Cyclosporine inhibits growth through the activating transcription factor/cAMP-responsive element-binding protein binding site in the cyclin D1 promoter

Förster Resonance Energy Transfer-Based Single-Cell Imaging Reveals Piezo1-Induced Ca2+ Flux Mediates Membrane Ruffling and Cell Survival

A mechanosensitive ion channel, Piezo1 induces non-selective cation flux in response to various mechanical stresses. However, the biological interpretation and underlying mechanisms of cells resulting from Piezo1 activation remain elusive. This study elucidates Piezo1-mediated Ca²⁺ influx driven by channel activation and cellular behavior using novel Förster Resonance Energy Transfer (FRET)-based biosensors and single-cell imaging analysis. Results reveal that extracellular Ca²⁺ influx via Piezo1 requires intact caveolin, cholesterol, and cytoskeletal support. Increased cytoplasmic Ca²⁺ levels enhance PKA, ERK, Rac1, and ROCK activity, which have the potential to promote cancer cell survival and migration. Furthermore, we demonstrate that Piezo1-mediated Ca²⁺ influx upregulates membrane ruffling, a characteristic feature of cancer cell metastasis, using spatiotemporal image correlation spectroscopy. Thus, our findings provide new insights into the function of Piezo1, suggesting that Piezo1 plays a significant role in the behavior of cancer cells.

Decoding the Phosphatase Code: Regulation of Cell Proliferation by Calcineurin

Calcineurin, a calcium-dependent serine/threonine phosphatase, integrates the alterations in intracellular calcium levels into downstream signaling pathways by regulating the phosphorylation states of several targets. Intracellular Ca²⁺ is essential for normal cellular physiology and cell cycle progression at certain critical stages of the cell cycle. Recently, it was reported that calcineurin is activated in a variety of cancers. Given that abnormalities in calcineurin signaling can lead to malignant growth and cancer, the calcineurin signaling pathway could be a potential target for cancer treatment. For example, NFAT, a typical substrate of calcineurin, activates the genes that promote cell proliferation. Furthermore, cyclin D1 and estrogen receptors are dephosphorylated and stabilized by calcineurin, leading to cell proliferation. In this review, we focus on the cell proliferative functions and regulatory mechanisms of calcineurin and summarize the various substrates of calcineurin. We also describe recent advances regarding dysregulation of the calcineurin activity in cancer cells. We hope that this review will provide new insights into the potential role of calcineurin in cancer development.

Targeting Ca2+ signaling: A new arsenal against cancer

The drug resistance of cancer cells is a major concern in medical oncology, resulting in the failure of chemotherapy. Ca²⁺ plays a pivotal role in inducing multidrug resistance in cancer cells. Calcium signaling is a critical regulator of many cancer hallmarks, such as angiogenesis, invasiveness, and migration. In this review, we describe the involvement of Ca²⁺ signaling and associated proteins in cancer progression and in the development of multidrug resistance in cancer cells. We also highlight the possibilities and challenges of targeting the Ca²⁺ channels, transporters, and pumps involved in Ca²⁺ signaling in cancer cells through structure-based drug design. This work will open a new therapeutic window to be used against cancer in upcoming years.

Targeting the Calcium Signalling Machinery in Cancer

Cancer is caused by excessive cell proliferation and a propensity to avoid cell death, while the spread of cancer is facilitated by enhanced cellular migration, invasion, and vascularization. Cytosolic Ca²⁺ is central to each of these important processes, yet to date, there are no cancer drugs currently being used clinically, and very few undergoing clinical trials, that target the Ca²⁺ signalling machinery. The aim of this review is to highlight some of the emerging evidence that targeting key components of the Ca²⁺ signalling machinery represents a novel and relatively untapped therapeutic strategy for the treatment of cancer.

Calcineurin regulates cyclin D1 stability through dephosphorylation at T286

The Calcineurin/NFAT (nuclear factor of activated T cells) pathway plays an essential role in the tumorigenic and metastatic properties in breast cancer. The molecular mechanism of the antiproliferative effect of calcineurin inhibition, however, is poorly understood. We found that calcineurin inhibition delayed cell cycle progression at G1/S, and promoted cyclin D1 degradation by inhibiting dephosphorylation at T286. Importantly, overexpression of cyclin D1 partially rescued delayed G1/S progression, thereby revealing cyclin D1 as a key factor downstream of calcineurin inhibition. Cyclin D1 upregulation is observed in human invasive breast cancers, and our findings indicate that dysregulation of T286 phosphorylation could play a role in this phenomenon. We therefore propose that targeting site specific phosphorylation of cyclin D1 could be a potential strategy for clinical intervention of invasive breast cancer.

