Mode of action of the ecdysone agonist tebufenozide (RH-5992), and an exclusion mechanism to explain resistance to it.
Spruce budworm larvae (Choristoneura fumiferana) upon ingesting tebufenozide (RH-5992) stop feeding and go into a precocious, incomplete molt, leading eventually to death. Like 20-hydroxyecdysone (20E), tebufenozide also acts at the receptor level and transactivates the expression of up-regulated genes but, because of its persistence, the down-regulated genes that are normally expressed in the absence of 20E are not expressed. While tebufenozide is lepidopteran-specific, an analog, RH-5849, is effective on dipterans. This is reflected in the respective effects of the two compounds on Cf-203 (C. fumiferana--203), a lepidopteran cell line and Dm-2 (Drosophila melanogaster--2), a dipteran cell line. Cf-203 cells accumulated [14C]tebufenozide and expressed CHR3 (Choristoneura hormone receptor 3), but Dm-2 cells excluded the material and did not express DHR3 (Drosophila hormone receptor 3). Using yeast ABC (ATP binding cassette) transporter mutants, we determined that PDR5 (pleiotropic drug resistance 5) was responsible for the exclusion. We discovered recently that older instars of the white-marked tussock moth (Orgyia leucostigma) are resistant to tebufenozide, perhaps as a result of such an exclusion system. We are currently cloning PDR5 (pleiotropic drug resistance 5), which is an essential step in studying the resistance mechanism.
Retnakaran
A
A
Forest Biotechnology Division, Great Lakes Forestry Centre, Canadian Forest Service, Sault Ste Marie, Ontario, P6A 2E5, Canada. aretnak@nrcan.gc.ca
Gelbic
I
I
Sundaram
M
M
Tomkins
W
W
Ladd
T
T
Primavera
M
M
Feng
Q
Q
Arif
B
B
Palli
R
R
Krell
P
P
D000818:Animals; D002460:Cell Line; D004268:DNA-Binding Proteins; D004175:Diptera / Q000033:anatomy & histology / Q000187:drug effects / Q000648:ultrastructure; D004440:Ecdysone / Q000819:agonists* / Q000031:analogs & derivatives / Q000737:chemistry; D005786:Gene Expression Regulation / Q000187:drug effects; D006834:Hydrazines / Q000378:metabolism / Q000494:pharmacology*; D007300:Insect Control; D019476:Insect Proteins; D007305:Insecticide Resistance; D007306:Insecticides / Q000378:metabolism / Q000494:pharmacology*; D007605:Juvenile Hormones / Q000819:agonists; D007915:Lepidoptera / Q000033:anatomy & histology / Q000187:drug effects / Q000648:ultrastructure; D008854:Microscopy, Electron; D018978:Molting / Q000187:drug effects; D009154:Mutation; D010641:Phenotype; D018010:Receptors, Invertebrate Peptide / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000502:physiology; D013045:Species Specificity; D015534:Trans-Activators
C104701:CHR3 protein, Choristoneura fumiferana; D004268:DNA-Binding Proteins; D006834:Hydrazines; D019476:Insect Proteins; D007306:Insecticides; D007605:Juvenile Hormones; D018010:Receptors, Invertebrate Peptide; D015534:Trans-Activators; D004440:Ecdysone; C082026:tebufenozide