Membrane damage by betulinic acid provides insights into cellular aging.

BACKGROUND: Cell senescence is a process of central importance to the understanding of aging as well as to the development of new drugs. It is related with genomic instability, which has been shown to occur in the presence of autophagy deficiency. Yet, the mechanism that triggers genomic instability and senescence from a condition of autophagy deficiency remains unknown. By analyzing the consequences of treating human keratinocytes (HaCaT) with the pentacyclic triterpenoid Betulinic Acid (BA) we were able to propose that cell senescence can develop as a response to parallel damage in the membranes of mitochondria and lysosome. METHODS: We performed biochemical, immunocytochemical and cytometric assays after challenging HaCaT cells with BA. We also evaluated membrane leakage induced by BA in liposomes and giant unilamellar vesicles. RESULTS: By destabilizing lipid bilayers of mitochondria and lysosomes, BA triggers the misbalance in the mitochondrial-lysosomal axis leading to perceived autophagy impairment, lipofuscinogenesis, genomic instability and cell senescence. The progressive accumulation of mitochondria and lipofuscin, which comes from imperfect mitophagy triggered by BA, provides a continuous source of reactive species further damaging lysosomes and leading to cell aging. CONCLUSIONS: This work reveals that the initial trigger of cell senescence can be the physical damage in the membranes of lysosomes and mitochondria. GENERAL SIGNIFICANCE: This concept will help in the search of new drugs that act as senescence-inductors. BA is under evaluation as chemotherapeutic agent against several types of tumors and induction of cell senescence should be considered as one of its main mechanisms of action.

Membrane-derived particles shed by PSMA-positive cells function as pro-angiogenic stimuli in tumors.

Cell membrane-derived particles (Mp) are rounded membrane-enclosed particles that are shed from tumor cells. Mp are formed from tumor membranes and are capable of tumor targeting and immunotherapeutic agents because they share membrane homology with parental cells; thus, they are under consideration as a drug delivery vehicle. Prostate-specific membrane antigen (PSMA), a transmembrane glycoprotein with enzymatic functionality, is highly expressed in Mp and extracellular vesicles (EV) from prostate cancer (PCa) with poor clinical prognosis. Although PSMA expression was previously shown in EV and Mp isolated from cell lines and from the blood of patients with high-grade PCa, no pathophysiological effects have been linked to PCa-derived Mp. Here, we compared Mp from PSMA-expressing (PSMA-Mp) and PSMA-non-expressing (WT-Mp) cells side by side in vitro and in vivo. PSMA-Mp can transfer PSMA and new phenotypic characteristics to the tumor microenvironment. The consequence of PSMA transfer to cells and increased secretion of vascular endothelial growth factor-A (VEGF-A), pro-angiogenic and pro-lymphangiogenic mediators, with increased 4E binding protein 1 (4EBP-1) phosphorylation.

Antitumoral activity of liraglutide, a new DNMT inhibitor in breast cancer cells in vitro and in vivo.

Breast cancer (BC) is the most frequently diagnosed female cancer and second leading cause of death. Despite the discovery of many antineoplastic drugs for BC, the current therapy is not totally efficient. In this study, we investigated the potential of repurposing the well-known diabetes type II drug liraglutide to modulate epigenetic modifications in BC cells lines in vitro and in vivo via Ehrlich mice tumors models. The in vitro results revealed a significant reduction on cell viability, migration, DNMT activity and displayed lower levels of global DNA methylation in BC cell lines after liraglutide treatment. The interaction between liraglutide and the DNMT enzymes resulted in a decrease profile of DNA methylation for the CDH1, ESR1 and ADAM33 gene promoter regions and, consequently, increased their gene and protein expression levels. To elucidate the possible interaction between liraglutide and the DNMT1 protein, we performed an in silico study that indicates liraglutide binding in the catalytic cleft via hydrogen bonds and salt bridges with the interdomain contacts and disturbs the overall enzyme conformation. The in vivo study was also able to reveal that liraglutide and the combined treatment of liraglutide and paclitaxel or methotrexate were effective in reducing tumor growth. Moreover, the modulation of CDH1 and ADAM33 mouse gene expression by DNA demethylation suggests a role for liraglutide in DNMT activity in vivo. Altogether, these results indicate that liraglutide may be further analysed as a new adjuvant treatment for BC.

