Quantitative analysis of Op18 phosphorylation in childhood acute leukemia

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.

Paclitaxel induces Stathmin 1 phosphorylation, microtubule stability and apoptosis in acute lymphoblastic leukemia cells

Acute lymphoblastic leukemia (ALL) is a hematological malignancy characterized by abnormal proliferation and accumulation of lymphoblasts in the hematopoietic system. Stathmin 1 is a proliferation marker for normal lymphocytes, which has been described as highly expressed in ALL patients and functionally important for leukemia phenotype. In the present study, we expand our previous observations and aim to investigate Stathmin 1 expression and its impact on laboratory features and clinical outcomes in an independent cohort of ALL patients, and to verify the effects of paclitaxel treatment on Stathmin 1 phosphorylation and cell viability in ALL cell lines. In ALL patients, Stathmin 1 expression was significantly increased, associated with lower age onset and positively correlated with white blood cell counts, but did not impact on clinical outcomes. Functional assays revealed that paclitaxel induces Stathmin 1 phosphorylation at serine 16 (an inhibitory site), microtubule stability and apoptosis in Jurkat and Namalwa cell lines. Paclitaxel treatment did not modulate cell viability of normal peripheral blood leukocytes. In conclusion, our data confirm increased levels of Stathmin 1 in ALL patients and that therapeutic doses of paclitaxel inhibits Stathmin 1 function and promote microtubule stability and apoptosis in ALL cells.

Stathmin 1 inhibition amplifies ruxolitinib-induced apoptosis in JAK2V617F cells

The JAK/STAT pathway is constitutively activated in myeloproliferative neoplasms and can be inhibited by ruxolitinib, a selective JAK1/2 inhibitor. The JAK2(V617F) mutation leads to constitutive STAT3 phosphorylation and potentially leads to inhibition of Stathmin 1 activity via STAT3. In support of this hypothesis, we found that, in HEL JAK2(V617F) cells, ruxolitinib treatment decreased STAT3 and Stathmin 1 association, induced Stathmin 1 activation and microtubule instability. Silencing of Stathmin 1 significantly reduced cell proliferation and clonal growth, and increased apoptosis induced by ruxolitinib. Stathmin 1 silencing also prevented ruxolitinib-induced microtubule instability. To phenocopy the effect of Stathmin 1 inhibition, cells were treated with paclitaxel, a microtubule-stabilizing drug, in association or not with ruxolitinib; combined treatment significantly increased apoptosis, when compared to monotherapy. Notably, Stathmin 1 mRNA levels were highly expressed in CD34(+) cells from primary myelofibrosis patients. We then proposed that an undesired effect of ruxolitinib treatment may constitute Stathmin 1 activation and microtubule instability in JAK2(V617F) cells. Induction of microtubule stability, through Stathmin 1 silencing or paclitaxel treatment, combined with ruxolitinib could be an effective strategy for promoting apoptosis in JAK2(V617F) cells.

Stathmin 1 in normal and malignant hematopoiesis

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

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

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

IMPLICATIONS

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

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

BACKGROUND

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

DATA SOURCES

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

RESULTS

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

CONCLUSIONS

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

Stathmin 1 is involved in the highly proliferative phenotype of high-risk myelodysplastic syndromes and acute leukemia cells

Stathmin 1 is an important cytoplasmic microtubule-destabilizing protein that plays critical roles in proliferation and accurate chromosome segregation through regulation of microtubule dynamics. High levels of Stathmin 1 expression have been reported in leukemia and solid tumors. However, Stathmin 1 has not been studied in myelodysplastic syndrome cells. We, herein, report that significantly higher Stathmin 1 levels were observed in proliferating hematopoietic cells, in high-risk MDS and acute leukemia cells. In addition, Stathmin 1 silencing in U937 and Namalwa leukemia cells reduced cell proliferation and clonogenicity. Our data suggest that Stathmin 1 expression may be related to the highly proliferative phenotype of hematopoietic cells and add new insights into the participation of Stathmin 1 in hematological malignancies.

