MBP-1 mediated apoptosis involves cytochrome c release from mitochondria

Chinese herbal medicine Yougui Pill reduces exogenous glucocorticoid-induced apoptosis in anterior pituitary cells

Long-term glucocorticoid use may result in sustained suppression of one or more secreted components from the hypothalamo-pituitary-adrenal axis, and often results in apoptosis. Yougui Pill (YGP), a 10-component traditional Chinese herbal medicine, has been shown to be clinically effective for glucocorticoid-induced suppression of the hypothalamo-pituitary-adrenal axis. However, the pharmacological and molecular mechanisms remain unclear. We hypothesized that YGP would exert an anti-apoptosis effect on dexamethasone-treated anterior pituitary cells. In vivo experiments showed that YGP significantly reduced the number of apoptotic cells, down-regulated mRNA expression of cytochrome c, caspase-3, and caspase-9, and up-regulated mRNA expression of Bcl-2. These findings suggest that YGP reduced glucocorticoid-induced apoptosis in rat anterior pituitary cells by regulating the mitochondria-mediated apoptosis pathway.

Proteomic analysis of differentially expressed proteins in 5-fluorouracil-treated human breast cancer MCF-7 cells

BACKGROUND

5-Fluorouracil (5-Fu) is a commonly used chemotherapeutic agent in clinical care of breast cancer patients. However, the mechanism of how the 5-Fu works is complex and still largely unknown.

OBJECTIVE

The objective of this study was to understand the mechanism further and explore the new targets of 5-Fu.

METHODS

The differentially expressed proteins induced by 5-Fu in human breast cancer MCF-7 cells were identified by proteomic analysis. Four differentially expressed proteins were validated using Western blot and quantitative real-time reverse-transcription polymerase chain reaction analysis for protein and mRNA levels. The effect of 5-Fu on MCF-7 cells was determined by cell viability assay, transmission electron microscopy and flow cytometry analysis.

RESULTS

5-Fu dose-dependently inhibited cell proliferation with the IC50 value of 98.2 μM. 5-Fu also induced obviously morphological change and apoptosis in MCF-7 cells. Twelve differentially expressed proteins involved in energy metabolism, cytoskeleton, cellular signal transduction and tumor invasion and metastasis were identified.

CONCLUSION

These results may provide a new insight into the molecular mechanism of 5-Fu in therapy of breast cancer.

Interaction of Sedlin with PAM14

Sedlin is an evolutionarily conserved and ubiquitously expressed protein that is encoded by the gene SEDL. Mutations in the latter are known to be causative for spondyloepiphyseal dysplasia tarda. However, the mechanism underlying this remains unclear. We have previously shown that Sedlin interacts with the intracellular chloride channel proteins CLIC1 and CLIC2 in the cytoplasm. In this report we show that Sedlin is also physically associated with protein associated with MRG 14 kDa (PAM14), a nuclear protein that interacts with the transcription factor MORF4-related gene on chromosome 15 (MRG15). This was suggested by yeast two-hybrid screening and was confirmed with GST pull-down and immunoprecipitation assays. Moreover, we demonstrate that the C-terminus of Sedlin and the N-terminus of PAM14 are critical for their interaction. Together, these results suggest that nucleus-localized Sedlin may play a role in regulation of transcriptional activities of the MRG family of transcription factors via binding to PAM14.

Hypoxia induces differential translation of enolase/MBP-1

Background

Hypoxic microenvironments in tumors contribute to transformation, which may alter metabolism, growth, and therapeutic responsiveness. The α-enolase gene encodes both a glycolytic enzyme (α-enolase) and a DNA-binding tumor suppressor protein, c-myc binding protein (MBP-1). These divergent α-enolase gene products play central roles in glucose metabolism and growth regulation and their differential regulation may be critical for tumor adaptation to hypoxia. We have previously shown that MBP-1 and its binding to the c-myc P₂ promoter regulates the metabolic and cellular growth changes that occur in response to altered exogenous glucose concentrations.

