Overexpression of a beta-galactoside binding protein causes transformation of BALB3T3 fibroblast cells.

Overexpression of an animal lectin, rat beta-galactoside binding protein (GBP) in mouse BALB3T3 fibroblast cells by stable introduction of a GBP cDNA expression plasmid results in the acquisition of transformed phenotype which includes a loss of anchorage dependence, reduced contact inhibition, colony formation in soft agar, and tumor formation in nude mice. The transformation depends on the level of the expression of both GBP and TGF gamma 2 activities confirming that both activities are ascribable to a single bifunctional protein TGF gamma 2/GBP. The results indicate that GBP acts as a growth regulator and is directly involved in regulation of cell proliferation.