CXCR4 and nasopharyngeal carcinoma: Previous studies revealed that TPST1 could sulfate the tyrosine of C-X-C motif chemokine receptor (CXCR4) (Seibert et al., 2008; Xu et al., 2013) and the tyrosine sulfation might contribute to nasopharyngeal carcinoma metastasis (Xu et al., 2013).