THE DEACTIVATION OF HCG BY NICKING AND DISSOCIATION
THE DEACTIVATION OF HCG BY NICKING AND DISSOCIATION
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DOI：
10.1210/jc.76.3.704
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发表时间：
1993-03-01
影响因子：
5.8
通讯作者：
BRAUNSTEIN, GD
中科院分区：
文献类型：
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作者：
COLE, LA;KARDANA, A;BRAUNSTEIN, GD
人绒毛膜促性腺激素(HCG)由α-和β-亚基组成，非共价连接。妊娠血清和尿样中一定比例的hCG分子有缺口，或者在贝塔亚基残基44和45或贝塔亚基残基47和48之间有缺失的多肽连接。这些缺口可抑制hCG的类固醇生成活性。我们检查了划痕的来源，以及怀孕期间产生的划痕hCG分子的发生和稳定性。我们调查了划痕的来源。将标准人绒毛膜促性腺激素加入三份全血样本中，在37℃孵育18h，未发现划痕程度的变化。然而，在妊娠早期胎盘外植体和JAR恶性滋养层细胞的培养液中，凝胶电泳法检测到hCGβ亚基的缺口(M(R)=17,000和M(R)=22,000，分别对应于多肽Beta1-47(44)和Beta48(45)-145)。我们推测划痕发生在滋养层组织分泌之前或之后。我们检查了划痕的发生。测定了233例妊娠4~40周孕妇血清和168例尿液中总hCG和完整hCG水平。根据这两项测量结果，估计了划痕的程度。孕周提前与划痕程度的增加呈线性关系(回归分析，月数与划痕百分比，95%的相关性)。在妊娠前2个月的血清中观察到最小的划痕(平均为hCG分子的9%)，在怀孕后的几个月中观察到更多的划痕，在妊娠最后2个月的样本中观察到最大的划痕(平均=21%的hCG分子，t检验前2个月与后2个月，P<；0.00005)。尿样也有类似的结果(前2个月均值为9%，后2个月均值为27%，t检验P<；0.00005)。我们得出的结论是，在hCG峰值之后(怀孕2个月后)，划痕更为普遍。最后，我们检查了划痕和完整hCG分子的稳定性。标准hCG(批号CR127，20%镍)和hCG制剂C5(100%镍)在全血中孵育不同时间。C5hCG迅速解离成游离的α和β亚基(解离半衰期22+/-5.2h)，比标准hCG(解离半衰期700h)快30倍以上。我们推测，NiCKhCG迅速解离，考虑到循环(37-41h)和解离半衰期，滋养层细胞产生的NICK分子的相对量可能是血清样品的3.4-3.6倍。如果镍分子迅速解离，那么游离亚单位的水平应该会随着划痕程度的增加而上升。从妊娠第1个月到最后一个月，划痕程度从hCG分子的8%-31%上升，尿中游离α-水平、游离β-亚基和β-核心片段(β-亚基的降解产物)水平以相似的比例上升，分别从76%-360%、18%-99%和58%-305%上升。人绒毛膜促性腺激素在怀孕的前两个月通过黄体维持孕酮的产生。在此之后，这种激素就没有已知的功能了。研究结果表明，hCG的缺口或失活发生在滋养层组织内或周围，当hCG没有已知功能时，缺口在妊娠头2个月后更为普遍，一旦被缺口，hCG迅速分解为游离的α和β亚基。
Human chorionic gonadotropin (hCG) is composed of an alpha- and a beta-subunit, joined noncovalently. A proportion of hCG molecules in pregnancy serum and urine samples have nicks or a missing peptide linkage between either beta-subunit residues 44 and 45 or beta-subunit residues 47 and 48. These nicks ablate the steroidogenic activity of hCG. We examined the source of nicking, and the occurrence and stability of nicked hCG molecules produced during pregnancy.We investigated the source of nicking. Standard hCG was added to three samples of whole blood, and incubated 18 h at 37 C. No change in extent of nicking was detected. However, nicking of hCG beta-subunit was detected by gel electrophoresis (bands at M(r) = 17,000 and M(r) = 22,000, corresponding to the peptides beta1-47(44) and beta48(45)-145, respectively) in culture fluids from first trimester placental explants and from JAr malignant trophoblast cells. We inferred that nicking occurs before or immediately upon secretion by trophoblast tissue.We examined the occurrence of nicking. Levels of total hCG (nicked + nonnicked) and intact hCG (nonnicked) were determined in 233 serum and 168 urine samples from 4-40 weeks of pregnancy. From the two measurements the extent of nicking was estimated. A linear relationship was indicated between advancing weeks of gestation and increasing extent of nicking (regression analysis, months vs. percent nicked, 95% correlation). Minimum nicking was observed in serum from the first 2 months of pregnancy (mean = 9% of hCG molecules), increased nicking in the months after, and maximum nicking in samples from the last 2 months of pregnancy (mean = 21% of hCG molecules, t test first 2 months vs. last 2 months, P < 0.00005). Similar results were observed with urine samples (first 2 months mean = 9%, last 2 months = 27%, t test P < 0.00005). We concluded that nicking is more prevalent after the hCG peak (after 2 months of pregnancy).Finally, we examined the stabilities of nicked and intact hCG molecules. Standard hCG (batch CR127, 20% nicked) and hCG preparation C5 (100% nicked) were incubated for varying times in whole blood. C5 hCG dissociated rapidly into free alpha- and beta-subunits (dissociation half-life 22 +/- 5.2 h), over 30 times faster than standard hCG (dissociation half-life 700 h). We inferred that nicked hCG rapidly dissociates, and that the relative amount of nicked molecules produced by the trophoblast may, considering circulating (37-41 h) and dissociation half-lives, be 3.4-3.6 times higher than that measured in serum samples. If nicked molecules rapidly dissociate then levels of free subunits should rise as the extent of nicking increases. From the first to the last month of pregnancy, extents of nicking rise from 8-31% of hCG molecules, urine free a-levels, free beta-subunit, and beta-core fragment (degradation product of beta-subunit) levels rise by similar proportions, from 76-360%,18-99%, and from 58-305% of hCG levels. hCG functions in the first 2 months of pregnancy to maintain progesterone production by the corpus luteum. After this period the hormone has no known function. The findings presented here indicate that nicking or deactivation of hCG occurs in or around trophoblast tissue, that nicking is more prevalent after the first 2 months of pregnancy when hCG has no known function, and that once nicked, hCG rapidly dissociates into free alpha- and beta-subunits.