Epidermal growth factor stimulates 3-hydroxy-3-methylglutaryl-coenzyme A reductase expression via the ErbB-2 pathway in human breast adenocarcinoma cells

Engineering γδT cells limits tonic signaling associated with chimeric antigen receptors

Despite the benefits of chimeric antigen receptor (CAR)-T cell therapies against lymphoid malignancies, responses in solid tumors have been more limited and off-target toxicities have been more marked. Among the possible design limitations of CAR-T cells for cancer are unwanted tonic (antigen-independent) signaling and off-target activation. Efforts to overcome these hurdles have been blunted by a lack of mechanistic understanding. Here, we showed that single-cell analysis with time course mass cytometry provided a rapid means of assessing CAR-T cell activation. We compared signal transduction in expanded T cells to that in T cells transduced to express second-generation CARs and found that cell expansion enhanced the response to stimulation. However, expansion also induced tonic signaling and reduced network plasticity, which were associated with expression of the T cell exhaustion markers PD-1 and TIM-3. Because this was most evident in pathways downstream of CD3ζ, we performed similar analyses on γδT cells that expressed chimeric costimulatory receptors (CCRs) lacking CD3ζ but containing DAP10 stimulatory domains. These CCR-γδT cells did not exhibit tonic signaling but were efficiently activated and mounted cytotoxic responses in the presence of CCR-specific stimuli or cognate leukemic cells. Single-cell signaling analysis enabled detailed characterization of CAR-T and CCR-T cell activation to better understand their functional activities. Furthermore, we demonstrated that CCR-γδT cells may offer the potential to avoid on-target, off-tumor toxicity and allo-reactivity in the context of myeloid malignancies.

Targeting the Mevalonate Pathway to Overcome Acquired Anti-HER2 Treatment Resistance in Breast Cancer

Despite effective strategies, resistance in HER2⁺ breast cancer remains a challenge. While the mevalonate pathway (MVA) is suggested to promote cell growth and survival, including in HER2⁺ models, its potential role in resistance to HER2-targeted therapy is unknown. Parental HER2⁺ breast cancer cells and their lapatinib-resistant and lapatinib + trastuzumab-resistant derivatives were used for this study. MVA activity was found to be increased in lapatinib-resistant and lapatinib + trastuzumab-resistant cells. Specific blockade of this pathway with lipophilic but not hydrophilic statins and with the N-bisphosphonate zoledronic acid led to apoptosis and substantial growth inhibition of R cells. Inhibition was rescued by mevalonate or the intermediate metabolites farnesyl pyrophosphate or geranylgeranyl pyrophosphate, but not cholesterol. Activated Yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ) and mTORC1 signaling, and their downstream target gene product Survivin, were inhibited by MVA blockade, especially in the lapatinib-resistant/lapatinib + trastuzumab-resistant models. Overexpression of constitutively active YAP rescued Survivin and phosphorylated-S6 levels, despite blockade of the MVA. These results suggest that the MVA provides alternative signaling leading to cell survival and resistance by activating YAP/TAZ-mTORC1-Survivin signaling when HER2 is blocked, suggesting novel therapeutic targets. MVA inhibitors including lipophilic statins and N-bisphosphonates may circumvent resistance to anti-HER2 therapy warranting further clinical investigation. IMPLICATIONS: The MVA was found to constitute an escape mechanism of survival and growth in HER2⁺ breast cancer models resistant to anti-HER2 therapies. MVA inhibitors such as simvastatin and zoledronic acid are potential therapeutic agents to resensitize the tumors that depend on the MVA to progress on anti-HER2 therapies.

Anti-cancer effect of doxorubicin is mediated by downregulation of HMG-Co A reductase via inhibition of EGFR/Src pathway

