Activation of caspases and cleavage of Bid are required for tyrosine and phenylalanine deficiency-induced apoptosis of human A375 melanoma cells

Deprivation of tyrosine (Tyr) and phenylalanine (Phe) inhibits growth and induces programmed cell death (apoptosis) of human A375 melanoma cells. Herein, we found that activation of caspases and release of mitochondrial cytochrome c are required for this process. Culturing A375 cells in Tyr/Phe-free medium, containing 10% dialyzed fetal bovine serum, results in activation of caspase-3-like activity. This is accompanied by decreased cell viability and increased apoptosis. Tyr/Phe deprivation also stimulates proteolytic cleavage of the DNA repair enzyme, poly(ADP-ribose) polymerase (PARP). Western blot analysis showed that caspases 3, 7, 8, and 9 are activated by deprivation of Tyr/Phe. Tyr/Phe deprivation decreases mitochondrial membrane potential, induces cleavage of Bid, increases translocation of Bax from the cytosol to mitochondria, and results in release of cytochrome c from the mitochondria to the cytosol. Apoptosis due to Tyr/Phe deprivation is almost completely inhibited by the broad-spectrum cell-permeable caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (Z.VAD.fmk). This inhibitor suppresses the cleavage of Bid, the release of cytochrome c from the mitochondria to the cytosol, and the cleavage of PARP. Decylubiquinone, a mitochondrial permeability transition pore inhibitor, does not suppress the activation of caspase 8 but suppresses release of cytochrome c, activation of caspase 9, and induction of apoptosis. These results indicate that activation of caspases, cleavage of Bid, and mitochondrial release of cytochrome c are required for apoptosis induced by Tyr/Phe deprivation.

U0126, a mitogen-activated protein kinase kinase inhibitor, inhibits the invasion of human A375 melanoma cells

The anti-invasive ability of the mitogen-activated protein kinase (MAPK) kinase inhibitor, U0126, was examined in human A375 melanoma cells in vitro. The effect was compared to that of PD98059, another commonly used MEK (MAPK kinase) inhibitor. U0126 or PD98059 showed a dose-dependent inhibition of A375 cell invasion through growth factor-reduced Matrigel. U0126 was more potent than PD98059 in suppressing tumor cell invasion. Both compounds significantly decreased urokinase plasminogen activator (uPA) and matrix metalloproteinases-9 (MMP-9) concentrations in conditioned media. At 5 microM, U0126 inhibited phosphorylation of the MEK 1/2 to a non-detectable level within 24 h. The phosphorylation of extracellular signal-related kinase 1/2 was also dramatically suppressed by the treatment with 10 microM U0126 or 40 microM PD98059. Both compounds suppressed the protein expression of c-Jun, but not c-Fos. The expression of uPA and MMP-9 was also inhibited. Our data suggest that U0126 is an effective agent in inhibiting human A375 melanoma cell invasion and that the effect is partially due to the decreased production of uPA and MMP-9.

Alcohol consumption promotes body weight loss in melanoma-bearing mice

BACKGROUND

Alcohol consumption is an important risk factor for cancer. Little is known about its effects on cancer progression. Previously, we showed that high ethanol consumption inhibited metastasis of B16BL6 melanoma-bearing mice without affecting primary tumor growth. On the other hand, ethanol-consuming tumor-bearing (TE) mice exhibited decreased survival and decreased body weight as compared to water-drinking, tumor-bearing (TW) mice. The focus of this study was to determine how alcohol promotes weight loss in melanoma-bearing mice.

METHODS

Female, C57BL/6 mice were given water or 20% w/v ethanol in the drinking water for 3 weeks to 6 months before subcutaneous inoculation of 1 x 10(6) B16BL6 melanoma cells. Mice continued to receive the same fluids. Biochemical parameters were evaluated at various times after tumor inoculation. Body weight, water content, tumor weight and carcass fat content were determined at necropsy.

RESULTS

TW mice elicted a modest weight loss. This response was magnified 2-fold by alcohol consumption. The weight loss in TE mice is not caused by dehydration, decreased energy intake, or loss of skeletal muscle mass. It resulted specifically from loss in body fat. Other alterations associated with the fat loss in TE mice were: (1) decreased glucose, (2) elevated fatty acids, (3) elevated beta-hydroxybutyrate, (4) elevated glucagon, and (5) increased leptin levels in plasma. Body temperature decreased about 2.9 degrees C in TE mice. Metabolic rate increased in TW mice. The fat loss due to alcohol consumption in tumor-bearing mice was not due to increased metabolic rate.

