Ras and Myc can drive oncogenic cell proliferation through individual D-cyclins

ANP32B inhibition suppresses the growth of prostate cancer cells by regulating c-Myc signaling

ANP32B is a histone chaperone that interacts with various transcription factors that regulate cancer cell proliferation, immigration, and apoptosis. c-Myc, a well-known oncogenic protein, is a principal player in the initiation and progression of prostate cancer (PC). The means by which ANP32B and c-Myc act remain unknown. We downloaded clinical data from the GEO, TCGA, and other databases to explore ANP32B expression and its effects on the survival of PC and normal tissues. ANP32B-knockdown cell lines were used to evaluate how ANP32B affected cell proliferation in vitro and in vivo. Gene set enrichment analysis and RNAseq were employed to define how ANP32B regulated PC pathways. Immunohistochemical measures were used to detect the expression levels of relevant proteins in xenografts and PC tissues. ANP32B expression increased in PC tissues; ANP32B knockdown inhibited cell growth but this was rescued by c-Myc signaling. ANP32B is thus a PC oncogene and may serve as a valuable therapeutic target when seeking to treat PC.

LncRNA PVT1: as a therapeutic target for breast cancer

A significant number of women are identified with breast cancer (BC) every year, making it among the most prevalent malignancies and one of the leading causes of mortality globally. Despite significant progress in understanding BC pathogenesis and treatment options, there is still a need to identify new therapeutic targets and develop more effective treatments. LncRNAs have been discovered as biomarkers and a promising target for various cancers, including BC. PVT1 is a particular one of these lncRNAs, and research has indicated that it has a significant impact on the appearance and progression of BC.PVT1 is an attractive therapeutic target for BC due to its role in promoting cancer cell growth, metastasis and invasion. In addition to its potential as a treatment strategy, PVT1 may also have diagnostic value in BC. In this article, we will discuss targeting PVT1 as a treatment strategy for BC.

The anti-leukemic activity of a luteolin-apigenin enriched fraction from an edible and ethnomedicinal plant, Elsholtzia stachyodes, is exerted through an ER stress/autophagy/cell cycle arrest/ apoptotic cell death signaling axis

BACKGROUND

Elsholtzia is a genus in the family Lamiaceae, and some species in this genus are commonly used for food and in ethnomedicinal formulations by some ethnic groups of China and Thailand. Despite their apparent utility, few studies have been conducted to evaluate their potential as sources of medicinally active agents.

PURPOSE

We aimed to investigate the cytotoxicity of ethanolic extracts from three selected edible plant species of the genus Elsholtzia and the most promising extract was further characterized for the bioactive constituents and signaling mechanisms associated with the anti-leukemic activity.

MATERIALS AND METHODS

Ethanolic extracts were screened for cytotoxicity using flow cytometry. HPLC and LC-MS were used to analyze the chemical constituents of the most potent fraction from E. stachyodes. The relevant mechanism of action was assessed by western blot and multispectral imaging flow cytometry (MIFC).

RESULTS

The most potent anti-leukemic activity was observed with the ethanolic extract from E. stachyodes. Luteolin and apigenin were characterized as the major constituents in the fraction from E. stachyodes. Mechanistically, the luteolin-apigenin enriched fraction (LAEF) induced the UPR, increased autophagic flux, induced cell cycle arrest and apoptotic cell death. LAEF showed significantly less cytotoxicity towards peripheral blood mononuclear cells (PBMCs) as compared to leukemia cell lines.

CONCLUSION

This study is the first to report E. stachyodes as a new source of luteolin and apigenin which are capable of triggering leukemic cell death. This could lead to a novel strategy against leukemia using ethnomedicinal plant extracts as an alternative or supplemental anti-cancer agent.

MYC: a multipurpose oncogene with prognostic and therapeutic implications in blood malignancies

MYC oncogene is a transcription factor with a wide array of functions affecting cellular activities such as cell cycle, apoptosis, DNA damage response, and hematopoiesis. Due to the multi-functionality of MYC, its expression is regulated at multiple levels. Deregulation of this oncogene can give rise to a variety of cancers. In this review, MYC regulation and the mechanisms by which MYC adjusts cellular functions and its implication in hematologic malignancies are summarized. Further, we also discuss potential inhibitors of MYC that could be beneficial for treating hematologic malignancies.

Selective inhibition of CDK4/6: A safe and effective strategy for developing anticancer drugs

The sustained cell proliferation resulting from dysregulation of the cell cycle and activation of cyclin-dependent kinases (CDKs) is a hallmark of cancer. The inhibition of CDKs is a highly promising and attractive strategy for the development of anticancer drugs. In particular, third-generation CDK inhibitors can selectively inhibit CDK4/6 and regulate the cell cycle by suppressing the G1 to S phase transition, exhibiting a perfect balance between anticancer efficacy and general toxicity. To date, three selective CDK4/6 inhibitors have received approval from the U.S. Food and Drug Administration (FDA), and 15 CDK4/6 inhibitors are in clinical trials for the treatment of cancers. In this perspective, we discuss the crucial roles of CDK4/6 in regulating the cell cycle and cancer cells, analyze the rationale for selectively inhibiting CDK4/6 for cancer treatment, review the latest advances in highly selective CDK4/6 inhibitors with different chemical scaffolds, explain the mechanisms associated with CDK4/6 inhibitor resistance and describe solutions to overcome this issue, and briefly introduce proteolysis targeting chimera (PROTAC), a new and revolutionary technique used to degrade CDK4/6.

A Driver Never Works Alone-Interplay Networks of Mutant p53, MYC, RAS, and Other Universal Oncogenic Drivers in Human Cancer

The knowledge accumulating on the occurrence and mechanisms of the activation of oncogenes in human neoplasia necessitates an increasingly detailed understanding of their systemic interactions. None of the known oncogenic drivers work in isolation from the other oncogenic pathways. The cooperation between these pathways is an indispensable element of a multistep carcinogenesis, which apart from inactivation of tumor suppressors, always includes the activation of two or more proto-oncogenes. In this review we focus on representative examples of the interaction of major oncogenic drivers with one another. The drivers are selected according to the following criteria: (1) the highest frequency of known activation in human neoplasia (by mutations or otherwise), (2) activation in a wide range of neoplasia types (universality) and (3) as a part of a distinguishable pathway, (4) being a known cause of phenotypic addiction of neoplastic cells and thus a promising therapeutic target. Each of these universal oncogenic factors—mutant p53, KRAS and CMYC proteins, telomerase ribonucleoprotein, proteasome machinery, HSP molecular chaperones, NF-κB and WNT pathways, AP-1 and YAP/TAZ transcription factors and non-coding RNAs—has a vast network of molecular interrelations and common partners. Understanding this network allows for the hunt for novel therapeutic targets and protocols to counteract drug resistance in a clinical neoplasia treatment.

Microhomology-mediated end joining drives complex rearrangements and overexpression of MYC and PVT1 in multiple myeloma

MYC is a widely acting transcription factor and its deregulation is a crucial event in many human cancers. MYC is important biologically and clinically in multiple myeloma, but the mechanisms underlying its dysregulation are poorly understood. We show that MYC rearrangements are present in 36.0% of newly diagnosed myeloma patients, as detected in the largest set of next generation sequencing data to date (n=1,267). Rearrangements were complex and associated with increased expression of MYC and PVT1, but not other genes at 8q24. The highest effect on gene expression was detected in cases where the MYC locus is juxtaposed next to super-enhancers associated with genes such as IGH, IGK, IGL, TXNDC5/BMP6, FAM46C and FOXO3 We identified three hotspots of recombination at 8q24, one of which is enriched for IGH-MYC translocations. Breakpoint analysis indicates primary myeloma rearrangements involving the IGH locus occur through non-homologous end joining, whereas secondary MYC rearrangements occur through microhomology-mediated end joining. This mechanism is different to lymphomas, where non-homologous end joining generates MYC rearrangements. Rearrangements resulted in overexpression of key genes and chromatin immunoprecipitation-sequencing identified that HK2, a member of the glucose metabolism pathway, is directly over-expressed through binding of MYC at its promoter.

