Magnolia dealbata seeds extract exert cytotoxic and chemopreventive effects on MDA-MB231 breast cancer cells.

CONTEXT: Cancer prevention remains a high priority for the scientific world. Magnolia dealbata Zucc (Magnoliaceae), a Mexican endemic species, is used for the empirical treatment of cancer. OBJECTIVE: To evaluate the cytotoxic and cancer chemopreventive effects of an ethanol extract of Magnolia dealbata seeds (MDE). MATERIALS AND METHODS: The cytotoxic effect of MDE, at concentrations ranging from 1 to 200 µg/ml, on human cancer cells and human nontumorigenic cells was evaluated using the MTT assay for 48 h. The apoptotic activities of MDE 25 µg/ml on MDA-MB231 breast cancer cells were evaluated using the TUNEL assay and the detection of caspase 3 using immunofluorescence analysis for 48 h, each. The chemopreventive effect was evaluated by administrating different doses of MDE, between 1 and 50 mg/kg, injected intraperitoneally daily into athymic mice which were implanted with MDA-MB231 cells during 28 days. The growth and weight of tumors were measured. RESULTS: MDE showed cytotoxic effects on MDA-MB231 cells (IC50 = 25 µg/ml) and exerted pro-apoptotic activities as determined by DNA fragmentation in MDA-MB231 cells. MDE 25 µg/ml also induces the activation of caspase 3 in MDA-MB231 cells. These results suggest that Magnolia dealbata may be an optimal source of the bioactive compounds: honokiol (HK) and magnolol (MG). MDE 50 mg/kg i.p. exerted chemopreventive effects by inhibiting the growth of MDA-MB231 tumor by 75% in athymic mice, compared to the control group. CONCLUSIONS: MDE exerts cytotoxic, apoptotic and chemopreventive activities on MDA-MB231 human cancer cells.

Activation of Akt pathway by transcription-independent mechanisms of retinoic acid promotes survival and invasion in lung cancer cells.

BACKGROUND: All-trans retinoic acid (ATRA) is currently being used in clinical trials for cancer treatment. The use of ATRA is limited because some cancers, such as lung cancer, show resistance to treatment. However, little is known about the molecular mechanisms that regulate resistance to ATRA treatment. Akt is a kinase that plays a key role in cell survival and cell invasion. Akt is often activated in lung cancer, suggesting its participation in resistance to chemotherapy. In this study, we explored the hypothesis that activation of the Akt pathway promotes resistance to ATRA treatment at the inhibition of cell survival and invasion in lung cancer. We aimed to provide guidelines for the proper use of ATRA in clinical trials and to elucidate basic biological mechanisms of resistance. RESULTS: We performed experiments using the A549 human lung adenocarcinoma cell line. We found that ATRA treatment promotes PI3k-Akt pathway activation through transcription-independent mechanisms. Interestingly, ATRA treatment induces the translocation of RARα to the plasma membrane, where it colocalizes with Akt. Immunoprecipitation assays showed that ATRA promotes Akt activation mediated by RARα-Akt interaction. Activation of the PI3k-Akt pathway by ATRA promotes invasion through Rac-GTPase, whereas pretreatment with 15e (PI3k inhibitor) or over-expression of the inactive form of Akt blocks ATRA-induced invasion. We also found that treatment with ATRA induces cell survival, which is inhibited by 15e or over-expression of an inactive form of Akt, through a subsequent increase in the levels of the active form of caspase-3. Finally, we showed that over-expression of the active form of Akt significantly decreases expression levels of the tumor suppressors RARß2 and p53. In contrast, over-expression of the inactive form of Akt restores RARß2 expression in cells treated with ATRA, indicating that activation of the PI3k-Akt pathway inhibits the expression of ATRA target genes. CONCLUSION: Our results demonstrate that rapid activation of Akt blocks transcription-dependent mechanism of ATRA, promotes invasion and cell survival and confers resistance to retinoic acid treatment in lung cancer cells. These findings provide an incentive for the design and clinical testing of treatment regimens that combine ATRA and PI3k inhibitors for lung cancer treatment.

IL-8 Secreted by Gastric Epithelial Cells Infected with Helicobacter pylori CagA Positive Strains Is a Chemoattractant for Epstein-Barr Virus Infected B Lymphocytes.

Helicobacter pylori and EBV are considered the main risk factors in developing gastric cancer. Both pathogens establish life-lasting infections and both are considered carcinogenic in humans. Different lines of evidence support that both pathogens cooperate to damage the gastric mucosa. Helicobacter pylori CagA positive virulent strains induce the gastric epithelial cells to secrete IL-8, which is a potent chemoattractant for neutrophils and one of the most important chemokines for the bacterium-induced chronic gastric inflammation. EBV is a lymphotropic virus that persists in memory B cells. The mechanism by which EBV reaches, infects and persists in the gastric epithelium is not presently understood. In this study, we assessed whether Helicobacter pylori infection would facilitate the chemoattraction of EBV-infected B lymphocytes. We identified IL-8 as a powerful chemoattractant for EBV-infected B lymphocytes, and CXCR2 as the main IL-8 receptor whose expression is induced by the EBV in infected B lymphocytes. The inhibition of expression and/or function of IL-8 and CXCR2 reduced the ERK1/2 and p38 MAPK signaling and the chemoattraction of EBV-infected B lymphocytes. We propose that IL-8 at least partially explains the arrival of EBV-infected B lymphocytes to the gastric mucosa, and that this illustrates a mechanism of interaction between Helicobacter pylori and EBV.

