Appears to play multiple roles in cell cycle progression, cytokinesis and apoptosis. The p110 isoforms have been suggested to be involved in pre-mRNA splicing, potentially by phosphorylating the splicing protein SFRS7. The p58 isoform 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-436 or Tyr-437 inactivates the enzyme, while phosphorylation at Thr-583 activates it. The cleaved p110 isoform, p110C, binds to the serine/threonine kinase PAK1. The p58 isoform but not the p110 isoform or p110C interacts with CCND3. The p110 isoforms are found in large molecular weight complexes containing CCNL1 and SFRS7. Additional isoforms seem to exist. Expressed ubiquitously. Some evidence of isoform-specific tissue distribution. The p58 isoform is specifically induced in G2/M phase of the cell cycle. During apoptosis, induced by Fas or tumor necrosis factor, specific CKD11 p110 isoforms are cleaved by caspases to produce a protein (p110C) that contains the C-terminal kinase domain of the CDK11 proteins. 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-345 of isoform SV6. 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.