Department of Medical Cell Biology, Uppsala University, Box 571, Husargatan 3, 75123 Uppsala, Sweden.
Mol Oncol. 2012 Jun;6(3):333-46. doi: 10.1016/j.molonc.2012.01.006. Epub 2012 Jan 31.
The Shb adapter protein is a signaling intermediate that operates downstream of vascular endothelial growth factor receptor-2 (VEGFR-2) in endothelial cells. The Shb knockout mouse displays a dysfunctional microvasculature and impaired growth of subcutaneously implanted tumor cells. We decided to investigate tumor growth and angiogenesis in the absence of Shb in an inheritable tumor model, the RIP-Tag2 mouse, which produces insulinomas in a manner highly dependent on de novo angiogenesis. We observed a reduced tumor incidence and burden in both RIP-Tag2 Shb-/- and RIP-Tag2 Shb+/- mice. This correlated with a reduced microvascular density, measured as a percentage of insulinoma area positive for CD31 staining, and altered vascular morphology. However, treatment with a VEGF-A blocking antibody was without effect on the Shb mutant tumor volume whereas it significantly inhibited tumor volume in the wild-type mice, suggesting that in mice with reduced Shb expression tumor angiogenesis was primarily sustained by VEGF-A independent pathway(s). This notion was further substantiated by gene expression analysis of angiogenic markers showing reduced VEGF-A expression in Shb-deficient tumors. Considerable heterogeneity with respect to the gene expression profiles of other angiogenic markers and the signal-transduction characteristics was observed between different tumors, suggesting that multiple "rescue" pathways could be operating. The numbers of invasive tumors or metastases were unchanged in the Shb mutant. It is concluded that the Shb mutant background reduces tumor frequency by chronically suppressing VEGF-A dependent angiogenesis. However, VEGF-A independent angiogenesis supports a significant degree of tumor expansion in Shb-deficient mice, indicating heterogeneity in the mechanisms by which tumor expansion is promoted. Interference with Shb signaling may provide novel means for future cancer therapy.
Shb 衔接蛋白是一种信号中间物，在血管内皮生长因子受体-2（VEGFR-2）下游的内皮细胞中发挥作用。Shb 敲除小鼠表现出功能性微血管功能障碍和皮下植入的肿瘤细胞生长受损。我们决定在可遗传的肿瘤模型 RIP-Tag2 小鼠中研究 Shb 缺失时的肿瘤生长和血管生成，该模型以高度依赖新血管生成的方式产生胰岛素瘤。我们观察到 RIP-Tag2 Shb-/-和 RIP-Tag2 Shb+/-小鼠的肿瘤发生率和负担均降低。这与微血管密度的降低相关，微血管密度以 CD31 染色阳性的胰岛素瘤面积的百分比来衡量，并且血管形态发生改变。然而，用 VEGF-A 阻断抗体治疗对 Shb 突变型肿瘤体积没有影响，而对野生型小鼠的肿瘤体积有显著抑制作用，这表明在 Shb 表达降低的小鼠中，肿瘤血管生成主要通过 VEGF-A 非依赖性途径（s）维持。这一观点进一步通过血管生成标志物的基因表达分析得到证实，结果显示 Shb 缺陷型肿瘤中 VEGF-A 表达降低。不同肿瘤之间观察到关于其他血管生成标志物的基因表达谱和信号转导特征的相当大的异质性，表明可能存在多种“拯救”途径。Shb 突变体的侵袭性肿瘤或转移瘤数量不变。结论是，Shb 突变体背景通过慢性抑制 VEGF-A 依赖性血管生成来降低肿瘤频率。然而，VEGF-A 非依赖性血管生成支持 Shb 缺陷型小鼠中肿瘤的显著扩张，表明肿瘤扩张的机制存在异质性。干扰 Shb 信号可能为未来的癌症治疗提供新的方法。