Differential inhibitor of Gbetagamma signaling to AKT and ERK derived from phosducin-like protein: effect on sphingosine 1-phosphate-induced endothelial cell migration and in vitro angiogenesis.

Differential inhibitors of Gbetagamma-effector regions are required to dissect the biological contribution of specific Gbetagamma-initiated signaling pathways. Here, we characterize PhLP-M1-G149, a Gbetagamma-interacting construct derived from phosducin-like protein 1 (PhLP) as a differential inhibitor of Gbetagamma, which, in endothelial cells, prevented sphingosine 1-phosphate-induced phosphorylation of AKT, glycogen synthase kinase 3beta, cell migration, and tubulogenesis, while having no effect on ERK phosphorylation or hepatocyte growth factor-dependent responses. This construct attenuated the recruitment of phosphoinositide 3-kinase gamma (PI3Kgamma) to the plasma membrane and the signaling to AKT in response to Gbetagamma overexpression. In coimmunoprecipitation experiments, PhLP-M1-G149 interfered with the interaction between PI3Kgamma and Gbetagamma. Other PhLP-derived constructs interacted with Gbetagamma but were not effective inhibitors of Gbetagamma signaling to AKT or ERK. Our results indicate that PhLP-M1-G149 is a suitable tool to differentially modulate the Gbetagamma-initiated pathway linking this heterodimer to AKT, endothelial cell migration, and in vitro angiogenesis. It can be also useful to further characterize the molecular determinants of the Gbetagamma-PI3Kgamma interaction.

Sphingosine-1-phosphate receptor S1P1 is regulated by direct interactions with P-Rex1, a Rac guanine nucleotide exchange factor.

Sphingosine-1-phosphate (S1P) receptors S1P(1) are emerging molecular targets for the treatment of cancer, vascular and immune diseases, due to their pivotal role in cell migration and survival of immune and endothelial cells. A therapeutic strategy to control S1P(1) function is based on agonists that promote changes on S1P(1) expression at the plasma membrane. Here, we explored the hypothesis that cell surface expression and function of S1P(1) are influenced by direct interactions with P-Rex1, a guanine nucleotide exchange factor for Rac. We demonstrate that P-Rex1-PDZ domains interact with S1P(1)-carboxyl terminal tail and full length receptor monomers and dimers. Endothelial cells transfected with P-Rex1-PDZ domains show an increased migratory response to S1P. S1P(1) trafficking to intracellular compartments is diminished by coexpression of P-Rex1. We conclude that S1P(1) signaling linked to cell migration is facilitated by a functional interaction with P-Rex1 via a mechanism that involves the maintenance of S1P(1) receptors at the cell membrane.

Calcium-sensing receptor endocytosis links extracellular calcium signaling to parathyroid hormone-related peptide secretion via a Rab11a-dependent and AMSH-sensitive mechanism.

The calcium-sensing receptor (CaR) helps to maintain the homeostasis of extracellular calcium by controlling the secretion of hormones associated with this process. The mechanism of agonist-induced endocytosis and down-regulation of CaR and the influence of this event on the secretion of CaR-regulated hormones is not fully understood. In this study, we show that CaR is constitutively endocytosed and recycled to the plasma membrane by a Rab11a-dependent mechanism; during this process, the level of total cellular CaR is maintained. This trafficking of CaR promotes the secretion of PTH-related peptide (PTHrP), as evidenced by a decrease on PTHrP secretion in the presence of a dominant-negative mutant of Rab11a. Interestingly, this Rab11a dominant-negative mutant does not interfere with CaR-dependent activation of ERK 1/2, suggesting that ERK signaling is not sufficient to promote PTHrP secretion downstream of CaR. In addition, AMSH (associated molecule with the SH3 domain of STAM), a CaR carboxyl-terminal binding protein, redirects CaR from slow recycling to down-regulation, reducing CaR expression and decreasing PTHrP secretion. Our results indicate that endocytosis and trafficking of CaR modulate PTHrP secretion.

The heat shock protein 60 promotes progesterone synthesis in mitochondria of JEG-3 cells.

