EVIDENCE FOR ALTERNATIVE SPLICING IN HEPATIC ALPHA(1B)-ADRENERGIC RECEPTOR GENE-EXPRESSION

The interactions of catecholamines with alpha(1B)-adrenergic receptors (alpha(1B)-AR) located on the surface of many cell types are responsi ble for physiologic and pathologic functions in mammalian systems. Tra nscription of the alpha(1B)-AR gene leads to the expression of multipl e alpha(1B)-AR mRNAs that are distributed in a tissue-specific fashion . The purpose of this study was to define the 5'-untranslated regions of the multiple alpha(1B)-AR gene transcripts. Evidence for a previous ly unidentified intron in the alpha(1B)-AR gene upstream of the recept or open reading frame was obtained via rapid amplification of cDNA end s. A product was amplified and was found to be missing the nucleotide interval from -708 to -194, (+1 is the start of translation). Evidence for tissue-specific alternative intron splicing was obtained from rib onuclease protection assays and RT-PCR experiments. Using an RNA probe extending from -240 to +93 and including 45 nucleotides into the puta tive intron, a single protected fragment was detected in heart RNA whi le two protected fragments were detected in liver RNA. RT-PCR amplific ation of the region spanning the intron resulted in detection of two P CR products in liver RNA and no detectable product in heart RNA. These findings emphasize the complexity of alpha(1B)-AR gene regulation and suggest that multiple alpha(1B)-AR mRNAs with different 5'-UTRs may p lay a role in regulating alpha(1B)-adrenergic responsiveness.