The polyamines regulate endothelial cell survival during hypoxic stress through PI3K/AKT and MCL-1

Exploring machine learning for untargeted metabolomics using molecular fingerprints

BACKGROUND

Metabolomics, the study of substrates and products of cellular metabolism, offers valuable insights into an organism's state under specific conditions and has the potential to revolutionise preventive healthcare and pharmaceutical research. However, analysing large metabolomics datasets remains challenging, with available methods relying on limited and incompletely annotated metabolic pathways.

METHODS

This study, inspired by well-established methods in drug discovery, employs machine learning on metabolite fingerprints to explore the relationship of their structure with responses in experimental conditions beyond known pathways, shedding light on metabolic processes. It evaluates fingerprinting effectiveness in representing metabolites, addressing challenges like class imbalance, data sparsity, high dimensionality, duplicate structural encoding, and interpretable features. Feature importance analysis is then applied to reveal key chemical configurations affecting classification, identifying related metabolite groups.

RESULTS

The approach is tested on two datasets: one on Ataxia Telangiectasia and another on endothelial cells under low oxygen. Machine learning on molecular fingerprints predicts metabolite responses effectively, and feature importance analysis aligns with known metabolic pathways, unveiling new affected metabolite groups for further study.

CONCLUSION

In conclusion, the presented approach leverages the strengths of drug discovery to address critical issues in metabolomics research and aims to bridge the gap between these two disciplines. This work lays the foundation for future research in this direction, possibly exploring alternative structural encodings and machine learning models.

Polyamines: the pivotal amines in influencing the tumor microenvironment

Cellular proliferation, function and survival is reliant upon maintaining appropriate intracellular polyamine levels. Due to increased metabolic needs, cancer cells elevate their polyamine pools through coordinated metabolism and uptake. High levels of polyamines have been linked to more immunosuppressive tumor microenvironments (TME) as polyamines support the growth and function of many immunosuppressive cell types such as MDSCs, macrophages and regulatory T-cells. As cancer cells and other pro-tumorigenic cell types are highly dependent on polyamines for survival, pharmacological modulation of polyamine metabolism is a promising cancer therapeutic strategy. This review covers the roles of polyamines in various cell types of the TME including both immune and stromal cells, as well as how competition for nutrients, namely polyamine precursors, influences the cellular landscape of the TME. It also details the use of polyamines as biomarkers and the ways in which polyamine depletion can increase the immunogenicity of the TME and reprogram tumors to become more responsive to immunotherapy.

Polyamines and hormesis: Making sense of a dose response dichotomy

The diverse biological effects of polyamines (putrescine, spermidine and spermine) were reviewed in the context of hormesis in an integrative manner for the first time. The findings illustrate that each of these polyamines commonly induces hormetic dose responses in a wide range of biological models and types of cells for multiple endpoints in numerous plant species and animal models. Plant research emphasized preconditioning experimental studies in which the respective polyamines conferred some protection against the damaging effects of a broad range of environmental stressors such as drought, salinity, cold/heat, heavy metals and UV-damage in an hormetic manner. Polyamine-based animal hormesis studies emphasized biomedical endpoints such as longevity and neuroprotection. These findings have important biological and biomedical implications and should guide experimental designs of low dose investigations.

Spermine oxidase induces DNA damage and sensitizes fusion negative rhabdomyosarcoma cells to irradiation

Rhabdomyosarcoma (RMS) is a pediatric myogenic soft tissue sarcoma that includes fusion-positive (FP) and fusion-negative (FN) molecular subtypes. FP-RMS expresses PAX3-FOXO1 fusion protein and often shows dismal prognosis. FN-RMS shows cytogenetic abnormalities and frequently harbors RAS pathway mutations. Despite the multimodal heavy chemo and radiation therapeutic regimens, high risk metastatic/recurrent FN-RMS shows a 5-year survival less than 30% due to poor sensitivity to chemo-radiotherapy. Therefore, the identification of novel targets is needed. Polyamines (PAs) such as putrescine (PUT), spermidine (SPD) and spermine (SPM) are low-molecular-mass highly charged molecules whose intracellular levels are strictly modulated by specific enzymes. Among the latter, spermine oxidase (SMOX) regulates polyamine catabolism oxidizing SPM to SPD, which impacts cellular processes such as apoptosis and DNA damage response. Here we report that low SMOX levels are associated with a worse outcome in FN-RMS, but not in FP-RMS, patients. Consistently, SMOX expression is downregulated in FN-RMS cell lines as compared to normal myoblasts. Moreover, SMOX transcript levels are reduced FN-RMS cells differentiation, being indirectly downregulated by the muscle transcription factor MYOD. Noteworthy, forced expression of SMOX in two cell lines derived from high-risk FN-RMS: 1) reduces SPM and upregulates SPD levels; 2) induces G0/G1 cell cycle arrest followed by apoptosis; 3) impairs anchorage-independent and tumor spheroids growth; 4) inhibits cell migration; 5) increases γH2AX levels and foci formation indicative of DNA damage. In addition, forced expression of SMOX and irradiation synergize at activating ATM and DNA-PKCs, and at inducing γH2AX expression and foci formation, which suggests an enhancement in DNA damage response. Irradiated SMOX-overexpressing FN-RMS cells also show significant decrease in both colony formation capacity and spheroids growth with respect to single approaches. Thus, our results unveil a role for SMOX as inhibitor of tumorigenicity of FN-RMS cells in vitro. In conclusion, our in vitro results suggest that SMOX induction could be a potential combinatorial approach to sensitize FN-RMS to ionizing radiation and deserve further in-depth studies.