Overexpression of stathmin 1 is associated with poor prognosis of patients with gastric cancer

Recently, stathmin 1 has been proposed to function as an oncogene based on some relevant studies in multiple types of human cancers. However, the role of stathmin 1 in gastric cancer carcinogenesis has not been elucidated yet. The aim of this study was to investigate the expression of stathmin 1 as well as its association with overall survival of gastric cancer patients. The expression of stathmin 1 was detected by real-time quantitative reverse transcription polymerase chain reaction and Western blotting in gastric cancer and adjacent nontumor tissues. In addition, stathmin 1 expression was analyzed by immunohistochemistry in paraffin samples from 210 primary gastric cancer patients. The expression levels of stathmin 1 mRNA and protein in gastric cancer tissues were both significantly higher than those in adjacent nontumor tissues. In addition, the expression of stathmin 1 is correlated with Lauren's classification, depth of invasion, lymph node metastases, and tumor node metastasis (TNM) stage (all P < 0.05). Univariate analysis showed that high stathmin 1 expression was associated with poor prognosis in gastric cancer patients (P = 0.040). Multivariate analysis demonstrated that only lymph node metastasis and TNM stage were the independent prognostic indicators for gastric cancer. Stathmin 1 expression status is not an independent prognostic factor for patients with gastric cancer. Further subgroup analysis revealed that stathmin 1 expression was significantly correlated with prognosis in diffuse type gastric cancer. This research showed that the stathmin 1 overexpression might play an important role in the pathogenesis and subsequent progression of gastric cancer. Stathmin 1 could also be a potential therapeutic target in gastric cancer, especially for diffuse type gastric cancer.

The microtubule cytoskeleton is required for a G2 cell cycle delay in cancer cells lacking stathmin and p53

In several cancer cell lines, depleting the microtubule (MT)-destabilizing protein stathmin/oncoprotein18 leads to a G2 cell cycle delay and apoptosis. These phenotypes are observed only in synergy with low levels of p53, but the pathway(s) activated by stathmin depletion to delay the cell cycle are unknown. We found that stathmin depletion caused greater MT stability in synergy with loss of p53, measured by the levels of acetylated α-tubulin and the rate of centrosomal MT nucleation. Nocodazole or vinblastine-induced MT depolymerization abrogated the stathmin-depletion induced G2 delay, measured by the percentage of cells staining positive for several markers (TPX2, CDK1 with inhibitory phosphorylation), indicating that MTs are required to lengthen G2. Live cell imaging showed that stathmin depletion increased time in G2 without an impact on the duration of mitosis, indicating that the longer interphase duration is not simply a consequence of a previous slowed mitosis. In contrast, stabilization of MTs with paclitaxel (8 nM) slowed mitosis without lengthening the duration of interphase, demonstrating that increased MT stability alone is not sufficient to delay cells in G2.

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.

Discovery and identification of potential biomarkers of pediatric acute lymphoblastic leukemia

Background

Acute lymphoblastic leukemia (ALL) is a common form of cancer in children. Currently, bone marrow biopsy is used for diagnosis. Noninvasive biomarkers for the early diagnosis of pediatric ALL are urgently needed. The aim of this study was to discover potential protein biomarkers for pediatric ALL.

Methods

Ninety-four pediatric ALL patients and 84 controls were randomly divided into a "training" set (45 ALL patients, 34 healthy controls) and a test set (49 ALL patients, 30 healthy controls and 30 pediatric acute myeloid leukemia (AML) patients). Serum proteomic profiles were measured using surface-enhanced laser desorption/ionization-time-of-flight mass spectroscopy (SELDI-TOF-MS). A classification model was established by Biomarker Pattern Software (BPS). Candidate protein biomarkers were purified by HPLC, identified by LC-MS/MS and validated using ProteinChip immunoassays.

Results

A total of 7 protein peaks (9290 m/z, 7769 m/z, 15110 m/z, 7564 m/z, 4469 m/z, 8937 m/z, 8137 m/z) were found with differential expression levels in the sera of pediatric ALL patients and controls using SELDI-TOF-MS and then analyzed by BPS to construct a classification model in the "training" set. The sensitivity and specificity of the model were found to be 91.8%, and 90.0%, respectively, in the test set. Two candidate protein peaks (7769 and 9290 m/z) were found to be down-regulated in ALL patients, where these were identified as platelet factor 4 (PF4) and pro-platelet basic protein precursor (PBP). Two other candidate protein peaks (8137 and 8937 m/z) were found up-regulated in the sera of ALL patients, and these were identified as fragments of the complement component 3a (C3a).

