Geranylgeranylated rho small GTPase(s) are essential for the degradation of p27Kip1 and facilitate the progression from G1 to S phase in growth-stimulated rat FRTL-5 cells

Redox regulation of macrophages

Redox signaling, a mode of signal transduction that involves the transfer of electrons from a nucleophilic to electrophilic molecule, has emerged as an essential regulator of inflammatory macrophages. Redox reactions are driven by reactive oxygen/nitrogen species (ROS and RNS) and redox-sensitive metabolites such as fumarate and itaconate, which can post-translationally modify specific cysteine residues in target proteins. In the past decade our understanding of how ROS, RNS, and redox-sensitive metabolites control macrophage function has expanded dramatically. In this review, we discuss the latest evidence of how ROS, RNS, and metabolites regulate macrophage function and how this is dysregulated with disease. We highlight the key tools to assess redox signaling and important questions that remain.

Decoding the crosstalk between mevalonate metabolism and T cell function

The mevalonate pathway is an essential metabolic pathway in T cells regulating development, proliferation, survival, differentiation, and effector functions. The mevalonate pathway is a complex, branched pathway composed of many enzymes that ultimately generate cholesterol and nonsterol isoprenoids. T cells must tightly control metabolic flux through the branches of the mevalonate pathway to ensure sufficient isoprenoids and cholesterol are available to meet cellular demands. Unbalanced metabolite flux through the sterol or the nonsterol isoprenoid branch is metabolically inefficient and can have deleterious consequences for T cell fate and function. Accordingly, there is tight regulatory control over metabolic flux through the branches of this essential lipid synthetic pathway. In this review we provide an overview of how the branches of the mevalonate pathway are regulated in T cells and discuss our current understanding of the relationship between mevalonate metabolism, cholesterol homeostasis and T cell function.

Anti-fibrotic effects of statin drugs: a review of evidence and mechanisms

Fibrosis is a pathological repair process common among organs, that responds to damage by replacement of tissue with non-functional connective tissue. Despite the widespread prevalence of tissue fibrosis, manifesting in numerous disease states across myriad organs, therapeutic modalities to prevent or alleviate fibrosis are severely lacking in quantity and efficacy. Alongside development of new drugs, repurposing of existing drugs may be a complementary strategy to elect anti-fibrotic compounds for pharmacologic treatment of tissue fibrosis. Drug repurposing can provide key advantages to de novo drug discovery, harnessing the benefits of previously elucidated mechanisms of action and already existing pharmacokinetic profiles. One class of drugs a wealth of clinical data and extensively studied safety profiles is the statins, a class of antilipidemic drugs widely prescribed for hypercholesterolemia. In addition to these widely utilized lipid-lowering effects, increasing data from cellular, pre-clinical mammalian, and clinical human studies have also demonstrated that statins are able to alleviate tissue fibrosis originating from a variety of pathological insults via lesser-studied, pleiotropic effects of these drugs. Here we review literature demonstrating evidence for direct effects of statins antagonistic to fibrosis, as well as much of the available mechanistic data underlying these effects. A more complete understanding of the anti-fibrotic effects of statins may enable a clearer picture of their anti-fibrotic potential for various clinical indications. Additionally, more lucid comprehension of the mechanisms by which statins exert anti-fibrotic effects may aid in development of novel therapeutic agents that target similar pathways but with greater specificity or efficacy.

USP28 controls SREBP2 and the mevalonate pathway to drive tumour growth in squamous cancer

SREBP2 is a master regulator of the mevalonate pathway (MVP), a biosynthetic process that drives the synthesis of dolichol, heme A, ubiquinone and cholesterol and also provides substrates for protein prenylation. Here, we identify SREBP2 as a novel substrate for USP28, a deubiquitinating enzyme that is frequently upregulated in squamous cancers. Our results show that silencing of USP28 reduces expression of MVP enzymes and lowers metabolic flux into this pathway. We also show that USP28 binds to mature SREBP2, leading to its deubiquitination and stabilisation. USP28 depletion rendered cancer cells highly sensitive to MVP inhibition by statins, which was rescued by the addition of geranyl-geranyl pyrophosphate. Analysis of human tissue microarrays revealed elevated expression of USP28, SREBP2 and MVP enzymes in lung squamous cell carcinoma (LSCC) compared to lung adenocarcinoma (LADC). Moreover, CRISPR/Cas-mediated deletion of SREBP2 selectively attenuated tumour growth in a KRas/p53/LKB1 mutant mouse model of lung cancer. Finally, we demonstrate that statins synergise with a dual USP28/25 inhibitor to reduce viability of SCC cells. Our findings suggest that combinatorial targeting of MVP and USP28 could be a therapeutic strategy for the treatment of squamous cell carcinomas.

Pitavastatin ameliorates autoimmune neuroinflammation by regulating the Treg/Th17 cell balance through inhibition of mevalonate metabolism

While Treg cells are responsible for self-tolerance and immune homeostasis, pathogenic autoreactive Th17 cells produce pro-inflammatory cytokines that lead to tissue damage associated with autoimmunity, as observed in multiple sclerosis. Therefore, the immunological balance between Th17 and Treg cells may represent a promising option for immune therapy. Statin drugs are used to treat dyslipidemia; however, besides their effects on preventing cardiovascular diseases, statins also have anti-inflammatory effects. Here, we investigated the role of pitavastatin on experimental autoimmune encephalomyelitis (EAE) and the differentiation of Treg and Th17 cells. EAE was induced by immunizing C57BL/6 mice with MOG35-55. EAE severity was determined by analyzing the clinical score and inflammatory parameters in the spinal cord. Naive CD4 T cells were cultured under Treg and Th17-skewing conditions in vitro in the presence of pitavastatin. We found that pitavastatin decreased EAE development, which was accompanied by a reduction of all parameters investigated. Pitavastatin also reduced the expression of IBA1 and pSTAT3 (Y705 and S727) in the spinal cords of EAE mice. Interestingly, the reduction of Th17 cell frequency in the draining lymph nodes of EAE mice treated with pitavastatin was followed by an increase of Treg cells. Indeed, pitavastatin directly affects T cell differentiation in vitro by decreasing Th17 and increasing Treg cell differentiation. Mechanistically, pitavastatin effects are dependent on mevalonate synthesis. Thus, our data show the potential anti-inflammatory effect of pitavastatin on the pathogenesis of the experimental neuroinflammation by modulating the Th17/Treg axis.

Role of RhoA-ROCK signaling in Parkinson's disease

Parkinson's disease (PD) is a complex and widespread neurodegenerative disease characterized by depletion of midbrain dopaminergic (DA) neurons. Key issues are the development of therapies that can stop or reverse the disease progression, identification of dependable biomarkers, and better understanding of the pathophysiological mechanisms of PD. RhoA-ROCK signals appear to have an important role in PD symptoms, making it a possible approach for PD treatment strategies. Activation of RhoA-ROCK (Rho-associated coiled-coil containing protein kinase) appears to stimulate various PD risk factors including aggregation of alpha-synuclein (αSyn), dysregulation of autophagy, and activation of apoptosis. This manuscript reviews current updates about the biology and function of the RhoA-ROCK pathway and discusses the possible role of this signaling pathway in causing the pathogenesis of PD. We conclude that inhibition of the RhoA-ROCK signaling pathway may have high translational potential and could be a promising therapeutic target in PD.

The Impact of Statin Therapy on the Survival of Patients with Gastrointestinal Cancer

Statins are 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors that may play an important role in the evolution of cancers, due to their effects on cancer cell metabolism. Statins affect several potential pathways, including cell proliferation, angiogenesis, apoptosis and metastasis. The number of trials assessing the putative clinical benefits of statins in cancer is increasing. Currently, there are several trials listed on the global trial identifier website clinicaltrials.gov. Given the compelling evidence from these trials in a variety of clinical settings, there have been calls for a clinical trial of statins in the adjuvant gastrointestinal cancer setting. However, randomized controlled trials on specific cancer types in relation to statin use, as well as studies on populations without a clinical indication for using statins, have elucidated some potential underlying biological mechanisms, and the investigation of different statins is probably warranted. It would be useful for these trials to incorporate the assessment of tumour biomarkers predictive of statin response in their design. This review summarizes the recent preclinical and clinical studies that assess the application of statins in the treatment of gastrointestinal cancers with particular emphasize on their association with cancer risk.