Doxorubicin is a widely used DNA damage-inducing anti-cancer drug. However, its use is limited by its dose-dependent side effects, such as cardiac toxicity. Cholesterol-lowering statin drugs increase the efficacy of some anti-cancer drugs. Cholesterol is important for cell growth and a critical component of lipid rafts, which are plasma membrane microdomains important for cell signaling. 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (HMG-CR) is a critical enzyme in cholesterol synthesis. Here, we show that doxorubicin downregulated HMG-CR protein levels and thus reduced levels of cholesterol and lipid rafts. Cholesterol addition attenuated doxorubicin-induced cell death, and cholesterol depletion enhanced it. Reduction of HMG-CR activity by simvastatin, a statin that acts as an HMG-CR inhibitor, or by siRNA-mediated HMG-CR knockdown enhanced doxorubicin cytotoxicity. Doxorubicin-induced HMG-CR downregulation was associated with inactivation of the EGFR-Src pathway. Furthermore, a high-cholesterol-diet attenuated the anti-cancer activity of doxorubicin in a tumor xenograft mouse model. In a multivulva model of Caenorhabditis elegans expressing an active-EGFR mutant, doxorubicin decreased hyperplasia more efficiently in the absence than in the presence of cholesterol. These data indicate that EGFR/Src/HMG-CR is a new pathway mediating doxorubicin-induced cell death and that cholesterol control could be combined with doxorubicin treatment to enhance efficacy and thus reduce side effects.

Engineering Approaches in Human Gamma Delta T Cells for Cancer Immunotherapy

Sharing both innate and adaptive immune properties, γδT cells are attractive candidates for cellular engineering. As the cancer immunotherapy field becomes increasingly busy, orthogonal approaches are required to drive advancement. Engineering of alternative effector cell types such as γδT cells represents one such approach. γδT cells can be modified using many of the techniques used in αβT cell engineering, with the added advantage of innate-like tumor recognition and killing. Progress has been made in T-cell receptor transfer to and from γδT cells as well as in a number of chimeric antigen receptor-based strategies. As the cancer immunotherapy field moves beyond repetitive iteration of established constructs to more creative solutions, γδT cells may offer an attractive chassis to drive anti-tumor responses that are not only broader, but also possess a more favorable safety profile.

Towards Deciphering the Hidden Mechanisms That Contribute to the Antigenic Activation Process of Human Vγ9Vδ2 T Cells

Vγ9Vδ2 T cells represent a major unconventional γδ T cell subset located in the peripheral blood of adults in humans and several non-human primates. Lymphocytes that constitute this transitional subset can sense subtle level changes of intracellular phosphorylated intermediates of the isoprenoid biosynthesis pathway (phosphoantigens, pAg), such as isopentenyl pyrophosphate, during cell stress events. This unique antigenic activation process operates in a rigorous framework that requires the expression of butyrophilin 3A1 (BTN3A1/CD277) molecules, which are type I glycoproteins that belong to the B7 family. Several studies have further shown that pAg specifically bind to the intracellular B30.2 domain of BTN3A1 linked to the antigenic activation of Vγ9Vδ2 T cells. Here, we highlight the recent advances in BTN3A1 dynamics induced upon the binding of pAg and the contribution of the different subunits to this activation process. Recent reports support that conformational modifications of BTN3A1 might represent a key step in the detection of infection or tumorigenesis by Vγ9Vδ2 T cells. A better understanding of this mechanism will help optimize novel immunotherapeutical approaches that target defined functions of this unique γδ T cell subset.

Avoidance of On-Target Off-Tumor Activation Using a Co-stimulation-Only Chimeric Antigen Receptor

Chimeric antigen receptors (CARs) combine T cell activation with antibody-mediated tumor antigen specificity, bypassing the need for T cell receptor (TCR) ligation. A limitation of CAR technology is on-target off-tumor toxicity caused by target antigen expression on normal cells. Using GD2 as a model cancer antigen, we hypothesized that this could be minimized by using T cells expressing Vγ9Vδ2 TCR, which recognizes transformed cells in a major histocompatibility complex (MHC)-unrestricted manner, in combination with a co-stimulatory CAR that would function independently of the TCR. An anti-GD2 CAR containing a solitary endodomain derived from the NKG2D adaptor DAP10 was expressed in Vγ9Vδ2+ T cells. Differential ligation of the CAR and/or TCR using antibody-coated beads showed that pro-inflammatory cytokine response depended on activation of both receptors. Moreover, in killing assays, GD2-expressing neuroblastoma cells that engaged the Vγ9Vδ2 TCR were efficiently lysed, whereas cells that expressed GD2 equivalently but did not engage the Vγ9Vδ2 TCR were untouched. Differentiation between X-on tumor and X-off tumor offers potential for safer immunotherapy and broader target selection.

