PROTEIN-KINASE A-REGULATED INSTABILITY SITE IN THE 3'-UNTRANSLATED REGION OF LACTATE DEHYDROGENASE-A SUBUNIT MESSENGER-RNA

Expression of the lactate dehydrogenase A subunit (LDH-A) gene can be controlled by transcriptional as well as posttranscriptional mechanism s, In rat C6 glioma cells, LDH-A mRNA is stabilized by activation and synergistic interaction of protein kinases A and C, In the present stu dy, we aimed to identify the sequence domain which determines and regu lates mRNA stability/instability by protein kinase A and focused our a ttention 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 lea st three sequence domains within the LDH-A 3'-UTR consisting of nucleo tides 1286-1351, 1453-1471, and 1471-1502 are responsible for the rela tively rapid rate of LDH-A mRNA turnover in the cytoplasm, Whereas chi meric globin/ldh mRNAs containing the base sequences 1286-1351 and 145 3-1471 were not stabilized by (S-p)-cAMPS, an activator of protein kin ase A, instability caused by the 1471-1502 domain was significantly re versed. 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 activ ity, Because of its functional characteristics, we named the 22-base r egion ''cAMP-stabilizing region.''