Conclusion

Platelet factor (PF4), connective tissue activating peptide III (CTAP-III) and two fragments of C3a may be potential protein biomarkers of pediatric ALL and used to distinguish pediatric ALL patients from healthy controls and pediatric AML patients. Further studies with additional populations or using pre-diagnostic sera are needed to confirm the importance of these findings as diagnostic markers of pediatric ALL.

Expression of stathmin/op18 as a significant prognostic factor for cervical carcinoma patients

PURPOSE

Stathmin (Oncoprotein18), a ubiquitous and highly conserved 19-kDa cytosolic phosphoprotein, has been reported to play a critical role in mitosis and possibly other cellular processes, which is associated with tumor carcinogenesis and development. The purpose of this study was to examine the involvement of stathmin in human cervical carcinogenesis and to evaluate its prognostic significance in human cervical carcinoma.

METHODS

Using semiquantitative RT-PCR and Western blotting, we detected the expression of stathmin in human normal cervical epithelial cell line, immortalized cervical epithelial cell lines, and cervical carcinoma cell lines. Additionally, we also detected the expression of stathmin protein in 15 cases of cervical carcinoma tissues and adjacent non-carcinomous margin tissues. Furthermore, specimens from 148 patients with different grade and stage cervical carcinoma were investigated by immunohistochemistry for stathmin expression. Correlations between the expression of stathmin and various clinicopathological factors were studied, while statistical analyses were performed to evaluate prognostic and diagnostic associations.

RESULTS

The levels of stathmin mRNA and protein expression were significantly higher in cervical carcinoma cells and immortalized cervical epithelial cells than in normal cervical epithelial cells (P < 0.05). Moreover, Western blotting revealed high stathmin protein expression in 73.3% (11/15) cervical carcinoma tissues, while stathmin were overexpressed in tumor tissues as compared with adjacent non-carcinomous margin samples (P = 0.017). In addition, immunohistochemical staining revealed stathmin immunoreactivity in 81.1% (120/148) of cervical carcinoma tissues and high stathmin expression was significantly correlated with clinical stage (P = 0.006), T classification (P = 0.012), regional lymph node metastasis (P = 0.005) and hematogenous metastasis (P = 0.021). Kaplan-Meier analysis showed that high stathmin positivity was significantly associated with a shorter survival time (P < 0.001). Clinical stage (P = 0.0022), T classification (P = 0.0035), regional lymph node (P = 0.0008) or hematogenous metastasis (P = 0.0015) were also associated with survival time. Furthermore, by Cox multivariate analysis, only lymph node (P = 0.0052) or hematogenous metastasis (P = 0.0046) maintained their significance as independent prognostic factors, although stathmin was not an independent prognostic factor (risk ratio: 1.45; P = 0.0624).

CONCLUSIONS

Stathmin expression correlates with cervical carcinogenesis and tumor progression. This molecule is a valuable prognostic marker in patients with cervical carcinoma.

Taxanes, microtubules and chemoresistant breast cancer

The taxanes, paclitaxel and docetaxel are microtubule-stabilizing agents that function primarily by interfering with spindle microtubule dynamics causing cell cycle arrest and apoptosis. However, the mechanisms underlying their action have yet to be fully elucidated. These agents have become widely recognized as active chemotherapeutic agents in the treatment of metastatic breast cancer and early-stage breast cancer with benefits gained in terms of overall survival (OS) and disease-free survival (DFS). However, even with response to taxane treatment the time to progression (TTP) is relatively short, prolonging life for a matter of months, with studies showing that patients treated with taxanes eventually relapse. This review focuses on chemoresistance to taxane treatment particularly in relation to the spindle assembly checkpoint (SAC) and dysfunctional regulation of apoptotic signaling. Since spindle microtubules are the primary drug targets for taxanes, important SAC proteins such as MAD2, BUBR1, Synuclein-gamma and Aurora A have emerged as potentially important predictive markers of taxane resistance, as have specific checkpoint proteins such as BRCA1. Moreover, overexpression of the drug efflux pump MDR-1/P-gp, altered expression of microtubule-associated proteins (MAPs) including tau, stathmin and MAP4 may help to identify those patients who are most at risk of recurrence and those patients most likely to benefit from taxane treatment.

How will haematologists use proteomics?

