Functional role of tumor metastases suppressor gene, KAl1, in tumor progression

描述(申请人提供)：超过95%的癌症患者死于转移，这是恶性肿瘤的标志。尽管最近的手术技术和化疗方法有了很大的进步，但目前的医学技术都没有“治愈”转移的疾病，获得转移癌症的患者不可避免地会死亡。因此，迫切需要开发一种针对转移瘤细胞的新的靶向特异性治疗方法，这就需要更全面地了解转移的分子机制。KAI1基因(又称CD82)是一种肿瘤转移抑制基因，在各种类型的肿瘤中表达显著下调，该基因的过表达能够在不影响体内原发肿瘤生长的情况下阻断转移。然而，抑制转移的确切分子机制还不是很清楚。我们最近发现(1)肿瘤细胞上的KAI1与内皮细胞上的DARC相互作用，(2)KAI1-DARC上调p21和下调TBX2的相互作用，(3)这种对TBX2-p21信号的调控导致肿瘤细胞衰老，(4)在DARC基因敲除小鼠中，KAI1的转移抑制活性显著降低。这些结果突出了DARC基因以前未被认识到的功能，并将KAI-DARC信号确定为潜在的转移性癌症治疗干预的新候选信号。根据我们的初步数据，我们假设KAI1与整合素、Tetraspanins和PKC形成一个“多蛋白复合体”，当癌细胞进入血管时，KAI1与内皮细胞上的DARC结合，随后PKC激活/失活，从而导致p21上调并诱导癌细胞衰老。为了验证这一假设，我们将(I)检测包括整合素、kitenin、EGFR、c-Met、CD63、CD9和PKC在内的多蛋白复合体中的每个因子在KAI1的转移抑制功能中的作用；(Ii)检测KAI1-DARC相互作用诱导衰老的信号通路；(Iii)通过检测抗KAI1抗体和识别小化学物质来检测靶向KAI1-DARC信号的治疗潜力。我们的长期目标是阐明KAI1在抑制肿瘤转移中的功能作用，并开发一种模拟KAI1基因功能的新的治疗方法。我们认为，拟议的实验结果应该为实现我们的最终目标--控制癌症患者的肿瘤转移--提供基本信息。

DESCRIPTION (provided by applicant): More than 95% of cancer patients succumb to the disease due to metastases which is the hallmark of malignant cancer. Despite significant improvements in recent surgical techniques and chemotherapies, none of the current medical technologies "cure" the metastatic disease, and the patients who have acquired metastatic cancer inevitably die. Therefore, there is an urgent need for developing a novel target-specific therapy to metastatic tumor cells, which requires more comprehensive understanding of the molecular mechanism of metastases. The KAI1 gene (also called CD82), is a tumor metastases suppressor whose expression is significantly down-regulated in various types of cancers, and over-expression of this gene is capable of blocking metastases without affecting the primary tumor growth in vivo. However, the exact molecular mechanism of the metastases suppression has not been well understood. We have recently found that (i) KAI1 on tumor cells interacts with DARC on endothelial cell, (ii) the interaction of KAI1-DARC up-regulated p21 and down-regulated TBX2, (iii) this modulation of TBX2-p21 signal lead to senescence of tumor cell, and (iv) metastases suppressor activity of KAI1 is significantly compromised in DARC knockout mouse. These results highlight a previously unappreciated function of the DARC gene and identified the KAI-DARC signal as a novel candidate for potential therapeutic intervention for metastatic cancer. Based on our preliminary data we hypothesize that KAI1 forms a "multi-protein complex" with integrins, tetraspanins and PKC and that when the cancer cell intravasates, KAI1 binds to DARC on an endothelial cell followed by activation/inactivation of PKC, which results in up-regulation of p21 and induction of senescence of the cancer cell. To test this hypothesis, we will (i) examine the role of each factor of the multi-protein complex including integrins, kitenin, EGFR, c-Met, CD63, CD9 and PKC in the metastasis suppressor function of KAI1, (ii) examine the signal pathway of senescence induced by KAI1-DARC interaction and (iii) examine therapeutic potential of targeting KAI1-DARC signal by testing anti-KAI1 antibody and also by identifying small chemicals. Our long-term goal is to elucidate the functional role of KAI1 in tumor metastases suppression and to develop a novel therapeutic method which mimics the function of the KAI1 gene. We believe that the results of the proposed experiments should provide fundamental information to accomplish our ultimate goal, the control of tumor metastasis in cancer patients.