CONCLUSIONS

The response elicited by alcohol consumption in tumor-bearing mice is complex and associated with alterations in metabolism and hormones. These findings suggest that alcohol abuse could be a risk factor for cancer patients because it invokes a strong depletion of body fat. This could facilitate wasting and shorten survival time.

Chronic ethanol consumption increases plasma leptin levels and alters leptin receptors in the hypothalamus and the perigonadal fat of C57BL/6 mice

BACKGROUND

Leptin, a protein secreted from adipocytes, and leptin receptors, expressed in the hypothalamus and fat tissue, regulate energy balance and adiposity. Leptin receptors exist as several forms that are delineated by the length of their cytoplasmic domains. Only the longest form is physiologically active through stimulation of the signal transducers and activators of transcription (STAT) second messenger system. Previous studies demonstrated that chronic ethanol consumption increases body adiposity and circulating leptin levels. This study examined the effect of chronic alcohol intake on the expression of leptin receptors and associated STAT second messengers in the hypothalamus and fat tissue.

METHODS

Female C57BL/6 mice were given water or 20% w/v ethanol and Purina 5001 laboratory chow ad libitum for 2 or 5 weeks. Plasma leptin levels were determined by radioimmunoassay and body adiposity was evaluated by measuring the amount of perigonadal fat. Expression of leptin receptors as well as STAT molecules in whole-cell lysates of the hypothalamus and the perigonadal fat were assayed by Western blot analysis.

RESULTS

Plasma leptin and perigonadal fat were increased after 5 weeks. The overall expression of leptin receptors was increased while the expression of the physiologically active long form of leptin receptor was decreased in the hypothalamus and the perigonadal fat of ethanol-consuming mice. Ethanol consumption also decreased hypothalamic expression of STAT3, a protein associated with leptin receptor activation in this region of the brain. In contrast, STAT1, a protein associated with leptin receptor activation in adipose tissue, was significantly elevated in the perigonadal fat of ethanol-consuming mice.

CONCLUSIONS

Chronic ethanol consumption increases the circulating level of leptin, and this is accompanied by altered expression of leptin-sensing molecules in the hypothalamus and peripheral adipose tissue. These results suggest that chronic ethanol intake affects metabolism by altering the leptin system that regulates energy balance.

Chronic ethanol inhibits NK cell cytolytic activity: role of opioid peptide beta-endorphin

The role of beta-endorphin (beta-EP) in ethanol-altered NK cell cytolytic activity is studied using male Fischer-344 rats as an animal model. Ethanol was administered for 1, 2, 3, or 4 wk in a liquid diet containing 8.7% ethanol (v/v), which means that 37% of the total calories were derived from ethanol. Rats treated with ethanol for 1 wk showed an increase in hypothalamic and plasma levels of immunoreactive (IR)-beta-EP, but displayed no significant effect on NK cell activity determined by (51)Cr release assay, as compared with those in pair-fed and ad libitum-fed animals. However, animals treated with ethanol for 2, 3, or 4 wk showed decreased hypothalamic and plasma levels of IR-beta-EP and decreased splenic NK cell activity. No significant decrease in the number of splenocytes and NK cells or in the percentage of NK cells was seen until after 3 and 4 wk of ethanol treatment. Exposure in vitro of splenic lymphocytes obtained from control animals to various concentrations of beta-EP increased NK cell activity. The opiate antagonist naltrexone blocked the beta-EP-stimulated effect. The in vitro NK cell response to beta-EP was reduced in the splenocytes obtained from animals treated with ethanol for 2 wk, but not in those obtained from animals treated with ethanol for 1 wk as compared with those in control animals. Additionally, beta-EP administration into the paraventricular nucleus of the hypothalamus stimulated NK cell cytolytic activity, whereas the opiate blocker administration reduced NK cell activity. The NK cell responses to paraventricular nucleus beta-EP were reduced in the animals treated with ethanol for 2 wk. These data provide evidence for the first time that ethanol inhibits NK cell cytolytic activity, possibly by reducing beta-EP-regulated splenic NK cell function.