Oncofetal Chondroitin Sulfate: A Putative Therapeutic Target in Adult and Pediatric Solid Tumors

Solid tumors remain a major challenge for targeted therapeutic intervention strategies such as antibody-drug conjugates and immunotherapy. At a minimum, clear and actionable solid tumor targets have to comply with the key biological requirement of being differentially over-expressed in solid tumors and metastasis, in contrast to healthy organs. Oncofetal chondroitin sulfate is a cancer-specific secondary glycosaminoglycan modification to proteoglycans expressed in a variety of solid tumors and metastasis. Normally, this modification is found to be exclusively expressed in the placenta, where it is thought to facilitate normal placental implantation during pregnancy. Informed by this biology, oncofetal chondroitin sulfate is currently under investigation as a broad and specific target in solid tumors. Here, we discuss oncofetal chondroitin sulfate as a potential therapeutic target in childhood solid tumors in the context of current knowhow obtained over the past five years in adult cancers.

Long non-coding RNA PVT1 interacts with MYC and its downstream molecules to synergistically promote tumorigenesis

Numerous studies have shown that non-coding RNAs play crucial roles in the development and progression of various tumor cells. Plasmacytoma variant translocation 1 (PVT1) mainly encodes a long non-coding RNA (lncRNA) and is located on chromosome 8q24.21, which constitutes a fragile site for genetic aberrations. PVT1 is well-known for its interaction with its neighbor MYC, which is a qualified oncogene that plays a vital role in tumorigenesis. In the past several decades, increasing attention has been paid to the interaction mechanism between PVT1 and MYC, which will benefit the clinical treatment and prognosis of patients. In this review, we summarize the coamplification of PVT1 and MYC in cancer, the positive feedback mechanism, and the latest promoter competition mechanism of PVT1 and MYC, as well as how PVT1 participates in the downstream signaling pathway of c-Myc by regulating key molecules. We also briefly describe the treatment prospects and research directions of PVT1 and MYC.

TAG-RNAi overcomes off-target effects in cancer models

RNA interference offers therapeutic opportunities for the clinical targeting of otherwise undruggable oncogenes. However RNAi can have off-target effects that considerably increase treatment risks. To manage these side effects and allow an easy subtraction of their activity in healthy tissues, we present here the TAG-RNAi approach where cells that are not designated targets do not have the mRNA tag. Using TAG-RNAi we first established the off-target signatures of three different siRNAs specific to the Cyclin D1 oncogene by RNA-sequencing of cultured cancer cells expressing a FLAG-HA-tagged-Cyclin D1. Then, by symmetrical allografts of tagged-cancer cells and untagged controls on the left and right flanks of model mice, we demonstrate that TAG-RNAi is a reliable approach to study the functional impact of any oncogene without off-target bias. Finally we show, as examples, that mutation-specific TAG-RNAi can be applied to downregulate two oncogenic mutants, KRAS-G12V or BRAF-V600E, while sparing the expression of the wild-type proteins. TAG-RNAi will thus avoid the traditional off-target limitations of RNAi in future experimental approaches.

Flavin Oxidase-Induced ROS Generation Modulates PKC Biphasic Effect of Resveratrol on Endothelial Cell Survival

Background: Dietary intake of natural antioxidants is thought to impart protection against oxidative-associated cardiovascular diseases. Despite many in vivo studies and clinical trials, this issue has not been conclusively resolved. Resveratrol (RES) is one of the most extensively studied dietary polyphenolic antioxidants. Paradoxically, we have previously demonstrated that high RES concentrations exert a pro-oxidant effect eventually elevating ROS levels leading to cell death. Here, we further elucidate the molecular determinants underpinning RES-induced oxidative cell death. Methods: Using human umbilical vein endothelial cells (HUVECs), the effect of increasing concentrations of RES on DNA synthesis and apoptosis was studied. In addition, mRNA and protein levels of cell survival or apoptosis genes, as well as protein kinase C (PKC) activity were determined. Results: While high concentrations of RES reduce PKC activity, inhibit DNA synthesis and induce apoptosis, low RES concentrations elicit an opposite effect. This biphasic concentration-dependent effect (BCDE) of RES on PKC activity is mirrored at the molecular level. Indeed, high RES concentrations upregulate the proapoptotic Bax, while downregulating the antiapoptotic Bcl-2, at both mRNA and protein levels. Similarly, high RES concentrations downregulate the cell cycle progression genes, c-myc, ornithine decarboxylase (ODC) and cyclin D1 protein levels, while low RES concentrations display an increasing trend. The BCDE of RES on PKC activity is abrogated by the ROS scavenger Tempol, indicating that this enzyme acts downstream of the RES-elicited ROS signaling. The RES-induced BCDE on HUVEC cell cycle machinery was also blunted by the flavin inhibitor diphenyleneiodonium (DPI), implicating flavin oxidase-generated ROS as the mechanistic link in the cellular response to different RES concentrations. Finally, PKC inhibition abrogates the BCDE elicited by RES on both cell cycle progression and pro-apoptotic gene expression in HUVECs, mechanistically implicating PKC in the cellular response to different RES concentrations. Conclusions: Our results provide new molecular insight into the impact of RES on endothelial function/dysfunction, further confirming that obtaining an optimal benefit of RES is concentration-dependent. Importantly, the BCDE of RES could explain why other studies failed to establish the cardio-protective effects mediated by natural antioxidants, thus providing a guide for future investigation looking at cardio-protection by natural antioxidants.

New chalcone-sulfonamide hybrids exhibiting anticancer and antituberculosis activity

New sulfonamides 5/6 derived from 4-methoxyacetophenone 1 were synthesized by N-sulfonation reaction of ammonia (3) and aminopyrimidinone (4) with its sulfonyl chloride derivative 2. Sulfonamides 5 and 6 were used as precursors of two new series of chalcones 8a-f and 9a-f, which were obtained through Claisen-Schmidt condensation with aromatic aldehydes 7a-f. Compounds 5/6, 8a-d, 8f, 9a-d, and 9f were screened by the US National Cancer Institute (NCI) at 10 μM against sixty different human cancer cell lines (one-dose trial). Chalcones 8b and 9b satisfied the pre-determined threshold inhibition criteria and were selected for screening at five different concentrations (100, 10, 1.0, 0.1, and 0.01 μM). Compound 8b exhibited remarkable GI₅₀ values ranging from 0.57 to 12.4 μM, with cytotoxic effects being observed in almost all cases, especially against the cell lines K-562 of Leukemia and LOX IMVI of Melanoma with GI₅₀ = 0.57 and 1.28 μM, respectively. Moreover, all compounds were screened against Mycobacterium tuberculosis H37Rv, chalcones 8a-c and 9a-c were the most active showing MIC values between 14 and 42 μM, and interestingly they were devoid of antibacterial activity against Mycobacterium smegmatis and Staphylococcus aureus. These antituberculosis hits showed however low selectivity, being equally inhibitory to M. tuberculosis and mammalian T3T cells. The chalcone-sulfonamide hybrids 8a-f and 9a-f resulted to be appealing cytotoxic agents with significant antituberculosis activity.

