Mxi1, a Myc antagonist, suppresses proliferation of DU145 human prostate cells

METTL3-mediated m6A modification of circGLIS3 promotes prostate cancer progression and represents a potential target for ARSI therapy

BACKGROUND

Circular RNAs (circRNAs) have been shown to be involved in tumorigenesis and progression. However, the role of circGLIS3 (hsa_circ_0002874) in prostate cancer (PCa) has yet not been reported.

METHODS

Candidate circRNA were determined through comprehensive analysis of public datasets, PCa cell lines, and tissues data. A series of cellular functional assays, including CCK-8, colony formation, wound healing, and transwell assays were performed. Subsequently, RNA sequencing, RNA immunoprecipitation, methylated RNA immunoprecipitation, microRNA pulldown, luciferase reporter assay, and western blot were used to explore the underlying molecular mechanisms. Moreover, the xenograft tumor mouse model was established to elucidate the function of circGLIS3.

RESULTS

CircGLIS3, derived from exon 2 of the parental GLIS3 gene, was identified as a novel oncogenic circRNA in PCa that was closely associated with the biochemical recurrence. Its expression levels were upregulated in PCa tissues and cell lines as well as enzalutamide high-resistant cells. The cellular functional assays revealed that circGLIS3 promoted PCa cell proliferation, migration, and invasion. METTL3-mediated N6-methyladenosine (m6A) modification maintained its upregulation by enhancing its stability. Mechanically, CircGLIS3 sponged miR-661 to upregulate MDM2, thus regulating the p53 signaling pathway to promote cell proliferation, migration, and invasion. Furthermore, in vitro and in vivo experiments, the knockdown of circGLIS3 improved the response of PCa cells to ARSI therapies such as enzalutamide.

CONCLUSIONS

METTL3-mediated m6A modification of circGLIS3 regulates the p53 signaling pathway via the miR-661/MDM2 axis, thereby facilitating PCa progression. Meanwhile, this study unveils a promising potential target for ARSI therapy for PCa.

Identifying subtle functional change in individuals with mild cognitive impairment: development and validation of the Healthy Brain Ageing - Functional Assessment Questionnaire

Accumulating research suggests that individuals with Mild Cognitive Impairment (MCI) experience subtle functional changes, but that available functional assessment tools are insensitive to this. To address this gap, we describe the development and validation of the self-report, "Healthy Brain Ageing Functional Assessment Questionnaire" (HBA-FAQ). We examined the factor structure and psychometric properties of the HBA-FAQ in 503 participants with normal cognition, subjective cognitive decline (SCD), MCI or dementia. Our results found the HBA-FAQ to have good reliability, validity and stronger discriminative ability between healthy control participants and those with SCD (0.734, p = .001), MCI (0.666, p = .012) and dementia (0.798, p < .001) compared to a widely-used instrumental activities of daily living screener. In conclusion, the HBA-FAQ is a valid, reliable self-report tool, providing an efficient and sensitive approach to identifying subtle changes in daily functioning in older people at risk of dementia.

Fibronectin Modulates the Expression of miRNAs in Prostate Cancer Cell Lines

Prostate cancer (PCa) is a significant cause of cancer-related deaths among men and companion animals, such as dogs. However, despite its high mortality and incidence rates, the molecular mechanisms underlying this disease remain to be fully elucidated. Among the many factors involved in prostate carcinogenesis, the extracellular matrix (ECM) plays a crucial role. This ECM in the prostate is composed mainly of collagen fibers, reticular fibers, elastic fibers, proteoglycans and glycoproteins, such as fibronectin. Fibronectin is a glycoprotein whose dysregulation has been implicated in the development of multiple types of cancer, and it has been associated with cell migration, invasion, and metastasis. Furthermore, our research group has previously shown that fibronectin induces transcriptional changes by modulating the expression of protein coding genes in LNCaP cells. However, potential changes at the post-transcriptional level are still not well understood. This study investigated the impact of exposure to fibronectin on the expression of a key class of regulatory RNAs, the microRNAs (miRNAs), in prostate cancer cell lines LNCaP and PC-3. Five mammalian miRNAs (miR-21, miR-29b, miR-125b, miR-221, and miR-222) were differentially expressed after fibronectin exposure in prostate cell lines. The expression profile of hundreds of mRNAs predicted to be targeted by these miRNAs was analyzed using publicly available RNA-Sequencing data (GSE64025, GSE68645, GSE29155). Also, protein-protein interaction networks and enrichment analysis were performed to gain insights into miRNA biological functions. Altogether, these functional analyzes revealed that fibronectin exposure impacts the expression of miRNAs potentially involved in PCa causing changes in critical signaling pathways such as PI3K-AKT, and response to cell division, death, proliferation, and migration. The relationship here demonstrated between fibronectin exposure and altered miRNA expression improves the comprehension of PCa in both men and other animals, such as dogs, which naturally develop prostate cancer.

Development of a Risk Score Model for Osteosarcoma Based on DNA Methylation-Driven Differentially Expressed Genes

Osteosarcoma (OS) is the commonest malignant bone tumor in adolescent patients, and patients face amputation, tumor metastasis, chemotherapy resistance, and even death. We investigated the potential connection between abnormal methylation differentially expressed genes and the survival rate of osteosarcoma patients. GSE36002 and GSE12865 datasets of GEO database were utilized for abnormal methylation differentially expressed genes, followed by function and pathway enrichment analyses, the protein-protein interaction network in the STRING database, and cluster analysis in the MCODE app of Cytoscape. The RNA-seq and clinical data from the TARGET-OS project of TCGA were used for univariate and least absolute shrinkage and selection operator (LASSO) Cox regression analyses to predict the risk genes of osteosarcoma. 1191 hypermethylation-downregulated genes might function through plasma membrane, negative regulation of transcription from the RNA polymerase II promoter, and pathways, including transcriptional misregulation in cancer. 127 hypomethylation-upregulated genes were enriched in proteolysis, negative regulation of the canonical Wnt signaling pathway, and metabolic signaling pathways. The univariate Cox analysis revealed 638 genes ( $P<0.01$ ), including 50 hypermethylation-downregulated genes and 4 hypomethylation-upregulated genes, subsequently based on LASSO Cox regression analysis for 54 aberrant methylation-driven genes, and three genes (COL13A1, MXI1, and TBRG1) were selected to construct the risk score model. The three genes (COL13A1, MXI1, and TBRG1) regulated by DNA methylation were identified to relate with the outcomes of OS patients, which might provide a new insight to the pathological mechanism of osteosarcoma.