Results

To examine the regulation of α-enolase and MBP-1 by a hypoxic microenvironment in breast cancer, MCF-7 cells were grown in low, physiologic, or high glucose under 1% oxygen. Our results demonstrate that adaptation to hypoxia involves attenuation of MBP-1 translation and loss of MBP-1-mediated regulation of c-myc transcription, evidenced by decreased MBP-1 binding to the c-myc P₂ promoter. This allows for a robust increase in c-myc expression, "early c-myc response", which stimulates aerobic glycolysis resulting in tumor acclimation to oxidative stress. Increased α-enolase mRNA and preferential translation/post-translational modification may also allow for acclimatization to low oxygen, particularly under low glucose concentrations.

Conclusions

These results demonstrate that malignant cells adapt to hypoxia by modulating α-enolase/MBP-1 levels and suggest a mechanism for tumor cell induction of the hyperglycolytic state. This important "feedback" mechanism may help transformed cells to escape the apoptotic cascade, allowing for survival during limited glucose and oxygen availability.

MBP-1 upregulates miR-29b that represses Mcl-1, collagens, and matrix-metalloproteinase-2 in prostate cancer cells

c-myc promoter binding protein (MBP-1) is a multi-functional protein known to regulate expression of targets involved in the malignant phenotype. We have previously demonstrated that exogenous expression of MBP-1 inhibits prostate tumor growth, although the mechanism of growth inhibition is not well understood. We hypothesized that MBP-1 may modulate microRNA (miRNA) expression for regulation of prostate cancer cell growth. In this study, we demonstrated that exogenous MBP-1 upregulates miR-29b by 5-9 fold in prostate cancer cells as measured by real-time quantitative reverse transcription-PCR. Subsequent studies indicated that exogenous expression of miR-29b inhibited Mcl-1, COL1A1, and COL4A1. Further, a novel target with potential implications for invasion and metastasis, matrix metallopeptidase-2 (MMP-2), was identified and confirmed to be a miR-29b target in prostate cancer cells. Together our results demonstrated that exogenous expression of miR-29b regulates prostate cancer cell growth by modulating anti-apoptotic and pro-metastatic matrix molecules, implicating therapeutic potential of miR-29b for prostate cancer inhibition.

Molecular and functional analysis of the stem cell compartment of chronic myelogenous leukemia reveals the presence of a CD34- cell population with intrinsic resistance to imatinib

We show the molecular and functional characterization of a novel population of lineage-negative CD34-negative (Lin(-)CD34(-)) hematopoietic stem cells from chronic myelogenous leukemia (CML) patients at diagnosis. Molecular karyotyping and quantitative analysis of BCR-ABL transcript demonstrated that approximately one-third of CD34(-) cells are leukemic. CML Lin(-)CD34(-) cells showed kinetic quiescence and limited clonogenic capacity. However, stroma-dependent cultures induced CD34 expression on some cells and cell cycling, and increased clonogenic activity and expression of BCR-ABL transcript. Lin(-)CD34(-) cells showed hematopoietic cell engraftment rate in 2 immunodeficient mouse strains similar to Lin-CD34(+) cells, whereas endothelial cell engraftment was significantly higher. Gene expression profiling revealed the down-regulation of cell-cycle arrest genes and genes involved in antigen presentation and processing, while the expression of genes related to tumor progression, such as angiogenic factors, was strongly up-regulated compared with normal counterparts. Phenotypic analysis confirmed the significant down-regulation of HLA class I and II molecules in CML Lin(-)CD34(-) cells. Imatinib mesylate did not reduce fusion transcript levels, BCR-ABL kinase activity, and clonogenic efficiency of CML Lin(-)CD34(-) cells in vitro. Moreover, leukemic CD34(-) cells survived exposure to BCR-ABL inhibitors in vivo. Thus, we identified a novel CD34(-) leukemic stem cell subset in CML with peculiar molecular and functional characteristics.

MBP-1 inhibits breast cancer growth and metastasis in immunocompetent mice

Breast cancer is the leading cause of cancer death among women. We have shown previously an antiproliferative effect of MBP-1 on several human cancer cells. In this study, we have examined the potential of MBP-1 as a gene therapeutic candidate in regression of breast cancer growth and metastasis in an immunocompetent mouse model. For this, we have used a mouse breast cancer cell line (EO771) and syngeneic C57BL/6 mice. EO771 cells were implanted into the mammary fat pad of C57BL/6 mice. Replication-deficient recombinant adenovirus expressing MBP-1 was administered intratumorally to determine gene therapeutic potential. The results showed a significant regression of primary and distant (lung) tumor growth. Animals exhibited prolonged survival on treatment with MBP-1 compared with the control group (dl312). Subsequent studies suggested that MBP-1 inhibits matrix metalloproteinase expression in human breast cancer cells. Cells transduced with MBP-1 displayed inhibition of migration in a wound-healing assay. The conditioned medium from MBP-1-transduced cells blocked in vitro tube formation assay and inhibited expression of several angiogenic molecules. Taken together, our study shows that MBP-1 acts as a double-edged sword by inhibiting primary and metastatic tumor growth and modulating matrix metalloproteinase expression with a therapeutic potential against breast cancer progression.

