Protein Kinase A-regulated Instability Site in the 3′-Untranslated Region of Lactate Dehydrogenase-A Subunit mRNA

Expression of the lactate dehydrogenase A subunit (LDH-A) gene can be controlled by transcriptional as well as posttranscriptional mechanisms. In rat C6 glioma cells, LDH-A mRNA is stabilized by activation and synergistic interaction of protein kinases A and C. In the present study, we aimed to identify the sequence domain which determines and regulates mRNA stability/instability by protein kinase A and focused our attention on the 3′-untranslated region (3′-UTR) of LDH-A mRNA. We have constructed various chimeric globin/lactate dehydrogenase (ldh) genes linked to the c- fos promoter and stably transfected them into rat C6 glioma cells. After their transfection, we determined the half-life of transcribed chimeric globin/ldh mRNAs. The results showed that at least three sequence domains within the LDH-A 3′-UTR consisting of nucleotides 1286–1351, 1453–1471, and 1471–1502 are responsible for the relatively rapid rate of LDH-A mRNA turnover in the cytoplasm. Whereas chimeric globin/ldh mRNAs containing the base sequences 1286–1351 and 1453–1471 were not stabilized by ( S p )-cAMPS, an activator of protein kinase A, instability caused by the 1471–1502 domain was significantly reversed. Additional deletion and mutational analyses demonstrated that the 3′-UTR fragment consisting of the 22 bases 1478–1499 is a critical determinant for the ( S p )-cAMPS-mediated LDH-A mRNA stabilizing activity. Because of its functional characteristics, we named the 22-base region “cAMP-stabilizing region.”