Mxi1 participates in the progression of lung cancer via the microRNA-300/KLF9/GADD34 Axis

The purpose of the current study was to define the role of MAX interactor 1 (Mxi1) in the pathogenesis of lung cancer and its underlying molecular mechanism. Bioinformatics analysis was performed to identify important regulatory pathway related to lung cancer. Dual luciferase reporter and ChIP assays were adopted to validate the interaction among Mxi1, miR-300 and KLF9. Loss- and gain-of-function studies were conducted to determine the roles of Mxi1, miR-300, and KLF9 in cell proliferation, migration, and invasion in vitro and their effects on myeloid-derived suppressor cell (MDSC) recruitment in vivo. Mxi1 was poorly expressed in lung cancer tissues and cells and its poor expression was associated with poor prognosis. Mxi1 inhibited miR-300 by suppressing its transcription. miR-300 suppressed the expression of KLF9, and KLF9 negatively regulated GADD34 expression in lung cancer cells. Mxi1 or KLF9 elevation or miR-300 repression inhibited lung cancer cell proliferation, as evidenced by reduced Ki67 and PCNA expression, and lowered invasion and migration. In vivo findings revealed that silencing KLF9 induced tumor growth by enhancing MDSC-mediated immunosuppression through upregulation of GADD34. Collectively, these findings suggest that Mxi1 can inhibit lung cancer progression by regulating the miR-300/KLF9 axis and GADD34-mediated immunosuppression.

Normal and Neoplastic Growth Suppression by the Extended Myc Network

Among the first discovered and most prominent cellular oncogenes is MYC, which encodes a bHLH-ZIP transcription factor (Myc) that both activates and suppresses numerous genes involved in proliferation, energy production, metabolism and translation. Myc belongs to a small group of bHLH-ZIP transcriptional regulators (the Myc Network) that includes its obligate heterodimerization partner Max and six "Mxd proteins" (Mxd1-4, Mnt and Mga), each of which heterodimerizes with Max and largely opposes Myc's functions. More recently, a second group of bHLH-ZIP proteins (the Mlx Network) has emerged that bears many parallels with the Myc Network. It is comprised of the Myc-like factors ChREBP and MondoA, which, in association with the Max-like member Mlx, regulate smaller and more functionally restricted repertoires of target genes, some of which are shared with Myc. Opposing ChREBP and MondoA are heterodimers comprised of Mlx and Mxd1, Mxd4 and Mnt, which also structurally and operationally link the two Networks. We discuss here the functions of these "Extended Myc Network" members, with particular emphasis on their roles in suppressing normal and neoplastic growth. These roles are complex due to the temporal- and tissue-restricted expression of Extended Myc Network proteins in normal cells, their regulation of both common and unique target genes and, in some cases, their functional redundancy.

MiR-93/miR-375: Diagnostic Potential, Aggressiveness Correlation and Common Target Genes in Prostate Cancer

Dysregulation of miRNAs has a fundamental role in the initiation, development and progression of prostate cancer (PCa). The potential of miRNA in gene therapy and diagnostic applications is well documented. To further improve miRNAs' ability to distinguish between PCa and benign prostatic hyperplasia (BPH) patients, nine miRNA (-21, -27b, -93, -141, -205, -221, -182, -375 and let-7a) with the highest reported differentiation power were chosen and for the first time used in comparative studies of serum and prostate tissue samples. Spearman correlations and response operating characteristic (ROC) analyses were applied to assess the capability of the miRNAs present in serum to discriminate between PCa and BPH patients. The present study clearly demonstrates that miR-93 and miR-375 could be taken into consideration as single blood-based non-invasive molecules to distinguish PCa from BPH patients. We indicate that these two miRNAs have six common, PCa-related, target genes (CCND2, MAP3K2, MXI1, PAFAH1B1, YOD1, ZFYVE26) that share the molecular function of protein binding (GO:0005515 term). A high diagnostic value of the new serum derived miR-182 (AUC = 0.881, 95% confidence interval, CI = 0.816-0.946, p < 0.0001, sensitivity and specificity were 85% and 79%, respectively) is also described.

Transcriptional regulators and regulatory pathways involved in prostate gland adaptation to a hypoandrogen environment

Anti-androgen therapies, including orchiectomy, are effective at promoting prostate cancer remission, but are followed by progression to the more aggressive castration-resistant prostate cancer (CRPC). Castration promotes gland and tumor shrinkage. However, prostate adaptation to androgen deprivation involves striking parallel events, all requiring changes in gene expression. We hypothesized that transcription factors (TF) and other transcription-related genes are needed to orchestrate those changes. In this work, downstream analysis using bioinformatic tools and published microarray data allowed us to identify sixty transcriptional regulators (including 10 TF) and to integrate their function in physiologically relevant networks. Functional associations revealed a connection between Arnt, Bhlhe41 and Dbp circadian rhythm genes with the Ar circuitry and a small gene network centered in Pex14, which might indicate a previously unanticipated metabolic shift. We have also identified human homologs and mapped the corresponding genes to human chromosome regions commonly affected in prostate cancer, with particular attention to the PTEN/HHEX/MXI1 cluster at 10q23-25 (frequently deleted in PCa) and to MAPK1 at 22q11.21 (delete in intermediate risk but not in high risk PCa). Twenty genes were found mutated or with copy number alterations in at least five percent of three cancer cohorts and six of them (PHOX2A, NFYC, EST2, EIF2S1, SSRP1 and PARP1) associated with impacted patient survival. These changes are specific to the adaptation to the hypoandrogen environment and seem important for the progression to CRPC when mutated.

Regulation of cell cycle by MDM2 in prostate cancer cells through Aurora Kinase-B and p21WAF1/CIP1 mediated pathways

Overexpression of MDM2 oncoprotein has been detected in a large number of diverse human malignancies and has been shown to play both p53-dependent and p53-independent roles in oncogenesis. Our study was designed to explore the impact of MDM2 overexpression on the levels of various cell cycle regulatory proteins including Aurora kinase-B (AURK-B), CDC25C and CDK1, which are known to promote tumor progression and increase metastatic potential. Our data from human cell cycle RT² profiler PCR array experiments revealed significant changes in the expression profile of genes that are involved in different phases of cell cycle regulation in LNCaP-MST (MDM2 transfected) prostate cancer cells. Our current study has demonstrated a significant increase in the expression level of AURK-B, CDC25C, Cyclin A2, Cyclin B and CDK1 in LNCaP-MST cells as compared with wild type LNCaP cells that were modulated by MDM2 specific inhibitor Nutlin-3. In fact, the expression levels of the above- mentioned proteins were significantly altered at both mRNA and protein levels after treating the cells with 20 μM Nutlin-3 for 24h. Additionally, the pro-apoptotic proteins including p53, p21, and Bax were elevated with the concomitant decrease in the key anti-apoptotic proteins following MDM2 inhibitor treatment. Also, Nutlin-3 treated cells demonstrated caspase-3 activation was observed with an in-vitro caspase-3 fluorescent assay performed with caspase 3/7 specific DEVD-amc substrate. Our results offer significant evidence towards the effectiveness of MDM2 inhibition in causing cell cycle arrest via blocking the transmission of signals through AURKB-CDK1 axis and inducing apoptosis in LNCaP-MST cancer cells. It is evident from our data that MDM2 overexpression probably is the primary cause for CDK1 up-regulation in the LNCaP-MST cells, which might have occurred possibly through activation of AURK-B. However, further studies in this direction should shed more light on the intracellular mechanisms involved in the regulation of Aurora kinase-B and CDK1 axis in MDM2 positive cancers.

