Delayed growth of glioma by Scutellaria flavonoids involve inhibition of Akt, GSK-3 and NF-κB signaling

Plants of the genus Scutellaria constitute one of the common components of Eastern as well as traditional American medicine against various human diseases, including cancer. In this study, we examined the in vivo anti-glioma activity of a leaf extract of Scutellaria ocmulgee (SocL) while also exploring their potential molecular mechanisms of action. Oral administration of SocL extract delayed the growth of F98 glioma in F344 rats, both in intracranial and subcutaneous tumor models. Immunohistochemistry revealed inhibition of Akt, GSK-3α/β and NF-κB phosphorylation in the subcutaneous tumors following treatment with Scutellaria. The SocL extract as well as the constituent flavonoid wogonin also showed dose- and time-dependent inhibition of Akt, GSK-3α/β and NF-κB in F98 cell cultures in vitro, as determined by western blot analysis. Pharmacologic inhibitors of PI3K and NF-κB also significantly inhibited the in vitro proliferation of F98 glioma cells, indicating the key role of these signaling molecules in the growth of malignant gliomas. Transfection of F98 cells with constitutively active mutant of AKT (AKT/CA), however, did not significantly reverse Scutellaria-mediated inhibition of proliferation, indicating that Scutellaria flavonoids either directly inhibited Akt kinase activity or acted downstream of Akt. In vitro Akt kinase assay demonstrated that the SocL extract or wogonin could indeed bind to Akt and inhibit its kinase activity. This study provides the first in vivo evidence and mechanistic support for anti-glioma activity of Scutellaria flavonoids and has implications in potential usage of Scutellaria flavonoids in adjuvant therapy for malignant tumors, including gliomas.

Differential sensitivity of normal and malignant breast epithelial cells to genistein is partly mediated by p21(WAF1)

Genistein, a soy metabolite, is a potential chemopreventive agent against various types of cancer. There are several studies documenting molecular alterations leading to cell cycle arrest and induction of apoptosis in a variety of cancer cells; however, no studies, to date, have shown the effect of genistein in isogenic normal and malignant breast epithelial cells. In this study, we investigated whether genistein shows any differential sensitivity to normal (MCF10A and MCF12A) and malignant (MCF10CA1a and MDA-MB-231) breast epithelial cells. We found that genistein causes a greater degree of G(2)-M arrest and induces apoptosis in malignant cell lines compared with normal breast epithelial cells. After genistein treatment, flow cytometric analysis revealed a hyperdiploid population in malignant cells that was not observed in normal cells. Cell cycle regulator p21(WAF1), which is known to be up-regulated by genistein treatment, was greatly induced at RNA and protein levels in normal cells, whereas its level was only slightly induced in malignant MDA-MB-231 cells and not detectable in malignant MCF10CA1a cells. Therefore, we investigated the causal role of p21(WAF1) in the differential sensitivity of genistein among these cell lines. We examined the effects of genistein on p21(WAF1) -/- and p21(WAF1) +/+ HCT116 cells, which were used as controls prior to studies on breast cancer cells. We found that there was a greater degree of cell cycle arrest and apoptosis in p21(WAF1) -/- cells compared with p21(WAF1) +/+ HCT116 cells after genistein treatment. Flow cytometric analysis after genistein treatment showed a significant number of p21(WAF1) -/- cells in the hyperdiploid population, which are probably programmed to die through apoptotic processes. To further confirm the causal role of p21(WAF1) in genistein-mediated cell cycle arrest and apoptosis, we down-regulated p21(WAF1) by antisense p21(WAF1) cDNA transfection experiments. We found that both normal and malignant p21(WAF1) antisense (AS)-expressing clones became more sensitive to G(2)-M arrest after genistein treatment. Flow cytometric analysis showed an increase in the hyperdiploid population in the AS clones. Further evaluation showed an increase in apoptosis in malignant AS clones but not in normal breast epithelial AS clones. These results suggest that p21(WAF1) may play an important role in determining the sensitivity of normal and malignant breast epithelial cells to genistein.

