Protein tyrosine kinase 7 plays a tumor suppressor role by inhibiting ERK and AKT phosphorylation in lung cancer

Protein tyrosine kinase 7 (PTK7) is a catalytically inactive receptor tyrosine kinase that is also known as colon carcinoma kinase-4 (CCK-4). Recent reports have shown that PTK7 plays an important role in carcinogenesis, and it is known to be upregulated in gastric, colon and esophageal cancer, as well as in liposarcoma. However, the role of PTK7 in lung cancer has not been investigated. The aim of the present study was to investigate the expression levels and the role of PTK7 in lung cancer. We found that PTK7 expression was downregulated at the mRNA as well as protein levels in human lung squamous cell carcinoma (LSCC). Upon investigation of the functional role of PTK7 in LSCC, we found that overexpression of PTK7 in LSCC cells resulted in inhibition of cell proliferation, invasion and migration. Furthermore, we confirmed that these phenotypic changes are associated with the inactivation of AKT and ERK. Our findings suggest that PTK7 has different oncogenic roles in organs and target tumors.