Insulin-like growth factor binding proteins in sera of pregnant nonhuman primates.
Insulin-like growth factors (IGFs) are mitogenic peptides that are important for fetal and maternal tissue growth during pregnancy. They circulate complexed primarily with a serum binding protein, IGFBP-3, which regulates the availability of the IGFs to their target tissues. We previously reported that in pregnant women, serum IGFBP-3 levels, assessed by Western ligand blotting, decline markedly beginning at 6 weeks gestation due to a circulating protease that cleaves IGFBP-3 into a 29-kilodalton (kDa) protein and lower mol wt (M(r)) fragments. In the current study, we compared IGFBP profiles, IGFBP-3 and IGFBP-1 levels, and IGFBP protease activities in sera from pregnant and nonpregnant women, baboons, and rhesus monkeys, using Western ligand blotting, IGFBP-specific immunoassays, IGFBP-3 protease assay, and zymographic gel electrophoresis. Serum IGFBP profiles in nonpregnant human and nonhuman primates were similar and were not cycle-dependent. IGFBP-3 (37-43 kDa), IGFBP-2 (31 kDa), and IGFBP-1 (28 kDa) were identified in all three species using IGFBP-specific human antisera. A 24-kDa IGFBP was also present and is believed to be IGFBP-4. Serum IGFBP-1 levels increased throughout gestation in human and nonhuman primates. Serum IGFBP-2 and putative IGFBP-4 were barely detectable in all three species from midgestation to term, but increased several days postpartum. In contrast, serum IGFBP-3 profiles differed markedly between species during gestation. Rather than the decrease seen in human pregnancy serum, there was an increase in circulating IGFBP-3 levels in nonhuman primates. Furthermore, for both baboon and rhesus monkey, the M(r) of serum IGFBP-3 was about 2 kDa greater in pregnant than in nonpregnant animals, and deglycosylation studies suggested that the higher M(r) forms may be alternatively glycosylated or may have a unique primary structure. As in nonpregnant women, serum IGFBP-3 protease activity was absent in nonpregnant and pregnant baboons. However, rhesus monkey serum contained a calcium-dependent protease that cleaved recombinant human IGFBP-3 into unique fragments, compared to the human pregnancy enzyme. Unlike human pregnancy serum, which proteolyzes IGFBP-3, in human nonpregnancy serum, rhesus serum incubated under similar conditions did not result in proteolysis of rhesus IGFBP-3, suggesting that the IGFBP-3 protease in human pregnancy serum is not present in the circulation of the rhesus monkey. To assess proteolytic activity in these sera, zymographic polyacrylamide gel analysis, using gelatin as a substrate, was performed. A minor band of proteolytic activity (72 kDa) was observed in all three species throughout gestation.(ABSTRACT TRUNCATED AT 400 WORDS)
Giudice
L C
LC
Department of Gynecology and Obstetrics, Stanford University Medical Center, California 94305.
Dsupin
B A
BA
de las Fuentes
Lisa
L
Gargosky
S E
SE
Rosenfeld
R G
RG
Zelinski-Wooten
M B
MB
Stouffer
R L
RL
Fazleabas
A T
AT
D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000097:blood*; D010450:Endopeptidases / Q000097:blood; D005260:Female; D006801:Humans; D007118:Immunoassay; D018969:Insulin-Like Growth Factor Binding Proteins; D008253:Macaca mulatta / Q000097:blood*; D010215:Papio / Q000097:blood*; D011233:Precipitin Tests; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000097:blood*; D013002:Somatomedins / Q000378:metabolism
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D013002:Somatomedins; D010450:Endopeptidases; C080473:insulin-like growth factor binding protein-3 protease