Antiproliferative and survival properties of PMA in MCF-7 breast cancer cell

Phorbol-12-myristate-13-acetate is a potent enhancer of B cells with a granzyme B+ regulatory phenotype

Introduction

The infusion of ex-vivo-generated regulatory B cells may represent a promising novel therapeutic approach for a variety of autoimmune and hyperinflammatory conditions including graft-versus-host disease.

Methods

Previously, we developed a protocol for the generation of a novel population of regulatory B cells, which are characterized by secretion of enzymatically active granzyme B (GraB cells). This protocol uses recombinant interleukin 21 (IL-21) and goat-derived F(ab)'2 fragments against the human B cell receptor (anti-BCR). Generally, the use of xenogeneic material for the manufacturing of advanced therapy medicinal products should be avoided to prevent adverse immune reactions as well as potential transmission of so far unknown diseases.

Results

In the present work we demonstrated that phorbol-12-myristate-13-acetate (PMA/TPA), a phorbol ester with a particular analogy to the second messenger diacylglycerol (DAG), is a potent enhancer of IL-21-induced differentiation of pre-activated B cells into GraB cells. The percentage of GraB cells after stimulation of pre-activated B cells with IL-21 and PMA/TPA was not significantly lower compared to stimulation with IL-21 and anti-BCR.

Discussion

Given that PMA/TPA has already undergone encouraging clinical testing in patients with certain haematological diseases, our results suggest that PMA/TPA may be a safe and feasible alternative for ex-vivo manufacturing of GraB cells.

Small Molecules as Drugs to Upregulate Metastasis Suppressors in Cancer Cells

It is well-recognized that the majority of cancer-related deaths is attributed to metastasis, which can arise from virtually any type of tumor. Metastasis is a complex multistep process wherein cancer cells must break away from the primary tumor, intravasate into the circulatory or lymphatic systems, extravasate, proliferate and eventually colonize secondary sites. Since these molecular processes involve the coordinated actions of numerous proteins, targeted disruptions of key players along these pathways represent possible therapeutic interventions to impede metastasis formation and reduce cancer mortality. A diverse group of proteins with demonstrated ability to inhibit metastatic colonization have been identified and they are collectively known as metastasis suppressors. Given that the metastasis suppressors are often downregulated in tumors, drug-induced re-expression or upregulation of these proteins represents a promising approach to limit metastasis. Indeed, over 40 compounds are known to exhibit efficacy in upregulating the expression of metastasis suppressors via transcriptional or post-transcriptional mechanisms, and the most promising ones are being evaluated for their translational potentials. These small molecules range from natural products to drugs in clinical use and they apparently target different molecular pathways, reflecting the diverse nature of the metastasis suppressors. In this review, we provide an overview of the different classes of compounds known to possess the ability to upregulate one or more metastasis suppressors, with an emphasis on their mechanisms of action and therapeutic potentials.

Claudin 1 Is Highly Upregulated by PKC in MCF7 Human Breast Cancer Cells and Correlates Positively with PKCε in Patient Biopsies

Recent studies provide compelling evidence to suggest that the tight junction protein claudin 1, aberrantly expressed in several cancer types, plays an important role in cancer progression. Dysregulation of claudin 1 has been shown to induce epithelial mesenchymal transition (EMT). Furthermore, activation of the ERK signaling pathway by protein kinase C (PKC) was shown to be necessary for EMT induction. Whether PKC is involved in regulating breast cancer progression has not been addressed. The PKC activator 12-O-tetradecanoylphorbol 13-acetate (TPA) was used to investigate the effect of PKC activity on claudin 1 transcription and protein levels, subcellular distribution, and alterations in EMT markers in human breast cancer (HBC) cell lines. As well, tissue microarray analysis (TMA) of a large cohort of invasive HBC biopsies was conducted to investigate correlations between claudin 1 and PKC isomers. TPA upregulated claudin 1 levels in all HBC cell lines analyzed. In particular, a high induction of claudin 1 protein was observed in the MCF7 cell line. TPA treatment also led to an accumulation of claudin 1 in the cytoplasm. Additionally, we demonstrated that the upregulation of claudin 1 was through the ERK signaling pathway. In patient biopsies, we identified a significant positive correlation between claudin 1, PKCα, and PKCε in ER+ tumors. A similar correlation between claudin 1 and PKCε was identified in ER- tumors, and high PKCε was associated with shorter disease-free survival. Collectively, these studies demonstrate that claudin 1 and the ERK signaling pathway are important players in HBC progression.

