By activating Fas/ceramide synthase 6/p38 kinase in lipid rafts, stichoposide D inhibits growth of leukemia xenografts.

Stichoposide D (STD) is a marine triterpene glycoside isolated from sea cucumbers. We examined the molecular mechanisms underlying the antitumor activity of STD in human leukemia cells. The role of Fas (CD95), ceramide synthase 6 (CerS6) and p38 kinase during STD-induced apoptosis was examined in human leukemia cells. In addition, the antitumor effects of STD in K562 and HL-60 leukemia xenograft models were investigated. We found that STD induces Fas translocation to lipid rafts, and thus mediates cell apoptosis. We also observed the activation of CerS6 and p38 kinase during STD-induced apoptosis. The use of methyl-ß-cyclodextrin and nystatin to disrupt lipid rafts prevents the clustering of Fas and the activation of CerS6 and p38 kinase, and also inhibits STD-induced apoptosis. Specific inhibition by Fas, CerS6, and p38 kinase siRNA transfection partially blocked STD-induced apoptosis. In addition, STD has antitumor activity through the activation of CerS6 and p38 kinase without displaying any toxicity in HL-60 and K562 xenograft models. We observed that the anti-tumor effect of STD is partially prevented in CerS6 shRNA-silenced xenograft models. We first report that Fas/CerS6/p38 kinase activation in lipid rafts by STD is involved in its anti-leukemic activity. We also established that STD is able to enhance the chemosensitivity of K562 cells to etoposide or Ara-C. These data suggest that STD may be used alone or in combination with other chemotherapeutic agents to treat leukemia.

Overexpression of PGC­1α enhances cell proliferation and tumorigenesis of HEK293 cells through the upregulation of Sp1 and Acyl-CoA binding protein.

Peroxisome proliferator-activated receptor γ coactivator-1α (PGC­1α), a coactivator interacting with multiple transcription factors, regulates several metabolic processes. Although recent studies have focused on the role of PGC­1α in cancer, the underlying molecular mechanism has not been clarified. Therefore, we evaluated the role of PGC­1α in cell proliferation and tumorigenesis using human embryonic kidney (HEK)293 cells and colorectal cancer cells. We established stable HEK293 cell lines expressing PGC­1α and examined cell proliferation, anchorage-independent growth, and oncogenic potential compared to parental HEK293 cells. To identify the molecular PGC­1α targets for increased cell proliferation and tumorigenesis, the GeneFishing™ DEG (differentially expressed genes) screening system was used. Western blot analysis and immunofluorescence staining were performed for a regulated gene product to confirm the results. Forced expression of PGC­1α in HEK293 cells promoted cell proliferation and anchorage-independent growth in soft agar. In addition, HEK293 cells that highly expressed PGC­1α showed enhanced tumor formation when subcutaneously injected into the bilateral flanks of immunodeficient mice. The results of the GeneFishing DEG screening system identified one upregulated gene (Acyl-CoA binding protein; ACBP). Real-time RT-PCR, western blot analysis, and immunofluorescence staining showed that ACBP was markedly increased in HEK293 cells stably overexpressing PGC­1α (PGC­1α-HEK293 cells) compared to those expressing an empty vector. In PGC­1α, ACBP, and specificity protein 1 (Sp1) siRNA knockdown experiments in PGC­1α-HEK293 and SNU-C4 cells, we also observed inhibition of cell proliferation, reduced expression of antioxidant enzymes, and increased H2O2-induced reactive oxygen species production and apoptosis. These findings suggest that PGC­1α may promote cell proliferation and tumorigenesis through upregulation of ACBP. We provide evidence that increased Sp1 expression might contribute to enhanced ACBP expression by PGC­1α. The current results also suggest that PGC­1α, whose expression is related to enhanced cell proliferation and tumorigenesis, may be a good candidate molecular target for cancer therapy.

Stichoposide C induces apoptosis through the generation of ceramide in leukemia and colorectal cancer cells and shows in vivo antitumor activity.

PURPOSE: Marine triterpene glycosides that are physiologically active natural compounds isolated from sea cucumbers (holothurians) and sponges have antifungal, cytotoxic, and antitumor activities, whose specific molecular mechanisms remain to be elucidated. In this study, we examined if and through which mechanisms stichoposide C (STC) from Thelenota anax (family Stichopodidae) induces apoptosis in leukemia and colorectal cancer cells. EXPERIMENTAL DESIGN: We examined STC-induced apoptosis in human leukemia and colorectal cancer cells in the context of mitochondrial injury and signaling pathway disturbances, and investigated the antitumor effect of STC in mouse CT-26 subcutaneous tumor and HL-60 leukemia xenograft models. RESULTS: We found that STC induces apoptosis in these cells in a dose-dependent manner and leads to the activation of Fas and caspase-8, cleavage of Bid, mitochondrial damage, and activation of caspase-3. STC activates acid sphingomyelinase (SMase) and neutral SMase, which resulted in the generation of ceramide. Specific inhibition of acid SMase or neutral SMase and siRNA knockdown experiments partially blocked STC-induced apoptosis. Moreover, STC markedly reduced tumor growth of HL-60 xenograft and CT-26 subcutaneous tumors and increased ceramide generation in vivo. CONCLUSIONS: Ceramide generation by STC, through activation of acid and neutral SMase, may in part contribute to STC-induced apoptosis and antitumor activity. Thus, STC may have therapeutic relevance for human leukemia and colorectal cancer.

Oromandibular dyskinesia as the initial manifestation of late-onset huntington disease.

Huntington's disease (HD) is a neurodegenerative disorder characterized by a triad of choreoathetosis, dementia and dominant inheritance. The cause of HD is an expansion of CAG trinucleotide repeats in the HD gene. Typical age at onset of symptoms is in the 40s, but the disorder can manifest at any time. Late-onset (≥ 60 years) HD is clinically different from other adult or juvenile onset HD and characterized by mild motor problem as the initial symptoms, shorter disease duration, frequent lack of family history, and relatively low CAG repeats expansion. We report a case of an 80-year-old female with oromandibular dyskinesia as an initial manifestation of HD and 40 CAG repeats.