Peptidyl-prolyl cis/trans isomerase (PPIase) that binds to and isomerizes specific phosphorylated Ser/Thr-Pro (pSer/Thr-Pro) motifs (PubMed:21497122, PubMed:23623683, PubMed:29686383). By inducing conformational changes in a subset of phosphorylated proteins, acts as a molecular switch in multiple cellular processes (PubMed:21497122, PubMed:22033920, PubMed:23623683). Displays a preference for acidic residues located N-terminally to the proline bond to be isomerized. Regulates mitosis presumably by interacting with NIMA and attenuating its mitosis-promoting activity. Down-regulates kinase activity of BTK (PubMed:16644721). Can transactivate multiple oncogenes and induce centrosome amplification, chromosome instability and cell transformation. Required for the efficient dephosphorylation and recycling of RAF1 after mitogen activation (PubMed:15664191). Binds and targets PML and BCL6 for degradation in a phosphorylation-dependent manner (PubMed:17828269). Acts as a regulator of JNK cascade by binding to phosphorylated FBXW7, disrupting FBXW7 dimerization and promoting FBXW7 autoubiquitination and degradation: degradation of FBXW7 leads to subsequent stabilization of JUN (PubMed:22608923). May facilitate the ubiquitination and proteasomal degradation of RBBP8/CtIP through CUL3/KLHL15 E3 ubiquitin-protein ligase complex, hence favors DNA double-strand repair through error-prone non-homologous end joining (NHEJ) over error-free, RBBP8-mediated homologous recombination (HR) (PubMed:23623683, PubMed:27561354). Upon IL33-induced lung inflammation, catalyzes cis-trans isomerization of phosphorylated IRAK3/IRAK-M, inducing IRAK3 stabilization, nuclear translocation and expression of pro-inflammatory genes in dendritic cells (PubMed:29686383). [protein]-peptidylproline (omega=180) = [protein]-peptidylproline (omega=0) Interacts with STIL (By similarity). Interacts with KIF20B (PubMed:11470801). Interacts with NEK6 (PubMed:16476580). Interacts (via WW domain) with PRKX (PubMed:19367327). Interacts with BTK (PubMed:16644721). Interacts (via PpiC domain) with DAPK1 (PubMed:21497122). Interacts with the phosphorylated form of RAF1 (PubMed:15664191). Interacts (via WW domain) with ATCAY; upon NGF stimulation (PubMed:18628984). Interacts with PML (isoform PML-4) (PubMed:22033920). Interacts with BCL6 (PubMed:17828269). Interacts with FBXW7, disrupting FBXW7 dimerization and promoting FBXW7 autoubiquitination and degradation (PubMed:22608923). Directly interacts with RBBP8/CtIP; this interaction depends upon RBBP8 phosphorylation (PubMed:23623683). Interacts (via WW domain) with IRAK3/IRAK-M (when phosphorylated at 'Ser-110') in response to IL33-mediated (but not TLR4 ligand LPS) dendritic cell stimulation (PubMed:29686383). Colocalizes with NEK6 in the nucleus (PubMed:16476580). Mainly localized in the nucleus but phosphorylation at Ser-71 by DAPK1 results in inhibition of its nuclear localization (PubMed:21497122). Expressed in immune cells in the lung (at protein level) (PubMed:29686383). The phosphorylated form at Ser-71 is expressed in normal breast tissue cells but not in breast cancer cells. The WW domain is required for the interaction with STIL and KIF20B. Phosphorylation at Ser-71 by DAPK1 results in inhibition of its catalytic activity, nuclear localization, and its ability to induce centrosome amplification, chromosome instability and cell transformation (PubMed:21497122). Ser-71 is dephosphorylated upon IL33-stimulation of dendritic cells (By similarity).