The activation of protein kinase G (PKG) by cyclic guanosine 3,5-monophosphate (cGMP) has become of considerable interest as a novel molecular approach for the induction of apoptosis in cancer cells. The present study was designed to examine the effects of cGMP and PKG on cell growth and apoptosis in the human breast cancer cell lines, MCF-7 and MDA-MB-468. To achieve this, 1-benzyl-3-(5P-hydroxymethyl-2P-furyl) indazole (YC-1), a soluble guanylyl cyclase activator, and 8-bromo-cGMP (8-br-cGMP), a membrane-permeant and phosphodiesterase-resistant analogue of cGMP, were employed in MCF-7 and MDA-MB-468 cells. Then, the role of PKG in the induction of apoptosis was evaluated using KT5823 and Rp-8-pCPT-cGMP as specific inhibitors of PKG. The expression of PKG isoforms in these cell lines was also investigated. KT5823 and Rp-8-pCPT-cGMP significantly attenuated the loss of cell viability caused by YC-1 and 8-br-cGMP in these cells. This study provides direct evidence that the activation of PKG by cGMP induces growth inhibition and apoptosis in MCF-7 and MDA-MB-468 breast cancer cell lines.

Our results suggest that adenosine induced apoptosis in prostate cancer cells via the mitochondrial pathway and is related to the adenosine receptors. These data might suggest that adenosine could be used as an agent for the treatment of prostate cancer.

Didscoidin domain receptor 1 (DDR1) is involved in the progression of prostate cancer metastasis through stimulation of epithelial-mesenchymal transition (EMT). So DDR1 inhibition can be a helpful target for cancer metastasis prevention. So, we studied the effects of DDR1 inhibition on EMT as well as induction of cell-cycle arrest and apoptosis in prostate cancer cell lines. DDR1 expression was evaluated using reverse-transcription polymerase chain reaction and western blot analysis. The EMT-associated protein expression was determined using the western blot analysis and immunocytochemistry following treatment with various concentrations of DDR1 inhibitor. The activation of DDR1 and also downstream-signaling molecules Pyk2 and MKK7 were determined using western blot analysis. Cell survival and proliferation after DDR1 inhibition were evaluated using 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide, bromodeoxyuridine, and colony formation assays. Flow cytometry analysis was used to determine the effects of DDR1 inhibition on cellcycle arrest and apoptosis using annexin V/propidium iodide-based flow cytometry. Results showed that the protein expression of N-cadherin and vimentin were decreased whereas protein expression of E-cadherin was increased after DDR1 inhibition. Results of our western blot analysis indicated that DDR1 inhibitor effectively downregulated P-DDR1, P-Pyk2, and P-MKK7 levels. This result also showed that DDR1 inhibition decreased cell survival and proliferation, induced G1 cell-cycle arrest, induced apoptosis by an increase in the Bax/Bcl-2 ratio and depletion of the mitochondrial membrane potential, and also by reactive oxygen species creation in prostate cancer cells. These data show that DDR1 inhibition can result in the EMT prevention via inhibition of Pyk2 and MKK7 signaling pathway and induces cell-cycle arrest and apoptosis in prostate cancer cell lines. Thus, this study identifies DDR1 as an important target for modulating EMT and induction of apoptosis in prostate cancer cells. K E Y W O R D S apoptosis, cell-cycle arrest, discoidin domain receptor 1 (DDR1), EMT

Induction of apoptosis in cancer cells can be a promising treatment method in cancer therapy. Naturally derived products had drawn growing attention as agent in cancer therapy. The main target of anticancer drugs may be distinct, but eventually, they lead to identical cell death pathway, which is apoptosis. Here, we indicated that britannin, a sesquiterpene lactone isolated from Asteraceae family, has antiproliferative activity on the MCF-7 and MDA-MB-468 human breast cancer cells. Annexin V/propidium iodide (PI) staining, Hoechst 33258 staining, and caspase-3/9 activity assay confirmed that britannin is able to induce apoptosis in MCF-7 and MDA-MB-468 cells. The Western blot analysis showed that the expression of Bcl-2 was noticeably decreased in response to britannin treatment, while the expression of Bax protein was increased, which were positively correlated with elevated expression of p53. Moreover, britannin also increased reactive oxygen species (ROS) generation which in turn triggered the loss of mitochondrial transmembrane potential (ΔΨm) and the subsequent release of cytochrome c from mitochondria into cytosol. Taken together, these results suggest that britannin inhibits growth of MCF-7 and MDA-MB-468 breast cancer cells through the activation of the mitochondrial apoptotic pathway and may potentially serve as an agent for breast cancer therapy.

Activation of protein kinase G (PKG) by cyclic guanosine 3,5-monophosphate (cGMP) has become of considerable interest as a novel molecular approach for the induction of apoptosis in cancer cells. This study was conducted to investigate the role of PKG isoforms in the regulation of cell growth in human breast cancer cell lines MCF-7 and MDA-MB468. The expression levels of PKG isoforms were also examined using real-time reverse transcriptase polymerase chain reaction. No differences in the gene expression of PKG isoforms were observed between MCF-7 and MDA-MB-468 cells. To investigate the effects of PKG isoforms on the regulation of cell growth, the cGMP analogues 8-APT-cGMP (PKGIα activator), 8-Br-PET-cGMP (PKGIβ activator) and 8-pCPT-cGMP (PKGII activator) were employed. Apoptosis was assessed with the Annexin-V-propidium iodide (PI) staining, cell cycle analysis and caspase-3/9 activity assay. Treatment of MCF-7 and MDA-MB-468 cells with 8-Br-PET-cGMP resulted in a concentration-dependent cell growth inhibition and apoptosis, whereas neither PKGIα nor PKGII activators had any effect on the cell growth. The role of PKGIβ in the inhibition of cell growth was confirmed using PKGI and PKGII inhibitors. The present study is the first to demonstrate the involvement of PKGIβ in the inhibition of cell growth and induction of apoptosis in breast cancer cells.