Differential Expression Pattern of THBS1 and THBS2 in Lung Cancer: Clinical Outcome and a Systematic-Analysis of Microarray Databases

Thrombospondin 1 and thrombospondin 2 (THBS1 and THBS2) share similar multifunctional domains, and are known to be antiangiogenic. However, the expression pattern of THBS1 and THBS2 is different, and the specific role of THBS2 in different subtypes of lung cancer remains largely unclear. To evaluate the significance of THBS1 and THBS2 in the development of lung cancer, the present study performed a microarray-based systematic-analysis to determine the transcript levels of thrombospondins and their relation to the prognosis in lung cancer. THBS1 was in general underexpressed in lung cancer; in contrast, mRNA levels of THBS2 were markedly overexpressed in a number of datasets of non-small cell lung carcinoma (NSCLC), including lung adenocarcinoma (AC) and squamous cell carcinoma. Similar expression pattern of THBS1 and THBS2 was verified in pulmonary AC cell lines with real-time PCR analysis. The survival of lung AC patients with high THBS2 mRNA expression levels was poorer than patients with low levels of expression of THBS2. In a microarray-based analysis, genes coexpressed with THBS1 or THBS2 were determined. Pulmonary AC patients with a high expression level of sevenTSHB1-coexpressed genes (CCL5, CDH11, FYB, GZMK, LA-DQA1, PDE4DIP, and SELL) had better survival rates than those with a low expression level. Patients with a high expression of seven TSHB2-coexpressed genes (CHI3L1, COL5A2, COL11A1, FAP, MXRA5, THY1, and VCAN) had poor survival rates. Downregulation of VCAN and THBS2 with shRNA inhibited the cell proliferation in the A549 cell line. In summary, THBS1 functions as a tumor suppressor in lung adenocarcinoma. However, THBS2 may play a double-edged role in the progression of lung AC, i.e. anti-angiogenic and oncogenic function. Further study on the mechanism underlying the activity of THBS2 is warranted to have further implications for cancer diagnosis and treatment of pulmonary AC.血小板反应蛋白1与血小板反应蛋白2（Thrombospondin 1 and thrombospondin 2, 即THBS1与THBS2）拥有相似的多功能结构域，且被证实具有抗血管生成活性。然而二者的表达模式存在显著差异，且THBS2在不同肺癌亚型中的具体功能仍有待阐明。为评估THBS1与THBS2在肺癌发生发展中的意义，本研究通过基于微阵列（microarray）的系统分析，检测了血小板反应蛋白家族的转录水平，并分析其与肺癌患者预后的关联。THBS1在肺癌组织中普遍呈低表达；与之相反，THBS2的mRNA水平在多项非小细胞肺癌（non-small cell lung carcinoma, NSCLC）数据集（包括肺腺癌（lung adenocarcinoma, AC）与鳞状细胞癌样本）中显著高表达。通过实时荧光定量PCR（real-time PCR）验证，肺腺癌细胞系中THBS1与THBS2的表达模式与上述结果一致。THBS2 mRNA高表达的肺腺癌患者，其总体生存情况显著劣于THBS2低表达患者。在本次微阵列分析中，研究人员还鉴定出了与THBS1或THBS2共表达的基因。其中，7个THBS1共表达基因（CCL5、CDH11、FYB、GZMK、LA-DQA1、PDE4DIP及SELL）高表达的肺腺癌患者，生存情况优于低表达该组基因的患者。而7个THBS2共表达基因（CHI3L1、COL5A2、COL11A1、FAP、MXRA5、THY1及VCAN）高表达的患者，生存情况则较差。通过短发夹RNA（shRNA）下调VCAN与THBS2的表达，可抑制A549细胞系的细胞增殖。综上，THBS1在肺腺癌中发挥肿瘤抑制因子的作用。而THBS2在肺腺癌进展中可能兼具双重功能：既具有抗血管生成活性，又可作为致癌因子促进肿瘤发展。未来需进一步阐明THBS2发挥功能的分子机制，以期为肺腺癌的临床诊断与治疗提供新的理论依据。