Periodic expression of an ecdysteroid-induced nuclear receptor in a lepidopteran cell line (IAL-PID2)

A set of DNA primers was designed within the DNA-binding domain of the Mand uca hormone receptor 3 (MHR3) cDNA. These primers were used in RT-PCR to is olate a 204 by cDNA fragment from IAL-PID2 cells exposed to 10(-6) M 20-hyd roxyecdysone (20E) for 12 h. The amino acid sequence deduced from the cDNA fragment presented 100% identity with the zinc finger domain of Manduca hor mone receptor 3 (MHR3), Galleria hormone receptor 3 (GHR3) and Choristoneur a hormone receptor 3 (CHR3). This cDNA fragment was used as a probe on tota l RNA from IAL-PID2 cells exposed to 20E and hybridized to mRNA, the size o f which was close to 4.5 kb and named Plodia hormone receptor 3 (PHR3). Kin etics of induction of PHR3 mRNA were similar to that of HR3 genes but varie d according to the position of cells in their cell cycle. The non-steroidal ecdysone agonist, RH-5992 induced the expression of PHR3 at lower concentr ations than 20E. From sequence similarity, mRNA size, 20E and RH-5992 induc ibilities, we conclude that PHR3 transcript could encode a Plodia hormone r eceptor 3 involved in the genetic signalling cascade of 20E. Thanks to its periodic expression, this putative orphan nuclear receptor could serve as a suitable cellular marker for studying changes of epidermal cell sensitivit y to 20E during the cell cycle. (C) 2001 Elsevier Science Ltd. All rights r eserved.