Department of Cancer Genetics, Roswell Park Cancer Institute, Buffalo, New York, 14263, USA.
Department of Cell Stress Biology, Roswell Park Cancer Institute, Buffalo, New York, USA.
BMC Cancer. 2018 Jun 19;18(1):670. doi: 10.1186/s12885-018-4587-z.
The breast cancer microenvironment promotes tumor vascularization through the complex interactions involving tumor-associated fibroblasts (TAFs). Emerging data indicate that TAFs increase production and signaling by TGF-β cytokines, while the role of TGF-β signaling in the regulation of tumor blood vessels is not fully understood. The current study presents evidence that TAFs enhance the organization of tumor blood capillaries, and TGF-β signaling plays an important role in this response.
Tumor vascularization was studied in xenograft models of breast carcinoma cells, alone and in combination with fibroblasts. TGF-β signaling in breast cancer cells was modulated by expression of kinase-inactive TGFBR1-K232R (dnTGFBR1) or constitutive-active TGFBR1-T204D (caTGFBR1) receptor mutants. The architecture of tumor blood capillaries was assessed by immune-histochemical analysis of endothelium and pericytes. The role of TGF-β-Smad signaling in fibronectin expression was examined using adenoviral transduction of signaling components.
Our studies revealed that TAFs significantly increase the lumen size of blood microvessels. Inactivation of TGF-β signaling in tumor cells by dnTGFBR1 reduced the microvessel density and lumen sizes, decreasing tumor growth. In contrast, caTGFBR1-tumors exhibited greater vessel density and lumen sizes. Tumors with inactive dnTGFBR1 showed lower amounts of TAFs, while caTGFBR1 increased amounts of TAFs compared to the control. Inspection of pericytes and endothelial cells in tumor vasculature revealed that TAFs enhanced vessel coverage by pericytes, vascular cells supporting capillaries. This effect was impaired in dnTGFBR1-tumors, whereas active caTGFBR1 enhanced the association of pericytes with endothelium. Accordingly, dnTGFBR1-tumors exhibited the presence of hemorrhages, a sign of fragile blood vessels. Biochemical analysis showed that TGFBR1-SMAD signaling up-regulates fibronectin, a prominent regulator of endothelium-pericyte interactions.
The current study indicates that tumor-fibroblast crosstalk enhances tumor vascularization by increasing the pericyte-endothelium association via a mechanism involving the TGFβ-fibronectin axis. The tumor-fibroblast model represents a useful system for dissecting the complex interactions governing tumor angiogenesis and developing new approaches to therapeutic targeting tumor vasculature.
乳腺癌微环境通过涉及肿瘤相关成纤维细胞（TAFs）的复杂相互作用促进肿瘤血管生成。新出现的数据表明，TAFs 增加 TGF-β 细胞因子的产生和信号转导，而 TGF-β 信号转导在调节肿瘤血管方面的作用尚不完全清楚。本研究提供的证据表明，TAFs 增强了肿瘤毛细血管的组织，TGF-β 信号转导在这一反应中起着重要作用。
在乳腺癌细胞的异种移植模型中单独研究和与成纤维细胞一起研究肿瘤血管生成。通过表达激酶失活 TGFBR1-K232R（dnTGFBR1）或组成型活性 TGFBR1-T204D（caTGFBR1）受体突变体来调节乳腺癌细胞中的 TGF-β 信号转导。通过免疫组织化学分析内皮细胞和周细胞来评估肿瘤毛细血管的结构。使用信号转导成分的腺病毒转导来研究 TGF-β-Smad 信号转导在纤维连接蛋白表达中的作用。
我们的研究表明，TAFs 可显著增加微血管的管腔大小。肿瘤细胞中 dnTGFBR1 的 TGF-β 信号转导失活减少了微血管密度和管腔大小，从而降低了肿瘤生长。相反，caTGFBR1-肿瘤表现出更高的血管密度和管腔大小。具有失活 dnTGFBR1 的肿瘤中 TAFs 的数量减少，而与对照相比，caTGFBR1 增加了 TAFs 的数量。对肿瘤血管中的周细胞和内皮细胞进行检查表明，TAFs 增强了周细胞对毛细血管的覆盖，周细胞是支持毛细血管的血管细胞。这种作用在 dnTGFBR1-肿瘤中受损，而活性 caTGFBR1 增强了周细胞与内皮细胞的关联。因此，dnTGFBR1-肿瘤存在出血，这是血管脆弱的迹象。生化分析表明，TGFBR1-SMAD 信号转导通过上调纤维连接蛋白而上调，纤维连接蛋白是内皮细胞-周细胞相互作用的主要调节因子。
本研究表明，肿瘤-成纤维细胞相互作用通过增加周细胞-内皮细胞的关联来增强肿瘤血管生成，其机制涉及 TGFβ-纤维连接蛋白轴。肿瘤-成纤维细胞模型代表了一种用于剖析控制肿瘤血管生成的复杂相互作用并开发新的靶向肿瘤血管治疗方法的有用系统。
