Plays multiple roles in cell cycle progression, cytokinesis and apoptosis. Involved in pre-mRNA splicing in a kinase activity-dependent manner. Isoform 7 may act as a negative regulator of normal cell cycle progression. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Phosphorylation at Thr-448 or Tyr-449 inactivates the enzyme, while phosphorylation at Thr-595 activates it. Cleaved isoform SV9 (p110C) binds to the serine/threonine kinase PAK1 and RANBP9. p110C interacts with RNPS1. Isoform 7, but not isoform SV9, nor its cleavage product p110C, interacts with CCND3. Interacts with CCNL1 and CCNL2. Forms complexes with pre-mRNA-splicing factors, including at least SRSF1, SRSF2 AND SRSF7/SLU7. Interacts with isoform 5 of MYO18A (PubMed:25965346). Expressed ubiquitously. Some evidence of isoform-specific tissue distribution. Isoform 7 is induced in G2/M phase of the cell cycle. During FAS- or TNF-induced apoptosis, isoform SV9 is cleaved by caspases to produce p110C, a fragment that contains the C-terminal kinase domain. Phosphorylation at Ser-115 creates a binding site for 14-3-3 proteins. p110C can be autophosphorylated. Duplicated gene. CDK11A and CDK11B encode almost identical protein kinases of 110 kDa that contain at their C-termini the open reading frame of a smaller 58 kDa isoform which is expressed following IRES-mediated alternative initiation of translation. Produced by alternative initiation at Met-357 of isoform SV9 via an internal ribosomal entry site (IRES). Belongs to the protein kinase superfamily. CMGC Ser/Thr protein kinase family. CDC2/CDKX subfamily. Many references talk about 'p110 isoforms' but it is not yet known if this refers to CDK11A and/or CDK11B or one/some of the isoforms of each. Extended N-terminus.