NDRG4 promoter hypermethylation is a mechanistic biomarker associated with metastatic progression in breast cancer patients.

The risk of developing metastatic disease in breast cancer patients is traditionally predictable based on the number of positive axillary lymph nodes, complemented with additional clinicopathological factors. However, since lymph node-negative patients have a 20-30% probability of developing metastatic disease, lymph node information alone is insufficient to accurately assess individual risk. Molecular approaches, such as multigene expression panels, analyze a set of cancer-related genes that more accurately predict the early risk of metastasis and the treatment response. Here, we present N-Myc downstream-regulated gene 4 (NDRG4) epigenetic silencing as a mechanistic biomarker of metastasis in ductal invasive breast tumors. While aberrant NDRG4 DNA hypermethylation is significantly associated with the development of metastatic disease, downregulation of NDRG4 transcription and protein expression is functionally associated with enhanced lymph node adhesion and cell mobility. Here, we show that epigenetic silencing of NDRG4 modulates integrin signaling by assembling ß1-integrins into large punctate clusters at the leading edge of tumor cells to promote an "adhesive switch," decreasing cell adhesion to fibronectin and increasing cell adhesion and migration towards vitronectin, an important component of human lymph nodes. Taken together, our functional and clinical observations suggest that NDRG4 is a potential mechanistic biomarker in breast cancer that is functionally associated with metastatic disease.

High IL-1R8 expression in breast tumors promotes tumor growth and contributes to impaired antitumor immunity.

Tumors develop numerous strategies to fine-tune inflammation and avoid detection and eradication by the immune system. The identification of mechanisms leading to local immune dysregulation is critical to improve cancer therapy. We here demonstrate that Interleukin-1 receptor 8 (IL-1R8 - previously known as SIGIRR/TIR8), a negative regulator of Toll-Like and Interleukin-1 Receptor family signaling, is up-regulated during breast epithelial cell transformation and in primary breast tumors. IL-1R8 expression in transformed breast epithelial cells reduced IL-1-dependent NF-κB activation and production of pro-inflammatory cytokines, inhibited NK cell activation and favored M2-like macrophage polarization. In a murine breast cancer model (MMTV-neu), IL-1R8-deficiency reduced tumor growth and metastasis and was associated with increased mobilization and activation of immune cells, such as NK cells and CD8+ T cells. Finally, immune-gene signature analysis in clinical specimens revealed that high IL-1R8 expression is associated with impaired innate immune sensing and T-cell exclusion from the tumor microenvironment. Our results indicate that high IL-1R8 expression acts as a novel immunomodulatory mechanism leading to dysregulated immunity with important implications for breast cancer immunotherapy.

Parallel damage in mitochondrial and lysosomal compartments promotes efficient cell death with autophagy: The case of the pentacyclic triterpenoids.

The role of autophagy in cell death is still controversial and a lot of debate has concerned the transition from its pro-survival to its pro-death roles. The similar structure of the triterpenoids Betulinic (BA) and Oleanolic (OA) acids allowed us to prove that this transition involves parallel damage in mitochondria and lysosome. After treating immortalized human skin keratinocytes (HaCaT) with either BA or OA, we evaluated cell viability, proliferation and mechanism of cell death, function and morphology of mitochondria and lysosomes, and the status of the autophagy flux. We also quantified the interactions of BA and OA with membrane mimics, both in-vitro and in-silico. Essentially, OA caused mitochondrial damage that relied on autophagy to rescue cellular homeostasis, which failed upon lysosomal inhibition by Chloroquine or Bafilomycin-A1. BA caused parallel damage on mitochondria and lysosome, turning autophagy into a destructive process. The higher cytotoxicity of BA correlated with its stronger efficiency in damaging membrane mimics. Based on these findings, we underlined the concept that autophagy will turn into a destructive outcome when there is parallel damage in mitochondrial and lysosomal membranes. We trust that this concept will help the development of new drugs against aggressive cancers.