Role of Anillin in Tumour: From a Prognostic Biomarker to a Novel Target

Anillin (ANLN), an actin-binding protein, reportedly plays a vital role in cell proliferation and migration, particularly in cytokinesis. Although there have been findings pointing to a contribution of ANLN to the development of cancer, the association of ANLN to cancer remains not fully understood. Here, we gather evidence to determine the applicability of ANLN as a prognostic tool for some types of cancer, and the impact that ANLN has on the hallmarks of cancer. We searched academic repositories including PubMed and Google Scholar to find and review studies related to cancer and ANLN. The conclusion is that ANLN could be a potent target for cancer treatment, but the roles ANLN, other than in cytokinesis and its influence on tumour microenvironment remodeling in cancer development, must be further elucidated, and specific ANLN inhibitors should be found.

Fatty acid desaturase 2 is up-regulated by the treatment with statin through geranylgeranyl pyrophosphate-dependent Rho kinase pathway in HepG2 cells

Statins have been reported to increase the plasma concentration of arachidonic acid (AA), an omega-6 long chain polyunsaturated fatty acid (LCPUFA) in several clinical studies indicating that statins affect the endogenous synthesis of LCUFAs. In the present study, we investigated the roles of the intrinsic mevalonate cascade and Rho-dependent pathway in LCPUFA synthesis, especially focusing on fatty acid desaturases (Fads) 2, using the human hepatocellular carcinoma cell line HepG2. Cell number and the activity of caspase-3 and 7 (caspase-3/7) was measured using a commercial kit. Gene expression was analyzed by quantitative real-time PCR. Protein expression was detected by Western blot analysis. Atorvastatin decreased cell viability and increased caspase-3/7 activity in a dose-dependent manner. At lower concentrations, atorvastatin stimulated both mRNA and protein expression of Fads2, and increased mRNA expression of FADS1 and ELVOL5. Both mevalonate and geranylgeranyl-pyrophosphate (GGPP), but not cholesterol, fully reversed atorvastatin-induced upregulation of Fads2, and mevalonate-effected reversal was inhibited by treatment with the Rho-associated protein kinase inhibitor Y-27632. These data clearly demonstrated that in human HepG2 cells, statins affect the endogenous synthesis of LCPUFAs by regulation of not only Fads2, but also Fads1 and Elovl5, through the GGPP-dependent Rho kinase pathway.

Statin drugs to reduce breast cancer recurrence and mortality

Epidemiologic studies have, variably, shown the concomitant use of statin drugs to be beneficial to cancer outcomes. Statin drugs have been FDA approved for three decades for the treatment of high cholesterol and atherosclerotic coronary artery disease and are widely used. This has engendered studies as to their influence on concomitant diseases, including cancers. In this context, statin use has been correlated, variably, with a decrease in deaths from breast cancer. However, there is no extant model for this effect, and the extent of efficacy is open to question.The overarching goal of this article is to communicate to the reader of the potential of statins to reduce breast cancer progression and mortality. This is the use as a secondary prevention measure, and not as a therapy to directly counter active cancer. First, salient aspects of statin pharmacology, as relates to cardiovascular disease, will be discussed. Second, the basic and clinical research studies that investigate statin usage in breast cancer will be presented. Additionally, statin effects in other cancer types will be included for context. Finally, proposals for future basic and clinical research studies to determine the role of statins in breast cancer management will be presented.

The antiangiogenic effects of polyisoprenylated cysteinyl amide inhibitors in HUVEC, chick embryo and zebrafish is dependent on the polyisoprenyl moiety

Angiogenesis is essential for solid tumor growth, therapeutic resistance and metastasis, the latest accounting for 90% of cancer deaths. Although angiogenesis is essential for the malignant transformations in solid tumors and therefore is an attractive target, few drugs are available that block tumor angiogenesis. The focus has been to block signaling by receptor tyrosine kinases (RTKs), such as for vascular endothelial growth factor (VEGF), whose activation abrogate apoptosis and promote angiogenesis. The polyisoprenylated cysteinyl amide inhibitors (PCAIs) were designed to modulate aberrant polyisoprenylated small G-proteins such as mutant Ras whose constitutive activation promotes RTKs signaling. Since polyisoprenylation is essential for protein-protein interactions and functions of G-proteins, we hypothesized that the PCAIs would disrupt the monomeric G-protein signaling thereby effectively inhibiting angiogenesis. In this study we determined the effects of PCAIs on human umbilical vein endothelial cells (HUVEC) tube formation, cell viability, cell migration and invasion as well as in vivo using the chick chorioallantoic membrane (CAM) and zebrafish models. At sub- to low micromolar concentrations, the PCAIs inhibit the native and VEGF-stimulated cell migration and invasion as well as tube formation and angiogenesis in CAM and zebrafish embryos. The concentrations that block the angiogenic processes were lower than those that induce cell death. Since angiogenesis is essential for tumor growth but otherwise limited to wound healing, feeding fat cells and uterine wall repair in adults, it is conceivable that these compounds can be developed into safer therapeutics for cancers and retinal neovascularization that leads to loss of vision.

Atorvastatin increases Fads1, Fads2 and Elovl5 gene expression via the geranylgeranyl pyrophosphate-dependent Rho kinase pathway in 3T3-L1 cells

Numerous clinical studies have reported that statins increase the plasma concentration of arachidonic acid, which is an ω-6 long-chain polyunsaturated fatty acid (LCPUFA), and decrease the concentrations of eicosapentaenoic acid and docosahexaenoic acid, which are ω‑3 LCPUFAs. These findings indicate that statins may affect the endogenous synthesis of LCPUFAs, which is regulated by fatty acid desaturases (FADSs) and elongation of very long‑chain fatty acids proteins (ELOVLs). The present study aimed to investigate the roles of the intrinsic mevalonate cascade and Rho‑dependent pathway in statin‑induced regulation of these desaturases and elongases, as well as cell viability using mouse 3T3‑L1 cells. mRNA expression was analyzed by quantitative polymerase chain reaction. Treatment with atorvastatin decreased cell viability and increased the mRNA expression levels of Fads1, Fads2 and ELOVL fatty acid elongase 5 (Elovl5) in a dose‑dependent manner. Mevalonate and geranylgeranyl pyrophosphate (GGPP), but not cholesterol, fully reversed the atorvastatin‑induced downregulation of cell viability and upregulation of gene expression; however, mevalonate itself did not affect cell viability and gene expression. The Rho‑associated protein kinase inhibitor Y‑27632 inhibited the mevalonate‑ and GGPP‑mediated reversal of atorvastatin‑induced upregulation of Fads1, Fads2 and Elovl5. These findings indicated that statins may affect the endogenous synthesis of LCPUFAs by regulating Fads1, Fads2 and Elovl5 gene expression via the GGPP‑dependent Rho kinase pathway in mouse 3T3-L1 cells.

RhoA phosphorylation mediated by Rho/RhoA-associated kinase pathway improves the anti-freezing potentiality of murine hatched and diapaused blastocysts

Embryonic cryopreservation has a relatively low survival rate because of cytoskeletal damage. However, molecular anti-freezing mechanisms have been largely unexplored. This study investigated the significance of RhoA, involved in embryonic development, and the Rho/RhoA-associated kinase (ROCK) signalling pathway in cryopreservation. The anti-freezing mechanism in murine dormant embryos, compared with normal blastocysts, was assessed by combining molecular, physiological and pharmacological approaches. Real-time PCR and western blotting experiments showed high RhoA expression in cryo-dormant and dormant embryos. RhoA GTPases were overexpressed on the surface of trophectoderm cells in dormant embryos. Treatment with Y-27632, a ROCK antagonist, decreased survival of both normal and dormant blastocysts, while recombinant RhoA protein remarkably increased survival, after freeze-thawing, of normal hatched blastocysts. Our findings elucidated the molecular mechanism of anti-freezing, involving RhoA phosphorylation, meditated by the Rho/ROCK signalling pathway, in hatched and diapaused murine blastocysts. In addition, evidence for a potentially protective additive suggests a new method for improving the anti-freezing potential of mammalian embryos, without protecting the zona pellucida.

