Chen Yuan, Pacyna-Gengelbach Manuela, Deutschmann Nicole, Niesporek Silvia, Petersen Iver
Institute of Pathology, University Hospital Charité, Schumannstr 20-21, D-10098 Berlin, Germany.
Int J Cancer. 2007 Sep 1;121(5):1021-7. doi: 10.1002/ijc.22753.
The homeobox containing gene HOP (Homeodomain Only Protein) was identified in the developing heart and lung where it functions downstream of Nkx2.5 and Nkx2.1 to modulate cardiac and lung gene expression. Previously, we found that HOP was downregulated in lung cancer. In this study, we constructed an expression vector containing the full-length cDNA of HOP and transfected it into a lung cancer cell line H2170. Stable transfection led to an increased expression of HOP confirmed by Northern blot analysis. HOP positive transfectants remarkably reduced the growth rate and the ability of anchorage-independent growth in soft agar, and moreover suppressed the tumor formation in nude mice compared to controls. Transient transfection of Nkx2.1 into H2170 resulted in the overexpression of HOP, and correspondingly, siRNA silencing of Nkx2.1 reduced the expression of HOP in lung cancer cells. Treatment with a differentiation modulating agent 5-bromodeoxyuridine (BrdU) led to restoration of HOP expression in a small cell lung cancer cell line H526. In 29 paired primary lung tumor samples, loss of heterozygosity (LOH) analysis was performed by using the 3 microsatellite markers D4S189, D4S231 and D4S392 around the region of chromosome 4q12 where HOP locates. LOH was only found in 4 out 23 cases (17.4%) indicating that allelic loss is a rare genetic event not responsible for the downregulation of HOP in lung cancer. Taken together, our data suggest that HOP is a potential tumor suppressor possibly involved in lung cancer differentiation, and functions downstream of Nkx2.1.
含有同源异型盒的基因HOP（仅含同源结构域蛋白）是在发育中的心脏和肺中发现的，它在Nkx2.5和Nkx2.1的下游发挥作用，调节心脏和肺的基因表达。此前，我们发现HOP在肺癌中表达下调。在本研究中，我们构建了一个包含HOP全长cDNA的表达载体，并将其转染到肺癌细胞系H2170中。通过Northern印迹分析证实，稳定转染导致HOP表达增加。与对照相比，HOP阳性转染子显著降低了生长速率和在软琼脂中不依赖贴壁生长的能力，此外还抑制了裸鼠体内的肿瘤形成。将Nkx2.1瞬时转染到H2170中导致HOP过表达，相应地，Nkx2.1的siRNA沉默降低了肺癌细胞中HOP的表达。用分化调节剂5-溴脱氧尿苷（BrdU）处理导致小细胞肺癌细胞系H526中HOP表达恢复。在29对原发性肺肿瘤样本中，使用位于HOP所在的4q12染色体区域周围的3个微卫星标记D4S189、D4S231和D4S392进行杂合性缺失（LOH）分析。仅在23例中的4例（17.4%）中发现了LOH，这表明等位基因缺失是一种罕见的遗传事件，与肺癌中HOP的下调无关。综上所述，我们的数据表明HOP是一种潜在的肿瘤抑制因子，可能参与肺癌分化，并在Nkx2.1的下游发挥作用。
