c-Myc Inhibits Ras-Mediated Differentiation of Pheochromocytoma Cells by Blocking c-Jun Up-Regulation

MYC-Mediated Inhibition of ARNT2 Uncovers a Key Tumor Suppressor in Glioblastoma

Tumor initiation and progression rely on intricate cellular pathways that promote proliferation while suppressing differentiation, yet the importance of pathways inhibiting differentiation in cancer remains incompletely understood. Here, we reveal a novel mechanism centered on the repression of the neuronal-specific transcription factor ARNT2 by the MYC oncogene that governs the balance between proliferation and differentiation. We found that MYC coordinates the transcriptional repression of ARNT2 through the activity of polycomb repressive complex 2 (PRC2). Notably, ARNT2, highly and specifically expressed in the central nervous system, is diminished in glioblastoma, inversely correlating with patient survival. Utilizing in vitro and in vivo models, we demonstrate that ARNT2 knockout (KO) exerts no discernible effect on the in vitro proliferation of glioblastoma cells, but significantly enhances the growth of glioblastoma cells in vivo. Conversely, ARNT2 overexpression severely dampens the growth of fully transformed glioblastoma cells subcutaneously or orthotopically xenografted in mice. Mechanistically, ARNT2 depletion diminishes differentiation and enhances stemness of glioblastoma cells. Our findings provide new insights into the complex mechanisms used by oncogenes to limit differentiation in cancer cells and define ARNT2 as a tumor suppressor in glioblastoma.

ERK2 stimulates MYC transcription by anchoring CDK9 to the MYC promoter in a kinase activity-independent manner

The transcription factor MYC regulates cell proliferation, transformation, and survival in response to growth factor signaling that is mediated in part by the kinase activity of ERK2. Because ERK2 can also bind to DNA to modify gene expression, we investigated whether it more directly regulates MYC transcription. We identified ERK2 binding sites in the MYC promoter and detected ERK2 at the promoter in various serum-stimulated cell types. Expression of nuclear-localized ERK2 constructs in serum-starved cells revealed that ERK2 in the nucleus-regardless of its kinase activity-increased MYC mRNA expression and MYC protein abundance. ERK2 bound to the promoter through its amino-terminal insert domain and to the cyclin-dependent kinase CDK9 (which activates RNA polymerase II) through its carboxyl-terminal conserved docking domain. Both interactions were essential for ERK2-induced MYC expression, and depleting ERK impaired CDK9 occupancy and RNA polymerase II progression at the MYC promoter. Artificially tethering CDK9 to the MYC promoter by fusing it to the ERK2 insert domain was sufficient to stimulate MYC expression in serum-starved cells. Our findings demonstrate a role for ERK2 at the MYC promoter acting as a kinase-independent anchor for the recruitment of CDK9 to promote MYC expression.

Impact of Reck expression and promoter activity in neuronal in vitro differentiation

Reck (REversion-inducing Cysteine-rich protein with Kazal motifs) tumor suppressor gene encodes a multifunctional glycoprotein which inhibits the activity of several matrix metalloproteinases (MMPs), and has the ability to modulate the Notch and canonical Wnt pathways. Reck-deficient neuro-progenitor cells undergo precocious differentiation; however, modulation of Reck expression during progression of the neuronal differentiation process is yet to be characterized. In the present study, we demonstrate that Reck expression levels are increased during in vitro neuronal differentiation of PC12 pheochromocytoma cells and P19 murine teratocarcinoma cells and characterize mouse Reck promoter activity during this process. Increased Reck promoter activity was found upon induction of differentiation in PC12 cells, in accordance with its increased mRNA expression levels in mouse in vitro models. Interestingly, Reck overexpression, prior to the beginning of the differentiation protocol, led to diminished efficiency of the neuronal differentiation process. Taken together, our findings suggest that increased Reck expression at early stages of differentiation diminishes the number of neuron-like cells, which are positive for the beta-3 tubulin marker. Our data highlight the importance of Reck expression evaluation to optimize in vitro neuronal differentiation protocols.

