lethal subtype of breast cancer due to its aggressive clinical features and the lack of effective therapeutic targets. To identify novel approaches for targeting TNBC, we examined the role of protein phosphatases in TNBC progression and chemoresistance. Protein phosphatase 1 regulatory subunit 14B (PPP1R14B), a poorly defined member of the protein phosphatase 1 regulatory subunits, was aberrantly upregulated in TNBC tissues and predicted poor prognosis. PPP1R14B was degraded mainly through the ubiquitin-proteasome pathway. RPS27A recruited deubiquitinase USP9X to deubiquitinate and stabilize PPP1R14B, resulting in overexpression of PPP1R14B in TNBC tissues. Gain- and loss-of-function assays demonstrated that PPP1R14B promoted TNBC cell proliferation, colony formation, migration, invasion, and resistance to paclitaxel in vitro. PPP1R14B also induced xenograft tumor growth, lung metastasis, and paclitaxel resistance in vivo. Mechanistic investigations revealed that PPP1R14B maintained phosphorylation and stability of oncoprotein stathmin 1 (STMN1), a microtubule-destabilizing phosphoprotein critically involved in cancer progression and paclitaxel resistance, which was dependent on PP1 catalytic subunits α and γ. Importantly, the tumor-suppressive effects of PPP1R14B deficiency could be partially rescued by ectopic expression of wild-type but not phosphorylation-deficient STMN1. Moreover, PPP1R14B decreased STMN1-mediated α-tubulin acetylation, microtubule stability, and promoted cell-cycle progression, leading to resistance of TNBC cells to paclitaxel. Collectively, these findings uncover a functional and mechanistic role of PPP1R14B in TNBC progression and paclitaxel resistance, indicating PPP1R14B is a potential therapeutic target for TNBC.

SIGNIFICANCE

PPP1R14B upregulation induced by RPS27A/USP9X in TNBC increases STMN1 activity, leading to cancer progression and paclitaxel resistance.

Overexpression of Stathmin 1 Predicts Poor Prognosis and Promotes Cancer Cell Proliferation and Migration in Ovarian Cancer

Purpose

The aim of this study was to investigate the expression of stathmin 1 (STMN1) in ovarian cancer and its effect on prognosis. The effect and mechanism of STMN1 on the proliferation and migration of ovarian cancer cells were also investigated.

Methods

Expression of STMN1 was measured by immunohistochemical staining in ovarian cancer tissues. The effects of STMN1 on the proliferation and migration capacity of ovarian cancer were evaluated using Cell Counting Kit-8 (CCK-8) assays, colony formation assays, immunofluorescence staining, wound healing assays, and Transwell assays. Transcription factors were predicted by bioinformatic analysis of TCGA database.

Results

STMN1 was upregulated in ovarian cancer tissues as compared to paracancerous tissues and associated with shorter overall survival. STMN1 expression significantly correlated with FIGO staging and tumor differentiation (P < 0.05). Furthermore, STMN1 promoted proliferation and migration in ovarian cancer cell lines. Bioinformatic analysis revealed that STMN1 was potentially regulated by E2F transcription factors. Then, we found that E2F1 regulated the expression of STMN1 and affected proliferation.

Conclusion

STMN1 is overexpressed in ovarian cancer, and its high expression suggests a poor prognosis. STMN1 promotes the proliferation and migration of ovarian cancer and is regulated by E2F1. Thus, STMN1 may serve as a negative prognostic factor and possible target for the treatment of ovarian cancer patients.

Susceptibility of cytoskeletal-associated proteins for tumor progression

The traditional functions of cytoskeletal-associated proteins (CAPs) in line with polymerization and stabilization of the cytoskeleton have evolved and are currently underrated in oncology. Although therapeutic drugs have been developed to target the cytoskeletal components directly in cancer treatment, several recently established therapeutic agents designed for new targets block the proliferation of cancer cells and suppress resistance to existing target agents. It would seem like these targets only work toward inhibiting the polymerization of cytoskeletal components or hindering mitotic spindle formation in cancer cells, but a large body of literature points to CAPs and their culpability in cell signaling, molecular conformation, organelle trafficking, cellular metabolism, and genomic modifications. Here, we review those underappreciated functions of CAPs, and we delineate the implications of cellular signaling instigated by evasive properties induced by aberrant expression of CAPs in response to stress or failure to exert normal functions. We present an analogy establishing CAPs as vulnerable targets for cancer systems and credible oncotargets. This review establishes a paradigm in which the cancer machinery may commandeer the conventional functions of CAPs for survival, drug resistance, and energy generation; an interesting feature overdue for attention.

A review on the role of tau and stathmin in gastric cancer metastasis

Gastric cancer is resistant to chemotherapy, especially in the later stages. The prevalence of gastric cancer increases after the age of 40, and its peak is in the 7th decade of life. The proteins tau (tubulin associated unit) and stathmin are overexpressed in gastric cancer and contribute to the progression of the disease by increasing cancer cell proliferation, invasion, and inducing drug resistance. This review summarizes the current knowledge on the expression of tau protein and stathmin in gastric cancer and their roles in drug resistance. Medline and PubMed databases were searched from 1990 till February 2021 for the terms "tau protein", "stathmin", and "gastric cancer." Two reviewers screened all articles and assessed prognostic studies on the role of tau and stathmin proteins in gastric cancer progression. Collectively, studies reported that both proteins are expressed at different concentrations in gastric cancer and could be significant molecular biomarkers for prognosis. Both proteins could be good candidates for targeted therapy of gastric cancer and are associated with resistance to taxanes.

UNC-45A Is Highly Expressed in the Proliferative Cells of the Mouse Genital Tract and in the Microtubule-Rich Areas of the Mouse Nervous System

UNC-45A (Protein unc-45 homolog A) is a cytoskeletal-associated protein with a dual and non-mutually exclusive role as a regulator of the actomyosin system and a Microtubule (MT)-destabilizing protein, which is overexpressed in human cancers including in ovarian cancer patients resistant to the MT-stabilizing drug paclitaxel. Mapping of UNC-45A in the mouse upper genital tract and central nervous system reveals its enrichment not only in highly proliferating and prone to remodeling cells, but also in microtubule-rich areas, of the ovaries and the nervous system, respectively. In both apparatuses, UNC-45A is also abundantly expressed in the ciliated epithelium. As regulators of actomyosin contractility and MT stability are essential for the physiopathology of the female reproductive tract and of neuronal development, our findings suggest that UNC-45A may have a role in ovarian cancer initiation and development as well as in neurodegeneration.

