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Synergistic activation of type III protein kinase C by cis-fatty acid and diacylglycerol.

ABSTRACT: Micromolar concentrations of cis-fatty acid synergistically activate type III protein kinase C with diacylglycerol. This synergistic effect occurs at low concentrations of cis-fatty acid and diacylglycerol, and it is capable of inducing almost full activation of this protein kinase C subtype at a physiologically relevant Ca2+ concentration (2 microM). The synergistic activation mode can be observed even in the absence of Ca2+, but micromolar Ca2+ significantly enhances the type III protein kinase C activation. cis-Fatty acid also augments the diacylglycerol-induced activation of other subtypes (type I and II), although the effect is smaller than that observed in type III. Neither the diacylglycerol- nor the cis-fatty acid-dependent mode of activation can fully activate any of these subtypes at a physiological concentration of Ca2+ (2 microM). Our results suggest that the generation of three second messengers, i.e. the increase in intracellular Ca2+ concentration and the generation of both cis-fatty acid and diacylglycerol in the cell, may be necessary signals for protein kinase C activation, particularly for type III protein kinase C.

SUBMITTER: Chen SG

PROVIDER: S-EPMC1130886 | biostudies-other | 1992 Feb

REPOSITORIES: biostudies-other

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Project description:Claviceps purpurea, the fungal pathogen that causes the cereal disease ergot, produces glycerides that contain high levels of ricinoleic acid [(R)-12-hydroxyoctadec-cis-9-enoic acid] in its sclerotia. Recently, a fatty acid hydroxylase (C. purpurea FAH [CpFAH]) involved in the biosynthesis of ricinoleic acid was identified from this fungus (D. Meesapyodsuk and X. Qiu, Plant Physiol. 147:1325-1333, 2008). Here, we describe the cloning and biochemical characterization of a C. purpurea type II diacylglycerol acyltransferase (CpDGAT2) involved in the assembly of ricinoleic acid into triglycerides. The CpDGAT2 gene was cloned by degenerate RT-PCR (reverse transcription-PCR). The expression of this gene restored the in vivo synthesis of triacylglycerol (TAG) in the quadruple mutant strain Saccharomyces cerevisiae H1246, in which all four TAG biosynthesis genes (DGA1, LRO1, ARE1, and ARE2) are disrupted. In vitro enzymatic assays using microsomal preparations from the transformed yeast strain indicated that CpDGAT2 prefers ricinoleic acid as an acyl donor over linoleic acid, oleic acid, or linolenic acid, and it prefers 1,2-dioleoyl-sn-glycerol over 1,2-dipalmitoyl-sn-glycerol as an acyl acceptor. The coexpression of CpFAH with CpDGAT2 in yeast resulted in an increased accumulation of ricinoleic acid compared to the coexpression of CpFAH with the native yeast DGAT2 (S. cerevisiae DGA1 [ScDGA1]) or the expression of CpFAH alone. Northern blot analysis indicated that CpFAH is expressed solely in sclerotium cells, with no transcripts of this gene being detected in mycelium or conidial cells. CpDGAT2 was more widely expressed among the cell types examined, although expression was low in conidiospores. The high expression of CpDGAT2 and CpFAH in sclerotium cells, where high levels of ricinoleate glycerides accumulate, provided further evidence supporting the roles of CpDGAT2 and CpFAH as key enzymes for the synthesis and assembly of ricinoleic acid in C. purpurea.

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Synergistic activation of type III protein kinase C by cis-fatty acid and diacylglycerol.

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