The MNT transcription factor autoregulates its expression and supports proliferation in MYC-associated factor X (MAX)-deficient cells

The MAX network transcriptional repressor (MNT) is an MXD family transcription factor of the basic helix-loop-helix (bHLH) family. MNT dimerizes with another transcriptional regulator, MYC-associated factor X (MAX), and down-regulates genes by binding to E-boxes. MAX also dimerizes with MYC, an oncogenic bHLH transcription factor. Upon E-box binding, the MYC-MAX dimer activates gene expression. MNT also binds to the MAX dimerization protein MLX (MLX), and MNT-MLX and MNT-MAX dimers co-exist. However, all MNT functions have been attributed to MNT-MAX dimers, and no functions of the MNT-MLX dimer have been described. MNT's biological role has been linked to its function as a MYC oncogene modulator, but little is known about its regulation. We show here that MNT localizes to the nucleus of MAX-expressing cells and that MNT-MAX dimers bind and repress the MNT promoter, an effect that depends on one of the two E-boxes on this promoter. In MAX-deficient cells, MNT was overexpressed and redistributed to the cytoplasm. Interestingly, MNT was required for cell proliferation even in the absence of MAX. We show that in MAX-deficient cells, MNT binds to MLX, but also forms homodimers. RNA-sequencing experiments revealed that MNT regulates the expression of several genes even in the absence of MAX, with many of these genes being involved in cell cycle regulation and DNA repair. Of note, MNT-MNT homodimers regulated the transcription of some genes involved in cell proliferation. The tight regulation of MNT and its functionality even without MAX suggest a major role for MNT in cell proliferation.

Resveratrol attenuates diabetes-associated cell centrosome amplification via inhibiting the PKCα-p38 to c-myc/c-jun pathway

Type 2 diabetes increases the risk for cancer. Centrosome amplification can initiate tumorigenesis. We have described that type 2 diabetes increases the centrosome amplification of peripheral blood mononuclear cells, with high glucose, insulin, and palmitic acid as the triggers, which suggests that centrosome amplification is a candidate biological mechanism linking diabetes to cancer. In this study, we aimed to further investigate the signaling pathways of the diabetes-associated centrosome amplification and to examine whether and how resveratrol inhibits the centrosome amplification. The results showed that treatment with high glucose, insulin, and palmitic acid, alone or in combination, could increase the protein levels of phospho-protein kinase C alpha (p-PKCα), phospho-p38 mitogen-activated protein kinases (p-p38), c-myc, and c-jun, as well as the mRNA levels of c-myc and c-jun. PKCα inhibitor could inhibit the treatment-induced increase in the protein levels of p-p38, c-myc, and c-jun. Inhibitor or siRNA of p38 was also able to inhibit the treatment-induced increase in the levels of p-p38, c-myc, and c-jun. Meanwhile, knockdown of c-myc or c-jun did not alter the treatment-induced increase in the phosphorylation of PKCα or p38. Importantly, inhibition of the phosphorylation of PKCα or p38 and knockdown of c-myc or c-jun could attenuate the centrosome amplification. In diabetic mice, the levels of p-PKCα, p-p38, c-myc, and c-jun were all increased in the colon tissues. Interestingly, resveratrol, but not metformin, was able to attenuate the treatment-induced increase in the levels of p-PKCα, p-p38, c-myc, and c-jun, as well as the centrosome amplification. In conclusion, our results suggest that PKCα-p38 to c-myc/c-jun is the signaling pathway of the diabetes-associated centrosome amplification, and resveratrol attenuates the centrosome amplification by inhibiting this signaling pathway.

Genetic and epigenetic differences of benign and malignant pheochromocytomas and paragangliomas (PPGLs)

Pheochromocytomas and paragangliomas (PPGLs) are tumors arising from the adrenal medulla and sympathetic/parasympathetic paraganglia, respectively. According to Th e Cancer Genome Atlas (TCGA), approximately 40% of PPGLs are due to germ line mutations in one of 16 susceptibility genes, and a further 30% are due to somatic alterations in at least seven main genes (VHL, EPAS1, CSDE1, MAX, HRAS, NF1, RET, and possibly KIF1B). Th e diagnosis of malignant PPGL was straight forward in most cases as it was defined as presence of PPGL in non-chromaffin tissues. Accordingly, there is an extreme need for new diagnostic marker(s) to identify tumors with malignant prospective. Th e aim of this study was to review all suggested genetic and epigenetic alterations that are remarkably different between benign and malignant PPGLs. It seems that more than two genetic mutation clusters in PPGLs and other genetic and methylation biomarkers could be targeted for malignancy discrimination in different studies.