Calcium signaling and cellular senescence

Cellular senescence is a stable cell proliferation arrest induced by a variety of stresses including telomere shortening, oncogene activation and oxidative stress. This process plays a crucial role in many physiopathological contexts, especially during aging when cellular senescence favors development of age-related diseases, shortening lifespan. However, the molecular and cellular mechanisms controlling senescence are still a matter of active research. In the last decade, there has been emerging literature indicating a key involvement of calcium signaling in cellular senescence. In this review we will initially give an account of the direct evidence linking calcium and the regulation of senescence. We will then review our current knowledge on the role of calcium in some senescence-associated features and physiopathological conditions, which will shed light on additional ways in which calcium signaling is implicated in cellular senescence.

Investigating the human Calcineurin Interaction Network using the πɸLxVP SLiM

Ser/thr phosphorylation is the primary reversible covalent modification of proteins in eukaryotes. As a consequence, it is the reciprocal actions of kinases and phosphatases that act as key molecular switches to fine tune cellular events. It has been well documented that ~400 human ser/thr kinases engage substrates via consensus phosphosite sequences. Strikingly, we know comparatively little about the mechanism by which ~40 human protein ser/thr phosphatases (PSPs) dephosphorylate ~15000 different substrates with high specificity. The identification of substrates of the essential PSP calcineurin (CN) has been exceptionally challenging and only a small fraction has been biochemically confirmed. It is now emerging that CN binds regulators and substrates via two short linear motifs (SLiMs), the well-studied PxIxIT SLiM and the LxVP SLiM, which remains controversial at the molecular level. Here we describe the crystal structure of CN in complex with its substrate NFATc1 and show that the LxVP SLiM is correctly defined as πɸLxVP. Bioinformatics studies using the πɸLxVP SLiM resulted in the identification of 567 potential CN substrates; a small subset was experimentally confirmed. This combined structural-bioinformatics approach provides a powerful method for dissecting the CN interaction network and for elucidating the role of CN in human health and disease.

Calcium signaling and cell proliferation

Cell proliferation is orchestrated through diverse proteins related to calcium (Ca(2+)) signaling inside the cell. Cellular Ca(2+) influx that occurs first by various mechanisms at the plasma membrane, is then followed by absorption of Ca(2+) ions by mitochondria and endoplasmic reticulum, and, finally, there is a connection of calcium stores to the nucleus. Experimental evidence indicates that the fluctuation of Ca(2+) from the endoplasmic reticulum provides a pivotal and physiological role for cell proliferation. Ca(2+) depletion in the endoplasmatic reticulum triggers Ca(2+) influx across the plasma membrane in an phenomenon called store-operated calcium entries (SOCEs). SOCE is activated through a complex interplay between a Ca(2+) sensor, denominated STIM, localized in the endoplasmic reticulum and a Ca(2+) channel at the cell membrane, denominated Orai. The interplay between STIM and Orai proteins with cell membrane receptors and their role in cell proliferation is discussed in this review.

Cyclic AMP-response element regulated cell cycle arrests in cancer cells

Recently, we have demonstrated that trichosanthin (TCS), a promising agent for the treatment of cervical adenocarcinoma, inhibited HeLa cell proliferation through the PKC/MAPK/CREB signal pathway. Furthermore, TCS down-regulated Bcl-2 expression was abrogated by a decoy oligonucleotide (OGN) to the cyclic AMP-responsive element (CRE). The decoy OGN blocked the binding of CRE-binding protein (CREB) to Bcl-2. These results suggested that CRE-mediated gene expression may play a pivotal role in HeLa cell proliferation. However, little is known about the effect of TCS on cell cycle arrests, particularly, whether the genes involved in cell cycle were regulated by CRE. Our present study shows that the arrests of S, G1 and G2/M phases were accompanied by the significant down-regulation of cyclin A, D1 and CDK 2, 4 in HeLa cells, cyclin D1, E and CDK 2, 4 in Caski and C33a cells, and cyclin A, B1, E and CDK 2 in SW1990 cells. However, the cell cycle arrests were reversed via the significant up-regulation of cyclin A and D1, by the combined treatment of TCS and CRE. In conclusion, these data demonstrate for the first time that specific cell cycle arrests in cancer cells can be induced by TCS by inhibiting the binding of CREB to CRE on genes related to cell proliferation.

