Versican is a large extracellular matrix (ECM) chondroitin sulfate (CS) proteoglycan found in most soft tissues, which is encoded by the VCAN gene. At least four major isoforms (V0, V1, V2, and V3) are generated via alternative splicing. The isoforms of versican are expressed and accumulate in various tissues during development and disease, where they contribute to ECM structure, cell growth and migration, and immune regulation, among their many functions. While several studies have identified the mRNA transcript for the V3 isoform in a number of tissues, little is known about the synthesis, secretion, and targeting of the V3 protein. In this study, we used lentiviral generation of doxycycline-inducible rat V3 with a C-terminal tag in stable NIH 3T3 cell lines and demonstrated that V3 is processed through the classical secretory pathway. We further show that N-linked glycosylation is required for efficient secretion and solubility of the protein. By site-directed mutagenesis, we identified amino acids 57 and 330 as the active N-linked glycosylation sites on V3 when expressed in this cell type. Furthermore, exon deletion constructs of V3 revealed that exons 11–13, which code for portions of the carboxy region of the protein (G3 domain), are essential for V3 processing and secretion. Once secreted, the V3 protein associates with hyaluronan along the cell surface and within the surrounding ECM. These results establish critical parameters for the processing, solubility, and targeting of the V3 isoform by mammalian cells and establishes a role for V3 in the organization of hyaluronan.

Versican 是一种大型细胞外基质 (ECM) 硫酸软骨素 (CS) 蛋白聚糖，存在于大多数软组织中，由VCAN编码基因。至少有四种主要亚型（V0、V1、V2 和 V3）是通过可变剪接生成的。versican 的亚型在发育和疾病期间在各种组织中表达和积累，在这些组织中，它们有助于 ECM 结构、细胞生长和迁移以及免疫调节，以及它们的许多功能。虽然一些研究已经在许多组织中确定了 V3 亚型的 mRNA 转录本，但对 V3 蛋白的合成、分泌和靶向知之甚少。在这项研究中，我们在稳定的 NIH 3T3 细胞系中使用慢病毒生成强力霉素诱导型大鼠 V3 和 C 末端标签，并证明 V3 通过经典分泌途径进行处理。我们进一步表明，N-连接糖基化是蛋白质有效分泌和溶解所必需的。通过定点诱变，当在这种细胞类型中表达时，我们将氨基酸 57 和 330 鉴定为 V3 上的活性 N-连接糖基化位点。此外，V3 的外显子缺失结构表明，编码蛋白质羧基区域部分（G3 结构域）的外显子 11-13 对 V3 加工和分泌至关重要。一旦分泌，V3 蛋白就会沿着细胞表面和周围 ECM 与透明质酸结合。这些结果确定了哺乳动物细胞对 V3 亚型的加工、溶解度和靶向的关键参数，并确定了 V3 在乙酰透明质酸组织中的作用。它编码蛋白质的羧基区域部分（G3 结构域），对于 V3 加工和分泌是必不可少的。一旦分泌，V3 蛋白就会沿着细胞表面和周围 ECM 与透明质酸结合。这些结果确定了哺乳动物细胞对 V3 亚型的加工、溶解度和靶向的关键参数，并确定了 V3 在乙酰透明质酸组织中的作用。它编码蛋白质的羧基区域部分（G3 结构域），对于 V3 加工和分泌是必不可少的。一旦分泌，V3 蛋白就会沿着细胞表面和周围 ECM 与透明质酸结合。这些结果确定了哺乳动物细胞对 V3 亚型的加工、溶解度和靶向的关键参数，并确定了 V3 在乙酰透明质酸组织中的作用。