Polyamines in cancer: integrating organismal metabolism and antitumour immunity

The natural mammalian polyamines putrescine, spermidine and spermine are essential for both normal and neoplastic cell function and replication. Dysregulation of metabolism of polyamines and their requirements is common in many cancers. Both clinical and experimental depletion of polyamines have demonstrated their metabolism to be a rational target for therapy; however, the mechanisms through which polyamines can establish a tumour-permissive microenvironment are only now emerging. Recent data indicate that polyamines can play a major role in regulating the antitumour immune response, thus likely contributing to the existence of immunologically 'cold' tumours that do not respond to immune checkpoint blockade. Additionally, the interplay between the microbiota and associated tissues creates a tumour microenvironment in which polyamine metabolism, content and function can all be dramatically altered on the basis of microbiota composition, dietary polyamine availability and tissue response to its surrounding microenvironment. The goal of this Perspective is to introduce the reader to the many ways in which polyamines, polyamine metabolism, the microbiota and the diet interconnect to establish a tumour microenvironment that facilitates the initiation and progression of cancer. It also details ways in which polyamine metabolism and function can be successfully targeted for therapeutic benefit, including specifically enhancing the antitumour immune response.

ZPI prevents ox-LDL-mediated endothelial injury leading to inhibition of EndMT, inflammation, apoptosis, and oxidative stress through activating Pi3k/Akt signal pathway

Oxidized low-density lipoprotein (ox-LDL)-mediated endothelial dysfunction exerts an essential role in the development of atherosclerosis. Protein Z-dependent protease inhibitor (ZPI), a member of the serine protease inhibitor superfamily, could inhibit the function of activated coagulation factor X (FXa) via interaction with protein Z (PZ). Studies have pointed out that ZPI was statistically related to atherosclerotic diseases, which may have a robust cardiovascular protective effect. However, the underlying mechanism of ZPI on ox-LDL-mediated endothelial injury requires further elucidation. Human umbilical vein endothelial cells (HUVECs) were treated with ox-LDL (100 μg/ml) and ZPI (10 μg/ml). Cell viability was measured by the Cell Counting Kit-8 (CCK-8) assay. Cell apoptosis, oxidative stress, and endothelial-to-mesenchymal transition (EndMT) were analyzed by immunofluorescence (IF). Cell migration was measured using a wound-healing assay. Quantitative real-time polymerase chain reaction and western blot analysis were performed to determine messenger RNA and protein expression. Ox-LDL (100 μg/ml, 48 h) significantly reduced cell viability and migration, increased EndMT, inflammation, apoptosis, and oxidative stress. The related protein expression of phosphatidylinositol 3 kinase/protein kinase B (Pi3k/Akt) signal pathway in HUVECs was also simultaneously decreased. We also discovered that ZPI treatment could prevent ox-LDL-mediated endothelial injury through the improvement of cell viability and alleviation of apoptosis, oxidative stress, EndMT, and inflammation. Thus, the protective effect of ZPI on HUVECs may be mediated by activation of the Pi3k/Akt signal pathway. ZPI may exert an important protective role in HUVECs dysfunction triggered by ox-LDL via activation of the Pi3k/Akt signal pathway. Therefore, ZPI may possess potential therapeutic effects on atherosclerotic endothelial injury-related diseases.

Polyamines: Functions, Metabolism, and Role in Human Disease Management

Putrescine, spermine, and spermidine are the important polyamines (PAs), found in all living organisms. PAs are formed by the decarboxylation of amino acids, and they facilitate cell growth and development via different cellular responses. PAs are the integrated part of the cellular and genetic metabolism and help in transcription, translation, signaling, and post-translational modifications. At the cellular level, PA concentration may influence the condition of various diseases in the body. For instance, a high PA level is detrimental to patients suffering from aging, cognitive impairment, and cancer. The levels of PAs decline with age in humans, which is associated with different health disorders. On the other hand, PAs reduce the risk of many cardiovascular diseases and increase longevity, when taken in an optimum quantity. Therefore, a controlled diet is an easy way to maintain the level of PAs in the body. Based on the nutritional intake of PAs, healthy cell functioning can be maintained. Moreover, several diseases can also be controlled to a higher extend via maintaining the metabolism of PAs. The present review discusses the types, important functions, and metabolism of PAs in humans. It also highlights the nutritional role of PAs in the prevention of various diseases.