Examining the role of cyclin D1 in breast cancer

Cyclin D1 overexpression is found in more than 50% of human breast cancers and causes mammary cancer in transgenic mice. Dysregulation of cyclin D1 gene expression or function contributes to the loss of normal cell cycle control during tumorigenesis. Recent studies have demonstrated that cyclin D1 conducts additional specific functions to regulate gene expression in the context of local chromatin, promote cellular migration and inhibit mitochondrial metabolism. It is anticipated that these additional functions contribute to the pathology associated with dysregulated cyclin D1 abundance. This article discusses evidence that examines the significance of cyclin D1 in breast cancer with emphasis on its role in breast cancer stem cell expansion.

The elements of human cyclin D1 promoter and regulation involved

Cyclin D1 is a cell cycle machine, a sensor of extracellular signals and plays an important role in G1-S phase progression. The human cyclin D1 promoter contains multiple transcription factor binding sites such as AP-1, NF-қB, E2F, Oct-1, and so on. The extracellular signals functions through the signal transduction pathways converging at the binding sites to active or inhibit the promoter activity and regulate the cell cycle progression. Different signal transduction pathways regulate the promoter at different time to get the correct cell cycle switch. Disorder regulation or special extracellular stimuli can result in cell cycle out of control through the promoter activity regulation. Epigenetic modifications such as DNA methylation and histone acetylation may involved in cyclin D1 transcriptional regulation.

Ca(2+) signaling, genes and the cell cycle

Changes in the concentration and spatial distribution of Ca(2+) ions in the cytoplasm constitute a ubiquitous intracellular signaling module in cellular physiology. With the advent of Ca(2+) dyes that allow direct visualization of Ca(2+) transients, combined with powerful experimental tools such as electrophysiological recordings, intracellular Ca(2+) transients have been implicated in practically every aspect of cellular physiology, including cellular proliferation. Ca(2+) signals are associated with different phases of the cell cycle and interfering with Ca(2+) signaling or downstream pathways often disrupts progression of the cell cycle. Although there exists a dependence between Ca(2+) signals and the cell cycle the mechanisms involved are not well defined and given the cross-talk between Ca(2+) and other signaling modules, it is difficult to assess the exact role of Ca(2+) signals in cell cycle progression. Two exceptions however, include fertilization and T-cell activation, where well-defined roles for Ca(2+) signals in mediating progression through specific stages of the cell cycle have been clearly established. In the case of T-cell activation Ca(2+) regulates entry into the cell cycle through the induction of gene transcription.

Lef-1 isoforms regulate different target genes and reduce cellular adhesion

The lymphoid enhancer factor 1 (Lef-1) belongs to the nuclear transducers of canonical Wnt-signalling in embryogenesis and cancer. Lef-1 acts, in cooperation with beta-catenin, as a context-dependent transcriptional activator or repressor, thereby influencing multiple cellular functions such as proliferation, differentiation and migration. Here we report that an increased Lef-1 expression in human pancreatic cancer correlates with advanced tumour stages. In pancreatic tumours, two different transcripts of Lef-1 have been detected in various stages, as demonstrated by RT-PCR analysis. One transcript was identified as the full length Lef-1 (Lef-1 FL), whereas the second, shorter transcript lacked exon VI (Lef-1 Deltaexon VI) compared to the published sequence. Comparative analysis of these two Lef-1 variants revealed that they exhibit different cellular effects after transient expression in pancreatic carcinoma cells. Forced expression of Lef-1 Deltaexon VI inhibited E-cadherin expression in a beta-catenin-independent way. Increased amounts of Lef-1 Deltaexon VI resulted in reduced cellular aggregation and increased cell migration. Expression of Lef-1 FL, but not the newly identified Lef-1 Deltaexon VI, induced the expression of the cell cycle regulating proteins c-myc and cyclin D1 in cooperation with beta-catenin and it enhanced cell proliferation. Our findings indicate that expression of alternatively spliced Lef-1 isoforms is involved in the determination of proliferative or migratory characteristics of pancreatic carcinoma cells.

