Evidence that a wortmannin-sensitive signal transduction pathway regulates aflatoxin biosynthesis.
A signal transduction pathway involving cAMP and protein kinase A (PKA) regulates aflatoxin accumulation and nor-1 and ver-1 (aflatoxin structural genes) promoter function in Aspergillus parasiticus by modulating expression of a key transcriptional activator, AflR. To understand the function of this pathway in greater detail we treated A. parasiticus in culture with wortmannin, a frequently used probe of phosphatidyl inositol (PI)-3 kinase activity. A. parasiticus D8D3 (nor-1::GUS reporter) and I4 (ver-1::GUS reporter) were grown on a defined solid growth medium (GMS agar) under aflatoxin-inducing conditions. GMS containing wortmannin (1 microM) reduced aflatoxin B1 accumulation up to 15-fold accompanied by a similarly large decrease in ver-1 and nor-1 promoter activity. Wortmannin inhibited growth (colony diameter) and asexual sporulation but to a much smaller extent. Wortmannin treatment increased intracellular cAMP levels up to 25-fold; total PKA activity also increased within 10 min of wortmannin exposure. These data support a regulatory model in which PI-3 kinase activity modulates intracellular cAMP accumulation and PKA activity. This in turn regulates AflR expression and activity, aflatoxin gene expression and aflatoxin accumulation.
Lee
Joo-Won
JW
Department of Pharmacology, Institute of Biomedical Science, Hanyang University, Seoul, South Korea.
Roze
Ludmila V
LV
Linz
John E
JE
D016604:Aflatoxin B1 / Q000096:biosynthesis*; D000730:Androstadienes / Q000378:metabolism / Q000494:pharmacology*; D001230:Aspergillus / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D000242:Cyclic AMP / Q000235:genetics / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D009183:Mycotoxins / Q000378:metabolism / Q000494:pharmacology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D015398:Signal Transduction / Q000187:drug effects*; D000077191:Wortmannin
D000730:Androstadienes; D005656:Fungal Proteins; D009183:Mycotoxins; D000081082:Phosphoinositide-3 Kinase Inhibitors; D016604:Aflatoxin B1; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D000077191:Wortmannin