Specific expression of the ret proto-oncogene in human neuroblastoma cell lines.

The expression of the ret proto-oncogene (proto-ret), which possibly encodes two isoforms of a receptor-type tyrosine kinase, was examined in human tumor cell lines. Expression of the proto-ret mRNA was detected in all 11 neuroblastoma cell lines examined. The level of mRNA varied more than 100-fold in these neuroblastoma cell lines and was particularly high in three of them. On the other hand, 19 non-neuroblastoma tumor cell lines derived from solid tumors and a human diploid fibroblast cell line did not express any detectable levels of proto-ret mRNA. No remarkable amplification of the proto-ret or gross structural changes in the coding region were found in these neuroblastoma cell lines. The specific expression of the proto-ret in neuroblastomas suggests that the proto-ret product may have a role in cellular functions specific to neuroblastoma cells.