Alteration of protein prenylation promotes spermatogonial differentiation and exhausts spermatogonial stem cells in newborn mice

Spermatogenesis in adulthood depends on the successful neonatal establishment of the spermatogonial stem cell (SSC) pool and gradual differentiation during puberty. The stage-dependent changes in protein prenylation in the seminiferous epithelium might be important during the first round of spermatogenesis before sexual maturation, but the mechanisms are unclear. We have previous found that altered prenylation in Sertoli cells induced spermatogonial apoptosis in the neonatal testis, resulting in adult infertility. Now we further explored the role of protein prenylation in germ cells, using a conditional deletion of geranylgeranyl diphosphate synthase (Ggpps) in embryonic stage and postmeiotic stage respectively. We observed infertility of Ggpps(-/-) Ddx4-Cre mice that displayed a Sertoli-cell-only syndrome phenotype, which resulted from abnormal spermatogonial differentiation and SSC depletion during the prepubertal stage. Analysis of morphological characteristics and cell-specific markers revealed that spermatogonial differentiation was enhanced from as early as the 7(th) postnatal day in the first round of spermatogenesis. Studies of the molecular mechanisms indicated that Ggpps deletion enhanced Rheb farnesylation, which subsequently activated mTORC1 and facilitated spermatogonial differentiation. In conclusion, the prenylation balance in germ cells is crucial for spermatogonial differentiation fate decision during the prepubertal stage, and the disruption of this process results in primary infertility.

Statin-induced depletion of geranylgeranyl pyrophosphate inhibits cell proliferation by a novel pathway of Skp2 degradation

Statins, such as lovastatin, can induce a cell cycle arrest in the G1 phase. This robust antiproliferative activity remains intact in many cancer cells that are deficient in cell cycle checkpoints and leads to an increased expression of CDK inhibitor proteins p27Kip1 and p21Cip1. The molecular details of this statin-induced growth arrest remains unclear. Here we present evidence that lovastatin can induce the degradation of Skp2, a subunit of the SCFSkp2 ubiquitin ligase that targets p27Kip1 and p21Cip1 for proteasomal destruction. The statin-induced degradation of Skp2 is cell cycle phase independent and does not require its well characterised degradation pathway mediated by APC/CCdh1- or Skp2 autoubiquitination. An N-terminal domain preceding the F-box of Skp2 is both necessary and sufficient for its statin mediated degradation. The degradation of Skp2 results from statin induced depletion of geranylgeranyl isoprenoid intermediates of cholesterol biosynthesis. Inhibition of geranylgeranyl-transferase-I also promotes APC/CCdh1- independent degradation of Skp2, indicating that de-modification of a geranylgeranylated protein triggers this novel pathway of Skp2 degradation.

MARCKS Signaling Differentially Regulates Vascular Smooth Muscle and Endothelial Cell Proliferation through a KIS-, p27kip1- Dependent Mechanism

Background

Overexpression of the myristolated alanine-rich C kinase substrate (MARCKS) occurs in vascular proliferative diseases such as restenosis after bypass surgery. MARCKS knockdown results in arrest of vascular smooth muscle cell (VSMC) proliferation with little effect on endothelial cell (EC) proliferation. We sought to identify the mechanism of differential regulation by MARCKS of VSMC and EC proliferation in vitro and in vivo.

Methods and Results

siRNA-mediated MARCKS knockdown in VSMCs inhibited proliferation and prevented progression from phase G₀/G₁ to S. Protein expression of the cyclin-dependent kinase inhibitor p27^kip1, but not p21^cip1 was increased by MARCKS knockdown. MARCKS knockdown did not affect proliferation in VSMCs derived from p27^kip1-/- mice indicating that the effect of MARCKS is p27^kip1-dependent. MARCKS knockdown resulted in decreased phosphorylation of p27^kip1 at threonine 187 and serine 10 as well as, kinase interacting with stathmin (KIS), cyclin D1, and Skp2 expression. Phosphorylation of p27^kip1 at serine 10 by KIS is required for nuclear export and degradation of p27^kip1. MARCKS knockdown caused nuclear trapping of p27^kip1. Both p27^kip1 nuclear trapping and cell cycle arrest were released by overexpression of KIS, but not catalytically inactive KIS. In ECs, MARCKS knockdown paradoxically increased KIS expression and cell proliferation. MARCKS knockdown in a murine aortic injury model resulted in decreased VSMC proliferation determined by bromodeoxyuridine (BrdU) integration assay, and inhibition of vascular wall thickening. MARCKS knockdown increased the rate of re-endothelialization.

Conclusions

MARCKS knockdown arrested VSMC cell cycle by decreasing KIS expression. Decreased KIS expression resulted in nuclear trapping of p27^kip1 in VSMCs. MARCKS knockdown paradoxically increased KIS expression in ECs resulting in increased EC proliferation. MARCKS knockdown significantly attenuated the VSMC proliferative response to vascular injury, but accelerated reestablishment of an intact endothelium. MARCKS is a novel translational target with beneficial cell type-specific effects on both ECs and VSMCs.

Preclinical model for identification of therapeutic targets for CML offers clues for handling imatinib resistance

Success of imatinib in chronic myeloid leukemia (CML) therapy has undoubtedly proved utility of signalling molecules as therapeutic targets. However, development of imatinib resistance and progression to blastic crisis are the current challenges in clinics. To develop therapeutic alternatives for CML, understanding of signalling events downstream of bcr-abl might be helpful. Current CML cell lines do not give comprehensive picture of signalling events involved in pathogenesis of CML. Hence, there is a major unmet need for a better preclinical model for CML. Here, we report on development of RIN9815/bcr-abl, a novel cell line model that mimics signalling events in CML PMNL. Studies on crucial signalling molecules i.e., ras, rac, rhoA and actin in this cell line identified rhoA as the key regulator involved in CML cell function as well as proliferation of both, imatinib sensitive and resistant cells. Hence, RIN9815/bcr-abl could serve as the unique preclinical model in understanding pathogenesis of CML and in drug development.

Lovastatin and perillyl alcohol inhibit glioma cell invasion, migration, and proliferation--impact of Ras-/Rho-prenylation

Alterations in small GTPase mediated signal transduction pathways have emerged as a central step in the molecular pathogenesis of glioblastoma (GBM), the most common malignant brain tumor in adults. Farnesylpyrophosphate (FPP) and geranylgeranylpyrophosphate (GGPP) are derived from mevalonate, whose production is catalyzed by 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase. Prenylation by FPP and GGPP is required for membrane insertion and oncogenic function of Ras- and Rho-proteins, within the stimulation of the Ras-Raf-MEK-ERK pathway. A straightforward prediction from HMG-CoA reductase inhibitor studies is that statins decrease FPP and GGPP levels and diminish ERK signaling ensuring less proliferation and migration of cancer cells. Perillyl alcohol (POH), a naturally occurring monoterpene inhibits prenyltransferases and is able to inhibit cancer cell growth, but the underlying mechanism is still unclear. We here report that lovastatin (LOV) and POH impair the regulation of the mevalonate- and the Ras-Raf-MEK-ERK pathway in U87 and U343 glioblastoma cells. Both compounds affected the post-translational modification of H-Ras and Rac1. While LOV diminished the substrates of the transferase reaction that catalyze prenylation, POH inhibited the enzymes itself. Our data highlight the impact of isoprenoids for post-translational modification of small GTPases promoting proliferation, migration and invasion capabilities in glioma cells.

