SIGNALING EVENTS IN STROMAL REGULATION OF BRAIN TUMOR GROWTH

描述(申请人提供)：生命的头四年是大脑发育最快的时期，也是脑瘤的高危时期。这些研究的目的是研究大脑生长和脑瘤形成之间的关系。阐明儿童脑肿瘤如何利用生长脑的微环境来刺激其生长，将促进我们对脑肿瘤生物学的理解，并为新型抗肿瘤药物的研究提供新的范式。 CXCL12及其受体CXCR4是正常脑发育和脑肿瘤生长的重要调控途径。CXCL12的S促生长活性在正常脑发育过程中受到严格调控，但在肿瘤细胞中不受调控。在已发表的研究中，G？I偶联受体CXCR4通过持续减少细胞内cAMP刺激脑瘤生长。通常，对G蛋白偶联受体的持续反应被称为脱敏的负反馈机制所阻止，该机制涉及G蛋白受体激酶对受体的磷酸化。在CXCL12诱导的cAMP持续抑制与CXCR4磷酸化缺失相关的肿瘤细胞中，这一过程是缺陷的。 这一建议解决了这样的假设，即CXCR4脱敏是调节其生长效应的分子开关：1)CXCR4脱敏必须被抑制，以便CXCR4刺激生长；2)在正常小脑发育期间，Sonic Hedgehog抑制CXCR4脱敏；以及3)在脱敏被禁用的髓母细胞瘤中，这一正常发育途径被选中。 利用三个平行的实验系统，包括从正常脑发育到恶性脑瘤生长的连续统，以确定CXCR4脱敏和生长效应之间的关系。1)在小脑组织和表达野生型或磷酸化突变型CXCR4的小脑颗粒神经元的原代培养中，将检测发育过程中CXCR4脱敏的调节以及Shh对CXCR4脱敏的调节。2)在髓母细胞瘤和其他脑肿瘤的原代培养中，将直接检测G蛋白受体激酶的表达、CXCR4的磷酸化和脱敏。3)GRK表达改变和CXCR4脱敏对颅内生长和抗肿瘤药物的异种移植反应的影响将在一个新的颅内原发人脑肿瘤异种移植系统中确定。

DESCRIPTION (provided by applicant): The first four years of life is the period of most rapid brain growth and a high-risk time for brain tumors. The intent of these studies is to examine the relationship between brain growth and brain tumor formation. Elucidating how pediatric brain tumors take advantage of the microenvironment of the growing brain to stimulate their growth will advance our understanding of brain tumor biology and constitute a new paradigm for research into novel anti-tumor agents. CXCL12 and its receptor, CXCR4, constitute an important regulatory pathway in normal brain development and in brain tumor growth. CXCL12's growth promoting activity is tightly regulated during normal brain development but unregulated in tumor cells. In published studies CXCR4, a G?i coupled receptor, stimulated brain tumor growth via sustained reductions in intracellular cAMP. Ordinarily, sustained responses to G protein coupled receptors are prevented by a negative feedback mechanism termed desensitization, which involves phosphorylation of the receptor by G protein receptor kinases. This process was deficient in tumor cells where sustained CXCL12-induced cAMP suppression was associated with a lack of CXCR4 phosphorylation. This proposal addresses the hypothesis that CXCR4 desensitization is a molecular switch that regulates its growth effects: That, 1) CXCR4 desensitization must be inhibited in order for CXCR4 to stimulate growth, 2) that sonic hedgehog inhibits CXCR4 desensitization during normal cerebellar development and 3) that this normal developmental pathway is co-opted in medulloblastoma where desensitization is disabled. Three parallel experimental systems are utilized that encompass a continuum from normal brain development to malignant brain tumor growth, to determine the relationship between CXCR4 desensitization and growth effects. 1) In cerebellar tissue and primary cultures of cerebellar granule neurons expressing wildtype or phosphorylation mutant forms of CXCR4, the regulation of CXCR4 desensitization during development and by Shh will be measured. 2) G protein receptor kinase expression, CXCR4 phosphorylation, and desensitization will be directly measured in primary cultures of medulloblastoma and other brain tumors. 3) The effect of altered GRK expression and CXCR4 desensitization on intracranial growth and xenograft responses to anti-tumor agents will be determined in a novel intracranial primary human brain tumor xenograft system.