EFFECTS OF THE N-TERMINAL CYSTEINE MUTATION ON PROLACTIN EXPRESSION AND SECRETION IN TRANSFECTED CELLS

We developed an experimental cell model to look for motif(s) of rat PR L sequence encoding a sorting signal to secretory granules. An efficie nt expression vector (pCMV-rPRL) was used to transfect several eukaryo tic cell lines in culture, i.e., one neuronal cell line (C6) and three glandular pituitary derived cell lines (AtT20, GC, GH3CDL). Despite t he ubiquitous transcription of pCMV-rPRL, the synthesis and secretion of rPRL were detected primarily in GH3CDL cells that derived from lact otrophs, suggesting a cell-specific post-transcriptional control of rP RL expression. During transient expression, exogenous native PRL was t ransported through intracellular compartments of the secretory pathway and underwent regulated release. Abolition by mutagenesis (C4S) of th e N-terminal disulfide bond increased by 50% the PRL secretion rate (m edium to cell ratio) and multiplied by 5 the specific activity of medi um PRL from pulse-labeled cells. These results support the hypothesis that N-terminal disulfide bond plays a role in the control of PRL intr acellular transit and storage.