Abstract
The differentiated human hepatoblastoma-derived cell line, HepG2, displayed two classes of specific membrane receptors for heparin-binding growth factor type 1 (HBGF-1). Specific membrane receptors were distinguished from nonreceptor heparin-like binding sites. Receptors with an apparent Kd of 9.2 +/- 0.9 pM and present at 15,000 +/- 900/cell correlated with HBGF-1 stimulation of HepG2 growth. Receptors with an apparent Kd of 2 +/- 0.4 nM and present at 180,000 +/- 18,000/cell correlated with inhibition of growth and changes in secretory products. Other hepatoma cell lines exhibited a simple positive mitogenic response to HBGF-1 and a single class of high affinity binding sites. HBGF-1 covalently cross-linked to hepatoma cell surface polypeptides of apparent mean molecular mass of 130 kilodaltons. At 37 degrees C, receptor-bound HBGF-1 was internalized (t 1/2 = 45 min) but not degraded for up to 6 h. The display of receptors decreased with increased cell density and expression of HBGF-1 mRNA and HBGF-1-like activity in the culture medium. Proliferating normal human hepatocytes also exhibited two classes of binding sites with affinities for HBGF-1 and apparent molecular weight similar to HepG2 cells. These results implicate HBGF-1 or homologues in human hepatoma cell growth and normal liver cell regeneration.
Highlights
The differentiated human hepatoblastoma-derived cell line, HepG2, displayedtwo classesof specific membrane receptors for heparin-binding growth factor type 1 (HBGF-1)
In studies to characterize autocrinegrowth factors for human hepatomacells, we demonstrated that extractosf bovine
The HBGF family is distinguished by affinity for heparin and consistosf two separate gene products which are 55%homologous in amino acidsequence (Abraham et al, 1986a; Jaye et al, 1986)
Summary
Biphasic Growth Effect of HBGF-1 on Human Hepatoblastoma-derived Cell Line(HepG2)”In contrasttomany cell. HBGF-1 concentrations between 200 PM and 2.5 nM revealed These data agree with theScatchard analysis that no discrete additional '251-labeledbands otherthan thebroad indicated an increase in high affinity binding sites with in- band with apparent mean molecularmass of 147kDa and the creased temperature. LZ5I-HBGFbound to Hep3B cells, which In this report, we show that levels of HBGF-1 that elicit exhibited only the high affinity class of detergent-extractable opposite mitogenic effects on the human hepatoblastomasites, was largely slow dissociating (Fig. 6). The apparent number of both high and low affinity sites on normal hepatocyte-like cells was near 10%of those displayed by HepG2 cells (Fig. 15, Miniprint). Results of the current studyshow that HBGF-1 is exceptionally stable even when internalized after binding to receptor These collective data suggest that HBGF may contribute to the nonproliferative state and quantitative expression of secretory products of liver cells through a high capacity low affinity receptor.
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