Suppression of TPA-induced cancer cell invasion by Peucedanum japonicum Thunb. extract through the inhibition of PKCα/NF-κB-dependent MMP-9 expression in MCF-7 cells

Metastatic cancers spread from their site of origin (the primary site) to other parts of the body. Matrix metalloproteinase-9 (MMP-9), which degrades the extracellular matrix, is important in metastatic cancers as it plays a major role in cancer cell invasion. The present study examined the inhibitory effect of an ethanol extract of Peucedanum japonicum Thunb. (PJT) on MMP-9 expression and the invasion of MCF-7 breast cancer cells induced by 12-O-tetradecanoylphorbol-13-acetate (TPA). Western blot analysis, gelatin zymography, and reverse transcription-quantitative PCR revealed that PJT significantly suppressed MMP-9 expression and activation in a dose-dependent manner. Furthermore, PJT attenuated TPA-induced nuclear translocation and the transcriptional activation of nuclear factor (NF)-κB. The results indicated that the PJT-mediated inhibition of TPA-induced MMP-9 expression and cell invasion involved the suppression of the PKCα/NF-κB pathway in MCF-7 cells. Thus, the inhibition of MMP-9 expression by PJT may have potential value as a therapy for restricting the invasiveness of breast cancer.

Antiproliferative Effect of Rottlerin on Sk-Mel-28 Melanoma Cells

Melanoma is the most aggressive and chemoresistant form of skin cancer. Mutated, constitutively active B-RAF is believed to play a crucial role, although the selective B-RAF inhibition has shown poor clinical success, since phenomena of resistance usually occur, likely arising from additional genetic aberrations, such as loss of function of p53 and PTEN, overexpression of cyclin D1, hyperactivation of NF-κB, and downregulation of p21/Cip1. Since all of them are present in the Sk-Mel-28 melanoma cells, this cell line could be an ideal, albeit hard to study, model to develop new therapeutic strategies. In the current study, we tested the cytostatic action of Rottlerin on Sk-Mel-28 melanoma cells, on the basis of the known Rottlerin effects on the main proliferative signaling pathways. We presented evidence that the drug inhibits cell growth by an Akt- and p21/Cip1-independent mechanism, involving the dual inhibition of ERK and NF-κB and downregulation of cyclin D1. In addition, we found that Rottlerin increases ERK phosphorylation, but, surprisingly, this resulted in decreased ERK activity. Pull-down experiments, using Rottlerin-CNBr-conjugated Sepharose beads, revealed that Rottlerin binds to ERK, independently from its phosphorylation status. This direct interaction could in part explain the paradoxical blockage of ERK downstream signaling and growth arrest.

We would like to dedicate this paper to the memory of our friend and colleague, prematurely deceased, Claudia Torricelli, who actively contributed to this project

Qifangweitong Granules regulates the expression of TFF1 in Helicobacter pylori-infected AGS cells via the ERK/NF-κB signaling pathway

AIM: To investigate the effect of Qifangweitong Granules on the expression of trefoil factor family 1 (TFF1) in human gastric cancer cell line AGS infected by Helicobacter pylori (H. pylori) and the possible regulatory mechanism involved.

