Pramanicin analog induces apoptosis in human colon cancer cells: critical roles for Bcl-2, Bim, and p38 MAPK signaling

Pramanicin (PMC) is an antifungal agent that was previously demonstrated to exhibit antiangiogenic and anticancer properties in a few in vitro studies. We initially screened a number of PMC analogs for their cytotoxic effects on HCT116 human colon cancer cells. PMC-A, the analog with the most potent antiproliferative effect was chosen to further interrogate the underlying mechanism of action. PMC-A led to apoptosis through activation of caspase-9 and -3. The apoptotic nature of cell death was confirmed by abrogation of cell death with pretreatment with specific caspase inhibitors. Stress-related MAPKs JNK and p38 were both activated concomittantly with the intrinsic apoptotic pathway. Moreover, pharmacological inhibition of p38 proved to attenuate the cell death induction while pretreatment with JNK inhibitor did not exhibit a protective effect. Resistance of Bax -/- cells and the protective nature of caspase-9 inhibition indicate that mitochondria play a central role in PMC-A induced apoptosis. Early post-exposure elevation of cellular Bim and Bax was followed by a marginal Bcl-2 depletion and Bid cleavage. Further analysis revealed that Bcl-2 downregulation occurs at the mRNA level and is critical to mediate PMC-A induced apoptosis, as ectopic Bcl-2 expression substantially spared the cells from death. Conversely, forced expression of Bim proved to significantly increase cell death. In addition, analyses of p53-/- cells demonstrated that Bcl-2/Bim/Bax modulation and MAPK activations take place independently of p53 expression. Taken together, p53-independent transcriptional Bcl-2 downregulation and p38 signaling appear to be the key modulatory events in PMC-A induced apoptosis

PEG−peptide conjugates

The remarkable diversity of the self-assembly behavior of PEG−peptides is reviewed, including self-assemblies formed by PEG−peptides with β-sheet and α-helical (coiled-coil) peptide sequences. The modes of self-assembly in solution and in the solid state are discussed. Additionally, applications in bionanotechnology and synthetic materials science are summarized

Pramanicin analog induces apoptosis in human colon cancer cells: critical roles for Bcl-2, Bim, and p38 MAPK signaling.

Pramanicin (PMC) is an antifungal agent that was previously demonstrated to exhibit antiangiogenic and anticancer properties in a few in vitro studies. We initially screened a number of PMC analogs for their cytotoxic effects on HCT116 human colon cancer cells. PMC-A, the analog with the most potent antiproliferative effect was chosen to further interrogate the underlying mechanism of action. PMC-A led to apoptosis through activation of caspase-9 and -3. The apoptotic nature of cell death was confirmed by abrogation of cell death with pretreatment with specific caspase inhibitors. Stress-related MAPKs JNK and p38 were both activated concomittantly with the intrinsic apoptotic pathway. Moreover, pharmacological inhibition of p38 proved to attenuate the cell death induction while pretreatment with JNK inhibitor did not exhibit a protective effect. Resistance of Bax -/- cells and the protective nature of caspase-9 inhibition indicate that mitochondria play a central role in PMC-A induced apoptosis. Early post-exposure elevation of cellular Bim and Bax was followed by a marginal Bcl-2 depletion and Bid cleavage. Further analysis revealed that Bcl-2 downregulation occurs at the mRNA level and is critical to mediate PMC-A induced apoptosis, as ectopic Bcl-2 expression substantially spared the cells from death. Conversely, forced expression of Bim proved to significantly increase cell death. In addition, analyses of p53-/- cells demonstrated that Bcl-2/Bim/Bax modulation and MAPK activations take place independently of p53 expression. Taken together, p53-independent transcriptional Bcl-2 downregulation and p38 signaling appear to be the key modulatory events in PMC-A induced apoptosis

Generation of Multiple Excitons in Ag2S Quantum Dots: Single High-Energy versus Multiple-Photon Excitation

We explored the carrier multiplications generated by single high-energy and multiple photon absorption in Ag2S quantum dots (QDs) using femtosecond broadband transient absorption spectroscopy

Transcriptional downregulation of Bcl-2 is critical to mediate PMC-A induced apoptosis.

<p>Wild type HCT116 cells were treated with indicated concentrations of PMC-A and harvested at 24 h post-exposure, lysed and immunoblotted with anti-Bcl-2 and anti-β-actin antibodies (A). β-actin was used as loading control. Downregulation of cellular Bcl-2 was amplified by increasing PMC-A dose. HCT116 wt cells were treated with indicated PMC-A concentrations, harvested after 24 h for total RNA extraction, cDNA synthesis and qRT-PCR analysis (B). A marginal (∼5-fold) decrease in Bcl-2 transcription was evident upon PMC-A treatment (p<0,01). HCT116 wt cells were transiently transfected with expression plasmids either carrying human Bcl-2 gene or mock vector only (C). Transfected cells were treated with 50 µM PMC-A before collection and flow cytometry analysis. The results from at least 3 independent experiments were shown as means ± SD. Difference of mean values between mock and Bcl-2-transfected cells were tested using paired student’s t-test; <b>**</b>P<0.01. Analysis indicates that ectopic Bcl-2 expression renders the cells more resistant against PMC-A induced apoptosis. Bcl-2 expression statuses of mock- and Bcl-2-transfected cells prior to PMC-A treatment are displayed as immunoblotting results obtained from cells that were harvested, lysed and immunoblotted with anti-Bcl-2 antibody (C). Results from one of three independent experiments are shown in immunoblotting results.</p

Synthesis of PMC analogs.

<p>Synthesis of PMC analogs.</p

Early upregulation of Bim is important to mediate PMC-A induced apoptosis.

<p>Wild type HCT116 cells were transfected with empty, human Bim gene carrying expression plasmids. Transfected and untransfected cells were treated with or without 50 µM PMC-A and harvested 24 h following treatment and analyzed by flow cytometry. The results from at least 3 independent experiments are shown as means ± SD. <b>**</b>P<0.01, mean value of PMC-A-treated mock-tansfected cells against that of untreated mock-transfected was tested using unpaired student’s t-test. <b>*</b>P<0.05, mean values of PMC-A-treated Bim-transfected cells against that of PMC-A-treated mock-transfected were tested using paired student’s t-test. Apoptotic induction by PMC-A treatment was significantly increased in cells overexpressing Bim compared to the cells that possess endogenous Bim expression. Cells transfected with mock vector or Bim were collected, lysed and immunoblotted with anti-Bim antibody to confirm transfection.</p