Compressive force induces reversible chromatin condensation and cell geometry-dependent transcriptional response

Fibroblasts exhibit heterogeneous cell geometries in tissues and integrate both mechanical and biochemical signals in their local microenvironment to regulate genomic programs via chromatin remodelling. While in connective tissues fibroblasts experience tensile and compressive forces (CFs), the role of compressive forces in regulating cell behavior and, in particular, the impact of cell geometry in modulating transcriptional response to such extrinsic mechanical forces is unclear. Here we show that CF on geometrically well-defined mouse fibroblast cells reduces actomyosin contractility and shuttles histone deacetylase 3 (HDAC3) into the nucleus. HDAC3 then triggers an increase in the heterochromatin content by initiating removal of acetylation marks on the histone tails. This suggests that, in response to CF, fibroblasts condense their chromatin and enter into a transcriptionally less active and quiescent states as also revealed by transcriptome analysis. On removal of CF, the alteration in chromatin condensation was reversed. We also present a quantitative model linking CF-dependent changes in actomyosin contractility leading to chromatin condensation. Further, transcriptome analysis also revealed that the transcriptional response of cells to CF was geometry dependent. Collectively, our results suggest that CFs induce chromatin condensation and geometry-dependent differential transcriptional response in fibroblasts that allows maintenance of tissue homeostasis.

S6K1 phosphorylation-dependent degradation of Mxi1 by β-Trcp ubiquitin ligase promotes Myc activation and radioresistance in lung cancer

Rationale: Mxi1 is regarded as a potential tumor suppressor protein that antagonizes the transcriptional activity of proto-oncogene Myc. However, the clinical significances and underlying mechanisms by which Mxi1 is regulated in lung cancer remain poorly understood.

Methods: Mass spectrometry analysis and immunoprecipitation assay were utilized to detect the protein-protein interaction. The phosphorylation of Mxi1 was evaluated by in vitro kinase assays. Poly-ubiquitination of Mxi1 was examined by in vivo ubiquitination assay. Lung cancer cells stably expressing wild-type Mxi1 or Mxi1-S160A were used for functional analyses. The expression levels of Mxi1 and S6K1 were determined by immunohistochemistry in lung cancer tissues and adjacent normal lung tissues.

Results: We found that Mxi1 is downregulated and correlated with poor prognosis in lung cancer. Using tandem affinity purification technology, we provided evidence that β-Trcp E3 ubiquitin ligase interacts with and promotes the ubiquitination and degradation of Mxi1. Furthermore, we demonstrated that Mxi1 is phosphorylated at S160 site by the protein kinase S6K1 and subsequently degraded via the ubiquitin ligase β-Trcp. Moreover, a phosphorylation mutant form of Mxi1 (Mxi1-S160A), which cannot be degraded by S6K1 and β-Trcp, is much more stable and efficient in suppressing the transcriptional activity of Myc and radioresistance in lung cancer cells. More importantly, a strong inverse correlation between S6K1 and Mxi1 expression was observed in human lung cancer tissues.

Conclusion: Our findings not only establish a crosstalk between the mTOR/S6K1 signaling pathway and Myc activation, but also suggest that targeting S6K1/Mxi1 pathway is a promising therapeutic strategy for the treatment of lung cancer.

Functional interactions among members of the MAX and MLX transcriptional network during oncogenesis

The transcription factor MYC and its related family members MYCN and MYCL have been implicated in the etiology of a wide spectrum of human cancers. Compared to other oncoproteins, such as RAS or SRC, MYC is unique because its protein coding region is rarely mutated. Instead, MYC's oncogenic properties are unleashed by regulatory mutations leading to unconstrained high levels of expression. Under both normal and pathological conditions MYC regulates multiple aspects of cellular physiology including proliferation, differentiation, apoptosis, growth and metabolism by controlling the expression of thousands of genes. How a single transcription factor exerts such broad effects remains a fascinating puzzle. Notably, MYC is part of a network of bHLHLZ proteins centered on the MYC heterodimeric partner MAX and its counterpart, the MAX-like protein MLX. This network includes MXD1-4, MNT, MGA, MONDOA and MONDOB proteins. With some exceptions, MXD proteins have been functionally linked to cell cycle arrest and differentiation, while MONDO proteins control cellular metabolism. Although the temporal expression patterns of many of these proteins can differ markedly they are frequently expressed simultaneously in the same cellular context, and potentially bind to the same, or similar DNA consensus sequence. Here we review the activities and interactions among these proteins and propose that the broad spectrum of phenotypes elicited by MYC deregulation is intimately connected to the functions and regulation of the other network members. Furthermore, we provide a meta-analysis of TCGA data suggesting that the coordinate regulation of the network is important in MYC driven tumorigenesis. This article is part of a Special Issue entitled: Myc proteins in cell biology and pathology.

Mxi1 and mxi1-0 antagonize N-myc function and independently mediate apoptosis in neuroblastoma

Neuroblastoma (NB) is the third most common malignancy of childhood, and outcomes for children with advanced disease remain poor; amplification of the MYCN gene portends a particularly poor prognosis. Mxi1 antagonizes N-Myc by competing for binding to Max and E-boxes. Unlike N-Myc, Mxi1 mediates transcriptional repression and suppresses cell proliferation. Mxi1 and Mxi1-0 (an alternatively transcribed Mxi1 isoform) share identical Max and DNA binding domains but differ in amino-terminal sequences. Because of the conservation of these critical binding domains, we hypothesized that Mxi1-0 antagonizes N-Myc activity similar to Mxi1. SHEP NB cells and SHEP cells stably transfected with MYCN (SHEP/MYCN) were transiently transfected with vectors containing full-length Mxi1, full-length Mxi1-0, or the common Mxi domain encoded by exons 2 to 6 (ex2-6). After incubation in low serum, parental SHEP/MYCN cell numbers were reduced compared with SHEP cells. Activated caspase-3 staining and DNA fragmentation ELISA confirmed that SHEP/MYCN cells undergo apoptosis in low serum, while SHEP/MYCN cells transfected with Mxi1 or Mxi1-0 do not. However, SHEP/MYCN cells transfected with Mxi1 or Mxi1-0 and grown in normal serum showed proliferation rates similar to SHEP cells. Mxi ex2-6 did not affect cell number in low or normal serum, suggesting that amino terminal domains of Mxi1 and Mxi1-0 are critical for antagonism. In the absence of N-Myc, Mxi1 and Mxi1-0 induce apoptosis independently through the caspase-8-dependent extrinsic pathway, while N-Myc activates the caspase-9-dependent intrinsic pathway. Together, these data indicate that Mxi1 and Mxi1-0 antagonize N-Myc but also independently impact NB cell survival.