MYC Oncogene Contributions to Release of Cell Cycle Brakes

Promotion of the cell cycle is a major oncogenic mechanism of the oncogene c-MYC (MYC). MYC promotes the cell cycle by not only activating or inducing cyclins and CDKs but also through the downregulation or the impairment of the activity of a set of proteins that act as cell-cycle brakes. This review is focused on the role of MYC as a cell-cycle brake releaser i.e., how MYC stimulates the cell cycle mainly through the functional inactivation of cell cycle inhibitors. MYC antagonizes the activities and/or the expression levels of p15, ARF, p21, and p27. The mechanism involved differs for each protein. p15 (encoded by CDKN2B) and p21 (CDKN1A) are repressed by MYC at the transcriptional level. In contrast, MYC activates ARF, which contributes to the apoptosis induced by high MYC levels. At least in some cells types, MYC inhibits the transcription of the p27 gene (CDKN1B) but also enhances p27's degradation through the upregulation of components of ubiquitin ligases complexes. The effect of MYC on cell-cycle brakes also opens the possibility of antitumoral therapies based on synthetic lethal interactions involving MYC and CDKs, for which a series of inhibitors are being developed and tested in clinical trials.

Piperlongumine, a piper alkaloid targets Ras/PI3K/Akt/mTOR signaling axis to inhibit tumor cell growth and proliferation in DMH/DSS induced experimental colon cancer

Colorectal cancer (CRC) is the most common carcinoma of the digestive tract. The slow growing nature of CRC offers a great opportunity for prevention strategies. The concept of chemoprevention of colorectal cancer using plant derived natural products is gaining substantial attention because it is an inherently safe and cost-effective alternative to conventional cancer therapies. Piperlongumine (PL), a natural alkaloid present in Piper longum Linn has been reported to exhibit notable anticancer effects in various in vitro studies. Nonetheless, the chemopreventive potential of PL has not been studied in experimentally induced colon cancer yet. Ras/PI3K/Akt/mTOR signaling axis plays a central role in promoting tumor cell growth, proliferation and survival by inhibiting apoptosis. In the present study, we demonstrated, for the first time, the chemopreventive effects of PL in DMH + DSS induced colon carcinogenesis animal model. We showed that PL displayed potent antineoplastic activity against colon cancer cell growth by targeting Ras proteins and PI3K/Akt signaling cascade. PL mediated inhibition of tumor cell growth was associated with inhibition of Ras protein levels and its preferred companion protein PI3K levels that led to suppressed activity of Akt/NF-κB, c-Myc and cyclin D1. It was also found that PL arrested the cell cycle progression at G2/M phase and induced mitochondrial apoptotic pathway by downregulating Bcl-2 levels. Furthermore, the results of liver and kidney toxicity suggested that PL exhibit no toxicity in animals. Our results suggest that PL may be an effective chemopreventive agent for colon cancer.

c-Myc is regulated by HIF-2α in chronic hypoxia and influences sensitivity to 5-FU in colon cancer

Colorectal cancers (CRCs) invariably become hypoxic as they enlarge, and this places unique metabolic demands upon the tumor cells. Hypoxic stress can enhance the invasiveness of cancer cells and induce chemoresistance. c-Myc, an oncogene regulated by hypoxia inducible factors (HIFs), plays a critical role in cell proliferation and metabolism. However, the interplay between c-Myc and HIFs and its clinical significance in hypoxic adaptation in CRCs are unknown. We demonstrate that c-Myc mRNA and protein levels in colon cancer cells are induced within 2 h of hypoxic stress (1% O₂) but are then significantly downregulated when exposed to prolonged hypoxia. In chronic hypoxia (over 8 h at 1% O₂), HIF-2α but not HIF-1α gradually accumulated in colon cancer cells. Knockdown of HIF-2α increased levels of c-Myc and its downstream target cyclinD1 in chronic hypoxia, indicating that HIF-2α may function to downregulate c-Myc. Chronic hypoxia suppressed the expression of cyclinD1, CDK4, and CDK6, inducing G1 phase block and 5-flurouracil (5-FU) chemoresistance. Overexpression of c-Myc reversed the inhibition of cyclinD1, CDK4, and CDK6, which accelerated the G1/S phase transition under hypoxia and enhanced sensitivity to 5-FU. In contrast, knockdown of c-Myc impaired 5-FU chemosensitivity in colon cancer cells. In summary, HIF-2α plays an important role in regulating the expression of c-Myc in chronic hypoxia, and consequently controls the sensitivity of colon cancer cells to 5-FU treatment in this environment.

LAST, a c-Myc-inducible long noncoding RNA, cooperates with CNBP to promote CCND1 mRNA stability in human cells

Cyclin D1 is a critical regulator of cell cycle progression and works at the G1 to S-phase transition. Here, we report the isolation and characterization of the novel c-Myc-regulated lncRNA LAST (LncRNA-Assisted Stabilization of Transcripts), which acts as a CCND1 mRNA stabilizer. Mechanistically, LAST was shown to cooperate with CNBP to bind to the 5′UTR of CCND1 mRNA to protect against possible nuclease targeting. In addition, data from CNBP RIP-seq and LAST RNA-seq showed that CCND1 mRNA might not be the only target of LAST and CNBP; three additional mRNAs were shown to be post-transcriptional targets of LAST and CNBP. In a xenograft model, depletion of LAST diminished and ectopic expression of LAST induced tumor formation, which are suggestive of its oncogenic function. We thus report a previously unknown lncRNA involved in the fine-tuned regulation of CCND1 mRNA stability, without which CCND1 exhibits, at most, partial expression.

Cell division involves a series of steps in which the cell grows, duplicates its contents, and then divides into two. Together these steps are called the cell cycle, and the transition between each step must be controlled to make sure that events take place in the right order. Any loss of control can cause cells to divide in an unrestrained manner, which may lead to cancer.

Proteins called cyclins control progression through the cell cycle. As such, these proteins need to be produced in the correct amounts and at the correct times. Transcription factors are proteins that switch genes on or off to help regulate how much protein is made from those genes. A transcription factor known as c-Myc regulates the expression of the genes that encode the cyclins. Among these genes, one called CCND1 is particularly important because it encodes a protein that controls a crucial transition in the cell cycle: it marks a ‘point of no return’, beyond which cells are committed to dividing.

When a transcription factor switches on a gene, the gene gets copied into a molecule of messenger RNA, which is then translated into protein. But, cells also contain genes that do not code for proteins. Transcription factors can bind to such non-coding genes, leading to the production of so-called long non-coding RNAs (often abbreviated to lncRNAs).

Many lncRNAs can affect the expression of other genes. Cao, Zhang et al. have now asked whether any lncRNAs regulate CCND1 in human cells. The analysis revealed that the transcription factor c-Myc promotes the expression of a previously unidentified lncRNA. Cao, Zhang et al. name this lncRNA LAST, which is officially short for LncRNA-assisted stabilization of transcripts, and show thatit makes the CCND1 messenger RNA more stable. In other words, it makes the messenger RNAs ‘last’ longer in the cell. This in turn, ensures that the cell cycle progresses in the correct manner, allowing cells to complete their division. In the absence of LAST, the CCND1 messenger RNA becomes unstable and as a result the cell cycle does not progress.

Cao, Zhang et al. then explored the role of LAST in cancer cells. When human colon cancer cells that expressed LAST were implanted into mice, they formed tumors. Yet, reducing the expression of LAST in the colon cancer cells made the tumors grow slower.

Future challenges will be to understand how LAST makes messenger RNAs stable and further explore its role in cancer. A better understanding of this molecule could reveal whether it can be used to help doctors diagnose or treat cancers.