RHOA inactivation enhances Wnt signalling and promotes colorectal cancer

Activation of the small GTPase RHOA has strong oncogenic effects in many tumour types, although its role in colorectal cancer remains unclear. Here we show that RHOA inactivation contributes to colorectal cancer progression/metastasis, largely through the activation of Wnt/β-catenin signalling. RhoA inactivation in the murine intestine accelerates the tumorigenic process and in human colon cancer cells leads to the redistribution of β-catenin from the membrane to the nucleus and enhanced Wnt/β-catenin signalling, resulting in increased proliferation, invasion and de-differentiation. In mice, RHOA inactivation contributes to colon cancer metastasis and reduced RHOA levels were observed at metastatic sites compared with primary human colon tumours. Therefore, we have identified a new mechanism of activation of Wnt/β-catenin signalling and characterized the role of RHOA as a novel tumour suppressor in colorectal cancer. These results constitute a shift from the current paradigm and demonstrate that RHO GTPases can suppress tumour progression and metastasis.

Developmental processes regulated by the 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) pathway: highlights from animal studies

The 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) is the rate-limiting enzyme in the biosynthesis of cholesterol and isoprenoids, which are substrates required for post-translational modification of signalling proteins that can potentially regulate various aspects of embryonic development. The HMGCR transcripts are detectable during early embryogenesis in both invertebrates and vertebrates, which suggests a conserved developmental requirement for mevalonate derivatives. Consistently, recent animal and in vitro studies have yielded valuable insights into potential morphogenic parameters that are modulated by HMGCR activity. These developmental end-points include brain and craniofacial morphogenesis, PGC migration and survival, myocardial epithelial migration and fusion, EC migration and survival, and vascular stabilization. By providing a synthesis of these studies, we hope that this review will highlight the need to comprehensively examine the entire suite of developmental processes regulated by HMGCR.

SUMOylation of RhoGDIα is required for its repression of cyclin D1 expression and anchorage-independent growth of cancer cells

Selective activation of Rho GTPase cascade requires the release of Rho from RhoGDI (GDP-dissociation inhibitors) complexes. Our previous studies identified RhoGDIα SUMOylation at Lys-138 and its function in the regulation of cancer cell invasion. In the current study, we demonstrate that RhoGDIα SUMOylation has a crucial role in the suppression of cancer cell anchorage-independent growth as well as the molecular mechanisms underlying this suppression. We found that ectopic expression of RhoGDIα resulted in marked inhibition of an anchorage-independent growth with induction of G0/G1 cell cycle arrest, while point mutation of RhoGDIα SUMOylation at residue Lys-138 (K138R) abrogated this growth suppression and G0/G1 cell cycle arrest in cancer cells. Further studies showed that SUMOylation at Lys-138 was critical for RhoGDIα down-regulation of cyclin D1 protein expression and that MEK1/2-Erk was a specific downstream target of SUMOylated RhoGDIα for its inhibition of C-Jun/AP-1 cascade, cyclin d1 transcription, and cell cycle progression. These results strongly demonstrate that SUMOylated RhoGDIα suppressed C-Jun/AP-1-dependent transactivation specifically via targeting MEK1/2-Erk, subsequently leading to the down-regulation of cyclin D1 expression and anti-cancer activity. Our results provide new mechanistic insights into the understanding of essential role of SUMOylation at Lys-138 in RhoGDIα's biological function.

Strategies for anti-fibrotic therapies

The fibrotic diseases encompass a wide spectrum of entities including such multisystemic diseases as systemic sclerosis, nephrogenic systemic fibrosis and sclerodermatous graft versus host disease, as well as organ-specific disorders such as pulmonary, liver, and kidney fibrosis. Collectively, given the wide variety of affected organs, the chronic nature of the fibrotic processes, and the large number of individuals suffering their devastating effects, these diseases pose one of the most serious health problems in current medicine and a serious economic burden to society. Despite these considerations there is currently no accepted effective treatment. However, remarkable progress has been achieved in the elucidation of their pathogenesis including the identification of the critical role of myofibroblasts and the determination of molecular mechanisms that result in the transcriptional activation of the genes responsible for the fibrotic process. Here we review the origin of the myofibroblast and discuss the crucial regulatory pathways involving multiple growth factors and cytokines that participate in the pathogenesis of the fibrotic process. Potentially effective therapeutic strategies based upon this new information are considered in detail and the major challenges that remain and their possible solutions are presented. It is expected that translational efforts devoted to convert this new knowledge into novel and effective anti-fibrotic drugs will be forthcoming in the near future. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

Mevalonate metabolism regulates Basal breast cancer stem cells and is a potential therapeutic target

There is increasing evidence that breast tumors are organized in a hierarchy, with a subpopulation of tumorigenic cancer cells, the cancer stem cells (CSCs), which sustain tumor growth. The characterization of protein networks that govern CSC behavior is paramount to design new therapeutic strategies targeting this subpopulation of cells. We have sought to identify specific molecular pathways of CSCs isolated from 13 different breast cancer cell lines of luminal or basal/mesenchymal subtypes. We compared the gene expression profiling of cancer cells grown in adherent conditions to those of matched tumorsphere cultures. No specific pathway was identified to be commonly regulated in luminal tumorspheres, resulting from a minor CSC enrichment in tumorsphere passages from luminal cell lines. However, in basal/mesenchymal tumorspheres, the enzymes of the mevalonate metabolic pathway were overexpressed compared to those in cognate adherent cells. Inhibition of this pathway with hydroxy-3-methylglutaryl CoA reductase blockers resulted in a reduction of breast CSC independent of inhibition of cholesterol biosynthesis and of protein farnesylation. Further modulation of this metabolic pathway demonstrated that protein geranylgeranylation (GG) is critical to breast CSC maintenance. A small molecule inhibitor of the geranylgeranyl transferase I (GGTI) enzyme reduced the breast CSC subpopulation both in vitro and in primary breast cancer xenografts. We found that the GGTI effect on the CSC subpopulation is mediated by inactivation of Ras homolog family member A (RHOA) and increased accumulation of P27(kip1) in the nucleus. The identification of protein GG as a major contributor to CSC maintenance opens promising perspectives for CSC targeted therapy in basal breast cancer.

Thyroglobulin (Tg) activates MAPK pathway to induce thyroid cell growth in the absence of TSH, insulin and serum

The growth of thyroid cells is tightly regulated by thyroid stimulating hormone (TSH) through the cyclic adenosine 3', 5'-monophosphate (cAMP) signaling pathway by potentiating the mitogenic activity of insulin and insulin-like growth factors (IGFs). However, we recently reported that thyroglobulin (Tg), a major product of the thyroid, also induces the growth of thyroid cells cultured in 0.2% serum in the absence of TSH and insulin. In this report, we demonstrate that Tg induced phosphorylation of molecules of the c-Raf/MEK/ERK pathway of the mitogen-activated protein kinase (MAPK). The MEK-1/2 inhibitor PD98059 suppressed Tg-induced phosphorylation of ERK1/2 and reduced bromodeoxyuridine (BrdU) incorporation. Tg also induced expression of the essential transcriptional factors c-Myc, c-Fos and c-Jun and phosphorylation of the retinoblastoma (Rb) protein. The present results, together with the previous report, suggest that Tg utilizes multiple signaling cascades to induce thyroid cell growth independent of TSH/cAMP stimulation.