Identification of Jun loss promotes resistance to histone deacetylase inhibitor entinostat through Myc signaling in luminal breast cancer

BACKGROUND

Based on promising phase II data, the histone deacetylase inhibitor entinostat is in phase III trials for patients with metastatic estrogen receptor-positive breast cancer. Predictors of sensitivity and resistance, however, remain unknown.

METHODS

A total of eight cell lines and nine mouse models of breast cancer were treated with entinostat. Luminal cell lines were treated with or without entinostat at their IC₅₀ doses, and MMTV/Neu luminal mouse tumors were untreated or treated with entinostat until progression. We investigated these models using their gene expression profiling by microarray and copy number by arrayCGH. We also utilized the network-based DawnRank algorithm that integrates DNA and RNA data to identify driver genes of resistance. The impact of candidate drivers was investigated in The Cancer Genome Atlas and METABRIC breast cancer datasets.

RESULTS

Luminal models displayed enhanced sensitivity to entinostat as compared to basal-like or claudin-low models. Both in vitro and in vivo luminal models showed significant downregulation of Myc gene signatures following entinostat treatment. Myc gene signatures became upregulated on tumor progression in vivo and overexpression of Myc conferred resistance to entinostat in vitro. Further examination of resistance mechanisms in MMTV/Neu tumors identified a portion of mouse chromosome 4 that had DNA copy number loss and low gene expression. Within this region, Jun was computationally identified to be a driver gene of resistance. Jun knockdown in cell lines resulted in upregulation of Myc signatures and made these lines more resistant to entinostat. Jun-deleted samples, found in 17-23% of luminal patients, had significantly higher Myc signature scores that predicted worse survival.

CONCLUSIONS

Entinostat inhibited luminal breast cancer through Myc signaling, which was upregulated by Jun DNA loss to promote resistance to entinostat in our models. Jun DNA copy number loss, and/or high MYC signatures, might represent biomarkers for entinostat responsiveness in luminal breast cancer.

Functional interplay between c-Myc and Max in B lymphocyte differentiation

The Myc family of oncogenic transcription factors regulates myriad cellular functions. Myc proteins contain a basic region/helix-loop-helix/leucine zipper domain that mediates DNA binding and heterodimerization with its partner Max. Among the Myc proteins, c-Myc is the most widely expressed and relevant in primary B lymphocytes. There is evidence suggesting that c-Myc can perform some of its functions in the absence of Max in different cellular contexts. However, the functional in vivo interplay between c-Myc and Max during B lymphocyte differentiation is not well understood. Using in vivo and ex vivo models, we show that while c-Myc requires Max in primary B lymphocytes, several key biological processes, such as cell differentiation and DNA replication, can initially progress without the formation of c-Myc/Max heterodimers. We also describe that B lymphocytes lacking Myc, Max, or both show upregulation of signaling pathways associated with the B-cell receptor. These data suggest that c-Myc/Max heterodimers are not essential for the initiation of a subset of important biological processes in B lymphocytes, but are required for fine-tuning the initial response after activation.

p73 is required for appropriate BMP-induced mesenchymal-to-epithelial transition during somatic cell reprogramming

