Regulates clathrin-mediated endocytosis by phosphorylating the AP2M1/mu2 subunit of the adaptor protein complex 2 (AP-2) which ensures high affinity binding of AP-2 to cargo membrane proteins during the initial stages of endocytosis. Isoform 1 and isoform 2 display similar levels of kinase activity towards AP2M1. Regulates phosphorylation of other AP-2 subunits as well as AP-2 localization and AP-2-mediated internalization of ligand complexes. Phosphorylates NUMB and regulates its cellular localization; promoting NUMB localization to endosomes. Binds to and stabilizes the activated form of NOTCH1; increases its localization in endosomes and regulates its transcriptional activity. {ECO:0000269|PubMed:12952931; ECO:0000269|PubMed:17494869; ECO:0000269|PubMed:18657069; ECO:0000269|PubMed:21464124}.