Morusin inhibits cell proliferation and tumor growth by down-regulating c-Myc in human gastric cancer

Morusin is a pure extract from the root bark of Morus australis (Moraceae). In recent years, morusin has been reported to exhibit anti-tumor biological activity in some types of human cancers through different mechanisms. Here, we attempted to investigate the inhibitory effect and mechanism of morusin on gastric cancer. Morusin markedly inhibited gastric cancer cell proliferation by down-regulating CDKs and Cyclins, such as CDK2, CDK4, Cyclin D1 and Cyclin E1. Additionally, morusin suppressed tumor growth in vitro and in vivo. Up-regulation of CDKs and Cyclins in gastric cancer cells was induced by c-Myc binding at the E-Box regions of CDKs and the Cyclin promoter. In addition, compared with the control group, the morusin-treated group showed reduced expression of c-Myc and c-Myc protein binding at the E-Box regions. Based on these results, we overexpressed c-Myc in gastric cancer cells and found that overexpressing c-Myc rescued morusin-induced inhibition of cell proliferation and tumor growth. These results suggest that morusin inhibits cell proliferation and tumor growth by down-regulating c-Myc in human gastric cancer.

Initiation of stem cell differentiation involves cell cycle-dependent regulation of developmental genes by Cyclin D

Coordination of differentiation and cell cycle progression represents an essential process for embryonic development and adult tissue homeostasis. These mechanisms ultimately determine the quantities of specific cell types that are generated. Despite their importance, the precise molecular interplays between cell cycle machinery and master regulators of cell fate choice remain to be fully uncovered. Here, we demonstrate that cell cycle regulators Cyclin D1-3 control cell fate decisions in human pluripotent stem cells by recruiting transcriptional corepressors and coactivator complexes onto neuroectoderm, mesoderm, and endoderm genes. This activity results in blocking the core transcriptional network necessary for endoderm specification while promoting neuroectoderm factors. The genomic location of Cyclin Ds is determined by their interactions with the transcription factors SP1 and E2Fs, which result in the assembly of cell cycle-controlled transcriptional complexes. These results reveal how the cell cycle orchestrates transcriptional networks and epigenetic modifiers to instruct cell fate decisions.

MYC: connecting selective transcriptional control to global RNA production

Two opposing models have been proposed to describe the function of the MYC oncoprotein in shaping cellular transcriptomes: one posits that MYC amplifies transcription at all active loci; the other that MYC differentially controls discrete sets of genes, the products of which affect global transcript levels. Here, we argue that differential gene regulation by MYC is the sole unifying model that is consistent with all available data. Among other effects, MYC endows cells with physiological and metabolic changes that have the potential to feed back on global RNA production, processing and turnover. The field is progressing steadily towards a full characterization of the MYC-regulated genes and pathways that mediate these biological effects and - by the same token - endow MYC with its pervasive oncogenic potential.

Changes in neuronal CycD/Cdk4 activity affect aging, neurodegeneration, and oxidative stress

Mitochondrial dysfunction has been implicated in human diseases, including cancer, and proposed to accelerate aging. The Drosophila Cyclin-dependent protein kinase complex cyclin D/cyclin-dependent kinase 4 (CycD/Cdk4) promotes cellular growth by stimulating mitochondrial biogenesis. Here, we examine the neurodegenerative and aging consequences of altering CycD/Cdk4 function in Drosophila. We show that pan-neuronal loss or gain of CycD/Cdk4 increases mitochondrial superoxide, oxidative stress markers, and neurodegeneration and decreases lifespan. We find that RNAi-mediated depletion of the mitochondrial transcription factor, Tfam, can abrogate CycD/Cdk4's detrimental effects on both lifespan and neurodegeneration. This indicates that CycD/Cdk4's pathological consequences are mediated through altered mitochondrial function and a concomitant increase in reactive oxygen species. In support of this, we demonstrate that CycD/Cdk4 activity levels in the brain affect the expression of a set of 'oxidative stress' genes. Our results indicate that the precise regulation of neuronal CycD/Cdk4 activity is important to limit mitochondrial reactive oxygen species production and prevent neurodegeneration.

The history and future of targeting cyclin-dependent kinases in cancer therapy

Cancer represents a pathological manifestation of uncontrolled cell division; therefore, it has long been anticipated that our understanding of the basic principles of cell cycle control would result in effective cancer therapies. In particular, cyclin-dependent kinases (CDKs) that promote transition through the cell cycle were expected to be key therapeutic targets because many tumorigenic events ultimately drive proliferation by impinging on CDK4 or CDK6 complexes in the G1 phase of the cell cycle. Moreover, perturbations in chromosomal stability and aspects of S phase and G2/M control mediated by CDK2 and CDK1 are pivotal tumorigenic events. Translating this knowledge into successful clinical development of CDK inhibitors has historically been challenging, and numerous CDK inhibitors have demonstrated disappointing results in clinical trials. Here, we review the biology of CDKs, the rationale for therapeutically targeting discrete kinase complexes and historical clinical results of CDK inhibitors. We also discuss how CDK inhibitors with high selectivity (particularly for both CDK4 and CDK6), in combination with patient stratification, have resulted in more substantial clinical activity.

Plasmacytomagenesis in Eμ-v-abl transgenic mice is accelerated when apoptosis is restrained

Mice susceptible to plasma cell tumors provide a useful model for human multiple myeloma. We previously showed that mice expressing an Eµ-v-abl oncogene solely develop plasmacytomas. Here we show that loss of the proapoptotic BH3-only protein Bim or, to a lesser extent, overexpression of antiapoptotic Bcl-2 or Mcl-1, significantly accelerated the development of plasmacytomas and increased their incidence. Disease was preceded by an increased abundance of plasma cells, presumably reflecting their enhanced survival capacity in vivo. Plasmacytomas of each genotype expressed high levels of v-abl and frequently harbored a rearranged c-myc gene, probably as a result of chromosome translocation. As in human multiple myelomas, elevated expression of cyclin D genes was common, and p53 deregulation was rare. Our results for plasmacytomas highlight the significance of antiapoptotic changes in multiple myeloma, which include elevated expression of Mcl-1 and, less frequently, Bcl-2, and suggest that closer attention to defects in Bim expression is warranted.

Myc and cell cycle control

Soon after the discovery of the Myc gene (c-Myc), it became clear that Myc expression levels tightly correlate to cell proliferation. The entry in cell cycle of quiescent cells upon Myc enforced expression has been described in many models. Also, the downregulation or inactivation of Myc results in the impairment of cell cycle progression. Given the frequent deregulation of Myc oncogene in human cancer it is important to dissect out the mechanisms underlying the role of Myc on cell cycle control. Several parallel mechanisms account for Myc-mediated stimulation of the cell cycle. First, most of the critical positive cell cycle regulators are encoded by genes induced by Myc. These Myc target genes include Cdks, cyclins and E2F transcription factors. Apart from its direct effects on the transcription, Myc is able to hyperactivate cyclin/Cdk complexes through the induction of Cdk activating kinase (CAK) and Cdc25 phosphatases. Moreover, Myc antagonizes the activity of cell cycle inhibitors as p21 and p27 through different mechanisms. Thus, Myc is able to block p21 transcription or to induce Skp2, a protein involved in p27 degradation. Finally, Myc induces DNA replication by binding to replication origins and by upregulating genes encoding proteins required for replication initiation. Myc also regulates genes involved in the mitotic control. A promising approach to treat tumors with deregulated Myc is the synthetic lethality based on the inhibition of Cdks. Thus, the knowledge of the Myc-dependent cell cycle regulatory mechanisms will help to discover new therapeutic approaches directed against malignancies with deregulated Myc. This article is part of a Special Issue entitled: Myc proteins in cell biology and pathology.