MeCP2 expression and promoter methylation of cyclin D1 gene are associated with cyclin D1 expression in developing rat epididymal duct

Hypermethylation-dependent silencing of the gene is achieved by recruiting methyl-CpG binding proteins (MeCPs). Among the MeCPs, MeCP2 is the most abundantly and ubiquitously expressed in various types of cells. We first screened the distribution and expression pattern of MeCP2 in adult and developing rat tissues and found strong MeCP2 expression, albeit rather ubiquitously among normal tissues, in ganglion cells and intestinal epithelium in the small intestine, in Purkinje cells and neurons in the brain, in spermatogonia and in epithelial cells in the epididymal duct of the testis. We then assessed the expression and the methylation pattern of the promoter region of cyclin D1 by immunohistochemistry and sodium bisulfite mapping, and found that cyclin D1 expression in the epididymal duct decreased rapidly during rat development: strong in newborn rats and very weak or almost negative in 7-day-old rats. Mirroring the decrease of cyclin D1 expression, methylated cytosine at both CpG and non-CpG loci in the cyclin D1 promoter was frequently observed in the epididymal duct of 7-day-old rats but not in that of newborn rats. Interestingly, MeCP2 expression also increased concomitant with the increase of methylation. Cyclin D1 expression in the epididymal duct may be efficiently regulated by the epigenetic mechanism of the cooperative increase of MeCP2 expression and promoter methylation.

Ca2+ signalling checkpoints in cancer: remodelling Ca2+ for cancer cell proliferation and survival

Increases in cytosolic free Ca2+ ([Ca2+]i) represent a ubiquitous signalling mechanism that controls a variety of cellular processes, including proliferation, metabolism and gene transcription, yet under certain conditions increases in intracellular Ca2+ are cytotoxic. Thus, in using Ca2+ as a messenger, cells walk a tightrope in which [Ca2+]i is strictly maintained within defined boundaries. To adhere to these boundaries and to sustain their modified phenotype, many cancer cells remodel the expression or activity of their Ca2+ signalling apparatus. Here, we review the role of Ca2+ in promoting cell proliferation and cell death, how these processes are remodelled in cancer and the opportunities this might provide for therapeutic intervention.

cAMP-response element binding protein (CREB) regulates cyclosporine-A-mediated down-regulation of cathepsin B and L synthesis

Cyclosporin A (CsA) is an immunosuppressant with severe side effects including gingival overgrowth. We have previously reported that CsA impairs the activity of the lysosomal enzymes cathepsin B and L in human gingival fibroblasts (HGFs). Here, we have examined the effects of CsA on the DNA-binding activity of the cyclic AMP response element-binding protein (CREB) and cell viability, and the effects of CREB on cathepsin B and L synthesis and activity in HGFs. We have confirmed that CsA down-regulates cathepsin B and L synthesis. Further, CsA has no effect on cell viability and dramatically impairs CREB-DNA binding activity. Importantly, the synthesis of cathepsin B and L is down-regulated, and their activity is also significantly impaired in HGFs transfected with plasmid expressing dominant-negative CREB. These results suggest that CREB is essential for the CsA-mediated down-regulation of cathepsin B and L synthesis in HGFs.

The immunophilin ligands cyclosporin A and FK506 suppress prostate cancer cell growth by androgen receptor-dependent and -independent mechanisms

The androgen receptor (AR) contributes to growth of prostate cancer even under conditions of androgen ablation. Thus, new strategies to target AR activity are needed. The AR interacts with the immunophilin FK506-binding protein 52 (FKBP52), and studies in the FKBP52 knockout mouse have shown that this protein is essential to AR activity in the prostate. Therefore, we tested whether the immunophilin ligand FK506 affected AR activity in prostate cancer cell lines. We also tested the hypothesis that the AR interacts with another immunophilin, cyclophilin 40 (Cyp40), and is regulated by its cognate ligand cyclosporin A (CsA). We show that levels of FKBP52, FKBP51, Cyp40, and a related co-chaperone PP5 were much higher in prostate cancer cells lines [(LNCaP), PC-3, and DU145] compared with primary prostate cells, and that the AR of LNCaP cells can interact with Cyp40. In the absence of androgen, CsA caused inhibition of cell growth in the AR-positive LNCaP and AR-negative PC-3 and DU145 cell lines. Interestingly, FK506 only inhibited LNCaP cells, suggesting a dependence on the AR for this effect. Both CsA and FK506 inhibited growth without inducing apoptosis. In LNCaP cells, CsA completely blocked androgen-stimulated growth, whereas FK506 was partially effective. Further studies in LNCaP cells revealed that CsA and FK506 were able to block or attenuate several stages of AR signaling, including hormone binding, nuclear translocation, and activity at several AR-responsive reporter and endogenous genes. These findings provide the first evidence that CsA and FK506 can negatively modulate proliferation of prostate cells in vitro. Immunophilins may now serve as new targets to disrupt AR-mediated prostate cancer growth.