The interplay between cell signalling and the mevalonate pathway in cancer

The mevalonate (MVA) pathway is an essential metabolic pathway that uses acetyl-CoA to produce sterols and isoprenoids that are integral to tumour growth and progression. In recent years, many oncogenic signalling pathways have been shown to increase the activity and/or the expression of MVA pathway enzymes. This Review summarizes recent advances and discusses unique opportunities for immediately targeting this metabolic vulnerability in cancer with agents that have been approved for other therapeutic uses, such as the statin family of drugs, to improve outcomes for cancer patients.

Sensing of Pyrophosphate Metabolites by Vγ9Vδ2 T Cells

The predominant population of γδ T cells in human blood express a T cell receptor (TCR) composed of a Vγ9 (Vγ2 in an alternate nomenclature) and Vδ2 domains. These cells came into the limelight when it was discovered they can respond to certain microbial infections and tumorigenic cells through the detection of small, pyrophosphate containing organic molecules collectively called “phosphoantigens” or “pAgs.” These molecules are intermediates in both eukaryotic and prokaryotic metabolic pathways. Chemical variants of these intermediates have been used in the clinic to treat a range of different cancers, however, directed optimization of these molecules requires a full understanding of their mechanism of action on target cells. We and others have identified a subclass of butyrophilin-related molecules (BTN3A1-3) that are directly involved in pAg sensing in the target cell, leading to engagement and activation of the T cell through the TCR. Our data and that of others support the pAg binding site to be the intracellular B30.2 domain of BTN3A1, which is the only isoform capable of mediating pAg-dependent stimulation of Vγ9Vδ2 T cells. Here, we review the data demonstrating pAg binding to the B30.2 domain and our studies of the structural conformations of the BTN3A extracellular domains. Finally, we synthesize a model linking binding of pAg to the intracellular domain with T cell detection via the extracellular domains in an “inside-out” signaling mechanism of the type characterized first for integrin molecule signaling. We also explore the role of Vγ9Vδ2 TCR variability in the CDR3 γ and δ loops and how this may modulate Vγ9Vδ2 cells as a population in surveillance of human health and disease.

Redirecting αβ T cells against cancer cells by transfer of a broadly tumor-reactive γδT-cell receptor

Major limitations of currently investigated αβT cells redirected against cancer by transfer of tumor-specific αβTCR arise from their low affinity, MHC restriction, and risk to mediate self-reactivity after pairing with endogenous α or βTCR chains. Therefore, the ability of a defined γ9δ2TCR to redirect αβT cells selectively against tumor cells was tested and its molecular interaction with a variety of targets investigated. Functional analysis revealed that a γ9δ2TCR efficiently reprograms both CD4(+) and CD8(+) αβT cells against a broad panel of cancer cells while ignoring normal cells, and substantially reduces but does not completely abrogate alloreactivity. γ9δ2TCR-transduced αβT cells reduced colony formation of progenitor cells of primary acute myeloid leukemia blasts and inhibited leukemia growth in a humanized mouse model. Thereby, metabolites of a dysregulated mevalonate pathway are targeted and the additional application of widely used biphosphonates is crucial for in vivo efficacy most likely because of its modulating effect on cytokine secretion of γ9δ2TCR-transduced αβT cells. Expression of NKG2D ligands and F1-ATPase contributed to the activity of γ9δ2TCR-transduced αβT cells but were not mandatory. In summary, γ9δ2 TCRs are an attractive alternative to broadly redirect αβT cells against cancer cells with both an improved efficacy and safety profile compared with currently used αβTCRs.

Expression and function of PD-1 in human γδ T cells that recognize phosphoantigens

Programmed cell death-1 (PD-1) is an inhibitory receptor and plays an important role in the regulation of αβ T cells. Little is known, however, about the role of PD-1 in γδ T cells. In this study, we investigated the expression and function of PD-1 in human γδ T cells. Expression of PD-1 was rapidly induced in primary γδ T cells following antigenic stimulation, and the PD-1(+) γδ T cells produced IL-2. When PD-1(+) γδ T cells were stimulated with Daudi cells with and without programmed cell death ligand-1 (PD-L1) expression, the levels of IFN-γ production and cytotoxicity in response to PD-L1(+) Daudi cells were diminished compared to the levels seen in response to PD-L1(-) Daudi cells. The attenuated effector functions were reversed by anti-PD-L1 mAb. When PD-1(+) γδ T cells were challenged by PD-L1(+) tumors pretreated with zoledronate (Zol), which induced γδ TCR-mediated signaling, the resulting reduction in cytokine production was only slight to moderate compared to the reduction seen when PD-1(+) γδ T cells were challenged by PD-L1(-) tumors. In addition, cytotoxic activity of PD-1(+) γδ T cells against Zol-treated PD-L1(+) tumors was comparable to that against Zol-treated PD-L1(-) tumors. These results suggest that TCR triggering may partially overcome the inhibitory effect of PD-1 in γδ T cells.

