PCTK proteins: the forgotten brain kinases?

PCTAIRE kinases (PCTKs) are highly conserved serine/threonine kinases that are closely related to cyclin-dependent kinases. They are enriched in post-mitotic neurons of adult brains, suggesting they might perform important neuron-specific functions independent of the cell cycle. So far, the biological functions of PCTKs in the brain have been largely neglected and remain to be discovered. This review summarises preliminary investigations into the expression and characterisation of PCTK kinase activity, providing a basis for further investigations. In particular, it identifies three key areas of priority for further research: (1) do PCTKs require activating phosphorylation by an upstream kinase or binding to an essential co-factor for maximal kinase activity; (2) what are the physiological substrates of PCTKs, and (3) what is the functional effect of PCTK kinase activity in primary neurons?