The generation of induced pluripotent stem cells (iPSCs) by somatic cell reprogramming holds great potential for modeling human diseases. However, the reprogramming process remains very inefficient and a better understanding of its basic biology is required. The mesenchymal-to-epithelial transition (MET) has been recognized as a crucial step for the successful reprogramming of fibroblasts into iPSCs. It has been reported that the p53 tumor suppressor gene acts as a barrier of this process, while its homolog p63 acts as an enabling factor. In this regard, the information concerning the role of the third homolog, p73, during cell reprogramming is limited. Here, we derive total Trp73 knockout mouse embryonic fibroblasts, with or without Trp53, and examine their reprogramming capacity. We show that p73 is required for effective reprogramming by the Yamanaka factors, even in the absence of p53. Lack of p73 affects the early stages of reprogramming, impairing the MET and resulting in altered maturation and stabilization phases. Accordingly, the obtained p73-deficient iPSCs have a defective epithelial phenotype and alterations in the expression of pluripotency markers. We demonstrate that p73 deficiency impairs the MET, at least in part, by hindering BMP pathway activation. We report that p73 is a positive modulator of the BMP circuit, enhancing its activation by DNp73 repression of the Smad6 promoter. Collectively, these findings provide mechanistic insight into the MET process, proposing p73 as an enhancer of MET during cellular reprogramming.

Molecular markers of paragangliomas/pheochromocytomas

Paragangliomas/pheochromocytomas comprise rare tumors that arise from the extra-adrenal paraganglia, with an incidence of about 2 to 8 per million people each year. Approximately 40% of cases are due to genetic mutations in at least one out of more than 30 causative genes. About 25-30% of pheochromocytomas/paragangliomas develop under the conditions of a hereditary tumor syndrome a third of which are caused by mutations in the VHL gene. Together, the gene mutations in this disorder have implicated multiple processes including signaling pathways, translation initiation, hypoxia regulation, protein synthesis, differentiation, survival, proliferation, and cell growth. The present review contemplates the mutations associated with the development of pheochromocytomas/paragangliomas and their potential to serve as specific markers of these tumors and their progression. These data will improve our understanding of the pathogenesis of these tumors and likely reveal certain features that may be useful for early diagnostics, malignancy prognostics, and the determination of new targets for disease therapeutics.

Expression of cancerous inhibitor of protein phosphatase 2A in human triple negative breast cancer correlates with tumor survival, invasion and autophagy

Cancerous inhibitor of protein phosphatase 2A (CIP2A) is a recently characterized oncoprotein which is involved in the progression of several human malignancies. The present study aimed to investigate its biological function in human triple negative breast cancer (TNBC). The expression of CIP2A in TNBC cells was examined and it was observed that CIP2A was elevated in the TNBC cell line compared with poorly invasive breast cancer cells. CIP2A depletion in TNBC cell lines inhibited proliferation, and induced apoptosis and autophagy. In addition, CIP2A depletion inhibited invasion and migration of TNBC cells. Furthermore, CIP2A depletion downregulated Akt/mTOR/P70S6K phosphorylation. These results validate the role of CIP2A as a invasion-associated oncoprotein and established CIP2A as a promising therapeutic target of TNBC.

Synergistic signaling of KRAS and thyroid hormone receptor β mutants promotes undifferentiated thyroid cancer through MYC up-regulation

Undifferentiated thyroid carcinoma is one of the most aggressive human cancers with frequent RAS mutations. How mutations of the RAS gene contribute to undifferentiated thyroid cancer remains largely unknown. Mice harboring a potent dominant negative mutant thyroid hormone receptor β, TRβPV (Thrb(PV/PV)), spontaneously develop well-differentiated follicular thyroid cancer similar to human cancer. We genetically targeted the Kras(G12D) mutation to thyroid epithelial cells of Thrb(PV/PV) mice to understand how Kras(G12D) mutation could induce undifferentiated thyroid cancer in Thrb(PV/PV)Kras(G12D) mice. Thrb(PV/PV)Kras(G12D) mice exhibited poorer survival due to more aggressive thyroid tumors with capsular invasion, vascular invasion, and distant metastases to the lung occurring at an earlier age and at a higher frequency than Thrb(PV/PV) mice did. Importantly, Thrb(PV/PV)Kras(G12D) mice developed frequent anaplastic foci with complete loss of normal thyroid follicular morphology. Within the anaplastic foci, the thyroid-specific transcription factor paired box gene 8 (PAX8) expression was virtually lost and the loss of PAX8 expression was inversely correlated with elevated MYC expression. Consistently, co-expression of KRAS(G12D) with TRβPV upregulated MYC levels in rat thyroid pccl3 cells, and MYC acted to enhance the TRβPV-mediated repression of the Pax8 promoter activity of a distant upstream enhancer, critical for thyroid-specific Pax8 expression. Our findings indicated that synergistic signaling of KRAS(G12D) and TRβPV led to increased MYC expression. Upregulated MYC contributes to the initiation of undifferentiated thyroid cancer, in part, through enhancing TRβPV-mediated repression of the Pax8 expression. Thus, MYC might serve as a potential target for therapeutic intervention.

