DIFFERENCES IN THE POSTTRANSLATIONAL MODIFICATION OF PROTEINS BY POLYAMINES BETWEEN WEAKLY AND HIGHLY METASTATIC B16 MELANOMA-CELLS

The identification of (gamma-glutamyl)polyamines in proteolytic digest of proteins from the cytosolic and particulate fractions of B16-F10 and B16-F10Lr6 cell lines, originating from a spontaneous tumor in C57BL/6 mice, indicates that polyamines are incorporated into melanoma cell proteins by transglutaminases (TGases-EC 2.3.2.13). The levels of spermidine-derived protein cross-links were found to be inversely related with the metastatic potential of the 2 melanoma lines. Characterization of TGase activity in the 2 tumor cell lines showed 3 types of enzyme. The soluble cellular TGase activity (TGase C) was higher, and increased more, during the growth of the least metastasizing clone B16-F10Lr6 than in the B16-F10 line, which is the most metastasizing. Consistently, N1,N8-bis(gamma-glutamyl) spermidine, which is responsible for protein cross-link formation, was present in greater amount in B16-F10Lr6 cells. The enhancement by theophylline of soluble-TGase activity and spermidine-dependent protein cross-links of B16-F10 cells reduced, with linear dose dependence, the ability of these cells to penetrate through human fibronectin-coated membrane in an in vitro assay of invasiveness. Our data confirm and extend earlier observations indicating that the propensity of a tumor to metastasize can be indirectly related to intracellular levels of TGase activity, and provide the basis for some speculation concerning the role of polyamines as modifiers of murine melanoma cell proteins in metastasis.