Department of Pathology, Haartman Institute, University of Helsinki, Haartmaninkatu 3, 00290 Helsinki, Finland.
Biochem J. 2011 May 1;435(3):619-28. doi: 10.1042/BJ20101599.
Slit diaphragms are specialized junctions between glomerular epithelial cells (podocytes) that are crucial for glomerular ultrafiltration. The Ig superfamily members nephrin and Neph1 are essential components of the slit diaphragm, whereas the role of Neph1 homologue Neph3 in the slit diaphragm is unknown. In the present paper we show that Neph3 homodimerizes and heterodimerizes with nephrin and Neph1. We further investigated whether these interactions play a role in cell adhesion by using mouse L fibroblasts that lack endogenous cell-adhesion activity and found that Neph1 and Neph3 are able to induce cell adhesion alone, whereas nephrin needs to trans-interact with Neph1 or Neph3 in order to promote formation of cell-cell contacts. Tyrosine phosphorylation of nephrin was down-regulated after nephrin trans-interacted with either Neph1 or Neph3 leading to formation of cell-cell contacts. We further found that the expression of Neph3 was increased in nephrin-deficient mouse podocytes. The findings of the present paper show that nephrin and Neph1 or Neph3 trans-interactions promote cell-contact formation, suggesting that they may also function together in slit diaphragm assembly.
裂孔隔膜是肾小球上皮细胞（足细胞）之间的特化连接，对于肾小球超滤至关重要。免疫球蛋白超家族成员 Nephrin 和 Neph1 是裂孔隔膜的重要组成部分，而 Neph1 同源物 Neph3 在裂孔隔膜中的作用尚不清楚。在本研究中，我们发现 Neph3 可以与 Nephrin 和 Neph1 形成同源二聚体和异源二聚体。我们进一步研究了这些相互作用是否通过使用缺乏内源性细胞黏附活性的小鼠 L 成纤维细胞参与细胞黏附，结果发现 Neph1 和 Neph3 能够独立诱导细胞黏附，而 Nephrin 需要与 Neph1 或 Neph3 相互作用才能促进细胞-细胞接触的形成。Nephrin 与 Neph1 或 Neph3 相互作用形成细胞-细胞接触后，Nephrin 的酪氨酸磷酸化被下调。我们进一步发现，Neph3 在 Nephrin 缺陷型小鼠足细胞中的表达增加。本研究的结果表明 Nephrin 与 Neph1 或 Neph3 的相互作用促进细胞接触的形成，提示它们可能在裂孔隔膜组装中也共同发挥作用。
