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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