Fibronectin affects transient MMP2 gene expression through DNA demethylation changes in non-invasive breast cancer cell lines.

Metastasis accounts for more than 90% of cancer deaths. Cells from primary solid tumors may invade adjacent tissues and migrate to distant sites where they establish new colonies. The tumor microenvironment is now recognized as an important participant in the signaling that induces cancer cell migration. An essential process for metastasis is extracellular matrix (ECM) degradation by metalloproteases (MMPs), which allows tumor cells to invade local tissues and to reach blood vessels. The members of this protein family include gelatinase A, or MMP-2, which is responsible for the degradation of type IV collagen, the most abundant component of the basal membrane, that separates epithelial cells in the stroma. It is known that fibronectin is capable of promoting the expression of MMP-2 in MCF7 breast cancer cells in culture. In addition, it was already shown that the MMP2 gene expression is regulated by epigenetic mechanisms. In this work, we showed that fibronectin was able to induce MMP2 expression by 30% decrease in its promoter methylation. In addition, a histone marker for an open chromatin conformation was significantly increased. These results indicate a new role for fibronectin in the communication between cancer cells and the ECM, promoting epigenetic modifications.

Targeting MAGE-C1/CT7 expression increases cell sensitivity to the proteasome inhibitor bortezomib in multiple myeloma cell lines.

The MAGE-C1/CT7 encodes a cancer/testis antigen (CTA), is located on the chromosomal region Xq26-27 and is highly polymorphic in humans. MAGE-C1/CT7 is frequently expressed in multiple myeloma (MM) that may be a potential target for immunotherapy in this still incurable disease. MAGEC1/CT7 expression is restricted to malignant plasma cells and it has been suggested that MAGE-C1/CT7 might play a pathogenic role in MM; however, the exact function this protein in the pathophysiology of MM is not yet understood. Our objectives were (1) to clarify the role of MAGE-C1/CT7 in the control of cellular proliferation and cell cycle in myeloma and (2) to evaluate the impact of silencing MAGE-C1/CT7 on myeloma cells treated with bortezomib. Myeloma cell line SKO-007 was transduced for stable expression of shRNA-MAGE-C1/CT7. Downregulation of MAGE-C1/CT7 was confirmed by real time quantitative PCR and western blot. Functional assays included cell proliferation, cell invasion, cell cycle analysis and apoptosis. Western blot showed a 70-80% decrease in MAGE-C1/CT7 protein expression in inhibited cells (shRNA-MAGE-C1/CT7) when compared with controls. Functional assays did not indicate a difference in cell proliferation and DNA synthesis when inhibited cells were compared with controls. However, we found a decreased percentage of cells in the G2/M phase of the cell cycle among inhibited cells, but not in the controls (p<0.05). When myeloma cells were treated with bortezomib, we observed a 48% reduction of cells in the G2/M phase among inhibited cells while controls showed 13% (empty vector) and 9% (ineffective shRNA) reduction, respectively (p<0.01). Furthermore, inhibited cells treated with bortezomib showed an increased percentage of apoptotic cells (Annexin V+/PI-) in comparison with bortezomib-treated controls (p<0.001). We found that MAGE-C1/CT7 protects SKO-007 cells against bortezomib-induced apoptosis. Therefore, we could speculate that MAGE-C1/CT7 gene therapy could be a strategy for future therapies in MM, in particular in combination with proteasome inhibitors.

