Effects of dibutyryl cAMP and bacterial toxins on indoleamine-induced encystment of dinoflagellates.
Dinoflagellates are the causative agents of red tides with worldwide occurrence and can be induced to encyst by in doleamines such as melatonin and 5-methoxytryptamine (5-MOT). This biological response may be mediated via indoleamine-binding proteins or receptors. Here we report the initial characterization of the signal transduction mechanisms by which indoleamines induce encystment of dinoflagellates. In particular, we explored the possible involvement of G proteins and cAMP in cyst formation. Both melatonin and 5-MOT promoted the encystment of Gonyaulax tamarensis and Crypthecodinium cohnii. Exposure of dinoflagellates to dibutyryl cAMP, which directly activates cAMP-dependent pathways, did not affect the ability of indoleamines to promote encystment. However, dibutyryl cAMP dose-dependently diminished the indoleamine-induced suppression of cell growth. Exposure of dinoflagellates to the bacterial toxins from Vibrio cholerae and Bordetella pertussis had no effect on the indoleamine-induced encystment response, indicating the lack of involvement of Gs or Gi-like proteins. Moreover, [32P]ADP ribosylation of dinoflagellate membranes by either toxin failed to identify substrate proteins. These results suggest that although the indoleamine-induced encystment of dinoflagellates may involve a G-protein-coupled signal transduction pathway, the identity of the G protein concerned may be distinct from those that regulate adenylyl cyclases in mammalian cells.
Tsim
S T
ST
Department of Biology, Hong Kong University of Science, Kowloon, Hong Kong.
Wong
J T
JT
Wong
Y H
YH
D008735:5-Methoxytryptamine / Q000494:pharmacology; D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D037361:Adenylate Cyclase Toxin; D000818:Animals; D001345:Autoradiography; D001427:Bacterial Toxins / Q000494:pharmacology*; D003994:Bucladesine / Q000494:pharmacology*; D002460:Cell Line; D002772:Cholera Toxin / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004141:Dinoflagellida / Q000187:drug effects*; D019204:GTP-Binding Proteins / Q000378:metabolism; D008550:Melatonin / Q000494:pharmacology; D051379:Mice; D037342:Pertussis Toxin; D015398:Signal Transduction / Q000187:drug effects; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D001427:Bacterial Toxins; D010566:Virulence Factors, Bordetella; D005576:Colforsin; D000246:Adenosine Diphosphate Ribose; D008735:5-Methoxytryptamine; D003994:Bucladesine; D002772:Cholera Toxin; D000242:Cyclic AMP; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D008550:Melatonin