The human CAS protein which is homologous to the CSE1 yeast chromosome segregation gene product is associated with microtubules and mitotic spindle

Integrated transcriptome analysis of CSE1L regarding poor prognosis and immune infiltration in bladder urothelial carcinoma and experimental verification

Background

Bladder urothelial carcinoma (BLCA) is one of the most prevalent tumors globally, with its incidence rising notably in developed countries, significantly affecting human health. CSE1L encodes a protein that is involved in various cellular processes and plays a critical role in cancer initiation and progression. However, its role in BLCA remains underexplored.

Methods

CSE1L expression in BLCA was analyzed using TCGA data and validated by qRT-PCR and Western blot in clinical samples. Survival analysis and Cox regression models were used to evaluate its prognostic value. Functional enrichment and protein interaction analyses were performed, and immune cell infiltration was assessed using CIBERSORT. Drug sensitivity was analyzed using GDSC data. In vitro assays evaluated the effects of CSE1L knockdown on cell proliferation, migration, and invasion.

Results

CSE1L was found to be significantly overexpressed in BLCA tissues compared to normal tissues. High CSE1L expression was associated with poor overall survival and unfavorable clinicopathological features. Functional enrichment analysis revealed that DEGs related to CSE1L were involved in cell cycle regulation and immune-related pathways. Immune infiltration analysis indicated a significant correlation between CSE1L expression and various immune cell types, particularly T cells and macrophages. Drug sensitivity analysis identified several chemotherapeutic agents, including MG-132, Palbociclib, and Nutlin-3a, which were more effective in the low-CSE1L expression group, while the high-CSE1L expression group showed sensitivity to drugs like S-Trityl-L-cysteine, Bleomycin, and Cisplatin. In vitro knockdown of CSE1L in BLCA cell lines inhibited cell proliferation, migration, and invasion.

Conclusions

The overexpression of CSE1L is associated with the progression and poor prognosis of bladder cancer, suggesting it could be a promising target for bladder cancer in the future.

A Novel Mutation in Cse1l Disrupts Brain and Eye Development with Specific Effects on Pax6 Expression

Forward genetics in the mouse continues to be a useful and unbiased approach to identifying new genes and alleles with previously unappreciated roles in mammalian development and disease. Here, we report a new mouse allele of Cse1l that was recovered from an ENU mutagenesis screen. Embryos homozygous for the anteater allele of Cse1l display a number of variable phenotypes, with craniofacial and ocular malformations being the most obvious. We provide evidence that Cse1l is the causal gene through complementation with a novel null allele of Cse1l generated by CRISPR-Cas9 editing. While the variability in the anteater phenotype was high enough to preclude a detailed molecular analysis, we demonstrate a very penetrant reduction in Pax6 levels in the developing eye along with significant ocular developmental phenotypes. The eye gene discovery tool iSyTE shows Cse1l to be significantly expressed in the lens from early eye development stages in embryos through adulthood. Cse1l has not previously been shown to be required for organogenesis as homozygosity for a null allele results in very early lethality. Future detailed studies of Cse1l function in craniofacial and neural development will be best served with a conditional allele to circumvent the variable phenotypes we report here. We suggest that human next-generation (whole genome or exome) sequencing studies yielding variants of unknown significance in CSE1L could consider these findings as part of variant analysis.

Nuclear export protein CSE1L interacts with P65 and promotes NSCLC growth via NF-κB/MAPK pathway

Non-small cell lung cancer (NSCLC) is characterized with high morbidity and mortality, mainly due to frequent recurrence and metastasis. However, the underlying molecular mechanisms of NSCLC tumorigenesis are largely unclear. Through data mining in the ONCOMINE and Gene Expression Omnibus (GEO) databases, the expression of CSE1L (chromosome segregation like 1 protein/CAS), an exportin, was identified to be significantly upregulated in NSCLC and positively associated with poor prognosis of patients. By use of in vitro and in vivo gain- and loss-of-function experiments, we found that CSE1L can promote NSCLC cell proliferation while inhibiting cell apoptosis. Through immunoprecipitation and mass spectrometry experiments, we demonstrated that CSE1L interacted with RELA (named as P65) and affected its location in the nucleus. Moreover, we found that one of the mechanisms by which CSE1L promotes proliferation and inhibits apoptosis is through activating the nuclear factor-κB (NF-κB)/mitogen-activated protein kinase (MAPK) signaling pathway. In summary, our findings indicated an oncogenic role of CSE1L in NSCLC tumorigenesis.

CSE1L participates in regulating cell mitosis in human seminoma

Objectives

CSE1L has been reported to be highly expressed in various tumours. Testicular germ cell tumours are common among young males, and seminoma is the major type. However, whether CSE1L has functions in the seminoma is unclear.

Materials and methods

The expression of CSE1L was detected by immunohistochemistry in seminoma tissues and non‐tumour normal testis tissues from patients. CSE1L distribution during cell mitosis was determined by immunofluorescent staining with CSE1L, α‐tubulin and γ‐tubulin antibodies. The effects of Cse1L knockdown on cell proliferation and cell cycle progression were determined by Cell Counting Kit‐8 assay, flow cytometry, PH3 staining and bromodeoxyuridine incorporation assay.

Results

CSE1L was significantly enriched in the seminoma tissue compared with the non‐tumour normal testis tissue. CSE1L also co‐localized with α‐tubulin in the cells with a potential to divide. In the seminoma cell line TCam‐2, CSE1L was associated with the spindles and the centrosomes during cell division. The knockdown of CSE1L in TCam‐2 cells attenuated the cells’ proliferative capacity. Cell cycle assay revealed that the CSE1L‐deficient cells were mainly arrested in the G0/G1 phase and moderately delayed in the G2/M phase. The proportion of cells with multipolar spindle and abnormal spindle geometry was obviously increased by CSE1L expression silencing in the TCam‐2 cells.