Proteomics technologies are emerging as a useful tool in the identification of disease biomarkers, and in defining and characterising both normal physiological and disease processes. Many cellular changes in protein expression in response to an external stimulus or mutation can only be characterised at the proteome level. In these cases protein expression is often controlled by altered rates of translation and/or degradation, making proteomics an important tool in the analysis of biological systems. In the leukaemias, post-translational modification of proteins (e.g. phosphorylation, acetylation) plays a key role in the molecular pathology of the disease: such modifications can now be detected with novel proteomic methods. In a clinical setting, serum remains a relatively un-mined source of information for prognosis and response to therapy. This protein rich fluid represents an opportunity for proteomics research to benefit hematologists and others. In this review, we discuss the technologies available for the study of the proteome that offer realistic opportunities in haematology.

Identification of Novel Biomarkers in Pediatric Primitive Neuroectodermal Tumors and Ependymomas by Proteome-Wide Analysis

The aim of this study was to identify aberrantly expressed proteins in pediatric primitive neuroectodermal tumors (PNETs) and ependymomas. Tumor tissue of 29 PNET and 12 ependymoma patients was subjected to 2-dimensional difference gel electrophoresis. Gel analysis resulted in 79 protein spots being differentially expressed between PNETs and ependymomas (p < 0.01, fold change difference in expression >2). Three proteins, stathmin, annexin A1, and calcyphosine, were chosen for validation by immunohistochemistry. Stathmin was expressed 2.6-fold higher in PNETs than in ependymomas, and annexin A1 and calcyphosine were expressed 2.5- and 37.6-fold higher, respectively, in ependymomas. All PNETs showed strong staining for stathmin, and all ependymomas were strongly positive for annexin A1, whereas control tissues were negative. Calcyphosine immunoreactivity was observed in 59% of the ependymomas and was most profound in ependymoma tissue showing epithelial differentiation. mRNA expression levels of stathmin, annexin A1, and calcyphosine significantly correlated (Rs = 0.65 [p < 0.0001], Rs = 0.50 [p = 0.001], and Rs = 0.72 [p < 0.0001], respectively) with protein expression levels. In conclusion, using a proteome-wide approach, stathmin, annexin A1, and calcyphosine were successfully identified as tumor-specific proteins in pediatric PNETs and ependymomas. Ongoing studies are focused on characterizing the role of these proteins as tumor markers and potential drug targets in pediatric brain tumors.

Proteomic analysis of acute promyelocytic leukemia: PML-RARalpha leads to decreased phosphorylation of OP18 at serine 63

In the present study, we employed 2-DE to characterize the effect of the acute promyelocytic leukemia (APL)-specific PML-RARalpha fusion protein on the proteome. Differentially expressed proteins, a number of which are related to the cell cycle function, including oncoprotein18 (OP18), heat shock protein70, glucose-regulated protein75, and peptidyl-prolyl isomerase, were identified by MS. Subsequent bioinformatic pathway discovery revealed an integrated network constituting SMARCB1, MYC, and TP53-regulated pathways. The data from the DNA microarray and proteomic experiments demonstrated the correlation between the translocation and higher expression of OP18 at mRNA and protein levels. Transient cotransfection assay revealed that PML-RARalpha is a potent activator of OP18 promoter and this transcriptional activation is retinoic acid sensitive. PML-RARalpha induction also leads to decreased phosphorylation on Ser63 residue of OP18, which is okadaic acid sensitive suggesting the involvement of a phosphatase pathway. Overexpression of a constitutively phosphorylated Ser63 mutant of OP18 in PML-RARalpha expressing APL patient, PR9, and NB4 cells led to a G2/M-phase arrest in contrast to a phosphorylation-deficient Ser63 mutant and untransfected control. Taken together, our results demonstrate the significance of decreased Ser63 phosphorylation of OP18 in PML-RARalpha-mediated effects on cell cycle.

