Engineering cell metabolism for high-density cell culture via manipulation of sugar transport.

Transporters mediate the influx of nutrients and excretion of metabolites in mammalian cells, playing a key role in the regulation of metabolism. They are natural targets for cell engineering to alter metabolic characteristics. The GLUT5 fructose transporter was stably expressed in a Chinese hamster ovary cell line, allowing clones to utilize fructose in place of glucose in culture medium. Compared to the ubiquitously expressed GLUT1 glucose transporter, the GLUT5 fructose transporter has a high K(m) value for its substrate. Fructose uptake by the GLUT5 transporter should supply sugar to cells at a more moderate rate, even in high fructose concentrations, avoiding the overflow of excess carbon to lactate. When cultured in fructose, selected GLUT5 expressing clones exhibited drastically reduced sugar consumption and lactate production rates. When those same clones were cultured in glucose, high sugar consumption and lactate production rates were observed. GLUT5 transcript expression levels and specific lactate production rates varied among the clones. Clones having a low expression level of the GLUT5 transporter were able to import fructose at more moderate rates in higher sugar concentrations. The reduced lactate production for these clones allowed a significant increase in the final cell concentration in fructose fed-batch processes.