Functional Genomics Approaches to Elucidate Vulnerabilities of Intrinsic and Acquired Chemotherapy Resistance

Drug resistance is a commonly unavoidable consequence of cancer treatment that results in therapy failure and disease relapse. Intrinsic (pre-existing) or acquired resistance mechanisms can be drug-specific or be applicable to multiple drugs, resulting in multidrug resistance. The presence of drug resistance is, however, tightly coupled to changes in cellular homeostasis, which can lead to resistance-coupled vulnerabilities. Unbiased gene perturbations through RNAi and CRISPR technologies are invaluable tools to establish genotype-to-phenotype relationships at the genome scale. Moreover, their application to cancer cell lines can uncover new vulnerabilities that are associated with resistance mechanisms. Here, we discuss targeted and unbiased RNAi and CRISPR efforts in the discovery of drug resistance mechanisms by focusing on first-in-line chemotherapy and their enforced vulnerabilities, and we present a view forward on which measures should be taken to accelerate their clinical translation.

Stathmin 1 deficiency induces erythro-megakaryocytic defects leading to macrocytic anemia and thrombocythemia in Stathmin 1 knock out mice

Stathmin 1 (STMN1) is a cytosolic phosphoprotein that was discovered as a result of its high level of expression in leukemic cells. It plays an important role in the regulation of mitosis by promoting depolymerization of the microtubules that make up the mitotic spindle and, aging has been shown to impair STMN1 levels and change microtubule stability. We have previously demonstrated that a high level of STMN1 expression during early megakaryopoiesis is necessary for proliferation of megakaryocyte progenitors and that down-regulation of STMN1 expression during late megakaryopoiesis is important for megakaryocyte maturation and platelet production. In this report, we examined the effects of STMN1 deficiency on erythroid and megakaryocytic lineages in the mouse. Our studies show that STMN1 deficiency results in mild thrombocytopenia in young animals which converts into profound thrombocythemia as the mice age. STMN1 deficiency also lead to macrocytic changes in both erythrocytes and megakaryocytes that persisted throughout the life of STMN1 knock-out mice. Furthermore, STMN1 knock-out mice displayed a lower number of erythroid and megakaryocytic progenitor cells and had delayed recovery of their blood counts after chemotherapy. These studies show an important role for STMN1 in normal erythro-megakaryopoietic development and suggests potential implications for disorders affecting these hematopoietic lineages.

SYTL4 downregulates microtubule stability and confers paclitaxel resistance in triple-negative breast cancer

Background: Taxanes are frontline chemotherapeutic drugs for patients with triple-negative breast cancer (TNBC); however, chemoresistance reduces their effectiveness. We hypothesized that the molecular profiling of tumor samples before and after neoadjuvant chemotherapy (NAC) would help identify genes associated with drug resistance.

Methods: We sequenced 10 samples by RNA-seq from 8 NAC patients with TNBC: 3 patients with a pathologic complete response (pCR) and the other 5 with non-pCR. Differentially expressed genes that predicted chemotherapy response were selected for in vitro functional screening via a small-scale siRNAs pool. The clinical and functional significance of the gene of interest in TNBC was further investigated in vitro and in vivo, and biochemical assays and imaging analysis were applied to study the mechanisms.

Results: Synaptotagmin-like 4 (SYTL4), a Rab effector in vesicle transport, was identified as a leading functional candidate. High SYTL4 expression indicated a poor prognosis in multiple TNBC cohorts, specifically in taxane-treated TNBCs. SYTL4 was identified as a novel chemoresistant gene as validated in TNBC cells, a mouse model and patient-derived organoids. Mechanistically, downregulating SYTL4 stabilized the microtubule network and slowed down microtubule growth rate. Furthermore, SYTL4 colocalized with microtubules and interacted with microtubules through its middle region containing the linker and C2A domain. Finally, we found that SYTL4 was able to bind microtubules and inhibit the in vitro microtubule polymerization.

Conclusion: SYTL4 is a novel chemoresistant gene in TNBC and its upregulation indicates poor prognosis in taxane-treated TNBC. Further, SYTL4 directly binds microtubules and decreases microtubule stability.

In search of the altering salivary proteome in metastatic breast and ovarian cancers

Breast and ovarian cancers, the most common cancers in women in India, are expected to rise in the next decade. Metastatic organotropism is a nonrandom, predetermined process which represents a more lethal and advanced form of cancer with increased mortality rate. In an attempt to study organotropism, salivary proteins were analyzed by mass spectrometry indicative of pathophysiology of breast and ovarian cancers and were compared to healthy and ovarian chemotherapy subjects. Collectively, 646 proteins were identified, of which 409 proteins were confidently identified across all four groups. Network analysis of upregulated proteins such as coronin-1A, hepatoma-derived growth factor, vasodilator-stimulated phosphoprotein (VASP), and cofilin in breast cancer and proteins like coronin-1A, destrin, and HSP90α in ovarian cancer were functionally linked and were known to regulate cell proliferation and migration. Additionally, proteins namely VASP, coronin-1A, stathmin, and suprabasin were confidently identified in ovarian chemotherapy subjects, possibly in response to combined paclitaxel and carboplatin drug therapy to ovarian cancer. Selected representative differentially expressed proteins (eg, gelsolin, VASP) were validated by western blot analysis. Results of this study provide a foundation for future research to better understand the organotropic behavior of breast and ovarian cancers, as well as neoadjuvant drug response in ovarian cancer.

miR-34a Regulates Expression of the Stathmin-1 Oncoprotein and Prostate Cancer Progression

In aggressive prostate cancers, the oncoprotein STMN1 (also known as stathmin 1 and oncoprotein 18) is often overexpressed. STMN1 is involved in various cellular processes, including cell proliferation, motility, and tumor metastasis. Here, it was found that the expression of STMN1 RNA and protein is elevated in metastatic prostate cancers. Knockdown of STMN1 resulted in reduced proliferation and invasion of cells and tumor growth and metastasis in vivo Furthermore, miR-34a downregulated STMN1 by directly binding to its 3'-UTR. Overexpression of miR-34a in prostate cancer cells reduced proliferation and colony formation, suggesting that it is a tumor suppressor. The transcriptional corepressor C-terminal binding protein 1 (CtBP1) negatively regulated expression of miR-34a. Furthermore, gene expression profiling of STMN1-modulated prostate cancer cells revealed molecular alterations, including elevated expression of growth differentiation factor 15 (GDF15), which is involved in cancer progression and potentially in STMN1-mediated oncogenesis. Thus, in prostate cancer, CtBP1-regulated miR-34a modulates STMN1 expression and is involved in cancer progression through the CtBP1\miR-34a\STMN1\GDF15 axis.Implications: The CtBP1\miR-34a\STMN1\GDF15 axis is a potential therapeutic target for treatment of aggressive prostate cancer. Mol Cancer Res; 16(7); 1125-37. ©2017 AACR.

