Fibroblast α11β1 Integrin Regulates Tensional Homeostasis in Fibroblast/A549 Carcinoma Heterospheroids

We have previously shown that fibroblast expression of α11β1 integrin stimulates A549 carcinoma cell growth in a xenograft tumor model. To understand the molecular mechanisms whereby a collagen receptor on fibroblast can regulate tumor growth we have used a 3D heterospheroid system composed of A549 tumor cells and fibroblasts without (α11+/+) or with a deletion (α11-/-) in integrin α11 gene. Our data show that α11-/-/A549 spheroids are larger than α11+/+/A549 spheroids, and that A549 cell number, cell migration and cell invasion in a collagen I gel are decreased in α11-/-/A549 spheroids. Gene expression profiling of differentially expressed genes in fibroblast/A549 spheroids identified CXCL5 as one molecule down-regulated in A549 cells in the absence of α11 on the fibroblasts. Blocking CXCL5 function with the CXCR2 inhibitor SB225002 reduced cell proliferation and cell migration of A549 cells within spheroids, demonstrating that the fibroblast integrin α11β1 in a 3D heterospheroid context affects carcinoma cell growth and invasion by stimulating autocrine secretion of CXCL5. We furthermore suggest that fibroblast α11β1 in fibroblast/A549 spheroids regulates interstitial fluid pressure by compacting the collagen matrix, in turn implying a role for stromal collagen receptors in regulating tensional hemostasis in tumors. In summary, blocking stromal α11β1 integrin function might thus be a stroma-targeted therapeutic strategy to increase the efficacy of chemotherapy.

我们此前已证实，成纤维细胞表达的整合素α11β1（integrin α11β1）可在异种移植肿瘤模型（xenograft tumor model）中促进A549癌细胞的增殖。为阐明成纤维细胞表面的胶原受体调控肿瘤生长的分子机制，我们构建了由A549肿瘤细胞与整合素α11基因野生型（α11+/+）或敲除型（α11-/-）成纤维细胞组成的三维异球体系统（3D heterospheroid system）。实验数据显示，α11-/-/A549异球体的体积显著大于α11+/+/A549异球体；且在Ⅰ型胶原凝胶（collagen I gel）中，α11-/-/A549异球体的A549细胞数量、迁移能力与侵袭能力均出现降低。对成纤维细胞/A549异球体中的差异表达基因进行基因表达谱分析后，我们发现CXCL5是成纤维细胞缺失α11时A549细胞中下调的关键分子之一。使用CXCR2抑制剂SB225002阻断CXCL5的功能后，异球体内部A549细胞的增殖与迁移能力均受到显著抑制；这表明在三维异球体微环境中，成纤维细胞整合素α11β1可通过刺激CXCL5的自分泌分泌，调控癌细胞的增殖与侵袭能力。此外我们提出，成纤维细胞/A549异球体中的成纤维细胞α11β1可通过压缩胶原基质来调节组织间液压力，这一结果也提示基质胶原受体在调控肿瘤张力稳态中具有重要作用。综上，阻断基质α11β1整合素的功能或可成为一种靶向肿瘤基质的治疗策略，用于提升化疗的临床疗效。