Heparin-binding growth factor type 1 (acidic fibroblast growth factor): a potential biphasic autocrine and paracrine regulator of hepatocyte regeneration.

Abstract

Heparin-binding growth factor type 1 (HBGF-1; sometimes termed acidic fibroblast growth factor) is potentially an important factor in liver regeneration. HBGF-1 alone (half-maximal effect at 60 pM) stimulated hepatocyte DNA synthesis and bound to a high-affinity receptor (Kd = 62 pM; 5000 per cell). Epidermal growth factor (EGF) neutralized or masked the mitogenic effect of HBGF-1 concurrent with appearance of low-affinity HBGF-1 binding sites. HBGF-1 reduced the inhibitory effect of transforming growth factor type .beta. (TGF-.beta.) on the EGF stimulus. Nanomolar levels of HBGF-1 decreased the EGF stimulus. An increase in hepatic HBGF-1 gene expression after partial hepatectomy precedes increases in expression of the EGF homolog, TGF-.alpha., and nonparenchymal-cell-derived TGF-.beta. in the regenerating liver. Expression of HBGF-1 mRNA occurs in both hepatocytes and nonparenchymal cells and persists for 7 days in liver tissue after partial hepatectomy. HBGF-1 acting through a high-affinity receptor is a candidate for the early autocrine stimulus that drives hepatocyte DNA synthesis prior to or concurrent with the EGF/TGF-.alpha. stimulus. It may allow hepatocyte proliferation to proceed in the presence of low levels of TGF-.beta.. An EGF/TGF-.alpha.-dependent change in HBGF-1 receptor phenotype and increasing levels of nonparenchymal-cell-derived HBGF-1 and TGF-.beta. may serve to limit hepatocyte proliferation.