Efficient killing of human colon cancer stem cells by gammadelta T lymphocytes

Colon cancer comprises a small population of cancer stem cells (CSC) that is responsible for tumor maintenance and resistant to cancer therapies, possibly allowing for tumor recapitulation once treatment stops. We previously demonstrated that such chemoresistance is mediated by autocrine production of IL-4 through the up-regulation of antiapoptotic proteins. Several innate and adaptive immune effector cells allow for the recognition and destruction of cancer precursors before they constitute the tumor mass. However, cellular immune-based therapies have not been experimented yet in the population of CSCs. Here, we show that the bisphosphonate zoledronate sensitizes colon CSCs to Vgamma9Vdelta2 T cell cytotoxicity. Proliferation and production of cytokines (TNF-alpha and IFN-gamma) and cytotoxic and apoptotic molecules (TRAIL and granzymes) were also induced after exposure of Vgamma9Vdelta2 T cells to sensitized targets. Vgamma9Vdelta2 T cell cytotoxicity was mediated by the granule exocytosis pathway and was highly dependent on isoprenoid production by of tumor cells. Moreover, CSCs recognition and killing was mainly TCR mediated, whereas NKG2D played a role only when tumor targets expressed several NKG2D ligands. We conclude that intentional activation of Vgamma9Vdelta2 T cells by zoledronate may substantially increase antitumor activities and represent a novel strategy for colon cancer immunotherapy.

Enhancement of anti-tumor cytotoxicity of expanded gammadelta T Cells by stimulation with monocyte-derived dendritic cells

In order to establish the method of generating powerful gammadelta T cells for anti-tumor immunotherapy, we investigated the effects of monocyte-derived dendritic cells (mo-DCs) on anti-tumor cytotoxicity of expanded gammadelta T cells. Activation of gammadelta T cells co-cultured for 2-3 days with immature or mature mo-DCs was evaluated by CD69 expression and anti-tumor cytotoxicity using two assays : the 5- (and 6-) carboxyfluorescein diacetate, succinimidyl ester-based cytotoxicity assay and the calcein-AM-based Terascan assay. gammadelta T cells were used as effector cells and myeloma cell line (RPMI8226) or chronic myelogenous leukemia blastic crisis cell line (C2F8) were used as target cells. CD69 expression on gammadelta T cells was enhanced by co-culture with both immature and mature mo-DCs in a cell-number-dependent fashion. CD69 expression was enhanced after addition of mo-DCs of either autologous or allogeneic origin. Activation of gammadelta T cells with mo-DCs enhanced anti-tumor cytotoxicity of gammadelta T cells against RPMI8226 and C2F8 in an effector-to-target ratio-dependent manner. Activation of gammadelta T cells by mo-DCs was associated with the enhancement of anti-tumor cytotoxicity of gammadelta T cells. Potent gammadelta T cells activated by mo-DCs were considered to be applicable to an efficient gammadelta T cell-mediated immunotherapy for tumors.

Transcriptional control of cholesterol biosynthesis in Schwann cells by axonal neuregulin 1

A characteristic feature of many vertebrate axons is their wrapping by a lamellar stack of glially derived membranes known as the myelin sheath. Myelin is a cholesterol-rich membrane that allows for rapid saltatory nerve impulse conduction. Axonal neuregulins instruct glial cells on when and how much myelin they should produce. However, how neuregulin regulates myelin sheath development and thickness is unknown. Here we show that neuregulin receptors are activated by drops in plasma membrane cholesterol, suggesting that they can sense sterol levels. In Schwann cells neuregulin-1 increases the transcription of the 3-hydroxy-3-methylglutarylcoenzyme A reductase, the rate-limiting enzyme for cholesterol biosynthesis. Neuregulin activity is mediated by the phosphatidylinositol 3-kinase pathway and a cAMP-response element located on the reductase promoter. We propose that by activating neuregulin receptors, neurons exploit a cholesterol homeostatic mechanism forcing Schwann cells to produce new membranes for the myelin sheath. We also show that a strong phylogenetic correlation exists between myelination and cholesterol biosynthesis, and we propose that the absence of the sterol branch of the mevalonate pathway in invertebrates precluded the myelination of their nervous system.