Targeting mitotic pathways for endocrine-related cancer therapeutics

A colossal amount of basic research over the past few decades has provided unprecedented insights into the highly complex process of cell division. There is an ever-expanding catalog of proteins that orchestrate, participate and coordinate in the exquisite processes of spindle formation, chromosome dynamics and the formation and regulation of kinetochore microtubule attachments. Use of classical microtubule poisons has still been widely and often successfully used to combat a variety of cancers, but their non-selective interference in other crucial physiologic processes necessitate the identification of novel druggable components specific to the cell cycle/division pathway. Considering cell cycle deregulation, unscheduled proliferation, genomic instability and chromosomal instability as a hallmark of tumor cells, there lies an enormous untapped terrain that needs to be unearthed before a drug can pave its way from bench to bedside. This review attempts to systematically summarize the advances made in this context so far with an emphasis on endocrine-related cancers and the avenues for future progress to target mitotic mechanisms in an effort to combat these dreadful cancers.

Stathmin and phospho-stathmin protein signature is associated with survival outcomes of breast cancer patients

Currently, Stathmin1 (STMN1) and phospho-STMN1 levels in breast cancers and their clinical implications are unknown. We examined the expression of STMN1 and its serine phospho-site (Ser16, Ser25, Ser38, and Ser63) status by immunohistochemistry. Using Cox regression analysis, a STMN1 expression signature and phosphorylation profile plus clinicopathological characteristics (STMN1-E/P/C) was developed in the training set (n = 204) and applied to the validation set (n = 106). This tool enabled us to separate breast cancer patients into high- and low-risk groups with significantly different disease-free survival (DFS) rates (P < 0.001). Importantly, this STMN1-E/P/C model had a greater prognostic value than the traditional TNM classifier, especially in luminal subtype breast cancer (P = 0.002). Further analysis showed that patients in the low-risk group would benefit more from adjuvant paclitaxel-based chemotherapy (P = 0.002). In conclusion, the STMN1-E/P/C signature is a reliable prognostic indicator for luminal subtype breast cancer and may predict the therapeutic response to paclitaxel-based treatments, potentially facilitating individualized management.

Predictive value of STMN1 gene promoter polymorphism (-2166T>C) in patients with advanced NSCLC treated with the combination of platinum compounds and vinorelbine

Purpose

The combination of platinum compounds and vinorelbine is often used as a first-line treatment in patients with locally advanced or metastatic non-small cell lung cancer (NSCLC), without activating EGFR mutations and ALK rearrangement. Unfortunately, less than half of the patients benefit from chemotherapy. Moreover, majority of patients are exposed to a number of side effects of chemotherapy. Stathmin-1 (STMN1, oncoprotein 18) affects significantly microtubule dynamics and formation of the mitotic spindle. Therefore, the change in the STMN1 gene may be a potential predictive factor of response to treatment regimens containing a cytostatics-disrupting microtubule dynamics (vinca alkaloids and taxoids). The aim of the study was to determine the relationship between a single nucleotide polymorphism (SNP) of the promoter of STMN1 gene −2166T>C) and the effectiveness of chemotherapy based on platinum compounds and vinorelbine in patients with NSCLC.

Methods

The investigated population consisted of 110 locally advanced or metastatic NSCLC patients treated with first-line chemotherapy, based on platinum compounds and vinorelbine. SNP was determined by SNaPshot™ PCR in DNA isolated from peripheral blood leukocytes.

Results

The median progression-free survival (PFS) was significantly shorter in carriers of TT genotype of the STMN1 gene compared with patients with CC or CT genotypes (2.75 vs. 6.5 months; p = 0.0033; HR 5.91, 95 % CI 1.81–19.33). Evaluated SNP did not significantly affect the response to treatment and the overall survival of the patients.

Conclusion

Rare TT genotype of STMN1 gene may be an unfavorable predictive factor of chemotherapy based on platinum compounds and vinorelbine, in patients with NSCLC.

Anti-STMN1 therapy improves sensitivity to antimicrotubule drugs in esophageal squamous cell carcinoma

Stathmin (STMN1) regulates microtubule dynamics by promoting depolymerization of microtubules and/or preventing polymerization of tubulin heterodimers. Several studies have shown that overexpression of STMN1 has been linked to chemoresistance of paclitaxel and vinblastine in tumor cells. This study aimed to investigate the effects of STMN1 silencing on chemosensitivities of paclitaxel or vinblastine in esophageal squamous cell carcinoma (ESCC). Immunocytochemistry and immunofluorescence assays showed that STMN1 gene was highly expressed in Eca109 and TE-1 cells. We demonstrated that lentiviral-mediated STMN1 short hairpin RNA (shRNA) specifically and efficiently downregulated STMN1 expression in Eca109 and TE-1 cells. The sensitivity of STMN1-silencing shRNA-transfected Eca109 and TE-1 cells increased 191.4- and 179.3-fold to paclitaxel, and 21.3- and 28.4-fold to vincristine, respectively. Flow cytometry and mitotic index assays showed that knockdown of STMN1 in Eca109 and TE-1 cells led to cell cycle arrest in G2/M phase. After treatment with paclitaxel or vincristine, STMN1-silencing shRNA-transfected Eca109 and TE-1 cells were more likely to enter G2 but less likely to enter mitosis than control cells. Therefore, these data suggests that silencing STMN1 gene could increase sensitivity of ESCC to paclitaxel and vincristine through G2/M phase block.