Conclusions

Overall, these findings showed that CSE1L plays a pivotal role in maintaining cell proliferation and cell division in seminomas.

CAS (CSE1L) signaling pathway in tumor progression and its potential as a biomarker and target for targeted therapy

CSE1L (chromosome segregation 1-like protein), also named as CAS (cellular apoptosis susceptibility protein), is highly expressed in most cancer types. CSE1L/CAS is a multiple functional protein that plays roles in apoptosis, cell survival, chromosome assembly, nucleocytoplasmic transport, microvesicle formation, and cancer metastasis; some of the functions are explicitly correlated. CSE1L is also a cancer serum biomarker. The phosphorylation of CAS is regulated by the extracellular signal-regulated kinase (ERK). The RAS/RAF/MAPK/ERK signaling pathways are the essential targets of most targeted cancer drugs, thus serum phosphorylated CSE1L may be a potential biomarker for monitoring drug resistance in targeted therapy. CSE1L can regulate Ras-induced ERK phosphorylation. CSE1L also regulates the expression and phosphorylation of CREB (cAMP response element binding protein) and MITF (microphthalmia-associated transcription factor) and is thus involved in the melanogenesis and progression of melanoma. CAS is an exosome/microvesicle membrane protein. Tumor cells consistently secrete microvesicles and tumor-derived microvesicles may be accumulated around tumors. Therefore, microvesicle membrane CSE1L may be a potential target for the development of high-efficacy antibody-drug conjugates (ADCs) for cancer therapy. This review will focus on CSE1L expression in cancers, its relationship to Ras/ERK and cAMP/PKA signaling pathways in melanoma development, its potential for the development of ADCs and tumor imaging reagents, and secretory phosphorylated CSE1L for monitoring the emergence of drug resistance in targeted cancer therapy.

Does CSE1L Overexpression Affect Distant Metastasis Development in Breast Cancer?

BACKGROUND

CSE1L (chromosome segregation 1-like) is the human homologue to the yeast gene CSE1, and is related to invasion and metastasis in cancer progression. The aim of this study was to investigate the potential role of CSE1L expression in distant metastasis of breast cancer.

PATIENTS AND METHODS

A total of 71 breast cancer patients were included in this study. Clinical characteristics and CSE1L status were evaluated. Immunohistochemistry was performed on formalin-fixed, paraffin-embedded archival breast tumor tissue. The results of CSE1L staining were analyzed according to the percentage of immunoreactive cells.

RESULTS

34 patients had distant metastasis and 37 did not. The mean age of the patients was 50.5 ± 12.1 years. Age, tumor size, and hormone receptor status were similar in patients with distant metastasis and in those without. A statistically significant relationship was found between nuclear CSE1L expression and distant metastasis of breast cancer. Lymph node metastasis and nuclear grade were other factors affecting distant metastasis.

CONCLUSION

There is a relationship between nuclear CSE1L overexpression and distant metastasis in breast cancer. CSE1L status may therefore become a valuable prognostic tool in the future.

hCAS/CSE1L regulates RAD51 distribution and focus formation for homologous recombinational repair

Homologous recombinational repair (HR) is one of the major repair systems for DNA double-strand breaks. RAD51 is a key molecule in HR, and the RAD51 concentration in the cell nucleus increases after DNA damage induction. However, the mechanism that regulates the intracellular distribution of RAD51 is still unclear. Here, we show that hCAS/CSE1L associates with RAD51 in human cells. We found that hCAS/CSE1L negatively regulates the nuclear protein level of RAD51 under normal conditions. hCAS/CSE1L is also required to repress the DNA damage-induced focus formation of RAD51. Moreover, we show that hCAS/CSE1L plays roles in the regulation of the HR activity and in chromosome stability. These findings suggest that hCAS/CSE1L is responsible for controlling the HR activity by directly interacting with RAD51.

The relationship between CSE1L expression and axillary lymph node metastasis in breast cancer

AIM

CSE1L is the human homologue to the yeast gene CSE1 and CSE1L is a gene related to cancer progression. Thus, CSE1L may regulate the invasion and metastasis of breast cancer. The aim of this study is to show the relationship between CSE1L and axillary lymph node metastasis.

METHODS

Sixty-six breast cancer patients were evaluated according to patient and tumor characteristics. Immunohistochemistry was carried out on formalin-fixed, paraffin-embedded archival breast tumor tissues. The results of CSE1L staining were analyzed according to the percentage of immunoreactive cells.

RESULTS

There were 29 patients without axillary lymph node metastasis and 37 patients with nodal metastasis. The mean age of the patients was 50.6 ± 11.3 years. Age, tumor size, nuclear grade and hormone receptor status were similar in the axillary lymph node positive and negative groups. There was a statistically significant relationship between cytoplasmic CSE1L expression and axillary lymph node metastasis. However, nuclear CSE1L expression did not have any effect on axillary lymph node metastasis.

CONCLUSIONS

Cytoplasmic CSE1L overexpression may be a valuable tool for prognosis of breast cancer in future.