METHODS: TAGS cells infected by H. pylori were exposed to Qifangweitong Granules in the presence or absence of U0126, a special inhibitor of ERK1/2 pathway. After treatment, the expression of TFF1 mRNA and protein in H. pylori-infected AGS cells was determined using real-time fluorescent quantitative polymerase chain reaction (RFQ-PCR) and Western blot, respectively.

RESULTS: Treatment with 10%, 20% and 30% Qifangweitong Granules drug serum significantly up-regulated the expression of TFF1 mRNA in AGS cells infected by H. pylori compared to control cells (271 ± 33, 305 ± 23, 327 ± 13 vs 187 ± 30, all P < 0.05). The protein expression of TFF1, p-ERK, and NF-κB in AGS cells treated with 10%, 20% and 30% Qifangweitong Granules drug serum was also significantly higher than that in control cells (TFF1: 271 ± 22, 358 ± 31, 428 ± 34 vs 210 ± 13, all P < 0.05). After blocking the ERK signal transduction pathway, the protein expression of TFF1 was significantly down-regulated compared to the control group (P < 0.05).

CONCLUSION: Treatment with Qifangweitong Granules regulates the expression of TFF1 in Helicobacter pylori-infected AGS cells possibly via the ERK/NF-κB signal transduction pathway.

Curcumin suppresses the TPA-induced invasion through inhibition of PKCα-dependent MMP-expression in MCF-7 human breast cancer cells

Curcumin (diferuloylmethane) is a polyphenol derived from the plant turmeric (Curcuma longa), which is commonly used as a spice. Although anti-carcinogenic, anti-oxidant, anti-inflammation, and anti-angiogenic properties have been reported, the effect of curcumin on breast cancer metastasis is unknown. Matrix metalloproteinase-9 (MMP-9) is a major component in cancer cell invasion. In this study, we investigated the inhibitory effect of curcumin on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced MMP-9 expression and cell invasion and the molecular mechanisms involved in MCF-7 cells. Our results showed that curcumin inhibits TPA-induced MMP-9 expression and cell invasion through suppressing NF-κB and AP-1 activation. Also, curcumin strongly repressed the TPA-induced phosphorylation of p38 and JNK and inhibited TPA-induced translocation of PKCα from the cytosol to the membrane, but did not affect the translocation of PKCδ. These results indicate that curcumin-mediated inhibition of TPA-induced MMP-9 expression and cell invasion involves the suppression of the PKCα, MAPK and NF-κB/AP-1 pathway in MCF-7 cells. Curcumin may have potential value in restricting breast cancer metastasis.

Epidermal growth factor receptor (EGFR)-mediated positive feedback of protein-tyrosine phosphatase epsilon (PTPepsilon) on ERK1/2 and AKT protein pathways is required for survival of human breast cancer cells

Increased tyrosine phosphorylation has been correlated with human cancer, including breast cancer. In general, the activation of tyrosine kinases (TKs) can be antagonized by the action of protein-tyrosine phosphatases (PTPs). However, in some cases PTPs can potentiate the activation of TKs. In this study, we have investigated the functional role of PTPε in human breast cancer cell lines. We found the up-regulation and activation of receptor PTPε (RPTPε) in MCF-7 cells and MDA-MB-231 upon PMA, FGF, and serum stimulation, which depended on EGFR and ERK1/2 activity. Diminishing the expression of PTPε in human breast cancer cells abolished ERK1/2 and AKT activation, and decreased the viability and anchorage-independent growth of the cells. Conversely, stable MCF-7 cell lines expressing inducible high levels of ectopic PTPε displayed higher activation of ERK1/2 and anchorage-independent growth. Our results demonstrate that expression of PTPε is up-regulated and activated in breast cancer cell lines, through EGFR, by sustained activation of the ERK1/2 pathway, generating a positive feedback regulatory loop required for survival of human breast cancer cells.

