Cold stress defense in the freshwater sponge Lubomirskia baicalensis. Role of okadaic acid produced by symbiotic dinoflagellates.
The endemic freshwater sponge Lubomirskia baicalensis lives in Lake Baikal in winter (samples from March have been studied) under complete ice cover at near 0 degrees C, and in summer in open water at 17 degrees C (September). In March, specimens show high metabolic activity as reflected by the production of gametes. L. baicalensis lives in symbiosis with green dinoflagellates, which are related to Gymnodinium sanguineum. Here we show that these dinoflagellates produce the toxin okadaic acid (OA), which is present as a free molecule as well as in a protein-bound state. In metazoans OA inhibits both protein phosphatase-2A and protein phosphatase-1 (PP1). Only cDNA corresponding to PP1 could be identified in L. baicalensis and subsequently isolated from a L. baicalensis cDNA library. The deduced polypeptide has a molecular mass of 36 802 Da and shares the characteristic domains known from other protein phosphatases. As determined by western blot analysis, the relative amount of PP1 is almost the same in March (under ice) and September (summer). PP1 is not inhibited by low OA concentrations (100 nm); concentrations above 300 nm are required for inhibition. A sponge cell culture system (primmorphs) was used to show that at low temperatures (4 degrees C) expression of hsp70 is strongly induced and hsp70 synthesis is augmented after incubation with 100 nm OA to levels measured at 17 degrees C. In the enriched extract, PP1 activity at 4 degrees C is close to that measured at 17 degrees C. Immunoabsorption experiments revealed that hsp70 contributes to the high protein phosphatase activity at 4 degrees C. From these data we conclude that the toxin OA is required for the expression of hsp70 at low temperature, and therefore contributes to the cold resistance of the sponge.
Müller
Werner E G
WE
Institut für Physiologische Chemie, Abteilung Angewandte Molekularbiologie, Universität Mainz, Germany. wmueller@uni-mainz.de
Belikov
Sergey I
SI
Kaluzhnaya
Oxana V
OV
Perović-Ottstadt
Sanja
S
Fattorusso
Ernesto
E
Ushijima
Hiroshi
H
Krasko
Anatoli
A
Schröder
Heinz C
HC
D000595:Amino Acid Sequence; D000818:Animals; D020134:Catalytic Domain; D003080:Cold Temperature; D018076:DNA, Complementary / Q000737:chemistry; D004141:Dinoflagellida / Q000378:metabolism / Q000502:physiology*; D005618:Fresh Water; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D046529:Microscopy, Electron, Transmission; D008954:Models, Biological; D008969:Molecular Sequence Data; D019319:Okadaic Acid / Q000378:metabolism / Q000494:pharmacology*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D011161:Porifera / Q000502:physiology*; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; D013559:Symbiosis / Q000502:physiology*
D018076:DNA, Complementary; D018840:HSP70 Heat-Shock Proteins; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2