Overexpression of heat shock protein 70 restores the structural stability and functional defects of temperature-sensitive mutant of large T antigen at nonpermissive temperature

Establishment and characterization of hepatocytes from an Immortomouse/SMP30/GNL knockout mouse hybrid lacking vitamin C to study vitamin C transport

Senescence marker protein-30 (SMP30) has been identified as the lactone-hydrolysing enzyme gluconolactonase (GNL), which is involved in vitamin C (L-ascorbic acid, AA) biosynthesis. We previously reported the development of SMP30/GNL knockout (KO) mice unable to synthesize AA in vivo. For more efficient study of the liver's AA uptake and as yet uncharacterized efflux system, we established an immortal hepatocyte line derived from a hybrid of SMP30/GNL KO mice and Immortomice. Immortomice express the thermolabile simian virus 40 (SV40) large T antigen tsA58. These SMP30/GNL KO immortal hepatocytes proliferate at the permissive temperature of 33°C but degrade rapidly at the non-permissive temperature of 39°C. Additionally, they are SMP30-/GNL-deficient, express SV40 large T antigen and proliferate steadily at 33°C. However, the cells' proliferation is arrested at 39°C. A phase contrast micrograph revealed that the cells are binucleated with an enlarged cytoplasm similar to that of primary cultured hepatocytes from wild-type mice. Dose-response and time-dependent study of AA uptake revealed that the cells, although unable to synthesize AA, took up AA from the culture medium. This property of our SMP30/GNL immortal hepatocytes makes them extremely useful for studying AA uptake and efflux systems in the liver.