Abstract
We found that rhabdomyosarcoma (RMS) subcellular membranes contain sialyltransferase activities for LcOse~4~Cer and GgOse~4~Cer acceptors. Chromatographic analyses and neuraminidase lability of the sialyltransferase products indicated that the principal site of sialylation was the non‐reducing terminal galactosyl moiety. In order to control for the effects of cell density in culture, metastatic S~4~T~18~ RMS cells and non‐metastatic F9‐4/21 RMS cells were harvested at 2 × 10^4^ to 6 × 10^4^ per cm^2^ prior to analyses. Irrespective of metastatic potential, we found that sialyltransferase‐specific activities were influenced by cell densities. F9‐4/21 cells, for example, at a density of 6 × 10^4^, produced membranes with sialyltransferase‐specific activities to LcOse~4~Cer 1.9‐fold higher than cells at 2.1 × 10^4^/cm^2^. Metastatic potential (predetermined in vivo) appeared to be correlated with an accelerated effect of cell density on the sialyltransferase activity to LcOse~4~ Cer. Metastatic S~4~T~18~ cells at 6.3 × 10^4^/cm^2^ yielded membranes with sialyltransferase‐specific activities 5.4‐fold higher than membranes from cells at 1.9 × 10^4^/cm^2^. Conversely, fucosyl‐transferase activities in the presence of LcOse~4~Cer were highest in non‐metastatic F9‐4/21 cells at low cell densities. Quantitative analyses of monosialoganglioside fractions of RMS cells were in agreement with the sialyl‐transferase studies. HPLC and HPTLC analyses demonstrated the presence of glucosamine‐containing monosialoganglioside with R~f~ identical with the radioactive products of LcOse~4~Cer sialylation, which increased 4.5‐fold on a per mg protein basis as cell densities increased in S~4~T~18~ cells in culture from 1.9 × 10^4^/cm^2^ to 6.3 × 10^4^/cm^2^. Plasma membrane marker Na^+^, K^+^, ATPase‐specific activity also increased in RMS metastatic cells in a manner comparable to that described for the sialyl‐transferase activity to LcOse~4~Cer. Our results suggest that metastatic potential is expressed in the rate of sialylation at specific membrane sites of RMS intercellular contact. We propose a process of selection for metastasis whereby specific cell surface non‐reducing galactosyl termini are recognized by intercellular transferases and lectins in the primary tumor, and the corresponding labile sialylated sites (on disseminated cells) are recognized by host neuraminidases.