Basic analysis for development of inhibitors of malignant glioma invasion

细胞表面粘附分子对迁移过程至关重要，因为它们将与细胞外基质（ECM）的相互作用耦合到细胞内的细胞骨架装置。CD44是几种细胞外基质成分的主要细胞粘附受体，主要是在脑组织中丰富的透明质酸。我们发现，在各种生理条件下，包括钙内流、PKC的激活和Ras原癌基因产物的激活，癌细胞中表达的CD44通过膜锚定的金属蛋白酶在外胞域进行蛋白水解裂解。我们发现这种切割负责CD44与细胞外基质之间相互作用的动态调节，并在癌细胞迁移中起关键作用。在本研究中，我们发现CD44在胞外结构域和胞内结构域经历了连续的蛋白水解裂解，导致CD44胞内结构域（CD44ICD）片段的释放。因此，CD44ICD作为一种信号转导分子，在那里它易位到细胞核并激活通过12- o -十四烷酰基磷酸酯（TPA）响应元件（TRE）介导的转录，该元件存在于参与不同细胞过程的许多基因中。我们证明CD44ICD增强了由转录辅激活因子CBP/p300介导的交易激活。此外，我们发现CD44基因是CD44ICD转录激活的潜在靶点之一。这些观察结果建立了一种新的信号通路，将细胞表面粘附分子的蛋白水解过程与细胞核中的转录激活联系起来。因此，CD44可能成为预防胶质瘤侵袭的新分子靶点。

Cell surface adhesion molecules are crucial for the migratory process, as they couple interactions with the extracellular matrix (ECM) to the cytoskeletal apparatus inside the cell. CD44 is the principal cell adhesion receptor for several extracellular matrix components, mainly hyaluronic acid which is abundant in brain tissue. We found that CD44 expressed in cancer cells is proteolytically cleaved at the ectodomain through membrane-anchored metalloproteases under various physiological conditions including calcium influx, activation of PKC and activation of Ras proto-oncogene product. We found that this cleavage is responsible for dynamic regulation of the interaction between CD44 and the extracellular matrix and plays a critical role in cancer cell migration. In the present study, we found that CD44 undergoes sequential proteolytic cleavage in the ectodomain and intracellular domain, resulting in the release of a CD44 intracellular domain (CD44ICD) fragment. Consequently, CD44ICD acts as a signal transduction molecule, where it translocates to the nucleus and activates transcription mediated through the 12-O-tetradecanoylphorbol 13-acetate (TPA) responsive element (TRE), which is found in numerous genes involved in diverse cellular processes. We demonstrate that CD44ICD potentiates transactivation mediated by the transcriptional coactivator CBP/p300. Furthermore, we show that the CD44 gene is one of the potential targets for transcriptional activation by CD44ICD. These observations establish a novel signaling pathway that links proteolytic processing of an adhesion molecule at the cell surface to transcriptional activation in the nucleus. Therefore, CD44 can be a novel molecular target for prevention of glioma invasion.