Identification of potentially useful combinations of epidermal growth factor receptor tyrosine kinase antagonists with conventional cytotoxic agents using median effect analysis

Targeted therapy for breast carcinoma has achieved a major advance with the use of trastuzumab in Her2/neu-positive tumors. The epidermal growth factor receptor superfamily thus becomes an attractive target for therapeutic agents. As the epidermal growth factor receptor tyrosine kinase family has a conformational binding site, which allows small molecules to interfere with its function, we have explored the effects of a dual kinase (epidermal growth factor receptor-1 and epidermal growth factor receptor-2) inhibitor (GW282974X) with a variety of cytotoxic agents looking for synergistic effects in vitro. Using a median effect model in four breast cancer cell lines in vitro, cytotoxic agents commonly used in treatment of human malignant disease were combined with trastuzumab or one of two epidermal growth factor receptor tyrosine kinase inhibitors in a 72-h culture and then analyzed for cytotoxic effect by 3-[26]-2,5-diphenyl-tetrazolium bromide assay. Combination index values within one standard deviation of unity were considered additive, less than unity as synergistic and more than unity as antagonistic. Synergistic results were confirmed by curve shift analysis and by an enzyme-linked immunosorbent assay measuring apoptosis by cytoplasmic histone-associated DNA fragments. Quantitative real-time polymerase chain reaction analysis was used to measure the expression of three of the critical enzymes in 5'-deoxy-5-fluorouridine metabolism and activity: thymidine phosphorylase, dihydropyrimidine dehydrogenase and thymidine synthase. 5'-Deoxy-5-fluorouridine with GW282974X demonstrated global synergy, both in high and low expressing epidermal growth factor receptor breast cancer cell lines. These results were confirmed by apoptosis assay and cell counts. RNA quantification following treatment with the dual kinase inhibitor suggested reduction in thymidine synthase levels to be a potential mechanism of synergy. The triplet of trastuzumab, GW282974X and 5'-deoxy-5-fluorouridine, and the triplet of GW282974X, epirubicin and 5'-deoxy-5-fluorouridine were highly synergistic in low expression cells (MCF7/wt) and high expression cells (MCF7/adr). These experiments suggest further studies of the dual kinase inhibitor with selected cytotoxics such as 5'-deoxy-5-fluorouridine are warranted.

Type I IFN-mediated enhancement of anti-leukemic cytotoxicity of gammadelta T cells expanded from peripheral blood cells by stimulation with zoledronate

BACKGROUND

In order to establish efficient gammadelta T-cell based tumor immunotherapy, we explored a method to enhance the cytotoxicity of gammadelta T cells against leukemia cells by stimulating gammadelta T cells with type I IFN.

METHODS

Gammadelta T cells were expanded from normal PBMC by culturing with zoledronate and a low concentration of IL-2 for 2 weeks. For the activation of gammadelta T cells, gammadelta T cells were cultured with type I IFN (HLBI, IFN-alpha2b and IFN-beta) for 1-3 days. The cytotoxicity of HLBI-activated gammadelta T cells against leukemia cell lines and fresh leukemia cells was evaluated by 51Cr-release assay.

RESULTS

Gammadelta T cells, which were expanded and purified with magnetic beads using an anti-gammadelta TCR MAb, were demonstrated to be cytotoxic against leukemia cell lines of both lymphoid and myeloid origin and fresh myeloid leukemia cells. By culturing expanded gammadelta T cells with type I IFN, the expression of the activation marker CD69 was increased and the cytometric bead array showed an elevated production of IFN-gamma by gammadelta T cells. In addition, the cytotoxicity of gammadelta T cells against leukemia cells was definitely enhanced by culturing gammadelta T cells with HLBI.

DISCUSSION

The present study has demonstrated that type I IFN could enhance the anti-leukemic cytotoxicity of expanded gammadelta T cells, which implies that in vitro bisphosphonate (such as zoledronate)-expanded and type I IFN-activated gammadelta T cells could be applied to immunotherapy for hematologic malignancies such as leukemia and lymphoma.