Specific amino acid deficiency alters the expression of genes in human melanoma and other tumor cell lines

This study determined the effect of tyrosine (Tyr) and phenylalanine (Phe) deprivation on protein expression and phosphorylation of mitogen-activated protein kinase kinase 4 (MKK4)/stress-activated protein/Erk kinase (SEK1), a metastasis suppressor gene. Differential display and suppressive subtractive hybridization techniques identified genes modulated by Tyr and Phe deprivation. Expression of MKK4/SEK1 protein varied widely among human A375, A375SM and SB2 melanoma, PC-3 and DU145 prostate cancer, and MDA-MB-231 breast cancer cell lines and within the different lines. Phosphorylation of the MKK4/SEK1 protein similarly varied. No differences in MKK4/SEK1 gene expression or in the 41 other metastasis and tumor suppressor genes were found in A375 melanoma cells cultured in Tyr- and Phe-deprived media. A number of up-regulated and down-regulated genes in A375 melanoma cells were identified by differential display and suppressive subtractive hybridization that were pertinent to regulation of cytoskeletal organization, cell movement, gene transcription and metastasis. Two tumor marker genes, the gene for enolase and FUS/CHOP, were down-regulated by Tyr and Phe deprivation. This study shows that tumor cells display heterogeneity in their response to deprivation of Tyr and Phe and that these amino acids may be signaling molecules that regulate gene expression and function in tumor cells.

UCN-01 dose-dependent inhibition of normal hyperproliferative cells in mice

UCN-01 is a hydroxylated derivative of staurosporine and a potent protein kinase C (PKC) inhibitor. Interest in the potential usefulness of this compound as an anticancer drug stems mainly from its unique anti-signaling, growth-arresting properties on tumor cells. This include activation of CDC2 kinase (CDK1) which interacts with either cyclin A or cyclin B1 at the G1 or G2/M border, suggeting that this event is one of the major consequences of the drug action on eukaryotic cells. Nonetheless, the antiproliferative activity of UCN-01 on normal rapidly dividing cells (intestinal epithelial and bone marrow cells) is not well documented. Thus, the main objective of this study was to investigate the in vivo antiproliferative activity of UCN-01 on these normal hyperproliferative cells and evaluate whether cellular response to UCN-01 could be modulated in the presence of DNA damage. Mice were injected i.m. with a single dose of UCN-01 (2.5 mg/kg-20 mg/kg) followed 3 and 24 h later by in vivo BrdU labeling for 1 h. At autopsy, bone marrow cells were collected and fixed for dual parameter BrdU/DNA flow cytometry. Different regions of the gut were also fixed for immunoperoxidase BrdU assays. Newly replicated cells were mainly located in the lower compartments of the crypt columns and were scored for BrdU stained nuclei using an image analysis system. A comparison between groups showed that 5 mg/kg UCN-01 induced inhibition in BrdU incorporation at 3 and 24 h, as compared to the other groups injected with various doses of UCN-01. Flow cytometric analysis of bone marrow cells stained with fluorescein tagged anti-BrdU (FITC) along with propidium iodide (PI) also showed inhibition in BrdU incorporation of S phase fraction cells in mice treated with 5 mg/kg UCN-01. These bone marrow cells were arrested primarily in the G1 phase of the cell cycle. The colony-forming unit (CFU) assay of the bone marrow cells was then used to determine the level of drug interaction of UCN-01 and, topotecan, a topoisomerase I inhibitor, at a fixed dose ratio. An antagonistic drug interaction (CI > 1) was observed as determined by the median-effect analysis. However, an additive interaction (CI = 1) was obtained with the use of camptothecin or 10,11-methylenedioxycamptothecin and UCN-01. The results of the in vitro drug interaction with UCN-01 may predict protection from topotecan-induced bone marrow toxicity.

Tob-mediated cross-talk between MARCKS phosphorylation and ErbB-2 activation

The biochemical path for the activation of ErbB-2 by PKC activator was investigated in MDA-MB-231 human breast cancer cells. We found that PMA-induced phosphorylation of myristoylated alanine-rich C kinase substrate (MARCKS) increased its binding with Tob that exerts an anti-proliferative effect through the binding with ErbB-2. The phosphorylation site domain (PSD) of MARCKS was relevant to its interaction with Tob. Decreased binding of Tob with ErbB-2 and subsequent activation of ErbB-2 were observed in MDA-MB-231 cells in response to PMA treatment. The present study proposes that MARCKS phosphorylation by PKC removes Tob from ErbB-2 by increasing its binding affinity with Tob, and thereby activates the ErbB-2 mediated signal transduction.

