SP1 and breast cancer: In the human breast cancer cell line, MCF-7, and in breast cancer samples, cross-talk between LCK and the protein tyrosine kinase syk plays a role in upregulating urokinase-type plasminogen activator (uPA) and matrix metalloproteinase 9 (MMP9) expression, which are associated with invasion and metastasis [21], via Sp1 transcription factor (SP1) activation under the hypoxia/reoxygenation conditions [22].