Overexpression of p27(Kip1) by doxycycline-regulated adenoviral vectors inhibits endothelial cell proliferation and migration and impairs angiogenesis

Metformin and insulin-resistant related diseases: Emphasis on the role of microRNAs

Metformin is one of the most prescribed drugs in type II diabetes (T2DM) which has recently found new applications in the prevention and treatment of various illnesses, from metabolic disorders to cardiovascular and age-related diseases. Metformin improves insulin resistance (IR) by modulating metabolic mechanisms and mitochondrial biogenesis. Alternation of microRNAs (miRs) in the treatment of IR-related illnesses has been observed by metformin therapy. MiRs are small non-coding RNAs that play important roles in RNA silencing, targeting the 3'untranslated region (3'UTR) of most mRNAs and inhibiting the translation of related proteins. As a result, their dysregulation is associated with many diseases. Metformin may alter miRs levels in the treatment of various diseases by AMPK-dependent or AMPK-independent mechanisms. Here, we summarized the therapeutic role of metformin by modifying the aberrant expression of miRs as potential biomarkers or therapeutic targets in diseases in which IR plays a key role.

P27 Protects Neurons from Ischemic Damage by Suppressing Oxidative Stress and Increasing Autophagy in the Hippocampus

p27^Kip1 (p27), a well-known cell regulator, is involved in the regulation of cell death and survival. In the present study, we observed the effects of p27 against oxidative stress induced by H₂O₂ in HT22 cells and transient ischemia in gerbils. Tat (trans-acting activator of transcription) peptide and p27 fusion proteins were prepared to facilitate delivery into cells and across the blood-brain barrier. The tat-p27 fusion protein, rather than its control protein Control-p27, was delivered intracellularly in a concentration and incubation time-dependent manner and showed its activity in HT22 cells. The localization of the delivered Tat-p27 protein was also confirmted in the HT22 cells and hippocampus in gerbils. In addition, the optimal concentration (5 μM) of Tat-p27 was determined to protect neurons from cell death induced by 1 mM H₂O₂. Treatment with 5 μM Tat-p27 significantly ameliorated H₂O₂-induced DNA fragmentation and the formation of reactive oxygen species (ROS) in HT22 cells. Tat-p27 significantly mitigated the increase in locomotor activity a day after ischemia and neuronal damage in the hippocampal CA1 region. It also reduced the ischemia-induced membrane phospholipids and ROS formation. In addition, Tat-p27 significantly increased microtubule-associated protein 1A/1B light chain 3A/3B expression and ameliorated the H₂O₂ or ischemia-induced increases of p62 and decreases of beclin-1 in the HT22 cells and hippocampus. These results suggest that Tat-p27 protects neurons from oxidative or ischemic damage by reducing ROS-induced damage and by facilitating the formation of autophagosomes in hippocampal cells.

An Overview of In Vitro, In Vivo, and Computational Techniques for Cancer-Associated Angiogenesis Studies

Angiogenesis is a crucial area in scientific research because it involves many important physiological and pathological processes. Indeed, angiogenesis is critical for normal physiological processes, including wound healing and embryonic development, as well as being a component of many disorders, such as rheumatoid arthritis, obesity, and diabetic retinopathies. Investigations of angiogenic mechanisms require assays that can activate the critical steps of angiogenesis as well as provide a tool for assessing the efficacy of therapeutic agents. Thus, angiogenesis assays are key tools for studying the mechanisms of angiogenesis and identifying the potential therapeutic strategies to modulate neovascularization. However, the regulation of angiogenesis is highly complex and not fully understood. Difficulties in assessing the regulators of angiogenic response have necessitated the development of an alternative approach. In this paper, we review the standard models for the study of tumor angiogenesis on the macroscopic scale that include in vitro, in vivo, and computational models. We also highlight the differences in several modeling approaches and describe key advances in understanding the computational models that contributed to the knowledge base of the field.

Advances in mammalian target of rapamycin kinase inhibitors: application to devices used in the treatment of coronary artery disease

Mammalian target of rapamycin (mTOR) inhibitors have been applied to vascular coronary devices to avoid neointimal growth and have become the predominant pharmacological agents used to prevent restenosis. mTOR inhibitors can affect not only proliferating vascular smooth muscle cells but also endothelial cells and therefore can result in delayed healing of the vessel including endothelialization. Emerging evidence suggests accelerated atherosclerosis due to the downstream negative effects on endothelial barrier functional recovery. The development of neoatherosclerosis within the neointima of drug-eluting stents can result in late thrombotic events. This type of problematic healing response may open the way for specific mTOR kinase inhibitors, such as ATP-competitive mTOR inhibitors. These inhibitors demonstrate a better healing profile than traditional limus-based drug-eluting stent and their clinical efficacy remains unknown.

Gene Therapy with Tetracycline-Regulated Human Recombinant COLIA1 cDNA Direct Adenoviral Delivery Enhances Fracture Healing in Osteoporotic Rats

A number of previous studies have indicated that the genetic variation at the collage type I alpha 1 (COLIA1) gene locus influences susceptibility to osteoporosis. However, seldom have studies reported the effect of gene delivery using an adenovirus vector carrying human recombinant COLIA1 cDNA on stimulating osteogenic activity of osteoblasts and enhancing fracture healing of ovariectomized rats. The current study was performed to demonstrate whether direct gene delivery using an adenovirus vector carrying human recombinant COLIA1 cDNA could stimulate osteogenic activity of osteoblast in vitro and enhance fracture healing of ovariectomized rats in vivo. In vitro, the tet-on system regulated COLIA1 gene adenovirus was constructed and transfected to osteoblasts. COLIA1 mRNA and collagen type I levels were assessed by reverse transcription polymerase chain reaction and enzyme-linked immunosorbent assay to determine whether adenovirus transfected successfully. Osteogenic activity of the osteoblasts was assessed by alkaline phosphatase activity, immunohistochemical staining, immunofluorescent staining, mineralized matrix formation, and extracellular calcium levels. In vivo, adenovirus-delivered COLIA1 gene was injected into the fracture site of the tibia in an ovariectomized rat model of osteoporosis, and bone callus condition was assessed to determine whether the COLIA1 gene could accelerate osteoporotic fracture healing. In vitro, the results showed that COLIA1 gene adenovirus transfection could increase osteoblast COLIA1 gene expression and collagen type I protein synthesis, increase alkaline phosphatase activity, and stimulate calcium nodules formation, which exhibited a direct osteogenic effect on the osteoblasts. In vivo, local injection of COLIA1 gene adenovirus increased collagen type I expression, restored bone mineral density, and accelerated fracture healing in ovariectomized rats, without increasing serum collagen type I and liver COLIA1 mRNA levels. This study suggests direct gene delivery using an adenovirus carrying human COLIA1 cDNA can stimulate the osteogenic activity of osteoblasts in vitro and enhance bone fracture healing in vivo. The tet-on system is an ideal gene regulatory system for effective and safe regulation of the therapeutic gene.