Biological significance of the importin-β family-dependent nucleocytoplasmic transport pathways

Importin-β family proteins (Imp-βs) are nucleocytoplasmic transport receptors (NTRs) that import and export proteins and RNAs through the nuclear pores. The family consists of 14-20 members depending on the biological species, and each member transports a specific group of cargoes. Thus, the Imp-βs mediate multiple, parallel transport pathways that can be regulated separately. In fact, the spatiotemporally differential expressions and the functional regulations of Imp-βs have been reported. Additionally, the biological significance of each pathway has been characterized by linking the function of a member of Imp-βs to a cellular consequence. Connecting these concepts, the regulation of the transport pathways conceivably induces alterations in the cellular physiological states. However, few studies have linked the regulation of an importin-β family NTR to an induced cellular response and the corresponding cargoes, despite the significance of this linkage in comprehending the biological relevance of the transport pathways. This review of recent reports on the regulation and biological functions of the Imp-βs highlights the significance of the transport pathways in physiological contexts and points out the possibility that the identification of yet unknown specific cargoes will reinforce the importance of transport regulation.

AKT activation drives the nuclear localization of CSE1L and a pro-oncogenic transcriptional activation in ovarian cancer cells

The human homolog of the yeast cse1 gene (CSE1L) is over-expressed in ovarian cancer. CSE1L forms complex with Ran and importin-α and has roles in nucleocytoplasmic traffic and gene expression. CSE1L accumulated in the nucleus of ovarian cancer cell lines, while it was localized also in the cytoplasm of other cancer cell lines. Nuclear localization depended on AKT, which was constitutively active in ovarian cancer cells, as the CSE1L protein translocated to the cytoplasm when AKT was inactivated. Moreover, the expression of a constitutively active AKT forced the translocation of CSE1L from the cytoplasm to the nucleus in other cancer cells. Nuclear accrual of CSE1L was associated to the nuclear accumulation of the phosphorylated Ran Binding protein 3 (RanBP3), which depended on AKT as well. Also in samples of human ovarian cancer, AKT activation was associated to nuclear accumulation of CSE1L and phosphorylation of RanBP3. Expression profiling of ovarian cancer cells after CSE1L silencing showed that CSE1L was required for the expression of genes promoting invasion and metastasis. In agreement, CSE1L silencing impaired motility and invasiveness of ovarian cancer cells. Altogether these data show that in ovarian cancer cells activated AKT by affecting RanBP3 phosphorylation determines the nuclear accumulation of CSE1L and likely the nuclear concentration of transcription factors conveying pro-oncogenic signals.

A natural product inspired tetrahydropyran collection yields mitosis modulators that synergistically target CSE1L and tubulin

A Prins cyclization between a polymer-bound aldehyde and a homoallylic alcohol served as the key step in the synthesis of tetrahydropyran derivatives. A phenotypic screen led to the identification of compounds that inhibit mitosis (as seen by the accumulation of round cells with condensed DNA and membrane blebs). These compounds were termed tubulexins as they target the CSE1L protein and the vinca alkaloid binding site of tubulin.

Cellular apoptosis susceptibility (chromosome segregation 1-like, CSE1L) gene is a key regulator of apoptosis, migration and invasion in colorectal cancer

Cellular apoptosis susceptibility (chromosome segregation 1-like, CSE1L) gene maps to chromosomal region 20q13.13, a region frequently amplified in solid tumours. In this study, we investigated the roles played by CSE1L in colorectal cancer by examining CSE1L expression and clinico-pathological parameters in colorectal cancer and investigating the effect of CSE1L on the viability, adhesion and migration of colorectal cancer cells. RT-PCR showed that CSE1L mRNA was over-expressed in colorectal cancer. CSE1L depletion by knock-down with CSE1L-specific siRNA significantly reduced viability in HCT116 cells (p = 0.004) and SW480 cells (p = 0.003) whilst significantly increasing the proportion of apoptotic HCT116 cells (p < 0.001) and SW480 cells (p < 0.001). Furthermore, CSE1L depletion significantly reduced the adhesive capacity of HCT116 (p = 0.003) and SW480 cells (p = 0.004). Analysis by qRT-PCR following CSE1L siRNA treatment of HCT116 and SW480 cells showed significant modulation of key apoptotic (p53, p73 and BAK) and adhesive (E-cadherin, Ep-CAM and ICAM-1) molecules. Immunohistochemistry of a colorectal cancer tissue microarray showed that CSE1L had a significantly increased level in colorectal cancer compared to normal colorectal epithelium (p < 0.001). There were significant decreases in both nuclear (p = 0.006) and cytoplasmic (p = 0.003) staining of CSE1L in tumours with lymph node metastasis (stage 3 tumours) compared with lymph node-negative tumours (stage 1 and 2 tumours). In lymph node-negative patients, poor survival was associated with increased CSE1L cytoplasmic expression (p = 0.042). These results indicate that CSE1L is associated with viability and apoptosis, cellular adhesion and invasion, thus implicating CSE1L in the progression of colorectal cancer.

Cellular apoptosis susceptibility (CSE1L/CAS) protein in cancer metastasis and chemotherapeutic drug-induced apoptosis

The cellular apoptosis susceptibility (CSE1L/CAS) protein is highly expressed in cancer, and its expression is positively correlated with high cancer stage, high cancer grade, and worse outcomes of patients. CSE1L (or CAS) regulates chemotherapeutic drug-induced cancer cell apoptosis and may play important roles in mediating the cytotoxicities of chemotherapeutic drugs against cancer cells in cancer chemotherapy. CSE1L was originally regarded as a proliferation-associated protein and was thought to regulate the proliferation of cancer cells in cancer progression. However, the results of experimental studies showed that enhanced CSE1L expression is unable to increase proliferation of cancer cells and CSE1L regulates invasion and metastasis but not proliferation of cancer cells. Recent studies revealed that CSE1L is a secretory protein, and there is a higher prevalence of secretory CSE1L in the sera of patients with metastatic cancer. Therefore, CSE1L may be a useful serological marker for screening, diagnosis and prognosis, assessment of therapeutic responses, and monitoring for recurrence of cancer. In this paper, we review the expression of CSE1L in cancer and discuss why CSE1L regulates the invasion and metastasis rather than the proliferation of cancer.

