Transcriptional regulation of intermolecular Ca2+ signaling in hibernating ground squirrel cardiomyocytes: The myocardin-junctophilin axis.

The contraction of heart cells is controlled by the intermolecular signaling between L-type Ca2+ channels (LCCs) and ryanodine receptors (RyRs), and the nanodistance between them depends on the interaction between junctophilin-2 (JPH2) in the sarcoplasmic reticulum (SR) and caveolin-3 (CAV3) in the transversal tubule (TT). In heart failure, decreased expression of JPH2 compromises LCC-RyR communication leading to deficient blood-pumping power. In the present study, we found that JPH2 and CAV3 transcription was concurrently regulated by serum response factor (SRF) and myocardin. In cardiomyocytes from torpid ground squirrels, compared with those from euthermic counterparts, myocardin expression was up-regulated, which boosted both JPH2 and CAV3 expression. Transmission electron microscopic imaging showed that the physical coupling between TTs and SRs was tightened during hibernation and after myocardin overexpression. Confocal Ca2+ imaging under the whole-cell patch clamp condition revealed that these changes enhanced the efficiency of LCC-RyR intermolecular signaling and fully compensated the adaptive down-regulation of LCCs, maintaining the power of heart contraction while avoiding the risk of calcium overload during hibernation. Our finding not only revealed an essential molecular mechanism underlying the survival of hibernating mammals, but also demonstrated a "reverse model of heart failure" at the molecular level, suggesting a strategy for treating heart diseases.

Pleckstrin-2-promoted PPM1B degradation plays an important role in transforming growth factor-ß-induced breast cancer cell invasion and metastasis.

Transforming growth factor-ß (TGF-ß) is known to promote breast cancer cell migration, invasion, and dissemination; however, the underlying molecular mechanisms are not yet well characterized. Here, we report that TGF-ß induces pleckstrin-2 (PLEK2) expression by Smad3 and signal transducer and activator of transcription 3 (STAT3) activating PLEK2 promoter activity. Higher PLEK2 expression is associated with poor prognosis in breast cancer patients. Overexpression and knockout experiments in MDA-MB-231 and MCF-7 breast cancer cells revealed that PLEK2 promotes cell migration, invasion, and dissemination in 2D and 3D cell culture. Moreover, PLEK2 promotes metastasis of breast cancer cells in vivo. Pleckstrin-2 localizes to the cell membrane and cell protrusions following TGF-ß treatment. Furthermore, inhibition of PI3K phosphorylation abolishes TGF-ß- and PLEK2-induced cell invasion. The carboxyl-terminal PH domain of PLEK2 is critical for TGF-ß- and PLEK2-induced Akt activation and plays an important role in cell invasion. Pleckstrin-2 interacts with PPM1B and promotes its ubiquitin-dependent degradation. The PLEK2-PPM1B axis utilizes nuclear factor-κB signaling to promote cell migration and invasion. Our data implicate the TGF-ß-STAT3/Smad3-PLEK2-PPM1B signaling cascade in TGF-ß-induced breast cancer cell migration and invasion. These findings suggest that PLEK2/PPM1B could represent novel targets for the intervention of breast cancer metastasis.

Abrin P2 suppresses proliferation and induces apoptosis of colon cancer cells via mitochondrial membrane depolarization and caspase activation.

To explore the cytotoxic mechanism of abrin P2 on human colon cancer HCT-8 cells, abrin P2 was isolated from the seed of Abrus precatorius L. It was found that abrin P2 exhibited cytotoxicity toward 12 different human cancer cell lines. Our results demonstrated that abrin P2 suppressed the proliferation of human colon cancer cells (HCT-8 cells) and induced cell cycle arrest at the S and G2/M phases. The mechanism by which abrin P2 inhibited cell proliferation was via the down-regulation of cyclin B1, proliferating cell nuclear antigen and Ki67, as well as the up-regulation of P21. In addition, abrin P2 induced a dose- and time-dependent increase in the rate of HCT-8 cell apoptosis. Treatment with both Z-VAD-FMK, a broad-spectrum caspase inhibitor, and abrin P2 demonstrated that abrin P2 induced HCT-8 cell apoptosis via the activation of caspases. Together, our results revealed that abrin P2-induced apoptosis in HCT-8 cells was associated with the activation of caspases-3/-8/-9, the reduction in the Bcl-2/Bax ratio, the loss of mitochondrial membrane potential, and the increase in cytochrome c release. We further showed that abrin P2 administration effectively suppressed the growth of colon cancer xenografts in nude mice. This is the first report that abrin P2 effectively inhibits colon cancer cell growth in vivo and in vitro by suppressing proliferation and inducing apoptosis.