Phosphoinositide-3-kinase signaling controls S-phase kinase-associated protein 2 transcription via E2F1 in pancreatic ductal adenocarcinoma cells

The phosphoinositide-3-kinase (PI3K)/AKT signaling pathway controls fundamental processes of cancer cell biology like proliferation and cell survival. The PI3K/AKT pathway is activated in pancreatic ductal adenocarcinoma (PDAC) cells. The molecular mechanisms linking PI3K signaling to the cell cycle machinery in PDAC cells are not investigated in detail. Using the PI3K inhibitor Ly294002 as well as small interfering RNA targeting AKT1 expression, we show that PI3K controls the proliferation and G(1) phase progression of PDAC cells. Gene profiling revealed several important regulators of G(1)-S phase progression controlled by PI3K signaling like p21(Cip1), S-phase kinase-associated protein 2 (SKP2), CDC25a, cyclin A, cyclin D2, CDK2, and cyclin E. We show that the F-box protein SKP2, an oncogene up-regulated in PDAC, is transcriptionally regulated by the PI3K/AKT1 pathway in PDAC cells. At the molecular level, the control of the SKP2 gene by PI3K is due to the regulation of E2F1 binding to the proximal SKP2 gene promoter. The complex and profound connection of PI3K/AKT1 signaling to the cell cycle qualifies this pathway as a suitable target for therapeutic intervention in PDAC.

Protein expression profiling identifies cyclophilin A as a molecular target in Fhit-mediated tumor suppression

Loss of fragile histidine triad (Fhit) expression is often associated with human malignancies, and Fhit functions as a tumor suppressor in controlling cell growth and apoptosis, although specific signal pathways are still undefined. We have used a proteomic approach to define proteins in the Fhit-mediated tumor suppression pathway. Because substitution of Tyr(114) (Y114) with phenylalanine (Y114F) diminishes Fhit functions, we did protein expression profiling to identify proteins differentially expressed in Fhit-negative H1299 lung cancer cells infected with wild-type (Ad-FHIT-wt) and Y114 mutant FHIT-expressing (Ad-FHIT-Y114F) adenoviruses. Among 12 distinct proteins that exhibited 4-fold differences in expression on comparison of the two infected cell lysates, cyclophilin A, the intracellular reporter of the immunosuppressive drug cyclosporine A, showed a remarkably decreased protein level in cells infected with Ad-FHIT-wt versus Ad-FHIT-Y114F. Conversely, loss of Fhit expression resulted in increased cyclophilin A expression in mouse tissues and cell lines. Restoration of Fhit expression led to down-regulated cyclophilin A protein expression and subsequently prevented cyclophilin A-induced up-regulation of cyclin D1, Cdk4, and resultant cell cycle progression (G(1)-S transition), which was independent of Ca(2+)/calmodulin-dependent kinase inhibitor, KN-93. Interestingly, Fhit down-modulation of phosphatase activity of calcineurin, which controls cyclin D1/Cdk4 activation, was reversed by cyclophilin A treatment in a concentration-dependent manner, a reversal that was inhibited by additional cyclosporine A treatment. Thus, cyclophilin A is a downstream target in Fhit-mediated cessation of cell cycle progression at late G(1) phase. Elucidation of the protein effectors of Fhit signaling may lead to identification of targets for lung cancer therapy.

IKKalpha controls p52/RelB at the skp2 gene promoter to regulate G1- to S-phase progression

The IkappaB-inducing kinase (IKK) is composed of two catalytic subunits, IKKalpha and IKKbeta, and a regulatory subunit, IKKgamma. IKK-regulated signaling pathways are believed to promote the proliferation of normal cells as well as the aberrant proliferation of cancer cells. The molecular mechanisms linking the IKK signaling pathway components to the cell cycle machinery are not entirely understood. To study the function(s) of the catalytic subunits of the IKK complex, we used pancreatic cancer cells, with constitutive IKK activity. We show that the G1 phase of the cell cycle is specifically regulated by the IKKalpha subunit, which regulates the stability of the cyclin-dependent kinase inhibitor p27(Kip1). Increased p27(Kip1) protein levels following the transfection of IKKalpha-specific siRNAs are a result of the downregulation of the F-box protein S-phase kinase-associated protein 2 (skp2). Additionally, we demonstrate that IKKalpha signaling regulates the transcription of the skp2 gene by controlling the composition of a RelB-containing NF-kappaB complex. Together, this work defines a novel IKKalpha-regulated growth pathway involving the p52/RelB-dependent transcriptional regulation of the skp2 gene.

