ACTIVATION OF GENE-TRANSCRIPTION BY TILAPIA PROLACTIN VARIANTS TIPRL188 AND TIPRL177

In the tilapia species Oreochromis niloticus, the pituitary releases t wo forms of prolactins (tiPRL(188) and tiPRL(177)) The binding paramet ers and the activation of tiPRL-induced JAK2/Stat5 signalling pathway were analysed using a mammalian cell line transiently transfected with the tiPRL receptor (tiPRLR). Our data indicate that the tiPRLR is abl e to mediate transcriptional activation of the PRL responsive element, At nanomolar concentrations, tiPRL(188) activates gene transcription whereas at micromolar concentrations it inhibits luciferase transcript ion from the lactogenic responsive element. This is consistent with a model of receptor dimerisation, In contrast, the activation by tiPRL17 7 was only reached at high (mu M) concentrations. The transcriptional activities induced by tiPRL(177) and tiPRL(188) are discussed in the c ontext of the physiology of these hormones. (C) 1998 Federation of Eur opean Biochemical Societies.