The effect of TGF-beta-induced epithelial-mesenchymal transition on the expression of intracellular calcium-handling proteins in T47D and MCF-7 human breast cancer cells.

The contribution of Ca(2+) in TGF-ß-induced EMT is poorly understood. We aimed to confirm the effect of TGF-ß on the gene expression of intracellular calcium-handling proteins and to investigate the potential underlying mechanisms in TGF-ß-induced EMT. T47D and MCF-7 cells were cultured in vitro and treated with TGF-ß. The mRNA expression of EMT marker genes and intracellular calcium-handling proteins were quantified by qRT-PCR. qRT-PCR and Western blot analysis results verified the changes of EMT marker gene expression. Furthermore, we found that TGF-ß induced cell morphological changes significantly with an increase of cell surface area and cell length. These results indicated that TGF-ß induced EMT. The mRNA expression levels of SPCA1, SPCA2 and MCU were not influenced by TGF-ß treatment, while NCX1 expression was decreased in T47D cells. In addition, the mRNA levels of SERCAs and IP3Rs were significantly changed due to TGF-ß-induced EMT. The TGF-ß-treated T47D cells exhibited markedly greater response to ATP than the control cells, and the descent velocity of cytosolic calcium concentration was faster in TGF-ß-treated cells than in control cells. This is the first report to demonstrate that TGF-ß-induced EMT in human breast cancer cells is associated with alterations in endoplasmic reticulum calcium homeostasis.

c-Src regulates cell cycle proteins expression through protein kinase B/glycogen synthase kinase 3 beta and extracellular signal-regulated kinases 1/2 pathways in MCF-7 cells.

We have demonstrated that c-Src suppression inhibited the epithelial to mesenchymal transition in human breast cancer cells. Here, we investigated the role of c-Src on the cell cycle progression using siRNAs and small molecule inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2). Western blot analysis demonstrated the down-regulation of cyclin D1 and cyclin E and up-regulation of p27 Kip1 after c-Src suppression by PP2. Incubation of cells in the presence of PP2 significantly blocked the phosphorylation of extracellular signal-regulated kinases 1/2 (ERK1/2), protein kinase B (AKT), and glycogen synthase kinase 3 beta (GSK3ß). Specific pharmacological inhibitors of MEK1/2/ERK1/2 and phosphatidylinositide 3-kinase/AKT pathways were used to demonstrate the relationship between the signal cascade and cell cycle proteins expression. The expression of cyclin D1 and cyclin E were decreased after inhibition of ERK1/2 or AKT activity, whereas the p27 Kip1 expression was increased. In addition, knockdown of c-Src by siRNAs reduced cell proliferation and phosphorylation of ERK1/2, AKT, and GSK3ß. After c-Src depletion by siRNAs, we observed significant down-regulation of cyclin D1 and cyclin E, and up-regulation of p27 Kip1. These results suggest that c-Src suppression by PP2 or siRNAs may regulate the progression of cell cycle through AKT/GSK3ß and ERK1/2 pathways.

Inhibition of epithelial to mesenchymal transition in metastatic breast carcinoma cells by c-Src suppression.

The aberrant activation of c-Src regulates multiple functions during tumor progression. This study was conducted to investigate the role of c-Src suppression in epithelial to mesenchymal transition (EMT) process in human breast carcinoma cells. c-Src suppression by PP2 (a Src-family kinase inhibitor) or small interfering RNA (siRNA) was carried out in MCF-7 and MDA-MB-231 cells. Cell migration was analyzed by wound-healing assay. The transcription and protein levels of EMT markers and transcription factors were evaluated by reverse transcription-PCR and Western blot analysis, respectively. The changed cell morphology was photographed by light microscope. c-Src suppression by PP2 or siRNA reversed the mesenchymal-like phenotype in MDA-MB-231 cells. E-cadherin was upregulated in MCF-7 and MDA-MB-231 cells after c-Src suppression, whereas vimentin was downregulated in MDA-MB-231 cells. Slug and SIP1 were downregulated after c-Src suppression in MCF-7 and MDA-MB-231 cells, whereas Twist was unchanged. These results suggest that c-Src suppression by PP2 or siRNA may inhibit EMT through regulation of different transcription factors in breast carcinoma cells that have different metastatic potential.

Efficient purification of GP-1D8 glycoprotein from human breast carcinoma tissue by immunoaffinity chromatography.