GADD45alpha is highly expressed in pancreatic ductal adenocarcinoma cells and required for tumor cell viability

Pancreatic ductal adenocarcinoma is one of the most common causes of cancer death in the western civilization. Recently, NF-kappaB has been shown to be activated in pancreatic ductal adenocarcinoma through constitutive activation of IkappaB kinase (IKK). Inhibition of NF-kappaB by a super-inhibitor of NF-kappaB--delta-N-IkappaBalpha--resulted in impaired proliferation and induction of apoptosis, suggesting an important role of NF-kappaB in pancreatic tumorigenesis. Downstream target genes of IkappaBalpha have not been elucidated in pancreatic ductal adenocarcinoma in detail. Using expression profiling by cDNA array analysis of pancreatic ductal adenocarcinoma cell lines stably transfected with super-IkappaBalpha, we identified GADD45alpha as a significant regulated gene. GADD45alpha is overexpressed in pancreatic ductal adenocarcinoma at the mRNA and protein level. Using RNAi we show that downregulation of GADD45alpha reduces proliferation and induces apoptosis in pancreatic cancer cells. These findings provide evidence that GADD45alpha contributes to pancreatic cancer cell proliferation and viability.

Epidermal growth factor activates nuclear factor-κB in human proximal tubule cells

The promotion of cell survival and regeneration in acute renal failure (ARF) is important for the restitution of renal function. Epidermal growth factor (EGF) has been implicated in the regulation of cell proliferation. We provide evidence for a direct link between EGF, nuclear factor-κB (NF-κB), and cell cycle regulation (cyclin D1). EGF was found to stimulate NF-κB-dependent gene transcription and DNA binding. In addition, EGF stimulated cyclin D1 promoter activity as well as cyclin D1 expression. Moreover, inhibition of NF-κB caused a pronounced reduction of EGF-induced cyclin D1 promoter activity. Furthermore, both EGF-mediated NF-κB activation and cyclin D1 expression were inhibited by coexpression of super IκB. Taken together, these data identify NF-κB and cyclin D1 as downstream targets of EGF and establish a molecular link between stimulation of EGF via activation of NF-κB and cyclin D1 expression in human proximal tubular cells.

The effect of cyclosporin A on airway cell proinflammatory signaling and pneumonia

Cyclosporin A (CsA) blocks T cell activation by interfering with the Ca2+-dependent phosphatase, calcineurin. Proinflammatory responses to bacteria that are activated by Ca2+-fluxes in airway cells are a potential target for CsA. Although local immunosuppression may be advantageous to control airway inflammation, it could also increase susceptibility to bacterial pneumonia and invasive infection. As aerosolized CsA is currently under study in lung transplantation, we examined its direct effects on airway cells as well as in a murine model of pneumonia. Epithelial interleukin-6 production was very effectively inhibited by CsA, whereas CXCL8 production, the major PMN chemokine, was only modestly diminished. Responses to a TLR2 agonist Pam3Cys were more sensitive to CsA inhibition than those activated by Pseudomonas aeruginosa. CsA substantially blocked activation of nuclear factor of activated T cells and cAMP-responsive element-binding protein (P<0.001), inhibited CCAAT/enhancer-binding protein by 50% (P<0.05), and minimally blocked activator protein-1 and nuclear factor-kappaB responses to bacteria in epithelial cells. The in vitro effects were confirmed in a mouse model of P. aeruginosa infection with similar rates of PMN recruitment, pneumonia and mortality in CsA treated and control mice. These studies indicate that airway epithelial signaling is a potential target for CsA, and such local immunosuppression may not increase susceptibility to invasive infection.

Effect of cyclosporin A treatment on the in vivo regulation of type I MHC gene expression