Proteomics-based strategy to identify biomarkers and pharmacological targets in leukemias with t(4;11) translocations

Translocations and other aberrations involving the MLL (mixed lineage leukemia) gene result in aggressive forms of leukemias. Heterogeneity in partner genes, in chromosomal breakpoints, in MLL itself, and in the different partner genes results in heterogeneous fusion transcripts that can be alternatively spliced, which complicates deciphering a unifying mechanism of leukemogenesis. However, recent microarray studies completed with clinical leukemia specimens have uncovered several distinct mRNA signatures within MLL leukemia that differ from other types of leukemia. A global proteomics strategy using MV4-11 and RS4:11 cells in culture was employed to investigate possible protein signatures common to different MLL leukemias and to identify disease biomarkers and protein targets for pharmacological intervention. Initial proteomics screening experiments with two-dimensional differential in-gel electrophoresis revealed heat shock protein 90 alpha (HSP90alpha) as a potential target for pharmacological inhibition and nucleoside diphosphate kinase (nm23) as a biomarker for measuring treatment efficacy. Using a modified stable isotope labeling of amino acids in cell culture (SILAC) approach, coupled with two-dimensional liquid chromatography tandem mass spectrometry (2D-LC-MS/MS), changes in abundance for over 500 proteins were measured. In addition, decreased expression of the novel biomarker nm23 was observed during HSP90 inhibition with 17-allylamino-17-demethoxygeldanamycin (17-AAG) in the MV4-11 cell line. The present study validates the use of a global proteomics strategy to uncover novel biomarkers and pharmacological targets for leukemias with MLL translocations. Additionally, several proteins were found to be expressed in concordance with microarray studies of mRNA expression in specimens from patients showing the value in comparing mRNA transcript and proteomic profiles. This work represents one of the most comprehensive proteomics screens of MLL leukemias that have been conducted to date.

Leukemia-associated antigenic isoforms induce a specific immune response in children with T-ALL

The potential immunogenicity of acute lymphoblastic leukemia of the T cell (T-ALL), a small subgroup of childhood leukemia with increased risk for treatment failure and early relapse, was addressed by serological identification of leukemia-derived antigens by recombinant expression cloning (SEREX). Thirteen antigens with homology to known genes that are involved in critical cellular processes were detected. Further characterization of the 4 novel isoforms revealed that 3 (HECTD1Delta, CX-ORF-15Delta and hCAP-EDelta) had restricted mRNA expression in more than 70% of T-ALLs (n = 22) and that specific antibodies against these isoforms were detected in up to 30% of patients (n = 16), with the highest frequency for HECTD1Delta. The latter protein was present at high abundance in T-ALLs but not in normal hematopoietic tissues. Given that the leukemia-associated antigens detected in this study have an intracellular localization, the generation of immune effector responses most likely requires antigen presentation. To test this assumption, dendritic cells were loaded with HECTD1Delta protein and used for T cell stimulation. A specific T cell response was induced in vitro in all 3 healthy donors studied, including a former T-ALL patient. These data suggest that T-ALL may induce a specific cellular and humoral antileukemia immune response in children, thereby supporting new approaches for immunotherapy.

Proteomic analysis of interleukin 6-induced differentiation in mouse myeloid leukemia cells

Cytokine-induced differentiation of myeloid leukemia cells has important therapeutic implications, but the mechanism remains to be clarified. M1 cell, a mouse acute myeloid leukemia cell line, which underwent growth inhibition, terminal differentiation and apoptosis in response to IL-6, was selected as an experimental model to study on the molecular mechanisms of myeloid cell differentiation on a proteome-wide scale. Cell differentiation was evaluated by cell morphology and CD11b expression. With two-dimensional (2D) gel analyses, 17 protein spots showed obvious changes in quantity during the process of differentiation were found. With matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF-MS) or/and nano-electrospray ionization MS/MS (ESI-MS/MS) analysis, 15 protein spots were identified. The mRNA levels of these 15 proteins during differentiation were also examined using a semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis. Except two proteins, the mRNA levels demonstrated similar expression patterns to what the proteomic analysis revealed. The identified proteins were known to be involved in different cellular functions, including protein synthesis, transcription, signal transduction, cell cycle control, cell rescue and defense, cellular organization, and metabolism. Notably, seven proteins were not described before to be involved in differentiation. Our data provide novel information for a better understanding of the mechanisms by which terminal differentiation of acute myeloid leukemia cells induced by IL-6.

Proteomic analysis of human acute leukemia cells: insight into their classification

PURPOSE

French-American-British (FAB) classification of acute leukemia with genetic heterogeneity is important for treatment and prognosis. However, the distinct protein profiles that contribute to the subtypes and facilitate molecular definition of acute leukemia classification are still unclear.