Indole-3-carbinol (I3C) induced cell growth inhibition, G1 cell cycle arrest and apoptosis in prostate cancer cells

Prostate cancer is one of the most common cancers in men and it is the second leading cause of cancer related death in men in the United States. Recent dietary and epidemiological studies have suggested the benefit of dietary intake of fruits and vegetables in lowering the incidence of prostate cancer. A diet rich in fruits and vegetables provides phytochemicals, particularly indole-3-carbinol (I3C), which may be responsible for the prevention of many types of cancer, including hormone-related cancers such as prostate. Studies to elucidate the role and the molecular mechanism(s) of action of I3C in prostate cancer, however, have not been conducted. In the current study, we investigated whether I3C had any effect against prostate cancer cells and, if so, attempts were made to identify the potential molecular mechanism(s) by which I3C elicits its biological effects on prostate cancer cells. Here we report for the first time that I3C inhibits the growth of PC-3 prostate cancer cells. Induction of G1 cell cycle arrest was also observed in PC-3 cells treated with I3C, which may be due to the observed effects of I3C in the up-regulation of p21(WAF1) and p27(Kip1) CDK inhibitors, followed by their association with cyclin D1 and E and down-regulation of CDK6 protein kinase levels and activity. The induction of p21(WAF1) appears to be transcriptionally upregulated and independent of the p53 responsive element. In addition, I3C inhibited the hyperpohosphorylation of the Retinoblastoma (Rb) protein in PC-3 cells. Induction of apoptosis was also observed in this cell line when treated with I3C, as measured by DNA laddering and poly (ADP-ribose) polymersae (PARP) cleavage. We also found an up-regulation of Bax, and down-regulation of Bcl-2 in I3C-treated cells. These effects may also be mediated by the down-regulation of NF-kappaB observed in I3C treated PC-3 cells. From these results, we conclude that I3C inhibits the growth of PC-3 prostate cancer cells by inducing G1 cell cycle arrest leading to apoptosis, and regulates the expression of apoptosis-related genes. These findings suggest that I3C may be an effective chemopreventive or therapeutic agent against prostate cancer.

Translocation of Bax to mitochondria induces apoptotic cell death in indole-3-carbinol (I3C) treated breast cancer cells

Epidemiological studies have suggested that the consumption of fruits and vegetables that provide several classes of compounds, including Indole-3-carbinol (I3C), may have chemopreventive activity against breast cancer. Several in vitro and in vivo animal studies also provide convincing evidence for the anti-tumor activity of I3C, however, the molecular mechanism(s) by which I3C exerts its biological effects on breast cancer cells has not been fully elucidated. In this study, we investigated the effects of I3C in Her-2/neu over-expressing MDA-MB-435 breast cancer cells and compared these results with parental cells transfected with control vector. We focused our investigation in elucidating the molecular mechanism(s) by which I3C induces apoptosis in breast cancer cells. Our data show that I3C inhibits breast cancer cell growth in a dose dependent manner in Her-2/neu over-expressing and in normal Her-2/neu expressing cells. Induction of apoptosis was also observed in these cell lines when treated with I3C, as measured by poly (ADPribose) polymerase (PARP) and caspase-3 activation. In addition, we found that I3C up-regulates Bax, down-regulates Bcl-2 and, thereby, increased the ratio of Bax to Bcl-2 favoring apoptosis. These results suggest that the alteration in the expression of these genes may play an important role in mediating the biological effects of I3C. Moreover, we also show the cellular localization of Bax by confocal microscopy, which showed diffuse distribution of Bax throughout the cytoplasmic compartment in breast cancer cells in control culture. However, in I3C treated cells, Bax showed a punctate pattern of distribution that was localized in the mitochondria. From these results, we conclude that the over-expression and translocation of Bax to mitochondria causes mitochondrial depolarization and activation of caspases, which may be one of the mechanism(s) by which I3C induces apoptotic processes in I3C treated breast cancer cells. Overall, our present data provide a novel molecular mechanism(s) by which I3C elicits its biological effects on both Her-2/neu over-expressing and with normal Her-2/neu expressing breast cancer cells, suggesting that I3C could be an effective agent in inducing apoptosis in breast cancer cells.