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.

Sin3b interacts with Myc and decreases Myc levels

Myc expression is deregulated in many human cancers. A yeast two-hybrid screen has revealed that the transcriptional repressor Sin3b interacts with Myc protein. Endogenous Myc and Sin3b co-localize and interact in the nuclei of human and rat cells, as assessed by co-immunoprecipitation, immunofluorescence, and proximity ligation assay. The interaction is Max-independent. A conserved Myc region (amino acids 186-203) is required for the interaction with Sin3 proteins. Histone deacetylase 1 is recruited to Myc-Sin3b complexes, and its deacetylase activity is required for the effects of Sin3b on Myc. Myc and Sin3a/b co-occupied many sites on the chromatin of human leukemia cells, although the presence of Sin3 was not associated with gene down-regulation. In leukemia cells and fibroblasts, Sin3b silencing led to Myc up-regulation, whereas Sin3b overexpression induced Myc deacetylation and degradation. An analysis of Sin3b expression in breast tumors revealed an association between low Sin3b expression and disease progression. The data suggest that Sin3b decreases Myc protein levels upon Myc deacetylation. As Sin3b is also required for transcriptional repression by Mxd-Max complexes, our results suggest that, at least in some cell types, Sin3b limits Myc activity through two complementary activities: Mxd-dependent gene repression and reduction of Myc levels.

Analyzing Ras-associated cell proliferation signaling

Ras-dependent signaling is an important regulator of cell cycle progression, proliferation, senescence, and apoptosis. Several of the downstream effectors of Ras play dual roles in each of these processes. Under one set of conditions, they promote cell cycle progression and proliferation; yet, in a different paradigm, they drive cell cycle arrest and apoptosis. Furthermore, there is cross talk between certain downstream effectors of Ras including the PI3K-AKT and Raf-MEK-ERK pathways. Here we describe a series of experiments used to dissect the effect of different Ras-dependent signaling pathways on cell cycle progression, proliferation, senescence, and apoptosis. Furthermore, we highlight the importance of consistent growth conditions of cells in culture when studying Ras-dependent signaling as we show that the activation of downstream effectors of Ras changes with the confluency at which the cells are grown.

An update on the genetics of pheochromocytoma

Pheochromocytomas (PHEOs) and paragangliomas (PGLs) are rare neuroendocrine tumors. About 30% or more of them are thought to be of inherited origin due to germ-line mutations in at least 10 well-characterized genes. There are data linking specific genotypes of these tumors to specific locations, typical biochemical phenotypes or future clinical behaviors. Conversely, clinical features, catecholamine production and immunohistochemistry evaluation can help with the proper order of genetic testing for PHEO and PGL. The identification of a germ-line mutation can lead to an early diagnosis, appropriate treatment, regular surveillance and better prognosis not only for the patient but also for their family members. Moreover, the latest discoveries in molecular pathogenesis of these tumors will provide an important basis for future personalized therapy.

p21 as a transcriptional co-repressor of S-phase and mitotic control genes

It has been previously described that p21 functions not only as a CDK inhibitor but also as a transcriptional co-repressor in some systems. To investigate the roles of p21 in transcriptional control, we studied the gene expression changes in two human cell systems. Using a human leukemia cell line (K562) with inducible p21 expression and human primary keratinocytes with adenoviral-mediated p21 expression, we carried out microarray-based gene expression profiling. We found that p21 rapidly and strongly repressed the mRNA levels of a number of genes involved in cell cycle and mitosis. One of the most strongly down-regulated genes was CCNE2 (cyclin E2 gene). Mutational analysis in K562 cells showed that the N-terminal region of p21 is required for repression of gene expression of CCNE2 and other genes. Chromatin immunoprecipitation assays indicated that p21 was bound to human CCNE2 and other p21-repressed genes gene in the vicinity of the transcription start site. Moreover, p21 repressed human CCNE2 promoter-luciferase constructs in K562 cells. Bioinformatic analysis revealed that the CDE motif is present in most of the promoters of the p21-regulated genes. Altogether, the results suggest that p21 exerts a repressive effect on a relevant number of genes controlling S phase and mitosis. Thus, p21 activity as inhibitor of cell cycle progression would be mediated not only by the inhibition of CDKs but also by the transcriptional down-regulation of key genes.

