To investigate the response of transfectomas to hyperosmotic stress, transfectoma cells (KR12H-2) producing a chimeric antibody were cultivated in the hyperosmolar medium (IMDM supplemented with 5% serum) resulting from sodium chloride addition. In the hyperosmolar medium, cells displayed depressed cell growth. When the osmolality increased from 285 to 425 mOsm/kg, specific growth rate (μ) decreased from 1.19 to 0.94 $day^{-1}$. On the other hand, their specific antibody productivity $(q_{Ab})$ significantly increased from 0.69 to 3.30 $\mu g/10^6$ cells/day. Like $q_{Ab}$, dry cell weight, total cellular protein per cell as well as intracellular levels of heavy (H) and light (L) chain polypeptides were also increased in the hyperosmolar medium.
To better understand the enhanced $q_{Ab}$ according to the hyperosmolar medium, intracellular responses of this transfectoma to hyperosmolality were examined as to how hyperosmolality influenced any of the main intracellular steps of antibody synthesis such as transcription, translation and secretion. Levels of heavy and light chain mRNAs also increased to the similar extent of $q_{Ab}$. Thus, hyperosmolality induced the remarkable activation of transcription level. Likewise, the translation levels of both heavy and light chain polypeptides were increased at hyperosmolality. And more IgG proteins were preferentially synthesized than non-IgG proteins at hyperosmolality.
Consequently, hyperosmolality induced the remarkable activation of transcription and then the transcribed mRNAs were preferentially synthesized using abundant ribosomal RNAs. Therefore, several post-transcriptional regulations, such as mRNA stability, translation, and assembly, enhance $q_{Ab}$ of transfectoma KR12H-2 at hyperosmolality as a whole.
