JAK2 kinase activity is required for ligand-induced EpoR colocalization with early endosomal marker EEA1. Cell-surface HA-EpoRs were labeled with anti-HA antibodies before Epo stimulation of 25 minutes. Cells were fixed and immunostained with anti-EEA1 antibodies followed by appropriate fluorescence-conjugated secondary antibodies. Representative confocal images (single section) for different conditions are presented. Images from negative controls with secondary antibodies alone are shown (original magnification ×40; Leica TCS SP5).