ADAM23 negatively modulates alpha(v)beta(3) integrin activation during metastasis.

The ADAM23 gene is frequently silenced in different types of tumors, and, in breast tumors, silencing is correlated with tumor progression, suggesting that it might be associated with the acquisition of a metastatic phenotype. ADAM23 exerts its function mainly through the disintegrin domain, because its metalloprotease domain is inactive. Analysis of ADAM23 binding to integrins has revealed a specific interaction with alpha(v)beta(3) integrin mediated by the disintegrin domain. Altered expression of alpha(v)beta(3) integrin has been observed in different types of tumors, and expression of this integrin in the activated form has been shown to promote metastasis formation. Here, we investigated the possibility that interaction between ADAM23 and alpha(v)beta(3) integrin might negatively modulate alpha(v)beta(3) activation during metastatic progression. ADAM23 expression was knocked down using short hairpin RNA in the MDA-MB-435 cell line, which has been extensively used as a model for alpha(v)beta(3) integrin activation. Ablation of ADAM23 enhanced alpha(v)beta(3) integrin activation by at least 2- to 4-fold and ADAM23 knockdown cells showed enhanced migration and adhesion to classic alpha(v)beta(3) integrin ligands. Ablation of ADAM23 expression also enhanced pulmonary tumor cell arrest in immunodeficient mice. To complement our findings with clinical evidence, we showed that silencing of ADAM23 gene by DNA promoter hypermethylation in a collection of 94 primary breast tumors was significantly associated with lower distant metastases-free and disease-specific survivals and was an independent prognostic factor for poor disease outcome. Our results strongly support a functional role of ADAM23 during metastatic progression by negatively modulating alpha(v)beta(3) integrin activation.

Fibroblast growth factor 2 restrains Ras-driven proliferation of malignant cells by triggering RhoA-mediated senescence.

Fibroblast growth factor 2 (FGF2) is considered to be a bona fide oncogenic factor, although results from our group and others call this into question. Here, we report that exogenous recombinant FGF2 irreversibly inhibits proliferation by inducing senescence in Ras-dependent malignant mouse cells, but not in immortalized nontumorigenic cell lines. We report the following findings in K-Ras-dependent malignant Y1 adrenocortical cells and H-Ras V12-transformed BALB-3T3 fibroblasts: (a) FGF2 inhibits clonal growth and tumor onset in nude and immunocompetent BALB/c mice, (b) FGF2 irreversibly blocks the cell cycle, and (c) FGF2 induces the senescence-associated beta-galactosidase with no accompanying signs of apoptosis or necrosis. The tyrosine kinase inhibitor PD173074 completely protected malignant cells from FGF2. In Y1 adrenal cells, reducing the constitutively high levels of K-Ras-GTP using the dominant-negative RasN17 mutant made cells resistant to FGF2 cytotoxicity. In addition, transfection of the dominant-negative RhoA-N19 into either Y1 or 3T3-B61 malignant cell lines yielded stable clonal transfectants that were unable to activate RhoA and were resistant to the FGF2 stress response. We conclude that in Ras-dependent malignant cells, FGF2 interacts with its cognate receptors to trigger a senescence-like process involving RhoA-GTP. Surprisingly, attempts to select FGF2-resistant cells from the Y1 and 3T3-B61 cell lines yielded only rare clones that (a) had lost the overexpressed ras oncogene, (b) were dependent on FGF2 for proliferation, and (c) were poorly tumorigenic. Thus, FGF2 exerted a strong negative selection that Ras-dependent malignant cells could rarely overcome.

c-Ki-ras oncogene amplification and FGF2 signaling pathways in the mouse Y1 adrenocortical cell line.