Decreased tissue plasminogen activator and increased plasminogen activator inhibitors and increased activator protein-1 and specific promoter 1 are associated with inhibition of invasion in human A375 melanoma deprived of tyrosine and phenylalanine

We previously found that dietary tyrosine (Tyr) and phenylalanine (Phe) restriction significantly decreased the metastatic phenotype of the pigmented murine B16BL6 melanoma in vivo and decreased the in vitro invasion of these cells. Here we report that invasion and chemoinvasion through GFR Matrigel of the human amelanotic A375 melanoma also is significantly inhibited by Tyr and Phe deprivation in vitro. Deprivation of these two amino acids decreased the secretion and protein expression of tissue-type plasminogen activator (tPA) while expression and secretion of plasminogen activator inhibitor (PAI-1 and PAI-2) were increased. Moreover, nuclear extracts of Tyr- and Phe-deprived cells exhibited increased binding of the transcription factors, activator protein-1 (AP-1) and specific promoter-1 (Sp1), to consensus oligonucleotides as determined by electrophoretic mobility shift assay. Nuclear binding activity to the oligonucleotide consensus sequence for AP-1 was inhibited by antibody against c-Fos and more effectively inhibited by an antibody against c-Jun. We conclude that decreased invasion and chemoinvasion of A375 melanoma cells deprived of Tyr and Phe are related to decreased secretion of tPA and increased secretion of PAIs. Increased AP-1 and Sp1 binding implicates these transcription factors in the regulation of PAI expression.

Inhibition of B16BL6 melanoma invasion by tyrosine and phenylalanine deprivation is associated with decreased secretion of plasminogen activators and increased plasminogen activator inhibitors

We previously found that dietary tyrosine (Tyr) and phenylalanine (Phe) limitation significantly decreased the metastatic phenotype of B16BL6 melanoma cells in vivo and decreased the in vitro invasion of these cells. To more specifically characterize the effects of Tyr and Phe deprivation we examined the three steps involved in invasion: attachment to host cells and components, elaboration of proteases that degrade basement membranes, and migration of invading tumor cells. Here we report that B16BL6 melanoma cell invasion through growth factor reduced (GFR) Matrigel is significantly decreased by Tyr and Phe deprivation. Tyr and Phe deprivation in vitro decreased the attachment of B16BL6 melanoma cells to GFR Matrigel, heparin sulfate proteoglycans (HSPG), neonatal murine epidermal (NME) cells and the extracellular matrix (ECM) from these cells. These cells also exhibited a decrease in chemotactic response to fetal bovine serum (FBS). Deprivation of these two amino acids decreased the secretion of urokinase plasminogen activator (uPA) and tissue plasminogen activator (tPA) while plasminogen activator inhibitor (PAI)-1 and -2 were increased in these cells. These observations suggest that Tyr and Phe deprivation decreases the in vitro chemotactic and invasive ability of B16BL6 melanoma cells by decreasing attachment and secreted PA activity and by increasing secreted PAIs in these cells.

The modulation of B16BL6 melanoma metastasis is not directly mediated by cytolytic activity of natural killer cells in alcohol-consuming mice

BACKGROUND

Previous studies in our laboratory indicate that alcohol consumption suppresses the metastasis of B16BL6 melanoma, whereas the cytolytic activity of natural killer (NK) cells is decreased in female C57BL/6 mice given 20% w/v alcohol in their drinking water. In the present study, we further evaluated the involvement of NK cells and alcohol consumption in the cytolytic activity of NK cells, the surface expression of NK phenotypic markers, and metastasis of B16BL6 melanoma in C57BL/6 beige (bgJ/bgJ) mutant mice, which possess inherently low NK-cell cytolytic activity.

METHODS

Beige and control (bgJ/+) mice were given either water or 20% w/v of alcohol in drinking water for 6 1/2 to 7 weeks before assay for cytolytic activity, surface marker expression, and inoculation with B16BL6 melanoma intravenously or into the pinna of the ear.

RESULTS

NK cytolytic activity was suppressed in beige mice, and alcohol consumption did not modulate further the cytolytic activity. Beige mice had a lower percentage of NK cells in the peripheral blood and spleen than control mice. Peripheral blood lymphocytes from beige mice also exhibited a reduced percentage of CD4+ T lymphocytes. Alcohol consumption similarly reduced the percentages of NK1.1- and LGL-1-expressing lymphocytes in the peripheral blood and spleen and reduced the percentage of CD8+ T lymphocytes in the peripheral blood in both control and beige mice. Tumor lung colonization was increased in beige mice relative to control mice after intravenous inoculation of B16BL6 melanoma. The increase was more pronounced in water-drinking beige mice than in control mice irrespective of alcohol consumption. Tumor lung colonization was significantly decreased (p < 0.05) by alcohol consumption in one experiment and partially decreased (p = 0.07) in the other. Mice that were inoculated into the pinna of the ear also exhibited a blunted antimetastatic response to alcohol consumption.