Polyamines and related signaling pathways in cancer

Polyamines are aliphatic compounds with more than two amino groups that play various important roles in human cells. In cancer, polyamine metabolism dysfunction often occurs, and regulatory mechanisms of polyamine. This review summarizes the existing research on the metabolism and transport of polyamines to study the association of oncogenes and related signaling pathways with polyamines in tumor cells. Drugs that regulate enzymes have been developed for cancer treatment, and in the future, more attention should be paid to treatment strategies that simultaneously modulate polyamine metabolism and carcinogenic signaling pathways. In addition, the polyamine pathway is a potential target for cancer chemoprevention. As an irreversible suicide inhibitor of the ornithine decarboxylase (a vital enzyme of polyamine synthesis), Difluoro-methylornithine had been shown to have the chemoprevention effect on cancer. Therefore, we summarized and analyzed the chemoprophylaxis effect of the difluoromethylornithine in this systematic review.

Spermidine as a target for cancer therapy

Spermidine, as a natural component from polyamine members, is originally isolated from semen and also existed in many natural plants, and can be responsible for cell growth and development in eukaryotes. The supplementation of spermidine can extend health and lifespan across species. Although the elevated levels of polyamines and the regulation of rate-limiting enzymes for polyamine metabolism have been identified as the biomarkers in many cancers, recent epidemiological data support that an increased uptake of spermidine as a caloric restriction mimic can reduce overall mortality associated with cancers. The possible mechanisms between spermidine and cancer development may be related to the precise regulation of polyamine metabolism, anti-cancer immunosurveillance, autophagy, and apoptosis. Increased intake of polyamine seems to suppress tumorigenesis, but appears to accelerate the growth of established tumors. Based on these observations and the absolute requirement for polyamines in tumor growth, spermidine could be a rational target for chemoprevention and clinical therapeutics of cancers.

Retracted: Tetramethylpyrazine partially relieves hypoxia-caused damage of cardiomyocytes H9c2 by downregulation of miR-449a

Inadequate oxygen supply is probably one of the most important pathophysiological mechanisms of cardiomyocyte damage in ischemic heart disease. Tetramethylpyrazine (TMP, also known as ligustrazine) is the main active ingredient isolated from the rhizome of Ligusticum chuanxiong Hort. A previous study reported that the TMP could exert cardioprotective activity. This study aimed to explore the molecular mechanism of the protective effects of TMP on cardiomyocyte damage caused by hypoxia. The viability and apoptosis of cardiomyocytes H9c2 were detected using cell counting kit-8 assay and annexin V-FITC/PI staining, respectively. Quantitative reverse transcription polymerase chain reaction was conducted to measure the expression level of microRNA-449a (miR-449a). Cell transfection was performed to upregulate the expression level of miR-449a or downregulate the expression level of sirtuin 1 (Sirt1). The protein expression levels of Sirt1 and key factors involved in cell apoptosis and phosphatidylinositol 3-kinase/protein kinase 3 (PI3K/AKT) pathway were evaluated using western blot analysis. We found that the hypoxia incubation inhibited H9c2 viability, induced cell apoptosis, and inactivated the PI3K/AKT pathway. TMP treatment partially relieved the hypoxia-caused H9c2 cell viability loss and apoptosis, as well as reversed the hypoxia-caused inactivation of the PI3K/AKT pathway. Moreover, TMP partially alleviated the upregulation of miR-449a in H9c2 cells caused by hypoxia. Overexpression of miR-449a weakened the effects of TMP on hypoxia-treated H9c2 cells. Furthermore, Sirt1 was a target gene of miR-449a. Knockdown of Sirt1 also weakened the effects of TMP on hypoxia-treated H9c2 cells. In conclusion, TMP partially relieved hypoxia-caused cardiomyocytes H9c2 viability loss and apoptosis at least through downregulating miR-499a, upregulating Sirt1, and then activating the PI3K/AKT pathway.

Polyamine metabolism and cancer: treatments, challenges and opportunities

Advances in our understanding of the metabolism and molecular functions of polyamines and their alterations in cancer have led to resurgence in the interest of targeting polyamine metabolism as an anticancer strategy. Increasing knowledge of the interplay between polyamine metabolism and other cancer-driving pathways, including the PTEN-PI3K-mTOR complex 1 (mTORC1), WNT signalling and RAS pathways, suggests potential combination therapies that will have considerable clinical promise. Additionally, an expanding number of promising clinical trials with agents targeting polyamines for both therapy and prevention are ongoing. New insights into molecular mechanisms linking dysregulated polyamine catabolism and carcinogenesis suggest additional strategies that can be used for cancer prevention in at-risk individuals. In addition, polyamine blocking therapy, a strategy that combines the inhibition of polyamine biosynthesis with the simultaneous blockade of polyamine transport, can be more effective than therapies based on polyamine depletion alone and may involve an antitumour immune response. These findings open up new avenues of research into exploiting aberrant polyamine metabolism for anticancer therapy.