Novel PKCs activate ERK through PKD1 in MCF-7 cells

PKCs can have opposite effects on ERK phosphorylation. Novel (n)PKCs can inhibit ERK by phosphorylation of Raf-1, classical and atypical PKCs can activate ERK by removing an inhibitory protein from Raf-1. The aim of this work was to clarify how PMA-activated PKCs lead to ERK activation in MCF-7 cells expressing mainly nPKCs. Using chemical inhibitors and antibodies against PKCs, delivered into cells by the Chariot transfection system, we found that nPKCs activate ERK through transphosphorylation of PKD1, the blockage of which prevented PMA-stimulated ERK activation. We conclude that the nPKCs/PKD1 cascade is determinant for ERK activation by PMA in MCF-7 cells.

Overexpression of p75(NTR) increases survival of breast cancer cells through p21(waf1)

The p75 neurotrophin receptor (p75(NTR)) plays a critical role in various neuronal and non-neuronal cell types by regulating cell survival, differentiation and proliferation. To evaluate the influence of p75(NTR) in breast cancer development, we have established and characterized breast cancer cells which stably overexpress p75(NTR). We showed that p75(NTR) overexpression per se promoted cell survival to apoptogens with a concomitant slowdown of cell growth. The pro-survival effect is associated with an increased expression of the inhibitor of apoptosis protein-1 (c-IAP1), a decrease of TRAIL-induced cleavage of PARP, procaspase 9 and procaspase 3, and a decrease of cytochrome C release from the mitochondria. The anti-proliferative effect is due to a cell accumulation in G0/G1, associated with a decrease of Rb phosphorylation and an increase of p21(waf1). Interestingly, inhibition of p21(waf1) with siRNA not only restores proliferation but also abolishes the pro-survival effect of p75(NTR), indicating the key role of p21(waf1) in the biological functions of p75(NTR). Finally, using a SCID mice xenograft model, we showed that p75(NTR) overexpression favors tumor growth and strongly increases tumor resistance to anti-tumoral treatment. Together, our findings suggest that p75(NTR) overexpression in breast tumor cells could favor tumor survival and contribute to tumor resistance to drugs. This provides a rationale to consider p75(NTR) as a potential target for the future design of innovative therapeutic strategies.

Differential up-regulation of MAP kinase phosphatases MKP3/DUSP6 and DUSP5 by Ets2 and c-Jun converge in the control of the growth arrest versus proliferation response of MCF-7 breast cancer cells to phorbol ester

Different levels of regulation account for the inactivation of MAP kinases by MAPK phosphatases (MKPs), in a cell type- and stimuli-dependent manner. MCF-7 human breast carcinoma cells treated with the phorbol 12-myristate 13-acetate (PMA) suffer growth arrest and show morphological alterations, which depend on the activation of the ERK1/2 MAP kinases. MKP3/DUSP6 and DUSP5 MAP kinase phosphatases, two negative regulators of ERK1/2, were specifically up-regulated in MCF-7 and SKBR3 cells in response to PMA. MKP3 and DUSP5 up-regulation required the prolonged activation of the ERK1/2 pathway, and correlated with the shutdown of this route. MKP3 induction relied on the activation of the Ets2 transcription factor, whereas DUSP5 induction depended on the activation of c-Jun. Diminishing the expression of MKP3 and DUSP5 raised the activation of ERK1/2, and accelerated growth arrest of PMA-treated MCF-7 cells. Conversely, MCF-7 cell lines expressing high levels of MKP3 or DUSP5 did not undergo PMA-triggered growth arrest, displayed a migratory phenotype, and formed colonies in soft agar. We propose that the differential up-regulation of MKP3 by Ets2 and of DUSP5 by c-Jun may converge in similar functional roles for these MAP kinase phosphatases in the growth arrest versus proliferation decisions of breast cancer cells.