Proteomic analysis of apoptosis related proteins regulated by proto-oncogene protein DEK

A nuclear phosphoprotein, DEK, is implicated in certain human diseases, such as leukemia and antoimmune disorders, and a major component of metazoan chromatin. Basically as a modulator of chromatin structure, it can involve in various DNA and RNA-dependent processes and function as either an activator or repressor. Despite of numerous efforts to suggest the biological role of DEK, direct target proteins of DEK in different physiological status remains elusive. To investigate if DEK protein triggers the changes in certain protein networks, DEK was knocked down at both types of cell clones using siRNA expression. Here we provide a catalogue of proteome profiles in total cell lysates derived from normal HeLa and DEK knock-down HeLa cells and a good in vitro model system for dissecting the protein networks due to this proto-oncogenic DEK protein. In this biological context, we compared total proteome changes by the combined methods of two-dimensional gel electrophoresis, quantitative image analysis and MALDI-TOF MS analysis. There were a large number of targets for DEK, which were differentially expressed in DEK knock-down cells and consisted of 58 proteins (41 up-regulated and 17 down-regulated) differentially regulated expression was further confirmed for some subsets of candidates by Western blot analysis using specific antibodies. In the identified 58 spots, 16% of proteins are known to be associated with apoptosis. Among others, we identified apoptosis related proteins such as Annexins, Enolase1, Lamin A, and Glutathione-S-transferase omega 1. These results are consistent with recent studies indicating the crucial role of DEK in apoptosis pathway. We further demonstrated by ChIP analysis that knock-down of DEK caused hyperacetylation of histones around Prx VI promoter which is upregulated in our profile. Using immunoblotting analysis, we have demonstrated the modulation of other caspase-dependent apoptosis related proteins by DEK knock-down and further implicate its role in apoptosis pathway.

Knockdown of MBP-1 in human foreskin fibroblasts induces p53-p21 dependent senescence

MBP-1 acts as a general transcriptional repressor. Overexpression of MBP-1 induces cell death in a number of cancer cells and regresses tumor growth. However, the function of endogenous MBP-1 in normal cell growth regulation remains unknown. To unravel the role of endogenous MBP-1, we knocked down MBP-1 expression in primary human foreskin fibroblasts (HFF) by RNA interference. Knockdown of MBP-1 in HFF (HFF-MBPsi-4) resulted in an induction of premature senescence, displayed flattened cell morphology, and increased senescence-associated beta-galactosidase activity. FACS analysis of HFF-MBPsi-4 revealed accumulation of a high number of cells in the G1-phase. A significant upregulation of cyclin D1 and reduction of cyclin A was detected in HFF-MBPsi-4 as compared to control HFF. Senescent fibroblasts exhibited enhanced expression of phosphorylated and acetylated p53, and cyclin-dependent kinase inhibitor, p21. Further analysis suggested that promyolocytic leukemia protein (PML) bodies are dramatically increased in HFF-MBPsi-4. Together, these results demonstrated that knockdown of endogenous MBP-1 is involved in cellular senescence of HFF through p53-p21 pathway.