Induction of growth inhibition and apoptosis in prostate cancer cells by flavopiridol

Flavopiridol is an inhibitor of several cyclin-dependent kinases, and exhibits potent growth-inhibitory activity against a number of human tumor cell lines both in vitro, and when grown as xenografts in mice. It has shown promising antineoplastic activity and is currently undergoing clinical phase II testing. Prostate cancer (PCa) remains a leading cause of morbidity and mortality among males in the United States. There are no effective treatments for hormone and/or radiation refractory PCa, suggesting that novel and newer treatment strategy may be useful in the management of PCa. Our previous study showed that flavopiridol induces cell growth inhibition and apoptosis in breast cancer cells. Here, we investigated whether flavopiridol was effective against prostate cancer cells. Flavopiridol was found to inhibit growth of PC3 prostate cancer cells. Induction of apoptosis was also observed in PC3 cells treated with flavopiridol, as measured by DNA laddering and PARP cleavage. We also found a significant down-regulation of Bcl-2 in flavopiridol-treated cells. These findings suggest that down-regulation of Bcl-2 may be one of the molecular mechanisms through which flavopiridol induces apoptosis and inhibits cell growth, suggesting that flavopiridol may be an effective chemotherapeutic agent against prostate cancer.

General role of GDP dissociation inhibitor 2 in membrane release of Rab proteins: modulations of its functional interactions by in vitro and in vivo structural modifications

The GDP dissociation inhibitors (GDIs) represent an important class of regulatory proteins in the functional cycle and recycling of Rab GTPases. Previous studies have demonstrated that GDI-1 can operate with multiple Rab proteins. In this study we have addressed a plausible general activity of GDI-2 in supporting Rab membrane release and have analyzed the requirements of sequence-conserved vs variable regions of GDI-2 in these functional interactions. The in vitro function of expressed recombinant GDI-2 wild-type-, point-, or deletion-mutant proteins was investigated toward several Rab family members, divergent in structure, localized and operating on different membranes, including Rab2, Rab4, Rab5, Rab8, Rab9, and Rab11. We demonstrate here a general and nearly invariant ability of GDI-2(WT) to release from membranes this subset of diverse Rabs. Deletion of an 18-residue segment from the C-terminal variable region yielded a fully functional or only slightly defective GDI-2. Conversely, substitution of Met at position 250 of the conserved region markedly abrogated the activity toward all Rabs. Surprisingly, a replacement of an adjacent conserved residue (Y249V) resulted in a selective Rab-dependent response and a profound gain of function toward specific Rabs. To further test whether the endogenous GDI-2 can adopt a gain-of-function conformation, we pharmacologically stimulated intact 3T3-L1 adipocytes to induce GDI-2 tyrosine phosphorylation. We found a pronounced increase of the Rab4 soluble form and its soluble complexes with the tyrosine-phosphorylated GDI-2. Together, these results indicate that (a) GDI-2 displays a general activity to release Rabs from membranes, (b) GDI-2-conserved residues, but not the C-terminal variable region, are essential for this activity, and (c) structural modifications in GDI-2 can enhance its functional activity, directing selective interactions with individual Rabs.

Arrest of endosome acidification by bafilomycin A1 mimics insulin action on GLUT4 translocation in 3T3-L1 adipocytes

In insulin-sensitive fat and muscle cells, the major glucose transporter GLUT4 is constitutively sequestered in endosomal tubulovesicular membranes, and moves to the cell surface in response to insulin. While sequence information within GLUT4 appears to be responsible for its constitutive intracellular sequestration, the regulatory elements and mechanisms that enable this protein to achieve its unique sorting pattern under basal and insulin-stimulated conditions are poorly understood. We show here that arrest of endosome acidification in insulin-sensitive 3T3-L1 adipocytes by bafilomycin A1, a specific inhibitor of the vacuolar proton pump, results in the rapid and dose-dependent translocation of GLUT4 from the cell interior to the membrane surface; the effects of maximally stimulatory concentrations of bafilomycin A1 (400-800 nM) were equivalent to 50-65% of the effects of acute insulin treatment. Like insulin, bafilomycin A1 induced the redistribution of GLUT1 and Rab4, but not that of other proteins whose membrane localization has been shown to be insulin-insensitive. Studies to address the mechanism of this effect demonstrated that neither autophosphorylation nor internalization of the insulin receptor was altered by bafilomycin A1 treatment. Bafilomycin-induced GLUT4 translocation was not blocked by cell pretreatment with wortmannin. Taken together, these data indicate that arrest of endosome acidification mimics insulin action on GLUT4 and GLUT1 translocation by a mechanism distal to insulin receptor and phosphatidylinositol 3-kinase activation, and suggest an important role for endosomal pH in the membrane dynamics of the glucose transporters.