CSE1L/CAS, the cellular apoptosis susceptibility protein, enhances invasion and metastasis but not proliferation of cancer cells

Background

The cellular apoptosis susceptibility (CAS) protein is regarded as a proliferation-associated protein that associates with tumour proliferation as it associates with microtubule and functions in the mitotic spindle checkpoint. However, there is no any actual experimental study showing CAS (or CSE1 and CSE1L) can increase the proliferation of cancer cells. Previous pathological study has reported that CAS was strongly positive stained in all of the metastasis melanoma that be examined. Thus, CAS may regulate the invasion and metastasis of cancers. CAS is highly expressed in cancers; if CAS is associated with cancer proliferation, then increased CAS expression should be able to increase the proliferation of cancer cells. We studied whether increased CAS expression can increase cancer cell proliferation and whether CAS regulates the invasion of cancer cells.

Methods

We enhanced or reduced CAS expression by transfecting CAS or anti-CAS expression vectors into human MCF-7 breast cancer cells. The proliferations of cells were determined by trypan blue exclusion assay and flow cytometry analysis. Invasion of cancer cells were determined by matrigel-based invasion assay.

Results

Our studies showed that increased CAS expression was unable to enhance cancer cell proliferation. Immunofluorescence showed CAS was distributed in cytoplasm areas near cell membrane and cell protrusions. CAS was localized in cytoplasmic vesicle and immunogold electronmicroscopy showed CAS was located in vesicle membrane. CAS overexpression enhanced matrix metalloproteinase-2 (MMP-2) secretion and cancer cell invasion. Animal experiments showed CAS reduction inhibited the metastasis of B16-F10 melanoma cells by 56% in C57BL/6 mice.

Conclusion

Our results indicate that CAS increases the invasion but not the proliferation of cancer cells. Thus, CAS plus ECM-degradation proteinases may be used as the markers for predicting the advance of tumour metastasis.

Spatial and temporal coordination of mitosis by Ran GTPase

The small nuclear GTPase Ran controls the directionality of macromolecular transport between the nucleus and the cytoplasm. Ran also has important roles during mitosis, when the nucleus is dramatically reorganized to allow chromosome segregation. Ran directs the assembly of the mitotic spindle, nuclear-envelope dynamics and the timing of cell-cycle transitions. The mechanisms that underlie these functions provide insights into the spatial and temporal coordination of the changes that occur in intracellular organization during the cell-division cycle.

CSE1L/CAS, a microtubule-associated protein, inhibits taxol (paclitaxel)-induced apoptosis but enhances cancer cell apoptosis induced by various chemotherapeutic drugs

CSE1L/CAS, a microtubule-associated, cellular apoptosis susceptibility protein, is highly expressed in various cancers. Microtubules are the target of paclitaxel-induced apoptosis. We studied the effects of increased or reduced CAS expression on cancer cell apoptosis induced by chemotherapeutic drugs including paclitaxel. Our results showed that CAS overexpression enhanced apoptosis induced by doxorubicin, 5-fluorouracil, cisplatin, and tamoxifen, but inhibited paclitaxel-induced apoptosis of cancer cells. Reductions in CAS produced opposite results. CAS overexpression enhanced p53 accumulation induced by doxorubicin, 5-fluorouracil, cisplatin, tamoxifen, and etoposide. CAS was associated with alpha-tubulin and beta-tubulin and enhanced the association between alpha-tubulin and beta-tubulin. Paclitaxel can induce G2/M phase cell cycle arrest and microtubule aster formation during apoptosis induction, but CAS overexpression reduced paclitaxel-induced G2/M phase cell cycle arrest and microtubule aster formation. Our results indicate that CAS may play an important role in regulating the cytotoxicities of chemotherapeutic drugs used in cancer chemotherapy against cancer cells.

Ceramide regulation of nuclear protein import

Nucleocytoplasmic trafficking is an essential and responsive cellular mechanism that directly affects cell growth and proliferation, and its potential to address metabolic challenge is incompletely defined. Ceramide is an antiproliferative sphingolipid found within vascular smooth muscle cells in atherosclerotic plaques, but its mechanism of action remains unclear. The hypothesis that ceramide inhibits cell growth through nuclear transport regulation was tested. In smooth muscle cells, exogenously supplemented ceramide inhibited classical nuclear protein import that involved the activation of cytosolic p38 mitogen-activated protein kinase (MAPK). After application of SB 202190, a specific and potent pharmacological antagonist of p38 MAPK, sphingolipid impingement on nuclear transport was corrected. Distribution pattern assessments of two essential nuclear transport proteins, importin-alpha and Cellular Apoptosis Susceptibility, revealed ceramide-mediated relocalization that was reversed upon the addition of SB 202190. Furthermore, cell counts, nuclear cyclin A, and proliferating cell nuclear antigen expression, markers of cellular proliferation, were diminished after ceramide treatment and effectively rescued by the addition of inhibitor. Together, these data demonstrate, for the first time, the sphingolipid regulation of nuclear import that defines and expands the adaptive capacity of the nucleocytoplasmic transport machinery.

