MMH cells: An in vitro model for the study of retinol-binding protein secretion regulated by retinol

The untransformed stable cell line Met murine hepatocytes (MMH), generated from liver explants of transgenic mice expressing a constitutively active t runcated form of the human hepatocyte growth factor receptor (cyto-Met), re presents an innovative tool for in vitro studies of liver function. In the present report, we show that the MMH-D3 line isolated from the liver of a 3 -day-old mouse is a useful model to investigate the regulation of the synth esis and secretion of retinol-binding protein (RBP) by retinol (vitamin A a lcohol). Experiments with Northern blot hybridization, metabolic labeling o f cellular proteins followed by immunoprecipitation, and Western blot analy sis demonstrated that, similarly to the in vivo situation, in MMH-D3 cells the presence of retinol does not affect transcriptional and translational r ate of the REP gene but is essential for regulating the secretion rate of t he protein. Unlike HepG2 human hepatocarcinoma cells used thus far in studi es of retinoid metabolism, including the synthesis and secretion of REP, vi tamin A deficiency causes, in MMH-D3 cells, the inhibition of REP secretion and the protein accumulation in the cell, whereas retinol repletion prompt ly results in REP secretion. This model will be very useful in future studi es on vitamin A distribution in the organism. J. Cell. Physiol. 181:24-32, 1999. (C) 1999 Wiley-Liss, Inc.