CERAMIDE-ACTIVATED PROTEIN PHOSPHATASE-2A ACTIVITY IN INSULIN-SECRETING CELLS

Okadaic acid (OKA)-sensitive phosphatase (PP2A) activity may modulate nutrient-induced insulin secretion front pancreatic beta cells [Kowlur u et al., Endocrinology 137 (1996) 2315-2323]. Ceramides, a new class of lipid second messengers may regulate PP2A [Dobrowsky and Hannun, J. Biol, Chem, (1992) 267, 5048-5051], and might play a role in cytokine -mediated apoptosis in beta cells [Sjoholm, FEBS Lett. 367 (1995) 283- 286]. Therefore, we investigated the regulation of PP2A-like activity by ceramides in isolated beta (HIT-T15 or INS-1) cells, Cell-permeable (C2, C6 or C18) ceramides stimulated OKA-sensitive (but not -insensit ive) phosphatase activity in a concentration-dependent manner (0-12.5 mu M), with maximal stimulation (+50-100%) at < 12.5 mu M. C2-dihydroc eramide (a biologically inactive analog of C2 ceramide) failed to augm ent PP2A-like activity, Stimulatory effects of ceramides do not appear to be mediated via activation of the carboxyl methylation of the cata lytic subunit of protein phosphatase 2A, since no effects of ceramides (up to 25 mu M) mere demonstrable on this parameter, These data ident ify a ceramide-activated protein phosphatase as a possible locus at wh ich ceramides might exert their effects on beta cells leading to alter ed insulin secretion, and decreased cell viability followed by apoptot ic cell demise. (C) 1997 Federation of European Biochemical Societies.