Genetics and clinical characteristics of hereditary pheochromocytomas and paragangliomas

Pheochromocytomas (PCCs) and paragangliomas (PGLs) are rare neuroendocrine tumors of the adrenal glands and the sympathetic and parasympathetic paraganglia. They can occur sporadically or as a part of different hereditary tumor syndromes. About 30% of PCCs and PGLs are currently believed to be caused by germline mutations and several novel susceptibility genes have recently been discovered. The clinical presentation, including localization, malignant potential, and age of onset, varies depending on the genetic background of the tumors. By reviewing more than 1700 reported cases of hereditary PCC and PGL, a thorough summary of the genetics and clinical features of these tumors is given, both as part of the classical syndromes such as multiple endocrine neoplasia type 2 (MEN2), von Hippel-Lindau disease, neurofibromatosis type 1, and succinate dehydrogenase-related PCC-PGL and within syndromes associated with a smaller fraction of PCCs/PGLs, such as Carney triad, Carney-Stratakis syndrome, and MEN1. The review also covers the most recently discovered susceptibility genes including KIF1Bβ, EGLN1/PHD2, SDHAF2, TMEM127, SDHA, and MAX, as well as a comparison with the sporadic form. Further, the latest advances in elucidating the cellular pathways involved in PCC and PGL development are discussed in detail. Finally, an algorithm for genetic testing in patients with PCC and PGL is proposed.

Expression of CIP2A in renal cell carcinomas correlates with tumour invasion, metastasis and patients' survival

Background:

Cancerous inhibitor of protein phosphatase 2A (CIP2A) drives cellular transformation. The objective of this study was to detect the potential effects of CIP2A in renal cell carcinomas (RCCs).

Methods:

A total of 107 RCC patients were involved in the study. Cancerous inhibitor of protein phosphatase 2A expression was investigated by real-time PCR and immunohistochemistry. In vitro, we examined the expression of CIP2A and c-Myc and tested the migration and invasion capability of A498 and KRC/Y cells with scratch migration assay and Matrigel invasion assay after down-regulating CIP2A expression using siRNA.

Results:

Cancerous inhibitor of protein phosphatase 2A was over-expressed in RCC tissues. Clear cell RCC showed an even higher-CIP2A expression level than papillary or chromophobe RCC did. The CIP2A immunostaining level was positively correlated with primary tumour stage, lymph node metastasis, distant metastasis, TNM stage and histological grade (all P<0.05). High-CIP2A expression implied poor survival for patients (P<0.05). Cancerous inhibitor of protein phosphatase 2A depletion by siRNA down-regulated c-Myc expression and attenuated the migration and invasion of RCC cells.

Conclusion:

Higher-CIP2A expression positively correlates with the aggressive phenotype of RCCs, and predicts poor prognosis for patients. Cancerous inhibitor of protein phosphatase 2A may be a novel target for prevention and treatment of RCC metastasis and recurrence.

MKK7γ1 reverses nerve growth factor signals: proliferation and cell death instead of neuritogenesis and protection

