ISG15 and colorectal carcinoma: The uniqueness of the induction of L1-mediated ISGylation is demonstrated in Figure 4D by showing that ISG15 overexpression in CRC cells does not result in increased ISGylation (Figure 4C, ISG15 cl1 and cl2), while suppression of endogenous ISG15 expression in L1-overexpressing cells eliminates both ISGylation and the effects on tumorigenesis (Figure 2G) and metastasis (Figure 3) conferred by L1.