Spermidine/spermine N1-acetyltransferase regulates cell growth and metastasis via AKT/β-catenin signaling pathways in hepatocellular and colorectal carcinoma cells

Hepatocellular carcinoma (HCC) and colorectal cancer (CRC) are among the most common cancers across the world. Therefore, identifying the potential molecular mechanisms that promote HCC and CRC progression and metastasis are urgently needed. Spermidine/spermine N¹-acetyltransferase (SSAT) is a catabolic enzyme that acetylates the high-order polyamines spermine and spermidine, thus decreasing the cellular content of polyamines. Several publications have suggested that depletion of intracellular polyamines inhibited tumor progression and metastasis in various cancer cells. However, whether and how SSAT regulates cell growth, migration and invasion in hepatocellular and colorectal carcinoma cells remains unclear. In this study, depletion of polyamines mediated by SSAT not only attenuated the tumor cell proliferation but also dramatically inhibited cell migration and invasion in hepatocellular and colorectal carcinoma cells. Subsequent investigations revealed introduction of SSAT into HepG2, SMMC7721 hepatocellular carcinoma cells and HCT116 colorectal carcinoma cells significantly suppressed p-AKT, p-GSK3β expression as well as β-catenin nuclear translocation, while inhibition of GSK3β activity or exogenous polyamines could restore SSAT-induced decreases in the protein expression of p-AKT, p-GSK3β and β-catenin. Conversely, knockdown of SSAT in Bel7402 hepatocellular carcinoma cells and HT-29 colorectal carcinoma cells which expressed high levels of SSAT endogenously significantly promoted the expression of p-AKT, p-GSK3β as well as β-catenin nuclear translocation. Taken together, our results indicated depletion of polyamines by SSAT significantly inhibited cell proliferation, migration and invasion through AKT/GSK3β/β-catenin signaling pathway in hepatocellular carcinoma and colorectal cancer cells.

Cyclocommunol induces apoptosis in human oral squamous cell carcinoma partially through a Mcl-1-dependent mechanism

BACKGROUND

Crude extract of breadfruit has been reported to have antitumor activity against various cancer cell lines with unknown mechanism.

PURPOSE

This study aims to investigate the proapoptotic effect of cyclocommunol (CYC), a prenylflavonoid from breadfruit, in two oral squamous cell carcinoma (OSCC) cell lines, SCC2095 and Ca922.

METHODS

The antiproliferative effects of CYC were assessed by MTT assays and PI/annexin V analysis. SCC2095 cells were transiently transfected with Mcl-1 plasmid in overexpression experiment. Other methods used to investigate the mechanism of CYC included Western blotting, acridine orange staining and confocal microscopic visualization.

RESULTS

Our results showed that CYC suppressed the viability of SCC2095 and Ca922 with IC₅₀ values at 48 h of 4.2 and 5.0 µM, respectively. This decrease in viability occurred in a caspase-dependent apoptotic manner. In addition, CYC down-regulated the phosphorylation/expression of Akt/mTOR and Mcl-1, accompanied by reactive oxygen species generation, and autophagy induction. Notably, overexpression of Mcl-1 using Mcl-1-tag-myc partially rescued CYC-mediated caspase-3 activation, PARP cleavage, and cytotoxicity. In summary, our study demonstrated the proapoptotic activity of CYC on OSCC, partially through down-regulation of Mcl-1.

CONCLUSION

CYC from breadfruit has translational value as a proapoptotic agent for OSCC.

Angiotensin II degrades myeloid cell leukemia 1 in human umbilical vein endothelial cells

Angiotensin II (Ang II) plays a central role in cardiovascular diseases by causing endothelial apoptosis and dysfunction. Myeloid cell leukemia 1 (Mcl-1) is an antiapoptotic member of the Bcl-2 family of apoptosis-regulating proteins. It has been reported that Mcl-1 plays a pivotal role in protecting cells against apoptosis. Presently, the effects of Ang II on the expression of Mcl-1 remain unknown. In this study, we report, for the first time, that the antiapoptotic protein Mcl-1 is degraded by the proteasome during Ang II-induced apoptosis in HUVECs. Notably, our results demonstrate that prior phosphorylation by GSK-3β is required for proteasomal degradation of Mcl-1. Notably, the reduced level of Mcl-1 was abolished by a specific GSK-3β inhibitor, suggesting that the phosphorylation of Mcl-1 by GSK-3β is required for proteasomal degradation of Mcl-1. Overexpression of Mcl-1 rescued apoptosis induced by Ang II, however, knockdown of Mcl-1 exacerbated Ang II-induced apoptosis, thereby indicating that the protein level of Mcl-1 determines the response of endothelial cells to this drug. © 2017 IUBMB Life, 69(5):321-327, 2017.