EXPERIMENTAL DESIGN

The proteins of leukemic cells from 61 cases of acute leukemia characterized by FAB classification were separated by two-dimensional electrophoresis, and the differentially expressed protein spots were identified by both matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometry (MALDI-TOF-MS) and tandem electrospray ionization MS (ESI-MS/MS).

RESULTS

The distinct protein profiles of acute leukemia FAB types or subtypes were successfully explored, including acute myeloid leukemia (AML), its subtypes (M2, M3, and M5) and acute lymphoid leukemia (ALL), which were homogeneous within substantial samples of the respective subgroups but clearly differed from all other subgroups. We found a group of proteins that were highly expressed in M2 and M3, rather than other subtypes. Among them, myeloid-related proteins 8 and 14 were first reported to mark AML differentiation and to differentiate AML from ALL. Heat shock 27 kDa protein 1 and other proteins that are highly expressed in ALL may play important roles in clinically distinguishing AML from ALL. Another set of proteins up-regulated was restricted to granulocytic lineage leukemia. High-level expression of NM23-H1 was found in all but the M3a subtype, with favorable prognosis.

CONCLUSIONS

These data have implications in delineating the pathways of aberrant gene expression underlying the pathogenesis of acute leukemia and could facilitate molecular definition of FAB classification. The extension of the present analysis to currently less well-defined acute leukemias will identify additional subgroups.

Two-dimensional electrophoresis protein profiling as an analytical tool for human acute leukemia classification

Two-dimensional electrophoresis (2-DE) was used to profile the proteins of leukemic cells from 61 cases of akute leukemia (AL) characterized by the French-American-British (FAB) classification. The differentially expressed protein spots were identified by matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) and electrospray ionization-tandem MS (ESI-MS/MS). The distinct protein profiles (DPPs) of AL FAB subtypes were explored successfully, including acute myeloid leukemia (AML), its subtypes (M2, M3, and M5), and acute lymphoid leukemia (ALL), which were homogeneous within different samples of the same subgroup but clearly differed from all other subgroups. We also found a group of proteins differentially expressed between AL cells and normal white blood cells. Among the DPPs of AL subtypes, some proteins have been reported, but most of them were first reported here to mark AML differentiation and to discriminate AML from ALL. These data show that 2-DE protein profiling could be used as an analytical tool for facilitating molecular definition of human AL classification and understanding the mechanism of leukemogensis, and the extension of the present analysis to the currently less well-defined AL will identify additional subgroups and may promote the identification of new targets for specific treatment approaches.

Thermodynamics of the Op18/stathmin-tubulin interaction

Op18/stathmin (stathmin) is an intrinsically disordered protein involved in the regulation of the microtubule filament system. One function of stathmin is to sequester tubulin dimers into assembly incompetent complexes, and recent studies revealed two tubulin binding sites per stathmin molecule. Using high sensitivity isothermal titration calorimetry, we document that at 10 degrees C and under the conditions of 80 mM PIPES, pH 6.8, 1 mM EGTA, 1 mM MgCl2, 1 mM GTP these two binding sites are of equal affinity with an equilibrium binding constant of K0 = 6.0 x 10(6) m(-1). The obtained large negative molar heat capacity change of deltaCp0 = -860 cal mol(-1) K(-1) (referring to tubulin) for the tubulin-stathmin binding equilibrium suggests that the hydrophobic effect is the major driving force of the binding reaction. Replacing GTP by GDP on beta-tubulin had no significant effect on the thermodynamic parameters of the tubulin-stathmin binding equilibrium. The proposed pH-sensitive dual function of stathmin was further evaluated by circular dichroism spectroscopy and nuclear magnetic resonance. At low temperatures, stathmin was found to be extensively helical but devoid of any stable tertiary structure. However, in complex with two tubulin subunits stathmin adopts a stable conformation. Both the stability and conformation of the individual proteins and complexes were not significantly affected by small changes in pH. A 4-fold decrease in affinity of stathmin for tubulin was revealed at pH 7.5 compared with pH 6.8. This decrease could be attributed to a weaker binding of the C terminus of stathmin. These findings do not support the view that stathmin works as a pH-sensitive protein.

