Differential mRNA stabilities affect mRNA levels in mutant mouse myeloma cells.

A series of mouse myeloma cell lines producing mutant gamma 2b immunoglobin heavy chains, which resemble heavy chain disease proteins, were analyzed for messenger RNA abundance as a function of mRNA alterations. A mutation effectively deleting the gamma 2b-CH1 domain of the mRNA had little or no effect on Ig heavy chain mRNA abundance on half-life (mutant 10.1). A mutation in the gamma 2b-CH2 and CH3 domain, causing premature termination of translation, had more deleterious effects on Ig heavy chain mRNA abundance and half-life (mutant I17). Substitution of the deleted portions of the gamma 2b mRNA with gamma 2a sequences by subclass switching in the cells (mutants K23 and K25) resulted in increased heavy chain abundance and half-life relative to the parent I17. In contrast, kappa light chain mRNA levels and half-lives remain constant among the mutants. The wild-type and mutant cell lines transcribed the Ig heavy chain gamma 2b locus equally when compared with an internal beta-actin standard by transcription run on studies. Therefore, half-life of the Ig heavy chain mRNA seems to be the principal determinant in cytoplasmic mRNA abundance in this system.