Natural products against cancer angiogenesis

The process of angiogenesis is quite well-known nowadays. Some medicines and extracts affecting this process are already used routinely in supporting the conventional treatment of many diseases that are considered angiogenic such as cancer. However, we must be aware that the area of currently used drugs of this type is much narrower than the theoretical possibilities existing in therapeutic angiogenesis. Plant substances are a large and diverse group of compounds that are found naturally in fruits, vegetables, spices, and medicinal plants. They also have different anticancer properties. The aim of this literature review article is to present the current state of knowledge concerning the molecular targets of tumor angiogenesis and the active substances (polyphenols, alkaloids, phytohormones, carbohydrates, and terpenes) derived from natural sources, whose activity against cancer angiogenesis has been confirmed.

Cysteine‑rich 61 RNA interference inhibits pathological angiogenesis via the phosphatidylinositol 3‑kinase/Akt‑vascular endothelial growth factor signaling pathway in endothelial cells

Hypoxia is a key factor in the pathogenesis of angiogenesis, and cysteine‑rich 61 (CCN1), an angiogenic factor, is involved in the development of pathological angiogenesis. The aim of the present study was to investigate the mechanism of CCN1 RNA interference (RNAi)‑induced inhibition of hypoxia‑induced pathological angiogenesis in endothelial cells. Human umbilical vein endothelial cells (HUVECs) were cultured under hypoxic conditions in vitro. The effects of inhibiting phosphoinositide 3‑kinase (PI3K)/Akt signaling using LY294002 were investigated in hypoxic HUVECs. The proliferation and apoptosis of HUVECs under hypoxia were assessed using CCN1 RNAi. The CCN1‑PI3K/Akt‑vascular endothelial growth factor (VEGF) pathway was analyzed under hypoxic conditions using reverse transcription‑quantitative polymerase chain reaction and western blotting. CCN1 RNAi inhibited the proliferation and induced the apoptosis of the HUVECs under hypoxia, with hypoxia significantly increasing the mRNA and protein expression levels of CCN1, Akt and VEGF. By contrast, CCN1 RNAi reduced the mRNA and protein expression levels of CCN1, Akt and VEGF in the HUVECs (P<0.05). Furthermore, LY294002 reduced the mRNA and protein expression levels of CCN1 in the hypoxic cells (P<0.05). These data indicated that CCN1 inhibits apoptosis and promotes proliferation in HUVECs. Therefore, CCN1 RNAi may offer a novel therapeutic strategy, which may aid in the treatment of pathological angiogenesis via inhibition of the PI3K/Akt‑VEGF pathway.

MicroRNAs in Hyperglycemia Induced Endothelial Cell Dysfunction

Hyperglycemia is closely associated with prediabetes and Type 2 Diabetes Mellitus. Hyperglycemia increases the risk of vascular complications such as diabetic retinopathy, diabetic nephropathy, peripheral vascular disease and cerebro/cardiovascular diseases. Under hyperglycemic conditions, the endothelial cells become dysfunctional. In this study, we investigated the miRNA expression changes in human umbilical vein endothelial cells exposed to different glucose concentrations (5, 10, 25 and 40 mM glucose) and at various time intervals (6, 12, 24 and 48 h). miRNA microarray analyses showed that there is a correlation between hyperglycemia induced endothelial dysfunction and miRNA expression. In silico pathways analyses on the altered miRNA expression showed that the majority of the affected biological pathways appeared to be associated to endothelial cell dysfunction and apoptosis. We found the expression of ten miRNAs (miR-26a-5p, -26b-5p, 29b-3p, -29c-3p, -125b-1-3p, -130b-3p, -140-5p, -192-5p, -221-3p and -320a) to increase gradually with increasing concentration of glucose. These miRNAs were also found to be involved in endothelial dysfunction. At least seven of them, miR-29b-3p, -29c-3p, -125b-1-3p, -130b-3p, -221-3p, -320a and -192-5p, can be correlated to endothelial cell apoptosis.

Endothelial cell survival during angiogenesis requires the pro-survival protein MCL1

Angiogenesis is essential to match the size of blood vessel networks to the metabolic demands of growing tissues. While many genes and pathways necessary for regulating angiogenesis have been identified, those responsible for endothelial cell (EC) survival during angiogenesis remain largely unknown. We have investigated the in vivo role of myeloid cell leukemia 1 (MCL1), a pro-survival member of the BCL2 family, in EC survival during angiogenesis. EC-specific deletion of Mcl1 resulted in a dose-dependent increase in EC apoptosis in the angiogenic vasculature and a corresponding decline in vessel density. Our results suggest this apoptosis was independent of the BH3-only protein BIM. Despite the known link between apoptosis and blood vessel regression, this was not the cause of reduced vessel density observed in the absence of endothelial MCL1. Rather, the reduction in vessel density was linked to ectopic apoptosis in regions of the angiogenic vasculature where EC proliferation and new vessel growth occurs. We have therefore identified MCL1 as an essential survival factor for ECs that is required for blood vessel production during angiogenesis.

