Breast cancer cell line proliferation blocked by the Src‐related Rak tyrosine kinase

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Abstract
Rak is a 54 kDa protein tyrosine kinase originally isolated from breast cancer cells and expressed in epithelial cells. It resembles the protooncogene Src structurally but lacks an amino‐terminal myristylation site and localizes to the nuclear and perinuclear regions of the cell. We report here that expression of Rak in 2 different breast cancer cell lines inhibits growth and causes G1 arrest of the cell cycle. This growth inhibition is kinase‐dependent but does not require the Rak SH2 or SH3 domain. Rak also binds to the pRb tumor‐suppressor protein but inhibits growth even in cells that lack pRb. These results suggest that Rak regulates cell growth by phosphorylating perinuclear proteins and has a function that is distinct from the Src‐related kinase family.