SIGNALING EVENTS IN STROMAL REGULATION OF BRAIN TUMOR GROWTH

描述（由申请人提供）：生命的前四年是大脑生长最快的时期，也是脑肿瘤的高风险时期。这些研究的目的是检查脑生长和脑肿瘤形成之间的关系。阐明小儿脑肿瘤如何利用大脑生长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，并构成研究新型抗肿瘤药物的新范式。 CXCL12及其受体CXCR4在正常脑发育和脑肿瘤生长中构成重要的调节途径。CXCL12的生长促进活性在正常脑发育期间受到严格调节，但在肿瘤细胞中不受调节。在已发表的研究CXCR4，一个G？I偶联受体，通过持续减少细胞内cAMP刺激脑肿瘤生长。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阻止，该机制涉及G蛋白受体激酶对受体的磷酸化。这一过程在肿瘤细胞中是缺乏的，其中持续的CXCL12诱导的cAMP抑制与CXCR4磷酸化的缺乏相关。 该提议解决了CXCR4脱敏是调节其生长效应的分子开关的假设：1）CXCR4脱敏必须被抑制以使CXCR4刺激生长，2）音刺猬在正常小脑发育期间抑制CXCR4脱敏，以及3）该正常发育途径在脱敏被禁用的髓母细胞瘤中被增选。 利用三个平行的实验系统，包括从正常脑发育到恶性脑肿瘤生长的连续体，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形式的CXCR4的小脑颗粒神经元的原代培养物中，将测量发育期间和Shh对CXCR4脱敏的调节。2)G蛋白受体激酶表达、CXCR4磷酸化和脱敏将在髓母细胞瘤和其他脑肿瘤的原代培养物中直接测量。3)将在新的颅内原发性人脑肿瘤异种移植系统中确定改变的GRK表达和CXCR4脱敏对颅内生长和异种移植物对抗肿瘤剂的反应的影响。

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.