Modulation of GDP-dissociation inhibitor protein membrane retention by the cellular redox state in adipocytes

Small GTPases of the Rab family play a key role in the regulation of vesicular transport in eukaryotic cells. As they cycle on and off membranes, Rab proteins rely on the escort services of the GDP-dissociation inhibitor (GDI) proteins. While specific recognition of Rab-GDI complexes by membrane targets is suggested, the mechanisms underlying the subsequent GDI release into the cytosol remain unknown. In this study, we demonstrate that modulations of the cellular redox status in intact rat fat cells, 3T3-L1 adipocytes in culture, and other cultured cell types result in rapid, effective, dose-dependent, and selective membrane dynamics of GDI-1 and -2, membrane retention under reduced redox state, or dissociation under oxidized conditions. GDI retention on adipocyte membranes is associated with a complete arrest of insulin-induced translocation of GLUT4 glucose transporters onto plasma membrane. Together, these data suggest, first, that following Rab delivery to membranes, GDI release is promoted by a shift in the redox state and, second, that arrest of GDIs on membranes inhibits intracellular membrane trafficking events.

Cathepsin D antigenic epitopes identified by the humoral responses of ovarian cancer patients

Previous studies implicated cathepsin D as one commonly recognized target of tumor-reactive immunoglobulins from ovarian cancer patients. These immunoglobulins are shown to be immunoreactive with both the 52-kDa procathepsin D and the 32-kDa mature cathepsin D derived from the UL-1 ovarian cancer cell line. Whether the carbohydrate domains or the core protein were associated with its immunogenicity was analyzed with cathepsin D isolated from tunicamycin-treated UL-1 cells. No significant difference was detected in the immunoreactivity of patient serum with the glycosylated and deglycosylated forms of the cathepsin D, suggesting that patient humoral responses are directed primarily against the core protein. To define the antigenic epitopes of cathepsin D, tryptic fragments were prepared from UL-1-derived procathepsin D. The epitopes of the core protein recognized by sera from more than one patient were identified using a peptide-specific enzyme-linked immunosorbent assay and microsequencing of positive immunoreactive peptides. This protocol identified four epitopes: two peptides within the propeptide, a third at the carboxy terminus and the fourth at the glycosylation site of the mature enzyme. This approach to the identification of specific antigenic epitopes may be useful in defining effective targets for directed active immunotherapy against cancer.

Humoral immune responses to cathepsin D and glucose-regulated protein 78 in ovarian cancer patients

Many cancer patients develop tumor-reactive immune responses against antigens that are either expressed on the surface of tumor cells or released from them into the peripheral circulation. In this study, tumor-reactive immunoglobulins, present in the sera of ovarian cancer patients, were used to identify commonly recognized tumor-associated antigens on ovarian tumor cells. Western immunoblot analysis of cellular proteins, obtained from UL-1 ovarian tumor cell line, demonstrated several commonly recognized immunoreactive proteins. Two of these proteins (Mr 32,000 and 71,000) were selected for further investigation. Cellular proteins isolated from normal human ovarian epithelia, in a similar fashion, failed to exhibit corresponding immunoreactivity to these proteins. As an additional control, sera from normal (nontumor-bearing) individuals failed to identify these proteins on Western immunoblots. Furthermore, the absorption of the ovarian cancer patients' sera with normal ovarian epithelial tissue did not remove the reactivity of these two proteins. The Mr 32,000 and 71,000 proteins were subsequently purified by reverse-phase high-performance liquid chromatography, separated by SDS-PAGE, transferred to the polyvinylidene difluoride membrane, and digested with trypsin. These resulting tryptic fragments were separated by microbore reverse-phase high-performance liquid chromatography, and selected fragments were sequenced by mass spectrometry. This sequence analysis identified the Mr 32,000 protein as cathepsin D and the Mr 71,000 as glucose-regulated protein 78 (member of the heat shock protein family). The identities of cathepsin D and glucose-regulated protein 78 were confirmed by Western blot analysis. Additionally, the presence of cathepsin D was demonstrated in association with immune complexes in vivo. Currently, the common antigenic epitopes of these proteins are being defined.