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，确定控制肿瘤微环境中ECM成分与细胞相互作用的因素对于进一步了解肿瘤血管生成至关重要。SPARC是一种参与ECM重塑和血管生成的基质细胞蛋白，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SPARC缺失动物对各种挑战（包括肿瘤植入）的反应，我们已经确定SPARC是ECM组装的关键因素。部分由于ECM沉积缺陷，SPARC-null小鼠生长的胰腺肿瘤比WT小鼠生长的肿瘤大3倍，转移率增加3倍。我们已经确定，在没有SPARC的情况下生长的肿瘤显示微血管密度减少20%，周细胞向血管募集减少50%，胶原相关的decorin水平大幅下降，胶原相关的decorin是控制TGF-？生物利用度。我们预测，由于血管通透性和灌注增加，sparc缺失小鼠的肿瘤负荷增加是由血管减少所支持的。初步研究还表明，SPARC-null细胞分泌后，与WT细胞相比，更多的胶原蛋白与细胞膜相关。基于这些观察，我们假设SPARC的主要功能是控制胶原-细胞相互作用，并增加胶原结合整合素的连接(1)。1和2？1)在缺乏SPARC的情况下，I型和IV型胶原对内皮细胞的作用导致1)ECM沉积减少，并伴有不规则的血管基底膜形成；通过一种被称为跨显性整合素抑制的机制激活，以及3)可溶性TGF-？，导致周细胞募集减少。我们将使用WT和SPARC缺失动物的原位胰腺肿瘤模型，以及体外方法，通过三个特定目的来评估我们的假设：(1)我们将确定SPARC是否会降低胶原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？3激活。(2)我们将描述由于SPARC缺失导致的血管基底膜组装和功能的具体差异。(3)我们将测定可溶性TGF-？在缺乏SPARC的情况下导致周细胞募集减少。整合素信号是血管生成的关键控制点，因此表征SPARC在胶原与整合素相互作用的调节中的功能，对于我们理解血管生成过程和改进癌症治疗的抗整合素策略至关重要。

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.