Tumor-suppressive effects of MBP-1 in non-small cell lung cancer cells

Lung cancer is the leading cause of cancer death among both men and women. Only approximately 15% of people diagnosed with non-small cell lung cancer (NSCLC) survive this disease beyond 5 years. Thus, novel therapeutic strategies are urgently needed to improve the clinical management of this devastating disease. We have previously shown the antiproliferative effect of MBP-1 on several human cancer cells. In this study, we have examined the potential of MBP-1 as a gene therapeutic candidate in regression of non-small cell lung tumor growth. We have observed that exogenous expression of MBP-1 in NSCLC cells (H1299) induces massive cell death. To determine the gene therapeutic potential of MBP-1, replication-deficient recombinant adenovirus expressing MBP-1 was given intratumorally in human lung cancer xenografts in nude mice. Our results showed a significant regression of lung tumor growth and prolonged survival on treatment with MBP-1 compared with the control groups (saline or dl312). Subsequently, the mechanism of MBP-1-mediated H1299 cell death was investigated. Our results suggested that MBP-1 induced poly(ADP-ribose) polymerase cleavage in H1299 cells; however, treatment with pan-caspase inhibitor did not protect against MBP-1-induced cell death. Cells transduced with MBP-1 displayed early plasma membrane permeability, mitochondrial damage without cytochrome c release, and extensive cytoplasmic vacuolation, yielding a morphotype that is typical of necrosis. Taken together, this study suggests that MBP-1 expression induces a novel form of necrosis-like cell death and MBP-1 could be a potential gene therapeutic candidate against non-small cell lung tumor growth.

Knockdown of MBP-1 in human prostate cancer cells delays cell cycle progression

We have previously shown that MBP-1 acts as a general transcriptional repressor, and forced expression of MBP-1 exerts an anti-proliferative effect on a number of human cancer cells. In this report, we have investigated the role of endogenous MBP-1 in cell growth regulation. For this, we generated human prostate cancer cells (PC3) stably transfected with short hairpin RNA targeting MBP-1. We have observed retarded growth and longer doubling time of MBP-1 knockdown PC3 cells as compared with control mock-transfected PC3 cells. Fluorescence-activated cell sorter analysis suggested that PC3 cells expressing MBP-1-specific small interfering RNA accumulated during G2/M phase of the cell cycle. Further analysis suggested that depletion of MBP-1 was associated with reduction of cyclin A and cyclin B1 expression when compared with that of the control cells. A delayed induction of cyclin A and B1 expression was observed in MBP-1-depleted PC3 cells (PC3-4.2) upon serum stimulation, although the level of expression was much lower than that of control PC3 cells. Supplementation of MBP-1 in PC3-4.2 cells restored cyclin A and cyclin B1 expression. Together, these results suggest that knockdown of MBP-1 in prostate cancer cells perturbs cell proliferation by inhibiting cyclin A and cyclin B1 expression.

Inhibition of hepatitis C virus core protein expression in immortalized human hepatocytes induces cytochrome c-independent increase in Apaf-1 and caspase-9 activation for cell death

Hepatitis C virus (HCV) core protein has multifunctional activities. We have previously reported that the core protein of HCV immortalizes primary human hepatocytes, which may relate to multistage hepatocarcinogenic events. These immortalized human hepatocytes (IHH) served as a model to study the mechanism of HCV core protein-mediated cell growth regulation. Inhibition of core protein expression in earlier stages after hepatocyte immortalization leads to the induction of apoptosis. Here, we have observed that introduction of antisense core (AS-Core) sequences for inhibition of core protein expression enhanced the expression of E2F1 and p53 levels in early passage IHH. Inhibition of core protein expression also altered the expression level of Bcl-2 family proteins, displaying an increase of the proapoptotic Bax and a decrease in the level of the anti-apoptotic Bcl-xL proteins. These alterations, however, did not result in the release of cytochrome c from the mitochondria. Apaf-1 is frequently deregulated under various pathologic conditions, and examination of AS-Core-expressing apoptotic cells indicated a significant increase in the level of Apaf-1, which coincided with caspase-9 activation. Knockdown of Apaf-1 or the transcriptional regulatory proteins, E2F1 or p53, by small interfering RNA (siRNA) duplexes inhibited the activation of caspase-9 and enhanced cell viability in AS-Core-expressing cells. These findings may contribute to the understanding of the pathophysiology of HCV core protein-mediated hepatocyte growth regulation and disease progression.

