Differential effects of hepatocyte growth factor isoforms on epithelial and endothelial tubulogenesis

Hepatocyte growth factor (HGF)/scatter factor (SF) is a pleiotropic cytokine that acts as a mitogen, motogen, and morphogen for a variety of cell types. HGF/NK1 and HGF/NK2 are two naturally occurring truncated variants of HGF/SF, which extend from the NH₂ terminus through the first and second kringle domain, respectively. Although these variants have been reported to have agonistic or antagonistic activity relative to HGF/SF in assays of cell proliferation and motility, their potential morphogenic activity has not been investigated. To address this issue, we assessed the ability of HGF/NK1 and HGF/NK2 to induce tube formation by (a) MCF-10A mammary epithelial cells grown within collagen gels and (b) human umbilical vein endothelial (HUVE) cells grown on Matrigel. We found that HGF/NK1 stimulated tubulogenesis by both MCF-10A and HUVE cells, whereas HGF/NK2 did not stimulate tubulogenesis, but efficiently antagonized the morphogenic effect of full-length HGF/SF. HGF/NK1 and HGF/NK2 also had agonistic and antagonistic effects, respectively, on MCF-10A cell proliferation and HUVE cell migration. These results demonstrate that HGF/NK1, which only consists of the NH₂-terminal hairpin and first kringle domain, is sufficient to activate the intracellular signaling pathways required to induce morphogenic responses in epithelial and endothelial cells. In contrast, HGF/NK2, which differs from HGF/NK1 by the presence of the second kringle domain, is devoid of intrinsic activity but opposes the effects of HGF/SF. The differential properties of the two HGF/SF isoforms provide a basis for the design of more potent HGF/SF agonists and antagonists.