CONCLUSIONS

These data suggest that the presence of the beige mutation diminishes the antimetastatic effect of alcohol consumption and that there is no interaction between alcohol consumption and NK-cell activity in the modulation of lung metastasis of B16BL6 melanoma cells.

Relationship between moderate intensity endurance training volume and natural killer cell cytolytic activity

BACKGROUND

This study was designed to examine the relationship between endurance training volume and natural killer cell (NK) cytolytic activity. We hypothesized that a dose dependent relationship exists between forced treadmill training volume and training induced increases in NK cell cytolytic activity.

METHODS

EXPERIMENTAL DESIGN

female, Swiss Webster mice were assigned to treadmill control (TC) or treadmill trained groups (n = 10 per group). Trained mice ran at 12 m per min. (8 degrees grade) for: 15 (EX15), 30 (EX30), or 60 minutes (EX60) per day, five days per week for 11 weeks. Splenic NK cell activity was expressed as median lytic unit (LU), median LU per asialo GM1 (AsGM1+) cell, and median LU per spleen.

RESULTS

Median NK activity was not significantly increased by training volume. A trend toward greater median LU per AsGM1+ cell was observed in EX30 group versus TC (p = 0.1). Training volumes less than or greater than this level produced smaller increases in NK cytolytic activity.

CONCLUSIONS

These data provide preliminary evidence indicating that training induced increases in splenic NK cell cytolytic activity do not exhibit a dose dependent relationship with treadmill training volume.

Modulation of perforin, granzyme A, and granzyme B in murine natural killer (NK), IL2 stimulated NK, and lymphokine-activated killer cells by alcohol consumption

Alcohol consumption in mice suppresses the cytolytic activity of natural killer (NK) and lymphokine-activated killer (LAK) cells through unknown mechanisms. Herein, we found that alcohol consumption decreased target cell-induced release of granzyme A activity in freshly isolated splenic NK cells, in NK cells stimulated for 18 h with 1000 IU/ml of interleukin 2, and in LAK cells. The total activity and protein expression of granzymes A and B also were lower in these cells than in cells isolated from water-drinking mice. Interleukin 2 increased granzyme A protein expression independent of alcohol consumption; however, this increase was associated with decreased enzyme activity. In contrast, granzyme B protein expression and enzymatic activity increased in response to interleukin 2. Perforin activity and protein expression were reduced in LAK cells generated from alcohol-consuming mice. We conclude that the mechanism underlying the suppression of NK and LAK cytolytic activity by alcohol consumption involves the collective reduction of target-induced release, activity, and expression of perforin and granular proteases.

Focal adhesion kinase-dependent apoptosis of melanoma induced by tyrosine and phenylalanine deficiency

We found previously that restriction of tyrosine (Tyr) and phenylalanine (Phe) inhibited growth and metastasis of B16BL6 murine melanoma and arrested these cells in the G0-G1 phase of the cell cycle. Here, we report that deprivation of these two amino acids in vitro induces apoptosis in B16BL6 and in human A375 melanoma cells but not in nontransformed, neonatal murine epidermal cells or human infant foreskin fibroblasts. Four days after deprivation of Tyr and Phe in vitro, 37% of B16BL6 and 51% of A375 melanoma cells were undergoing apoptosis. Apoptosis was not associated with elevation in intracellular calcium or alteration in p53 or c-myc protein expression. Expression and Tyr phosphorylation of focal adhesion kinase (FAK) were inhibited in both melanoma cell lines by deprivation of Tyr and Phe but not by deprivation of glutamine or serum. Tyr phosphorylation of FAK in Tyr- and Phe-deprived melanoma cells was enhanced within 30 min of refeeding with complete DMEM. FAK protein expression recovered within 60 min, and cell viability recovered within 24 h. Genistein, a tyrosine kinase inhibitor that specifically inhibits Tyr phosphorylation of FAK, did not induce apoptosis in A375 melanoma cells at a concentration of 50 microM. Genistein prevented the recovery of cell viability upon refeeding with Tyr and Phe to previously deprived A375 melanoma cells. These data collectively indicate that apoptosis induced by Tyr and Phe deprivation is FAK-dependent.

