J. Biol. Chem., Vol. 262, Issue 23, 11071-11079, 08, 1987
Receptor binding properties and insulin-like effects of human growth hormone and its 20 kDa-variant in rat adipocytes
J Smal, J Closset, G Hennen and P De Meyts
The natural 20 kDa-variant of human growth hormone (hGH) binds with high
affinity to IM-9 human lymphocyte receptors, in agreement with its potency
in biological assays for growth promoting and lactogenic activities. In
contrast, 20 kDa-hGH has only 3% of the potency of 22 kDa-hGH in binding to
the receptors of normal and hypophysectomized rat adipocytes. In agreement
with the binding potency, 20 kDa-hGH is only 3% as potent as 22 kDa-hGH in
stimulating lipogenesis in normal rat adipocytes preincubated for a few
hours in hGH-free medium. The 20 kDa- hGH is also much weaker than 22
kDa-hGH in stimulating lipogenesis in adipocytes from hypophysectomized
rats. These data strongly support the concept that the rat adipocyte
receptor, which mediates the insulin- like effects of growth hormone, is
different from the receptor found on human IM-9 lymphocytes. Preincubation
of rat adipocytes with hGH induces a refractoriness to subsequent
activation of lipogenesis by hGH but does not abolish the response to
insulin, while preincubation with insulin slightly potentiates the hGH
response and does not change the insulin response. Additivity studies and a
detailed comparison of the lipogenic effects of insulin and hGH suggest
that hGH shares only a subset of the metabolic pathways activated by
insulin.