Shear-induced Notch-Cx37-p27 axis arrests endothelial cell cycle to enable arterial specification

Establishment of a functional vascular network is rate-limiting in embryonic development, tissue repair and engineering. During blood vessel formation, newly generated endothelial cells rapidly expand into primitive plexi that undergo vascular remodeling into circulatory networks, requiring coordinated growth inhibition and arterial-venous specification. Whether the mechanisms controlling endothelial cell cycle arrest and acquisition of specialized phenotypes are interdependent is unknown. Here we demonstrate that fluid shear stress, at arterial flow magnitudes, maximally activates NOTCH signaling, which upregulates GJA4 (commonly, Cx37) and downstream cell cycle inhibitor CDKN1B (p27). Blockade of any of these steps causes hyperproliferation and loss of arterial specification. Re-expression of GJA4 or CDKN1B, or chemical cell cycle inhibition, restores endothelial growth control and arterial gene expression. Thus, we elucidate a mechanochemical pathway in which arterial shear activates a NOTCH-GJA4-CDKN1B axis that promotes endothelial cell cycle arrest to enable arterial gene expression. These insights will guide vascular regeneration and engineering.

Cell-cycle arrest in mature adipocytes impairs BAT development but not WAT browning, and reduces adaptive thermogenesis in mice

We previously reported brown adipocytes can proliferate even after differentiation. To test the involvement of mature adipocyte proliferation in cell number control in fat tissue, we generated transgenic (Tg) mice over-expressing cell-cycle inhibitory protein p27 specifically in adipocytes, using the aP2 promoter. While there was no apparent difference in white adipose tissue (WAT) between wild-type (WT) and Tg mice, the amount of brown adipose tissue (BAT) was much smaller in Tg mice. Although BAT showed a normal cellular morphology, Tg mice had lower content of uncoupling protein 1 (UCP1) as a whole, and attenuated cold exposure- or β3-adrenergic receptor (AR) agonist-induced thermogenesis, with a decrease in the number of mature brown adipocytes expressing proliferation markers. An agonist for the β3-AR failed to increase the number of proliferating brown adipocytes, UCP1 content in BAT, and oxygen consumption in Tg mice, although the induction and the function of beige adipocytes in inguinal WAT from Tg mice were similar to WT mice. These results show that brown adipocyte proliferation significantly contributes to BAT development and adaptive thermogenesis in mice, but not to induction of beige adipocytes.

SIAH ubiquitin ligases regulate breast cancer cell migration and invasion independent of the oxygen status

Seven-in-absentia homolog (SIAH) proteins are evolutionary conserved RING type E3 ubiquitin ligases responsible for the degradation of key molecules regulating DNA damage response, hypoxic adaptation, apoptosis, angiogenesis, and cell proliferation. Many studies suggest a tumorigenic role for SIAH2. In breast cancer patients SIAH2 expression levels correlate with cancer aggressiveness and overall patient survival. In addition, SIAH inhibition reduced metastasis in melanoma. The role of SIAH1 in breast cancer is still ambiguous; both tumorigenic and tumor suppressive functions have been reported. Other studies categorized SIAH ligases as either pro- or antimigratory, while the significance for metastasis is largely unknown. Here, we re-evaluated the effects of SIAH1 and SIAH2 depletion in breast cancer cell lines, focusing on migration and invasion. We successfully knocked down SIAH1 and SIAH2 in several breast cancer cell lines. In luminal type MCF7 cells, this led to stabilization of the SIAH substrate Prolyl Hydroxylase Domain protein 3 (PHD3) and reduced Hypoxia-Inducible Factor 1α (HIF1α) protein levels. Both the knockdown of SIAH1 or SIAH2 led to increased apoptosis and reduced proliferation, with comparable effects. These results point to a tumor promoting role for SIAH1 in breast cancer similar to SIAH2. In addition, depletion of SIAH1 or SIAH2 also led to decreased cell migration and invasion in breast cancer cells. SIAH knockdown also controlled microtubule dynamics by markedly decreasing the protein levels of stathmin, most likely via p27(Kip1). Collectively, these results suggest that both SIAH ligases promote a migratory cancer cell phenotype and could contribute to metastasis in breast cancer.

Guidelines for the selection of functional assays to evaluate the hallmarks of cancer

The hallmarks of cancer capture the most essential phenotypic characteristics of malignant transformation and progression. Although numerous factors involved in this multi-step process are still unknown to date, an ever-increasing number of mutated/altered candidate genes are being identified within large-scale cancer genomic projects. Therefore, investigators need to be aware of available and appropriate techniques capable of determining characteristic features of each hallmark. We review the methods tailored to experimental cancer researchers to evaluate cell proliferation, programmed cell death, replicative immortality, induction of angiogenesis, invasion and metastasis, genome instability, and reprogramming of energy metabolism. Selecting the ideal method is based on the investigator's goals, available equipment and also on financial constraints. Multiplexing strategies enable a more in-depth data collection from a single experiment - obtaining several results from a single procedure reduces variability and saves time and relative cost, leading to more robust conclusions compared to a single end point measurement. Each hallmark possesses characteristics that can be analyzed by immunoblot, RT-PCR, immunocytochemistry, immunoprecipitation, RNA microarray or RNA-seq. In general, flow cytometry, fluorescence microscopy, and multiwell readers are extremely versatile tools and, with proper sample preparation, allow the detection of a vast number of hallmark features. Finally, we also provide a list of hallmark-specific genes to be measured in transcriptome-level studies. Although our list is not exhaustive, we provide a snapshot of the most widely used methods, with an emphasis on methods enabling the simultaneous evaluation of multiple hallmark features.

Cell cycle, cytoskeleton dynamics and beyond: the many functions of cyclins and CDK inhibitors

While targeting experiments carried out on the genes encoding many cell cycle regulators have challenged our views of cell cycle control, they also suggest that redundancy might not be the only explanation for the observed perplexing phenotypes. Indeed, several observations hint at functions of cyclins and CDK inhibitors that cannot be accounted for by their sole role as kinase regulators. They are found involved in many cellular transactions, depending or not on CDKs that are not directly linked to cell cycle control, but participating to general mechanisms such as transcription, DNA repair or cytoskeleton dynamics. In this review we discuss the roles that these alternative functions might have in cancer cell proliferation and migration that sometime even challenge their definition as proliferation markers.

The non-canonical functions of p27(Kip1) in normal and tumor biology

p27(Kip1) was first discovered as a key regulator of cell proliferation. The canonical function of p27(Kip1) is inhibition of cyclin-dependent kinase (CDK) activity. In addition to its initial identification as a CDK inhibitor, p27(Kip1) has also emerged as an intrinsically unstructured, multifunctional protein with numerous non-canonical, CDK-independent functions that exert influence on key processes such as cell cycle regulation, cytoskeletal dynamics and cellular plasticity, cell migration, and stem-cell proliferation and differentiation. Many of these non-canonical functions, depending on the cell-specific contexts such as oncogenic activation of signaling pathways, have the ability to turn pro-oncogenic in nature and even contribute to tumor-aggressiveness and metastasis. This review discusses the various non-canonical, CDK-independent mechanisms by which p27(Kip1) functions either as a tumor-suppressor or tumor-promoter.

