Suppression of Extracellular Signal-related Kinase and Activation of p38 MAPK Are Two Critical Events Leading to Caspase-8- and Mitochondria-mediated Cell Death in Phytosphingosine-treated Human Cancer Cells

Abstract

We previously demonstrated that the phytosphingosine-induced apoptosis was accompanied by the concomitant induction of both the caspase-8-mediated and mitochondrial activation-mediated apoptosis pathways. In the present study, we investigated the role of mitogen-activated protein kinases (MAPKs) in the activation of these two distinct cell death pathways induced by phytosphingosine in human cancer cells. Phytosphingosine caused strong induction of caspase-8 activity and caspase-independent Bax translocation to the mitochondria. A rapid decrease of phosphorylated ERK1/2 and a marked increase of p38 MAPK phosphorylation were observed within 10 min after phytosphingosine treatment. Activation of ERK1/2 by pretreatment with phorbol 12-myristate 13-acetate or forced expression of ERK1/2 attenuated phytosphingosine-induced caspase-8 activation. However, Bax translocation and caspase-9 activation was unaffected, indicating that down-regulation of the ERK activity is specifically required for the phytosphingosine-induced caspase-8-dependent cell death pathway. On the other hand, treatment with SB203580, a p38 MAPK-specific inhibitor, or expression of a dominant negative form of p38 MAPK suppressed phytosphingosine-induced translocation of the proapoptotic protein, Bax, from the cytosol to mitochondria, cytochrome c release, and subsequent caspase-9 activation but did not affect caspase-8 activation, indicating that activation of p38 MAPK is involved in the mitochondrial activation-mediated cell death pathway. Our results suggest that phytosphingosine can utilize two different MAPK signaling pathways for amplifying the apoptosis cascade, enhancing the understanding of the molecular mechanisms utilized by naturally occurring metabolites to regulate cell death. Molecular dissection of the signaling pathways that activate the apoptotic cell death machinery is critical for both our understanding of cell death events and development of cancer therapeutic agents.

p38 MAPK as a negative regulator of VEGF/VEGFR2 signaling pathway in serum deprived human SK-N-SH neuroblastoma cells

“…3B) and cell death (Fig. 1B) is also consistent with reports showing that a downregulation in ERK1/2 activation accompanies p38 MAPK-mediated apoptosis in both neuronal and nonneuronal cells [17,20,24].…”

Combination treatment with arsenic trioxide and phytosphingosine enhances apoptotic cell death in arsenic trioxide–resistant cancer cells

“…Western Blot Analysis Western blot analysis was done as described (22). Briefly, cell lysates were prepared by extracting proteins with lysis buffer [40 mmol/L Tris-HCl (pH 8), 120 mmol/L NaCl, 0.1% NP40] supplemented with protease inhibitors.…”

Inactivation of CaMIT1 Inhibits Candida albicans Phospholipomannan β-Mannosylation, Reduces Virulence, and Alters Cell Wall Protein β-Mannosylation

“…One explanation for PLM-induced yeast survival is the induction of mitochondrial apoptosis (15) initiated by p90 dephosphorylation (46). Interestingly, among the molecules that can trigger such an apoptotic effect are yeast phytosphingosines (47), which are lipid moieties of C. albicans PLM (10). It is possible that the mit1⌬ cell wall defects may render this mutant more sensitive to phagocytosis.…”