Calling in SYK: SYK's dual role as a tumor promoter and tumor suppressor in cancer

• SYK can have both tumor promoting and tumor suppressing activity.
• SYK promotes cell survival in multiple tumor types.
• SYK inhibits motility and metastasis in many invasive carcinomas.
• SYK alters cellular differentiation programs that regulate EMT.

SYK (spleen tyrosine kinase) is well-characterized in the immune system as an essential enzyme required for signaling through multiple classes of immune recognition receptors. As a modulator of tumorigenesis, SYK has a bit of a schizophrenic reputation, acting in some cells as a tumor promoter and in others as a tumor suppressor. In many hematopoietic malignancies, SYK provides an important survival function and its inhibition or silencing frequently leads to apoptosis. In cancers of non-immune cells, SYK provides a pro-survival signal, but can also suppress tumorigenesis by restricting epithelial–mesenchymal transition, enhancing cell–cell interactions and inhibiting migration.

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