Figure 9. Overview of molecules associating and cooperating with palmitoylated cld7.

(A) Only palmitoylated cld7 is enriched in GEM, where it associates in a direct protein-protein interaction with EpC. Interactions with additional transmembrane proteins, predominantly tetraspanins, integrins, CD44v6, transmembrane metalloproteases, ADAMs, uPAR and NOTCH likely are indirect and promoted by the special lipid composition of GEM and the catcher activity of tetraspanins, which may be first order partners for some of the listed membrane molecules. The majority of associations with cytoplamic molecules are indirect and promoted by the lipid composition of GEM. Thus, the multiple deficiencies associated with cld7^mPalm in migration, invasion, apoptosis resistance and EMT are due to exclusion from GEM (or recruitment into TJ) and persistence in the cytosol, the latter being demonstrated for Pten phosphorylation. (B) Cld7 is recovered in exosomes. There is evidence that only palmitoylated cld7 is recovered in those exosomes, where biogenesis/vesicle transport depends on tetraspanins rather than ESCRT complexes and lipids. Whether cld7 actively contributes to the biogenesis of these “tetraspanin-dependent” exosomes remains to be explored. Taken together, there is strong evidence that TJ-integrated cld7 and palmitoylated GEM-integrated cld7 fulfill non-overlapping activities. Whether cld7 palmitoylation is linked to the metastatic phenotype or is also observed in non-transformed cells and under which conditions remains to be explored.