Changes in angiotensin II receptors in dopamine-rich regions of the mouse brain with age and ethanol consumption

The density of angiotensin II (Ang II) receptors was determined in three dopaminergic nerve terminal-rich brain regions (caudate putamen, nucleus accumbens, and ventral pallidum) of mice that were given either water (control) or 20% w/v ethanol (EtOH) to drink for either 2-8 weeks (young) or 46 weeks (old). The receptors were labeled with 125I-sarcosine1, isoleucine8 angiotensin II (125I-SI Ang II) and measured by quantitative densitometric image analysis (receptor autoradiography) or by saturation binding assays on homogenates of these brain regions. The selective AT2 receptor subtype antagonist PD 123319 (10 microM) was used to inhibit 125I-SI Ang II binding to AT2 receptors to determine AT1 receptor density in brain sections. In young control mice the density of Ang II receptor binding sites in the caudate putamen was 407+/-26 fmol/g, in the nucleus accumbens the density was 346+/-27 fmol/g, and in the ventral pallidum the density was 317+/-27 fmol/g. Less than 5% of specific 125I-SI Ang II binding was displaced by PD 123319, suggesting that nearly all of the Ang II receptors in these brain regions were the AT1 subtype. The Bmax in homogenates of these three regions in young control mice was 11.0+/-2.1 fmol/mg protein. The KD was 0.49+/-0.13. Ang II receptors in old mouse brains were decreased, respectively, by 32%, 35% and 30% in the caudate putamen, nucleus accumbens and ventral pallidum (p<0.001). Ang II receptors were slightly, but not significantly increased in both young and old EtOH-consuming mice.

Influence of tyrosine and phenylalanine limitation of cytotoxicity of chimeric TGF-alpha toxins on B16BL6 murine melanoma in vitro

Previous research in animals supports the use of tyrosine and phenylalanine (Tyr-Phe) restriction as an adjuvant to the treatment of cancer. In this regard, dietary restriction of Tyr-Phe specifically inhibits the growth of B16BL6 melanoma tumors, dramatically suppresses spontaneous hematogenous metastasis, and modulates the sensitivity of these tumor cells to growth factors. Two chimeric toxins, HB-TGF alpha-PE4EKDEL and TGF alpha-PE4EKDEL, were examined for their toxicity against the B16BL6 melanoma cell line, and the ability of Tyr-Phe limitation to modulate the potential of these toxins was examined. Tyr-Phe limitation significantly enhanced the cytotoxic effects of HB-TGF alpha-PE4EKDEL approximately 10-fold toward B16BL6 melanoma, and free heparin diminished the cytotoxicity of HB-TGF alpha-PE4EKDEL. Although TGF alpha-PE4EKDEL is cytotoxic to this cell line, Tyr-Phe limitation did not effect the cytotoxicity of this toxin. Tyr-Phe limitation inhibited the synthesis and secretion of heparin-binding proteins but did not alter the expression of surface heparan sulfate proteoglycans. These data suggest that cell surface heparan sulfate proteoglycan is a target for binding and execution of the cytotoxicity of HB-TGF alpha-PE4EKDEL and that augmentation of cytotoxicity by Tyr-Phe limitation is due to the inhibition of heparin-binding protein production.

Tyrosine and phenylalanine restriction induces G0/G1 cell cycle arrest in murine melanoma in vitro and in vivo

Tyr-Phe and Met limitation in vitro inhibited cell proliferation and proliferating cell nuclear antigen (PCNA) expression to a greater extent than serum limitation. Tyr-Phe and serum limitation arrested cells in the G0/G1 phase; Met limitation blocked cells in the G0/G1 and S phases. Tyr-Phe limitation progressively decreased cyclin D1 expression to 30% of control within four days and did not affect expression of cyclin D3 or cyclin-dependent kinase (CDK2, CDK4, and CDK5) expression, Met limitation decreased cyclin D3 expression to 25% of control and CDK2 expression to 32% of control by Day 4 and did not affect expression of cyclin D1, CDK4, and CDK5. Serum limitation inhibited cyclin D1 and cyclin D3 expression to 24% of control after four days and did not effect CDK expression. Expression of two CDK inhibitors, p21WAF1/Cip1 and p27Kip1, was not changed by amino acid or serum limitation. Dietary restriction of Tyr-Phe in mice bearing subcutaneous B16BL6 melanoma tumors decreased tumor growth rate compared with mice fed a normal diet. Tumors from Tyr-Phe-restricted mice exhibited decreased PCNA expression, G0/G1 phase cell cycle arrest, and reduced cyclin D1 expression. These data indicate that decreased tumor growth in vivo associated with dietary restriction of Tyr and Phe is cell cycle specific.

