The presence of Nef accelerates endocytosis and lysosomal degradation of the transmembrane glycoprotein CD4. CD4 has its own internalization motif, though this motif is normally concealed by CD4 interaction with Lck, a tyrosine kinase. Nef is known to disrupt this interaction and then facilitate a cascade of protein interactions that ultimately result in the degradation of internalized CD4 protein. The final set of protein interactions that direct Nef to the beta-subunit of the COPI coatomers are at this time unclear.
A benefit for the virus from CD4 down-modulation is abolition of interaction between the receptor and the Env protein of the budding virus, which likely increases HIV release from infected cell as well as infectivity of viral particles.