Original ArticleCXCL1 from tumor-associated lymphatic endothelial cells drives gastric cancer cell into lymphatic system via activating integrin β1/FAK/AKT signaling
Introduction
Gastric cancer/GC is the fifth most common cancer and ranks third regarding global cancer mortality [1]. The most common way for gastric cancer to spread is through the lymphatic system. Lymph node metastasis is regarded as a significant prognostic factor for gastric cancer [2], [3], [4]. Lymphatic metastasis is a complex process involving the interactions between tumor cells and lymphatic endothelial cells (LECs) [5]. On one hand, tumor cells secrete lymphangiogenic factors, such as vascular endothelial growth factor-C/VEGF-C, to promote lymphangiogenesis and lymph node metastasis in several cancer types [6], [7], [8]. On the other hand, cytokines released from LECs can recruit cancer cells and accelerate the lymphatic vessels metastasis of cancer cells [9], [10]. Furthermore, increasing evidence has demonstrated that cytokine profiles of T-LEC were highly altered after interacting with malignant cells [11], [12]. The different cytokine profiles are important to account for the function of T-LECs on supporting tumorigenesis and attract researchers' attentions.
CXCL1 is a member of CXC chemokine family that was originally characterized by Richmond et al. [13] for its ability to promote the growth of melanoma cells. CXCL1 functions as a tumor-promoting agent in many malignancies. Increasing evidence demonstrated that CXCL1 plays an important role in tumorigenesis, metastasis, and chemoresistance [14], [15]. However, previous studies demonstrating pro-tumorigenic signaling by CXCL1 had mostly described autocrine signaling by tumor cells, but not paracrine signaling from stromal cells [16]. Although the high expression of CXCL1 in stromal cells has been found in several types of cancer [16], [17], the functions of CXCL1 from stromal cells has not been well understood. Our previous study also showed that the CXCL1 in LECs cocultured with GC cells was elevated and promoted the metastasis of GC in vitro [18]. However, the mechanism whereby CXCL1 from T-LECs effects the tumor progression has not been fully defined.
Integrin β1 is one member of a large family of αβ heterodimeric transmembrane cell adhesion proteins [19]. Integrin β1 receptor binds extracellular matrix to activate multiple intracellular pathways and has multiple functions in cell adhesion, migration, and proliferation [20], [21]. Integrin β1 receptor can regulate numerous signaling pathways such as FAK/AKT or FAK/ERK pathway [22], [23]. It was reported that CXCL1 can upregulate the expression of Integrin β1 in glioma [24]. The effect of CXCL1 from lymphatic endothelial cells on the Integrin β1/FAK/AKT Signaling in cancer cells remains unexplored as previous studies.
Here, we employed a coculture system to explore the effects of T-LECs-derived CXCL1. We demonstrated that CXCL1 secreted by T-LECs promoting GC progression by Integrin β1/FAK/AKT Signaling.
Section snippets
Cell culture and reagents
Human dermal lymphatic endothelial cells (HDLECs) were purchased from Sciencell (Carlsbad, CA, USA) and grown in Endothelial Cell Medium (ECM) (Sciencell, Carlsbad, CA, USA) supplemented with 1% endothelial cell growth supplement, 5% fetal bovine serum, and 1% penicillin/streptomycin, according to the manufacturer's instructions. The SGC7901, MKN-1, and BGC823 cell lines were purchased from the Cell Bank of the Chinese Academy of Sciences (Shanghai, China). Recombinant human CXCL1 was purchased
The CXCL1 expression in T-LECs was elevated compared with N-LECs
Previously, we reported that CXCL1 mRNA is upregulated in LECs after being cocultured with gastric cancer cells in vitro [18]. To further explore whether CXCL1 is upregulated in situ, co-expression of the lymphatic marker podoplanin/D2-40 and CXCL1 was analyzed in 15 paired normal and tumor tissues (Fig. 1A). The results showed that CXCL1 production in T-LECs was clearly upregulated, compared with that in N-LECs (Fig. 1B, P = 0.001). We also detected the total CXCL1 expression in 20 clinical
Discussion
It is well known that paracrine signaling from tumor-associated non-malignant cells plays a crucial role in promoting cancer cells proliferation and migration [34], [35]. The functions of the lymphatic endothelial cell, a member of stromal cells in the tumor environment, have been implicated in several types of human cancers, including cervical cancer, epithelial ovarian tumors, breast cancer, and so on [9], [12], [36]. In this study, we identified a novel mechanism, whereby CXCL1 from
Disclosure
All authors declare that no conflict of interest exists that could affect the impartiality of the results reported.
Acknowledgments
Funding: This work was supported by the National Natural Science Foundation of China (Grant No. 81272637 and Nos. 81472260), the Natural Science Foundation of Guangdong Province, (Grant Nos. S2013020012724 and No. 2015A030313053), the Science and Technology Program of Guangzhou (No. 201510010146), and the Young Teachers Cultivation Program of Sun Yat-sen University (Grant No. 15ykpy17).
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