The Molecular Biology of Liver Regeneration 
LRF- 1 (liver regeneration factor) is one of the 
proteins that we have further characterized. It is 
highly expressed in regenerating liver and func- 
tions as a DNA-binding protein, controlling the 
expression of target genes. It falls into the cate- 
gory , of so-called leucine zipper proteins, in 
which a stretch of amino acids containing evenly 
spaced leucine residues allows one molecule of 
LRF-1 to interact with another, or with related 
proteins. LRF-1 has a characteristic temporal ex- 
pression pattern during liver regeneration and ac- 
tivates or inhibits the expression of target genes 
in a singular manner, implying that LRF-1 has a 
unique role in regulating events in the regenera- 
tive process. 
We have begun studying the function of a pro- 
tein secreted during liver regeneration that could 
have a role as a growth factor. We found that a 
gene encoding a protein that binds to so-called 
insulin-like growth factor, termed insulin-like 
growth factor-binding protein- 1 (IGFBP-1), is 
highly expressed during the early phases of liver 
regeneration. IGFBP-1 is not expressed in other 
growing cells we have examined. This protein 
has been implicated in enhancing the growth- 
promoting effects of insulin-like growth factor. 
Because IGFBP-1 could potentially act as a 
growth factor during liver regeneration, we have 
further studied its expression and function in 
liver regeneration. 
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