Particle Radiation-Induced Nontargeted Effects in Bone-Marrow-Derived Endothelial Progenitor Cells

Bone-marrow- (BM-) derived endothelial progenitor cells (EPCs) are critical for endothelial cell maintenance and repair. During future space exploration missions astronauts will be exposed to space irradiation (IR) composed of a spectrum of low-fluence protons ((1)H) and high charge and energy (HZE) nuclei (e.g., iron-(56)Fe) for extended time. How the space-type IR affects BM-EPCs is limited. In media transfer experiments in vitro we studied nontargeted effects induced by (1)H- and (56)Fe-IR conditioned medium (CM), which showed significant increase in the number of p-H2AX foci in nonirradiated EPCs between 2 and 24 h. A 2-15-fold increase in the levels of various cytokines and chemokines was observed in both types of IR-CM at 24 h. Ex vivo analysis of BM-EPCs from single, low-dose, full-body (1)H- and (56)Fe-IR mice demonstrated a cyclical (early 5-24 h and delayed 28 days) increase in apoptosis. This early increase in BM-EPC apoptosis may be the effect of direct IR exposure, whereas late increase in apoptosis could be a result of nontargeted effects (NTE) in the cells that were not traversed by IR directly. Identifying the role of specific cytokines responsible for IR-induced NTE and inhibiting such NTE may prevent long-term and cyclical loss of stem and progenitors cells in the BM milieu.

A selective microRNA-based strategy inhibits restenosis while preserving endothelial function

Drugs currently approved to coat stents used in percutaneous coronary interventions do not discriminate between proliferating vascular smooth muscle cells (VSMCs) and endothelial cells (ECs). This lack of discrimination delays reendothelialization and vascular healing, increasing the risk of late thrombosis following angioplasty. We developed a microRNA-based (miRNA-based) approach to inhibit proliferative VSMCs, thus preventing restenosis, while selectively promoting reendothelialization and preserving EC function. We used an adenoviral (Ad) vector that encodes cyclin-dependent kinase inhibitor p27(Kip1) (p27) with target sequences for EC-specific miR-126-3p at the 3' end (Ad-p27-126TS). Exogenous p27 overexpression was evaluated in vitro and in a rat arterial balloon injury model following transduction with Ad-p27-126TS, Ad-p27 (without miR-126 target sequences), or Ad-GFP (control). In vitro, Ad-p27-126TS protected the ability of ECs to proliferate, migrate, and form networks. At 2 and 4 weeks after injury, Ad-p27-126TS-treated animals exhibited reduced restenosis, complete reendothelialization, reduced hypercoagulability, and restoration of the vasodilatory response to acetylcholine to levels comparable to those in uninjured vessels. By incorporating miR-126-3p target sequences to leverage endogenous EC-specific miR-126, we overexpressed exogenous p27 in VSMCs, while selectively inhibiting p27 overexpression in ECs. Our proof-of-principle study demonstrates the potential of using a miRNA-based strategy as a therapeutic approach to specifically inhibit vascular restenosis while preserving EC function.

The Ran GTPase-activating protein (RanGAP1) is critically involved in smooth muscle cell differentiation, proliferation and migration following vascular injury: implications for neointima formation and restenosis

Differentiation and dedifferentiation, accompanied by proliferation play a pivotal role for the phenotypic development of vascular proliferative diseases (VPD), such as restenosis. Increasing evidence points to an essential role of regulated nucleoporin expression in the choice between differentiation and proliferation. However, whether components of the Ran GTPase cycle, which is of pivotal importance for both nucleocytoplasmic transport and for mitotic progression, are subject to similar regulation in VPD is currently unknown. Here, we show that differentiation of human coronary artery smooth muscle cell (CASMC) to a contractile phenotype by stepwise serum depletion leads to significant reduction of RanGAP1 protein levels. The inverse event, dedifferentiation of cells, was assessed in the rat carotid artery balloon injury model, a well-accepted model for neointima formation and restenosis. As revealed by temporospatial analysis of RanGAP1 expression, neointima formation in rat carotid arteries was associated with a significant upregulation of RanGAP1 expression at 3 and 7 days after balloon injury. Of note, neointimal cells located at the luminal surface revealed persistent RanGAP1 expression, as opposed to cells in deeper layers of the neointima where RanGAP1 expression was less or not detectable at all. To gain first evidence for a direct influence of RanGAP1 levels on differentiation, we reduced RanGAP1 in human coronary artery smooth muscle cells by siRNA. Indeed, downregulation of the essential RanGAP1 protein by 50% induced a differentiated, spindle-like smooth muscle cell phenotype, accompanied by an upregulation of the differentiation marker desmin. Reduction of RanGAP1 levels also resulted in a reduction of mitogen induced cellular migration and proliferation as well as a significant upregulation of the cyclin-dependent kinase inhibitor p27KIP1, without evidence for cellular necrosis. These findings suggest that RanGAP1 plays a critical role in smooth muscle cell differentiation, migration and proliferation in vitro and in vivo. Appropriate modulation of RanGAP1 expression may thus be a strategy to modulate VPD development such as restenosis.

Prevention of hypoxic pulmonary hypertension by hypoxia-inducible expression of p27 in pulmonary artery smooth muscle cells

Hypoxia-induced proliferation of pulmonary artery smooth muscle cells (SMCs) is important in the development of hypoxic pulmonary hypertension (HPH). We constructed a lentivirial vector containing a smooth muscle-specific promoter and six copies of hypoxia response element to co-drive the expression of p27, the key cyclin-dependent kinase inhibitor that blocks the G1 to S phase transition in cell cycle progression, in pulmonary artery SMCs in hypoxia. Then in vivo we examined the prevention effects of the vector on HPH in mice and in vitro the specificity on the hypoxia-inducible expression of p27 in pulmonary artery SMCs. Hypobaric hypoxia for 4 weeks resulted in significant increases in the right ventricular systolic pressure, the ratio of right ventricle to left ventricle plus septal weight and the muscularization of pulmonary vessels in mice. Administration of the vector before hypoxia significantly prevented the effects of hypoxia. In vitro, the vector exhibited hypoxic inducibility and relatively specific expression in pulmonary artery SMCs, inhibited the hypoxia-induced proliferation of pulmonary artery SMCs and arrested more cells at G0/G1 phase. These results demonstrate that the hypoxia-inducible p27 expression prevents the development of HPH in mice.

Loss of p27 upregulates MnSOD in a STAT3-dependent manner, disrupts intracellular redox activity and enhances cell migration

Cell migration is a dynamic process that is central to a variety of physiological functions as well as disease pathogenesis. The modulation of cell migration by p27 (officially known as CDKN1B) has been reported, but the exact mechanism(s) whereby p27 interacts with downstream effectors that control cell migration have not been elucidated. By systematically comparing p27(+/+) mouse embryonic fibroblasts (MEFs) with genetically ablated p27(-/-) MEFs using wound-healing, transwell and time-lapse microscopic analyses, we provide direct evidence that p27 inhibits both directional and random cell migration. Identical results were obtained with normal and cancer epithelial cells using complementary knockdown and overexpression approaches. Additional studies revealed that overexpression of manganese superoxide dismutase (MnSOD, officially known as SOD2) and reduced intracellular oxidation played a key role in increased cell migration in p27-deficient cells. Furthermore, we identified signal transducer and activator of transcription 3 (STAT3) as the transcription factor responsible for p27-regulated MnSOD expression, which was further mediated by ERK- and ATF1-dependent transactivation of the cAMP response element (CRE) within the Stat3 promoter. Collectively, our data strongly indicate that p27 plays a crucial negative role in cell migration by inhibiting MnSOD expression in a STAT3-dependent manner.

