Missense mutations in the signal peptide of the porcine GH gene affect cellular synthesis and secretion

In previous investigations, we have demonstrated the mutations in the signal peptide of porcine GH gene were associated with the body size. In this study, the fusion gene expression vectors which consisted of eight signal peptide mutants of GH gene and EGFP gene were constructed according to three missense mutations (p.Val9Ala, p.Gln22Arg and p.Asp25Gly), and they were transfected into the GH3 cell line. The inhibition levels of EGFP gene transcriptions with different signal peptide mutants were significantly different. Typically, the allelic variants carrying Val in codon nine showed higher protein synthesis (P < 0.05), and the allelic variants carrying neutral Gln in codon 22 and Gly in codon 25 showed higher secretion proportion (P < 0.05) compared with the other groups as assessed by western blotting. In silico RNA folding prediction indicated that the mutations gave rise to different RNA secondary structures, suggesting that they might affect translation and protein synthesis. We conclude that the missense mutations within the signal sequence influence the expression and the secretion of the protein. To the best of our knowledge, this is the first report addressing the functional consequences of the mutations in the signal peptide of porcine GH gene.