N-Myc differentially regulates expression of MXI1 isoforms in neuroblastoma

Amplification of the MYCN proto-oncogene is associated with a poor prognosis in patients with metastatic neuroblastoma (NB). MYCN encodes the N-Myc protein, a transcriptional regulator that dimerizes with the Max transcription factor, binds to E-box DNA sequences, and regulates genes involved in cell growth and apoptosis. Overexpression of N-Myc leads to transcriptional activation and an increase in NB cell proliferation. Mxi1, a member of the Myc family of transcriptional regulators, also binds to Max. However, Mxi1 is a transcriptional repressor and inhibits proliferation of NB cells, suggesting that Mxi1 functions as an N-Myc antagonist. Our laboratory previously identified Mxi1-0, an alternatively transcribed Mxi1 isoform. Mxi1-0 has properties distinct from those of Mxi1; in contrast to Mxi1, Mxi1-0 is unable to suppress c-Myc-dependent transcription. We now show that Mxi1-0 expression increases in response to MYCN overexpression in NB cells, with a positive correlation between MYCN and MXI1-0 RNA levels. We also show that N-Myc expression differentially regulates the MXI1 and MXI1-0 promoters: Increased MYCN expression suppresses MXI1 promoter activity while enhancing transcription through the MXI1-0 promoter. Finally, induction of Mxi1-0 leads to increased proliferation, whereas expression of Mxi1 inhibits cell growth, indicating differential roles for these two proteins. These data suggest that N-Myc differentially regulates the expression of MXI1 and MXI1-0 and can alter the balance between the two transcription factors. Furthermore, MXI1-0 appears to be a downstream target of MYCN-dependent signaling pathways and may contribute to N-Myc-dependent cell growth and proliferation.

MYC and MXI1 protein expression: potential prognostic significance in women with breast cancer in China

OBJECTIVE

To investigate the expression levels and the clinical significance of MYC and MXI1 proteins in breast cancer.

METHODS

The expression levels of MYC and MXI1 were detected by immunohistochemical assay in 166 cases of breast cancer; the relationships among MYC, MXI1 and the clinicopathological parameters were analyzed by χ2 test. Univariate analysis and Cox's proportional hazards model were used to evaluate the prognostic significance of the 2 proteins.

RESULTS

27.71% of the tumor specimens showed high staining intensity for MYC (high-expression group, HEG-MYC) and 22.89% showed high staining intensity for MXI1 (HEG-MXI1); the expression of 2 proteins was negatively correlated (r = -0.177 p = 0.022). The Kaplan-Meier method for survival analysis showed that patients of the MYC-HEG demonstrated a significantly worse disease-specific survival than those of the MYC-low-expression group (LEG) (χ2 = 11.102, p = 0.001). However, patients of the MXI1-HEG had a significantly better disease-specific survival than those of the MXI1-LEG (χ2 = 7.858, p = 0.005). Both univariate analysis and Cox's proportional hazards model indicated that MYC and MXI1 could be independent prognostic molecular markers.

CONCLUSION

MYC-HEG and MXI1-LEG levels are associated with poor prognosis in patients with breast cancer, suggesting that they may be useful molecular markers in breast cancer prognosis prediction.

Change of MAX interactor 1 expression in an anti-Thy1 nephritis model and its effect on mesangial cell proliferation

BACKGROUND/AIMS

During the disease process of mesangial proliferative glomerulonephritis, the expression of various factors that influence mesangial proliferation is altered. MAX interactor 1 (Mxi1) antagonizes the transcription factor Myc and is believed to be a tumor suppressor. However, no studies have investigated its effect on mesangial cell proliferation.

METHODS

To investigate the effect of Mxi1 on renal mesangial cell proliferation, we established a classic rat anti-Thy1 mesangial proliferative glomerulonephritis model. Mesangial proliferation was estimated by immunohistochemical analysis of Ki67. Mxi1 expression at each time point was assessed by real-time RT-PCR and Western blot analyses. Furthermore, we altered the expression level of Mxi1 by a plasmid and siRNA to detect its effect on rat mesangial cell proliferation in vitro.

RESULTS

Mxi1 expression decreased significantly during the proliferative period of anti-Thy1 nephritis model and then gradually increased as proliferation declined, indicating that Mxi1 may be linked to mesangial cell proliferation. Upregulation of Mxi1 expression via plasmid transfection in vitro reduced the expression of the positive-acting cell cycle regulatory proteins cyclin B1, cyclin D1, cyclin E, CDC2 and CDK2; significantly reduced mesangial cell proliferation; reduced the percentage of S phase cells; and increased the percentage of G2/M phase cells. Inhibition of Mxi1 expression by siRNA in vitro produced the opposite effects: increased expression of cyclin B1, cyclin D1, cyclin E, CDC2 and CDK2; markedly increased cell proliferation; higher percentage of S phase cells; and dramatically lower percentage of G2/M phase cells. Transcription factor c-myc protein expression showed no obvious difference after Mxi1 plasmid and siRNA transfection. The expressions of cell cycle regulatory proteins mentioned above were negative correlated with Mxi1 expression in anti-Thy1 nephritis model.

CONCLUSION

These results suggest that Mxi1 expression levels were inversely correlated with proliferation in anti-Thy1 nephritis rats and it may influence cell cycle progression and thus the rate of mesangial cell proliferation by regulating the expression of c-myc target cell cycle regulatory proteins.