Ect2, an ortholog of Drosophila Pebble, regulates formation of growth cones in primary cortical neurons

In collaboration with Marshall Nirenberg, we performed in vivo RNA interference (RNAi) genome-wide screening in Drosophila embryos. Pebble has been shown to be involved in Drosophila neuronal development. We have also reported that depletion of Ect2, a mammalian ortholog of Pebble, induces differentiation in NG108-15 neuronal cells. However, the precise role of Ect2 in neuronal development has yet to be studied. Here, we confirmed in PC12 pheochromocytoma cells that inhibition of Ect2 expression by RNAi stimulated neurite outgrowth, and in the mouse embryonic cortex that Ect2 was accumulated throughout the ventricular and subventricular zones with neuronal progenitor cells. Next, the effects of Ect2 depletion were studied in primary cultures of mouse embryonic cortical neurons: Loss of Ect2 did not affect the differentiation stages of neuritogenesis, the number of neurites, or axon length, while the numbers of growth cones and growth cone-like structures were increased. Taken together, our results suggest that Ect2 contributes to neuronal morphological differentiation through regulation of growth cone dynamics.

Pharmacological actions of statins: a critical appraisal in the management of cancer

Statins, among the most commonly prescribed drugs worldwide, are cholesterol-lowering agents used to manage and prevent cardiovascular and coronary heart diseases. Recently, a multifaceted action in different physiological and pathological conditions has been also proposed for statins, beyond anti-inflammation and neuroprotection. Statins have been shown to act through cholesterol-dependent and -independent mechanisms and are able to affect several tissue functions and modulate specific signal transduction pathways that could account for statin pleiotropic effects. Typically, statins are prescribed in middle-aged or elderly patients in a therapeutic regimen covering a long life span during which metabolic processes, aging, and concomitant novel diseases, including cancer, could occur. In this context, safety, toxicity, interaction with other drugs, and the state of health have to be taken into account in subjects treated with statins. Some evidence has shown a dichotomous effect of statins with either cancer-inhibiting or -promoting effects. To date, clinical trials failed to demonstrate a reduced cancer occurrence in statin users and no sufficient data are available to define the long-term effects of statin use over a period of 10 years. Moreover, results from clinical trials performed to evaluate the therapeutic efficacy of statins in cancer did not suggest statin use as chemotherapeutic or adjuvant agents. Here, we reviewed the pharmacology of the statins, providing a comprehensive update of the current knowledge of their effects on tissues, biological processes, and pathological conditions, and we dissected the disappointing evidence on the possible future use of statin-based drugs in cancer therapy.

Identification and characterization of mechanism of action of P61-E7, a novel phosphine catalysis-based inhibitor of geranylgeranyltransferase-I

Small molecule inhibitors of protein geranylgeranyltransferase-I (GGTase-I) provide a promising type of anticancer drugs. Here, we first report the identification of a novel tetrahydropyridine scaffold compound, P61-E7, and define effects of this compound on pancreatic cancer cells. P61-E7 was identified from a library of allenoate-derived compounds made through phosphine-catalyzed annulation reactions. P61-E7 inhibits protein geranylgeranylation and blocks membrane association of geranylgeranylated proteins. P61-E7 is effective at inhibiting both cell proliferation and cell cycle progression, and it induces high p21(CIP1/WAF1) level in human cancer cells. P61-E7 also increases p27(Kip1) protein level and inhibits phosphorylation of p27(Kip1) on Thr187. We also report that P61-E7 treatment of Panc-1 cells causes cell rounding, disrupts actin cytoskeleton organization, abolishes focal adhesion assembly and inhibits anchorage independent growth. Because the cellular effects observed pointed to the involvement of RhoA, a geranylgeranylated small GTPase protein shown to influence a number of cellular processes including actin stress fiber organization, cell adhesion and cell proliferation, we have evaluated the significance of the inhibition of RhoA geranylgeranylation on the cellular effects of inhibitors of GGTase-I (GGTIs). Stable expression of farnesylated RhoA mutant (RhoA-F) results in partial resistance to the anti-proliferative effect of P61-E7 and prevents induction of p21(CIP1/WAF1) and p27(Kip1) by P61-E7 in Panc-1 cells. Moreover, stable expression of RhoA-F rescues Panc-1 cells from cell rounding and inhibition of focal adhesion formation caused by P61-E7. Taken together, these findings suggest that P61-E7 is a promising GGTI compound and that RhoA is an important target of P61-E7 in Panc-1 pancreatic cancer cells.

Deleted in liver cancer 2 suppresses cell growth via the regulation of the Raf-1-ERK1/2-p70S6K signalling pathway

BACKGROUND

Deleted in liver cancer 2 (DLC2) gene, a putative tumour suppressor gene, encodes a Rho GTPase-activating protein (RhoGAP) with GAP activity specific for RhoA. It exhibits tumour suppressor functions and inhibits tumour cell proliferation, migration as well as transformation.

AIMS

In this study, we aimed to investigate the underlying mechanisms of the DLC2 gene in suppressing cell migration and cell growth. HepG2 hepatoma cells were stably transfected with the DLC2γ isoform, which contains the RhoGAP domain.

METHODS AND RESULTS

On performing immunofluorescence staining and Western blot analysis, the expression of the focal adhesion protein paxillin was found to be much reduced in DLC2γ-stable clones. Upon flow cytometric analysis of the cell cycle profiles, the DLC2γ-stable clones were shown to have a higher population of cells arrested at the G1 phase than the EGFP vector-stable clone, suggesting that downregulation of RhoA activity in DLC2γ-stable clones inhibited cell cycle progression. In the DLC2γ-stable clone, the levels of Raf-1 and extracellular signal-regulated kinase (ERK) 1/2 were decreased as compared with those of the parental HepG2, EGFP vector and DLC2γ-GAP defective mutant-stable clones. Furthermore, the ribosomal kinase p70S6K, a downstream target of ERK1/2, was suppressed in the DLC2-stable clones. On the contrary, when DLC2 was knocked down by siRNA in HepG2 cells, the expression levels of phospho-p70S6K and phospho-ERK1/2 were upregulated.

CONCLUSION

Our data show that DLC2 inhibits the activity of Raf-1-ERK1/2-p70S6K via its RhoGAP function, resulting in the suppression of cell growth. Further studies on the molecular signalling between DLC2 and p70S6K may provide an insight into its growth suppressor function.

Thyroglobulin (Tg) induces thyroid cell growth in a concentration-specific manner by a mechanism other than thyrotropin/cAMP stimulation

Thyroglobulin (Tg), a major product of the thyroid gland, serves as a macromolecular precursor of thyroid hormone biosynthesis. In addition, Tg stored in the thyroid follicles is a potent regulator of thyroid-specific gene expression. In conjunction with thyroid stimulating hormone (TSH) and iodide, Tg regulates thyroid follicle function, which is the minimal functional unit of the thyroid gland. In the present study, we show that Tg stimulates growth of FRTL-5 thyroid cells in the absence of TSH, insulin and serum. Unlike TSH, Tg did not increase cellular cyclic AMP (cAMP) levels; rather, the TSH signal counteracted Tg-induced cell growth. A specific inhibitor of A-kinase, H-89, did not modulate the effect of Tg. Tg increased kinase activity of Akt to the same level as TSH, insulin and 5% serum, while LY294002 abolished Tg-induced growth. Interestingly, low Tg concentrations maximized growth-promotion activity and induction of the apical iodide transporter (PDS; SLC26A4), whereas high Tg concentrations suppressed both cell growth and the expression of thyroid-specific genes. These results suggest that a low levels of Tg in the follicular lumen might stimulates cell growth and iodide transport to accelerate the iodide organification process; however, elevated Tg levels in the follicle might then shut down all of these functions.

cAMP activation by PACAP/VIP stimulates IL-6 release and inhibits osteoblastic differentiation through VPAC2 receptor in osteoblastic MC3T3 cells

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP), a member of the glucagon/vasoactive intestinal peptide (VIP) superfamily, stimulates cyclic AMP accumulation initiating a variety of biological processes such as: neurotropic actions, immune and pituitary function, learning and memory, catecholamine biosynthesis and regulation of cardiopulmonary function. Both osteoclasts and osteoblasts have been shown to express receptors for PACAP/VIP implicated in their role in bone metabolism. To further understand the role of PACAP/VIP family in controlling bone metabolism, we investigated differentiation model of MC3T3-E1 cells, an osteoblastic cell line derived from mouse calvaria. Quantitative RT-PCR analysis demonstrated that MC3T3-E1 cells expressed only VPAC2 receptor and its expression was upregulated during osteoblastic differentiation, whereas VPAC1 and PAC1 receptors were not expressed. Consistent with expression of receptor subtype, both PACAP and VIP stimulate cAMP accumulation in a time- and dose-dependent manner with the similar potency in undifferentiated and differentiated cells, while Maxadilan, a specific agonist for PAC1-R, did not. Furthermore, downregulation of VPAC2-R by siRNA completely blocked cAMP response mediated by PACAP and VIP. Importantly, PACAP/VIP as well as forskolin markedly suppressed the induction of alkaline phosphatase mRNA upon differentiation and the pretreatment with 2',5'-dideoxyadenosine, a cAMP inhibitor, restored its inhibitory effect of PACAP. We also found that PACAP and VIP stimulated IL-6 release, a stimulator of bone resorption, and VPAC2-R silencing inhibited IL-6 production. Thus, PACAP/VIP can activate adenylate cyclase response and regulate IL-6 release through VPAC2 receptor with profound functional consequences for the inhibition of osteoblastic differentiation in MC3T3-E1 cells.

