XCR1 Forms a Heterodimer with CXCR4 and Regulates Its Internalization / 中国生物化学与分子生物学报

ABSTRACT

Chemokine signal pathways are important for the regulation of tumour metastasis. Chemokine receptors CXCR4 (C-X-C chemokine receptor type 4) and XCR1 (chemokine XC receptor 1) are involved in the metastasis of breast cancer, while the interaction between them remains unclear. Here we first identified the interaction between CXCR4 and XCR1 based on membrane protein yeast two-hybrid assays. Bioluminescence resonance energy transfer (BRET) showed that XCR1 could competitively bind to CXCR4 to form a heterodimer (P < 0.01). Results of wound healing assays via transient transfection of XCR1 and CXCR4 into HEK293 cells showed that 41.55% of the migration area rate in the co-transformation group was lower than 58.75% in the CXCR4-alone group after adding 30 nmol/L S D F-β. The co-expression of XCR1 inhibited the cellular motility, possibly mediated by the SDF-1β (stromal cell-derived factor 1)/CXCR4 signal pathway (P < 0.05). Furthermore, CXCR4 on the cell surface after co-expression of XCR1 in CXCR4-EGFP transgenic HEK293 cells was detected by flow cytometry. And the result suggested that XCR1 could accelerate the internalization of CXCR4 into the heterodimer induced by 30 nmol/L SDF-1β (P<0.05), which increased the internalization rate from 14.38% to 64.10%. Finally, the phosphorylation of Akt and ERK, which were involved in cell proliferation and migration, respectively, were examined. After 10 minutes of SDF-1β stimulation, ERK phosphorylation in the CXCR4-alone group showed a 3.59-fold increase, whereas the increase of ERK phosphorylation in the co-transfected group was only 2.08-fold. Interestingly, heterodimer formation reduced the phosphorylation level of ERK and shortened the activation time, whereas the phosphorylation level of Akt remained unchanged. Collectively, our findings revealed the hetero-dimerization of CXCR4 and XCR1 and its effects on CXCR4-mediated cellular motility, receptor internalization, and ERK pathway phosphorylation. Therefore, XCR1-targeting drugs could be candidates for cross-desensitization of CXCR4 and might represent a possible option for inhibiting breast cancer metastasis.