Matricellular proteins as regulators of tumor progression

描述(申请人提供)：细胞外基质(ECM)组装是肿瘤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的相互作用的因素对于加深我们对肿瘤血管生成的理解是至关重要的。SPARC是一种基质细胞蛋白，参与ECM重塑和血管生成，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缺失型动物对包括肿瘤植入在内的各种挑战的反应，我们发现SPARC是ECM组装的关键因素。部分由于细胞外基质沉积的缺陷，与生长在WT小鼠中的肿瘤相比，生长在SPARC基因缺失小鼠中的胰腺肿瘤大小是WT小鼠的3倍，转移率是WT小鼠的3倍。我们已经证实，在没有SPARC的情况下生长的肿瘤显示出微血管密度减少20%，周细胞向血管内募集减少50%，以及胶原相关核心蛋白的水平显著降低，这是控制转化生长因子？生物利用度。我们预测，SPARC基因缺失小鼠肿瘤负担的增加是由较少的血管支持的，这是由于血管渗透性和灌注量的增加。初步研究还表明，SPARC阴性细胞分泌的胶原蛋白比WT细胞分泌的胶原蛋白更多。基于这些观察，我们假设SPARC的主要功能是控制胶原与细胞的相互作用，并且在没有SPARC的情况下，胶原结合整合素(？1？1和？2？1)在没有SPARC的情况下增加对内皮细胞的连接，导致1)细胞外基质沉积减少，伴随着不规则的血管基底膜形成，2)通过一种称为跨显性整合素抑制的机制抑制？V？3的激活，以及3)增加可溶性的转化生长因子-1，从而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，通过三个特定的目的来评估我们的假设：(1)我们将确定SPARC是否减少I型和/或IV型胶原与内皮细胞整合素的结合，以及这是否导致抑制？V？3的激活。(2)我们将描述由于缺乏SPARC而导致的血管基底膜组装和功能的具体差异。(3)测定血清中可溶性转化生长因子-α是否升高。是在没有SPARC的情况下周细胞募集减少的原因。整合素信号是血管生成的关键控制点，因此，研究SPARC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完善肿瘤治疗的抗整合素策略是至关重要的。

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.