c-Jun N-terminal kinases (JNKs) are the exclusive downstream substrates of mitogen-activated protein kinase kinase 7 (MKK7). Recently, we have shown that a single MKK7 splice variant, MKK7γ1, substantially changes the functions of JNKs in naïve PC12 cells. Here we provide evidence that MKK7γ1 blocks NGF-mediated differentiation and sustains proliferation by interfering with the NGF-triggered differentiation programme at several levels: (i) down-regulation of the NGF receptors TrkA and p75; (ii) attenuation of the differentiation-promoting pathways ERK1/2 and AKT; (iii) increase of JNK1 and JNK2, especially the JNK2 54kDa splice variants; (iv) repression of the cyclin-dependent kinase inhibitor p21(WAF1/CIP1), which normally supports NGF-mediated cell cycle arrest; (v) strong induction of the cell cycle promoter CyclinD1, and (vi) profound changes of p53 functions. Moreover, MKK7γ1 substantially changes the responsiveness to stress. Whereas NGF differentiation protects PC12 cells against taxol-induced apoptosis, MKK7γ1 triggers an escape from cell cycle arrest and renders transfected cells sensitive to taxol-induced death. This stress response completely differs from naïve PC12 cells, where MKK7γ1 protects against taxol-induced cell death. These novel aspects on the regulation of JNK signalling emphasise the importance of MKK7γ1 in its ability to reverse basic cellular programmes by simply using JNKs as effectors. Furthermore, our results highlight the necessity for the cells to balance the expression of JNK activators to ensure precise intracellular processes.

Parafibromin expression is an independent prognostic factor for colorectal carcinomas

Parafibromin is a protein encoded by hyperparathyroidism 2, and its down-regulated expression is involved in the pathogenesis of parathyroid, breast, and gastric carcinomas. This study aimed to clarify the roles of parafibromin expression in tumorigenesis, progression, and prognosis of colorectal carcinomas. Parafibromin-expressing plasmid was transfected into DLD-1 cells with the phenotypes, and related molecules were examined. Parafibromin expression was examined in colorectal samples by immunohistochemistry, in situ hybridization, Western blot, or reverse transcription polymerase chain reaction. It was found that parafibromin overexpression could cause G1 arrest and enhance differentiation of DLD-1 cells. There was a high expression of p21, p27, and cyclin E, but low expression of cyclin D1 messenger RNA, phospho-cdc2, and phospho-cdc25c proteins. Parafibromin could inhibit c-myc messenger RNA expression by binding to c-myc promoter. Expression levels of nuclear parafibromin and parafibromin messenger RNA were decreased from colorectal nonneoplastic mucosa and adenomas to carcinomas (P < .05). Immunohistochemically, parafibromin expression was inversely correlated with tumor size, depth of invasion, lymph node metastasis, clinicopathologic staging, and poor prognosis of carcinomas (P < .05). It was suggested that parafibromin overexpression might suppress cell cycle progression and promote differentiation of DLD-1 cells. Aberrant parafibromin expression possibly contributes to the pathogenesis, growth, invasion, and metastasis of colorectal carcinomas and could be regarded as an independent factor to indicate a favorable prognosis for patients with colorectal carcinomas.

Reviewing once more the c-myc and Ras collaboration: converging at the cyclin D1-CDK4 complex and challenging basic concepts of cancer biology

The c-myc is a proto-oncogene that manifests aberrant expression at high frequencies in most types of human cancer. C-myc gene amplifications are often observed in various cancers as well. Ample studies have also proved that c-myc has a potent oncogenicity, which can be further enhanced by collaborations with other oncogenes such as Bcl-2 and activated Ras. Studies on the collaborations of c-myc with Ras or other genes in oncogenicity have established several basic concepts and have disclosed their underlying mechanisms of tumor biology, including "immortalization" and "transformation". In many cases, these collaborations may converge at the cyclin D1-CDK4 complex. In the meantime, however, many results from studies on the c-myc, Ras and cyclin D1-CDK4 also challenge these basic concepts of tumor biology and suggest to us that the immortalized status of cells should be emphasized. Stricter criteria and definitions for a malignantly transformed status and a benign status of cells in culture also need to be established to facilitate our study of the mechanisms for tumor formation and to better link up in vitro data with animal results and eventually with human cancer pathology.

Candidate genes associated with malignant pheochromocytomas by genome-wide expression profiling

OBJECTIVE

To improve our understanding of the molecular mechanisms involved in malignant pheochromocytoma by examining differences in the gene expression profile between benign and malignant tumors.

BACKGROUND

The molecular events involved in the malignant transformation of pheochromocytoma are poorly understood. There are also no reliable and uniformly accepted histopathologic criteria to distinguish benign from malignant pheochromocytoma.