Blockade of protein geranylgeranylation inhibits Cdk2-dependent p27Kip1 phosphorylation on Thr187 and accumulates p27Kip1 in the nucleus: implications for breast cancer therapy

We describe the design of a potent and selective peptidomimetic inhibitor of geranylgeranyltransferase I (GGTI), GGTI-2418, and its methyl ester GGTI-2417, which increases the levels of the cyclin-dependent kinase (Cdk) inhibitor p27(Kip1) and induces breast tumor regression in vivo. Experiments with p27(Kip1) small interfering RNA in breast cancer cells and p27(Kip1) null murine embryonic fibroblasts demonstrate that the ability of GGTI-2417 to induce cell death requires p27(Kip1). GGTI-2417 inhibits the Cdk2-mediated phosphorylation of p27(Kip1) at Thr187 and accumulates p27(Kip1) in the nucleus. In nude mouse xenografts, GGTI-2418 suppresses the growth of human breast tumors. Furthermore, in ErbB2 transgenic mice, GGTI-2418 increases p27(Kip1) and induces significant regression of breast tumors. We conclude that GGTIs' antitumor activity is, at least in part, due to inhibiting Cdk2-dependent p27(Kip1) phosphorylation at Thr187 and accumulating nuclear p27(Kip1). Thus, GGTI treatment might improve the poor prognosis of breast cancer patients with low nuclear p27(Kip1) levels.

Distinct modes of activation of phosphatidylinositol 3-kinase in response to cyclic adenosine 3', 5'-monophosphate or insulin-like growth factor I play different roles in regulation of cyclin D1 and p27Kip1 in FRTL-5 cells

Bioactivities of IGFs in various cells are often potentiated in the presence of other hormones. In previous studies we showed that pretreatment of rat FRTL-5 thyroid cells with TSH or other cAMP-generating agents markedly potentiated DNA synthesis induced by IGF-I. Under these conditions we found that phosphatidylinositol (PI) 3-kinase was activated in response to either cAMP or IGF stimulus, and both activation modes were indispensable for the potentiation of DNA synthesis. The present studies were undertaken to elucidate how cAMP and/or IGF-I stimulus regulated the G1 cyclin-cyclin dependent kinase (CDK)-inhibitor system, and to determine the roles of PI 3-kinase activation by cAMP or IGF-I stimulus in this system. We found that cAMP pretreatment enhanced IGF-I-dependent increases in cyclin D1, due to synergistic increases in mRNA and elevation of translation rates. Furthermore, cAMP pretreatment enhanced IGF-I-induced protein degradation of the CDK inhibitor, p27(Kip1). These changes well explained an increase in cyclin E, leading to marked activation of G1 CDKs, followed by retinoblastoma protein phosphorylation. Our results using a PI 3-kinase inhibitor showed that cAMP-dependent PI 3-kinase activation plays an important role in the increase in cyclin D1 translation. In contrast, IGF-I-dependent PI 3-kinase activation was required for the increase in cyclin D1 mRNA levels and degradation of p27(Kip1). Together, the present study elucidates the role of cAMP and IGF-I in differentially activating PI 3-kinase as a mediator of multiple molecular events. These events converge in the regulation of cyclin D1 and p27(Kip1), leading to cAMP-dependent potentiation of IGF-I-dependent CDK activation and DNA synthesis.

Zoledronic acid is unable to induce apoptosis, but slows tumor growth and prolongs survival for non-small-cell lung cancers

BACKGROUND

Although zoledronic acid (ZOL), a third-generation nitrogen-containing bisphosphonate, has been identified as an attractive therapeutic agent against breast cancer, prostate cancer, multiple myeloma as well as small-cell lung cancer (SCLC), as best as we are aware, the anti-tumor effect of ZOL upon non-small-cell lung cancer (NSCLC) remains to be effectively investigated. This study examined the effects of ZOL upon the line-1 tumor cell, using a murine lung adenocarcinoma cell line similar to the behavior of human lung adenocarcinoma.

METHODS

We investigated the anti-tumor effects of ZOL (3-100 microM) on line-1 tumor cells in vitro, including cellular proliferation, by means of an MTT assay, cell-cycle analysis by flow cytometry and by assessing the level of apoptosis by annexin V/propidium iodide (PI) and 4'-6-diamidino-2-phenylindole (DAPI) staining. Further, we evaluated the growth and survival of line-1 tumor cells following ZOL treatment (1 microg/kg/week) using an animal model. We also examined the in vivo cell-cycle pattern using lacZ-expressing line-1 cells (line-1/lacZ).

RESULTS

ZOL significantly slowed the line-1 tumor growth in a dose-dependent manner in vitro. The treated line-1 tumor cells typically arrested at the S/G2/M-phase of the cell-cycle following ZOL exposure, but no apoptotic cells could be detected by either annexin V/PI or DAPI staining. When the ZOL was washed out, the drug-inhibited cells continued to proliferate again and the cell-cycle prolongation elicited earlier by the drug, then disappeared. Within 72-96 h following drug removal, the cell-cycle of the treated cells revealed a similar distribution to that of the untreated controls. In vivo studies demonstrated that ZOL significantly slowed the line-1 tumor growth. Indeed, mice lived significantly longer when they had been ZOL-treated than was the case for untreated mice (p<0.05). Using line-1/lacZ cells, the in vivo cell-cycle distribution of line-1 tumor cells subsequent to ZOL exposure revealed S/G2/M-phase arrest that was identical to the in vitro culture.

CONCLUSIONS

ZOL maintains the potential to reduce tumor burden and prolong survival for murine pulmonary adenocarcinoma. The flow cytometrical analysis of cell-cycle demonstrated that ZOL induces no apoptosis but is able to arrest line-1 tumor cells at the S/G2/M-phase. Although the clinical relevance of these results warrants verification for human lung cancer patients, ZOL combined with chemotherapy and/or radiotherapy appears to be a new therapeutic strategy for the effective treatment of NSCLC.

Molecular markers and targets for colorectal cancer prevention

Colorectal cancer is the third most prevalent cancer in the world. If detected at an early stage, treatment often might lead to cure. As prevention is better than cure, epidemiological studies reveal that having a healthy diet often protects from promoting/ developing cancer. An important consideration in evaluating new drugs and devices is determining whether a product can effectively treat a targeted disease. There are quite a number of biomarkers making their way into clinical trials and few are awaiting the preclinical efficacy and safety results to enter into clinical trials. Researchers are facing challenges in modifying trial design and defining the right control population, validating biomarker assays from the biological and analytical perspective and using biomarker data as a guideline for decision making. In spite of following all guidelines, the results are disappointing from many of the large clinical trials. To avoid these disappointments, selection of biomarkers and its target drug needs to be evaluated in appropriate animal models for its toxicities and efficacies. The focus of this review is on the few of the potential molecular targets and their biomarkers in colorectal cancers. Strengths and limitations of biomarkers/surrogate endpoints are also discussed. Various pathways involved in tumor cells and the specific agents to target the altered molecular biomarker in biomolecular pathway are elucidated. Importance of emerging new platforms siRNAs and miRNAs technology for colorectal cancer therapeutics is reviewed.

