生物體內的器官多數是軟的，一旦發生器官纖維化或是癌化的病變，都會造成生物體部分位置整體相對硬度的增加。許多的研究已指出，這種由外界基質所造成的物理性質上的改變和化學性質同等重要，並會調控細胞命運的走向；而細胞如何感受外界基質的軟硬度，勢必成為重要的研究議題。我們實驗室致力於研究正常上皮細胞的細胞機械受力感受器調控所造成的細胞命運改變；在先前的研究發現：beta1 integrin在上皮細胞扮演重要機械感受器的角色，並且可能受到基質軟硬度的調控其活化與否；但基質軟硬度如何進一步調控beta1 integrin的表現仍尚未明瞭。因此本研究的目的在瞭解軟性基質如何調控上皮細胞之beta1 integrin表現及其可能機轉。從本論文我們得知，當細胞生長於相對較硬的環境時，會有較多的beta1 integrin的表現；相對的，當細胞生長在相對較軟的環境時beta1 integrin的表現量就會明顯的下降。研究顯示基質軟硬度對細胞的調控非常的廣泛，不管是在基因轉錄或是後基因轉譯皆有參與對beta1 integrin的調控。並且在進一步針對beta 1 integrin後基因轉譯研究時發現，基質軟硬度引發beta 1 integrin的降解主要是經由溶小體造成的蛋白酵解。在軟性基質造成beta1 integrin降解的同時，細胞膜上的lipid raft組成之一的蛋白質caveolin-1也同時被降解。在大量表現caveolin-1後，軟性基質所造成的beta1 integrin降解會明顯的減少。由以上實驗得知，軟性基質是部份藉由轉錄及部份藉由蛋白酵解的方式調控beta1 integrin在細胞的表現。此研究的結果讓我們進一步瞭解基質軟硬度調控beta1 integrin 的方式及 caveolin-1 在基質軟硬度調控beta1 integrin 的表現中所扮演的角色。

Extracellular matrix (ECM) provides chemical and physical environment to support cell survival and cell fate decision. Recently, increasing evidences have shown that the physical properties of ECM are as important as the chemical properties in determining cell differentiation, cell growth, spreading, migration and survival. The primary cites of cell adhesion to the ECM are focal adhesions, which link the extracellular matrix (ECM), via membrane bound receptor, the integrins, to the cytoskeleton of the cells. Among these family members, beta 1 integrin plays important role for its ubiquitous expression in different types of cells. Our lab has demonstrated that beta 1 integrin function as a key mediator of the substratum stiffness mechanosensing machinery in epithelial cells. However, how substratum stiffness regulates beta 1 integrin gene expression is still unclear. To elucidate how substratum stiffness regulates beta 1 integrin, we employed various stiffness of polyacrylamide gel coated with type I collagen. We observed the levels of beta 1 integrin were increased in epithelial cells grown on stiffer substratum in time and dose dependent manner. However, beta 1 integrin level was diminished in epithelial cells grown on low substratum stiffness within 4h. Exploring the molecular mechanism of beta 1 integrin downregulation, we found that both transcription and post-transcription regulation were involved. The results showed that lysosomal degradation pathway was the main course in low substratum stiffness-induced downregulation of beta 1 integrin. In addition to the levels of beta 1 integrin, we found that low substratum stiffness also downregulated the levels of caveolin-1, the main structure protein in lipid raft. We found that overexpression of caveolin-1 could rescue low substratum stiffness-induced beta 1 integrin downregulation. This study provides a basic understanding of how low substratum stiffness regulated the beta 1 integrin degradation pathway and the possible mechanism relative to caveolin-1expression.

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