Downregulation of tumstatin expression by overexpression of ornithine decarboxylase

Tumor angiogenesis, a pivotal process for cancer growth and metastasis, requires both upregulation of pro‑angiogenic molecules and downregulation of anti‑angiogenic molecules. Anti-angiogenesis therapy represents a promising way for cancer treatment. Tumstatin, a novel endogenous angiogenesis inhibitor, inhibits endothelial cell proliferation, pathological angiogenesis and tumor growth. Ornithine decarboxylase (ODC), overexpressed in various cancers, is associated with cell transformation, tumor invasion and angiogenesis. We found that the expression of tumstatin was suppressed in ODC-overexpressing human cancer cells and renal carcinoma tissues. We presumed that ODC overexpression may downregulate the expression of tumstatin. To be able to test this hypothesis, we generated HEK293 cells that overexpress ODC (ODC transfectants) and characterized the following experimental groups: PBS-treated group, mock transfectants, ODC transfectants, ODC transfectants transfected with pcDNA-ODCr (an antisense ODC-expressing plasmid) group and putrescine-treated group. The effect of ODC overexpression on tumstatin expression was examined by reverse transcriptase-polymerase chain reaction (RT-PCR), western blot analysis and dual luciferase reporter assay. ODC-overexpressing cells and putrescine-treated cells showed suppressed tumstatin mRNA and protein expression, and decreased tumstatin gene promoter activity. Thus, ODC overexpression suppresses the expression of tumstatin, which may provide fundamental evidence for the combination of anti-angiogenic therapy and conventional therapy for cancer treatment.

Enhanced apoptotic effects by downregulating Mcl-1: evidence for the improvement of photodynamic therapy with Celecoxib

Tumor cells exposed to sub-lethal photodynamic therapy (PDT) cause cellular rescue responses that lead to resistance to the therapy, including expression of angiogenic factors and survival molecules. However, the mechanisms contributing to the resistance are yet to be fully understood. Here, we show for the first time that Mcl-1, an anti-apoptotic protein, plays an important role in protecting cells from PDT-induced apoptosis. In contrast to the reduction in the anti-apoptotic proteins Bcl-2 and Bcl-xl, sub-lethal PDT induces an increase in Mcl-1 expression. Silencing Mcl-1 sensitizes tumor cells to PDT-induced apoptosis, and ectopic expression of Mcl-1 significantly delays Bax translocation to mitochondria and inhibits caspase-3 activity following PDT. Mcl-1 expression is associated closely with activated AKT signaling following PDT. AKT can regulate Mcl-1 expression through GSK-3β and NF-κB at the protein and transcriptional levels, respectively. Inhibition of AKT by Wortmannin or siRNA significantly reduces the levels of Mcl-1 mRNA and protein and enhances PDT-induced apoptosis. Treatment with Celecoxib, a non-steroidal anti-inflammatory drug (NSAID), is shown to downregulate Mcl-1 expression, and enhances PDT-induced apoptosis both in vitro and in vivo. This down-regulation is closely related to the inhibition effect of Celecoxib on the AKT/GSK-3β pathway, and was blocked upon addition of GSK-3β inhibitor LiCl or the proteasome inhibitor MG132. These results suggest that Mcl-1 is a potential target for improving the antitumor efficiency of PDT. A loss in Mcl-1 by inhibiting AKT promotes PDT-induced apoptosis through the mitochondrial pathway. This also provides a novel rationale for utilizing Celecoxib to improve the efficacy of PDT.

Polyamine production is downstream and upstream of oncogenic PI3K signalling and contributes to tumour cell growth

PI3K (phosphoinositide 3-kinase) signalling pathways regulate a large array of cell biological functions in normal and cancer cells. In the present study we investigated the involvement of PI3K in modulating small molecule metabolism. A LC (liquid chromatography)-MS screen in colorectal cancer cell lines isogenic for oncogenic PIK3CA mutations revealed an association between PI3K activation and the levels of polyamine pathway metabolites, including 5-methylthioadenosine, putrescine and spermidine. Pharmacological inhibition confirmed that the PI3K pathway controls polyamine production. Despite inducing a decrease in PKB (protein kinase B)/Akt phosphorylation, spermidine promoted cell survival and opposed the anti-proliferative effects of PI3K inhibitors. Conversely, polyamine depletion by an ornithine decarboxylase inhibitor enhanced PKB/Akt phosphorylation, but suppressed cell survival. These results suggest that spermidine mediates cell proliferation and survival downstream of PI3K/Akt and indicate that these two biochemical pathways control each other's activities, highlighting a mechanism by which small molecule metabolism feeds back to regulate kinase signalling. Consistent with this feedback loop having a functional role in these cell models, pharmacological inhibitors of PI3K and ornithine decarboxylase potentiated each other in inhibiting tumour growth in a xenograft model. The results of the present study support the notion that the modulation of spermidine concentrations may be a previously unrecognized mechanism by which PI3K sustains chronic proliferation of cancer cells.