Signal transduction disturbance related to hepatocarcinogenesis in mouse by prolonged exposure to Nanjing drinking water

Toxicogenomic approaches were used to investigate the potential hepatocarcinogenic effects on mice by oral exposure to Nanjing drinking water (NJDW). Changes in the hepatic transcriptome of 3 weeks male mice (Mus musculus) were monitored and dissected after oral exposure to NJDW for 90 days. No preneoplastic and neoplastic lesions were observed in the hepatic tissue by the end of NJDW exposure. However, total of 746 genes were changed transcriptionally. Thirty-one percent of differentially expressed genes (DEGs) were associated with the functional categories of cell cycle regulation, adhesion, growth, apoptosis, and signal transduction, which are closely implicated in tumorigenesis and progression. Interrogation of Kyoto Encyclopedia of Genes and Genomes revealed that 43 DEGs were mapped to several crucial signaling pathways implicated in the pathogenesis of hepatocellular carcinoma (HCC). In signal transduction network constructed via Genes2Networks software, Egfr, Akt1, Atf2, Ctnnb1, Hras, Mapk1, Smad2, and Ccnd1 were hubs. Direct gene-disease relationships obtained from Comparative Toxicogenomics Database and scientific literatures revealed that the hubs have direct mechanism or biomarker relationships with hepatocellular preneoplastic lesions or hepatocarcinogenesis. Therefore, prolonged intake of NJDW without employing any indoor water treatment strategy might predispose mouse to HCC. Furthermore, Egfr, Akt1, Ctnnb1, Hras, Mapk1, Smad2, and Ccnd1 were identified as promising biomarkers of the potential combined hepatocarcinogenicity.

The enzymatic activity of apoptosis-inducing factor supports energy metabolism benefiting the growth and invasiveness of advanced prostate cancer cells

Apoptosis-inducing factor (AIF) promotes cell death yet also controls mitochondrial homeostasis and energy metabolism. It is unclear how these activities are coordinated, and the impact of AIF upon human disease, in particular cancer, is not well documented. In this study we have explored the contribution of AIF to the progression of prostate cancer. Analysis of archival gene expression data demonstrated that AIF transcript levels are elevated in human prostate cancer, and we found that AIF protein is increased in prostate tumors. Suppression of AIF expression in the prostate cancer cell lines LNCaP, DU145, and PC3 demonstrated that AIF does not contribute to cell toxicity via a variety of chemical death triggers, and growth under nutrient-rich conditions is largely unaffected by AIF ablation. However, under growth stress conditions, AIF depletion from DU145 and PC3 cell lines led to significant reductions in cell survival and growth that were not observed in LNCaP cells. Moreover AIF-deficient PC3 cells exhibited substantial reduction of tumorigenic growth in vivo. This reduced survival correlated with decreased expression of mitochondrial complex I protein subunits and concomitant changes in glucose metabolism. Finally, restoration of AIF-deficient PC3 cells with AIF variants demonstrated that the enzymatic activity of AIF is required for aggressive growth. Overall these studies show that AIF is an important factor for advanced prostate cancer cells and that through control of energy metabolism and redox balance, the enzymatic activity of AIF is critical for this support.

Chemical-genetic analysis of cyclin dependent kinase 2 function reveals an important role in cellular transformation by multiple oncogenic pathways

A family of conserved serine/threonine kinases known as cyclin-dependent kinases (CDKs) drives orderly cell cycle progression in mammalian cells. Prior studies have suggested that CDK2 regulates S-phase entry and progression, and frequently shows increased activity in a wide spectrum of human tumors. Genetic KO/knockdown approaches, however, have suggested that lack of CDK2 protein does not prevent cellular proliferation, both during somatic development in mice as well as in human cancer cell lines. Here, we use an alternative, chemical-genetic approach to achieve specific inhibition of CDK2 kinase activity in cells. We directly compare small-molecule inhibition of CDK2 kinase activity with siRNA knockdown and show that small-molecule inhibition results in marked defects in proliferation of nontransformed cells, whereas siRNA knockdown does not, highlighting the differences between these two approaches. In addition, CDK2 inhibition drastically diminishes anchorage-independent growth of human cancer cells and cells transformed with various oncogenes. Our results establish that CDK2 activity is necessary for normal mammalian cell cycle progression and suggest that it might be a useful therapeutic target for treating cancer.

Drosophila cyclin D/Cdk4 regulates mitochondrial biogenesis and aging and sensitizes animals to hypoxic stress

Drosophila cyclinD (CycD) is the single fly ortholog of the mammalian cyclin D1 and promotes both cell cycle progression and cellular growth. However, little is known about how CycD promotes cell growth. We show here that CycD/Cdk4 hyperactivity leads to increased mitochondrial biogenesis (mitobiogenesis), mitochondrial mass, NRF-1 activity (Tfam transcript levels) and metabolic activity in Drosophila, whereas loss of CycD/Cdk4 activity has the opposite effects. Surprisingly, both CycD/Cdk4 addition and loss of function increase mitochondrial superoxide production and decrease lifespan, indicating that an imbalance in mitobiogenesis may lead to oxidative stress and aging. In addition, we provide multiple lines of evidence indicating that CycD/Cdk4 activity affects the hypoxic status of cells and sensitizes animals to hypoxia. Both mitochondrial and hypoxia-related effects can be detected at the global transcriptional level. We propose that mitobiogenesis and the hypoxic stress response have an antagonistic relationship, and that CycD/Cdk4 levels regulate mitobiogenesis contemporaneous to the cell cycle, such that only when cells are sufficiently oxygenated can they proliferate.

Dampened ERK signaling in hematopoietic progenitor cells in rheumatoid arthritis

In rheumatoid arthritis (RA), hematopoietic progenitor cells (HPC) have age-inappropriate telomeric shortening suggesting premature senescence and possible restriction of proliferative capacity. In response to hematopoietic growth factors RA-derived CD34(+) HPC expanded significantly less than age-matched controls. Cell surface receptors for stem cell factor (SCF), Flt 3-Ligand, IL-3 and IL-6 were intact in RA HPC but the cells had lower transcript levels of cell cycle genes, compatible with insufficient signal strength in the ERK pathway. Cytokine-induced phosphorylation of ERK1/2 was diminished in RA HPC whereas phosphorylated STAT3 and STAT5 molecules accumulated to a similar extent as in controls. Confocal microscopy demonstrated that the membrane-proximal colocalization of K-Ras and B-Raf was less efficient in RA-derived CD34(+) cells. Thus, hyporesponsiveness of RA HPC to growth factors results from dampening of the ERK signaling pathways; with a defect localized in the very early steps of the ERK signaling cascade.