V gamma 9V delta 2 T cell response to colon carcinoma cells

During analysis of CD8 T cells derived from ascites of a colon cancer patient, we isolated a Vgamma9Vdelta2 T cell clone showing strong reactivity against autologous tumor cell lines. This clone killed a large fraction of allogeneic colon carcinoma and melanoma cell lines, but did not affect a normal colon cell line, colon fibroblasts, or melanocytes. Tumor cell recognition was TCR and NKG2D dependent and induced TNF-alpha and IFN-gamma secretion by the clone; accordingly, tumor targets expressed several NKG2D ligands, such as MHC class I chain-related gene A and UL16-binding protein molecules. Colon tumor recognition by Vgamma9Vdelta2 T cells was highly dependent on isopentenyl pyrophosphate production and ICAM-1 expression by target cells. Finally, similar reactivity patterns against colon carcinoma cell lines were observed using polyclonal Vgamma9Vdelta2 T cells of various origins, and Vgamma9Vdelta2 lymphocytes were present in the majority of colon tumor samples studied. Together, these results suggest that Vgamma9Vdelta2 T cells contribute to the natural immune surveillance against colon cancers. Therefore, this study provides a strong rationale for the use of Vgamma9Vdelta2 T cell agonists in immunotherapies targeting colon tumors.

Non-peptide antigens activating human Vγ9/Vδ2 T lymphocytes

Various non-peptidic ligands which specifically activate most of circulating human Vgamma9/Vdelta2 T lymphocytes are now known. Most of these are so-called phosphoantigens and directly trigger the Vgamma9/Vdelta2 TCR expressing cells, without need for MHC-restricted presentation molecules. Although some potent phosphoantigens currently involved in clinical trials are chemically-synthesized molecules, most of the natural antigens were isolated from microbial cultures. The structures and biosynthesis of phosphoantigens are reviewed here and the possible physiological significance of their recognition by gammadelta T lymphocytes is discussed.

Human T cell receptor gammadelta cells recognize endogenous mevalonate metabolites in tumor cells

T lymphocytes expressing the T cell receptor (TCR)-gammadelta recognize unknown antigens on tumor cells. Here we identify metabolites of the mevalonate pathway as the tumor ligands that activate TCR-gammadelta cells. In tumor cells, blockade of hydroxy-methylglutaryl-CoA reductase (HMGR), the rate limiting enzyme of the mevalonate pathway, prevents both accumulation of mevalonate metabolites and recognition by TCR-gammadelta cells. When metabolite accumulation is induced by overexpressing HMGR or by treatment with nitrogen-containing bisphosphonate drugs, tumor cells derived from many tissues acquire the capacity to stimulate the same TCR-gammadelta population. Accumulation of mevalonate metabolites in tumor cells is a powerful danger signal that activates the immune response and may represent a novel target of tumor immunotherapy.

Plant-derived monoterpenes suppress hamster kidney cell 3-hydroxy-3-methylglutaryl coenzyme a reductase synthesis at the post-transcriptional level

The rate-limiting enzyme for mevalonate and cholesterol synthesis in mammalian cells is 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase. Control occurs through both transcriptional and post-transcriptional actions signaled by the end product, cholesterol, and by isoprenoid intermediates. End products of plant mevalonate metabolism, i.e., plant-derived isoprenoids, also suppress mammalian HMG-CoA reductase. Previous studies reported that isoprenoids suppress reductase synthesis at a post-transcriptional level. We tested the hypothesis that plant-derived isoprenoids also regulate mammalian HMG-CoA reductase synthesis at a post-transcriptional level by incubating lovastatin-treated C100 cells with mevalonate or a plant-derived isoprenoid (the monoterpenes, limonene, perillyl alcohol or geraniol) either alone or combined with the oxysterol, 25-hydroxycholesterol (25-OH C). Mevalonate decreased HMG-CoA reductase synthesis and mRNA levels by 65 and 66%, respectively (P < 0.05). The cyclic monoterpenes, limonene and perillyl alcohol, lowered HMG-CoA reductase synthesis by 70 and 89%, respectively (P < 0.05); although neither reduced HMG-CoA reductase mRNA levels (P = 0.88). Geraniol, an acyclic monoterpene, suppressed HMG-CoA reductase synthesis by 98% and lowered mRNA levels by 66% (P < 0.05). A combination of 25-OH C and either mevalonate or any three monoterpenes reduced HMG-CoA reductase mRNA levels (P < 0.05) compared with lovastatin-only treated cells. However, the dual combination of 25-OH C and either mevalonate or a monoterpene resulted in a greater decrease in HMG-CoA reductase synthesis than in mRNA levels. The difference between changes in HMG-CoA reductase synthesis and mRNA levels reflects a specific effect of isoprenoids on HMG-CoA reductase synthesis at the translational level. Mevalonate enhanced HMG-CoA reductase degradation, but no such effect was observed for the monoterpenes. These results indicate that the three plant-derived isoprenoids primarily suppress HMG-CoA reductase synthesis at a post-transcriptional level by attenuating HMG-CoA reductase mRNA translational efficiency.