MicroRNA-205 inhibits Src-mediated oncogenic pathways in renal cancer

The Src family of protein kinases (SFK) plays key roles in regulating fundamental cellular processes, including cell growth, differentiation, cell shape, migration, and survival, and specialized cell signals in various malignancies. The pleiotropic functions of SFKs in cancer make them promising targets for intervention. Here, we sought to investigate the role of microRNA-205 (miR-205) in inhibition of Src-mediated oncogenic pathways in renal cancer. We report that expression of miR-205 was significantly suppressed in renal cancer cell lines and tumors when compared with normal tissues and a nonmalignant cell line and is correlated inversely with the expression of SFKs. miR-205 significantly suppressed the luciferase activity of reporter plasmids containing the 3'-UTR (untranslated region) sequences complementary to either Src, Lyn, or Yes, which was abolished by mutations in these 3'-UTR regions. Overexpression of miR-205 in A498 cells reduced Src, Lyn, and Yes expression, both at mRNA and protein levels. Proliferation of renal cancer cells was suppressed by miR-205, mediated by the phospho-Src-regulated ERK1/2 pathway. Cell motility factor FAK (focal adhesion kinase) and STAT3 activation were also inhibited by miR-205. Transient and stable overexpression of miR-205 in A498 cells resulted in induction of G₀/G₁ cell-cycle arrest and apoptosis, as indicated by decreased levels of cyclin D1 and c-Myc, suppressed cell proliferation, colony formation, migration, and invasion in renal cancer cells. miR-205 also inhibited tumor cell growth in vivo. This is the first study showing that miR-205 inhibits proto-oncogenic SFKs, indicating a therapeutic potential of miR-205 in the treatment of renal cancer.

Integration of genetic signature and TNM staging system for predicting the relapse of locally advanced colorectal cancer

PURPOSE

To identify potential genetic markers in treated stage II-III colorectal cancer patients and predict 3-year tumor relapse using statistical models based on important clinical factors and significant genetic markers.

METHODS

Gene expression profiling by cDNA-mediated Annealing, Selection, extension and Ligation assay was performed in a prospectively collected 95 stage II-III colorectal cancer patients with Fluorouracil-based adjuvant chemotherapy. We studied the gene expression level of 502 genes for patients with different outcomes. The prognostic effect of genetic signature was evaluated in multivariate analysis. We further integrated the genetic signature to clinical Classification of Malignant Tumors (TNM) staging system for predicting of 3-year tumor relapse.

RESULTS

An 8-gene signature was identified to well discriminate patients with different treatment outcomes. An integrated risk factor, which including 8-gene signature and TNM staging has been developed. ROC curve revealed that our integrated risk factor was better than genetic signature or current sixth edition TNM staging system alone.

CONCLUSIONS

Our 8-gene signature was promising in predicting 3-year disease-free survival rate for locally advanced colorectal cancer. The integrated risk factor, which combining genetic signature with clinical TNM staging system may further improve the outcome prediction.

The role of MAPK-ERK pathway in 67-kDa laminin receptor-induced FasL expression in human cholangiocarcinoma cells

BACKGROUND AND AIMS

Cancer cells are thought to possess immune evasion properties due to FasL overexpression in many types of human tumors. In the present study, we set out to investigate the role of MAPK-ERK pathway in 67-kDa laminin receptor induced FasL expression and FasL-mediated apoptosis in human cholangiocarcinoma cells.

METHODS

The expression of FasL and its promoter activity in cultured cholangiocarcinoma cells were examined after treatment with laminin or transfection with plasmids containing siRNA targeted to 67-kDa laminin receptor. The effects of MAPK-ERK cascade inhibitor and c-Myc inhibition by siRNA on 67-kDa laminin receptor-induced FasL expression were determined. Apoptosis assay was performed to analyze the apoptosis of lymphocytes cocultured with cholangiocarcinoma cells treated with or without MAPK-ERK cascade inhibitor.

RESULTS

Our results revealed that the specific MAPK-ERK cascade inhibitor, PD98059, significantly attenuated phosphorylation of c-Myc on Ser-62 and FasL upregulation in QBC-939 cells and these cells showed decreased cytotoxicity against Fas-sensitive Jurkat T cells. A luciferase reporter assay revealed that FasL promoter activity was significantly reduced in cells treated with PD98059 or transfected with c-Myc siRNA.

CONCLUSIONS

Based on these results, we conclude that 67LR induces FasL expression and cytotoxicity against Fas-sensitive Jurkat T cells in human cholangiocarcinoma cells through the phosphorylation of c-Myc on Ser-62 and the subsequent activation of the FasL promoter through the ERK pathway.

Gene expression profile of multipotent mesenchymal stromal cells: Identification of pathways common to TGFbeta3/BMP2-induced chondrogenesis

Multipotent mesenchymal stromal cells (MSC) display a high potential for the development of novel treatment strategies for cartilage repair. However, the pathways involved in their differentiation to functional non hypertrophic chondrocytes remain largely unknown, despite the work on embryologic development and the identification of key growth factors including TGFbeta, Hh, Wnt and FGF. In this study, we asked if we could identify specific biological networks common to the growth factors used (TGFbeta3 or BMP-2). To address this question, we used DNA microarrays and performed large-scale expression profiling of MSC at different time points during their chondrogenic differentiation. By comparing these data with those obtained during the differentiation of MSC into osteoblasts and adipocytes, we identified 318 genes specific for chondrogenesis and developed a new algorithm to classify the genes according to their kinetic profile. We distributed the selected genes in five classes according to their kinetic of expression. We could reconstruct three phases characterized by functional pathways. The first phase corresponds to cell attachment and apoptosis induction; the second phase is characterized by a proliferation/differentiation step, and the third phase is characterized by a differentiation/hypertrophy pathway. Indeed, these data propose new pathways to understand the complexity of MSC differentiation to chondrocytes.

Cellular quiescence in mammary stem cells and breast tumor stem cells: got testable hypotheses?

Cellular quiescence is a state of reversible cell cycle arrest and has more recently been shown to be a blockade to differentiation and to correlate with resistance to cancer chemotherapeutics and other xenobiotics; features that are common to adult stem cells and possibly tumor stem cells. The biphasic kinetics of mammary regeneration, coupled to its cyclic endocrine control suggest that mammary stem cells most likely divide during a narrow window of the regenerative cycle and return to a state of quiescence. This would enable them to retain their proliferative capacity, resist differentiation signals and preserve their prolonged life span. There is accumulating evidence that mammary stem cells and other adult stem cells utilize quiescence for this purpose, however the degree to which tumor stem cells do so is largely unknown. The retained proliferative capacity of mammary stem cells likely enables them to accumulate and harbor mutations that lead to breast cancer initiation. However it is currently unclear if these causative lesions lead to defective or deranged quiescence in mammary stem cells. Evidence of such effects could potentially lead to the development of diagnostic systems that monitor mammary stem cell quiescence or activation. Such systems may be useful for the evaluation of patients who are at significant risk of breast cancer. Additionally quiescence has been postulated to contribute to therapeutic resistance and tumor recurrence. This review aims to evaluate what is known about the mechanisms governing cellular quiescence and the role of tumor stem cell quiescence in breast cancer recurrence.

