ROLE OF CYSTATIN M IN BREAST TUMOR PROGRESSION

细胞间相互作用的丧失、基底膜的降解和恶性上皮细胞对基质组织的侵袭是原发乳腺肿瘤向局部和远处转移的关键事件。越来越多的证据表明，蛋白水解酶或蛋白水解酶与肿瘤进展有关。近年来，几种内体/溶酶体半胱氨酸蛋白酶已被克隆，并被证明在肿瘤组织中过表达。然而，尽管新疗法的发展潜力巨大，但我们仍然对其蛋白分解活性的调节知之甚少。半胱氨酸氨基转移酶抑制剂如半胱氨酸半胱氨酸酶M是内切/溶酶体半胱氨酸蛋白酶的内源性蛋白抑制剂。Cystatin M在原发乳腺癌中表达，但在转移性乳腺组织和许多癌细胞系中表达下调，因此可能是一种新的转移抑制基因。我们研究的长期目标是确定胱抑素M在肿瘤生长、侵袭和转移过程中控制的关键步骤。我们的工作假设是，胱抑素M使原发乳腺肿瘤处于休眠和非侵袭性阶段。肿瘤在体内的发展本质上是复杂的。因此，我们将从已建立的体外模型开始我们的工作，以确定：1.胱抑素M是否能够抑制肿瘤细胞介导的基质降解和侵袭。第一个特定目标是利用重组半胱氨酸氨基转移酶M以及构建表达改变的人乳腺癌细胞系。这些体外研究将极大地帮助首席研究者设计和执行针对特定目的的研究2，分析半胱氨酸氨基转移酶M对SCID小鼠原发肿瘤生长、侵袭和转移的抑制作用(S)。这个项目的整体研究应该产生的新见解可能会导致设计治疗原发浸润性人类乳腺癌和/或其转移的新药。

Loss of cell-cell interactions, degradation of the basement membrane and invasion of the underlying stromal tissue by malignant epithelial cells are key events in the progression of a primary breast tumor to local and distant metastases. There is increasing evidence that proteolytic enzymes, or proteases, are involved in tumor progression. In recent years several endosomal/lysosomal cysteine proteases have been cloned and shown to be overexpressed in cancer tissues. However, despite the enormous potential for development of novel therapeutics, we still understand little about the regulation of their proteolytic activity. Cystatins such as cystatin M are potent endogenous protein inhibitors of endosomal/lysosomal cysteine proteases. Cystatin M is expressed in primary human breast cancer but is downregulated in metastatic breast tissue and many cancer cell lines and could therefore represent a novel metastasis suppressor gene. The long-term objective of our studies is to define the critical steps controlled by cystatin M during tumor growth, invasion and metastasis. Our working hypothesis is that cystatin M maintains primary breast tumors in a dormant and non-invasive phase. Tumor progression in vivo is complex in nature. We will therefore begin our work with established in vitro models to determine: 1. whether cystatin M is able to inhibit tumor cell-mediated matrix degradation and invasion. The first specific aim will be addressed using recombinant cystatin M as well as engineering human breast cancer cell lines with altered expression of cystatin M. These in vitro studies should greatly help the principal investigator in designing and performing studies for specific aim 2 that will analyze the suppressing function(s) of cystatin M on primary tumor growth, invasion and metastasis in SCID mice. The new insights that should be generated by the overall research of this project may lead to the design of novel drugs for the treatment of primary invasive human breast cancers and/or their metastases.