METHODS

We performed genome-wide expression profiling of 58 pheochromocytomas (29 benign and sporadic, 16 benign and hereditary, 13 malignant) with technical and biologic replication.

RESULTS

Unsupervised cluster analysis showed 3 main clusters of tumors that did not have complete concordance with the clinical and pathologic groupings of pheochromocytomas. Supervised cluster analysis showed almost completely separate clustering between benign and malignant tumors. The differentially expressed genes with known function belonged to 8 biologic process categories; signal transduction, transcription, protein transport, protein synthesis, smooth muscle contraction, ion transport, chemotaxis, and electron transport. Gene set enrichment analysis revealed significant correlation between the microarray profiles of malignant pheochromocytomas and several known molecular pathways associated with carcinogenesis and dedifferentiation. Ten differentially expressed genes had high diagnostic accuracy, and 5 of these genes (CFC1, FAM62B, HOMER1, LRRN3, TBX3, ADAMTS) in combination had an area under the receiver operating characteristic (ROC) curve of 0.96 for distinguishing benign versus malignant tumors.

CONCLUSIONS

Differentially expressed genes between benign and malignant pheochromocytomas distinguish between these tumors with high diagnostic accuracy. Our findings provide new insight into the genes and molecular pathways that may be involved in malignant pheochromocytomas.

Anti-DR5 mAb ameliorate adjuvant arthritis rats through inducing synovial cells apoptosis

OBJECTIVE

Study the therapeutic effects and immunoregulatory mechanisms of anti-DR5 mAb on adjuvant arthritis (AA) rats.

METHODS

AA rats induced by CFA, were treated with anti-DR5 mAb through mainline administration. Effect on the synovial membranes of the tissues was detected by H&E staining. Flow cytometry and MTT assay were used for detecting the induced apoptosis in an in vitro system and TUNEL assay was used for analysis in an in vivo system. The involvement of the apoptotic pathway was further proved by a caspase inhibition assay.

RESULTS

Anti-DR5 mAb could induce synovial cell apoptosis in an in vitro system, which was related with the mRNA expression of DR5 on the cell surface. The mRNA expressions of c-myc and bcl-2 were decreased in synovial cells and those of p21, p53, and bax were increased. The protein expressions of caspase-8/3/9, RANKL, JNK2, and c-Jun were raised and that of bcl-2 was decreased. When the caspase inhibitor was added to the synovial cells treated with anti-DR5 mAb, it showed a dose-dependence inhibition effect, indicating that anti-DR5 mAb inducing apoptosis might be through the caspase pathway.

CONCLUSION

This study shows that anti-DR5 mAb can ameliorate arthritic symptoms. The mechanisms of the treatment are related to the increase in synovial cell apoptosis by regulating the mRNA expression of DR5 and apoptosis-related genes, prolonging the duration of the cell cycle by modulation of the mRNA expression of cell cycle-related genes, and the protein expression of the molecules in the caspase pathway and RANKL, JNK2, and c-Jun.

Large-scale directional relationship extraction and resolution

Background

Relationships between entities such as genes, chemicals, metabolites, phenotypes and diseases in MEDLINE are often directional. That is, one may affect the other in a positive or negative manner. Detection of causality and direction is key in piecing pathways together and in examining possible implications of experimental results. Because of the size and growth of biomedical literature, it is increasingly important to be able to automate this process as much as possible.

Results

Here we present a method of relation extraction using dependency graph parsing with SVM classification. We tested the SVM classifier first on gold standard corpora from GENIA and find it achieved 82% precision and 94.8% recall (F-measure of 87.9) on these standardized test sets. We then applied the entire system to all available MEDLINE abstracts for two target interactions with known effects. We find that while some directional relations are extracted with low ambiguity, others are apparently contradictory, at least when considered in an isolated context. When examined, it is apparent some are dependent upon the surrounding context (e.g. whether the relationship referred to short-term or long-term effects, or whether the focus was extracellular versus intracellular).

Conclusion

Thesaurus-based directional relation extraction can be done with reasonable accuracy, but is prone to false-positives on larger corpora due to noun modifiers. Furthermore, methods of resolving or disambiguating relationship context and contingencies are important for large-scale corpora.