Ribosome readthrough accounts for secreted full-length factor IX in hemophilia B patients with nonsense mutations

• Published in: Human mutation Vol. 33; no. 9; pp. 1373 - 1376
• Main Authors: Pinotti, Mirko, Caruso, Pierpaolo, Canella, Alessandro, Campioni, Matteo, Tagariello, Giuseppe, Castaman, Giancarlo, Giacomelli, Sofia, Belvini, Donata, Bernardi, Francesco
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.09.2012; Hindawi Limited
• Subjects: Blotting, Western; coagulation factor; Codon, Nonsense - genetics; Factor IX - genetics; Factor IX - metabolism; Half-Life; Hemophilia B - genetics; Hemophilia B - metabolism; Humans; Mutagenesis, Site-Directed; nonsense mutations; Predictive Value of Tests; readthrough; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; ribosome; Ribosomes - genetics; Ribosomes - metabolism; RNA Stability; RNA, Messenger - genetics; RNA, Messenger - metabolism
• ISSN: 1059-7794; 1098-1004
• DOI: 10.1002/humu.22120

We investigated the spontaneous ribosome readthrough, virtually unexplored in genes encoding secreted proteins, over coagulation F9 nonsense mutations. Expression of recombinant factor IX (FIX) in eukaryotic cells demonstrated appreciable levels of secreted FIX molecules for the mutations p.R162* (5 ± 0.3% of rFIX‐wt antigen levels), p.R294* (3.1 ± 1.1%) and p.R298* (2.5 ± 0.7%), but not for the p.L103*. Western blotting revealed a large proportion of truncated molecules, which correlated with small amounts of full‐length FIX (rFIX‐162*, ∼0.5%; rFIX‐294*; and rFIX‐298*, ∼0.2%). Western blotting of plasma from FIX deficient (Hemophilia B) patients revealed traces of full‐length FIX for the p.R294* and p.R298* mutations, but not for the p.L103* mutation that triggered major FIX mRNA decay. The detection of full‐length proteins has clinical implication, particularly for post‐therapeutic immunological complications in Hemophilia. Data in patients' plasma and in vitro, obtained in the proper protein context, support a ribosome readthrough gradient, consistent with its predicted determinants of efficiency. Hum Mutat 33:1373–1376, 2012. © 2012 Wiley Periodicals, Inc.