Modulation of NK cell cytolytic activity by macrophages in chronically exercise-stressed mice

This study was designed to investigate the effects of moderate-intensity endurance training on basal natural killer (NK) cell cytolytic activity in murine splenocytes that were enriched for 1) NK1.1+ cells or 2) macrophages and NK1.1+ cells. Mice were assigned to sedentary (Sed), treadmill control (TM), or treadmill-trained (Trn) groups. Splenocyte number, the percentages of NK1.1+, large granular lymphocytes (NK1.1+, LGL-1+), and other subpopulations did not change in Trn mice. Approximately 70% of cells enriched for NK1.1+ expressed this surface antigen. Lytic units (LU) expressed per LGL-1+ cell were significantly lower in Trn [83.9 +/- 3.2 (SE)] compared with Sed (109.5 +/- 7.5) and TM (101.3 +/- 6.4) groups. When macrophages remained in the in vitro assay, LU per LGL-1(+) cell did not differ across groups. The results indicate that highly enriched NK1.1+ cells from Trn mice had lower NK cell activity compared with Sed mice. No differences in NK cell activity were observed when cells were enriched for NK1.1+ cells and macrophages. These findings support the hypothesis that macrophage modulation of NK cells may be one mechanism contributing to augmented basal NK cell activity in endurance-trained individuals.

Ethanol modulates metastatic potential of B16BL6 melanoma and host responses

The experimental metastatic potential (lung-colonizing ability) of B16BL6 melanoma cells was examined in C57BL/6 mice after exposure to ethanol in vitro and in vivo. In vitro, tumor cells were cultured with ethanol (0.3% v/v), or medium alone, for three passages at 5-day intervals. In vivo, B16BL6 melanoma was exposed to ethanol by administering ethanol (10% or 20% w/v) to mice following subcutaneous inoculation of tumor cells into the dorsal hip. All tumor cells were subsequently inoculated intravenously into the lateral tail vein of water-drinking mice to assess changes in metastatic phenotype. Tumor cells cocultured in vivo with ethanol produced significantly higher numbers of superficial lung colonies, compared with tumor cells cultured in control medium. Experimental metastasis of tumor cells obtained from 20% w/v ethanol-consuming mice was also significantly increased, compared with cells obtained from water-drinking mice. Metastasis of B16BL6 melanoma cells previously obtained from mice consuming 10% w/v ethanol did not differ from controls. In other experiments, water-drinking and ethanol-consuming (2.5%, 10%, and 20% w/v) mice were inoculated subcutaneously into the dorsal hip with B16BL6 melanoma cells, and monitored for tumor growth rate and survival time. In these experiments, survival times were significantly shorter in mice consuming 20% ethanol, compared with all other groups. Subcutaneous tumor growth rate was unaffected by ethanol consumption. Lung metastasis resulting from subcutaneous tumor implantation of B16BL6 melanoma was respectively inhibited, or absent, in 10% and 20% ethanol-consuming groups. Thus, tumor growth rate and incidence of lung metastases were not apparent determinants of decreased survival in 20% ethanol-consuming mice. The results of this study indicate that the experimental metastatic potential of B16BL6 melanoma is increased during exposure to ethanol; however, metastasis from subcutaneous tumor-bearing mice is suppressed. This latter finding is consistent with previous results in which spontaneous metastasis was also suppressed after inoculation of the tumor into the pinna of the ear. Although ethanol increases the ability of B16BL6 melanoma to colonize the lung after intravenous inoculation, this effect is abated in the presence of host factors in ethanol-consuming mice.

