MARK3 (microtubule affinity regulating kinase 3) is a serine/threonine protein kinase that regulates multiple cellular pathways through phosphorylation of key targets 1. The kinase phosphorylates microtubule-associated proteins including MAP2, MAP4, and tau (MAPT), as well as cell cycle regulators like CDC25C and CDC25B 2. MARK3 functions as a critical regulator of the Hippo signaling pathway, where it antagonizes LATS1 phosphorylation and promotes YAP/TAZ activity 3. The LKB1-MARK3 axis acts as a metabolic stress-activated checkpoint that induces G2/M cell cycle arrest through CDC25B/C phosphorylation 2. In cancer contexts, MARK3 demonstrates dual roles: it serves as an absolute catalytic requirement for YAP/TAZ function in diverse carcinomas and sarcomas, making it a potential therapeutic target 3, while also functioning as a tumor suppressor in high-grade serous ovarian carcinoma where its downregulation correlates with poor prognosis 2. MARK3 also regulates protein localization through phosphorylation of HDAC7 and MITF, promoting their cytoplasmic retention via 14-3-3 binding 1. Additionally, MARK3 variants have been associated with bone mineral density regulation and vitamin D metabolism 4.