Stathmin1 regulates p27 expression, proliferation and drug resistance, resulting in poor clinical prognosis in cholangiocarcinoma

Patients with extrahepatic cholangiocarcinoma (EHCC) have a poor prognosis; postoperative survival depends on cancer progression and therapeutic resistance. The mechanism of EHCC progression needs to be clarified to identify ways to improve disease prognosis. Stathmin1 (STMN1) is a major cytosolic phosphoprotein that regulates microtubule dynamics and is associated with malignant phenotypes and chemoresistance in various cancers. Recently, STMN1 was reported to interact with p27, an inhibitor of cyclin-dependent kinase complexes. Eighty EHCC cases were studied using immunohistochemistry and clinical pathology to determine the correlation between STMN1 and p27 expression; RNA interference to analyze the function of STMN1 in an EHCC cell line was also used. Cytoplasmic STMN1 expression correlated with venous invasion (P = 0.0021) and nuclear p27 underexpression (P = 0.0011). Patients in the high-STMN1-expression group were associated with shorter recurrence-free survival and overall survival than those in the low-expression group. An in vitro protein-binding assay revealed that cytoplasmic STMN1 bound to p27 in the cytoplasm, but not in the nucleus of EHCC cells. Moreover, p27 accumulated in EHCC cells after STMN1 suppression. STMN1 knockdown inhibited proliferation and increased the sensitivity of EHCC cells to paclitaxel. STMN1 contributes to a poor prognosis and cancer progression in EHCC patients. Understanding the regulation of p27 by STMN1 could provide new insights for overcoming therapeutic resistance in EHCC.

Stathmin Regulates Hypoxia-Inducible Factor-1α Expression through the Mammalian Target of Rapamycin Pathway in Ovarian Clear Cell Adenocarcinoma

Stathmin, a microtubule-destabilizing phosphoprotein, is highly expressed in ovarian cancer, but the pathophysiological significance of this protein in ovarian carcinoma cells remains poorly understood. This study reports the involvement of stathmin in the mTOR/HIF-1α/VEGF pathway in ovarian clear cell adenocarcinoma (CCA) during hypoxia. HIF-1α protein and VEGF mRNA levels were markedly elevated in RMG-1 cells, a CCA cell line, cultured under hypoxic conditions. Rapamycin, an inhibitor of mTOR complex 1, reduced the level of HIF-1α and blocked phosphorylation of ribosomal protein S6 kinase 1 (S6K), a transcriptional regulator of mTOR, demonstrating that hypoxia activates mTOR/S6K/HIF-1α signaling in CCA. Furthermore, stathmin knockdown inhibited hypoxia-induced HIF-1α and VEGF expression and S6K phosphorylation. The silencing of stathmin expression also reduced Akt phosphorylation, a critical event in the mTOR/HIF-1α/VEGF signaling pathway. By contrast, stathmin overexpression upregulated hypoxia-induced HIF-1α and VEGF expression in OVCAR-3 cells, another CCA cell line. In addition, suppression of Akt activation by wortmannin, a phosphoinositide 3-kinase (PI3K) inhibitor, decreased HIF-1α and VEGF expression. These results illustrate that regulation of HIF-1α through the PI3K/Akt/mTOR pathway is controlled by stathmin in CCA. Our findings point to a new mechanism of stathmin regulation during ovarian cancer.

Bisphosphorylated PEA-15 sensitizes ovarian cancer cells to paclitaxel by impairing the microtubule-destabilizing effect of SCLIP

Paclitaxel is a standard chemotherapeutic agent for ovarian cancer. PEA-15 (phosphoprotein enriched in astrocytes-15 kDa) regulates cell proliferation, autophagy, apoptosis, and glucose metabolism and also mediates AKT-dependent chemoresistance in breast cancer. The functions of PEA-15 are tightly regulated by its phosphorylation status at Ser104 and Ser116. However, the effect of PEA-15 phosphorylation status on chemosensitivity of cancer cells remains unknown. Here, we tested the hypothesis that PEA-15 phosphorylated at both Ser104 and Ser116 (pPEA-15) sensitizes ovarian cancer cells to paclitaxel. We first found that knockdown of PEA-15 in PEA-15-high expressing HEY and OVTOKO ovarian cancer cells resulted in paclitaxel resistance, whereas re-expression of PEA-15 in these cells led to paclitaxel sensitization. We next found that SKOV3.ip1-DD cells (expressing phosphomimetic PEA-15) were more sensitive to paclitaxel than SKOV3.ip1-AA cells (expressing nonphosphorylatable PEA-15). Compared with SKOV3.ip1-vector and SKOV3.ip1-AA cells, SKOV3.ip1-DD cells displayed reduced cell viability, inhibited anchorage-independent growth, and augmented apoptosis when treated with paclitaxel. Furthermore, HEY and OVTOKO cells displayed enhanced paclitaxel sensitivity when transiently overexpressing phosphomimetic PEA-15 and reduced paclitaxel sensitivity when transiently overexpressing nonphosphorylatable PEA-15. These results indicate that pPEA-15 sensitizes ovarian cancer cells to paclitaxel. cDNA microarray analysis suggested that SCLIP (SCG10-like protein), a microtubule-destabilizing protein, is involved in pPEA-15-mediated chemosensitization. We found that reduced expression and possibly posttranslational modification of SCLIP following paclitaxel treatment impaired the microtubule-destabilizing effect of SCLIP, thereby promoting induction of mitotic arrest and apoptosis by paclitaxel. Our findings highlight the importance of pPEA-15 as a promising target for improving the efficacy of paclitaxel-based therapy in ovarian cancer.

Effects of monoclonal antibodies against human stathmin combined with paclitaxel on proliferation of the QG-56 human lung carcinoma cell line

OBJECTIVE

To explore whether monoclonal antibodies against stathmin and the chemotherapuetic agent paclitaxel have synergenic effects in inhibiting growth and inducing apoptosis in human QG-56 cells.

METHODS

QG-56 cells were treated with monoclonal antibodies against stathmin or paclitaxel alone or in combination, with untreated cells used as controls. After 24, 48, 72 and 96 hours the cell growth condition was observed under an inverted microscope and inhibition was studied by MTT assay; apoptosis was analyzed by flow cytometry.

RESULTS

The populations decreased and cell shape and size changed after the various treatments. Monoclonal antibodies against stathmin and paclitaxel used alone or incombination inhibited the proliferation of QG-56 cells, especially in combination with synergism (P<0.05). Combined treatment also resulted in a significantly higher apoptosis rate than in the other groups (P<0.05).

CONCLUSIONS

Monoclonal antibodies against stathmin and paclitaxel used alone or in combination can inhibit proliferation of QG-56 cells and induce apoptosis when applied together, The observed synergistic effects may have important implications for clinical application.

