Lawrence C.-M. Chiu

Avian Influenza Virus A/HK/483/97(H5N1) NS1 Protein Induces Apoptosis in Human Airway Epithelial Cells

ABSTRACT Avian H5N1 influenza virus causes a remarkably severe disease in humans, with an overall case fatality rate of greater than 50%. Human influenza A viruses induce apoptosis in infected cells, which can lead to organ dysfunction. To verify the role of H5N1-encoded NS1 in inducing apoptosis, the NS1 gene was cloned and expressed in human airway epithelial cells (NCI-H292 cells). The apoptotic events posttransfection were examined by a terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick-end-labeling assay, flow cytometric measurement of propidium iodide, annexin V staining, and Western blot analyses with antibodies specific for proapoptotic and antiapoptotic proteins. We demonstrated that the expression of H5N1 NS1 protein in NCI-H292 cells was sufficient to induce apoptotic cell death. Western blot analyses also showed that there was prominent cleavage of poly(ADP-ribose) polymerase and activation of caspase-3, caspase-7, and caspase-8 during the NS1-induced apoptosis. The results of caspase inhibitor assays further confirmed the involvement of caspase-dependent pathways in the NS1-induced apoptosis. Interestingly, the ability of H5N1 NS1 protein to induce apoptosis was much enhanced in cells pretreated with Fas ligand (the time posttransfection required to reach >30% apoptosis was reduced from 24 to 6 h). Furthermore, 24 h posttransfection, an increase in Fas ligand mRNA expression of about 5.6-fold was detected in cells transfected with H5N1 NS1. In conclusion, we demonstrated that the NS1 protein encoded by avian influenza A virus H5N1 induced apoptosis in human lung epithelial cells, mainly via the caspase-dependent pathway, which encourages further investigation into the potential for the NS1 protein to be a novel therapeutic target.

Host Immune Defense Peptide LL-37 Activates Caspase-Independent Apoptosis and Suppresses Colon Cancer

Cathelicidins are a family of bacteriocidal polypeptides secreted by macrophages and polymorphonuclear leukocytes (PMN). LL-37, the only human cathelicidin, has been implicated in tumorigenesis, but there has been limited investigation of its expression and function in cancer. Here, we report that LL-37 activates a p53-mediated, caspase-independent apoptotic cascade that contributes to suppression of colon cancer. LL-37 was expressed strongly in normal colon mucosa but downregulated in colon cancer tissues, where in both settings its expression correlated with terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling-positive apoptotic cells. Exposure of colon cancer cells to LL-37 induced phosphatidylserine externalization and DNA fragmentation in a manner independent of caspase activation. Apoptogenic function was mediated by nuclear translocation of the proapoptotic factors, apoptosis-inducing factor (AIF) and endonuclease G (EndoG), through p53-dependent upregulation of Bax and Bak and downregulation of Bcl-2 via a pertussis toxin-sensitive G-protein-coupled receptor (GPCR) pathway. Correspondingly, colonic mucosa of cathelicidin-deficient mice exhibited reduced expression of p53, Bax, and Bak and increased expression of Bcl-2 together with a lower basal level of apoptosis. Cathelicidin-deficient mice exhibited an increased susceptibility to azoxymethane-induced colon tumorigenesis, establishing pathophysiologic relevance in colon cancer. Collectively, our findings show that LL-37 activates a GPCR-p53-Bax/Bak/Bcl-2 signaling cascade that triggers AIF/EndoG-mediated apoptosis in colon cancer cells.

A rice bran polyphenol, cycloartenyl ferulate, elicits apoptosis in human colorectal adenocarcinoma SW480 and sensitizes metastatic SW620 cells to TRAIL-induced apoptosis.

High intake of whole grain food has been suggested as an important factor for reducing the risk of colon cancer, owing to the abundance of indigestible fibers. Our findings demonstrated that, among various rice bran phenolic compounds tested, cycloartenyl ferulate (CF) showed the most prominent in vitro growth inhibition on human colorectal adenocarcinoma SW480, but had low toxicity on normal colon CCD-18-Co cells. The anticancer activity of CF was further illustrated by its ability to induce significant regression of SW480 xenograft in nude mice. CF elevated the death receptors DR4 and DR5 and triggered both the death receptor and the mitochondrial apoptosis pathways. Depletion of anti-apoptotic Bcl-2 and up-regulation of pro-apoptotic Bak were observed, accompanied by dissipation of the mitochondrial membrane potential and release of cyto c and SMAC/DIABLO from mitochondria into the cytosol. Bid was found to be cleaved by caspase-8, so that the death receptor pathway might be exaggerated by the mitochondrial pathway. Strikingly, we showed for the first time that CF also sensitized the metastatic and resistant colon cancer SW620 to TRAIL-induced apoptosis and the mechanisms involved at least enhanced activation of caspase-8 and -3. This study provides a clear evidence that the health-beneficial properties of whole grain consumption are not only limited by the presence of dietary fibers but also other molecules that can either act as a chemopreventive agent to directly induce tumor regression or as a sensitizer to enhance TRAIL-induced apoptosis in metastatic cancer cells.