Platelet-derived growth factor CC-mediated neuroprotection against HIV Tat involves TRPC-mediated inactivation of GSK 3beta

Platelet-derived growth factor-CC (PDGF-CC) is the third member of the PDGF family, and has been implicated both in embryogenesis and development of the CNS. The biological function of this isoform however, remains largely unexplored in the context of HIV-associated dementia (HAD). In the present study, we demonstrate that exposure of human neuroblastoma cells SH-SY5Y to HIV transactivator protein Tat resulted in decreased intrinsic expression of PDGF-CC as evidenced by RT-PCR and western blot assays. Reciprocally, pretreatment of SH-SY5Y cells with PDGF-CC abrogated Tat-mediated neurotoxicity by mitigating apoptosis and neurite & MAP-2 loss. Using pharmacological and loss of function approaches we identified the role of phosphatidylinositol 3-kinase (PI3K)/Akt signaling in PDGF-CC-mediated neuroprotection. We report herein a novel role about the involvement of transient receptor potential canonical (TRPC) channel 1 in modulation of calcium transients in PDGF-CC-mediated neuroprotection. Furthermore we also demonstrated PDGF-CC-mediated inactivation of the downstream mediator - glycogen synthase kinase 3β (GSK3β) evidenced by its phosphorylation at Ser-9. This was further validated by gain and loss of function studies using cells transfected with either the wild type or mutant GSK3β constructs. Intriguingly, pretreatment of cells with either the PI3K inhibitor or TRPC blocker resulted in failure of PDGF-CC to inactivate GSK3β, thereby suggesting the intersection of PI3K and TRPC signaling at GSK3β. Taken together our findings lead to the suggestion that PDGF-CC could be developed as a therapeutic target to reverse Tat-mediated neurotoxicity with implications for HAD.

53BP1 suppresses tumor growth and promotes susceptibility to apoptosis of ovarian cancer cells through modulation of the Akt pathway

53BP1 has been extensively studied as a key component of the DNA damage response, but little is known regarding the role of 53BP1 in preventing tumor development. The present study was designed to assess the impact of the modification of 53BP1 gene expression on the biological behavior of ovarian cancer cell lines and to elucidate the cellular pathway(s) triggered by 53BP1 in cancer cells. DNA liposome transfection technology was employed to increase and to knock down the expression of 53BP1 in A2780 and HO-8910PM cells, respectively. Viability, clonogenicity and cell cycle profiles were evaluated. Cell apoptosis was analyzed using flow cytometric assay. The expression of proteins related to apoptosis and cell signal transduction was assessed using western blotting. Increased expression of 53BP1 decreased the viability and the clonogenicity, and induced G₂/M arrest and apoptosis of the treated cells. The protein expression of Bax, P21 and caspase-3 was upregulated, while the levels of Bcl-2 and p-Akt were reduced to a statistically significant level. In contrast, deregulation of 53BP1 significantly increased proliferative ability. Collectively, our data suggest that 53BP1 is involved in several important steps in controlling cell proliferation and growth and preventing tumor development.

Polyamines on the reproductive landscape

The polyamines are ubiquitous polycationic compounds. Over the past 40 yr, investigation has shown that some of these, namely spermine, spermidine, and putrescine, are essential to male and female reproductive processes and to embryo/fetal development. Indeed, their absence is characterized by infertility and arrest in embryogenesis. Mammals synthesize polyamines de novo from amino acids or import these compounds from the diet. Information collected recently has shown that polyamines are essential regulators of cell growth and gene expression, and they have been implicated in both mitosis and meiosis. In male reproduction, polyamine expression correlates with stages of spermatogenesis, and polyamines appear to function in promoting sperm motility. There is evidence for polyamine involvement in ovarian follicle development and ovulation in female mammals, and polyamine synthesis is required for steroidogenesis in the ovary. Studies of the embryo indicate a polyamine requirement that can be met from maternal sources before implantation, whereas elimination of polyamine synthesis abrogates embryo development at gastrulation. Polyamines play roles in embryo implantation, in decidualization, and in placental formation and function, and polyamine privation during gestation results in intrauterine growth retardation. Emerging information implicates dietary arginine and dietary polyamines as nutritional regulators of fertility. The mechanisms by which polyamines regulate these multiple and diverse processes are not yet well explored; thus, there is fertile ground for further productive investigation.

