Department of Pathology, Nagoya University Graduate School of Medicine, Nagoya, Japan.
Oncogene. 2010 Apr 15;29(15):2181-91. doi: 10.1038/onc.2009.506. Epub 2010 Jan 25.
CD109 is a glycosylphosphatidylinositol (GPI)-anchored glycoprotein, whose expression is upregulated in squamous cell carcinomas of the lung, esophagus, uterus and oral cavity. CD109 negatively regulates transforming growth factor (TGF)-beta signaling in keratinocytes by directly modulating receptor activity. In this study, we further characterized CD109 regulation of TGF-beta signaling and cell proliferation. We found that CD109 is produced as a 205 kDa glycoprotein, which is then processed in the Golgi apparatus into 180 kDa and 25 kDa proteins by furin (furinase). 180 kDa CD109 associated with GPI-anchored 25 kDa CD109 on the cell surface and was also secreted into the culture medium. To investigate whether furinase cleavage of CD109 is necessary for its biological activity, we mutated arginine 1273 in the CD109 furinase cleavage motif (amino acid 1270-RRRR-1273) to serine (R1273S). Interestingly, CD109 R1273S neither significantly impaired TGF-beta signaling nor affected TGF-beta-mediated suppression of cell growth, although it was expressed on the cell surface as a 205 kDa protein. Consistent with this finding, the 180 kDa and 25 kDa CD109 complex, but not CD109 R1273S, associated with the type I TGF-beta receptor. These findings indicate that processing of CD109 into 180 kDa and 25 kDa proteins by furin, followed by complex formation with the type I TGF-beta receptor is required for the regulation of TGF-beta signaling in cancer cells and keratinocytes.
CD109 是一种糖基磷脂酰肌醇（GPI）锚定糖蛋白，其表达在上皮细胞癌（包括肺癌、食管癌、子宫癌和口腔癌）中上调。CD109 通过直接调节受体活性，负调控角质形成细胞中的转化生长因子（TGF）-β信号。在本研究中，我们进一步研究了 CD109 对 TGF-β信号和细胞增殖的调控。我们发现，CD109 作为 205 kDa 糖蛋白产生，然后在高尔基体内被 furin（furinase）加工成 180 kDa 和 25 kDa 的蛋白。180 kDa 的 CD109 与细胞表面的 GPI 锚定的 25 kDa CD109 结合，并分泌到培养基中。为了研究 CD109 的 furinase 切割是否是其生物学活性所必需的，我们将 CD109 的 furinase 切割基序（氨基酸 1270-RRRR-1273）中的精氨酸 1273 突变为丝氨酸（R1273S）。有趣的是，CD109 R1273S 既没有显著抑制 TGF-β信号，也没有影响 TGF-β介导的细胞生长抑制，尽管它作为 205 kDa 蛋白表达在细胞表面。与这一发现一致的是，180 kDa 和 25 kDa 的 CD109 复合物，但不是 CD109 R1273S，与 I 型 TGF-β受体结合。这些发现表明，CD109 被 furin 加工成 180 kDa 和 25 kDa 的蛋白，然后与 I 型 TGF-β受体形成复合物，是调节癌细胞和角质形成细胞中 TGF-β信号所必需的。