Rac1-dependent transcriptional up-regulation of p27Kip1 by homophilic cell-cell contact in vascular endothelial cells

The mechanism for the transcriptional up-regulation of p27Kip1 due to the formation of the cell-cell contact was investigated in vascular endothelial cells. The induction of the cell-cell contact by adding an extra number of endothelial cells activated Rac1, up-regulated p27Kip1 mRNA and protein, and also facilitated the cell cycle arrest. Transduction of the Rac1 inhibitor protein using the cell-penetrating peptide or treatment with a Rac1 inhibitor NSC23766 inhibited the p27Kip1 up-regulation and delayed the cell cycle arrest. Rac1 was therefore suggested to mediate the contact-induced transcriptional up-regulation of p27Kip1. The role of Rac1 in the regulation of the p27Kip1 promoter activity was next examined with a luciferase reporter assay. The promoter activity was increased by inducing the cell-cell contact, which was significantly inhibited by the Rac1 inhibitory protein and NSC23766. The evaluation of various truncated promoter regions determined region -620 to -573 nucleotides from the initiation codon to be responsible for the contact-induced, Rac1-dependent activation of the p27Kip1 promoter. The present study thus demonstrated for the first time that the activation of Rac1 due to the cell-cell contact plays a critical role in the transcriptional up-regulation of p27Kip1 in vascular endothelial cells.

A transcription factor of lipid synthesis, sterol regulatory element-binding protein (SREBP)-1a causes G(1) cell-cycle arrest after accumulation of cyclin-dependent kinase (cdk) inhibitors

Sterol regulatory element-binding protein (SREBP)-1a is a unique membrane-bound transcription factor highly expressed in actively growing cells and involved in the biosynthesis of cholesterol, fatty acids, and phospholipids. Because mammalian cells need to synthesize membrane lipids for cell replication, the functional relevance of SREBP-1a in cell proliferation has been considered a biological adaptation. However, the effect of this potent lipid-synthesis activator on cell growth has never been explored. Here, we show that induction of nuclear SREBP-1a, but not SREBP-2, completely inhibited cell growth in inducible Chinese hamster ovary (CHO) cell lines. Growth inhibition occurred through G(1) cell-cycle arrest, which is observed in various cell types with transient expression of nuclear SREBP-1a. SREBP-1a caused the accumulation of cyclin-dependent kinase (cdk) inhibitors such as p27, p21, and p16, leading to reduced cdk2 and cdk4 activities and hypophosphorylation of Rb protein. In contrast to transactivation of p21, SREBP-1a activated p27 by enhancing stabilization of the protein through inhibition of SKP2 and KPC1. In vivo, SREBP-1a-expressing livers of transgenic mice exhibited impaired regeneration after partial hepatectomy. SREBP-1-null mouse embryonic fibroblasts had a higher cell proliferation rate than wild-type cells. The unexpected cell growth-inhibitory role of SREBP-1a provides a new paradigm to link lipid synthesis and cell growth.

Statins prevent cholinesterase inhibitor blockade of sympathetic alpha7-nAChR-mediated currents in rat superior cervical ganglion neurons

Statins are reported to be beneficial in treating a multitude of disorders including dementia due to Alzheimer disease (AD) and vascular dementia (VaD) with varying, yet-to-be determined mechanisms of actions. Although cholinesterase inhibitors (ChEIs) are still recommended as the primary drug of choice for AD and related diseases, their efficacy is frequently questioned. We recently reported that alpha7-neuronal acetylcholine nicotinic receptor (alpha7-nAChR)-mediated neurogenic vasodilation of porcine cerebral arteries was blocked by ChEIs, and this blockade was prevented by statin pretreatment. The exact mechanism of interaction between ChEIs and statins remains unclear. Activation of alpha7-nAChRs located on perivascular postganglionic sympathetic nerve terminals releases norepinephrine, which then acts on presynaptic beta(2)-adrenoceptors located on neighboring nitrergic nerve terminals, resulting in nitric oxide release and vasodilation. The present study, therefore, was designed to determine whether interaction of ChEIs and statins occurs at the alpha7-nAChR level. We examined effects of concurrent application of ChEIs and statins on alpha7-nAChR-mediated inward currents in primary neuronal cultures of rat superior cervical ganglion cells, the origin of the perivascular sympathetic innervation to the cerebral arteries. The results indicated that physostigmine, neostigmine, and galantamine inhibited choline- and nicotine-induced whole cell currents in a concentration-dependent manner. This inhibition, which was noncompetitive in nature, was prevented by concurrent application of mevastatin and lovastatin in a concentration-dependent manner. These results suggest that statins protect alpha7-nAChR function directly at the receptor level. Since alpha7-nAChR is neuroprotective, having beneficial effects on memory and cerebral vascular function, its functional inhibition by ChEIs may explain in part the limitation of its effectiveness in AD and VaD therapy. Protection of alpha7-nAChR function from ChEI inhibition by concurrent administration of statins may provide an alternative strategy in improving the efficacy of AD and VaD therapy.

DNA topoisomerase inhibitor, etoposide, enhances GC-box-dependent promoter activity via Sp1 phosphorylation

Modification of transcription factors by anticancer agents plays an important role in both apoptotic and survival signaling. Here we report that both DNA topoisomerase I and II inhibitors such as SN-38 and etoposide, but not cisplatin, 5-fluorouracil or actinomycin D, can induce phosphorylation of the transcription factor Sp1. Furthermore, DNA topoisomerase inhibitors were shown to transactivate GC-box-dependent promoters such as the SV40 and vascular endothelial growth factor promoters. The phosphorylated form of Sp1 was detectable within 30 min of etoposide treatment and was greatly diminished by the presence of the PI3K inhibitor wortmannin and by DNA-dependent protein kinase (DNA-PK) knockdown. We also confirmed that the phosphorylated form of DNA-PK was increased by treatment with both etoposide and SN-38. Taken together, these findings demonstrate a novel genomic response to anticancer agents that induce Sp1 phosphorylation, and might contribute to tumor progression and drug resistance.

Simvastatin inactivates beta1-integrin and extracellular signal-related kinase signaling and inhibits cell proliferation in head and neck squamous cell carcinoma cells

The 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors, also called statins, are commonly used as lipid-lowering drugs that inhibit cholesterol biosynthesis. An anticancer effect, as a pleiotropic function of certain statins, has been hypothesized. In the present study, we investigated the effect of simvastatin, one of the natural statins, on cell proliferation, cell cycle, invasive activity, and molecular expressions associated with cell-extracellular matrix adhesion, signal transduction, and DNA synthesis in Tu167 and JMAR cells from head and neck squamous cell carcinoma. The addition of simvastatin resulted in a dose-dependent inhibition of cell growth and migration into the extracellular matrix. Considerable morphological changes occurred after treatment with simvastatin, demonstrating loss of cell adhesion and disruption of actin filaments in cytoplasm. The inhibitory effect of simvastatin on cell proliferation seemed to be associated with cell cycle arrest and increased expression of p21, p27, and activated caspase-3. The expression of beta1-integrin, a counter adhesion for the extracellular matrix, phosphorylated FAK, and phosphorylated ERK was decreased by treatment with simvastatin. The proapoptotic effect of simvastatin was inhibited by treatment with mevalonate. cDNA microarray assay demonstrated that molecular changes resulting from treatment with simvastatin included the up-regulation of cell cycle regulators and apoptosis-inducing factors and the down-regulation of integrin-associated molecules and cell proliferation markers. Of down-regulated genes induced by simvastatin treatment, a significant depletion of thymidylate synthase was confirmed using western blot analysis. These results imply that simvastatin has the potential to be effective for the prevention of the growth and metastasis of cancer cells.

