Sadeghi H, Wang B S, Lumanglas A L, Logan J S, Baumbach W R
Immunology Group, American Cyanamid Co., Princeton, New Jersey 08540.
Mol Endocrinol. 1990 Dec;4(12):1799-805. doi: 10.1210/mend-4-12-1799.
GH specifically interacts with a soluble binding protein in serum. The GH-binding protein (GHBP) has been shown to contain the extracellular portion of the cell surface GH receptor (GHR). In rats and mice there is a unique mRNA that encodes the GHBP. This mRNA contains an alternatively spliced exon that replaces the transmembrane and intracellular domains of the receptor with a short hydrophilic carboxy-terminus of 17 and 25 amino acids, respectively, in rats and mice. In humans and other species no mRNAs encoding the GHBP have been identified, suggesting that the GHBP is in these cases a proteolytically processed GHR. In this study a monoclonal antibody (GHBP 4.3) was raised to the rat GHBP using as immunogen a synthetic peptide containing the unique C-terminal 17 amino acids that are not found in the rat GHR. As predicted, this antibody is specific to rat GHBP and does not cross-react with rat GHR. In combination with polyclonal and monoclonal antibodies that recognize both GHBP and GHR, this antibody was used to show that all, or most, of the GHBP in rat serum is indeed derived from the alternatively spliced GHBP mRNA and not from proteolytic processing of the GHR. In addition, endogenous rat serum GHBP was found to exist in two forms, with apparent mol wt of 52 and 44 kDa, arising from a single protein core of 32 kDa by extensive glycosylation. The concentrations of GHBP in male and female rat plasma were also estimated to be 300 and 575 ng/ml, respectively (measured in nonglycosylated GHBP equivalents).
生长激素（GH）特异性地与血清中的一种可溶性结合蛋白相互作用。已证明生长激素结合蛋白（GHBP）包含细胞表面生长激素受体（GHR）的细胞外部分。在大鼠和小鼠中，有一种独特的mRNA编码GHBP。该mRNA包含一个选择性剪接的外显子，分别用大鼠和小鼠中17个和25个氨基酸的短亲水性羧基末端取代了受体的跨膜和细胞内结构域。在人类和其他物种中，尚未鉴定出编码GHBP的mRNA，这表明在这些情况下，GHBP是经蛋白水解加工的GHR。在本研究中，使用包含大鼠GHR中不存在的独特C末端17个氨基酸的合成肽作为免疫原，制备了针对大鼠GHBP的单克隆抗体（GHBP 4.3）。正如所预测的，该抗体对大鼠GHBP具有特异性，并且不与大鼠GHR发生交叉反应。与识别GHBP和GHR的多克隆和单克隆抗体相结合，该抗体被用于证明大鼠血清中所有或大部分GHBP确实源自选择性剪接的GHBP mRNA，而非来自GHR的蛋白水解加工。此外，发现内源性大鼠血清GHBP以两种形式存在，表观分子量分别为52 kDa和44 kDa，由一个32 kDa的单一蛋白核心通过广泛糖基化产生。雄性和雌性大鼠血浆中GHBP的浓度估计分别为300 ng/ml和575 ng/ml（以非糖基化GHBP当量测量）。