The influence of high glucose on the Cip/Kip family expression profiles in HRECs

Neovascularization is the main characteristic of the proliferative stage of diabetic retinopathy. It has been proven that cell cycle regulation is involved in angiogenesis. The cell cycle regulators, Cip/Kip protein family, belong to the cyclin-dependent kinase inhibitors, are versatile proteins, and except for their function in cell cycle regulation, they also participate in transcription, apoptosis and migration. The expression profiles of the Cip/Kip family in human retina microvascular endothelial cells (HRECs) under normal or high glucose conditions has not been described before. This study was undertaken to determine the expression profiles of the Cip/Kip family proteins, e.g., proteins which are influenced by high glucose and in what manner. Western blot and immunofluorescence analyses were used to investigate the protein expression profiles. Only p21(cip1) and p27(kip1) were detected in HRECs, and they were located in the nucleus. P21(cip1) protein abundance was higher than p27(kip1) in HRECs. Incubation of HRECs in medium containing 30 mM D-glucose for 48 h resulted in downregulation of p21(cip1) protein expression, but had no influence on p27(kip1) protein levels or p21(cip1) mRNA abundance. These results were accompanied by cell cycle G1 phase exit and a lower cell survival rate. Our data show for the first time that high glucose changes the Cip/Kip family expression profiles in HRECs, which may be the foundation for the investigation of the role of the Cip/Kip family in the pathogenesis of diabetic retinopathy.

An essential role of p27 downregulation in fenvalerate-induced cell growth in human uterine leiomyoma and smooth muscle cells

Previously, we reported that fenvalerate (Fen) promotes proliferation of human uterine leiomyoma (UtLM) cells by enhancing progression of cells from G(0)-G(1) to S phase through molecular mechanisms independent of estrogen receptor-α and -β. The cyclin-dependent kinase (CDK) inhibitor p27, which blocks G(1) to S phase transitions and is an important regulator of CDK2, is often decreased in hormonally regulated diseases, including uterine leiomyomas. Therefore, we were interested in whether Fen could regulate the expression of p27 and whether p27 might play a role in Fen-induced cell proliferation. Expression of p27 in Fen-treated UtLM and uterine smooth muscle cells (UtSMCs) was examined. We found that p27 mRNA was significantly downregulated and that protein levels were decreased in both cell types treated with 10 μM Fen for 24 h compared with respective controls. Overexpression of p27 in UtLM cells and UtSMCs using an adenovirus doxycycline (Dox)-regulated Tet-off system abrogated the proliferative effects of Fen, as evidenced by decreased total cell numbers and BrdU incorporation. Fen treatment increased CDK2 mRNA expression levels; however, overexpression of p27 also abolished this effect. In contrast, Dox treatment dramatically restored the above muted responses. Finally, we utilized siRNA to knock down p27 expression. After transfection, mRNA levels of p27 were downregulated in UtLM cells and UtSMCs and total cell numbers and BrdU incorporation increased significantly compared with nontransfected cells. Fen treatment in the presence of p27 silencing enhanced the increased cell counts and BrdU labeling in UtLM cells and UtSMCs. Taken together, these results indicate that p27 downregulation is critical for Fen-induced cell proliferation.

Thymosin β4 promotes the recovery of peripheral neuropathy in type II diabetic mice

Peripheral neuropathy is one of the most common complications of diabetes mellitus. Using a mouse model of diabetic peripheral neuropathy, we tested the hypothesis that thymosin β4 (Tβ4) ameliorates diabetes-induced neurovascular dysfunction in the sciatic nerve and promotes recovery of neurological function from diabetic peripheral neuropathy. Tβ4 treatment of diabetic mice increased functional vascular density and regional blood flow in the sciatic nerve, and improved nerve function. Tβ4 upregulated angiopoietin-1 (Ang1) expression, but suppressed Ang2 expression in endothelial and Schwann cells in the diabetic sciatic nerve. In vitro, incubation of Human Umbilical Vein Endothelial Cells (HUVECs) with Tβ4 under high glucose condition completely abolished high glucose-downregulated Ang1 expression and high glucose-reduced capillary-like tube formation. Moreover, incubation of HUVECs under high glucose with conditioned medium collected from Human Schwann Cells (HSCs) treated with Tβ4 significantly reversed high glucose-decreased capillary-like tube formation. PI3K/Akt signaling pathway is involved in Tβ4-regulated Ang1 expression on endothelial and Schwann cells. These data indicate that Tβ4 likely acts on endothelial cells and Schwann cells to preserve and/or restore vascular function in the sciatic nerve which facilitates improvement of peripheral nerve function under diabetic neuropathy. Thus, Tβ4 has potential for the treatment of diabetic peripheral neuropathy.

Down-regulation of estrogen receptor α (ERα) transcriptional activity by p27 is mediated by inhibition of ERα nuclear localization and modulation of the ERα transcriptional complex

To investigate the role of p27 on estrogen receptor (ER)α-mediated transcription, we generated MCF-7 cells with knocked down p27 via retroviral delivery of p27 shRNA. Suppression of p27 expression in MCF-7 cells resulted in up-regulation of ERα-mediated transcription by estradiol compared to the levels in control MCF-7 cells. Accordingly, transient transfection studies in 293T cells revealed that overexpression of p27 reduced ERα-mediated transcription. The effect of p27 on ERα transcriptional activity was independent of cell cycle arrest by p27, as cell cycle arrest induced by serum starvation did not significantly affect ERα-mediated transcription. Further, we observed that p27 inhibited nuclear localization of ERα, and that p27 was associated with ERα in the cytoplasm. We also investigated the role of p27 in the modulation of ERα transcriptional activity in the nucleus. We found that p27 negatively modulated ERα transcriptional activity by inhibiting association of cyclin D1 with ERα and recruiting BRCA1 to ERα transcriptional complex. Taken together, these data suggest that p27 inhibits ERα transcriptional activity by two independent mechanisms, namely, physical nuclear exclusion of ERα, and modulation of the ERα transcriptional complex.

TRB3 mediates homocysteine-induced inhibition of endothelial cell proliferation

Hyperhomocysteinemia (HHcy) has been shown to induce endothelial dysfunction, an early event in the progression of atherosclerosis. However, the underlying mechanism of endothelial cell injury in HHcy has not been clearly elucidated. In this study, we examined the effect of homocysteine on tribbles-related protein 3 (TRB3)-mediated cell-cycle arrest in human umbilical vein endothelial cells (HUVECs). Treatment of HUVECs with homocysteine (0-250 µmol/L) resulted in inhibition of cell proliferation assessed by [(3)H]-thymidine incorporation into DNA. Homocysteine induced cell-cycle arrest in the G1 phase by up-regulating the protein levels of p27(kip1). Under these conditions, homocysteine did not induce endoplasmic reticulum stress. However, homocysteine up-regulated the expression of TRB3, thus leading to the dephosphorylation of Akt (Thr308). Knock-down of endogenous TRB3 using siRNA significantly suppressed the inhibitory effect of homocysteine on the proliferation of HUVECs. Homocysteine-induced TRB3 expression was mediated by the cAMP/cAMP response element-binding protein (CREB) pathway. These results demonstrate that TRB3 is a critical molecule in the homocysteine-mediated cell-cycle arrest in endothelial cells.

