Protein kinase that seems to act exclusively upon threonine residues (By similarity). Required for normal entry into proliferative arrest after a limited number of cell divisions, also called replicative senescence. Required for normal cell cycle arrest in response to double-stranded DNA damage. {ECO:0000250|UniProtKB:Q9Z1J2, ECO:0000269|PubMed:22851694}. This is the function of NEK4 (NIMA related kinase 4, Ensembl gene identifier ENSG00000114904).