The function of LMTK3 (lemur tyrosine kinase 3, ENSG00000142235) is as follows. Protein kinase which phosphorylates ESR1 (in vitro) and protects it against proteasomal degradation. May also regulate ESR1 levels indirectly via a PKC-AKT-FOXO3 pathway where it decreases the activity of PKC and the phosphorylation of AKT, thereby increasing binding of transcriptional activator FOXO3 to the ESR1 promoter and increasing ESR1 transcription (PubMed:21602804). Involved in endocytic trafficking of N-methyl-D-aspartate receptors (NMDAR) in neurons (By similarity). {ECO:0000250|UniProtKB:Q5XJV6, ECO:0000269|PubMed:21602804}.