Anti-GP-1D8 monoclonal antibody was produced in our laboratory. Immunoaffinity purification of GP-1D8 glycoprotein from human breast carcinoma tissues, on column with the monospecific antibody, is developed. The procedure permits purification of GP-1D8 to a highly purified state. It appeared as a single band in sodium dodcyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The molecular mass of GP-1D8 was determined to be 66 kDa by mass spectrometry. Its antigenicity was stable between 0 and 70 degrees C. It was breast cancer specific, as determined by immunohistochemistry and immunocytochemistry. The preparation of anti-GP-1D8 monoclonal antibody will facilitate further detection of, and functional study on, GP-1D8. The study also provides a simple, economical, and efficient method for affinity purification of target proteins from human or animal tissues.

STIM1 plays an important role in TGF-ß-induced suppression of breast cancer cell proliferation.

Store-operated calcium entry (SOCE) signaling is involved in cancer progression. Stromal interaction molecule 1 (STIM1) triggers store-operated calcium channels to induce SOCE. Transforming growth factor-ß (TGF-ß) influences a wide range of cellular behaviors, including cell proliferation. However, little is known about the relationship between calcium signaling and TGF-ß signaling in cancer cell proliferation. Here, we found that TGF-ß induced cell cycle arrest at the G0/G1 phase and suppressed cell proliferation in MDA-MB-231 and MCF-7 breast cancer cells. These effects were impaired by extracellular Ca2+ chelator EGTA or SOCE specific inhibitor SKF96365 in MDA-MB-231 cells. Treating MDA-MB-231 cells with TGF-ß for 24 and 48 h markedly decreased STIM1 expression and thapsigargin-induced SOCE. A transcriptional inhibitor of STIM1, Wilm's tumor suppressor 1 (WT1), was upregulated in TGF-ß-treated MDA-MB-231 cells, and knockdown of WT1 expression partially restored the TGF-ß-induced downregulation of STIM1. Stably overexpressing STIM1 in MDA-MB-231 cells restored the TGF-ß-induced effects. The p21 mRNA level increased in SKF96365- or TGF-ß-treated MDA-MB-231 cells, whereas that for cyclin E1 decreased. Our findings demonstrate for the first time that STIM1 and SOCE are involved in the TGF-ß-induced suppression of cell proliferation. Furthermore, our studies also provide a new approach to inhibit breast cancer cell proliferation with small molecules targeting STIM1 and SOCE.

The role of enoyl-CoA hydratase short chain 1 and peroxiredoxin 3 in PP2-induced apoptosis in human breast cancer MCF-7 cells.

We show that 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2) induces apoptosis and down-regulates the expression of enoyl-CoA hydratase short chain 1 (ECHS1) and peroxiredoxin 3 (PRDX3) in human breast cancer MCF-7 cells. The decrease of ECHS1 and PRDX3 was validated by Western blot and quantitative real-time reverse transcription-PCR in MCF-7 and other carcinoma cells. Knockdown and over-expression of ECHS1 and/or PRDX3 further supported the key role of ECHS1 and PRDX3 in regulation of PP2-induced apoptosis. These results suggest a possible apoptotic pathway whereby down-regulation of ECHS1 and PRDX3 potentiates PP2-induced apoptosis in MCF-7 cells.

Purification and characterization of 66-kDa glycoprotein from human breast carcinoma.

We extracted a 66-kDa glycoprotein (GP-1D8) from breast invasive ductal carcinoma tissues. The monoclonal antibody (mAb) against GP-1D8 was prepared in our laboratory. Western blotting with the purified protein using the mAb demonstrated a single band of 66 kDa. Immunocytochemical and immunohistochemical analysis revealed strong expression of GP-1D8 protein in the cytoplasm of MCF-7 cells and different types of breast carcinoma tissues, but GP-1D8 is absent in normal breast and benign breast tumor tissues. Glycosylation analysis showed GP-1D8 contained methylated salic acid. GP-1D8 was identified using mass-spectrometric techniques and N-terminal sequencing. These data were used to identify the protein through the SWISSPROT protein sequence database and BLAST homology search. These results showed GP-1D8 had some similarity to human albumin precursor. Co-immunoprecipitation assays of lysate from MCF-7 cells and mass spectrometric analysis revealed the interaction of GP-1D8 with beta-tubulin. This is the first time human breast carcinoma tissues and MCF-7 cells have been shown to express a 66-kDa glycoprotein similar to human albumin precursor. These results might be important in the detection of novel potential biomarkers and may provide insight into the molecular mechanisms of tumorigenesis.