The mouse Y1 adrenocortical tumor cell line is highly responsive to FGF2-(Fibroblast Growth Factor 2) and possesses amplified and over-expressed c-Ki-ras proto-oncogene. We previously reported that this genetic lesion leads to high constitutive levels of activation of the c-Ki-Ras-GTP-->PI3K-->Akt signaling pathway (Forti et al. 2002). On the other hand, activation levels of another important pathway downstream of c-Ki-Ras-GTP, namely, Raf-->MEK-->ERK, remain strictly dependent on FGF2 stimulation (Rocha et al. 2003). Here we show that, first, FGF2 transiently up-regulates the c-Ki-Ras-GTP-->PI3K-->Akt pathway, in spite of its high basal levels. Second, c-Ki-Ras-GTP transient up-regulation likely underlies activation of the ERK1/2 pathway by FGF2. Third, c-Ki-Ras-GTP high basal levels suppress activation of the c-H-Ras onco-protein. But, Y1 cells, expressing dominant negative mutant RasN17, display a rapid and transient up-regulation of c-H-Ras-GTP upon FGF2 treatment. Elucidation of FGF2-signaling pathways in Y1 tumor cells can uncover new targets for drug development of interest in cancer therapy.

Molecular mechanisms of cell cycle control in the mouse Y1 adrenal cell line.

Y1 adrenocortical tumor cells possess amplified and overexpressed c-Ki-ras proto-oncogene, displaying chronic high levels of the c-Ki-Ras-GTP protein. Despite this oncogenic lesion, we previously reported that Y1 cells retain tight regulatory mechanisms of cell cycle control typified by the mitogenic response triggered by FGF2 in G0/G1-arrested cells. ACTH, on the other hand, elicits cAMP/PKA-mediated antimitogenic mechanisms involving Akt/PKB dephosphorylation/deactivation and c-Myc protein degradation, blocking G1 phase progression stimulated by FGF2. In this paper we report that ACTH does not directly antagonize any of the early or late sequential steps comprising the mitogenic response triggered by FGF2. In effect, ACTH targets deactivation of constitutively phosphorylated-Akt, restraining the potential of c-Ki-Ras-GTP to subvert Y1 cell cycle control. Thus, we can consider ACTH a tumor suppressor rather than an antimitogenic hormone. In addition, we present initial results showing that high constitutive levels of c-Ki-Ras-GTP render Y1 cells susceptible to dye upon FGF2 treatment. This surprising FGF2 death-effect, that is independent of the well known FGF2-mitogenic activity, might involve a natural unsuspected mechanism for restraining oncogene-induced proliferation.

c-Ki-ras oncogene amplification and FGF2 signaling pathways in the mouse Y1 adrenocortical cell line

A linhagem tumoral Y1, originada de adrenocórtex decamundongo responde a FGF2 (Fator de Crescimento de Fibroblasto), possui o proto-oncogene c-ki-ras amplificado e a proteína c-Ki-Ras super-expressa e ativa (c-Ki-Ras-GTP). Em trabalhos anteriores mostramos que esta lesão genética causa ativação constitutiva da via de sinalização: c-Ki-Ras-GTP®PI3K®Akt (Forti et al. 2002). Por outro lado, a ativação da via de Raf® MEK®ERK, permanece estritamente dependente de estímulos de FGF2 (Rocha et al. 2003). Neste trabalho mostramos, primeiro, que estímulos de FGF2 ativam transientemente a via c-Ki-Ras-GTP®PI3K®Akt para níveis superiores aos expressos constitutivamente. Segundo, a ativação transiente de c-Ki-Ras-GTP por FGF2 permite a ativação da via de ERK1/2. Terceiro, os níveis basais elevados de c-Ki-Ras-GTP inibem a ativação da proteína c-H-Ras, pois células Y1 expressando o mutante negativo RasN17 apresentam uma rápida e transiente ativação de c-H-Ras-GTP após tratamentos de FGF2. Estes estudos das vias de sinalização acionadas por FGF2 em células adrenais tumorais Y1 podem fornecer novos alvos para o desenvolvimento de drogas de interesse para terapia oncogênica.