PTK2 and colorectal carcinoma: SphK1 regulates tumor cell proliferation, apoptosis, and invasion in CRC by inducing epithelial-mesenchymal transition (EMT) through the focal adhesion kinase/Akt/matrix metalloproteinase (FAK/Akt/MMP) axis, and by suppressing p38 and stress-activated protein kinases/Jun amino-terminal kinases (SAPK/JNK) signaling [39,40].