Transcriptional regulation of the albumin gene in cultured rat hepatocytes. Role of basement-membrane matrix

Abstract

The expression of tissue-specific functions by hepatocytes in primary culture is enhanced in the presence of an extracellular matrix. A basement membrane-like substratum, derived from the Engelbreth-Holm-Swarm mouse sarcoma (EHS) and termed EHS gel, supports synthesis and secretion of albumin for at least three weeks, in contrast to a conventional substratum (plastic or collagen-coated plastic), on which cells rapidly lose this function. The presence of an EHS matrix (as a substratum or added to the medium as a dilute gel) supports transcriptional activity at 30 to 35% and specific mRNA at 70 to 80% of initial values after five days of culture, at a time when transcription in cells plated in conventional culture is undetectable. For examining the cis elements required for transcriptional regulation by EHS matrix, we are utilizing recombinant adenoviruses to introduce DNA into hepatocytes, as an alternative to transfection of DNA fragments. Initial studies are presented, in which hepatocytes are cultured on either collagen-coated plastic or on EHS gel. At various times after plating, the cultures are infected with an adenovirus containing the proximal 5' regulatory region (to -441 base-pair) of the albumin gene. The results indicate no effect of EHS gel on this proximal promoter region, implying that matrix-responsive element(s) lie further upstream, possibly within the previously described enhancer at about -10,000 base-pairs.