Overexpression of forkhead box M1 transcription factor (FOXM1) is a potential prognostic marker and enhances chemoresistance for docetaxel in gastric cancer

BACKGROUND

Mammalian forkhead box transcription factor 1 (FoxM1) has been overexpressed and correlated with pathogenesis in a variety of human malignancies. We investigated the expression status and clinical significance of its overexpression in gastric adenocarcinoma. Furthermore, we demonstrated correlations between FoxM1 overexpression and drug resistance to chemotherapeutic agents in gastric cancer cells and gastric cancer patients treated with chemotherapy.

METHODS

Fifty-three (69%) of 77 tumors were diagnosed as positive for FoxM1 by immunohistochemistry. Multivariate analysis identified FoxM1 expression as a significant independent prognostic predictor for overall and disease-free survival in gastric cancer patients (hazard ratio 3.9 and 3.5, respectively). Furthermore, we investigated associations between FoxM1 overexpression and clinical response of chemotherapy for patients with advanced gastric cancer.

RESULTS

Our clinical results showed that FoxM1 overexpression was significantly associated with resistance in chemotherapy of docetaxel in addition to 5-fluorouracil (5-FU) plus S-1 plus cisplatin (CDDP) and was not significant in chemotherapy of 5-FU plus CDDP for patients with advanced gastric cancer. In vitro experiments showed that Mkn7 transfected FoxM1 siRNA significantly reduced chemoresistance to docetaxel over that with parental cell lines and Mkn45 transfected with FoxM1 significantly enhanced chemoresistance to docetaxel over that with parental cell lines.

CONCLUSIONS

Our study showed that FoxM1 was an independent prognostic factor in gastric cancer. Furthermore, we showed that FoxM1 was a critical molecule for chemoresistance to a microtubule-stabilizing anticancer agent, docetaxel. Taken together, those results suggest that inhibition of overexpressed FoxM1 will be a promising therapeutic strategy for advanced gastric cancer.

Suspected leukemia oncoproteins CREB1 and LYL1 regulate Op18/STMN1 expression

Stathmin (STMN1) is a microtubule destabilizing protein with a key role in cell cycle progression and cell migration that is up-regulated in several cancers and may contribute to the malignant phenotype. However, the factors that regulate its expression are not well understood. Loss as well as gain-of-function p53 mutations up-regulate STMN1 and in acute myelogenous leukemia where p53 is predominantly wild-type, STMN1 is also over-expressed. Here we show regulatory control of STMN1 expression by the leucine zipper transcription factor (TF) CREB1 and the basic helix-loop-helix TF LYL1. By ChIP-chip experiments we demonstrate in vivo the presence of LYL1 and CREB1 in close proximity on the STMN1 promoter and using promoter assays we reveal co-regulation of STMN1 by CREB1 and LYL1. By contrast, TAL1, another suspected oncoprotein in leukemia and close relative of LYL1, exerts no regulatory effect on the STMN1 promoter. NLI, LMO2 and GATA2 are previously described co-activators of Tal1/Lyl1-E47 transcriptional complexes and potentiate Lyl1 activation of the STMN1 promoter while having no effect on TAL1 transactivation. Promoter mutations that abrogate CREB1 proximal binding or mutations of the DNA-binding domain of CREB1 abolish LYL1 transcriptional activation. These results show that CRE and Ebox sites function as coordinated units and support previous evidence of joint CREB1-and LYL1 transcription events activating an aberrant subset of promoters in leukemia. CREB1 or LYL1 shRNA knock-down down-regulate STMN1 expression. Because down-regulation of STMN1 has been shown to have anti-proliferative effects, while CREB1 and LYL1 are suspected oncoproteins, interference with CREB1-LYL1 interactions may complement standard chemotherapy and yield additional beneficial effects.

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.

Chemotherapy dosing schedule influences drug resistance development in ovarian cancer

Drug resistance leads to chemotherapy failure and is responsible for the death of a great majority of patients with metastatic, late-stage ovarian cancer. The present study addressed whether changes in the chemotherapy dosing schedule affect the development, further worsening, or circumvention of drug resistance in chemosensitive and chemoresistant ovarian cancer. Severe combined immunodeficient mice bearing HeyA8 and HeyA8-MDR xenografts were treated with docetaxel intermittently (1×/wk or 3×/wk) or continuously for 21 days. Tumor mRNA expression of genes implicated in docetaxel resistance was measured by quantitative real-time-PCR. Analyzed genes included those encoding for the drug efflux transporters mdr1 and mrp7 and for molecules that interfere with or overcome the effects of docetaxel, including β-tubulinIII, actinin4, stathmin1, bcl2, rpn2, thoredoxin, and akt2. In both models, continuous docetaxel resulted in greater antitumor efficacy than 1×/wk or 3×/wk dosing and did not induce upregulation of any analyzed genes. Once weekly dosing caused upregulation of various drug resistance-related genes, especially in chemoresistant xenografts. More frequent, 3×/wk dosing diminished this effect, although levels of various genes were higher than for continuous chemotherapy. Drug efflux transporter expression was further examined by Western blotting, confirming that intermittent, but not continuous, docetaxel induced significant upregulation. Overall, our results show that the presence and length of treatment-free intervals contribute to the development of drug resistance. Elimination of these intervals by continuous dosing resulted in superior antitumor efficacy and prevented drug resistance induction in chemosensitive and chemoresistant disease. These results encourage the clinical implementation of continuous chemotherapy to overcome and/or prevent drug resistance in newly diagnosed and recurrent, refractory ovarian cancer.

Proteomic analysis of cisplatin resistance in human ovarian cancer using 2-DE method

Platinum-based chemotherapy, such as cisplatin, is the primary treatment for human ovarian cancer. However, overcoming drug resistance has become an important issue in cancer chemotherapy. In this study, we performed 2-DE and ESI-Q-TOF MS/MS analysis to identify differential proteins expression between cisplatin-sensitive (A2780S) and cisplatin-resistant (A2780-CP) ovarian cancer cell lines. Of the 14 spots identified as differentially expressed (±over twofold, P < 0.05) between the two cell lines, ten spots (corresponding to ten unique proteins) were positively identified by ESI-Q-TOF MS/MS analysis. These proteins include capsid glycoprotein, fructose-bisphosphate aldolase C, heterogeneous nuclear ribonucleoproteins A2/B1, putative RNA-binding protein 3, Ran-specific GTPase-activating protein, ubiquitin carboxyl-terminal hydrolase isozyme L1, stathmin, ATPSH protein, chromobox protein homolog3 and phosphoglycerate kinase 1. The proteins identified in this study would be useful in revealing the mechanisms underlying cisplatin resistance and also provide some clues for further research.

