GENERATION OF TRUNCATED FORMS OF THE NG2 PROTEOGLYCAN BY CELL-SURFACE PROTEOLYSIS
GENERATION OF TRUNCATED FORMS OF THE NG2 PROTEOGLYCAN BY CELL-SURFACE PROTEOLYSIS
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DOI：
10.1091/mbc.6.12.1819
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发表时间：
1995-12-01
影响因子：
3.3
通讯作者：
STALLCUP, WB
中科院分区：
文献类型：
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作者：
NISHIYAMA, A;LIN, XH;STALLCUP, WB
NG2是一种硫酸软骨素蛋白多糖，表达于包括胶质细胞、肌肉和软骨在内的几个谱系的分裂祖细胞上。它是一种完整的膜蛋白多糖，其核心糖蛋白为300 kDa。在本研究中，我们研究了不同细胞系表达的NG2核心蛋白的三种分子形式。许多表达全长300 kDa NG2核心蛋白的细胞系也会将290 kDa的形式释放到培养液中。本种缺乏细胞质区域，但几乎包含整个胞外区域。两种核心蛋白，即完整的300 kDa形式和截短的275 kDa形式，在NG2转基因细胞系U251NG52的表面表达。275kDa的物种缺乏胞质结构域和至少胞外结构域的氨基酸。B49细胞的温和胰酶也产生了275 kDa的物种，这表明这种成分是由300 kDa的蛋白质分解产生的。在U251NG52细胞中，300 kDa的物种转换为275 kDa的形式受到佛波酯等试剂的刺激，佛波酯可以激活蛋白激酶C。佛波酯还可以诱导胶原酶和基质分解素等金属蛋白酶的表达，这可能是300 kDa核心蛋白被切割的原因。尽管b49细胞不会自发产生截短的275 kDa的成分，但使用抗NG2的单抗来阻断NG2和VI型胶原之间的相互作用会导致这些细胞中出现275 kDa的成分。因此，NG2和VI型胶原之间的相互作用可能保护蛋白多糖免受蛋白水解酶的影响。VI型胶原在α3链中包含一个库尼茨型蛋白酶抑制序列。这与观察到的U251NG52细胞在表面锚定VI型胶原方面的缺陷是一致的。
NG2 is a chondroitin sulfate proteoglycan that is expressed on dividing progenitor cells of several lineages including glia,muscle, and cartilage. It is an integral membrane proteoglycan with a core glycoprotein of 300 kDa. In the present study we have characterized three molecular forms of the NG2 core protein expressed by different cell lines. Many cell lines that express the full length 300-kDa NG2 core protein also release a 290-kDa form into the medium. This species lacks the cytoplasmic domain but contains almost the entire ectodomain. Two core protein species, the intact 300-kDa form and a truncated 275-kDa form, are expressed at the surface of an NG2-transfected cell line U251NG52. The 275-kDa species lacks the cytoplasmic domain and at least 64 amino acids of the ectodomain. Mild trypsinization of B49 cells also generates the 275-kDa species, suggesting that this component is produced by proteolysis of the 300-kDa form. Conversion of the 300-kDa species to the 275-kDa form in U251NG52 cells is stimulated by reagents such as phorbol esters, which activate protein kinase C. Phorbol esters are also known to induce expression of metalloproteinases such as collagenase and stromelysin, which could be responsible for cleavage of the 300-kDa core protein. Although B49 cells do not spontaneously produce the truncated 275-kDa species, use of monoclonal antibodies against NG2 to block the interaction between NG2 and type VI collagen results in the appearance of the 275-kDa component in these cells. Thus the interaction between NG2 and type VI collagen, which contains a Kunitz-type proteinase inhibitor sequence in the alpha 3 chain, may protect the proteoglycan against proteolysis. This is consistent with the observed deficiency of U251NG52 cells in anchoring type VI collagen at the surface.