Rat soleus muscle consists predominantly of slow type I fibers. We have shown previously through deletion analysis that the highest level of reporter activity that we measure when injecting type I myosin heavy chain (MHC) promoter (MHC1)-linked luciferase plasmid into soleus muscles depends on the presence of a 550-bp upstream enhancer (3,450–2,900) region of the promoter. Because the calcineurin-nuclear factor of activated T cells (NFAT) pathway has been implicated in the regulation of the slow muscle gene program, particularly the MHC1isoform, and the MHC1promoter contains several putative NFAT sites, we examined via deletion and mutation analyses whether this pathway is involved in the regulation of promoter activity in soleus. Nine days of treatment with the calcineurin inhibitor cyclosporin A (CsA) caused a significant decrease in activity of the −3,500- and −3,450-bp promoters compared with vehicle-treated rats. Truncation of the promoter to −2,900 bp or smaller reduced the activity and also eliminated the CsA responsiveness, thus implying that the enhancer region is required for CsA responsiveness. Surprisingly, mutating the two NFAT elements within the enhancer region had no obvious effect on promoter activity. CsA treatment resulted in an increase in the mRNA levels of fast-type IIa and IIx MHC isoforms, but RT-PCR analysis of MHC1pre-mRNA and mature mRNA expression in soleus muscles revealed no differences between vehicle- and CsA-treated rats. Although CsA affects the activity of the MHC1promoter, it appears that its effect is not through direct binding of NFAT to sites on the promoter.

Targeted expression of calmodulin increases ventricular cardiomyocyte proliferation and deoxyribonucleic acid synthesis during mouse development

The cell signaling pathways that control ventricular cardiomyocyte proliferation during development are poorly understood. Here we show that increasing levels of the ubiquitous Ca(2+) receptor calmodulin (CaM) can regulate cardiomyocyte proliferation in vivo. Targeted overexpression of calmodulin in the heart during embryonic development leads to a 37% or a 79% increase in the number of ventricular myocytes present at embryonic d 17 in mice heterozygous or homozygous for the transgene, respectively. Whereas all homozygous mice die within 10 d after birth, most of the heterozygous mice survive even though they contain 40% more ventricular myocytes relative to the wild-type mice throughout development and into adulthood. The CaM transgene continues to be overexpressed postnatally and, although cell proliferation ceases soon after birth, the elevated levels of CaM lead to an increase in DNA synthesis, which correlates with an increase in the degree of ventricular myocyte polyploidy. Only after proliferation has ceased and polyploidy has become maximal does the continued presence of overexpressed CaM lead to ventricular hypertrophy. However, unlike the case for myocyte number, turning off expression of the CaM transgene results in regression of the hypertrophic response. Together, our results reveal that excess CaM enhances the extent of cell proliferation and DNA synthesis as well as development of hypertrophy of ventricular myocytes in vivo, in a manner consistent with the normal timing of these events during heart development.

Characterization of the role of Sp1 and NF-Y in differential regulation of PTTG/securin expression in tumor cells

Pituitary tumor transforming gene (PTTG), also known as securin, is a regulator of cell division that is overexpressed in many tumors. Its expression is cell cycle regulated, although its transcriptional regulation is yet to be determined. The 5' RACE analysis of the human testis mRNA revealed the existence of a previously unreported transcription start site at 317 bp upstream of the translation start site (ATG). This gene is known to be composed of five exons and four introns, which is now changed to six exons and five introns. To map the promoter region, and to understand its regulation, we designed several fusion constructs of the 5' flanking region of PTTG including the sequence from nucleotide -1373 to -3 (relative to the translation start site) to a luciferase reporter gene. Transient transfection of these constructs in prostate cancer cell line (PC-3) and fibroblast cell line (HS27) confirmed the existence of promoter for PTTG between nucleotides -161 and -3 (in relation to translation start site). The 5' and 3' deletion analysis of the PTTG flanking region and electrophoretic mobility shift assays revealed binding of Sp1 and NF-Y transcription factors within nucleotides -540 to -500. Chromatin immunoprecipitation (ChIP) assays of the HS27 and PC-3 cells revealed the binding of Sp1 protein to PTTG promoter sequence in vivo. Site-directed mutagenesis of the Sp1 consensus sequence resulted in approximately 70% reduction of the overall transcriptional activation of the PTTG promoter, whereas mutation of the NF-Y sequence resulted in approximately 25% reduction. Deletion of both Sp1 and NF-Y consensus sequences resulted in 90% loss of PTTG promoter activity. It was further observed, by Western blot analysis, that the levels of Sp1 protein are higher in PC-3 cells when compared to levels in HS27 cells, possibly contributing to a tissue-specific effect. Our studies indicate an important role of Sp1 in transcription regulation of PTTG expression in tumors.

Involvement of neuron-derived orphan receptor-1 (NOR-1) in LDL-induced mitogenic stimulus in vascular smooth muscle cells: role of CREB

OBJECTIVE

Low density lipoproteins (LDLs) modulate the expression of key genes involved in atherogenesis. Recently, we have shown that the transcription factor neuron-derived orphan receptor-1 (NOR-1) is involved in vascular smooth muscle cell (VSMC) proliferation. Our aim was to analyze whether NOR-1 is involved in LDL-induced mitogenic effects in VSMC.