Ornithine decarboxylase activity in rat organs and tissues under artificial hypobiosis

The influence of hypothermia-hypoxia-hypercapnia on ornithine decarboxylase (ODC, EC 4.1.1.17) activities in rat organs and tissues and also on the thymocyte distribution throughout the cell cycle stages was studied. The state of artificial hypobiosis in rats on decrease in the body temperature to 14.4-18.0°C during 3.0-3.5 h was accompanied by drops in the ODC activities in the neocortex and liver by 50-60% and in rapidly proliferating tissues (thymus, spleen, and small intestine mucosa) by 80% of the control value. In kidneys the ODC activity raised to 200% of the control level. Twenty-four hours after termination of the cooling and replacing the rats under the standard conditions, the ODC activities in the neocortex, liver, kidneys, spleen, and intestinal mucosa returned to the control values, but remained decreased in the thymus. Forty-eight hours later the ODC activities in the thymus and spleen exceeded the normal level. The distribution of thymocytes throughout the cell cycle stages did not change in rats in the state of hypothermia (hypobiosis); 24 and 48 h after termination of the cooling the fraction of thymocytes in the S stage was decreased and the fraction of the cells in the G(0)+G(1) stage was increased. The normal distribution of thymocytes throughout the cell cycle stages recovered in 72 h. Thus, in the thymus the diminution of the ODC activity preceded the suppression of the cell proliferation rate. The tissue-specific changes in the ODC activity are suggested to reflect adaptive changes in the functional and proliferative activities of organs and tissues during the development of hypobiosis under conditions of hypothermia-hypoxia-hypercapnia.

Ornithine decarboxylase and extracellular polyamines regulate microvascular sprouting and actin cytoskeleton dynamics in endothelial cells

The polyamines are essential for cancer cell proliferation during tumorigenesis. Targeted inhibition of ornithine decarboxylase (ODC), i.e. a key enzyme of polyamine biosynthesis, by alpha-difluoromethylornithine (DFMO) has shown anti-neoplastic activity in various experimental models. This activity has mainly been attributed to the anti-proliferative effect of DFMO in cancer cells. Here, we provide evidence that unperturbed ODC activity is a requirement for proper microvessel sprouting ex vivo as well as the migration of primary human endothelial cells. DFMO-mediated ODC inhibition was reversed by extracellular polyamine supplementation, showing that anti-angiogenic effects of DFMO were specifically related to polyamine levels. ODC inhibition was associated with an abnormal morphology of the actin cytoskeleton during cell spreading and migration. Moreover, our data suggest that de-regulated actin cytoskeleton dynamics in DFMO treated endothelial cells may be related to constitutive activation of the small GTPase CDC42, i.e. a well-known regulator of cell motility and actin cytoskeleton remodeling. These insights into the potential role of polyamines in angiogenesis should stimulate further studies testing the combined anti-tumor effect of polyamine inhibition and established anti-angiogenic therapies in vivo.

A novel fragment derived from the beta chain of human fibrinogen, beta43-63, is a potent inhibitor of activated endothelial cells in vitro and in vivo

BACKGROUND

Angiogenesis and haemostasis are closely linked within tumours with many haemostatic proteins regulating tumour angiogenesis. Indeed we previously identified a fragment of human fibrinogen, fibrinogen E-fragment (FgnE) with potent anti-angiogenic properties in vitro and cytotoxic effects on tumour vessels in vivo. We therefore investigated which region of FgnE was mediating vessel cytotoxicity.

METHODS

Human dermal microvascular endothelial cells (ECs) were used to test the efficacy of peptides derived from FgnE on proliferation, migration, differentiation, apoptosis and adhesion before testing the efficacy of an active peptide on tumour vasculature in vivo.

RESULTS

We identified a 20-amino-acid peptide derived from the beta chain of FgnE, beta43-63, which had no effect on EC proliferation or migration but markedly inhibited the ability of activated ECs to form tubules or to adhere to various constituents of the extracellular matrix - collagen IV, fibronectin and vitronectin. Furthermore, our data show that beta43-63 interacts with ECs, in part, by binding to alpha(v)beta(3), so soluble alpha(v)beta(3) abrogated beta43-63 inhibition of tubule formation by activated ECs. Finally, when injected into mice bearing tumour xenografts, beta43-63 inhibited tumour vascularisation and induced formation of significant tumour necrosis.

CONCLUSIONS

Taken together, these data suggest that beta43-63 is a novel anti-tumour peptide whose anti-angiogenic effects are mediated by alpha(v)beta(3).

Mammalian polyamine metabolism and function

Polyamines are ubiquitous small basic molecules that play multiple essential roles in mammalian physiology. Their cellular content is highly regulated and there is convincing evidence that altered metabolism is involvement in many disease states. Drugs altering polyamine levels may therefore have a variety of important targets. This review will summarize the current state of understanding of polyamine metabolism and function, the regulation of polyamine content, and heritable pathological conditions that may be derived from altered polyamine metabolism.