Identification of a mechanism underlying regulation of the anti-angiogenic forkhead transcription factor FoxO1 in cultured endothelial cells and ischemic muscle

Chronic limb ischemia, a complication commonly observed in conjunction with cardiovascular disease, is characterized by insufficient neovascularization despite the up-regulation of pro-angiogenic mediators. One hypothesis is that ischemia induces inhibitory signals that circumvent the normal capillary growth response. FoxO transcription factors exert anti-proliferative and pro-apoptotic effects on many cell types. We studied the regulation of FoxO1 protein in ischemic rat skeletal muscle following iliac artery ligation and in cultured endothelial cells. We found that FoxO1 expression was increased in capillaries within ischemic muscles compared with those from rats that underwent a sham operation. This finding correlated with increased expression of p27(Kip1) and reduced expression of Cyclin D1. Phosphorylated Akt was reduced concurrently with the increase in FoxO1 protein. In skeletal muscle endothelial cells, nutrient stress as well as lack of shear stress stabilized FoxO1 protein, whereas shear stress induced FoxO1 degradation. Endogenous FoxO1 co-precipitated with the E3 ubiquitin ligase murine double minute-2 (Mdm2) in endothelial cells, and this interaction varied in direct relation to the extent of Akt and Mdm2 phosphorylation. Moreover, ischemic muscles had a decreased level of Mdm2 phosphorylation and a reduced interaction between Mdm2 and FoxO1. Our results provide novel evidence that the Akt-Mdm2 pathway acts to regulate endothelial cell FoxO1 expression and illustrate a potential mechanism underlying the pathophysiological up-regulation of FoxO1 under ischemic conditions.

Targeting p27Kip1 protein: its relevance in the therapy of human cancer

INTRODUCTION

Cell division cycle progression is achieved by a sequential and stringently concerted activation of a family of serine-threonine kinases, namely the cyclin-dependent kinases (CDKs). p27(Kip1) is a pivotal CDK inhibitor and a tight modulator of CDK-dependent phenotypes. Thus, p27(Kip1) plays a fundamental role in key cellular processes such as proliferation, differentiation, apoptosis, substrate adhesion and motility. Intriguingly, when p27(Kip1) is localized in the nucleus, it acts as an antiproliferative protein, while, in the cytosol, p27(Kip1) promotes cytoskeleton remodeling and might positively influence metastatization. Downregulation of p27(Kip1) nuclear level or its cytosolic mislocalization are consistently correlated with poor prognosis of numerous types of human epithelial and non-epithelial cancers.

AREAS COVERED

This review illustrates the basic structural features of p27(Kip1) protein, its metabolism and alterations in human malignancies, along with describing anticancer strategies based on targeting p27(Kip1).

EXPERT OPINION

Given the role of p27(Kip1) in the control of cell proliferation and its decreased level observed in malignancies with poor outcome, drugs able to handle the protein levels and localization might represent an important goal for novel specific and effective anticancer strategies. Although no convincing proofs have been reported, putative negative consequences of p27(Kip1) targeting might be also conceivable.

STK35L1 associates with nuclear actin and regulates cell cycle and migration of endothelial cells

BACKGROUND

Migration and proliferation of vascular endothelial cells are essential for repair of injured endothelium and angiogenesis. Cyclins, cyclin-dependent kinases (CDKs), and cyclin-dependent kinase inhibitors play an important role in vascular tissue injury and wound healing. Previous studies suggest a link between the cell cycle and cell migration: cells present in the G(1) phase have the highest potential to migrate. The molecular mechanism linking these two processes is not understood.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we explored the function of STK35L1, a novel Ser/Thr kinase, localized in the nucleus and nucleolus of endothelial cells. Molecular biological analysis identified a bipartite nuclear localization signal, and nucleolar localization sequences in the N-terminal part of STK35L1. Nuclear actin was identified as a novel binding partner of STK35L1. A class III PDZ binding domains motif was identified in STK35L1 that mediated its interaction with actin. Depletion of STK35L1 by siRNA lead to an accelerated G(1) to S phase transition after serum-stimulation of endothelial cells indicating an inhibitory role of the kinase in G(1) to S phase progression. Cell cycle specific genes array analysis revealed that one gene was prominently downregulated (8.8 fold) in STK35L1 silenced cells: CDKN2A alpha transcript, which codes for p16(INK4a) leading to G(1) arrest by inhibition of CDK4/6. Moreover in endothelial cells seeded on Matrigel, STK35L1 expression was rapidly upregulated, and silencing of STK35L1 drastically inhibited endothelial sprouting that is required for angiogenesis. Furthermore, STK35L1 depletion profoundly impaired endothelial cell migration in two wound healing assays.

CONCLUSION/SIGNIFICANCE

The results indicate that by regulating CDKN2A and inhibiting G1- to S-phase transition STK35L1 may act as a central kinase linking the cell cycle and migration of endothelial cells. The interaction of STK35L1 with nuclear actin might be critical in the regulation of these fundamental endothelial functions.

p27kip1: a new multiple endocrine neoplasia gene?

Multiple endocrine neoplasias (MEN) are autosomal dominant disorders characterized by the occurrence of tumors in at least two endocrine glands. Two types of MEN syndromes have long been known: MEN type 1 (MEN1) and MEN type 2 (MEN2), associated with a different spectrum of affected organs. MEN1 and MEN2 are caused by germline mutations in the MEN1 tumor suppressor gene and the RET proto-oncogene, respectively. Lately, a new type of MEN was identified (named MEN4) which is due to mutations in the CDKN1B gene, encoding for p27kip1 (p27), a cyclin-dependent kinase (Cdk) inhibitor that regulates the transition of cells from G1 to S phase. p27 is a non-canonical tumor suppressor since it is usually not somatically mutated in human cancers but it is often downregulated by post-translational mechanisms. The discovery of MEN4 has defined a new role for CDKN1B as a tumor susceptibility gene for multiple endocrine tumors. To date, six germline CDKN1B mutations have been found in patients with a MEN1-like phenotype but negative for MEN1 mutations. Due to the limited number of patients so far identified, the phenotypic features of MEN4 are not clearly defined. Here, we review the clinical and molecular characteristics of the MEN4 syndrome and summarize the main functions of p27 to better comprehend how their alteration can predispose to neuroendocrine tumors.

Garlic components inhibit angiotensin II-induced cell-cycle progression and migration: Involvement of cell-cycle inhibitor p27(Kip1) and mitogen-activated protein kinase

Garlic has been used for prevention and treatment of hypertension; however, the molecular mechanisms of garlic's effects remain to be elucidated. In this study, the mechanisms of the in vitro effect of organosulphur compounds derived from garlic on growth and migration of cultured aortic smooth muscle cells isolated from spontaneously hypertensive rats were investigated. We demonstrated that allyl methyl sulphide (AMS) and diallyl sulphide (DAS) inhibited aortic smooth muscle cell angiotensin II-stimulated cell-cycle progression and migration. Neither cell viability nor annexin-V-binding analysis revealed cytotoxic effects of both organosulphur compounds at the used concentrations. Instead, their inhibitory effects were associated to the prevention of the cell-cycle inhibitor p27(Kip1) (p27) downregulation and the reduction of extracellular signal-regulated kinase 1/2 phosphorylation. When we assessed the antioxidant activity of AMS and DAS, we found that both organosulphur compounds inhibited angiotensin II-reactive oxygen species generation. Our findings show that AMS and DAS, compounds derivate from garlic, could be effective antioxidants targeted at the arterial remodelling seen in hypertension.