METHODS AND RESULTS

LDL induced NOR-1 expression in a time- and dose-dependent manner. Antisense oligonucleotides against NOR-1 inhibit DNA synthesis induced by LDL in VSMCs as efficiently as antisense against the protooncogene c-fos. The upregulation of NOR-1 mRNA levels by LDL involves pertusis-sensitive G protein-coupled receptors, Ca2+ mobilization, protein kinases A (PKA) and C (PKC) activation, and mitogen-activated protein kinase pathways (MAPK) (p44/p42 and p38). LDL promotes cAMP response element binding protein (CREB) activation (phosphorylation in Ser133). In transfection assays a dominant-negative of CREB inhibits NOR-1 promoter activity, while mutation of specific (cAMP response element) CRE sites in the NOR-1 promoter abolishes LDL-induced NOR-1 promoter activity.

CONCLUSIONS

In VSMCs, LDL-induced mitogenesis involves NOR-1 upregulation through a CREB-dependent mechanism. CREB could play a role in the modulation by LDL of key genes (containing CRE sites) involved in atherogenesis.

Calcineurin regulates cyclin D1 accumulation in growth-stimulated fibroblasts

Calcium (Ca(2+)) and calmodulin (CaM) are required for progression of mammalian cells from quiescence into S phase. In multiple cell types, cyclosporin A causes a G(1) cell cycle arrest, implicating the serine/threonine phosphatase calcineurin as one Ca(2+)/CaM-dependent enzyme required for G(1) transit. Here, we show, in diploid human fibroblasts, that cyclosporin A arrested cells in G(1) before cyclin D/cdk4 complex activation and retinoblastoma hyperphosphorylation. This arrest occurred in early G(1) with low levels of cyclin D1 protein. Because cyclin D1 mRNA was induced normally in the cyclosporin A-treated cells, we analyzed the half-life of cyclin D1 in the presence of cyclosporin A and found no difference from control cells. However, cyclosporin A treatment dramatically reduced cyclin D1 protein synthesis. Although these pharmacological experiments suggested that calcineurin regulates cyclin D1 synthesis, we evaluated the effects of overexpression of activated calcineurin on cyclin D1 synthesis. In contrast to the reduction of cyclin D1 with cyclosporin A, ectopic expression of calcium/calmodulin-independent calcineurin promoted synthesis of cyclin D1 during G(1) progression. Therefore, calcineurin is a Ca(2+)/CaM-dependent target that regulates cyclin D1 accumulation in G(1).

Gene expression profiles of I3C- and DIM-treated PC3 human prostate cancer cells determined by cDNA microarray analysis

Studies from our laboratory and others have shown that indole-3-carbinol (I3C) and its in vivo dimeric product, 3,3'-diindolylmethane (DIM), inhibit the growth of PC3 prostate cancer cells and induce apoptosis by inhibiting nuclear factor (NF)-kappaB and Akt pathways. To obtain comprehensive gene expression profiles altered by I3C- and DIM-treated PC3 cells, we utilized cDNA microarray to interrogate the expression of 22,215 known genes using the Affymetrix Human Genome U133A Array. We found a total of 738 genes that showed a greater than twofold change after 24 h of DIM treatment. Among these genes, 677 genes were down-regulated and 61 were up-regulated. Similarly, 727 genes showed a greater than twofold change in expression, with down-regulation of 685 genes and up-regulation of 42 genes in I3C-treated cells. The altered expressions of genes were observed as early as 6 h and were more evident with longer treatment. Upon cluster analysis, we found that both I3C and DIM up-regulated the expression of genes that are related to the Phase I and Phase II enzymes, suggesting their increased capacity for detoxification of carcinogens or chemicals. We also found that I3C and DIM down-regulated the expression of genes that are critically involved in the regulation of cell growth, cell cycle, apoptosis, signal transduction, Pol II transcription factor and oncogenesis. Real-time reverse transcription-polymerase chain reaction analysis was conducted to confirm the cDNA microarray data, and the results were consistent. We conclude that I3C and DIM affected the expression of a large number of genes that are related to the control of carcinogenesis, cell survival and physiologic behaviors. This may help determine the molecular mechanism(s) by which I3C and DIM exert their pleiotropic effects on PC3 prostate cancer cells; in addition, this information could be further exploited for devising chemopreventive and/or therapeutic strategies for prostate cancer.