Introduction. Renal cell carcinoma (RCC) refers to cancer originating from the renal epithelium and accounts for 2% of all cancer diagnoses and cancer deaths worldwide (1). CXC chemokine receptor 4 (CXCR4) nuclear localization has been observed in many different cancers including RCC and may play a role in tumor progression and metastasis. There are currently no established biomarkers to monitor RCC progression, and current treatment planning relies on imaging (2). Here, the authors describe how CXCR4 nuclear localization increases RCC tumorigenicity both in vitro and in vivo. CXCR4 and hypoxia inducible factor-1α (HIF-1α) are shown to colocalize and interact in RCC cells. Nuclear localization of CXCR4 and HIF-1α are promising potential biomarkers that may help monitor RCC progression. Methods. Endogenous CXCR4 was knocked down in RCC cell lines with lentiviral shRNA and ectopically expressed CXCR4 with mutated NLS. Transwell migration and wound healing assays were used to assess tumorigenicity of wild type and mutated-NLS (m-NLS) CXCR4 in RCC cell lines in vitro. Subcutaneous tumor-bearing nude mouse models were reconstituted with wild type or m-NLS CXCR4 to observe tumorigenicity in vivo. Western blotting and immunofluorescence staining were used to determine the effect of nuclear CXCR4 on HIF-1α nuclear localization, as well as the effect of HIF-1α on CXCR4 expression. Duolink assay was used to determine the physical interaction between CXCR4 and HIF-1α in the nucleus. The prognostic potential of subcellular HIF-1α and CXCR4 was evaluated by determining negative, cytoplasmic, or nuclear localization in 98 primary RCC tumor tissues. Nomograms were constructed to predict metastasis-free survival. Results. Nuclear CXCR4 was associated with RCC invasion, migration, and tumor growth. Nuclear CXCR4 was associated with increased HIF-1α entry into the nucleus, and increased CXCR4 expression was seen with nuclear HIF-1α levels (3). CXCR4 and HIF-1α were shown to colocalize and interact in the nucleus (3). Subcellular CXCR4 and HIF-1α independently predicted RCC metastasis and showed improved prognostic probability when combined with TNM staging (3). Conclusion. Increased RCC tumorigenicity is associated with nuclear localization of CXCR4. A reciprocal relationship between CXCR4 and HIF-1α was established in which nuclear CXCR4 led to nuclear entry of HIF-1α and nuclear HIF-1α led to increased CXCR4 expression. Subcellular CXCR4 and HIF-1α improve prediction of metastasis-free survival and can serve as potential biomarkers (3).
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