Activation of the JNK pathway promotes phosphorylation and degradation of BimEL—a novel mechanism of chemoresistance in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemias (T-ALLs) are highly malignant tumors with 20% of patients continues to fail therapy, in part due to chemoresistance of T-ALL cells via largely unknown mechanisms. Here, we showed that lack of Bcl-2-interacting mediator of cell death (Bim)(EL) protein expression, a BH3-only member of the Bcl-2 family proteins, conferred resistance of a T-ALL cell line, Sup-T1, to etoposide-induced apoptosis. Overexpression of Bim(EL) significantly restored its sensitivity to etoposide-induced caspase activation and poly(ADP-ribose) polymerase cleavage. Surprisingly, we found that constitutive activation of the c-Jun N-terminal kinase (JNK) pathway in Sup-T1 cells promoted phosphorylation and degradation of Bim(EL) via the proteosome. Blocking with a proteosome inhibitor yielded an elevated level of Bim(EL) and accumulation of Bim(EL) species phosphorylated at Ser(69). Pretreatment of Sup-T1 cells with a specific JNK inhibitor, SP600125, also increased the Bim(EL) level and resensitized the cells to etoposide-induced apoptosis. Together, our findings suggest that the JNK activation status may correlate with the Bim(EL) level and in turn can control the sensitivity of T-ALL cells to chemotherapeutic agents.

Cytostatic and cytotoxic effects of cyclooxygenase inhibitors and their synergy with docosahexaenoic acid on the growth of human skin melanoma A-375 cells

Recent studies have suggested the inhibition of cyclooxygenase-2 (COX-2) as strategy to prevent colorectal cancer. In this study, the cytostatic and cytotoxic effects of different non-steroidal anti-inflammatory drugs (NSAIDs), all of them are reported COX inhibitors, were investigated in human skin melanoma A-375 cells. Using BrdU-cell proliferation assay, we showed that 50 and 100 microM of celecoxib (CEL) reduced proliferation of the melanoma cells at 72-h incubations by 34.0% and 82.7%, respectively. As determined by Toxilight-cytotoxicity assay, the drug was only toxic to the cancer cells at 100 microM. Indomethacin (IND) also inhibited the cell proliferation by about 40% at 240 and 480 pM and was only slightly toxic to the melanoma. Neither aspirin (ASP) nor piroxicam (PIR) exhibited cytostatic or cytotoxic effect on the cancer cells. Combinatory effects of the above NSAIDs with dietary docosahexaenoic acid (DHA) on inhibiting growth of the melanoma cells were further elucidated. Each of the NSAIDs, at doses 10-480 pM, was incubated simultaneously with the melanoma cells and 160 pM of DHA for 72 h. Results from MTT assay showed that both CEL and IND, starting from 20 microM. exhibited additive effects on the DHA-induced growth inhibition. ASP also enhanced the DHA-induced growth inhibition by 42.8% at 480 microM. To our surprise, although PRX did not suppress the melanoma growth, the drug at 40-240 microM enhanced the DHA-induced growth inhibition by 15.9-66.4%, respectively. Results from these studies suggest that the anticancer effects of NSAIDs may not be explained solely by their COX-inhibitory activities. Further studies are therefore required to understand their modes of action, before they could be used alone or in combinations with other agents for cancer chemoprevention.

Chemical composition and antiproliferative activity of essential oil from the leaves of a medicinal herb, Schefflera heptaphylla.

Schefflera heptaphylla (L.) Frodin is a medicinal herb widely used as a main ingredient of the popular health tea formulation against infections in Southern China. Twenty‐seven volatile compounds were identified by GC‐MS analysis from the essential oil obtained from the leaves of S. heptaphylla, and 17 of them belonged to monoterpenes or sesquiterpenes. The main volatile constituent in S. heptaphylla was found to be a monoterpene, β‐pinene, comprising about 22% of the total volatile components. The essential oil showed significant antiproliferative activity against three cancer cell lines, MCF‐7, A375 and HepG2 cells, with IC50 values of 7.3 µg/mL, 7.5 µg/mL and 6.9 µg/mL, respectively. The result of the cytotoxicity assay indicates that (−)‐β‐pinene and (+)‐β‐pinene (commercially available from Sigma) also possessed antiproliferative activity against the cancer cells MCF‐7, A375 and HepG2 with IC50 values ranging from 147.1 to 264.7 µm. Copyright

Docosahexaenoic acid from a cultured microalga inhibits cell growth and induces apoptosis by upregulating Bax/Bcl-2 ratio in human breast carcinoma MCF-7 cells.

Abstract: Docosahexaenoic acid (DHA) is an ω‐3 fatty acid that comprises 22 carbons and 6 alternative double bonds in its hydrocarbon chain (22:6ω3). Previous studies have shown that DHA from fish oil controls the growth and development of different cancers; however, safety issues have been raised repeatedly about contamination of toxins in fish oil that makes it no longer a clean and safe source of the fatty acid. We investigated the cell growth inhibition of DHA from the cultured microalga Crypthecodinium cohnii (algal DHA [aDHA]) in human breast carcinoma MCF‐7 cells. aDHA exhibited growth inhibition on breast cancer cells dose‐dependently by 16.0% to 59.0% of the control level after 72‐h incubations with 40 to 160 μM of the fatty acid. DNA flow cytometry shows that aDHA induced sub‐G1 cells, or apoptotic cells, by 64.4% to 171.3% of the control levels after incubations with 80 mM of the fatty acid for 24, 48, and 72 h. Western blot studies further show that aDHA did not modulate the expression of proapoptotic Bax protein but induced the downregulation of anti‐apoptotic Bcl‐2 expression time‐dependently, causing increases of Bax/Bcl‐2 ratio by 303.4% and 386.5% after 48‐ and 72‐h incubations respectively with the fatty acid. Results from this study suggest that DHA from the cultured microalga is also effective in controlling cancer cell growth and that downregulation of antiapoptotic Bcl‐2 is an important step in the induced apoptosis.