Src family kinase oncogenic potential and pathways in prostate cancer as revealed by AZD0530

Prostate cancer is the most frequently diagnosed cancer in American men. We have previously demonstrated that Src mediates androgen-independent proliferation in prostate cancer. We sought to investigate the Src-mediated oncogenic pathways and tumor biology using AZD0530, a novel Src family kinase/Abl dual-kinase inhibitor that is entering phase II clinical trials. We show that while both Src and Abl are expressed in all prostate cancer cell lines, Src but not Abl is activated in the prostate. Furthermore, Src activation is inhibited by AZD0530 in a rapid and dose-dependent manner. We show that Src mediates cell proliferation in DU145 and PC3 cells at the G1 phase of cell cycle. Src inhibition resulted in decreased binding of beta-catenin to the promoters of G1 phase cell cycle regulators cyclin D1 and c-Myc. C-Myc may also be regulated at the protein level by extracellular signal-regulated kinase 1/2 and GSK3beta. Cell motility factors focal adhesion kinase, p130CAS and paxillin activation in DU145 and PC3 cells were also inhibited. Administration of AZD0530 in mice reduced orthotopic DU145 xenograft growth by 45%. We have further delineated the Src-mediated oncogenic growth and migration pathways in prostate cancer and established mechanistic rationale for Src inhibition as novel therapy in the treatment of prostate cancer.

Hypoxia selects for androgen independent LNCaP cells with a more malignant geno- and phenotype

Hypoxia confers resistance to common cancer therapies, however, it has also has been shown to result in genetic alterations which may allow a survival advantage and increase the tumorigenic properties of cancer cells. Additionally, it may exert a selection pressure, allowing expansion of tumor cells with a more aggressive phenotype. To further assess the role of hypoxia in malignant progression in prostate cancer we exposed human androgen dependent prostate cancer cells (LNCaP) to cycles of chronic hypoxia and isolated a subline, LNCaP-H1. This article describes the partial characterization of this cell line. The LNCaP-H1 subline showed altered growth characteristics and exhibited androgen independent growth both in vitro and in vivo. Furthermore, these cells were resistant to mitochondrial-mediated apoptosis, probably since the endogenous levels of Bax was lower and Bcl-2 higher than in the parental LNCaP cells. Microarray analysis revealed that a complex array of pathways had differential gene expression between the 2 cell lines, with LNCaP-H1 cells exhibiting a genetic profile which suggests that they may be more likely metastasize to distant organs, especially bone. This was supported by an in vitro invasion assay, and an in vivo metastasis study. This study shows that hypoxia can select for androgen independent prostate cancer cells which have a survival advantage and are more likely to invade and metastasize.

Motility-related actinin alpha-4 is associated with advanced and metastatic ovarian carcinoma

Advanced and metastatic ovarian cancer is a leading cause of death from gynecologic malignancies. A more detailed understanding of the factors controlling invasion and metastasis may lead to novel anti-metastatic therapies. To model cellular interactions that occur during intraperitoneal metastasis, comparative cDNA microarray analysis and confirmatory real-time reverse transcription PCR (RT-PCR) were employed to uncover changes in gene expression that may occur in late stage ovarian cancer in response to microenvironmental cues, particularly native three-dimensional collagen I. Gene expression in human ovarian carcinoma tissues was evaluated on the RNA and protein level using real-time RT-PCR and immunohistochemistry. Cell invasion and migration were evaluated in a collagen invasion assay and a scratch wound assay. Three-dimensional collagen I culture led to differential expression of several genes. The role of actinin alpha-4 (ACTN4), a cytoskeleton-associated protein implicated in the regulation of cell motility, was examined in detail. ACTN4 RNA and protein expression were associated with advanced and metastatic human ovarian carcinoma. This report demonstrates that a cytoskeletal-associated protein ACTN4 is upregulated by three-dimensional collagen culture conditions, leading to increased invasion and motility of ovarian cancer cells. Expression of ACTN4 in human ovarian tumors was found to be associated with advanced-stage disease and peritoneal metastases.

Induction of Mxi1-SR alpha by FOXO3a contributes to repression of Myc-dependent gene expression

Forkhead transcription factors of the O class (FOXOs) are important targets of the phosphatidylinositol 3-kinase (PI3-kinase)/Akt pathway. FOXOs have been implicated in the regulation of cell cycle progression, oxidative stress resistance, and apoptosis. Using DNA microarrays, we analyzed the transcriptional response to FOXO3a activation by gene expression analysis in DLD-1 colon cancer cells stably expressing a FOXO3a.A3-ER fusion protein. We found that activation of FOXO3a resulted in repression of a number of previously identified Myc target genes. Furthermore, FOXO3a activation induced expression of several members of the Mad/Mxd family of transcriptional repressors, most notably Mxi1. The induction of Mxi1 by FOXO3a was specific to the Mxi1-SR alpha isoform and was mediated by three highly conserved FOXO binding sites within the first intron of the gene. Activation of FOXO3a in response to inhibition of Akt also resulted in activation of Mxi1-SR alpha expression. Silencing of Mxi1 by small interfering RNA (siRNA) reduced FOXO3a-mediated repression of a number of Myc target genes. We also observed that FOXO3a activation induced a switch in promoter occupancy from Myc to Mxi1 on the E-box containing promoter regions of two Myc target genes, APEX and FOXM1. siRNA-mediated transient silencing of Mxi1 or all Mad/Mxd proteins reduced exit from S phase in response to FOXO3a activation, and stable silencing of Mxi1 or Mad1 reduced the growth inhibitory effect of FOXO3a. We conclude that induction of Mad/Mxd proteins contributes to the inhibition of proliferation in response to FOXO3a activation. Our results provide evidence of direct regulation of Mxi1 by FOXO3a and imply an additional mechanism through which the PI3-kinase/Akt/FOXO pathway can modulate Myc function.

Gene copy number profiling of soft-tissue leiomyosarcomas by array-comparative genomic hybridization

Leiomyosarcoma (LMS) is a rare malignant mesenchymal tumor of smooth muscle cells. Chromosomal aberrations in LMS have been studied, but the cytogenetic data that have been published so far are complex, limited, and incomplete. Here, we performed for the first time a high-resolution genome-wide array comparative genomic hybridization (CGH) analysis (aCGH) on a pool of 14 low- and high-grade LMS cases to obtain gene-level information about the amplified and deleted regions that may play a role in the development and progression of LMS. Our aCGH results indicated that 2,218 genes were involved in 25 altered chromosomal regions; 9 regions in low-grade LMS, 12 regions in high-grade LMS, and 4 minimal common regions shared by low- and high-grade LMS. The frequency of DNA copy number gains in high-grade LMS was threefold compared to low-grade LMS, whereas losses in low-grade LMS were almost twice as frequent as in high-grade LMS. Both low- and high-grade tumors shared two minimal common regions of gain (15q26 approximately qter and 17p13.1 approximately q11) and loss (6p12 approximately p21.3 and 13q14.3 approximately qter). Moreover, our findings indicated that low- and high-grade LMS and osteosarcoma share 12 genes located in the 17p amplicon. In conclusion, by using aCGH, we were able to define the precise location of the altered chromosomal areas and to identify putative tumor suppressor genes and oncogenes therein. The list of altered genes in the minimal common regions is available as at our web site (http://www.helsinki.fi/cmg/microarray_data).