CCAAT/enhancer-binding protein beta inhibits proliferation in monocytic cells by affecting the retinoblastoma protein/E2F/cyclin E pathway but is not directly required for macrophage morphology

Monocytic differentiation is orchestrated by complex networks that are not fully understood. This study further elucidates the involvement of transcription factor CCAAT/enhancer-binding protein β (C/EBPβ). Initially, we demonstrated a marked increase in nuclear C/EBPβ-liver-enriched activating protein* (LAP*)/liver-enriched activating protein (LAP) levels and LAP/liver-enriched inhibiting protein (LIP) ratios in phorbol 12-myristate 13-acetate (PMA)-treated differentiating THP-1 premonocytic cells accompanied by reduced proliferation. To directly study C/EBPβ effects on monocytic cells, we generated novel THP-1-derived (low endogenous C/EBPβ) cell lines stably overexpressing C/EBPβ isoforms. Most importantly, cells predominantly overexpressing LAP* (C/EBPβ-long), but not those overexpressing LIP (C/EBPβ-short), exhibited a reduced proliferation, with no effect on morphology. PMA-induced inhibition of proliferation was attenuated in C/EBPβ-short cells. In C/EBPβ^WT macrophage-like cells (high endogenous C/EBPβ), we measured a reduced proliferation/cycling index compared with C/EBPβ^KO. The typical macrophage morphology was only observed in C/EBPβ^WT, whereas C/EBPβ^KO stayed round. C/EBPα did not compensate for C/EBPβ effects on proliferation/morphology. Serum reduction, an independent approach known to inhibit proliferation, induced macrophage morphology in C/EBPβ^KO macrophage-like cells but not THP-1. In PMA-treated THP-1 and C/EBPβ-long cells, a reduced phosphorylation of cell cycle repressor retinoblastoma was found. In addition, C/EBPβ-long cells showed reduced c-Myc expression accompanied by increased CDK inhibitor p27 and reduced cyclin D1 levels. Finally, C/EBPβ-long and C/EBPβ^WT cells exhibited low E2F1 and cyclin E levels, and C/EBPβ overexpression was found to inhibit cyclin E1 promoter-dependent transcription. Our results suggest that C/EBPβ reduces monocytic proliferation by affecting the retinoblastoma/E2F/cyclin E pathway and that it may contribute to, but is not directly required for, macrophage morphology. Inhibition of proliferation by C/EBPβ may be important for coordinated monocytic differentiation.

The PKB/FOXO switch in aging and cancer

Aging is characterized by the general decline in tissue and body function and the increased susceptibility to age-related pathologies, such as cancer. To maintain optimal tissue and body function, organisms have developed complex mechanisms for tissue homeostasis. Importantly, it is becoming apparent that these same mechanisms when deregulated also result in the development of age-related disease. The build in fail safe mechanisms of homeostasis, which prevent skewing toward disease, themselves contribute to aspects of aging. Thus, longevity is limited by an intrinsic trade-off between optimal tissue function and disease. Consequently, aging and age-related diseases, such as cancer and diabetes are driven by the same genetic determinants. Illustrative in this respect is the insulin/IGF-1 signaling pathway acting through PI3K/PKB and FOXO. Loss of PKB signaling contributes to diabetes, whereas gain of function of PKB drives cancer. Enhanced FOXO activity, at least in model organism contributes to extended lifespan and acts as a tumor suppressive mechanism. Here, we focus on the linkage between PKB and FOXO as a central switch in contributing to tissue homeostasis and age-related diseases in particular cancer. This article is part of a Special Issue entitled: P13K-AKT-FoxO axis in cancer and aging.

Cyclin D1 is a selective modifier of androgen-dependent signaling and androgen receptor function

D-type cyclins regulate cellular outcomes in part through cyclin-dependent, kinase-independent mechanisms that modify transcription factor action, and recent in vivo studies showed that cyclin D1 associates with a large number of transcriptional regulators in cells of the retina and breast. Given the frequency of cyclin D1 alterations in cancer, it is imperative to delineate the molecular mechanisms by which cyclin D1 controls key transcription factor networks in human disease. Prostate cancer was used as a paradigm because this tumor type is reliant at all stages of the disease on androgen receptor (AR) signaling, and cyclin D1 has been shown to negatively modulate AR-dependent expression of prostate-specific antigen (KLK3/PSA). Strategies were employed to control cyclin D1 expression under conditions of hormone depletion, and the effect of cyclin D1 on subsequent androgen-dependent gene expression was determined using unbiased gene expression profiling. Modulating cyclin D1 conferred widespread effects on androgen signaling and revealed cyclin D1 to be a selective effector of hormone action. A subset of androgen-induced target genes, known to be directly regulated by AR, was strongly suppressed by cyclin D1. Analyses of AR occupancy at target gene regulatory loci of clinical relevance demonstrated that cyclin D1 limits AR residence after hormone stimulation. Together, these findings reveal a new function for cyclin D1 in controlling hormone-dependent transcriptional outcomes and demonstrate a pervasive role for cyclin D1 in regulating transcription factor dynamics.

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.

MYC in oncogenesis and as a target for cancer therapies

MYC proteins (c-MYC, MYCN, and MYCL) regulate processes involved in many if not all aspects of cell fate. Therefore, it is not surprising that the MYC genes are deregulated in several human neoplasias as a result from genetic and epigenetic alterations. The near "omnipotency" together with the many levels of regulation makes MYC an attractive target for tumor intervention therapy. Here, we summarize some of the current understanding of MYC function and provide an overview of different cancer forms with MYC deregulation. We also describe available treatments and highlight novel approaches in the pursuit for MYC-targeting therapies. These efforts, at different stages of development, constitute a promising platform for novel, more specific treatments with fewer side effects. If successful a MYC-targeting therapy has the potential for tailored treatment of a large number of different tumors.

Oncogenic Kras initiates leukemia in hematopoietic stem cells

How oncogenes modulate the self-renewal properties of cancer-initiating cells is incompletely understood. Activating KRAS and NRAS mutations are among the most common oncogenic lesions detected in human cancer, and occur in myeloproliferative disorders (MPDs) and leukemias. We investigated the effects of expressing oncogenic Kras^G12D from its endogenous locus on the proliferation and tumor-initiating properties of murine hematopoietic stem and progenitor cells. MPD could be initiated by Kras^G12D expression in a highly restricted population enriched for hematopoietic stem cells (HSCs), but not in common myeloid progenitors. Kras^G12D HSCs demonstrated a marked in vivo competitive advantage over wild-type cells. Kras^G12D expression also increased the fraction of proliferating HSCs and reduced the overall size of this compartment. Transplanted Kras^G12D HSCs efficiently initiated acute T-lineage leukemia/lymphoma, which was associated with secondary Notch1 mutations in thymocytes. We conclude that MPD-initiating activity is restricted to the HSC compartment in Kras^G12D mice, and that distinct self-renewing populations with cooperating mutations emerge during cancer progression.

Ras proteins act as molecular switches that relay growth signals from outside the cell. This mechanism is often subverted in cancer, and Ras proteins are activated directly by RAS gene mutations in approximately one-third of human malignancies. We have modeled this in mice engineered to have a Ras mutation. These mice develop a disease similar to chronic leukemias in humans called myeloproliferative disorders. It is marked by a fatal accumulation of mature and immature cells in the blood and bone marrow. We investigated whether some or all of these neoplastic cells were immortal. In agreement with the “cancer stem cell” hypothesis, we found that immortal cells were extremely rare in the bone marrow of diseased mice. They were found only in the same cell populations that contain normal bone marrow stem cells. However, these cells had high rates of replication and produced large numbers of daughter cells. Furthermore, many mice went on to develop acute lymphoid leukemia after acquiring additional mutations in maturing lymphoid cells. These studies exemplify the evolution of malignant stem cells during cancer progression. They also highlight the importance of rare, long-lived cells in the genesis and, potentially, therapy of high-risk chronic leukemias caused by abnormal Ras proteins.

TheKras^G12D oncogene causes excessive proliferation of stem cells, promoting their preferential expansion and initiating myeloproliferative disease.Kras^G12D does not alter self-renewal, but secondary mutations in lymphoid progenitors allow progression to acute leukemia.

Growth factor control of pancreatic islet regeneration and function

Type 1 and type 2 diabetes mellitus together are predicted to affect over 300 million people worldwide by the year 2020. A relative or absolute paucity of functional β-cells is a central feature of both types of disease, and identifying the pathways that mediate the embryonic origin of new β-cells and mechanisms that underlie the proliferation of existing β-cells are major efforts in the fields of developmental and islet biology. A poor secretory response of existing β-cells to nutrients and hormones and the defects in hormone processing also contribute to the hyperglycemia observed in type 2 diabetes and has prompted studies aimed at enhancing β-cell function. The factors that contribute to a greater susceptibility in aging individuals to develop diabetes is currently unclear and may be linked to a poor turnover of β-cells and/or enhanced susceptibility of β-cells to apoptosis. This review is an update on the recent work in the areas of islet/β-cell regeneration and hormone processing that are relevant to the pathophysiology of the endocrine pancreas in type 1, type 2 and obesity-associated diabetes.

