CXCR4 and non-small cell lung carcinoma: Overexpression of CXCR4 stimulated STAT3 phosphorylation, but knockdown of CXCR4 constitutively decreased phosphorylation of STAT3 at the tyrosine 705 (pY-STAT3), but not at the serine 727 sites (pS-STAT3) in NSCLC cells (Fig. 4A).