The emerging role of the thioredoxin system in angiogenesis

Although there have been a multitude of studies, the mechanisms of angiogenesis remain incompletely understood. Increasing evidence suggests that cellular redox homeostasis is an important regulator of angiogenesis. The thioredoxin (TRX) system functions as an endogenous antioxidant that can exert influence over endothelial cell function via modulation of cellular redox status. It has become apparent that the cytosolic TRX1 isoform participates in both canonical and novel angiogenic signaling pathways and may represent an avenue for therapeutic exploitation. Recent studies have further identified a role for the mitochondrial isoform TRX2 in ischemia-induced angiogenesis. TRX-interacting protein (TXNIP) is the endogenous inhibitor of TRX redox activity that has been implicated in growth factor-mediated angiogenesis. As TXNIP is strongly induced by glucose, this molecule could be of consequence to disordered angiogenesis manifest in diabetes mellitus. This review will focus on data implicating the TRX system in endothelial cell homeostasis and angiogenesis.

Propranolol suppresses angiogenesis in vitro: inhibition of proliferation, migration, and differentiation of endothelial cells

Propranolol, a non-selective β-adrenergic blocking drug, was recently reported to control the growth of hemangiomas, the most common vascular tumor of infancy. However, the mechanisms involved in this effect remain unknown. Here, we demonstrate that propranolol dose-dependently inhibited growth factor-induced proliferation of cultured human umbilical vein endothelial cells (HUVECs) through a G₀/G₁ phase cell cycle arrest. This was correlated to decreased cyclin D1, cyclin D3, and cyclin-dependent kinase CDK6 protein levels, while increases in the CDK inhibitors p15(INK4B), p21(WAF1/Cip1) and p27(Kip1) were observed. Chemotactic motility and differentiation of HUVECs into capillary-like tubular structures in Matrigel were also inhibited by propranolol. Furthermore, inhibition by propranolol of vascular endothelial growth factor (VEGF)-induced tyrosine phosphorylation of VEGF receptor-2 lead to inhibition of downstream signaling such as the activation of the extracellular signal-regulated kinase-1/2 and the secretion of the extracellular matrix degrading enzyme MMP-2. Taken together, these results demonstrate that propranolol interferes with several essential steps of neovascularization and opens up novel therapeutic opportunities for the use of β-blockers in the treatment of angiogenesis-dependent human diseases.

Inhibition of melanoma angiogenesis by telomere homolog oligonucleotides

Telomere homolog oligonucleotides (T-oligos) activate an innate telomere-based program that leads to multiple anticancer effects. T-oligos act at telomeres to initiate signaling through the Werner protein and ATM kinase. We wanted to determine if T-oligos have antiangiogenic effects. We found that T-oligo-treated human melanoma (MM-AN) cells had decreased expression of vascular endothelial growth factor (VEGF), VEGF receptor 2, angiopoeitin-1 and -2 and decreased VEGF secretion. T-oligos activated the transcription factor E2F1 and inhibited the activity of the angiogenic transcription factor, HIF-1α. T-oligos inhibited EC tubulogenesis and total tumor microvascular density matrix invasion by MM-AN cells and ECs in vitro. In melanoma SCID xenografts, two systemic T-oligo injections decreased by 60% (P < .004) total tumor microvascular density and the functional vessels density by 80% (P < .002). These findings suggest that restriction of tumor angiogenesis is among the host's innate telomere-based anticancer responses and provide further evidence that T-oligos may offer a powerful new approach for melanoma treatment.

Tumor suppressor p27(Kip1) undergoes endolysosomal degradation through its interaction with sorting nexin 6

A large body of evidence supports the hypothesis that proteasomal degradation of the growth suppressor p27(Kip1) (p27) facilitates mammalian cell cycle progression. However, very few studies have addressed the possibility of proteasome-independent mechanisms of p27 proteolysis. Here we provide evidence for a novel pathway of p27 degradation via the lysosome that is mediated by its interaction with the endosomal protein sorting nexin 6 (SNX6), a member of the sorting nexin family of vesicular trafficking regulators. p27 and SNX6 interact in vitro and in vivo in mammalian cells, partially colocalize in endosomes, and are present in purified endosomal fractions. Gain- and loss-of-function studies revealed that SNX6 induces endosomal accumulation of p27. Moreover, p27 is detected in lysosomes and inhibition of lysosome-dependent proteolysis impairs serum-mediated down-regulation of p27 in a SNX6-dependent manner. To validate the localization of p27 in these organelles, we analyzed several cell lines using two different anti-p27 antibodies, several organelle-specific markers [e.g., early endosome antigen 1, lysosomal-associated membrane protein (LAMP) 1, LAMP2, and LysoTracker], and overexpression of fluorescent p27 and SNX6. Remarkably, silencing of SNX6 attenuates p27 down-regulation in the G(1) phase of the mitotic cell cycle and delays cell cycle progression. We therefore conclude that, in addition to the proteasome-dependent pathway, SNX6-mediated endolysosomal degradation of p27 also contributes to cell cycle progression in mammalian cells.

p27kip1 controls cell morphology and motility by regulating microtubule-dependent lipid raft recycling

p27(kip1) (p27) is an inhibitor of cyclin/cyclin-dependent kinase complexes, whose nuclear loss indicates a poor prognosis in various solid tumors. When located in the cytoplasm, p27 binds Op18/stathmin (stathmin), a microtubule (MT)-destabilizing protein, and restrains its activity. This leads to MT stabilization, which negatively affects cell migration. Here, we demonstrate that this p27 function also influences morphology and motility of cells immersed in three-dimensional (3D)matrices. Cells lacking p27 display a decrease in MT stability, a rounded shape when immersed in 3D environments, and a mesenchymal-amoeboid conversion in their motility mode. Upon cell contact to extracellular matrix, the decreased MT stability observed in p27 null cells results in accelerated lipid raft trafficking and increased RhoA activity. Importantly, cell morphology, motility, MT network composition, and distribution of p27 null cells were rescued by the concomitant genetic ablation of Stathmin, implicating that the balanced expression of p27 and stathmin represents a crucial determinant for cytoskeletal organization and cellular behavior in 3D contexts.

Rapamycin regulates endothelial cell migration through regulation of the cyclin-dependent kinase inhibitor p27Kip1

Rapamycin is a macrolide antibiotic that inhibits vascular smooth muscle cell proliferation and migration and that is used clinically on drug-eluting stents to inhibit in-stent restenosis. Although inhibition of cell migration is an asset in preventing restenosis, it also leads to impaired stent endothelialization, a significant limitation of current drug-eluting stent technology that necessitates prolonged antiplatelet therapy. We measured the ability of rapamycin to inhibit the migration of human umbilical vein endothelial cells (HUVECs) and human coronary artery endothelial cells (HCAEC) toward the chemoattractant vascular endothelial cell growth factor. Although acute administration of rapamycin had no effect, exposure for 24 h inhibited HUVEC and HCAEC migration. Disruption of the mTORC2 via small interfering RNA was also effective in inhibiting HCAEC migration. Treatment of HCAECs for this period with rapamycin produced an increase in the cyclin-dependent kinase inhibitor p27(Kip), through a decrease in the targeting of the protein for degradation by phosphorylation at Thr(187). ECs isolated from a knock-in mouse expressing p27(Kip1) with a mutation of this residue to an alanine, blocking this phosphorylation, exhibited reduced migration compared with wild-type controls. Silencing of p27(Kip1) with small interfering RNA blocked the effects of rapamycin on migration and tube formation as well as RhoA activation and cytoskeletal reorganization. We conclude that prolonged exposure of ECs to rapamycin increases p27(Kip1) and in turn inhibits RhoA activation, blocking cell migration and differentiation. These data elucidate the molecular mechanism underlying regulation of p27(Kip1) protein and cell migration by rapamycin.

