J. Biol. Chem., Vol. 265, Issue 14, 7939-7944, 05, 1990
Human growth hormone-variant demonstrates a receptor binding profile distinct from that of normal pituitary growth hormone
J Ray, H Okamura, PA Kelly, NE Cooke and SA Liebhaber
Howard Hughes Medical Institute, University of Pennsylvania, Philadelphia 19104-6145.
We have recently established that the human growth hormone-variant (hGH- V)
gene is functional in vivo by documenting its expression in the placenta.
We have subsequently generated transformed murine cell lines stably
expressing the genes for normal pituitary growth hormone (hGH- N), hGH-V,
and each of two chimeric genes generated by exon 3 exchanges, hGH-NV3 and
hGH-VN3. In the present study, we utilize these cell lines as sources of
hormone to characterize and compare the receptor binding profiles of hGH-N
with hGH-V. hGH-V was found to displace 125I-ovine prolactin bound to rat
liver microsomes (lactogen binding) and to displace 125I-hGH bound to
rabbit liver microsomes (somatogen binding). Therefore, hGH-V would be
predicted to display both somatogenic and lactogenic bioactivity, a dual
specificity previously thought to be unique to hGH-N. The concentrations of
hormone necessary to displace 50% (IC50) of the 125I-hGH from somatogen
receptors and 125I-ovine prolactin from lactogen receptors was expressed as
a ratio, IC50 somatogen: IC50 lactogen, for each hormone tested. A 7.4-fold
difference in this ratio was observed for hGH-N compared to hGH-V,
suggesting significantly greater selectivity by hGH- V in binding to the
somatogen receptor. The intermediate binding ratios of the hGH-NV3 and
hGH-VN3 chimeric proteins confirmed the distinct receptor binding profiles
of the two parent hormones and served to identify three amino acids of
potential importance in defining their respective receptor binding
specificities.