Studies on regulation of IGF (insulin-like growth factor)-binding protein (IGFBP) 4 proteolysis by pregnancy-associated plasma protein-A (PAPP-A) in cells treated with phorbol ester.
Studies on regulation of IGF (insulin-like growth factor)-binding protein (IGFBP) 4 proteolysis by pregnancy-associated plasma protein-A (PAPP-A) in cells treated with phorbol ester.
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在佛波酯处理的细胞中，研究妊娠相关血浆蛋白 A (PAPP-A) 对 IGF（胰岛素样生长因子）结合蛋白 (IGFBP) 4 蛋白水解的调节。
DOI：
10.1042/bj20030937
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
Qin,Xuezhong
中科院分区：
文献类型：
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作者：
Sivanandam,ArunS;Mohan,Subburaman;Kita,Hirohito;Kapur,Sanjay;Chen,Shin-Tai;Linkhart,ThomasA;Bagi,Gyorgy;Baylink,DavidJ;Qin,Xuezhong
PAPP-A（妊娠相关血浆蛋白-a）由hsf（人皮肤成纤维细胞）和hOBs（人成骨细胞）产生，并通过降解IGFBP-4（胰岛素样生长因子结合蛋白4）增强IGFs（胰岛素样生长因子）的有丝分裂活性。这些细胞中的PKC（蛋白激酶C）激活导致IGFBP-4蛋白水解减少。本研究旨在确定PKC激活抑制IGFBP-4蛋白水解的机制。用TPA （PMA; 100 nM）处理hsf /hOBs可减少IGFBP-4蛋白水解，但不显著降低CM（条件培养基）中的ppp - a水平。从TPA处理的细胞（TPA CM）的CM中免疫缺失嗜酸性粒细胞主要碱性蛋白（proMBP）的形式（一种已知的PAPP-A抑制剂）未能增加IGFBP-4的蛋白水解活性。用proMBP逆转录病毒转导hsf可使proMBP浓度升高至30 ng/ml，并导致IGFBP-4蛋白水解适度降低。相比之下，TPA处理阻断了IGFBP-4蛋白水解，但未能在CM中诱导可检测量的proMBP。虽然proMBP过表达导致共价proMBP - PAPP-A复合物的形成，并减少了PAPP-A在SDS/PAGE上的迁移，但TPA处理剂量和时间依赖性地增加了≈470 kDa的PAPP-A形式（PAPP-A470）到≈400 kDa的PAPP-A形式（PAPP-A400）的转化。由于未还原的papp - a400与400 kDa的重组PAPP-A同二聚体共迁移，并且还原后的papp - a470和papp - a400的PAPP-A单体在SDS/PAGE上共迁移，因此不太可能由PAPP-A的蛋白水解裂解引起papp - a470向papp - a400的转化。与数据显示PAPP-A400/PAPP-A470比值的增加与IGFBP-4蛋白水解降低程度相关一致，部分纯化的PAPP-A400与PAPP-A470相比，IGFBP-4蛋白水解活性降低了4倍。这些数据表明，一种新的机制，即将papp - a470转化为活性较低的PAPP-A400，可以解释tpa诱导的PAPP-A活性抑制。
PAPP-A (pregnancy-associated plasma protein-A) is produced by hSFs (human skin fibroblasts) and hOBs (human osteoblasts) and enhances the mitogenic activity of IGFs (insulin-like growth factors) by degradation of IGFBP-4 (insulin-like growth factor-binding protein 4). PKC (protein kinase C) activation in these cells led to reduction in IGFBP-4 proteolysis. This study was undertaken to determine the mechanism by which activation of PKC suppresses IGFBP-4 proteolysis. Treatment of hSFs/hOBs with TPA (PMA; 100 nM) reduced IGFBP-4 proteolysis without significantly decreasing the PAPP-A level in the CM (conditioned medium). Immunodepletion of the proform of eosinophil major basic protein (proMBP), a known PAPP-A inhibitor, from CM of TPA-treated cells (TPA CM) failed to increase IGFBP-4 proteolytic activity. Transduction of hSFs with proMBP retrovirus increased the concentration of proMBP up to 30 ng/ml and led to a moderate reduction in IGFBP-4 proteolysis. In contrast, TPA treatment blocked IGFBP-4 proteolysis but failed to induce a detectable amount of proMBP in the CM. While proMBP overexpression led to the formation of a covalent proMBP–PAPP-A complex and reduced the migration of PAPP-A on SDS/PAGE, TPA treatment dose- and time-dependently increased the conversion of a ≈470 kDa PAPP-A form (PAPP-A470) to a ≈400 kDa PAPP-A form (PAPP-A400). Since unreduced PAPP-A400co-migrated with the 400 kDa recombinant PAPP-A homodimer and since PAPP-A monomers from reduced PAPP-A470and PAPP-A400co-migrated on SDS/PAGE, conversion of PAPP-A470to PAPP-A400is unlikely to be caused by proteolytic cleavage of PAPP-A. Consistent with the data showing that the increase in the ratio of PAPP-A400/PAPP-A470is correlated with the extent of reduction in IGFBP-4 proteolysis, partially purified PAPP-A400exhibited a 4-fold reduction in IGFBP-4 proteolytic activity compared with PAPP-A470. These data suggest that a novel mechanism, namely conversion of PAPP-A470to the less-active PAPP-A400, could account for the TPA-induced suppression of PAPP-A activity.