引领肿瘤成团侵袭的“先导细胞”（leader cell）是启动肿瘤转移的新发现，是近年研究的热点。但诱导先导细胞形成的分子机制不清楚。据报道微环境是决定肿瘤迁移特性的关键因素，影响先导细胞侵袭能力。透明质酸（HA）是细胞外基质的主要成分，与其受体CD44共同形成适合肿瘤生长的微环境。本课题前期示①乳腺癌HA表达增高，与转移呈正相关②乳腺癌细胞表面CD44处于活化态，与HA结合活性强；正常乳腺上皮细胞是静息态，不能与HA结合③单层培养下HA-CD44介导乳腺癌细胞迁移。提示HA-CD44相互作用对先导细胞侵袭可能有重要影响。基于此，本研究首次探讨HA与活化的CD44相互作用对先导细胞向周围正常组织迁移和侵袭的影响。内容①阐明微环境HA-CD44对乳腺癌“先导细胞”形成的调控及机制②探讨HA-CD44在引发乳腺癌成团侵袭(collective invasion)中的作用，以期揭示乳腺癌转移机制

Recent evidence suggests that leader cells initiate and maintain collective invasion of malignant cells. However, the mechanisms about how to induce malignant characteristics of leader cells, is unknown. The importance of the micro-environment in tumor metastasis is now well established. HA is the main component of extracellular matrix and may support cell growth and invasion by providing cancer cells with a suitable microenvironment through its cell surface receptor CD44. Previous work from our laboratory showed that ① HA is over-expressed in breast cancer cells and is positively correlated with metastasis ② CD44 is in active state on cancer cells whereas inactive on normal cells ③ The HA-CD44 interactions mediated migration of tumor cells in vitro. The evidences prompted us to hypothesize that the HA-CD44 interactions might play a crucial role in collective invasion triggered by the leader cells. For the first time, this project try to understand the effects of HA-CD44 interactions on the leader cells in human breast cancer invasion and its mechanisms involved, including two parts: ①To investigate the effects of the interactions at the plasma membrane between CD44 and sromal HA in malignant breast cancer, that have an HA-rich ECM, and the mechanisms invovled. ②To study the role of the HA-CD44 interactions in triggering the collective invasion in breast cancer. The project may provide a theoretical basis for understanding cancer metastasis.