Aeromonas hydrophila Cytotoxic Enterotoxin Activates Mitogen-activated Protein Kinases and Induces Apoptosis in Murine Macrophages and Human Intestinal Epithelial Cells

A cytotoxic enterotoxin (Act) of Aeromonas hydrophila possesses several biological activities, induces an inflammatory response in the host, and causes apoptosis of murine macrophages. In this study, we utilized five target cell types (a murine macrophage cell line (RAW 264.7), bone marrow-derived transformed macrophages, murine peritoneal macrophages, and two human intestinal epithelial cell lines (T84 and HT-29)) to investigate the effect of Act on mitogen-activated protein kinase (MAPK) pathways and mechanisms leading to apoptosis. As demonstrated by immunoprecipitation/kinase assays or Western blot analysis, Act activated stress-associated p38, c-Jun NH(2)-terminal kinase (JNK), and extracellular signal-regulated kinase 1/2 (ERK1/2) in these cells. Act also induced phosphorylation of upstream MAPK factors (MAPK kinase 3/6 (MKK3/6), MKK4, and MAP/ERK kinase 1 (MEK1)) and downstream effectors (MAPK-activated protein kinase-2, activating transcription factor-2, and c-Jun). Act evoked cell membrane blebbing, caspase 3-cleavage, and activation of caspases 8 and 9 in these cells. In macrophages that do not express functional tumor necrosis factor receptors, apoptosis and caspase activities were significantly decreased. Immunoblotting of host whole cell lysates revealed Act-induced up-regulation of apoptosis-related proteins, including the mitochondrial proteins cytochrome c and apoptosis-inducing factor. However, mitochondrial membrane depolarization was not detected in response to Act. Taken together, the data demonstrated for the first time Act-induced activation of MAPK signaling and classical caspase-associated apoptosis in macrophages and intestinal epithelial cells. Given the importance of MAPK pathways and apoptosis in inflammation-associated diseases, this study provided new insights into the mechanism of action of Act on host cells.

Prognostic relevance of 20q13 gains in sporadic colorectal cancers: a FISH analysis

BACKGROUND

Amplification of 20q13 is a frequent chromosomal alteration in solid tumors and harbors a number of putative oncogenes (CAS/CSE1-L, NABC1, or Aurora2). Amplifications on 20q13 have been identified as an independent prognostic marker indicating worse survival in breast and ovarian cancer. However, little is known about the prognostic significance of 20q13 gains in sporadic colorectal cancers. The aim of this study was to correlate 20q13 gains in sporadic colorectal cancers with other known prognostic factors, tumor progression, and overall survival.

METHODS

Nuclei were extracted from 146 paraffin-embedded colorectal cancers of different UICC stages and used for fluorescence in situ hybridization (FISH) with a directly labeled probe for 20q13.2 (VYSIS). Signals were counted in 120 nuclei per sample. 20q13 was considered gained when > or =40% of the nuclei showed 3 or more FISH signals. Statistical correlations were tested with log-rank tests and Kaplan-Meier survival curves.

RESULTS

Signal numbers for 20q13.2 were gained in 78 cases (53%). Cases with gains on 20q13.2 showed worse outcome than cases without: the gain of 20q13.2 was an independent prognostic marker for overall survival (P=0.006) as well as tumor progression (P=0.012) in univariate and multivariate analyses. Gains on 20q13.2 did not correlate with tumor stage. However, there was a significant association between 20q13.2 gains and tumor location in the left-sided colon and an inverse correlation between histologic grade and 20q13.2 gains.

CONCLUSION

These data indicate that gains on 20q13.2 correlate with faster tumor progression and worse patient survival independent from tumor size and lymph node involvement. Therefore, alterations on 20q13 are an important biological event in colorectal tumor progression with independent prognostic relevance.

Age-associated reduction of nuclear protein import in human fibroblasts

Age-dependent decreases in the protein concentrations of the nucleocytoplasmic transport factors karyopherin alpha2, CAS, and RanBP1 were found by comparing fibroblast cultures obtained from young, mature, and old human donors. Karyopherin beta1 levels do not change with age and present very little variation among donors. The decrease in the concentration of transport factors is accompanied by a reduction in the protein import rate in fibroblasts from old donors, as detected by a change in the intracellular localization of a test transport substrate that shuttles between the cytoplasm and the nucleus. Measurements of concentrations of the same import factors in organs and tissues of old mice revealed a decrease of CAS in kidney, lung, and spleen. The import reduction in old age is expected to lead to impaired activity of proteins whose functions depend on timely import into the nuclei.

Dcas is required for importin-alpha3 nuclear export and mechano-sensory organ cell fate specification in Drosophila

We have studied the in vivo function and tissue specificity of Dcas, the Drosophila ortholog of CAS, the importin beta-like export receptor for importin alpha. While dcas mRNA is specifically expressed in the embryonic central nervous system, Dcas protein is maternally supplied to all embryonic cells and its nuclear/cytoplasmic distribution varies in different tissues and times in development. Unexpectedly, hypomorphic alleles of dcas show specific transformations in mechano-sensory organ cell identity, characteristic of mutations that increase Notch signaling. Dcas is essential for efficient importin-alpha3 nuclear export in mechano-sensory cells and the surrounding epidermal cells and is indirectly required for the import of one component of the Notch pathway, but not others tested. We interpret the specificity of the dcas phenotype as indicating that one or more Notch signaling components are particularly sensitive to a disruption in nuclear protein import. We propose that mutations in house keeping genes often cause specific developmental phenotypes, such as those observed in many human genetic disorders.

