Polyunsaturated fatty acids do not activate protein kinase C in the testis of the goldfish (Carassius auratus) |
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Authors: | Michael G Wade Patrice M Jacobson Glen Van Der Kraak |
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Institution: | (1) Department of Zoology, University of Guelph, Guelph Ontario, Canada, N1G 2W1, Canada |
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Abstract: | Earlier studies have established that polyunsaturated fatty acids (PUFA) such as eicosapentaenoic acid and docosahexaenoic
acid inhibit steroid production in the goldfish testis. As PUFA inhibit testicular steroidogenesis in the rat through activation
of protein kinase C (PKC), the present studies were undertaken to characterize the properties of PKC in the goldfish testis
and to test the effects of selected PUFA on PKC activity. PKC activity was quantified in goldfish testis homogenate following
partial purification by DEAE-cellulose chromatography by determining the transfer of radiolabelled phosphate from γ - 32P]ATP to histone III-S. Testicular PKC activity was defined by the amount of protein phosphorylation in the presence of phosphatidylserine,
phasphatidylcholine, Ca2+ ions and diolein (a 1,2-diacylglycerol analog) above that obtained in response to Ca2+ ions alone. Western blot analysis of a crude testis homogenate using an antibody specific to the α and β isoforms of mammalian
PKC led to the identification a single band of protein (80 kD) that co-migrated with PKC from rabbit brain cytosol. Addition
of arachidonic, eicosapentaenoic or docosahexaenoic acids failed to activate PKC. However, PKC activity stimulated by phospholipid,
Ca2+ ions and diolein was inhibited in a dose related fashion by all of these fatty acids. These studies suggest that the inhibitory
effects of EPA and DHA on testicular steroidogenesis are not mediated by activation of PKC. The lack of effect of PUFA on
PKC activity in the goldfish testis suggests that either the distribution of PKC isoforms differs between the testis of mammals
and fish or that PKC is not activated by PUFA in the goldfish. |
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Keywords: | goldfish arachidonic acid eicosapentaenoic acid protein kinase C testis PKC activation polyunsaturated fatty acids phosphorylation activity |
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