Control of cell proliferation in atherosclerosis: insights from animal models and human studies

Excessive hyperplastic cell growth within occlusive vascular lesions has been recognized as a key component of the inflammatory response associated with atherosclerosis, restenosis post-angioplasty, and graft atherosclerosis after coronary artery bypass. Understanding the molecular mechanisms that regulate arterial cell proliferation is therefore essential for the development of new tools for the treatment of these diseases. Mammalian cell proliferation is controlled by a large number of proteins that modulate the mitotic cell cycle, including cyclin-dependent kinases, cyclins, and tumour suppressors. The purpose of this review is to summarize current knowledge about the role of these cell cycle regulators in the development of native and graft atherosclerosis that has arisen from animal studies, histological examination of specimens from human patients, and genetic studies.

A critical analysis of current in vitro and in vivo angiogenesis assays

The study of angiogenesis has grown exponentially over the past 40 years with the recognition that angiogenesis is essential for numerous pathologies and, more recently, with the advent of successful drugs to inhibit angiogenesis in tumours. The main problem with angiogenesis research remains the choice of appropriate assays to evaluate the efficacy of potential new drugs and to identify potential targets within the angiogenic process. This selection is made more complex by the recognition that heterogeneity occurs, not only within the endothelial cells themselves, but also within the specific microenvironment to be studied. Thus, it is essential to choose the assay conditions and cell types that most closely resemble the angiogenic disease being studied. This is especially important when aiming to translate data from in vitro to in vivo and from preclinical to the clinic. Here we critically review and highlight recent advances in the principle assays in common use including those for endothelial cell proliferation, migration, differentiation and co-culture with fibroblasts and mural cells in vitro, vessel outgrowth from organ cultures and in vivo assays such as chick chorioallantoic membrane (CAM), zebrafish, sponge implantation, corneal, dorsal air sac, chamber and tumour angiogenesis models. Finally, we briefly discuss the direction likely to be taken in future studies, which include the use of increasingly sophisticated imaging analysis systems for data acquisition.

The tumor suppressor functions of p27(kip1) include control of the mesenchymal/amoeboid transition

In many human cancers, p27 downregulation correlates with a worse prognosis, suggesting that p27 levels could represent an important determinant in cell transformation and cancer development. Using a mouse model system based on v-src-induced transformation, we show here that p27 absence is always linked to a more aggressive phenotype. When cultured in three-dimensional contexts, v-src-transformed p27-null fibroblasts undergo a morphological switch from an elongated to a rounded cell shape, accompanied by amoeboid-like morphology and motility. Importantly, the acquisition of the amoeboid motility is associated with a greater ability to move and colonize distant sites in vivo. The reintroduction of different p27 mutants in v-src-transformed p27-null cells demonstrates that the control of cell proliferation and motility represents two distinct functions of p27, both necessary for it to fully act as a tumor suppressor. Thus, we highlight here a new p27 function in driving cell plasticity that is associated with its C-terminal portion and does not depend on the control of cyclin-dependent kinase activity.

In vivo gene regulation using tetracycline-regulatable systems

Numerous preclinical studies have demonstrated the efficacy of viral gene delivery vectors, and recent clinical trials have shown promising results. However, the tight control of transgene expression is likely to be required for therapeutic applications and in some instances, for safety reasons. For this purpose, several ligand-dependent transcription regulatory systems have been developed. Among these, the tetracycline-regulatable system is by far the most frequently used and the most advanced towards gene therapy trials. This review will focus on this system and will describe the most recent progress in the regulation of transgene expression in various organs, including the muscle, the retina and the brain. Since the development of an immune response to the transactivator was observed following gene transfer in the muscle of nonhuman primate, focus will be therefore, given on the immune response to transgene products of the tetracycline inducible promoter.

Alternative functions of core cell cycle regulators in neuronal migration, neuronal maturation, and synaptic plasticity

Recent studies have demonstrated that boundaries separating a cycling cell from a postmitotic neuron are not as concrete as expected. Novel and unique physiological functions in neurons have been ascribed for proteins fundamentally required for cell cycle progression and control. These "core" cell cycle regulators serve diverse postmitotic functions that span various developmental stages of a neuron, including neuronal migration, axonal elongation, axon pruning, dendrite morphogenesis, and synaptic maturation and plasticity. In this review, we detail the nonproliferative postmitotic roles that these cell cycle proteins have recently been reported to play, the significance of their expression in neurons, mechanistic insight when available, and future prospects.

Local TAT-p27Kip1 fusion protein inhibits cell proliferation in rat carotid arteries

INTRODUCTION

p27(Kip1) is a cyclin kinase inhibitor that induces cell cycle arrest. In this study, the efficacy of fusion protein TAT- p27(Kip1) to inhibit cell proliferation in rat perivascular injured carotid arteries was tested.

METHODS

The cDNA of p27(Kip1) and GFP (green fluorescein protein) fused to the TAT epitope, which allows cell penetration, yielded TAT-p27 (Kip1) and TAT-GFP fusion proteins. In vitro biological activity on cell proliferation was evaluated by [(3)H] thymidine DNA incorporation in rabbit aortic endothelial cells (REC). An in vivo model used a silicone collar filled with saline positioned around the carotid vessel for 14 days to produce an increased adventitia cross-sectional area.

RESULTS

TAT-p27(Kip1) inhibited REC proliferation in vitro using either 100, 200, and 500 nM compared to control (88.2 +/- 4.4, 81.3 +/- 7, 71.9 +/- 4.2 vs. 100 +/- 6.7%, N = 3, respectively, p < 0.05). This response was stable for purified proteins stored at -20*C for at least 23 days. In vivo , TAT-p27(Kip1) solution reduced adventitia cross-sectional area in a dose-dependent manner compared to TAT-GFP (area in mm(2) - TAT-p27(Kip1): 200 nM, 0.160 +/- 0.018; 500 nM, 0.050 +/- 0.005 vs. TAT-GFP: 500 nM, 0.595 +/- 0.066 vs. the contralateral: 0.047 +/- 0.005, N = 7, p < 0.01).

CONCLUSION

Taken together, these results provide evidence that TAT-p27(Kip1) can inhibit vascular cells proliferation. It is the first successful demonstration that the cell permeable TAT-p27(Kip1) has potential as a vascular anti-proliferative agent.