Oxidative stress and liver toxicity in rats and human hepatoma cell line induced by pentachlorophenol and its major metabolite tetrachlorohydroquinone

Pentachlorophenol (PCP) is a pesticide used worldwide in industrial and domestic applications. It is used extensively as biocide and wood preservatives. Metabolic studies carried out in rodents and human liver homogenates have indicated that PCP undergoes oxidative dechlorination to form tetrachlorohydroquinone (TCHQ). Free radical catalyzed tissue injury is thought to play a fundamental role in human disease. In the present study, we examined the effects of PCP and TCHQ on the induction of lipid peroxidation and liver injury in rats. In addition, the cytotoxic dose, cell death mechanisms and related gene expressions induced by PCP and TCHQ were also determined for human hepatoma cell line (Hep G2). The results indicated that more toxic effects could be observed both in rats and human hepatoma cell line treated with TCHQ than its parent compound, PCP. Oxygen species may be involved in the mechanism of TCHQ intoxication since the urinary 8-epi-PGF2alpha and AST, ALT activities can be induced by TCHQ and attenuated by vitamin E treatment. Apoptosis features were found in cells treated with TCHQ but not PCP. TCHQ-induced cell damage may issue signals for the induction of HSPs, the decrease of the bcl/bax protein ratio and the decrease of CAS gene, whereas the PCP-induced damage may not.

Different cell death mechanisms and gene expression in human cells induced by pentachlorophenol and its major metabolite, tetrachlorohydroquinone

Pentachlorophenol (PCP) and its salt are used extensively as biocide and wood preservative. Due to improper disposal, PCP has become an environmental pollutant and is now considered to be ubiquitos. Metabolic studies carried out in rodents or human liver homogenate have indicated that PCP undergoes oxidative dechlorination to form tetrachlorohydroquinone (TCHQ). The cytotoxicity, cell death mechanisms and gene expression of PCP and TCHQ are investigated in human liver and bladder cells and show that TCHQ induces apoptosis and DNA genomic fragmentation in bladder cells but not liver cells. No apoptotic features could be induced by treatment of PCP in both cell lines. The concentrations of PCP required to cause 50% cell death in T-24 and Chang liver cells were 5-10-fold greater than the concentrations of TCHQ. Several gene products are important in controlling the apoptotic and necrotic processes. Of these, hsp 70, CAS, bcl-2 and bax were studied. The expression of the hsp70 gene increased significantly (2-3-fold) in cells treated with TCHQ. However, no significant change was found in the cells treated with PCP. The expression of CAS gene decreased significantly in T-24 cells treated with both TCHQ and PCP. Whereas, no significant change was found in Chang liver cells with the same treatment. In addition, the expression of the bcl-2/bax protein decreased significantly in these two cell lines treated with TCHQ but not PCP.

Evidence for separable functions of Srp1p, the yeast homolog of importin alpha (Karyopherin alpha): role for Srp1p and Sts1p in protein degradation

Srp1p (importin alpha) functions as the nuclear localization signal (NLS) receptor in Saccharomyces cerevisiae. The srp1-31 mutant is defective in this nuclear localization function, whereas an srp1-49 mutant exhibits defects that are unrelated to this localization function, as was confirmed by intragenic complementation between the two mutants. RPN11 and STS1 (DBF8) were identified as high-dosage suppressors of the srp1-49 mutation but not of the srp1-31 mutation. We found that Sts1p interacts directly with Srp1p in vitro and also in vivo, as judged by coimmunoprecipitation and two-hybrid analyses. Mutants of Sts1p that cannot interact with Srp1p are incapable of suppressing srp1-49 defects, strongly suggesting that Sts1p functions in a complex with Srp1p. STS1 also interacted with the second suppressor, RPN11, a subunit of the 26S proteasome, in the two-hybrid system. Further, degradation of Ub-Pro-beta-galactosidase, a test substrate for the ubiquitin-proteasome system, was defective in srp1-49 but not in srp1-31. This defect in protein degradation was alleviated by overexpression of either RPN11 or STS1 in srp1-49. These results suggest a role for Srp1p in regulation of protein degradation separate from its well-established role as the NLS receptor.

Tissue-specific alternative splicing of the CSE1L/CAS (cellular apoptosis susceptibility) gene

CSE1L/CAS (CAS) is a nuclear transport factor that plays a role in proliferation and apoptosis. The CAS gene consists of 25 exons. mRNA homologous over its entire length to the yeast homologue CSE1 is the predominant transcript in proliferating tissues. Additional mRNAs are generated by alternative splicing in a tissue-specific manner. An extended 3'-end is found in fetal and adult brain. A mRNA containing the 5'-end of CAS up to position 690 and an alternative 3'-end is expressed in trachea and encodes a truncated Ran-binding domain. Fetal liver expresses a mRNA with deletions of a central portion of CAS and additional sequences encoded by the last intron. SW480 colon cancer cells express another approximately 1500-base mRNA. Western blot analyses of various human tissues and immunohistology of mouse embryos show a correlation of CAS transcripts and CAS protein in different tissues. CAS isoforms may control nuclear transport of tissue-specific proteins.

The regulation of apoptosis by microbial pathogens

In the past few years, there has been remarkable progress unraveling the mechanism and significance of eukaryotic programmed cell death (PCD), or apoptosis. Not surprisingly, it has been discovered that numerous, unrelated microbial pathogens engage or circumvent the host's apoptotic program. In this chapter, we briefly summarize apoptosis, emphasizing those studies which assist the reader in understanding the subsequent discussion on PCD and pathogens. We then examine the relationship between virulent bacteria and apoptosis. This section is organized to reflect both common and diverse mechanisms employed by bacteria to induce PCD. A short discussion of parasites and fungi is followed by a detailed description of the interaction of viral pathogens with the apoptotic machinery. Throughout the review, apoptosis is considered within the broader contexts of pathogenesis, virulence, and host defense. Our goals are to update the reader on this rapidly expanding field and identify topics in the current literature which demand further investigation.