FoxM1 mediates resistance to herceptin and paclitaxel

Inherent and acquired therapeutic resistance in breast cancer remains a major clinical challenge. In human breast cancer samples, overexpression of the oncogenic transcription factor FoxM1 has been suggested to be a marker of poor prognosis. In this study, we report that FoxM1 overexpression confers resistance to the human epidermal growth factor receptor 2 monoclonal antibody Herceptin and microtubule-stabilizing drug paclitaxel, both as single agents and in combination. FoxM1 altered microtubule dynamics to protect tumor cells from paclitaxel-induced apoptosis. Mechanistic investigations revealed that the tubulin-destabilizing protein Stathmin, whose expression also confers resistance to paclitaxel, is a direct transcriptional target of FoxM1. Significantly, attenuating FoxM1 expression by small interfering RNA or an alternate reading frame (ARF)-derived peptide inhibitor increased therapeutic sensitivity. Our findings indicate that targeting FoxM1 could relieve therapeutic resistance in breast cancer.

Identification and characterization of a spontaneous ovarian carcinoma in Lewis rats

Background

Ovarian carcinoma is the fourth most common cause of death from cancer in women. Limited progress has been made toward improving the survival rate of patients with this disease in part because of the lack of a good animal model. We present here a model of spontaneous ovarian carcinoma arising in a normal Lewis rat.

Methods

A spontaneously occurring tumor of the left ovary was found in a normal Lewis rat during necropsy, which was sectioned for histological examination and placed into single cell suspension. Tumor cells were passaged in vivo by intraperitoneal injection into immunocompetent Lewis rats, and in vitro culture resulted in generation of a cell line. Tumor cells were examined by flow cytometry for expression of estrogen receptor α, progesterone receptor, androgen receptor, her-2/neu, epithelial cell adhesion molecule, and CA125. β-catenin expression and cellular localization was assessed by immunocytochemistry. RNA was harvested for gene expression profiling and studying the expression of cytokines.

Results

The tumor, designated FNAR, could be serially transplanted into Lewis rats and propagated as a cell line in vitro, maintaining the properties of the original tumor. The FNAR cells displayed striking morphologic similarities to human ovarian carcinoma, resembling the endometrioid carcinoma subtype of surface epithelial neoplasms. The cells expressed estrogen receptor α, progesterone receptor, androgen receptor, her-2/neu, epithelial cell adhesion molecule, CA125, and nuclear β-catenin. A gene expression profile showed upregulation of a number of genes that are also upregulated in human ovarian carcinoma.

Conclusion

This reliable model of ovarian carcinoma should be helpful in better understanding the biology of the disease as well as the development of novel treatment strategies.

Stathmin and tubulin expression and survival of ovarian cancer patients receiving platinum treatment with and without paclitaxel

BACKGROUND

Paclitaxel interacts with microtubules to exert therapeutic effects. Molecules that affect microtubule activity, such as betaIII-tubulin and stathmin, may interfere with the treatment. In this study, the authors analyzed betaIII-tubulin and stathmin expression in ovarian tumors and examined their associations with treatment response and patient survival.

METHODS

The study included 178 patients with epithelial ovarian cancer who underwent cytoreductive surgery followed by platinum-based chemotherapy; of these patients, 75 also received paclitaxel. Fresh tumor samples that were collected at surgery were analyzed for messenger RNA expression of betaIII-tubulin and stathmin using real-time polymerase chain reaction analysis. Associations of these molecules with treatment response, disease progression, and overall survival were evaluated.

RESULTS

High stathmin expression was associated with worse disease progression-free and overall survival compared with low stathmin expression. This association was independent of patient age, disease stage, tumor grade, histology, and residual tumor size and was observed in patients who received platinum plus paclitaxel, but not in patients who received platinum without paclitaxel, suggesting that stathmin expression in tumor tissue may interfere with paclitaxel treatment. Similar effects were not observed for betaIII-tubulin, although high betaIII-tubulin expression was associated with disease progression among patients who received platinum without paclitaxel. No associations were observed between treatment response and tubulin or stathmin expression. Expression levels of betaIII-tubulin and stathmin were correlated significantly.

CONCLUSIONS

High stathmin expression predicted an unfavorable prognosis in patients with ovarian cancer who received paclitaxel and platinum chemotherapy. This finding supports the possibility that stathmin may interfere with paclitaxel treatment, leading to a poor prognosis for patients with ovarian cancer.

Stathmin 1: a novel therapeutic target for anticancer activity

Stathmin 1 (STMN1), also known as p17, p18, p19, 19K, metablastin, oncoprotein 18, LAP 18 and Op18, is a 19 kDa cytosolic protein. It was the first discovered member of a family of phylogenetically related microtubule-destabilizing phosphoproteins critically involved in the construction and function of the mitotic spindle. A threshold level of STMN1 is required for orderly progression through mitosis in a variety of cell types. STMN1 is overexpressed across a broad range of human malignancies (leukemia, lymphoma, neuroblastoma; ovarian, prostatic, breast and lung cancers and mesothelioma). It is also upregulated in normally proliferating cell lines but is only rarely upregulated in nonproliferating cell lines with the exception of neurons, anterior pituitary cells and glial cells. Its expression is also upregulated in hepatocytes during regeneration and in lymphoid cells when they are signaled to proliferate. In this review, we summarize available data as rationale for the therapeutic manipulation of STMN1 in cancer patients.

Paclitaxel and docetaxel resistance: molecular mechanisms and development of new generation taxanes

Taxanes represent one of the most promising classes of anticancer agents. Unfortunately, their clinical success has been limited by the insurgence of cellular resistance, mainly mediated by the expression of the MDR phenotype or by microtubule alterations. However, the remarkable relevance of paclitaxel and docetaxel in clinical oncology stimulated intensive efforts in the last decade to identify new derivatives endowed with improved activities towards resistant tumor cells, resulting in a huge number of novel natural and synthetic taxanes. Among them, several structurally different derivatives were found to exhibit a promising behavior against the MDR phenotype in terms of either MDR inhibiting properties, or enhanced cytotoxicity compared to parental drugs, or both. On the other hand, only in more recent years have the first taxanes retaining activity against resistant cancer cells bearing alterations of the tubulin/microtubule system emerged. This review describes the main molecular mechanisms of resistance to paclitaxel and docetaxel identified so far, focusing on the advances achieved in the development of new taxanes potentially useful for the treatment of resistant tumors.

