Carboxypeptidase A4 promotes migration and invasion of lung cancer cells, and is closely associated with lymph node metastasis

Abstract Objective The incidence and mortality rate of lung cancer ranks first among all malignant tumors. Lymph node metastasis is the most common mode of metastasis in lung cancer, and it is also an important indicator for treatment strategies and prognosis. Several studies have shown that the carboxypeptidase family plays important roles in cancer metastasis. In the present study, we investigated the effect of carboxypeptidase A4 (CPA4) on human lung cancer cells, and the clinical significance of its levels in lung cancer tissues and corresponding lymph node metastasis tissues. Methods Real‐time quantitative polymerase chain reaction and western blotting were used to detect the expression levels of CPA4 in cancer cells after transfecting them with CPA4 interference sequence (siRNA‐CPA4) and the negative control sequence. Transwell assay with/without Matrigel was used to assess the effect of CPA4 on cell invasion and migration. CPA4 expression was detected in eight normal lung tissues, 46 lung cancer tissues, and the corresponding lymph node metastasis tissues using immunohistochemistry. Results Reverse transcription polymerase chain reaction and western blot showed that siRNA‐CPA4 significantly decreased CPA4 mRNA levels in H226 and SKMES‐1 cells compared with the control cells. Knockdown of CPA4 in lung cancer cells significantly inhibited cell invasion by 62.3% and 77.3% in H226 and SKMES‐1 cell, respectively. Furthermore, siRNA‐CPA4 significantly suppressed cell migration in H226 and SKMES‐1 cells by 48.1% and 42.4%, respectively. Immunohistochemistry results showed that the positive expression rate of CPA4 in lung normal tissues, cancer tissues, and lymph node metastatic tissues was 12.5% (1/8), 50.0% (23/46), and 76.1% (35/46), respectively. Importantly, the levels of CPA4 in the lymph node metastatic tissues were significantly higher than those in corresponding primary lung cancer tissues (t = 5.176, P