A growth-related oncogene/CXC chemokine receptor 2 autocrine loop contributes to cellular proliferation in esophageal cancer

Growth-related oncogene (GRO), a member of the CXC chemokine subfamily, plays a major role in inflammation and wound healing. CXC chemokines have been found to be associated with tumorigenesis, angiogenesis, and metastasis. Although elevated expression of GRO has been reported in several human cancers, the expression and role of GRO and its receptor, CXCR2, in esophageal cancer are poorly understood. This study used real-time reverse transcription-PCR (RT-PCR) and immunohistochemical approaches to show that GRO alpha, GRO beta, and CXCR2 are up-regulated in esophageal tumor tissue. Furthermore, GRO alpha, GRO beta, and CXCR2 are constitutively expressed in WHCO1, an esophageal cancer cell line that was used as a model system here. GRO beta enhances transcription of EGR-1, via the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway, which can be blocked by a specific antagonist of CXCR2 (SB 225002) or specific antibody to GRO beta. WHCO1 cells treated with SB 225002 exhibited a 40% reduction in cell proliferation. A stable WHCO1 GRO alpha RNA interference (RNAi) clone displayed a 43% reduction in GRO alpha mRNA levels as determined by real-time RT-PCR, reduced levels of GRO alpha by fluorescence microscopy, and a 60% reduction in the levels of phosphorylated ERK1/2. A stable clone expressing GRO beta RNAi displayed > 95% reduction in GRO beta mRNA levels, reduced levels of GRO beta by fluorescence microscopy, and an 80% reduction in the levels of phosphorylated ERK1/2. Moreover, these GRO alpha RNAi- and GRO beta RNAi-expressing clones displayed a 20% and 50% decrease in cell proliferation, respectively. Our results suggest that GRO alpha-CXCR2 and GRO beta-CXCR2 signaling contributes significantly to esophageal cancer cell proliferation and that this autocrine signaling pathway may be involved in esophageal tumorigenesis.