The LIM-only protein FHL2 mediates ras-induced transformation through cyclin D1 and p53 pathways

Background

Four and a half LIM-only protein 2 (FHL2) has been implicated in multiple signaling pathways that regulate cell growth and tissue homeostasis. We reported previously that FHL2 regulates cyclin D1 expression and that immortalized FHL2-null mouse embryo fibroblasts (MEFs) display reduced levels of cyclin D1 and low proliferative activity.

Methodology/Principal Findings

Here we address the contribution of FHL2 in cell transformation by investigating the effects of oncogenic Ras in FHL2-null context. We show that H-RasV12 provokes cell cycle arrest accompanied by accumulation of p53 and p16^INK4a in immortalized FHL2^−/− MEFs. These features contrast sharply with Ras transforming activity in wild type cell lines. We further show that establishment of FHL2-null cell lines differs from conventional immortalization scheme by retaining functional p19^ARF/p53 checkpoint that is required for cell cycle arrest imposed by Ras. However, after serial passages of Ras-expressing FHL2^−/− cells, dramatic increase in the levels of D-type cyclins and Rb phosphorylation correlates with the onset of cell proliferation and transformation without disrupting the p19^ARF/p53 pathway. Interestingly, primary FHL2-null cells overexpressing cyclin D1 undergo a classical immortalization process leading to loss of the p19^ARF/p53 checkpoint and susceptibility to Ras transformation.

Conclusions/Significance

Our findings uncover a novel aspect of cellular responses to mitogenic stimulation and illustrate a critical role of FHL2 in the signalling network that implicates Ras, cyclin D1 and p53.

Differential expression of cell cycle proteins during ageing of pancreatic islet cells

One of the major challenges for developmental biologists and investigators in the field of diabetes over the last few decades has been to dissect the origin of pancreatic endocrine cells and to accurately understand the mechanisms that regulate islet cell regeneration. While significant advances have been made recently, there continues to be a paucity of knowledge regarding the growth factor signalling pathways that directly regulate the proteins involved in islet cell cycle control. We will discuss recent work in these areas and provide insights from our studies into age-dependent alterations in the expression of growth factor signalling proteins and cell cycle proteins in islet cells.

The role of the RB tumour suppressor pathway in oxidative stress responses in the haematopoietic system

Exposure to pro-oxidants and defects in the repair of oxidative base damage are associated with disease and ageing and also contribute to the development of anaemia, bone marrow failure and haematopoietic malignancies. This Review assesses emerging data indicative of a specific role for the RB tumour suppressor pathway in the response of the haematopoietic system to oxidative stress. This is mediated through signalling pathways that involve DNA damage sensors, forkhead box O (Foxo) transcription factors and p38 mitogen-activated protein kinases and has downstream consequences for cell cycle progression, antioxidant capacity, mitochondrial mass and cellular metabolism.

Hepatocarcinogenic Susceptibility of Fenofibrate and Its Possible Mechanism of Carcinogenicity in a Two-Stage Hepatocarcinogenesis Model of rasH2 Mice

Fenofibrate (FF) has previously been shown to induce hepatocellular neoplasia in a conventional mouse bioassay (NDA 1993), but there has been no report to examine the carcinogenic susceptibility of rasH2 mice to this chemical. In the present study, male rasH2 mice were subjected to a two-thirds partial hepatectomy (PH), followed by an N-diethylnitrosamine (DEN) initiation twenty-four hours after PH, and given a diet containing 0, 1200, or 2400 ppm FF for seven weeks. The incidences of preneoplastic foci were significantly increased in mice from the FF-treated groups. Immunohistochemistry revealed that significant increases in proliferating cell nuclear antigen (PCNA)-positive cells and cytokeratin 8/18 positive foci were observed in FF-treated groups. In addition, the transgene and several downstream molecules such as c- myc, c- jun, activating transcription factor 3 (ATF3), and cyclin D1 were overexpressed in these groups. These results suggest that the hepatocarcinogenic activity of rasH2 mice to FF can be detected in this hepatocarcinogenesis model and that up-regulation of genes for the ras/MAPK pathway and cell cycle was probably involved in the hepatocarcinogenic mechanism of rasH2 mice.

VRK1 phosphorylates CREB and mediates CCND1 expression

Vaccinia virus B1 kinase plays a key role in viral DNA replication. The homologous mammalian vaccinia-related kinases (VRKs) are also implicated in the regulation of DNA replication, although direct evidence remains elusive. Here we show that VRK1 regulates cell cycle progression in the DNA replication period by inducing cyclin D1 (CCND1) expression. Furthermore, depletion of VRK1 in human cancer cells reduces the fraction of cells in S phase at a given time. VRK1 specifically enhances activity of the cAMP-response element (CRE) in the CCND1 promoter by facilitating the recruitment of phospho-CREB to this locus. VRK1 phosphorylates CREB at Ser133 in vitro and the expression of a kinase-dead mutant of VRK1 or knockdown of VRK1 using siRNA fails to activate CREB and subsequently activate CRE. Finally, we show that VRK1 is a critical link in the CCND1 gene expression pathway stimulated by Myc overexpression. Our results indicate that VRK1 is a novel regulator of CCND1 expression.

Genes, chromosomes and the development of testicular germ cell tumors of adolescents and adults

Testicular germ cell tumors (TGCTs) of adults and adolescents are thought to be derived from primordial germ cells or gonocytes. TGCTs develop postpuberty from precursor lesions known as intratubular germ cell neoplasia undifferentiated. The tumors can be divided into two groups based on their histology and clinical behavior; seminomas resemble primordial germ cells or gonocytes and nonseminomas resemble embryonic or extraembryonic tissues at various stages of differentiation. The most undifferentiated form of nonseminoma, embryonal carcinoma, resembles embryonic stem cells in terms of morphology and expression profiling, both mRNAs and microRNAs. Evidence supports both environmental factors and genetic predisposition underlying the development of TGCTs. Various models of development have been proposed and are discussed. In TGCTs, gain of material from the short arm of chromosome 12 is invariable: genes from this region include the proto-oncogene KRAS, which has activating mutations in approximately 10% of tumors or is frequently overexpressed. A number of different approaches to increase the understanding of the development and progression of TGCTs have highlighted the involvement of KIT, RAS/RAF/MAPK, STAT, and PI3K/AKT signaling. We review the role of these signaling pathways in this process and the potential influence of environmental factors in the development of TGCTs.

Androgen receptor-dependent regulation of Bcl-xL expression: Implication in prostate cancer progression

BACKGROUND

Recently we reported that silencing the androgen receptor (AR) gene reduced Bcl-xL expression that was associated with a profound apoptotic cell death in prostate cancer cells. In this study we further investigated AR-regulated Bcl-xL expression.

METHODS

Prostate cancer cell line LNCaP and its sublines, LNCaP/PURO and LNCaP/Bclxl, were used for cell proliferation assay and xenograft experiments in nude mice. Luciferase gene reporters driven by mouse or human bcl-x gene promoter were used to determine androgen regulation of Bcl-xL expression. RT-PCR and Western blot assays were conducted to assess Bcl-xL gene expression. Chromatin immunoprecipitation assay was performed to determine AR interaction with Bcl-xL promoter. Bcl-xL-induced alteration of gene expression was examined using cDNA microarray assay.

