The involement of PECAM-1 in cancer metastasis

目的：包括内皮细胞在内的基质细胞是肿瘤微环境(TME)的关键成分，释放促进肿瘤生长的因子。尽管TME在原发肿瘤的生长和扩散中的作用已经被研究，但关于TME在调节转移瘤病灶的进展中可能起到的作用还知之甚少。基于大量的初步数据，我们假设在转移肿瘤进展的晚期，血管内皮细胞PECAM-1调节TME，诱导增殖的肿瘤细胞基因表达谱，促进转移瘤的生长。为了验证这一点，建议进行以下研究：(I)确定内皮细胞PECAM-1参与肿瘤肺转移的分子基础(特异性目标1)；(Ii)确定调节肺转移肿瘤生长和进展的依赖于PECAM-1的内皮衍生介质(特异性目标2)；以及(Iii)表征内皮PECAM-1对肺转移肿瘤基因谱的影响(特异性目标3)。 研究方法： 具体目的1.确定内皮细胞PECAM-1参与肿瘤肺转移的分子基础。PECAM-1缺失的小鼠肺内皮细胞将被转导野生型PECAM-1或其介导配体结合或细胞内信号转导能力突变的PECAM-1。然后，所得到的细胞将用于肿瘤-内皮共培养研究，以评估干扰PECAM-1功能对肿瘤细胞增殖的影响。 特定目的2.确定PECAM-1依赖的、内皮细胞衍生的调节肺转移肿瘤生长和进展的介质。在体外，将研究在肿瘤-内皮共培养的条件培养液中培养的肿瘤细胞的细胞增殖，在这种情况下，可疑的、PECAM-1调节的内皮衍生因子的表达水平已经改变。这些研究暗示的作为PECAM-1调节的分泌蛋白的任何因子的体内意义将通过评估注射过表达感兴趣因子的肿瘤的小鼠的肺转移来证实。 具体目的3.研究内皮细胞PECAM-1对肺转移瘤基因表达谱的影响。在静脉和自发肺转移模型中，使用抗PECAM-1抗体处理的野生型小鼠和PECAM-1缺失的小鼠，将确定候选的、PECAM-1调节的、促进生长的基因在肿瘤细胞中的基因表达水平，以及上调或下调它们的影响。临床关系：由于绝大多数癌症死亡是由转移性疾病引起的，对肿瘤转移所涉及的事件有更全面的了解，对于开发治疗晚期癌症患者的新疗法至关重要。 影响/意义：微小转移性肿瘤向肉眼可见肿瘤的晚期进展以及TME在这一过程中可能发挥的作用尚未得到有力的研究。血管上表达的PECAM-1可能通过对TME的调节参与了转移瘤的晚期进展。这代表了PECAM-1的一个意想不到的，但潜在的非常重要的新功能，可能对晚期癌症的机制理解和治疗具有重要意义。

Objectives: Stromal cells, including endothelial cells (ECs), are critical elements of the tumor microenvironment (TME), releasing factors that facilitate tumor growth. Although the role of the TME in the growth and spread of primary tumors has been investigated, less is known about the role the TME might play in regulating the progression of metastatic tumor foci. Based on extensive preliminary data we hypothesize that during the late stages of metastatic tumor progression, vascular endothelial PECAM-1 modulates the TME to induce a proliferative tumor cell gene expression profile that promotes metastatic tumor growth. To test this, studies are proposed that will (i) determine the molecular basis for the involvement of endothelial PECAM-1 in tumor metastasis to the lung (Specific Aim 1); (ii) identify PECAM-1-dependent, endothelial-derived mediators that regulate metastatic tumor growth and progression in the lung (Specific Aim 2); and (iii) characterize the influence of endothelial PECAM-1 on the gene profile of metastatic tumors in the lung (Specific Aim 3). Methodology: Specific Aim 1. Determine the molecular basis for the involvement of endothelial PECAM-1 in tumor metastasis to the lung. PECAM-1-null endothelial cells from murine lung will be transduced with wild type PECAM-1 or PECAM-1 mutated in its ability to mediate ligand binding or intracellular signaling. The resulting cells will then be used in tumor-endothelial co-culture studies to assess the effects of perturbing PECAM-1 function on tumor cell proliferation. Specific Aim 2. Identify PECAM-1-dependent, endothelial-derived mediators that regulate metastatic tumor growth and progression in the lung. In vitro cell proliferation will be studied in tumor cells cultured in conditioned media derived from tumor-endothelial co-cultures, for which the levels of expression of suspected, PECAM-1-regulated, endothelial-derived factors have been altered. The in vivo significance of any factor implicated as a PECAM-1-regulated secreted protein by these studies will then be confirmed by assessing lung metastasis in mice injected with tumors over-expressing the factor of interest. Specific Aim 3. Characterize the influence of endothelial PECAM-1 on the gene profile of metastatic tumors in the lung. The gene expression levels in tumor cells of candidate, PECAM-1- regulated, growth-promoting genes, as well as the effects of up- or down-regulating them, will be determined in intravenous and spontaneous models of lung metastasis, using wild type mice treated with anti-PECAM-1 antibody and PECAM-1-null mice. Clinical Relationship: As the vast majority of cancer deaths are caused by metastatic disease, developing a more complete understanding of the events involved in tumor metastasis will be critical to developing novel treatments for patients with advanced cancer. Impact/Significance: The late progression of micro-metastatic tumor foci to macroscopic, clinically apparent tumors and the role that the TME might play in that process has not been vigorously investigated. PECAM-1 expressed on vessels may be a mediator of the late progression of metastatic tumors through a modulation of the TME. This represents an unanticipated, but potentially very important new function for PECAM-1 that may have significant implications for the mechanistic understanding and treatment of late-stage cancer.