Serine/threonine-protein kinase (By similarity). Phosphorylates the microtubule-associated protein MAPT/TAU (By similarity). Also phosphorylates the microtubule-associated proteins MAP2 and MAP4 (By similarity). Involved in regulation of the microtubule network, causing reorganization of microtubules into bundles (By similarity). Required for the initiation of axoneme extension during cilium assembly (By similarity). Regulates the centrosomal location of ODF2 and phosphorylates ODF2 in vitro (By similarity). Plays a role in cell cycle progression, specifically in the G1/S checkpoint (By similarity). Reduces neuronal cell survival (By similarity). Plays a role in energy homeostasis by regulating satiety and metabolic rate (PubMed:22992738). Promotes adipogenesis by activating JNK1 and inhibiting the p38MAPK pathway, and triggers apoptosis by activating the JNK1 pathway (PubMed:24989893). Phosphorylates mTORC1 complex member RPTOR and acts as a negative regulator of the mTORC1 complex, probably due to disruption of the interaction between phosphorylated RPTOR and the RRAGA/RRAGC heterodimer which is required for mTORC1 activation (By similarity). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by phosphorylation on Thr-214. Interacts with MAPT/TAU. Interacts with gamma-tubulin. Interacts with ODF2. Interacts with USP9X. Interacts with YWHAQ (By similarity). Localized at the tips of neurite-like processes in differentiated neuroblast cells. Detected in the cytoplasm and neuropil of the hippocampus. Isoform 1 and isoform 2 show similar expression patterns in the central nervous system and are present in the same subsets of neurons including pyramidal and non-pyramidal neurons in the cerebral cortex and hippocampus, cerebellar Purkinje cells, and interneurons and motor neurons in the spinal cord but not in glial cells (at protein level) (PubMed:16973293). Isoform 2 is the major isoform in brain and cerebellum (PubMed:16973293, PubMed:15009667). Also expressed in spleen, liver, small intestine, colon, kidney, tongue, testis and lung (PubMed:16973293, PubMed:15009667). Isoform 1 and isoform 2 are expressed at similar levels in heart (PubMed:16973293). Ubiquitinated with 'Lys-29'- and 'Lys-33'-linked polyubiquitins which appear to impede LKB1-mediated phosphorylation. Deubiquitinated by USP9X (By similarity). Phosphorylated at Thr-214 by STK11/LKB1 in complex with STE20-related adapter-alpha (STRADA) pseudo kinase and CAB39. Phosphorylated throughout the cell cycle. Hyperphagia, hyperactivity and hypermetabolism leading to protection from diet-induced obesity, and improved glucose homeostasis due to up-regulation of AMPK kinase activity. Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family. SNF1 subfamily.