ALTERNATIVELY POLYADENYLATED VASOACTIVE-INTESTINAL-PEPTIDE MESSENGER-RNAS ARE DIFFERENTIALLY REGULATED AT THE LEVEL OF STABILITY

The role of cis-acting destabilizing RNA sequences in the determinatio n of endocrine gene expression has been investigated using a novel par adigm, in which the differential regulation of two alternatively polya denylated RNA transcripts may be observed both in vivo and in vitro. I n the rat anterior pituitary gland in vivo, we have shown that, after the termination of an estrogen stimulus, a 1.7-kilobase (kb) vasoactiv e intestinal peptide (VIP) RNA containing an extensive 3'-untranslated region (UTR), is preferentially down-regulated with respect to a 1.0 kb VIP transcript that is uniquely abundant in this tissue. Differenti al regulation of the anterior pituitary VIP transcripts can be modeled in an explant culture system in which we defined both transcriptional and posttranscriptional phases of VIP gene regulation in vitro, and s howed that selective down-regulation of the 1.7-kb transcript is postt ranscriptional. Inhibitors of transcription and translation have also allowed us to show in vitro that differential regulation of VIP transc ripts occurs through an active process that appears to involve the syn thesis of a labile, destabilizing factor. In order to confirm the role of RNA destabilization as the primary mechanism of differential postt ranscriptional regulation, we have also performed cell-free stability assays in which explant extracts were incubated with P-32-labeled run- off transcripts corresponding to the two alternatively polyadenylated VIP RNAs. The resultant estimates of RNA half-life showed significantl y lower values for the synthetic VIP transcript containing the 3'-UTR. Our findings demonstrate the presence of functional destabilizing seq uences in the 3'-UTR of the rat VIP RNA which appear to act in the phy siological control of VIP gene expression.