Phosphorylates BSK1, BSK3, BSK5, BSK6, BSK8 AND BSK11 in vitro (PubMed:23496207). May mediate extracellular signals to regulate transcription in differentiating cells (By similarity). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Binds to KIB1 (PubMed:28575660). Interacts with BSK6 (PubMed:23496207). Autophosphorylated mainly on threonine and serine residues. Belongs to the protein kinase superfamily. CMGC Ser/Thr protein kinase family. GSK-3 subfamily.