Carboxyl-Terminal Repressor Domain of MBP-1 is Sufficient for Regression of Prostate Tumor Growth in Nude Mice

Prostate cancer is the most frequently diagnosed cancer in men and the second leading cause of male cancer death in the United States. Early detection and improved procedures for surgical intervention and radiation therapy have reduced the fatalities; however, there is no effective cure for men with advanced disease and additional therapy is urgently needed. We have previously shown that MBP-1 acts as a general transcriptional repressor and exerts an antiproliferative effect on several human cancer cells. MBP-1 possesses two repressor domains, located at the amino and carboxyl termini. In this study, we have examined the potential of the repressor domains of MBP-1 as a gene therapeutic candidate in regression of prostate tumor growth. Our results suggested that replication-deficient adenovirus-mediated delivery of amino-terminal (MBP-AR) or carboxyl-terminal (MBP-CR) repressor domain of MBP-1 exerted an antiproliferative effect, like the full-length MBP-1, and induced caspase-independent apoptosis in prostate cancer cells. Next, we investigated the therapeutic effectiveness of MBP-1 repressor domain on prostate tumors. When tested in human tumor xenografts in nude mice, MBP-CR suppressed prostate tumor growth more effectively than full-length MBP-1, whereas MBP-AR delayed prostate tumor growth. Together, these results suggested that MBP-CR expression has an antiproliferative effect in human prostate cancer cells, being more effective than the full-length MBP-1 in preventing tumor growth.

c-myc Promoter-binding protein 1 (MBP-1) regulates prostate cancer cell growth by inhibiting MAPK pathway

Prostate cancer is the most common and invasive type of cancer among American men, and the second leading cause of cancer-elated deaths in the United States. Unfortunately, an effective therapeutic regimen is still lacking for advance stages of the disease. Recently, MEK5 has been shown to overexpress in prostate cancer and is associated with poor survival outcome. MEK5 exists as alpha- and beta-isoforms. MEK5alpha induces cell proliferation by activating its downstream molecules, whereas MEK5beta expression is associated with inhibition of cell growth. We have recently shown that exogenous expression of c-myc promoter-binding protein 1 (MBP-1) induces prostate cancer cell death (Ghosh, A. K., Steele, R., and Ray, R. B. (2005) Cancer Res. 65, 718-721). In this study, we have investigated whether inhibition of MEK5 signaling pathway can modulate prostate cancer cell growth. MBP-1 is a general transcriptional repressor and modulates a number of cellular genes. Therefore, we examined the endogenous expression status of MEK5 in androgen-independent prostate cancer cells upon recombinant adenovirus-mediated introduction of MBP-1. Our results demonstrated that MBP-1 expression reduced the endogenous MEK5alpha protein level; on the other hand, MEK5beta expression was enhanced significantly. Transduction of MBP-1 modulates the downstream signaling molecules of MEK5, such as activation of the cyclin D1 promoter and MEF2C transcriptional activities in androgen-independent prostate cancer cells. MBP-1 expression also modulates MEK5-mediated activation of NF-kappaB. Further analysis suggested that MBP-1 physically associates with MEK5 and induces proteasome-mediated degradation of the MEK5 protein, which appears to occur independently of ubiquitination. Together, our results suggested a novel role of MBP-1 for suppression of prostate cancer cell growth by regulating the MEK5-mediated signaling pathway.

Hepatitis C virus NS5A mediated STAT3 activation requires co-operation of Jak1 kinase

Hepatitis C virus (HCV) is a major etiologic agent for chronic hepatitis worldwide and often leads to cirrhosis and hepatocellular carcinoma. However, the mechanism for development of chronic hepatitis or hepatocarcinogenesis by HCV remains unclear. Signal transducers and activators of transcription (STATs) family proteins function as the downstream effectors of cytokine signaling and play a critical role in cell growth regulation. In many cancers including liver, STAT3 is often constitutively activated, although the mechanism of persistent activation of STAT3 is unknown. The nonstructural protein 5A (NS5A) encoded from the HCV genome has shown cell growth regulatory properties. In this study, we have observed that HCV NS5A activates STAT3 phosphorylation, which in turn translocates into the nucleus. In vivo activation of STAT3 was also observed in the liver of transgenic mice expressing HCV NS5A. Introduction of NS5A in hepatoma cells modulated STAT3 downstream molecules Bcl-xL and p21 expression. To determine if STAT3 activation by NS5A could induce STAT3 mediated gene expression, a luciferase reporter construct based on a synthetic promoter was used to transfect hepatoma cells. Activation of endogenous cellular STAT3 by HCV NS5A induced luciferase gene expression through STAT3 specific binding elements. Our subsequent studies suggested that NS5A forms a complex with Jak1 and recruits STAT3 for activation. Taken together, our results suggested that NS5A activates STAT3 through co-operation of Jak1 kinase and activated STAT3 may contribute to HCV-mediated pathogenesis.