Differential impact of CX3CL1 on lung cancer prognosis in smokers and non-smokers

CX3CL1 is a unique chemokine, expressed in both soluble and membrane bound forms, which mediates different biological activities. Recent studies have revealed the potential of CX3CL1 signaling pathway as a target for the treatment of inflammation and cancer. The correlation between expression of CX3CL1 and prognosis of patients varies among cancers. In this study, based on CX3CL1 immunohistochemistry in non-small cell lung cancer, CX3CL1 levels were positively associated with cancer stage (Pearson chi-square, P=0.048) and lymph node status (P=0.033). Interestingly, survival effects of CX3CL1 were only observed in patients with smoking history and adenocarcinoma (AD, log rank, P=0.027), but not in patients with squamous cell carcinoma (SQ). The median survival time of patients with smoking history and low level CX3CL1 expressing AD was 1538 days, while that of patients with smoking history and high level CX3CL1 expressing AD was 396 days. Cox regression models showed adverse effects of high CX3CL1 levels only in AD patients with smoking history (hazard ratio=3.01, p=0.034), but not in AD patients without smoking history or in SQ patients with smoking history. The results of this study suggest that CX3CL1 plays different roles in lung tumorigenesis in smokers and non-smokers, and different CX3CL1-based therapeutic strategies are needed depending on patient smoking status and tumor type. Furthermore, high level of CX3CL1 expression enhances nodal metastasis by activating JNK & MMP2/MMP9 activity in lung cancer cells.