The effects of PACAP on neural cell proliferation

PACAP and its receptors are expressed in growth zones of the brain. By stimulating PAC(1)-receptors PACAP can enhance, as well as reduce, the proliferation rate in a cell-type dependent manner. PACAP can enhance the proliferation rate by activating phospholipase C and protein kinase C, although other signal transduction pathways may also be responsible. PACAP can suppress proliferation by inhibiting protein complexes of the cyclins D and E with the cyclin-dependent kinases 4/6 and 2, respectively, which are necessary for entry into the cell cycle. PACAP seems to exert these inhibitory effects by acting via the Sonic hedgehog glycoprotein and the small GTPase RhoA. Also, the activation of a cyclin-dependent kinase inhibitor has been suggested. The signal transduction pathways mediating the effects of PACAP on proliferation are discussed.

Inhibitors of the mevalonate pathway as potential therapeutic agents in multiple myeloma

Clinical studies have suggested that bisphosphonates may prolong the survival of sub-sets of myeloma patients. Newer nitrogen containing bisphosphonates such as zoledronate act, at least in part, by inhibiting farnesyl diphosphate synthase and subsequent protein prenylation, furthermore, limited data suggests that zoledronate exerts a direct anti-tumour effect against human myeloma cell lines. We therefore investigated the anti-myeloma potential of zoledronate in comparison to, and in combination with, two other inhibitors of the mevalonate pathway: the HMGCoA reductase inhibitor fluvastatin and the farnesyl transferase inhibitor SCH66336. We found that fluvastatin was able to inhibit the proliferation of myeloma cells more effectively than zoledronate or SCH66336 and that combinations of zoledronate and fluvastatin, but not zoledronate and SCH66336 acted synergistically. Our data indicated that the anti-proliferative effect of mevalonate pathway inhibitors is mediated principally via prevention of geranylgeranylation and is the result of both cell cycle arrest and apoptosis induction. Microarray and quantitative real-time PCR analyses further demonstrated that genes related to apoptosis, cell cycle control, and the mevalonate pathway were particularly affected by zoledronate and fluvastatin, and that some of these genetic effects were synergistic. We conclude that the mechanisms of geranylgeranylation inhibition mediated anti-myeloma effects warrant further evaluation and may provide novel targets for future therapeutic development.

Geranylgeranyl-pyrophosphate (GGPP) synthase is down-regulated during differentiation of osteoblastic cell line MC3T3-E1

Isoprenylation of geranylgeranyl-pyrophosphate (GGPP) is critical for activation of small GTPases. We examined the roles of GGPP synthase (GGPPS) during the differentiation induced by the cell-to-cell contact in osteoblastic cell line MC3T3-E1 cells. We found that (1) both mRNA and protein expression of GGPPS was reduced with decrement of its activity during the differentiation, (2) GGOH, which is converted to GGPP in the cells, inhibited differentiation. These results suggest that the decrement of GGPP is critical for the cell-to-cell contact-induced differentiation, in which the down-regulation of GGPPS might be involved.

The role of geranylgeranylated proteins in human mesangial cell proliferation

The Rho family of guanine 5'-triphosphatases (GTPases) play a key role in regulating cell proliferation, tubulointerstitial fibrosis, and glomerular hemodynamics. The post-translational prenylation of RhoGTPases by the addition of a geranylgeranyl moiety is critical for cellular localization and signaling activity. This study investigates the effects of (i) inhibiting geranylgeranylation (GG) in human mesangial cell (HMC) proliferation and apoptosis, using GGTI 298, a specific inhibitor of GG and (ii) lovastatin, an HMG-coacetyl A-reductase inhibitor, which depletes the availability of prenylation substrates. HMC proliferation was assessed using an assay of viable cell number and measuring bromodeoxyuridine (BrdU) incorporation. Hoechst 33342 staining was used to determine apoptosis. Extracellular signal-regulated protein kinase (Erk)1/2 and Akt activation were analysed by Western blotting. Rho activation was determined using the Rhotekin pull-down assay. Immunocytochemistry was performed to study the effects on the actin cytoskeleton and RhoA localization. GGTI 298 (10-20 muM) and lovastatin (5-10 muM) potently inhibited platelet-derived growth factor and serum-stimulated HMC proliferation and induced apoptosis. These effects of lovastatin were attenuated by co-incubation with geranylgeranylpyrophosphate. C3 exoenzyme, a clostridial toxin that specifically targets Rho also inhibited BrdU incorporation and promoted apoptosis. GGTI 298 increased cytosolic expression of RhoA, prevented RhoA activation, and inhibited the activation of Erk1/2 and the survival protein Akt. GGTI 298, lovastatin, and C3 exoenzyme inhibit HMC proliferation and promote apoptosis. Inhibiting GG increases cytosolic RhoA expression, disrupts the actin cytoskeleton, and inhibits RhoA activation. These results suggest that targeting geranylgeranylated proteins with statins or GGTI 298 is a promising therapeutic strategy in human mesangioproliferative renal disease.

The Rho GTPase effector ROCK regulates cyclin A, cyclin D1, and p27Kip1 levels by distinct mechanisms

The members of the Rho GTPase family are well known for their regulation of actin cytoskeletal structures. In addition, they influence progression through the cell cycle. The RhoA and RhoC proteins regulate numerous effector proteins, with a central and vital signaling role mediated by the ROCK I and ROCK II serine/threonine kinases. The requirement for ROCK function in the proliferation of numerous cell types has been revealed by studies utilizing ROCK-selective inhibitors such as Y-27632. However, the mechanisms by which ROCK signaling promotes cell cycle progression have not been thoroughly characterized. Using a conditionally activated ROCK-estrogen receptor fusion protein, we found that ROCK activation is sufficient to stimulate G1/S cell cycle progression in NIH 3T3 mouse fibroblasts. Further analysis revealed that ROCK acts via independent pathways to alter the levels of cell cycle regulatory proteins: cyclin D1 and p21(Cip1) elevation via Ras and the mitogen-activated protein kinase pathway, increased cyclin A via LIM kinase 2, and reduction of p27(Kip1) protein levels. Therefore, the influence of ROCK on cell cycle regulatory proteins occurs by multiple independent mechanisms.

Bacterial lipopolysaccharide stimulates the thyrotropin-dependent thyroglobulin gene expression at the transcriptional level by involving the transcription factors thyroid transcription factor-1 and paired box domain transcription factor 8

The bacterial lipopolysaccharide (LPS) is a biological activator that induces expression of multiple genes in several cell types. LPS has been proposed as an etiopathogenic agent in autoimmune diseases. However, whether LPS affects the expression of autoantigens has not been explored. Thyroglobulin (TG) is a key protein in thyroid hormonogenesis and one of the major thyroid autoantigens. This study aimed to analyze the action of LPS on TG gene expression in Fisher rat thyroid cell line FRTL-5 thyroid cells. We demonstrate that LPS increases the TSH-induced TG protein and mRNA level. Evidence that the effect of LPS is exerted at the transcriptional level was obtained by transfecting the minimal TG promoter. The C element of the TG promoter, which contains sequences for paired box domain transcription factor 8 (Pax8) and thyroid transcription factor (TTF)-1 binding, is essential for full TG promoter expression under TSH stimulation. The transcriptional activity of a construct containing five tandem repeats of the C site is increased by LPS, indicating a possible involvement of the C site in the LPS-induced TG gene transcription. We demonstrate that the TG promoter mutated at the Pax8 or TTF-1 binding element in the C site does not respond to LPS. In band shift assays, binding of Pax8 and TTF-1 to the C site is increased by LPS. The Pax8 and TTF-1 mRNA and protein levels are augmented by LPS. The half-lives of TG, Pax8, and TTF-1 are increased in endotoxin-treated cells. Our results reveal the ability of LPS to stimulate the expression of TG, a finding of potential pathophysiological implication.