Proteomic analysis of ubiquitin-proteasome effects: insight into the function of eukaryotic initiation factor 5A

The global effect of ubiquitin-proteasome (UP) inhibitors on leukemic cell proteome was analysed. A total of 39 protein spots, affected by UP inhibitors, were identified, including 11 new apoptosis-associated proteins. They are involved in different cellular functions and four were associated with caspase-3 activation. Eukaryotic initiation factor 5A (eIF-5A) was identified in two spots; however, the peptide mass-fingerprinting for the accumulated one included a peptide with lysine50, indicating that hypusine formation was suppressed during UP inhibitor-induced apoptosis. Hypusine modification ensues immediately following translation of eIF-5A precursor, unless cells are treated with the modification inhibitors diaminoheptane. However, UP inhibitors induced a much stronger accumulation of unmodified eIF-5A compared to the effect of diaminoheptane. We further showed the unmodified eIF-5A was regulated in a proteasome-dependent manner. Inhibition of hypusine formation by diaminoheptane triggered apoptosis, but of particular interest is the finding that eIF-5A expression inhibition by antisense oligodeoxynucleotides significantly enhanced the stimulating effect of GM-CSF on cell growth. Therefore, the eIF-5A accumulation played important roles in the apoptosis induced by UP inhibitors. Moreover, hypusine inhibition in apoptosis was further revealed to be associated with the subcellular localization of eIF-5A. Our data pave the way to a better understanding of the mechanisms by which UP system has been linked to apoptosis.

Overexpression of oncoprotein 18 correlates with poor differentiation in lung adenocarcinomas

We examined the expression of oncoprotein 18 (Op18) in 93 lung adenocarcinomas and 10 uninvolved lung samples using quantitative two-dimensional PAGE analysis with confirmation by mass spectrometry and two-dimensional Western blot analysis. mRNA expression was examined using oligonucleotide microarrays, and the cellular localization of the Op18 protein was examined using immunohistochemical analysis of tissue microarrays. Three phosphorylated forms and one unphosphorylated form of the Op18 protein were identified and found to be overexpressed in lung adenocarcinomas as compared with normal lung. The percentage of phosphorylated to total Op18 protein isoforms increased from 3.2% in normal lung to 7.9% in lung tumors. Both the phosphorylated and unphosphorylated Op18 proteins were significantly increased in poorly differentiated tumors as compared with moderately or well differentiated lung adenocarcinomas (p<0.03), suggesting that up-regulated expression of Op18 reflects a poor differentiation status and higher cell proliferation rates. This was further verified in A549 and SKLU1 lung adenocarcinoma cell lines by examining Op18 levels and phosphorylation status following treatment that altered either cell proliferation or differentiation. The increased expression of Op18 protein was significantly correlated with its mRNA level indicating that increased transcription likely underlies elevated expression of Op18. The overexpression of Op18 proteins in poorly differentiated lung adenocarcinomas and the elevated expression of the phosphorylated forms of Op18 may offer a new target for drug- or gene-directed therapy and may have potential utility as a tumor marker.

Proteomics in translational cancer research: toward an integrated approach

Proteomics provides powerful tools for the study of clinically relevant samples in the context of translational cancer research. Here we briefly review applications of gel-based proteomics for the study of bladder and lung cancer using fresh tissue biopsies. In general, these studies have emphasized the potential of the technology for biomarker discovery, as well as for addressing the issue of cancer heterogeneity.

Proteomics in cancer research

With the human genome sequence now determined, the field of molecular medicine is moving beyond genomics to proteomics. In the field of cancer research, the key question is: how can oncologists best use techniques of proteomics in basic research and clinical application? In the postgenomic era, proteomics promises the discovery of biomarkers and tumor markers for early detection and diagnosis, novel protein-based drug targets for anticancer therapy, and new endpoints for the assessment of therapeutic efficacy and toxicity. This review paper will explore key themes in proteomics and their application in clinical cancer research.

The promise of biomarkers in cancer screening and detection

Despite the recent decline in the incidence of cancer, long-term mortality rates remain unchanged. One of the most important factors in the survival of cancer is detection at an early stage. Clinical assays that detect the early events of cancer offer an opportunity to intervene and prevent cancer progression. Biomarkers are important molecular signatures of the phenotype of a cell that aid in early cancer detection and risk assessment. Although new information and technologies are clearly important for new biomarker discovery, we face major hurdles in translating new findings into clinical application. Here, we discuss examples of recent advances and limitations in cancer biomarker identification and validation, and the implications for cancer prevention.