Stat1 phosphorylation determines Ras oncogenicity by regulating p27 kip1

Inactivation of p27 Kip1 is implicated in tumorigenesis and has both prognostic and treatment-predictive values for many types of human cancer. The transcription factor Stat1 is essential for innate immunity and tumor immunosurveillance through its ability to act downstream of interferons. Herein, we demonstrate that Stat1 functions as a suppressor of Ras transformation independently of an interferon response. Inhibition of Ras transformation and tumorigenesis requires the phosphorylation of Stat1 at tyrosine 701 but is independent of Stat1 phosphorylation at serine 727. Stat1 induces p27 Kip1 expression in Ras transformed cells at the transcriptional level through mechanisms that depend on Stat1 phosphorylation at tyrosine 701 and activation of Stat3. The tumor suppressor properties of Stat1 in Ras transformation are reversed by the inactivation of p27 Kip1. Our work reveals a novel functional link between Stat1 and p27 Kip1, which act in coordination to suppress the oncogenic properties of activated Ras. It also supports the notion that evaluation of Stat1 phosphorylation in human tumors may prove a reliable prognostic factor for patient outcome and a predictor of treatment response to anticancer therapies aimed at activating Stat1 and its downstream effectors.

Argyrin a reveals a critical role for the tumor suppressor protein p27(kip1) in mediating antitumor activities in response to proteasome inhibition

A reduction in the cellular levels of the cyclin kinase inhibitor p27(kip1) is frequently found in many human cancers and correlates directly with patient prognosis. In this work, we identify argyrin A, a cyclical peptide derived from the myxobacterium Archangium gephyra, as a potent antitumoral drug. All antitumoral activities of argyrin A depend on the prevention of p27(kip1) destruction, as loss of p27(kip1) expression confers resistance to this compound. We find that argyrin A exerts its effects through a potent inhibition of the proteasome. By comparing the cellular responses exerted by argyrin A with siRNA-mediated knockdown of proteasomal subunits, we find that the biological effects of proteasome inhibition per se depend on the expression of p27(kip1).

Genetic screening reveals an essential role of p27kip1 in restriction of breast cancer progression

The genetic changes and mechanisms underlying the progression of estrogen-dependent breast cancers to estrogen-independent, antiestrogen-resistant, and metastatic breast cancers are unclear despite being a major problem in endocrine therapy. To identify genes responsible for this progression, we carried out a genetic screening by an enhanced retroviral mutagen (ERM)-mediated random mutagenesis in the estrogen-dependent T47D breast cancer cells. We found that T47D cells contain only one p27kip1 (p27) allele coding for the p27 cyclin-dependent kinase (CDK) inhibitor. An ERM insertion into the p27 locus of T47D cells disrupted the p27 gene and created estrogen-independent and antiestrogen-resistant breast cancer cells that still maintained functional estrogen receptors. Disruption of p27 in T47D cells resulted in several changes, and most of these changes could be rescued by p27 restoration. First, CDK2 activity was increased in the absence of estrogen or in the presence of estrogen antagonists tamoxifen or ICI 182780; second, amplified in breast cancer 1 (AIB1), a cancer overexpressed transcriptional coactivator, was hyperphosphorylated, which made AIB1 a better coactivator for E2F1; and third, growth factor receptor binding protein 2-associated binder 2 (Gab2) and Akt activity were increased following E2F1 overactivation, leading to a significant enhancement of cell migration and invasion. Furthermore, the p27-deficient cells, but not T47D control cells, developed lung metastasis in an ovarian hormone-independent manner when they were i.v. injected into nude mice. In sum, loss of p27 activated AIB1, E2F1, Gab2, and Akt; increased cell migration and invasion; caused antiestrogen insensitivity; and promoted metastasis of breast cancer cells. These findings suggest that p27 plays an essential role in restriction of breast cancer progression.

Rescue and production of vaccine and therapeutic adenovirus vectors expressing inhibitory transgenes

Expression of certain transgenes from an adenovirus vector can be deleterious to its own replication. This can result in the inhibition of virus rescue, reduced viral yields, or, in the worst case, make it impossible to construct a vector expressing the inhibiting transgene product. A gene regulation system based on the tet operon was used to allow the rescue and efficient growth of adenovectors that express transgenes to high levels. A key advantage to this system is that repression of transgene expression is mediated by the packaging cell line, thus, expression of regulatory products from the adenovector are not required. This provides a simple, broadly applicable system wherein transgene repression is constitutive during vector rescue and growth and there is no effect on adenovector-mediated expression of gene products in transduced cells. Several high-level expression vectors based on first- and second-generation adenovectors were rescued and produced to high titer that otherwise could not be grown. Yields of adenovectors expressing inhibitory transgene products were increased, and the overgrowth of cultures by adenovectors with nonfunctional expression cassettes was prevented. The gene regulation system is a significant advancement for the development of adenovirus vectors for vaccine and other gene transfer applications.

Tumor necrosis factor-alpha receptor p75 is required in ischemia-induced neovascularization

BACKGROUND

Aging is a risk factor for coronary and peripheral artery disease. Tumor necrosis factor-alpha (TNF-alpha), a proinflammatory cytokine, is expressed in ischemic tissue and is known to modulate angiogenesis. Little is known about the role of TNF-alpha receptors (TNFR1/p55 and TNFR2/p75) in angiogenic signaling.

METHODS AND RESULTS

We studied neovascularization in the hindlimb ischemia model in young and old TNFR2/p75 knockout (p75KO) and wild-type age-matched controls. Between days 7 to 10 after hindlimb surgery, 100% of old p75KOs experienced autoamputation of the operated limbs, whereas none of the age-matched wild-type mice exhibited hindlimb necrosis. Poor blood flow recovery in p75KO mice was associated with increased endothelial cell apoptosis, decreased capillary density, and significant reductions in the expression of vascular endothelial growth factor and basic fibroblast growth factor-2 mRNA transcripts in ischemic tissue and in circulating endothelial progenitor cells. The number of circulating bone marrow-derived endothelial progenitor cells was significantly reduced in p75KO mice. Transplantation of wild-type bone marrow mononuclear cells into irradiated old p75KO mice 1 month before hindlimb surgery prevented limb loss.

CONCLUSIONS

Our present study suggests that ischemia-induced endothelial progenitor cell-mediated neovascularization is dependent, at least in part, on p75 TNF receptor expressed in bone marrow-derived cells. Specifically, endothelial cell/endothelial progenitor cell survival, vascular endothelial growth factor expression, endothelial progenitor cell mobilization from bone marrow, endothelial progenitor cell differentiation, and ultimately ischemia-induced collateral vessel development are dependent on signaling through TNFR2/p75. Furthermore, because TNFR2/p75 becomes an age-related limiting factor in postischemic recovery, it may be a potential gene target for therapeutic interventions in adult vascular diseases.

Up-regulation of GPR48 induced by down-regulation of p27Kip1 enhances carcinoma cell invasiveness and metastasis

A reduced expression level of the cyclin-dependent kinase inhibitor p27(Kip1) is associated with increased tumor malignancy and poor prognosis in individuals with various types of cancer. To investigate the basis for this relation, we applied microarray analysis to screen for genes differentially expressed between p27(+/-) and parental (p27(+/+)) HCT116 human colon carcinoma cells. Expression of the gene for G protein-coupled receptor 48 (GPR48) was increased in the p27(+/-) cells. Forced expression of GPR48 increased both in vitro invasive activity and lung metastasis potency of HCT116 cells. In contrast, depletion of endogenous GPR48 by RNA interference reduced the invasive potential of HeLa and Lewis lung carcinoma cells not only in vitro but also in vivo. Moreover, GPR48 expression was significantly associated with lymph node metastasis and inversely correlated with p27 expression in human colon carcinomas. GPR48 may thus play an important role in invasiveness and metastasis of carcinoma and might therefore represent a potential prognostic marker or therapeutic target.