Regulation of translation by upstream translation initiation codons of surfactant protein A1 splice variants.
Surfactant protein A (SP-A), a molecule with roles in lung innate immunity and surfactant-related functions, is encoded by two genes in humans: SFTPA1 (SP-A1) and SFTPA2 (SP-A2). The mRNAs from these genes differ in their 5'-untranslated regions (5'-UTR) due to differential splicing. The 5'-UTR variant ACD' is exclusively found in transcripts of SP-A1, but not in those of SP-A2. Its unique exon C contains two upstream AUG codons (uAUGs) that may affect SP-A1 translation efficiency. The first uAUG (u1) is in frame with the primary start codon (p), but the second one (u2) is not. The purpose of this study was to assess the impact of uAUGs on SP-A1 expression. We employed RT-qPCR to determine the presence of exon C-containing SP-A1 transcripts in human RNA samples. We also used in vitro techniques including mutagenesis, reporter assays, and toeprinting analysis, as well as in silico analyses to determine the role of uAUGs. Exon C-containing mRNA is present in most human lung tissue samples and its expression can, under certain conditions, be regulated by factors such as dexamethasone or endotoxin. Mutating uAUGs resulted in increased luciferase activity. The mature protein size was not affected by the uAUGs, as shown by a combination of toeprint and in silico analysis for Kozak sequence, secondary structure, and signal peptide and in vitro translation in the presence of microsomes. In conclusion, alternative splicing may introduce uAUGs in SP-A1 transcripts, which in turn negatively affect SP-A1 translation, possibly affecting SP-A1/SP-A2 ratio, with potential for clinical implication.
['Tsotakos|Nikolaos|N|', 'Silveyra|Patricia|P|', 'Lin|Zhenwu|Z|', 'Thomas|Neal|N|', 'Vaid|Mudit|M|', 'Floros|Joanna|J|']
D017398:Alternative Splicing D000893:Anti-Inflammatory Agents D045744:Cell Line, Tumor D018387:Codon, Initiator D003907:Dexamethasone D004731:Endotoxins D005091:Exons D005260:Female D006801:Humans D008168:Lung D008297:Male D008861:Microsomes D009154:Mutation D021382:Protein Sorting Signals D037662:Pulmonary Surfactant-Associated Protein A D012333:RNA, Messenger
uAUG ribosome binding site scanning mechanism translation regulation