Progesterone synthesis in human placenta is essential to maintain pregnancy. The limiting step in placental progesterone synthesis is cholesterol transport from the cytoplasm to the inner mitochondrial membrane. Multiple proteins located in mitochondrial contact sites seem to play a key role in this process. Previously, our group identified the heat shock protein 60 (HSP60) as part of mitochondrial contact sites in human placenta, suggesting its participation in progesterone synthesis. Here, we examined the role of HSP60 in progesterone synthesis. Our results show that over-expression of HSP60 in human placental choriocarcinoma cells (JEG-3) and human embryonic kidney 293 cells (HEK293) promotes progesterone synthesis. Furthermore, incubation of the HSP60 recombinant protein with intact isolated mitochondria from JEG-3 cells also promotes progesterone synthesis in a dose-related fashion. We also show that HSP60 interacts with STARD3 and P450scc proteins from mitochondrial membrane contact sites. Finally, we show that the HSP60 recombinant protein binds cholesterol. Ours results demonstrate that HSP60 participates in mitochondrial progesterone synthesis. These findings provide novel insights into progesterone synthesis in the human placenta and its role in maintaining pregnancy.

All-Trans Retinoic Acid Induces Proliferation, Survival, and Migration in A549 Lung Cancer Cells by Activating the ERK Signaling Pathway through a Transcription-Independent Mechanism.

All-trans retinoic acid (ATRA) has been used as an antineoplastic because of its ability to promote proliferation, inhibition, and differentiation, primarily in leukemia; however, in other types of cancer, such as lung cancer, treatment with ATRA is restricted because not all the patients experience the same results. The ERK signaling pathway is dysregulated in cancer cells, including lung cancer, and this dysregulation promotes proliferation and cell invasion. In this study, we demonstrate that treatment with ATRA can activate the ERK signaling pathway by a transcription-independent mechanism through a signaling cascade that involves RARα and PI3K, promoting growth, survival, and migration in lung cancer cells. Until now, this mechanism was unknown in lung cancer cells. The inhibition of the ERK signaling pathway restores the beneficial effects of ATRA, reduces proliferation, increases apoptosis, and blocks the cell migration process in lung cancer cells. In conclusion, our results suggest that the combination of ATRA with ERK inhibitor in clinical trials for lung cancer is warranted.

Kaempferitrin induces apoptosis via intrinsic pathway in HeLa cells and exerts antitumor effects.

ETHNOPHARMACOLOGICAL RELEVANCE: Justicia spicigera is used for the empirical treatment of cervical cancer in Mexico. Recently, we showed that Justicia spicigera extracts exerted cytotoxic and antitumoral effects and the major component of this extract was kaempferitrin (KM). MATERIALS AND METHODS: The cytotoxic and apoptotic effect of KM on human cancer cells and human nontumorigenic cells were evaluated using MTT and TUNEL assays, and Annexin V/Propidium iodide detection by flow cytometry. The effect of KM on cell cycle was analyzed by flow cytometry with propidium iodide. The apoptotic and cell cycle effects were also evaluated by western blot analysis. Also, different doses of KM were injected intraperitoneally daily into athymic mice bearing tumors of HeLa cells during 32 days. The growth and weight of tumors were measured. RESULTS: KM induces high cytotoxic effects in vitro and in vivo against HeLa cells. The general mechanisms by which KM induces cytotoxic effects include: cell cycle arrest in G1 phase and apoptosis via intrinsic pathway in a caspase dependent pathway. Also, KM exerts chemopreventive and antitumor effects. CONCLUSION: KM exerts cytotoxic and antitumor effects against HeLa cells.

G protein-coupled receptor-promoted trafficking of Gbeta1gamma2 leads to AKT activation at endosomes via a mechanism mediated by Gbeta1gamma2-Rab11a interaction.

G-protein coupled receptors activate heterotrimeric G proteins at the plasma membrane in which most of their effectors are intrinsically located or transiently associated as the external signal is being transduced. This paradigm has been extended to the intracellular compartments by studies in yeast showing that trafficking of Galpha activates phosphatidylinositol 3-kinase (PI3K) at endosomal compartments, suggesting that vesicle trafficking regulates potential actions of Galpha and possibly Gbetagamma at the level of endosomes. Here, we show that Gbetagamma interacts with Rab11a and that the two proteins colocalize at early and recycling endosomes in response to activation of lysophosphatidic acid (LPA) receptors. This agonist-dependent association of Gbetagamma to Rab11a-positive endosomes contributes to the recruitment of PI3K and phosphorylation of AKT at this intracellular compartment. These events are sensitive to the expression of a dominant-negative Rab11a mutant or treatment with wortmannin, suggesting that Rab11a-dependent Gbetagamma trafficking promotes the activation of the PI3K/AKT signaling pathway associated with endosomal compartments. In addition, RNA interference-mediated Rab11a depletion, or expression of a dominant-negative Rab11a mutant attenuated LPA-dependent cell survival and proliferation, suggesting that endosomal activation of the PI3K/AKT signaling pathway in response to Gbetagamma trafficking, via its interaction with Rab11, is a relevant step in the mechanism controlling these fundamental events.