Down-regulation of c-Myc following MEK/ERK inhibition halts the expression of malignant phenotype in rhabdomyosarcoma and in non muscle-derived human tumors

Background

Expression of c-myc proto-oncogene is inappropriate in a wide range of human tumors, and is a downstream target of Ras/Raf/ERK pathway, which promotes c-Myc stability by enhancing c-Myc expression and activity.

The aim of this study was to investigate whether the oncogenic phenotype in the human muscle-derived Rhabdomyosarcoma (RD) cell line and in non muscle-derived human tumor cell lines (SW403, IGR39 and PC3) can be blocked by disrupting the c-Myc pathway either by means of pharmacological MEK/ERK inhibition or by direct inactivation of the c-Myc protein.

Results

We demonstrate that, in all the tumor cell lines used, the MEK/ERK inhibitor U0126 rapidly induces c-Myc de-phosphorylation, which is followed by a marked reduction in its expression level, by inhibition of proliferation and by reversion of anchorage-independent growth. These data suggest that the targeting of pathways controlling c-Myc expression or stability reverses deregulated growth of different tumor-derived cell lines. Indeed, in RD cells, we found a marked down-regulation of cyclins E2, A and B and CDK2, all of which are known to be targets of c-Myc. Moreover, ectopic MadMyc chimera, a c-Myc function antagonist, causes dramatic growth arrest, CDK and cyclin modulation as well as inhibition of anchorage-independent growth in RD cells, as occurs in U0126-treated cells. In particular, we found that the mere inhibition of c-Myc by MadMyc chimera rescues the myogenic program, MHC expression and the acquisition of the myogenic-like phenotype in RD cells.

Conclusion

Our data provide evidence of the key role played by the MEK/ERK pathway in the growth arrest and transformation phenotype of Rhabdomyosarcoma and of non muscle-derived tumor cell lines. In fact, MEK/ERK inhibitor, U0126, induces growth arrest, anchorage-dependent growth of these cell lines. In addition, the results of this study demonstrate that the direct inactivation of c-Myc by Mad/Myc chimera rescues myogenic program and leads to the reversal of the Rhabdomyosarcoma phenotype. In conclusion these data strongly suggest that the targeting of c-Myc by means of the MEK inhibitor can be tested as a promising strategy in anti-cancer therapy.

Mxi1 is essential for neurogenesis in Xenopus and acts by bridging the pan-neural and proneural genes

We have isolated and characterized Xenopus Mxi1, a member of the Myc/Max/Mad family of bHLHZip transcription factors. Xmxi1 transcripts are present during gastrulation and early neurula stages, earlier and in broader domains as compared to the neuronal determination factor neurogenin (X-ngnr-1). Consistent with an early role in neurogenesis, Xmxi1 is positively regulated by Sox3, SoxD, and proneural genes, as well as negatively by the Notch pathway. Loss-of-function experiments demonstrate an essential role for Xmxi1 in the establishment of a mature neural state that can be activated by factors that induce neuronal differentiation, such as SoxD and X-ngnr-1. Overexpression of Xmxi1 in Xenopus embryos results in ectopic activation of Sox3, an early pan-neural marker of proliferating neural precursor cells. Within the neural plate, the neuronal differentiation marker N-tubulin and cell cycle control genes such as XPak3 and p27(Xic1) are inhibited, but the expression of early determination and differentiation markers, including X-ngnr-1 and X-MyT1, is not affected. Inhibition of neuronal differentiation by Xmxi1 is only transient, and, at early tailbud stages, both endogenous and ectopic neurogenesis are observed. While Xmxi1 enhances cell proliferation and apoptosis in the early Xenopus embryo, both activities appear not to be required for the function of Xmxi1 in primary neurogenesis.

cDNA microarray analysis of early gene expression profiles associated with hepatitis B virus X protein-mediated hepatocarcinogenesis

Chronic hepatitis B virus (HBV) infection is one of the major causes of hepatocellular carcinoma. HBV encodes an oncogenic hepatitis B virus X protein (HBx), which can transactivate host cell transcriptional machinery and mediate cellular transformation. To disclose the early genetic response in HBx-mediated transformation process, we constructed a conditional HBx-expressing hepatocyte cell line, which allows us to compare the gene expression profiles under controllable HBx induction. A cDNA microarray containing more than 8700 mouse genes and ESTs was utilized to examine the gene expression profiles. We identified 260 candidate genes and 259 ESTs which have shown aberrant expression under HBx induction. Most of them are involved in signal transduction pathway, cell cycle control, metastasis, transcriptional regulation, immune response, and metabolism. These results provide additional insight into early cellular targets of HBx, which could give us a better understanding of the function of HBx and their progressive changes during HBx-mediated hepatocarcinogenesis.

Mxi1-0, an alternatively transcribed Mxi1 isoform, is overexpressed in glioblastomas

The c-Myc transcription factor regulates expression of genes related to cell growth, division, and apoptosis. Mxi1, a member of the Mad family, represses transcription of c-Myc-regulated genes by mediating chromatin condensation via histone deacetylase and the Sin3 corepressor. Mxi1 is a c-Myc antagonist and suppresses cell proliferation in vitro. Here, we describe the identification of Mxi1-0, a novel Mxi1 isoform that is alternatively transcribed from an upstream exon. Mxi1-0 and Mxi1 have different amino-terminal sequences, but share identical Max- and DNA-binding domains. Both isoforms are able to bind Max, to recognize E-box binding sites, and to interact with Sin3. Despite these similarities and in contrast to Mxi1, Mxi1-0 is predominantly localized to the cytoplasm and fails to repress c-Myc-dependent transcription. Although Mxi1-0 and Mxi1 are coexpressed in both human and mouse cells, the relative levels of Mxi1-0 are higher in primary glioblastoma tumors than in normal brain tissue. This variation in the levels of Mxi1-0 and Mxi1 suggests that Mxi1-0 may modulate the Myc-inhibitory activity of Mxi1. The identification of Mxi1-0 as an alternatively transcribed Mxi1 isoform has significant implications for the interpretation of previous Mxi1 studies, particularly those related to the phenotype of the mxi1 knockout mouse.

