Suppression of hypoxic cell death by APIP-induced sustained activation of AKT and ERK1/2.

Apaf-1-interacting protein (APIP) was previously isolated as an inhibitor of mitochondrial cell death interacting with Apaf-1. Here, we report a hypoxia-selective antiapoptotic activity of APIP that induces the activation of AKT and extracellular signal-regulated kinase (ERK)1/2. Stable expression of APIP in C2C12 (C2C12/APIP) cells suppressed cell death induced by hypoxia and etoposide. Unlike etoposide, however, APIP induces the sustained activation of AKT and ERK1/2 and the phosphorylation of caspase-9 during hypoxia. Inhibition of AKT and ERK1/2 activation by the treatments with phosphatidylinositol 3'-kinase and mitogen-activated protein kinase kinase (MEK)1/2 inhibitors sensitized C2C12/APIP cells to hypoxic cell death and abolished the hypoxia-induced phosphorylation of caspase-9. Further, overexpression of phosphorylation-mimic caspase-9 mutants (caspase-9-T125E and caspase-9-S196D), but not phosphorylation-defective caspase-9 mutants (caspase-9-T125A and caspase-9-S196A), effectively suppressed hypoxia-induced death of C2C12 cells. These results elucidate a novel Apaf-1-independent antiapoptotic activity of APIP during hypoxic cell death, inducing the sustained activation of AKT and ERK1/2 and leading to caspase-9 phosphorylation.

Capsaicin can alter the expression of tumor forming-related genes which might be followed by induction of apoptosis of a Korean stomach cancer cell line, SNU-1.

Capsaicin (CAP) has been known to inhibit some tumor development in vivo (J.J. Jang, S.H. Kim, T.K. Yun, Inhibitory effect of capsaicin on mouse lung tumor development, in vivo, J. Korean Med. Sci. 3 (1989) 49-53; J.J. Jang, K.J. Cho, Y.S. Lee, J.H. Bae, Different modifying responses of capsaicin in a wide-spectrum initiation model of F344 rat, J. Korean Med. 6 (1991) 31-36) [1,2] even though its mechanism of action is not well understood. The objectives of this study were to examine the effect of CAP on expression of tumor forming-related genes in a Korean stomach tumor cell, SNU-1. We used slot blot hybridization to investigate its effect on a wide spectrum of proto-oncogenes. It was found that CAP enhanced the transcripts of two proto-oncogenes (c-myc and c-Ha-ras) and tumor suppressor gene p53. While a low concentration of CAP (0.01 microM) did not significantly increase the level of p53 transcript in SNU-1, it did increase it by a factor of 3.5 at a 10 microM dose of CAP. Consequently, SNU-1 cells are sensitive to CAP in the overexpression of tumor suppressor gene, p53 and proto-oncogenes, c-myc and c-Ha-ras, but not those of c-erbB-2, c-jun and bcl-2 genes. Both cell death and DNA fragmentation were shown in SNU-1 cells with treatment of CAP. Our results suggest that CAP induces apoptotic cell death in human gastric cancer cells (SNU-1) in vitro which may be possibly mediated by the overexpression of p53 and/or c-myc genes. Because cell suicide is arguably the most potent natural defense against cancer, the correlation between the induction of apoptosis and the change of tumor forming-related gene expression after CAP treatment should be further studied in detail.