Generalized substitution of isoencoding codons shortens the duration of papillomavirus L1 protein expression in transiently gene-transfected keratinocytes due to cell differentiation

Recently we reported that gene codon composition determines differentiation-dependent expression of the PV L1 genes in mouse primary keratinocytes (KCs) in vitro and in vivo (Zhao et al. 2005, Mol. Cell Biol. 25: 8643-8655). Here, we investigated whether generalized substitution of isoencoding codons affects the duration of expression of PV L1 genes in mouse and human KCs in day 1 culture transiently transfected with native (Nat) and codon modified (Mod) L1 genes. Following transient transfection, KC continuously transcribed both Nat and Mod PV L1 genes for at least 12 days, with the levels of L1 mRNAs from the Mod L1 genes significantly higher than those from the Nat L1 genes. However, continuous L1 protein expression at day 9 post-transfection was observed for both mouse and human KCs transfected with the Nat L1 genes only. Further, aa-tRNAs prepared from D8 KC cultures enhanced translation of two PV Nat L1 DNAs in RRL lysate and PV Nat L1 mRNAs in D0 cell-free lysate, whereas aa-tRNAs from D0 KCs enhanced translation of PV Mod L1 mRNAs in D8 cell-free lysate. It appears that aa-tRNAs in less-differentiated and differentiated KCs differentially match the PV Nat and Mod L1 mRNAs to regulate their translations in vitro.