Prognostic significance of stathmin expression in correlation with metastasis and clinicopathological characteristics in human ovarian carcinoma

Stathmin, also called oncoprotein 18, is a founding member of the family of microtubule-destabilizing proteins that play a critical role in the regulation of mitosis. Stathmin is non-expressed in normal tissues, but stathmin gene is expressed at high levels in many human malignancies and the relationships between the levels of this gene expression in tumors and prognosis of the patients have been addressed. In this report, we explored the relationships between stathmin mRNA expression in ovarian carcinoma tissues and clinicopathological parameters. We collected and analyzed paraffin wax-embedded ovarian tumor biopsy tissues from 42 ovarian cancer patients in our hospital. We employed RT-PCR method and performed a densitometric analysis to determine the ratio of stathmin relative to beta-actin as an internal marker. Results showed that the stathmin mRNA expression was detected in all the ovarian carcinoma tissue samples and those samples with metastasis had higher levels of stathmin mRNA expression in initial biopsy specimens (P<0.05). Moreover, the levels of stathmin mRNA expression between samples with and without metastasis showed a statistically significant difference (P<0.05).

Microtubule-associated proteins as targets in cancer chemotherapy

Natural and synthetic compounds that disrupt microtubule dynamics are among the most successful and widely used cancer chemotherapeutic agents. However, lack of reliable markers that predict sensitivity of cancers to these agents and development of resistance remain vexing issues. There is accumulating evidence that a family of cellular proteins that are associated with and alter the dynamics of microtubules can determine sensitivity of cancer cells to microtubule-targeting agents and play a role in tumor cell resistance to these agents. This growing family of microtubule-associated proteins (MAP) includes products of oncogenes, tumor suppressors, and apoptosis regulators, suggesting that alteration of microtubule dynamics may be one of the critical events in tumorigenesis and tumor progression. The objective of this review is to integrate the knowledge on these seemingly unrelated proteins that share a common function and examine their relevance to microtubule-targeting therapies and highlight MAPs-tubulin-drug interactions as a novel avenue for new drug discovery. Based on the available evidence, we propose that rational microtubule-targeting cancer therapeutic approaches should ideally include proteomic profiling of tumor MAPs before administration of microtubule-stabilizing/destabilizing agents preferentially in combination with agents that modulate the expression of relevant MAPs.

Mitotic drug targets and the development of novel anti-mitotic anticancer drugs

Drugs that interfere with the normal progression of mitosis belong to the most successful chemotherapeutic compounds currently used for anti-cancer treatment. Classically, these drugs are represented by microtubule binding drugs that inhibit the function of the mitotic spindle in order to halt the cell cycle in mitosis and to induce apoptosis in tumor cells. However, these compounds act not only on proliferating tumor cells, but exhibit significant side effects on non-proliferating cells including neurons that are highly dependent on intracellular transport processes mediated by microtubules. Therefore, there is a particular interest in developing novel anti-mitotic drugs that target non-microtubule structures. In fact, recently several novel drugs that target mitotic kinesins or the Aurora and polo-like kinases have been developed and are currently tested in clinical trials. In addition, approaches of cell cycle checkpoint abrogation during mitosis and at the G2/M transition inducing mitosis-associated tumor cell death are promising new strategies for anti-cancer therapy. It is expected that this "next generation" of anti-mitotic drugs will be as successful as the classical anti-microtubule drugs, while avoiding some of the adverse side effects.

Reversal of stathmin-mediated resistance to paclitaxel and vinblastine in human breast carcinoma cells

Antimicrotubule agents are commonly used chemotherapy drugs for the treatment of breast and other cancers. However, these agents have variable activity partly because of microtubule regulatory proteins. Stathmin, an 18-kDa phosphoprotein that promotes microtubule depolymerization, was found to be frequently overexpressed in breast cancer. We previously identified stathmin-mediated mechanisms of resistance to antimicrotubule agents, including altered drug binding and delayed transit from G(2) into M phase, where these agents are effective in disrupting microtubule dynamics. We hypothesized that by reversing stathmin-mediated depolymerization of microtubules or by promoting entry into mitosis, this could increase sensitivity to antimicrotubule agents in human breast cancer cells overexpressing stathmin. We found that targeting stathmin or wee-1 expression with RNA interference can induce microtubule polymerization and promote G(2)/M progression, respectively, and sensitize stathmin-overexpressing breast cancer cells to paclitaxel and vinblastine. Furthermore, targeting wee-1 led to the phosphorylation of stathmin, which is known to attenuate its activity. Therefore, these data suggest a novel approach to improving the efficacy of certain antimicrotubule agents against breast cancer by regulating the function of stathmin.

Proteomic analysis reveals a novel role for the actin cytoskeleton in vincristine resistant childhood leukemia--an in vivo study

Intrinsic or acquired resistance to vincristine (VCR), an antimicrotubule agent used in the treatment of childhood acute lymphoblastic leukemia (ALL), is a major clinical problem. Using a clinically relevant NOD/SCID mouse xenograft model of ALL, we established that alterations in the actin and tubulin cytoskeleton are involved in in vivo VCR resistance. Altered protein expression between VCR-sensitive ALL xenografts, and xenografts with intrinsic or acquired VCR resistance, was identified using 2-D DIGE coupled with MS. Of the 19 proteins displaying altered expression, 11 are associated with the actin cytoskeleton. Altered expression of the actin- and/or tubulin-binding proteins gelsolin, moesin, ezrin, tropomyosin, CAP-G, HSP27, HSP70, TCP-1, and stathmin were associated with in vivo VCR resistance. The actin-regulating protein gelsolin was increased in both acquired and resistant leukemia as confirmed by immunoblotting and gene expression. The major cytoskeletal protein, gamma-actin, was down-regulated in the VCR-resistant leukemia xenografts; in contrast, there was no significant change in beta-actin expression. This study provides the first evidence for a role of the actin cytoskeleton in intrinsic and acquired in vivo antimicrotubule drug resistance in childhood leukemia and highlights the power of 2-D DIGE for the discovery of resistance markers, pharmacoproteomics, and signaling pathways in cancer.