Kalopanaxsaponin A inhibits PMA-induced invasion by reducing matrix metalloproteinase-9 via PI3K/Akt- and PKCdelta-mediated signaling in MCF-7 human breast cancer cells

Induction of matrix metalloproteinase (MMP)-9 is particularly important for the invasiveness of breast cancers. We investigated the inhibitory effect of kalopanaxsaponin A (KPS-A) on cell invasion and MMP-9 activation in phorbol 12-myristate 13-acetate (PMA)-treated MCF-7 human breast cancer cells. KPS-A inhibited PMA-induced cell proliferation and invasion. PMA-induced cell invasion was blocked in the presence of a primary antibody of MMP-9, and KPS-A suppressed the increased expression and/or secretion of MMP-9 and tissue inhibitor of metalloproteinase (TIMP)-1. Using specific inhibitors, we confirmed that PMA-induced cell invasion and MMP-9 expression is primarily regulated by nuclear factor-kappa B (NF-kappaB) activation via phosphatidylinositol 3-kinase (PI3K)/Akt and activator protein-1 (AP-1) activation via extracellular signal-regulated kinase (ERK)1/2. KPS-A decreased PMA-induced transcriptional activation of NF-kappaB and AP-1 and inhibited PMA-induced phosphorylation of ERK1/2 and Akt. Treatment with the protein kinase C (PKC)delta inhibitor rottlerin caused a marked decrease in PMA-induced MMP-9 secretion and cell invasion, as well as ERK/AP-1 activation, and KPS-A reduced PMA-induced membrane localization of PKCdelta. Furthermore, oral administration of KPS-A led to a substantial decrease in tumor volume and expression of proliferating cell nuclear antigen, MMP-9, TIMP-1 and PKCdelta in mice with MCF-7 breast cancer xenografts in the presence of 17beta-estradiol. These results suggest that KPS-A inhibits PMA-induced invasion by reducing MMP-9 activation, mainly via the PI3K/Akt/NF-kappaB and PKCdelta/ERK/AP-1 pathways in MCF-7 cells and blocks tumor growth and MMP-9-mediated invasiveness in mice with breast carcinoma. Therefore, KPS-A may be a promising anti-invasive agent with the advantage of oral dosing.

Activation of ERK signaling pathway reduces the chemotherapy sensitivity in gastric cancer cells

AIM: To investigate the relationship between the activation of mitogen-activated protein kinase (MAPK)/extracelluar regulated protein kinases (ERK) signaling pathway and chemoresistance in human gastric cancer cell lines SGC7901 and BGC823.

METHODS: Cells were exposed to etoposide with or without PD98059 (a special inhibitor of MAPK/ERK pathway). Cell cycle distribution and cell apoptosis analysis were determined using flow cytometry and Hoechst 33258 staining. Cytotoxicity was assessed by determining cell survival with 3-(4, 5-dimethyl thiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT). Western blotting was performed to evaluate the phosphorylation level of ERK1/2 and protein expression of c-Myc and P53.

RESULTS: Etoposide caused a time- and dose-dependent reduction of cell viability in SGC7901 and BGC823 cells. PD98059 enhanced the cell inhibitory efficiency of etoposide. Compared with control group, the apoptosis rate was elevated in etoposide group (19.48% ± 1.57% vs 5.67% ± 0.81%, 17.38% ± 1.49% vs 4.97% ± 0.73%, all P < 0.01). Cells treated with and PD98059 showed significantly higher level of apoptotic phenotype than those treated with etoposide alone. The apotosis rate was 34.35% ± 2.84% and 32.11% ± 3.25% in etoposide and PD98059 groups, respectively (P < 0.01). Phosphorylation level of ERK1/2 and expression of c-Myc were significantly induced by etoposide in a time-dependent manner, but there was slight effect on protein expression of P53. PD98059 up-regulated expression of P53 and suppressed the up-regulated c-Myc expression induced by etoposide, strikingly.

CONCLUSION: Chemotherapy agent etoposide was able to activate MAPK/ERK signaling pathway of gastric cancer cells SGC7901 and BGC823, which decrease the chemotherapy sensitivity via suppressing the expression of P53 and enhancing the expression of c-Myc. This may be one of the mechanisms responsible for gastric cancer chemoresistance.