The multivesicular body (MVB) sorting pathway is a mechanism for delivering 
transmembrane proteins into the lumen of the lysosome for degradation. ESCRT-III 
is the final complex in the pathway that assembles on endosomes and executes 
membrane scission of intraluminal vesicles. In addition, proteins of this 
complex are involved in other topologically similar processes such as 
cytokinesis, virus egress and autophagy. Here we show that protein kinase CK2α 
is involved in the phosphorylation of the ESCRT-III subunits CHMP3 and CHMP2B, 
as well as of VPS4B/SKD1, an ATPase that mediates ESCRT-III disassembly. This 
phosphorylation is observed both in vitro and in cells. While we do not observe 
recruitment of CK2α to endosomes, we demonstrate the localization of CK2α to 
midbodies during cytokinesis. Phosphomimetic and non-phosphorylatable mutants of 
ESCRT-III proteins can still bind endosomes and localize to midbodies, 
indicating that CK2α does not regulate ESCRT-III localization. Finally, we 
analyzed two cellular functions where CHMP3, CHMP2B and VPS4 are known to be 
involved, epidermal growth factor degradation and cytokinetic abscission. We 
demonstrate that the former is impaired by CK2α downregulation whereas the 
latter is not affected. Taken together, our results indicate that CK2α regulates 
the function of ESCRT-III proteins in MVB sorting.