Monitoring the gene expression profiles of doxorubicin-resistant acute myelocytic leukemia cells by DNA microarray analysis

Acquired drug-resistance phenotype is a key factor in the relapse of patients suffering hematological malignancies. In order to investigate the genes involved in drug resistance, a human leukemia cell line that is resistant to doxorubicin, an anthracycline anticancer agent (AML-2/DX100), was selected and its gene expression profile was analyzed using a cDNA microarray. A number of genes were differentially expressed in the AML-2/DX100 cells, compared with the wild type (AML-2/WT). Pro-apoptotic genes such as TNFSF7 and p21 (Cip1/Waf1) were significantly down-regulated, whereas the IKBKB, PCNA, stathmin 1, MCM5, MMP-2 and MRP1 genes, which are involved in anti-apoptotic or cell cycle progression, were over-expressed. The AML-2/DX100 cells were also resistant to other anticancer drugs, including daunorubicin and camptothecin, and the expression levels of the differentially regulated genes such as STMN1, MMP-2 and CTSG, were constantly maintained. This suggests that the deregulated genes obtained from the DNA microarray analysis in a cell line model of drug resistance might contribute to the acquired drug resistance after chronic exposure.

Regulation of Class II β-Tubulin Expression by Tumor Suppressor p53 Protein in Mouse Melanoma Cells in Response toVincaAlkaloid

The continuous exposure of antimicrotubule drugs to tumors often results in the emergence of drug-resistant tumor cells with altered expression of several beta-tubulin isotypes. We found that Vinca alkaloid enhanced expression of class II beta-tubulin isotype (mTUBB2) in mouse B16F10 melanoma cells via alteration of the tumor suppressor p53 protein. Vincristine treatment stimulated an increase in mTUBB2 mRNA expression and promoted accumulation of this isotype around the nuclei. Transient transfection assays employing a reporter construct, together with site-directed mutagenesis studies, suggested that the p53-binding site found in the first intron was a critical region for mTUBB2 expression. Electrophoretic mobility shift assay and associated antibody supershift experiments showed that vincristine promoted release of p53 protein from the binding site. In addition, exogenous induction of TAp63gamma (p51A), a homologue of p53, canceled the effect of vincristine on mTUBB2 expression. These results suggest that p53 protein may function as a suppressor of mTUBB2 expression and vincristine-mediated inhibition of p53 binding results in enhanced mTUBB2 expression. This phenomenon could be related with the emergence of drug-resistant tumor cells induced by Vinca alkaloid and may participate in determining the fate of these cells.

Distinct and sequential upregulation of genes regulating cell growth and cell cycle progression during hepatic ischemia-reperfusion injury

Ischemia-reperfusion injury (IRI) in liver and other organs is manifested as an injury phase followed by recovery and resolution. Control of cell growth and proliferation is essential for recovery from the injury. We examined the expression of three related regulators of cell cycle progression in liver IRI: spermidine/spermine N-acetyltransferase (SSAT), p21 (a cyclin-dependent kinase inhibitor), and stathmin. Mice were subjected to hepatic IRI, and liver tissues were harvested at timed intervals. The expression of SSAT, the rate-limiting enzyme in the polyamine catabolic pathway, had increased fivefold 6 h after IRI and correlated with increased putrescine levels in the liver, consistent with increased SSAT enzymatic activity in IRI. The expression of p21, which is transactivated by p53, was undetectable in sham-operated animals but was heavily induced at 12 and 24 h of reperfusion and declined to undetectable baseline levels at 72 h of reperfusion. The interaction of the polyamine pathway with the p53-p21 pathway was shown in vitro, where activation of SSAT with polyamine analog or the addition of putrescine to cultured hepatocytes induced the expression of p53 and p21 and decreased cell viability. The expression of stathmin, which is under negative transcriptional regulation by p21 and controls cell proliferation and progression through mitosis, remained undetectable at 6, 12, and 24 h of reperfusion and was progressively and heavily induced at 48 and 72 h of reperfusion. Double-immunofluorescence labeling with antibodies against stathmin and PCNA, a marker of cell proliferation, demonstrated colocalization of stathmin and PCNA at 48 and 72 h of reperfusion in hepatocytes, indicating the initiation of cell proliferation. The distinct and sequential upregulation of SSAT, p21, and stathmin, along with biochemical activation of the polyamine catabolic pathway in IRI in vivo and the demonstration of p53-p21 upregulation by SSAT and putrescine in vitro, points to the important role of regulators of cell growth and cell cycle progression in the pathophysiology and/or recovery in liver IRI. The data further suggest that SSAT may play a role in the initiation of injury, whereas p21 and stathmin may be involved in the resolution and recovery after liver IRI.

Expression of stathmin, a developmentally controlled cytoskeleton-regulating molecule, in demyelinating disorders

Understanding the biological relevance of reexpression of developmental molecules in pathological conditions is crucial for the development of new therapies. In this study, we report the increased expression of stathmin, a developmentally regulated tubulin-binding protein, in the brains of patients with multiple sclerosis (MS). In physiological conditions, stathmin immunoreactivity was observed in polysialic acid-neural cell adhesion molecule-positive migratory progenitors in the subventricular zone, and its expression progressively decreased as the cells matured into oligodendrocytes (OLs). In MS patients, however, stathmin levels were elevated in 2',3'-cyclic nucleotide 3'-phosphodiesterase-positive OLs, in 10 of 10 bioptic samples analyzed. Increased levels of stathmin were confirmed by Western blot analysis of normal-appearing white matter samples from MS brains. In addition, using mass spectrometry, stathmin was identified as the main component of a specific myelin protein fraction consistently increased in MS preparations compared with controls. To test the biological relevance of increased stathmin levels, primary OL progenitors were transfected using a myc-tagged stathmin cDNA and were allowed to differentiate. Consistent with a distinct role played by this molecule in cells of the OL lineage at different developmental stages, transient transfection in progenitors favored the bipolar migratory phenotype but did not affect survival. However, sustained stathmin levels in differentiating OLs, because of overexpression, resulted in enhanced apoptotic susceptibility. We conclude that stathmin expression in demyelinating disorders could have a dual role. On one hand, by favoring the migratory phenotype of progenitors, it may promote myelin repair. On the other hand, stathmin in mature OLs may indicate cell stress and possibly affect survival.