Lung cancer is the leading cause of cancer death and its prevention is a major worldwide challenge. Non-small cell lung cancer (NSCLC) accounts for more than 80 % of lung cancers [
1,
2]. The classifications of NSCLC include large cell carcinoma, adenocarcinoma, and squamous cell carcinoma. Approximately one-half of lung cancers become metastatic, and the most common sites of metastasis are found in the lymph nodes, liver, adrenal glands, bone, and brain. The most frequently reported lung carcinoma subtype is lung adenocarcinoma. In the past decades, many genes have been found to be modulated in cancer cells. These proteins expressed from these modulated genes, such as Wnt5A, KFL6, cyclin D1, ER-α, UPA, PAI-1, HER2, and c-myc, were determined with essential roles in cancer initiation and progression [
3‐
5]. Among the upregulated proteins, YKL-40 was frequently proposed for its role in cancer metastasis [
6‐
8].
YKL-40, a member of mammalian chitinase-like proteins, is overexpressed in many pathological conditions that includes fibroblastic change in liver cirrhosis, increased deposition of connective tissue components and hyperplastic synovium in rheumatoid arthritis, and increased cellular infiltration as well as epithelial proliferation in chronic colitis [
4]. YKL-40 is also up-regulated in many chronic inflammatory conditions such as inflamed tissues in ulcerative colitis, Crohn’s disease, rheumatoid arthritis, osteoarthritis, asthma, chronic obstructive pulmonary disease (COPD), and liver cirrhosis. The levels of YKL-40 were determined to be upregulated in in solid cancers arising from bone, brain, breast, cartilage, cervix, colon, germ cell, head and neck, kidney, liver, lung, lymph node, ovary, pancreas, prostate, skin, and thyroid, when compared with their respective normal tissues or cells [
5‐
7]. Aside from its association with inflamed tissues, YKL-40 expression is also regulated by many inflammatory cytokines. It is believed that inflammatory mediators such as pro-inflammatory cytokines of IL-1, TNF-α, IL-6, and IL-13, regulate YKL-40 expression in inflammatory conditions [
8]. Furthermore, YKL-40 expression is also controlled by hormones such as vasopressin, and parathyroid hormone-related protein in both macrophages and epithelial cells [
9,
10]. Despite the association of increased expression of YKL-40 with many diseases, its biological function is still largely unknown. Further studies have determined that YKL-40 interacts with many components of the extracellular matrix (ECM), including hyaluronic acid, fibronectin, and collagen I, II, III and IV [
11]. The ability to adhere to extracellular matrix is especially important for cancer cell migration and invasion [
4,
12]. YKL-40 protein is involved in proliferation of fibroblasts and modulation of collagen formation, facilitating tumor invasion, and metastasis [
13]. These mesenchymal functions have been verified in a microarray analysis with high-grade gliomas. The analyses determined that YKL-40 is upregulated, together with other genes, in mesenchymal tissues and are associated with poor prognosis (adult malignant gliomas) [
14,
15]. However, the function of YKL-40 in cancer metastasis is still unclear.
Therefore, this study, was aimed to investigate the relationship between YKL-40 and tumor migration and invasion in NCLC. The phenotypic characteristics of YKL-40 NSCLC cell lines were determined and compared. Further analysis was performed to determine the influence of YKL-40 in regulating EMT through the AKT signaling pathways for enhanced cancer migration and invasion. We believe that YKL-40 may serve as therapeutic targets for NSCLC patients in the future.