Sam68 haploinsufficiency delays onset of mammary tumorigenesis and metastasis.

The Src-associated substrate in mitosis Sam68 is a KH type RNA-binding protein known to be a substrate of numerous tyrosine kinases, and often referred to as a STAR (signal transduction activator of RNA) protein. Herein, we observed that Sam68-null mice display mammary gland and the uterine development defects. Moreover, we report that Sam68 haploinsufficiency impedes mammary tumor onset in vivo driven by the potent mammary-targeted polyoma middle T-antigen (MMTV-PyMT) oncogene. The effect was cell autonomous as the Sam68 knockdown in PyMT-transformed cell lines also delayed tumorigenesis and metastasis formation in nude mice. Interestingly, tumor extracts isolated from PyMT/Sam68(+/-) mice compared with PyMT/Sam68(+/+) mice contained activated Src and FAK kinases. These findings suggest that Sam68 may be a modulator of tyrosine kinase activity in vivo and a signaling requirement for mammary tumorigenesis and metastasis.