Sepsis syndrome stimulates proximal tubule cholesterol synthesis and suppresses the SR-B1 cholesterol transporter

BACKGROUND

Previous studies demonstrate that renal cortical/proximal tubule cholesterol accumulation is part of the renal "stress response." The present study was performed to help define underlying mechanisms, using experimental sepsis as a test model.

METHODS

Male CD-1 mice and female low-density lipoprotein receptor (LDLR) knockout mice were injected with a heat-killed Escherichia coli suspension. Renal cortex and serum were obtained from these and control mice either 4, 6, or 18 hours later. Tissues samples were assayed for free cholesterol (FC), cholesteryl esters (CE), HMG CoA reductase (HMGCR) mRNA, and SR-B1 [the high-density lipoprotein (HDL) receptor/cholesterol transporter]. Statin effects on renal cortical HMGCR mRNA and FC/CE levels also were assessed. Finally, the impact of serum from septic versus normal mice on cultured proximal tubule (HK-2) cell cholesterol levels was assessed.

RESULTS

Sepsis induced approximately 30% and 300 to 500% increases in renal FC and CE content, respectively. Cholesterol accumulation was not blunted in LDLR-/- mice versus their controls. Statin therapy also did not alter sepsis-induced renal FC/CE accumulation. However, statin treatment exerted no discernible intra-renal activity (for example, no rise in renal HMGCR mRNA), despite significant extra-renal activity (25% reduction in serum cholesterol; 400% increase in hepatic HMGCR mRNA). HK-2 cells exposed to septic serum sustained a 40% cholesterol increase, compared to cells exposed to control serum. This response was completely statin inhibited, proving that de novo synthesis was involved. Sepsis markedly suppressed renal levels of SR-B1 (an FC efflux protein). Renal HMGCR mRNA did not fall despite sepsis triggered cholesterol loading, indicating a failure of negative feedback activity.

CONCLUSIONS

Sepsis-induced renal cholesterol accumulation is not simply an intrinsic renal response, since it can be enhanced by circulating "stress factors" that drive HMGCR activity. Sepsis also down-regulates SR-B1. Thus, decreased cell FC efflux, coupled with increased synthesis, may synergistically induce the post-sepsis cholesterol overload state.

3-hydroxy-3-methylglutaryl-coenzyme a reductase inhibitors reduce human pancreatic cancer cell invasion and metastasis

BACKGROUND & AIMS

Inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase blocks the mevalonate metabolic pathway, which is necessary for the isoprenylation of a number of small guanosine triphosphatases. We examined the effects of HMG-CoA reductase inhibitors, fluvastatin and lovastatin, on human pancreatic cancer cell invasion in vitro and experimental liver metastasis in vivo.

METHODS

Cell invasion was studied in a modified Boyden chamber assay. The translocation of RhoA was assessed by immunoblotting. Experimental liver metastases were induced in nude mice by intrasplenic inoculation of ASPC-1 human pancreatic cancer cells.

RESULTS

Fluvastatin and lovastatin inhibited the in vitro cancer cell invasion induced by epidermal growth factor (EGF) in a manner sensitive to C3 transferase, a specific inhibitor of Rho. Treatment of ASPC-1 cells with fluvastatin markedly attenuated the EGF-induced translocation of RhoA from the cytosol to the membrane fraction and caused cell rounding. The effects of fluvastatin could be reversed by the addition of all-trans-geranylgeraniol. Administration of fluvastatin to nude mice reduced both metastatic tumor formation in the liver and the growth of established liver metastases at doses recommended for the treatment of hypercholesterolemia in humans.