Expression of the proliferation and apoptosis-associated CAS protein in benign and malignant cutaneous melanocytic lesions

We have examined the expression of the cellular apoptosis susceptibility protein, a nuclear transport factor that plays a role in apoptosis and cell proliferation, in benign and malignant melanocytic lesions. Tissue samples of 55 formalin-fixed, paraffin-embedded melanoma (primary n=32, metastatic n=23) and of 27 control cases (junctional dermal, compound, Spitz, Reed, blue nevi, balloon-cell nevus, lentigo maligna) were analyzed by immunohistochemistry with anti-cellular apoptosis susceptibility antibodies. The percentage of cellular apoptosis susceptibility-positive cells as well as the intensity on a four-point scale was evaluated. In normal skin, expression of cellular apoptosis susceptibility was primarily found in the basal cell layer of the epidermis. Benign melanocytic lesions that stained positive for cellular apoptosis susceptibility (13 of 27) showed a homogeneously distributed staining pattern with a mean of 5+/-12% cellular apoptosis susceptibility positive cells. Five out of 7 lentigo maligna melanoma, 11 out of 12 superficial spreading melanoma and all acrolentiginous (n=7) and nodular (n=6) melanoma showed immunoreactivity of medium (++) to high ( ) intensity. Vertical growth phases of primary cutaneous melanoma stained stronger than horizontally growing cell clusters. All metastases (n= 23) stained strongly positive, the staining pattern being inhomogeneous. Cellular apoptosis susceptibility detection in clinical stages according to UICC showed an increase from 43+/-34% cellular apoptosis susceptibility positive cells in stage I, to 53+/-26% in stage II, 68+/-24% in stage III and 72+/-24% in stage IV, respectively. Because the expression of cellular apoptosis susceptibility correlates predominantly with advanced stages of melanoma, staining with anti-cellular apoptosis susceptibility antibodies may be useful for diagnosis of melanoma and possibly as an immunohistochemical prognostic factor in cutaneous melanocytic lesions.

Cse1p is involved in export of yeast importin alpha from the nucleus

Proteins bearing a nuclear localization signal (NLS) are targeted to the nucleus by the heterodimeric transporter importin. Importin alpha binds to the NLS and to importin beta, which carries it through the nuclear pore complex (NPC). Importin disassembles in the nucleus, evidently by binding of RanGTP to importin beta. The importin subunits are exported separately. We investigated the role of Cse1p, the Saccharomyces cerevisiae homologue of human CAS, in nuclear export of Srp1p (yeast importin alpha). Cse1p is located predominantly in the nucleus but also is present in the cytoplasm and at the NPC. We analyzed the in vivo localization of the importin subunits fused to the green fluorescent protein in wild-type and cse1-1 mutant cells. Srp1p but not importin beta accumulated in nuclei of cse1-1 mutants, which are defective in NLS import but not defective in NLS-independent import pathways. Purified Cse1p binds with high affinity to Srp1p only in the presence of RanGTP. The complex is dissociated by the cytoplasmic RanGTP-binding protein Yrb1p. Combined with the in vivo results, this suggests that a complex containing Srp1p, Cse1p, and RanGTP is exported from the nucleus and is subsequently disassembled in the cytoplasm by Yrb1p. The formation of the trimeric Srp1p-Cse1p-RanGTP complex is inhibited by NLS peptides, indicating that only NLS-free Srp1p will be exported to the cytoplasm.

The hCSE1/CAS protein is phosphorylated by HeLa extracts and MEK-1: MEK-1 phosphorylation may modulate the intracellular localization of CAS

hCSE1/CAS (CAS), the human homologue of the yeast chromosome segregation gene CSE1, is a nuclear transport factor that plays a role in proliferation and apoptosis. A MEK-1 phosphorylation sequence in CAS raises the possibility that MEK-phosphorylation regulates the function of CAS. CAS protein from cell extracts shows covalent charge modifications; one of these charge variants contains phosphotyrosine. CAS protein can be captured from cell extracts by immobilized anti-phosphotyrosine antibodies. We have produced recombinant protein fragments containing the N-terminal or central portion of CAS and found that the N-terminal fragment, which contains a putative MEK phosphorylation site, is phosphorylated by the HeLa extracts and MEK-1. Treatment of cells with an inhibitor of MEK-1 phosphorylation in vivo changes the intracellular localization of CAS from predominantly cytoplasmic to nuclear. This suggests that a function of CAS in nuclear transport may be regulated by phosphorylation.

Cse1p functions as the nuclear export receptor for importin alpha in yeast

CSE1 is essential for yeast cell viability and has been implicated in chromosome segregation. Based on its sequence similarity, Cse1p has been grouped into the family of importin beta-like nucleocytoplasmic transport receptors with highest homology to the recently identified human nuclear export receptor for importin alpha, CAS. We demonstrate here that Cse1p physically interacts with yeast Ran and yeast importin alpha (Srp1p) in the yeast two-hybrid system and that recombinant Cse1p, Srp1p and Ran-GTP form a trimeric complex in vitro. Re-export of Srp1p from the nucleus into the cytoplasm and nuclear uptake of a reporter protein containing a classical NLS are inhibited in a cse1 mutant strain. These findings suggest that Cse1p is the exportin of importin alpha in yeast.

Control of cyclin B1 localization through regulated binding of the nuclear export factor CRM1

Activation of the Cyclin B/Cdc2 kinase complex triggers entry into mitosis in all eukaryotic cells. Cyclin B1 localization changes dramatically during the cell cycle, precipitously transiting from the cytoplasm to the nucleus at the beginning of mitosis. Presumably, this relocalization promotes the phosphorylation of nuclear targets critical for chromatin condensation and nuclear envelope breakdown. We show here that the previously characterized cytoplasmic retention sequence of Cyclin B1, responsible for its interphase cytoplasmic localization, is actually an autonomous nuclear export sequence, capable of directing nuclear export of a heterologous protein, and able to bind specifically to the recently identified export mediator, CRM1. We propose that the observed cytoplasmic localization of Cyclin B1 during interphase reflects the equilibrium between ongoing nuclear import and rapid CRM1-mediated export. In support of this hypothesis, we found that treatment of cells with leptomycin B, which disrupted Cyclin B1-CRM1 interactions, led to a marked nuclear accumulation of Cyclin B1. In mitosis, Cyclin B1 undergoes phosphorylation at several sites, a subset of which have been proposed to play a role in Cyclin B1 accumulation in the nucleus. Both CRM1 binding and the ability to direct nuclear export were affected by mutation of these phosphorylation sites; thus, we propose that Cyclin B1 phosphorylation at the G2/M transition prevents its interaction with CRM1, thereby reducing nuclear export and facilitating nuclear accumulation.

