They subsequently showed that some proteins from MCF-7 cells undergo retinoylation and are also targets for E2 ligands.121 Treatment with tunicamycin, an inhibitor of both protein N-glycosylation and palmitoylation, decreased palmitoylation while enhancing retinoylation of proteins, indicating a potential opposing relationship between these modifications.122 XPO1 is an example of a protein potentially regulated by both palmitoylation and retinoylation, with functional relevance to breast cancer. This evidence concerns the gene XPO1 and breast carcinoma.