Upon serum stimulation, phosphorylates CDKN1B/p27Kip1, thus controlling CDKN1B subcellular location and cell cycle progression in G1 phase. May be involved in trafficking and/or processing of RNA (By similarity). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with stathmin and CDKN1B/p27Kip1 (By similarity). Interacts with PAM. Widely expressed, with highest levels in skeletal muscle, kidney, placenta and peripheral blood leukocytes. Regulated in a cell-cycle dependent manner, with lowest levels during S phase and highest at G1 phase (at protein level). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.