Matricellular proteins as regulators of tumor progression

描述（由申请人提供）：细胞外基质（ECM）组装是肿瘤中新血管形成的关键方面。 因此，识别控制ECM成分与肿瘤微环境中细胞相互作用的因子对于进一步理解肿瘤血管生成至关重要。 ECM是一种基质细胞蛋白，参与ECM重塑和血管生成，并在许多类型的癌症中由基质细胞显著表达。 通过研究野生型（WT）和无SPARC动物对各种挑战（包括肿瘤植入）的反应，我们已经确定了ECM组装中的关键因素。 部分由于ECM沉积的缺陷，与在WT小鼠中生长的肿瘤相比，在SPARC缺失小鼠中生长的胰腺肿瘤大3倍，并且转移增加3倍。 我们已经确定，肿瘤生长的情况下，显示微血管密度减少20%，周细胞招募到血管减少50%，以及胶原相关的核心蛋白聚糖，在控制TGF-？生物利用度 我们预测，由于血管通透性和灌注的增加，SPARC基因敲除小鼠的肿瘤负荷增加得到了血管减少的支持。 初步研究还表明，与WT对应物相比，从SPARC-无效细胞分泌后，更大量的胶原蛋白与细胞膜结合。 基于这些观察，我们假设，一个主要的功能是控制胶原细胞的相互作用，增加连接的胶原结合整合素（？一个？1、？两个人？1)在没有血管内皮细胞的情况下，胶原I和IV对内皮细胞的作用导致1）ECM沉积减少，伴随着不规则的血管基底膜形成，2）抑制？v？3）通过称为反式显性整合素抑制的机制激活，和3）可溶性TGF-β增加，这导致周细胞募集减少。 我们将使用WT和SPARC-无效动物的原位胰腺肿瘤模型以及体外方法，通过三个具体目标来评估我们的假设：（1）我们将确定是否cardiac降低胶原I和/或IV与内皮细胞整合素的结合，以及这是否会导致抑制？v？3激活。(2)我们将描述血管基底膜组装和功能的具体差异，导致缺乏血管内皮细胞。 (3)我们将确定是否增加可溶性TGF-？在没有血管紧张素Ⅱ的情况下， 整合素信号传导是血管生成的关键控制点，因此表征整合素在调节胶原与整合素相互作用中的功能对于我们理解血管生成过程和改进用于癌症治疗的抗整合素策略是必不可少的。

DESCRIPTION (provided by applicant): Extracellular matrix (ECM) assembly is a critical aspect of new blood vessel formation in tumors. Hence identification of factors that control the interaction of ECM components with cells in the tumor microenvironment is of paramount importance for furthering our understanding of tumor angiogenesis. SPARC is a matricellular protein that participates in ECM remodeling and angiogenesis and is expressed prominently by stromal cells in many types of cancer. By studying the response of wild-type (WT) and SPARC-null animals to various challenges, including tumor implantation we have identified SPARC as a critical factor in assembly of ECM. Due in part to defects in ECM deposition, pancreatic tumors grown in SPARC-null mice are 3-fold larger and have a 3-fold increase in metastases in comparison to tumors grown in WT mice. We have established that tumors grown in the absence of SPARC show a 20% reduction in microvessel density and a 50% reduction in pericyte recruitment to blood vessels, as well as a substantial decrease in the level of collagen-associated decorin, a key factor in controlling TGF-? bioavailability. We predict that increased tumor burden in SPARC-null mice is supported by fewer blood vessels due to increases in vascular permeability and in perfusion. Preliminary studies also indicate that greater amounts of collagen associate with cell membranes after secretion from SPARC-null cells than WT counterparts. Based on these observations, we hypothesize that a primary function of SPARC is to control collagen-cell interaction and that increased ligation of collagen-binding integrins (?1?1 and ?2?1) on endothelial cells by collagens I and IV in the absence of SPARC results in 1) decreased ECM deposition accompanied by irregular vascular basement membrane formation, 2) inhibition of ?v?3 activation by a mechanism termed transdominant integrin inhibition, and 3) an increase in soluble TGF-?, which results in reduced pericyte recruitment. We will use an orthotopic pancreatic tumor model in WT and SPARC-null animals, as well as in vitro methods, to evaluate our hypothesis through three specific aims: (1) We will determine if SPARC decreases collagen I and/or IV binding to endothelial cell integrins and whether this results in inhibition of ?v?3 activation. (2) We will delineate specific differences in vascular basement membrane assembly and function resulting from the absence of SPARC. (3) We will determine whether increased soluble TGF-? is responsible for decreased pericyte recruitment in the absence of SPARC. Integrin signaling is a pivotal control point for angiogenesis and therefore characterization of the function of SPARC in the regulation of collagen interaction with integrins is essential for our understanding of the angiogenic process and the refinement of anti-integrin strategies for cancer therapy.