CONCLUSIONS

HMG-CoA reductase inhibitors can be antimetastatic agents with the potential for useful clinical applications.

Sterol-independent regulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase in tumor cells

Elevated 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase expression supports synthesis of prenyl pyrophosphate intermediates required for tumor growth. In this study, the copy number of HMG-CoA reductase mRNA was determined in solid tumor and leukemic cell lines using competitive reverse transcriptase-polymerase chain reaction. Reductase mRNA was increased about eight-fold in Caco2 human colon adenocarcinoma cells compared with that in CCD18 normal colon cells. We also found a 50-fold enhancement of reductase mRNA in stimulated human lymphocytes compared with unstimulated cells. In CEM human leukemia cells, reductase mRNA was increased 8.6 times compared with that in stimulated lymphocytes. Greater low density lipoprotein receptor mRNA was also observed in tumor cells compared with normal counterparts. We hypothesized that elevated reductase mRNA was due to attenuation of sterol-mediated control of tumor reductase promoter activity. We first compared the methylation status of CpG dinucleotides in the promoters of reductase and p16 tumor suppressor genes from solid tumor, leukemic, and normal cells. As reported for other tumor cells the p16 promoter region was hypermethylated in Caco2 and CEM cells but was hypomethylated in corresponding normal cells. However, reductase promoter sequences in both normal and tumor cells were hypomethylated, demonstrating that methylation is not involved in sterol-independent reductase regulation. We addressed altered transcription factor binding to the tumor cell reductase promoter by transiently transfecting Caco2 and CCD18 with a plasmid vector containing a hamster HMG-CoA reductase promoter fused to the luciferase gene. We found that increased reductase mRNA was partially due to an approximately three-fold higher reductase promoter activity in Caco2 than in CCD18, measured by luciferase reporter assays. Thus, differential binding of transcription factor or factors on the tumor cell reductase promoter attenuates normal sterol-mediated regulation of reductase activity.

Estrogen-induced activation of Erk-1 and Erk-2 requires the G protein-coupled receptor homolog, GPR30, and occurs via trans-activation of the epidermal growth factor receptor through release of HB-EGF

Estrogen rapidly activates the mitogen-activated protein kinases, Erk-1 and Erk-2, via an as yet unknown mechanism. Here, evidence is provided that estrogen-induced Erk-1/-2 activation occurs independently of known estrogen receptors, but requires the expression of the G protein-coupled receptor homolog, GPR30. We show that 17beta-estradiol activates Erk-1/-2 not only in MCF-7 cells, which express both estrogen receptor alpha (ER alpha) and ER beta, but also in SKBR3 breast cancer cells, which fail to express either receptor. Immunoblot analysis using GPR30 peptide antibodies showed that this estrogen response was associated with the presence of GPR30 protein in these cells. MDA-MB-231 breast cancer cells (ER alpha-, ER beta+) are GPR30 deficient and insensitive to Erk-1/-2 activation by 17beta-estradiol. Transfection of MDA-MB-231 cells with a GPR30 complementary DNA resulted in overexpression of GPR30 protein and conversion to an estrogen-responsive phenotype. In addition, GPR30-dependent Erk-1/-2 activation was triggered by ER antagonists, including ICI 182,780, yet not by 17alpha-estradiol or progesterone. Consistent with acting through a G protein-coupled receptor, estradiol signaling to Erk-1/-2 occurred via a Gbetagamma-dependent, pertussis toxin-sensitive pathway that required Src-related tyrosine kinase activity and tyrosine phosphorylation of tyrosine 317 of the Shc adapter protein. Reinforcing this idea, estradiol signaling to Erk-1/-2 was dependent upon trans-activation of the epidermal growth factor (EGF) receptor via release of heparan-bound EGF (HB-EGF). Estradiol signaling to Erk-1/-2 could be blocked by: 1) inhibiting EGF-receptor tyrosine kinase activity, 2) neutralizing HB-EGF with antibodies, or 3) down-modulating HB-EGF from the cell surface with the diphtheria toxin mutant, CRM-197. Our data imply that ER-negative breast tumors that continue to express GPR30 may use estrogen to drive growth factor-dependent cellular responses.