PSKH1 (protein serine kinase H1) is a serine/threonine protein kinase with multiple cellular localizations and regulatory functions. The protein localizes to centrosomes, Golgi apparatus, nuclear speckles, and cytoplasm, with centrosomal localization enhanced during osmotic stress 1. PSKH1 associates with splicing factor compartments (SFCs) and can redistribute SR proteins into more diffuse nuclear patterns, suggesting involvement in pre-mRNA processing regulation 2. The kinase activity is subject to complex allosteric regulation: Ca²⁺-calmodulin activates PSKH1, while reticulocalbin-3 (a CREC family Ca²⁺ sensor) suppresses its activity, and UNC119B acts as an activating interactor 3. PSKH1 undergoes intermolecular autophosphorylation at serine residues in its C-terminal region, with activity repressed by Ca²⁺/calmodulin 1. Disease-wise, loss-of-function mutations in PSKH1 cause a novel hepatorenal ciliopathy with progressive familial intrahepatic cholestasis, characterized by abnormally long cilia 4. Additionally, PSKH1 is overexpressed in various cancers including osteosarcoma, where it promotes proliferation and invasion via p38/MAPK signaling 5, and prostate cancer, where its knockdown inhibits cell growth 6. Higher PSKH1 expression correlates with treatment response in colorectal cancer patients receiving cetuximab plus irinotecan 7.