Identification of novel targets for cancer therapy using expression proteomics

Although most drugs target proteins, the proteome has remained largely untapped for the discovery of drug targets. The sequencing of the human genome has had a tremendous impact on proteomics and has provided a framework for protein identification. There is currently substantial interest in implementing proteomics platforms for drug target discovery. Although the field is still in the early stages, current proteomic tools include a variety of technologies that could be implemented for large-scale protein expression analysis of cells and tissues, leading to discovery of novel drug targets. Proteomics uniquely allows delineation of global changes in protein expression patterns resulting from transcriptional and post-transcriptional control, post-translational modifications and shifts in proteins between different cellular compartments. Some of the current technologies for proteome profiling and the application of proteomics to the analysis of leukemias by our group are reviewed.

Gene expression profiling: monitoring transcription and translation products using DNA microarrays and proteomics

Novel and powerful technologies such as DNA microarrays and proteomics have made possible the analysis of the expression levels of multiple genes simultaneously both in health and disease. In combination, these technologies promise to revolutionize biology, in particular in the area of molecular medicine as they are expected to reveal gene regulation events involved in disease progression as well as to pinpoint potential targets for drug discovery and diagnostics. Here, we review the current status of these technologies and highlight some studies in which they have been applied in concert to the analysis of biopsy specimens.

Cancer proteomics: from identification of novel markers to creation of artifical learning models for tumor classification

Studies of global protein expression in human tumors have led to the identification of various polypeptide markers, potentially useful as diagnostic tools. Many changes in gene expression recorded between benign and malignant human tumors are due to post-translational modifications, not detected by analyses of RNA. Proteome analyses have also yielded information about tumor heterogeneity and the degree of relatedness between primary tumors and their metastases. Results from our own studies have shown a similar pattern of changes in protein expression in different epithelial tumors, such as decreases in tropomyosin and cytokeratin expression and increases in proliferating cell nuclear antigen (PCNA) and heat shock protein expression. Such information has been used to create artificial learning models for tumor classification. The artificial learning approach has potential to improve tumor diagnosis and cancer treatment prediction.

Mining protein data from two-dimensional gels: tools for systematic post-planned analyses

There is a considerable need to develop comprehensive, systematic mechanisms to analyze the vast number of proteins that orchestrate various cellular functions and to identify proteins associated with disease or that are affected by pharmacological agents. Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) continues to be relied upon to analyze protein constituents of cells and tissues. We have developed a Laboratory Information Processing System (LIPS) as a computer-based tool for capturing quantitative and qualitative changes in thousands of proteins detected in 2-D gels of various types. Protein databases have been developed to serve as a repository for data processing of the basic and derived data and of findings derived from different studies. There have been remarkable advances both in database technology as well as in the computer hardware that have benefited our effort at mining protein data from 2-D gels. We here review our current efforts aimed at improving the performance and features of our 2-D related protein databases, with particular emphasis on the tools we utilize for database mining via a systematic analysis of information known as post-planned analysis.

Mining the human proteome: experience with the human lymphoid protein database

We have undertaken an effort in the past five years aimed at developing a database of lymphoid proteins detectable by two-dimensional (2-D) polyacrylamide gel electrophoresis. The database contains 2-D patterns and derived information pertaining to: (i) polypeptide constituents of unstimulated and stimulated mature T cells and immature thymocytes; (ii) cultured T cells and cell lines that have been manipulated by transfection with a variety of constructs or by treatment with specific agents; (iii) single cell-derived T and B cell clones; (iv) cells obtained from patients with lymphoproliferative disorders and leukemia; and (v) a variety of other relevant cell populations. The database has experienced a substantial expansion in 2-D patterns it contains, numbering currently 9167 individual 2-D patterns. This number represents a fraction of the 30,682 2-D patterns maintained in our databases. The capacity to design and undertake experiments, produce high-quality 2-D patterns, and to undertake simple or rudimentary analyses of 2-D patterns to meet the basic needs of the experiments for which the 2-D gels were produced has exceeded the capacity to fully and uniformly integrate information generated from any gel image or experiment, across all images and experiments. While only a fraction of the information in the 2-D patterns contained in the lymphoid database has been mined, novel findings derived from querying the database point to the merits of this protein based approach. Additional resources have recently been put into place to mine more effectively data pertaining to protein expression in lymphoid cells.