Developmental regulation of the translational repressor NAT1 during cardiac development

The process of translation initiation has been postulated to play an import ant role in the regulation of cellular growth and proliferation. Here, We r eport the identification and differential expression of a fundamental trans lational repressor NAT1, during early postnatal cardiac development. Differ ential display analysis of RNA obtained from 3-day and 4-week-old rat heart s: resulted in the cloning and identification of a 396 bp cDNA fragment (DR CF-6) which corresponded to the 3' terminal portion of NAT1. Northern blot analysis revealed that the mRNA expression of NAT1 was markedly elevated du ring the first 2 weeks of postnatal life. with an apparent peak level of ex pression occurring at 1 week. NAT1 mRNA levels then steadily decreased to 4 weeks of age. The NAT1 transcript has previously been shown to be extensiv ely edited by the enzyme APOBEC-1, which deaminates specific cytidine bases to uridine, cytidine deamination at a glutamine codon (CAA) results in the formation of a stop codon (UAA) and consequently. premature termination of translation. Accordingly, Western blot analysis detected the presence of s everal smaller proteins in addition to the full length NAT1 protein (97 kDa ), each exhibiting a distinct pattern of expression during cardiac developm ent. APOBEC-1 editing of NAT1 during cardiac development was further suppor ted by primer extension analysis of cytidine 1699, which was found to be pr edominantly edited to uridine. Immunohistochemical staining showed that NAT 1 is expressed predominantly in atrial and ventricular myocytes, although s taining was also detected in vascular smooth muscle cells and in the endoca rdium. These results suggest that NAT1 may play a role in the postnatal dev elopment of the heart and demonstrate that APOBEC-1 editing may possibly be a novel mechanism by which translation is regulated during cardiac develop ment. (C) 1999 Academic Press.