RESULTS

In cultured prostate cancer LNCaP cells, androgen treatment significantly increased Bcl-xL expression at mRNA and protein levels via an AR-dependent mechanism. Promoter analyses demonstrated that the AR mediated androgen-stimulated bcl-x promoter activation and that the AR interacted with bcl-x promoter. Enforced expression of Bcl-xL gene dramatically increased cell proliferation in vitro and promoted xenograft tumor growth in vivo. Genome-wide gene profiling analysis revealed that Bcl-xL expression was significantly higher in metastatic and castration-resistant diseases compared to normal prostate tissues or primary cancers. Bcl-xL overexpression significantly increased the expression of cyclin D2, which might be responsible for Bcl-xL-induced cell proliferation and tumor growth.

CONCLUSIONS

Taken together, our data strongly suggest that androgen stimulates Bcl-xL expression via the AR and that increased Bcl-xL expression plays a versatile role in castration-resistant progression of prostate cancer.

Stromally expressed c-Jun regulates proliferation of prostate epithelial cells

Stromal-epithelial interactions play a critical role in development of benign prostatic hyperplasia. We have previously shown that stromal cells associated with prostatic carcinoma can potentiate proliferation and reduce cell death of prostatic epithelial cells. Genetic alterations in stromal cells affect stromal-epithelial interactions and modulate epithelial growth. The c-Jun proteins that are early transcription factor molecules have been shown to regulate stromal-epithelial interactions via paracrine signals. Moreover, the Jun-family member proteins have been shown to play an important role in proper development of the genitourinary organs. In this study, we show that c-Jun protein in fibroblasts regulates production and paracrine signals of insulin-like growth factor-1 (IGF-1). c-jun(+/+) fibroblasts secrete higher levels of IGF-1 and stimulate benign prostatic hyperplasia-1 cellular proliferation. In addition, stromally produced IGF-1 up-regulates epithelial mitogen-activated protein kinase, Akt, and cyclin D protein levels while down-regulating the cyclin-dependent kinase inhibitor p27. These data suggest that stromally expressed c-Jun may promote prostatic epithelial proliferation through IGF-1 as a paracrine signal that, in turn, can promote prostate epithelial proliferation. Identification of the signal transduction pathways between prostate epithelial cells and the surrounding stromal cells will improve our understanding of the normal and abnormal biology in prostatic diseases.

The small Rho GTPase Rac1 controls normal human dermal fibroblasts proliferation with phosphorylation of the oncoprotein c-myc

Proliferation of dermal fibroblasts is crucial for the maintenance of skin. The small Rho GTPase, Rac1, has been identified as a key transducer of proliferative signals in various cell types, but in normal human dermal fibroblasts its significance to cell growth control has not been studied. In this study, we applied the method of RNA interference to suppress endogenous Rac1 expression and examined the consequences on human skin fibroblasts. Rac1 knock-down resulted in inhibition of DNA synthesis. This effect was not mediated by inhibition of the central transducer of proliferative stimuli, ERK1/2 or by activation of the pro-apoptotic p38. Rather, as a consequence of the suppressed Rac1 expression we observed a significant decrease in phosphorylation of c-myc, revealing for the first time that in human fibroblasts Rac1 exerts control on proliferation through c-myc phosphorylation. Thus Rac1 activates proliferation of normal fibroblasts through stimulation of c-myc phosphorylation without affecting ERK1/2 activity.

CD30 Activates Both the Canonical and Alternative NF-κB Pathways in Anaplastic Large Cell Lymphoma Cells

CD30 is a member of the tumor necrosis factor receptor superfamily whose expression is up-regulated on anaplastic large cell lymphoma (ALCL) and Hodgkin lymphoma (HL) cells. Many different outcomes of CD30 stimulation have been reported, including cell cycle arrest, apoptosis, and activation of the prosurvival transcription factor, NF-kappaB, although this last activity is much less well defined in ALCL cells. In order to better understand the signaling properties of CD30 in cancer, we established a system for the stimulation of CD30 with its physiological ligand. Using this system, CD30 was stimulated on ALCL and HL cells, and the subsequent CD30 signaling properties were characterized. We show that a fraction of ALCL cells rapidly underwent apoptosis following CD30 stimulation, whereas HL cells were unaffected. The surviving ALCL cells exhibited robust activation of both the canonical and alternative NF-kappaB pathways as measured by nuclear translocation of RelA, p50, RelB, and p52, and this culminated in the transactivation of classical NF-kappaB-responsive genes. With prolonged CD30 stimulation, ALCL cells underwent cell cycle arrest that correlated with expression of the cell cycle inhibitor p21(waf1). Furthermore, p21(waf1) expression and cell cycle arrest were found to depend predominantly on the canonical NF-kappaB pathway, since it was reversed by RNA interference-mediated suppression of RelA. In contrast, suppression of the p100/p52 NF-kappaB subunit had little effect on p21(waf1). These data reveal that in ALCL cells, in contrast to other cell types, CD30 stimulation elicits p21(waf1)-mediated arrest through the canonical but not the alternative NF-kappaB pathway.

c-Jun NH2-terminal kinase 2 is required for Ras transformation independently of activator protein 1

Active Ras oncogene is expressed in approximately 30% of human cancers. Yet, very little is known about the molecular mechanisms responsible for its transforming potential. Here, we show that H-Ras-mediated transformation requires isoform 2 of the c-Jun-NH(2)-terminal kinase (JNK). H-Ras-transduced JNK2-deficient (Jnk2-/-) murine embryonic fibroblasts (MEFs) were severely inhibited in colony formation and growth in soft agar in vitro as well as in tumor formation in immunodeficient mice as compared with corresponding Jnk1-/- and wild-type MEFs. Accordingly, the RNA interference-based depletion of JNK2 form wild-type MEFs also resulted in defective Ras transformation. The extra barrier against H-Ras transformation in Jnk2-/- MEFs was not due to their inability to inactivate p53 signaling because all JNK2-deficient MEF lines had lost p19(Arf). Furthermore, expression of the E6 protein of the human papilloma virus failed to overcome the transformation defect. It could, however, be overcome by coexpression of H-Ras with the SV40 large T antigen or c-Myc. Surprisingly, the H-Ras-transduced JNK2-deficient MEFs exhibited higher activity of activator protein-1 and higher levels of c-Jun expression compared with H-Ras-transduced JNK1-deficient or wild-type cells, indicating that the key target of JNK2 during Ras transformation was divergent from activator protein-1. These results clearly show that a single kinase, JNK2, could control Ras transformation and thus point out a vulnerable control point that may prove important for the tumor development in general.

The possible mechanism of enhanced carcinogenesis induced by genotoxic carcinogens in rasH2 mice

Microarray and RT-PCR analyses were performed for the transgene and Ras-related genes in forestomach squamous cell carcinomas (SCCs) induced by 7,12-dimethylbenz[a]anthracene (DMBA) in rasH2 mice; these results were compared with our previous molecular data of N-ethyl-N-nitrosourea-induced forestomach SCCs and urethane-induced lung adenomas in rasH2 mice. Overexpression of the transgene was detected in the DMBA-induced SCCs, suggesting that the transgene plays an important role in enhanced carcinogenesis in rasH2 mice. In addition, the mouse endogenous ras genes were up-regulated in the DMBA-induced SCCs, and are probably involved in the tumorigenesis of forestomach SCCs. Genes such as osteopontin, Cks1b, Tpm1, Reck, gelsolin, and amphiregulin that were commonly altered in these three different carcinogen-induced tumors may contribute to the development of tumors in rasH2 mice.