Syndecan-2 functions as an adhesion receptor in colon cancer cells

Abstract

Syndecan-2 is one of transmembrane heparan sulfate proteoglycans that act as cell surface receptor during cell-extracellular matrix interaction. At cell adhesion sites, syndecan-2 can impact on various adhesion-related cell functions, but details of the regulatory mechanism governing syndecan-2 are not well known. Here, I examined the regulatory role of syndecan-2 as an adhesion receptor in colon cancer cells. Overexpression of syndecan-2 enhanced collagen adhesion, cell migration and invasion of normal rat intestinal epithelial cells(RIE1), and increased integrin 2 expression levels. Interestingly, RIE1 cells transfected with either syndecan-2 or integrin 2 showed similar adhesion and migration patterns, and a function-blocking anti-integrin 2 antibody abolished syndecan-2-mediated adhesion and migration. Consistent with these findings, transfection of integrin 2 siRNA diminished syndecan-2-induced cell migration in HCT116 human colon cancer cells, suggesting a novel cooperation between syndecan-2 and integrin 21 in adhesion-mediated cell migration and invasion. Interestingly, colon cancer cells transfected with various syndecan-2-encoding genes with deletions in the cytoplasmic domain showed that syndecan-2-induced migration activity requires the EFYA sequence of the C-terminal region; deletion of these residues abolished the rise in cell migration seen when the wild-type gene was transfected and syndecan-2 interaction with syntenin-1, suggesting that syntenin-1 functioned as a cytosolic signal effector downstream from syndecan-2. Colon cancer cells overexpressing the syntenin-1 gene showed increased migratory activity, whereas migration was decreased in cells in which syntenin-1 was knock-down using small inhibitory RNA. In addition, syntenin-1 expression potentiated colon cancer cell migration induced by syndecan-2, and syndecan-2-mediated cell migration was reduced when syntenin-1 expression diminished. However, syntenin-1-mediated migration enhancement was not noted in colon cancer cells transfected with a gene encoding a syndecan-2 mutant lacking the cytoplasmic domain. Furthermore, in line with the increase in cell migration, syntenin-1 mediated Rac activation stimulated by syndecan-2. Therefore, the cytoplasmic domain of syndecan-2 seems to regulate colon cancer cell migration via interaction with syntenin-1. Taken together, all these results demonstrate that syndecan-2 plays an important role as an adhesion receptor regulating adhesion-mediated functions in colon cancer cells. This interactive dynamics between syndecan-2 and other cell surface receptor (e.g. integrin α2β1) and/or cytosolic effector (e.g. syntenin-1) might be a possible mechanism underlying the tumorigenic activities of colon cancer cells.;Ttransmembrane heparin sulfate proteoglycan 인 Syndecan 은 adhesion receptor 로서 세포부착과 이동에 관여를 하고 있으나, 그 세부적인 기작에 대해서 아직도 많은 연구가 수행되고 있다. 본 연구에서는 Syndecan-2 의 adhesion receptor, 세포질내의 interaction, oligomerization 등을 통한 대장암세포에서의 세포 이동에 대한 영향을 알아보고자 하였다. Nomal rat intestinal epithelial cells(RIEI)에 syndecan-2 를 과발현 시켰을 때, 대표적인 cell adhesion receptor 인 integrin α2 의 발현이 증가함을 확인할 수 있었다. 또한 syndecan과 integrin α2 의 발현을 각각 증가시켰을 때, 모두 cell migration이 증가함을 확인할 수 있었으며, 놀랍게도 integrin α2 를 억제시켰을 때, syndecan-2 에 의해 유도되는 cell adhesion 과 migration 이 감소됨을 알 수 있었다. 이러한 것은 syndecan-2 의 발현을 억제하였을 때도 같은 결과를 얻었다. 이러한 syndecan-2 와 integrin α2와의 관계가 RIEI cells 에서 뿐 만이 아니라, colon cancer cells 에서도 동일함을 확인할 수 있었다. Syndecan 은 세포질내에서 다양한 단백질들과 결합하여, 세포부착 및 이동 등 다양한 역할을 수행하고 있다. 이러한 세포질 내에서의 기능을 알아보기 위하여 syndecan-2 의 다양한 construct를 발현시키고, 이미 syndecan-2 와 결합한다고 알려진 syntenin 과의 결합이 cell migration 에 어떤 영향을 주는지 알아보았다. Syntenin 과 syndecan-2 cytoplasmic domain 의 결합으로 cell migration이 증가하고 그 downstream 인 Rac 이 activation 됨을 확인할 수 있었다. Syndecan 을 포함한 receptor 들은 대부분 dimerization 등을 통하여 활성화기작이 유도된다. Syndecan 의 경우, non-covalent dimerization 이 유도됨이 알려져 있다. 본 연구에서는 fibronectin matrix 하에서 syndecan 을 과발현 시켰을 때, cell spreading 및 migration 이 증가함을 확인하였고, 이러한 증가에 transmembrane에 의해 유도된 dimerization 이 중요함을 확인할 수 있었다. 이러한 모든 결과를 통해 syndecan-2 가 integrin α2 의 coreceptor로서 작용을 하며, syndecan-2 의 cytoplasmic domain 과 syntenin 의 결합 및 oligomerization 이 cell migration 증가에 영향을 줌을 알 수 있었다.