Ceramide-dependent regulation of p42/p44 mitogen-activated protein kinase and c-Jun N-terminal-directed protein kinase in cultured airway smooth muscle cells

Previous studies have demonstrated that a number of biochemical actions of ceramide are mediated through protein kinase signalling pathways, such as p 42/p44 mitogen-activated protein kinase (p42/p44 MAPK) and c-Jun N-terminal directed protein kinase (JNK). Ceramide-activated protein kinases, such as the kinase suppressor of Ras (KSR) and protein kinase C zeta (PKC zeta), a re involved in the regulation of c-Raf, which promotes sequential activatio n of MEK-1 and p42/p44 MAPK in mammalian cells. However, in cultured airway smooth muscle (ASM) cells, neither KSR nor PKC zeta are involved in the C2 -ceramide (C2-Cer)-dependent activation of this kinase cascade. Instead, we found that C2-Cer utilises a novel pathway involving tyrosine kinases, pho sphoinositide 3-kinase (PI3K) and conventional PKC isoform(s). We also foun d that despite its ability to stimulate p42/p44 MAPK, C2-Cer inhibited plat elet-derived growth factor (PDGF)stimulated DNA synthesis. The possibility that growth arrest could be mediated by JNK was discounted on the basis tha t PDGF, as well as ceramide, stimulated JNK in these cells. Therefore, grow th arrest in response to ceramide is mediated by an alternative mechanism. (C) 2000 Elsevier Science Inc. All rights reserved.