Cell cycle-regulated processing of HEF1 to multiple protein forms differentially targeted to multiple subcellular compartments

HEF1, p130(Cas), and Efs/Sin constitute a family of multidomain docking proteins that have been implicated in coordinating the regulation of cell adhesion. Each of these proteins contains an SH3 domain, conferring association with focal adhesion kinase; a domain rich in SH2-binding sites, phosphorylated by or associating with a number of oncoproteins, including Abl, Crk, Fyn, and others; and a highly conserved carboxy-terminal domain. In this report, we show that the HEF1 protein is processed in a complex manner, with transfection of a single cDNA resulting in the generation of at least four protein species, p115(HEF1), p105(HEF1), p65(HEF1), and p55(HEF1). We show that p115(HEF1) and p105(HEF1) are different phosphorylation states of the full-length HEF1. p55(HEF1), however, encompasses only the amino-terminal end of the HEF1 coding sequence and arises via cleavage of full-length HEF1 at a caspase consensus site. We find that HEF1 proteins are abundantly expressed in epithelial cells derived from breast and lung tissue in addition to the lymphoid cells in which they have been predominantly studied to date. In MCF-7 cells, we find that expression of the endogenous HEF1 proteins is cell cycle regulated, with p105(HEF1) and p115(HEF1) being rapidly upregulated upon induction of cell growth, whereas p55(HEF1) is produced specifically at mitosis. While p105(HEF1) and p115(HEF1) are predominantly cytoplasmic and localize to focal adhesions, p55(HEF1) unexpectedly is shown to associate with the mitotic spindle. In support of a role at the spindle, two-hybrid library screening with HEF1 identifies the human homolog of the G2/M spindle-regulatory protein Dim1p as a specific interactor with a region of HEF1 encompassed in p55(HEF1). In sum, these data suggest that HEF1 may directly connect morphological control-related signals with cell cycle regulation and thus play a role in pathways leading to the progression of cancer.

Effect of microtubule disruption on cell adhesion and spreading

Microtubules have been involved in a variety of cellular processes. In this study, we examined the role of the microtubular system in the adhesion and spreading of the adenocarcinoma cell line HT29-D4. Disruption of microtubules by nocodazole or navelbine resulted in an increase in cell adhesion to purified ECM proteins. This enhanced cell adhesion is mediated by integrins, but is not attributable to quantitative changes in the number of integrin receptors at the cell surface, as determined by flow cytometric analysis. In contrast to attachment, spreading of HT29-D4 cells was reduced by nocodazole treatment in a dose-dependent manner. Thus, microtubule depolymerization appears to increase initial attachment of cells to extracellular matrix, while impeding subsequent cell spreading.

Localization of the cell proliferation and apoptosis-associated CAS protein in lymphoid neoplasms

We have evaluated the expression and distribution of the cellular apoptosis susceptibility (CAS) protein in normal lymphoid tissue and malignant lymphomas. CAS protein, the product of the CAS gene, is associated with microtubules and the mitotic spindle. Immunohistochemistry with an antibody to CAS shows many CAS-positive cells in normal tonsils. The majority of strongly CAS-positive cells were localized to the dark zone of the follicles, whereas the mantle zone and interfollicular areas were essentially negative. Double staining for CAS and Ki-67 revealed co-expression of the two proliferation markers in approximately 85 to 90% of the CAS-positive cells. Different subtypes of lymphomas exhibited varying patterns of CAS expression. Low-grade non-Hodgkin's lymphoma generally revealed weak staining with CAS, with 10 to 60% of all cells being positive. In contrast, highly malignant non-Hodgkin's lymphoma and malignant cells of Hodgkin's disease displayed very strong CAS positivity, with staining of up to 80% of the atypical cells. Overall, the staining pattern of CAS and Ki-67 was superimposable within a particular lymphoma subtype. However, in all lymphomas we observed a significant fraction of CAS-positive normal and malignant lymphocytes that were Ki-67 negative, probably because they were momentarily noncycling cells. We conclude that a high expression of CAS correlates with proliferation of normal and malignant lymphoid cells. The fact that detection of CAS protein identifies a higher portion of proliferating and malignant cells than Ki-67 warrants further evaluation of CAS protein as a marker with a diagnostic potential.

Identification of BIME as a subunit of the anaphase-promoting complex

The initiation of anaphase and exit from mitosis require the activation of a proteolytic system that ubiquitinates and degrades cyclin B. The regulated component of this system is a large ubiquitin ligase complex, termed the anaphase-promoting complex (APC) or cyclosome. Purified Xenopus laevis APC was found to be composed of eight major subunits, at least four of which became phosphorylated in mitosis. In addition to CDC27, CDC16, and CDC23, APC contained a homolog of Aspergillus nidulans BIME, a protein essential for anaphase. Because mutation of bimE can bypass the interphase arrest induced by either nimA mutation or unreplicated DNA, it appears that ubiquitination catalyzed by APC may also negatively regulate entry into mitosis.