THE ROLE OF SPARC IN GLIOMA INVASION

描述(申请人提供)：胶质瘤患者预后差的主要原因是这些肿瘤的高度侵袭性。富含半胱氨酸的酸性分泌蛋白(SPARC)在胶质瘤中高表达。我们已经证明SPARC在体外和体内有不同的作用，促进胶质瘤的侵袭，同时减缓胶质瘤的增殖。改变这些表型的能力使其成为治疗胶质瘤的主要治疗靶点。然而，目前尚不清楚这两种机制是否可以单独靶向，从而抑制其在侵袭中的作用，但允许其抑制生长的作用。此外，肿瘤的侵袭表型很复杂，既需要改变肿瘤细胞的运动性，也需要细胞外基质(ECM)的降解，为浸润性细胞提供空间。SPARC在这两项职能中的作用可能也需要单独瞄准。此外，还不知道SPARC是否在细胞内发挥作用，或者如果有的话，大脑内源性SPARC可能对这一过程做出什么贡献。我们认为SPARC通过不同的机制调节ECM的降解、肿瘤细胞的运动和肿瘤细胞的增殖。以下具体目标旨在描述这些独立的途径。在特定的目标1中，我们将描述SPARC在体外调控侵袭的细胞外机制。这一目标将集中在SPARC通过增加邻近ECM的降解来促进入侵的能力。特别是，我们将研究它与ECM蛋白Vitronectin、调节ECM降解的SPARC上调的酶(MMP-2、MT1-MMP、PAL-1)以及αv整合素的相互作用。在特定的目标2中，我们将描述SPARC调节体内侵袭的细胞外机制。我们将在体内进行平行实验，以确定内源性SPARC是否在SPARC诱导的侵袭中发挥作用，以及是否可以通过干扰整合素和/或基质金属蛋白酶的活性来抑制诱导的侵袭。在特定的目标3中，我们将确定肿瘤细胞中SPARC的缺失是否足以抑制肿瘤的侵袭，促进体内肿瘤的生长和增殖。我们将使用一种新的肿瘤模型，包括P53-/-/Sparc+/+与P53-/-/Sparc-/-转化的星形胶质细胞，以确定SPARC的缺失是否将高侵袭性的P53-/-/Sparc+/+肿瘤转化为非侵袭性、高增殖的肿瘤。在特定的目标4中，我们将确定SPARC是否通过β1整合素依赖或独立的细胞内信号介导运动，但不是增殖。我们还将确定SPARC对表型的调节是否源于细胞和细胞外定位的差异。

DESCRIPTION (provided by applicant): The poor prognosis of glioma patients is largely due to the highly invasive nature of these tumors. Secreted protein acidic and rich in cysteine (SPARC) is highly expressed in gliomas. We have demonstrated that SPARC has disparate effects in vitro and in vivo, promoting glioma invasion while slowing glioma proliferation. The ability to alter these phenotypes makes it a prime therapeutic target for the treatment of gliornas. However, it is not known whether these two mechanisms can be targeted independently, thereby allowing the inhibition of its role in invasion but permitting its growth-suppressive effect. In addition the invasive phenotype is complex, requiring both changes in tumor cell motility as well as degradation of the extracellular matrix (ECM) to provide space for infiltrating cells. SPARC's role in both of these functions may also need to be targeted separately. Furthermore, it is not known if SPARC functions within the cell, or what contribution, if any, brain endogenous SPARC may contribute to the process. We propose that SPARC modulates ECM degradation, tumor cell motility, and tumor cell proliferation via separate mechanisms. The following Specific Aims are directed at characterizing these independent pathways. In Specific Aim 1, we will characterize the extracellular mechanisms by which SPARC modulates invasion in vitro. This aim will focus on SPARC's ability to promote invasion by increasing the degradation of the adjacent ECM. In particular, we will examine its interactions with the ECM protein vitronectin, with the SPARC-upregulated enzymes that modulate ECM degradation (MMP-2, MT1-MMP, PAl-1), and the alpha v integrins. In Specific Aim 2, we will characterize the extracellular mechanisms by which SPARC modulates invasion in vivo. We will perform parallel experiments in vivo to determine whether endogenous SPARC plays a role in SPARC-induced invasion and whether the induced invasion can be inhibited by interfering with integrin and/or MMP activity. In Specific Aim 3, we will determine whether the loss of SPARC in tumor cells is sufficient to inhibit tumor invasion and increase tumor growth and proliferation in vivo. We will use a novel tumor model consisting of p53-/- / Sparc +/+ versus p53-/- / Sparc -/-transformed astrocytes to determine whether the loss of SPARC converts the highly invasive p53-/- / Sparc +/+ tumors into noninvasive, highly proliferative tumors. In Specific Aim 4, we will determine whether SPARC mediates motility, but not proliferation, via beta1 integrin-dependent or -independent intracellular signaling. We will also determine whether SPARC's regulation of the phenotypes results from differences in cellular versus extracellular localization.