PIM1 is a member of the PIM family of proto-oncogenes that functions as a distinct class of serine/threonine protein kinases involved in growth factor signaling. PIM1 was originally identified as a target of proviral activation in T-cell lymphomas induced by Moloney murine leukemia virus. PIM1 appears to play a role in many aspects of cell growth, proliferation, and apoptosis. PIM1 is required for efficient cell cycle induction of peripheral T-cells in response to IL-2 signaling. PIM1 substrates include p21 cip1/waf1, CDC25A, PTP-U2, NuMA, and PAP-1.