Ethanol consumption suppresses the IL2-induced proliferation of NK cells

Ethanol (20% w/v) given to female, C57BL/6 mice in their drinking water suppresses natural killer (NK) and lymphokine activated killer cell cytolytic activity in mixed splenocytes and in splenocytes highly enriched for NK cells. The present study examined the effects of ethanol consumption on rIL2-induced proliferation of enriched NK cells. Mice were given 20% w/v ethanol in the drinking water for 2 weeks. Splenic NK cells were harvested and enriched up to 88% based on surface expression of NK1.1. The enriched NK cells were cultured in the presence of 1000 IU/ml (20 pg/ml) murine recombinant interleukin 2 (rIL2). There were fewer cells (p < 0.02) from ethanol-consuming mice compared to cells from water-drinking control mice after incubation with IL2 at 2, 4, and 6 days of culture. Ethanol consumption was associated with significantly lower [3H]thymidine uptake (p < 0.05). Ethanol consumption did not affect apoptosis or intracellular levels of interferon-gamma, tumor necrosis factor-alpha, or granulocyte macrophage colony-stimulating factor in NK cells. Ethanol consumption did not affect the expression of c-myc mRNA in NK cells that were cultured for 10 min or 4, 8, and 18 hr in rIL2. Suppression of IL2-induced NK cell proliferation is associated with ethanol consumption, and suppression is not due to altered IL2 receptor expression, increased apoptosis, intracellular cytokine levels, or c-myc expression.

Attachment, invasion, chemotaxis, and proteinase expression of B16-BL6 melanoma cells exhibiting a low metastatic phenotype after exposure to dietary restriction of tyrosine and phenylalanine

We previously reported that low levels of tyrosine (Tyr) and phenylalanine (Phe) alter the metastatic phenotype of B16-BL6 (BL6) murine melanoma and select for tumor cell populations with decreased lung colonizing ability. To more specifically characterize the effects of Tyr and Phe restriction on the malignant phenotype of BL6, we investigated in vitro attachment, invasion, proteinase expression, and chemotaxis of high and low metastatic BL6 variants. High metastatic variant cells were isolated from subcutaneous tumors of mice fed a nutritionally complete diet (ND cells) and low metastatic variant cells were isolated from mice fed a diet restricted in Tyr and Phe (LTP cells). Results indicate that attachment to reconstituted basement membrane (Matrigel) was significantly reduced in LTP cells as compared to ND cells. Attachment to collagen IV, laminin, and fibronectin were similar between the two variants. Invasion through Matrigel and growth factor-reduced Matrigel were significantly decreased in LTP cells as compared to ND cells. Zymography revealed the presence of M(r) 92,000 and M(r) 72,000 progelatinases, tissue plasminogen activator, and urokinase plasminogen activator in the conditioned medium of both variants; however, there were no differences in activity of these secreted proteinases between the two variants. Growth of the variants on growth factor-reduced Matrigel similarly induced expression of the M(r) 92,000 progelatinase. The variants exhibited similar chemotactic responses toward laminin. However, the chemotactic response toward fibronectin by LTP cells was significantly increased. MFR5, a monoclonal antibody which selectively blocks function of the alpha 5 chain of the alpha 5 beta 1 integrin, VLA-5, decreased the chemotactic response toward fibronectin of ND cells by 37%; the chemotactic response by LTP cells was reduced by 49%. This effect was specific for fibronectin-mediated chemotaxis since the chemotaxis toward laminin and invasion through Matrigel were not altered by the presence of MFR5. The surface expression of VLA-5 was significantly increased in LTP cells as compared to ND cells by flow cytometric analysis. These observations suggest that limitation of Tyr and Phe either directly modifies BL6 or selects for subpopulations with altered in vitro invasion, chemotaxis, and integrin expression.

Phorbol 12-myristate 13-acetate enhances nm23 gene expression in murine melanocytes but not in syngeneic B16-BL6 melanoma variants

The nm23 gene has been described as a potential metastasis suppressor gene in certain rodent and human tumors. We previously demonstrated that tyrosine and phenylalanine restriction suppresses metastatic heterogeneity of B16-BL6 murine melanoma and selects for tumor variants with decreased metastatic potential. In this study, we investigated nm23 expression in the highly metastatic B16-BL6 (ND) melanoma, its nutritionally derived poorly metastatic (LT) variant, and the syngeneic non-tumorigenic Mel-ab melanocytes. No differences in nm23 expression were observed between ND and LT cells, and nm23 expression varied between different isolates. Previously, we showed that metastatic potential of 1-ND cells decreases and is not altered in 1-LT cells after prolonged in vitro cell passage; however, nm23 expression is equivalently increased by 2-fold. In 2-ND and 2-LT cells, expression of nm23 is not different at higher in vitro cell passage. Expression of nm23 decreased about 2-fold when phorbol 12-myristate 13-acetate (PMA) was removed from Mel-ab cells, which induces these cells to become quiescent. Although membrane-associated protein kinase C (PKC) activity decreased after prolonged PMA treatment in all cells, neither nm23 expression nor proliferation of ND and LT cells was affected by PMA. These data indicate that nm23 expression is related to proliferative activity rather than to the suppression of metastatic potential.