Antisense therapy targeting MDM2 oncogene in prostate cancer: Effects on proliferation, apoptosis, multiple gene expression, and chemotherapy

This study was undertaken to investigate the role of mouse double minute 2 (MDM2) oncogene in prostate cancer growth and the potential of MDM2 as a target for prostate cancer therapy. An antisense anti-human-MDM2 mixed-backbone oligonucleotide was tested in human prostate cancer models with various p53 statuses, LNCaP (p53wt/wt), DU145 (p53mt/mt), and PC3 (p53null). In a dose- and time-dependent manner, it specifically inhibited MDM2 expression and modified expression of several genes, at both mRNA and protein levels. In LNCaP cells, p53, p21, Bax, and hypophosphorylated retinoblastoma tumor suppressor protein (pRb) levels increased, whereas Bcl2, pRb protein, and E2F transcription factor 1 (E2F1) levels decreased. In DU145 cells, p21 levels were elevated and E2F1 levels decreased, although mutant p53, Rb, and Bax levels remained unchanged. In PC3 cells, MDM2 inhibition resulted in elevated p21, Bax, and pRb levels and decreased ppRb and E2F1 levels. In all three cell lines, MDM2 inhibition reduced cell proliferation, induced apoptosis, and potentiated the effects of the chemotherapeutic agents 10-hydroxycamptothecin and paclitaxel. The anti-MDM2 oligonucleotide showed antitumor activity and increased therapeutic effectiveness of paclitaxel in both LNCaP and PC3 xenografts, causing changes in gene expression similar to those seen in vitro. In summary, this study demonstrates that MDM2 has a role in prostate cancer growth via p53-dependent and p53-independent mechanisms and that multiple genes are involved in the process. MDM2 inhibitors such as second-generation antisense oligonucleotides have a broad spectrum of antitumor activities in human cancers regardless of p53 status, providing novel approaches to therapy of human prostate cancer.

Experimental therapy of human prostate cancer by inhibiting MDM2 expression with novel mixed-backbone antisense oligonucleotides: in vitro and in vivo activities and mechanisms

BACKGROUND

MDM2 oncogene is overexpressed in many human cancers including prostate cancer and MDM2 levels are associated with poor prognosis. This study was undertaken to investigate the functions of MDM2 oncogene in prostate cancer growth and the value of MDM2 as a drug target for prostate cancer therapy by inhibiting MDM2 expression.

METHODS

Antisense anti-human-MDM2 mixed-backbone oligonucleotide and its mismatch control were tested in in vitro and in vivo human prostate cancer models (LNCaP, DU 145, and PC-3) for anti-tumor activity. Targeted gene products and related proteins were analyzed and the anti-tumor activity was determined when the oligonucleotides were used alone or in combination with cancer therapeutics.

RESULTS

The antisense oligonucleotide specifically inhibited MDM2 expression in a dose- and time-dependent manner, resulting in significant anti-tumor activity in vitro and in vivo. In LNCaP cells, p53 and p21 levels were elevated. The antisense oligonucleotide also potentiated the effects of p53 activation and p21 induction by chemotherapeutic agents 10-hydroxycamptothecin, adriamycin, 5-fluorouracil, and paclitaxel. In DU145 cells, following inhibition of MDM2 expression, p21 levels were elevated although p53 levels remained unchanged. In both cell lines, the antisense oligonucleotide inhibited tumor cell growth and induced apoptosis in vitro. In a dose-dependent manner, the antisense oligonucleotide showed anti-tumor activity in nude mice bearing DU145 or PC-3 xenografts. It significantly increased therapeutic effectiveness of the chemotherapeutic agent irinotecan and slightly improved the effects of paclitaxel and Rituxan.

CONCLUSIONS

These results indicate that MDM2 has a role in prostate tumor growth through both p53-dependent and p53-independent mechanisms, indicating that MDM2 inhibitors have a broad spectrum of anti-tumor activities in human prostate cancers regardless of p53 status.

Transcriptomic classification of antitumor agents: application to the analysis of the antitumoral effect of SR31747A

SR31747A is a sigma ligand that exhibits a potent antitumoral activity on various human tumor cell lines both in vitro and in vivo. To understand its mode of action, we used DNA microarray technology combined with a new bioinformatic approach to identify genes that are modulated by SR31747A in different human breast or prostate cancer cell lines. The SR31747A transcriptional signature was also compared with that of seven different representative anticancer drugs commonly used in the clinic. To this aim, we performed a two-dimensional hierarchical clustering analysis of drugs and genes which showed that 1) standard molecules with similar mechanism of action clustered together and 2) SR31747A does not belong to any previously characterized class of standard anticancer drugs. Moreover, we showed that 3) SR31747A mainly exerted its antiproliferative effect by inhibiting the expression of genes playing a key role in DNA replication and cell cycle progression. Finally, contrasting with other drugs, we obtained evidence that 4) SR31747A strongly inhibited the expression of three key enzymes of the nucleotide synthesis pathway (i.e., dihydrofolate reductase, thymidylate synthase, and thymidine kinase) with the latter shown both at the mRNA and protein levels. These results, obtained through a novel molecular approach to characterize and compare anticancer agents, showed that SR31747A exhibits an original mechanism of action, very likely through unexpected targets whose modulations may account for its antitumoral effect.

The myc oncogene: MarvelouslY Complex

The activated product of the myc oncogene deregulates both cell growth and death check points and, in a permissive environment, rapidly accelerates the affected clone through the carcinogenic process. Advances in understanding the molecular mechanism of Myc action are highlighted in this review. With the revolutionary developments in molecular diagnostic technology, we have witnessed an unprecedented advance in detecting activated myc in its deregulated, oncogenic form in primary human cancers. These improvements provide new opportunities to appreciate the tumor subtypes harboring deregulated Myc expression, to identify the essential cooperating lesions, and to realize the therapeutic potential of targeting Myc. Knowledge of both the breadth and depth of the numerous biological activities controlled by Myc has also been an area of progress. Myc is a multifunctional protein that can regulate cell cycle, cell growth, differentiation, apoptosis, transformation, genomic instability, and angiogenesis. New insights into Myc's role in regulating these diverse activities are discussed. In addition, breakthroughs in understanding Myc as a regulator of gene transcription have revealed multiple mechanisms of Myc activation and repression of target genes. Moreover, the number of reported Myc regulated genes has expanded in the past few years, inspiring a need to focus on classifying and segregating bona fide targets. Finally, the identity of Myc-binding proteins has been difficult, yet has exploded in the past few years with a plethora of novel interactors. Their characterization and potential impact on Myc function are discussed. The rapidity and magnitude of recent progress in the Myc field strongly suggests that this marvelously complex molecule will soon be unmasked.