Cloning and Expression of the Ret Proto-oncogene Encoding a Tyrosine Kinase with Two Potential Transmembrane Domains

The nucleotide sequence of the ret proto-oncogene has been determined from cDNA clones isolated from a cDNA library of a THP-1 human monocytic leukemia cell line. Analysis of this sequence indicates that it encodes a protein which is structurally related to transmembrane receptors with a cytoplasmic tyrosine kinase domain. Unlike most growth factor receptors, it contains two hydrophobic regions which are potential transmembrane domains. Comparison of the sequence of the ret proto-oncogene with that of the ret transforming gene revealed that, in addition to the amino-terminal truncation, the last 51 carboxy-terminal amino acids of the ret proto-oncogene were replaced with 9 unrelated amino acids of the ret transforming gene. The focus forming activity of the ret cDNA, containing both amino-terminal and caboxy-terminal truncations, was approximately 13-fold higher than that of cDNA containing only the amino-terminal truncation. This suggests a possible role for the carboxy-terminal sequence in activation of transforming potential of the ret proto-oncogene. When transcription of the ret proto-oncogene was examined in a variety of mouse tissues, we detected its transcription in normal mouse spinal cord and lymphadenopathy of C3H/HeJ-gld/gld and MRL/Mp-lpr/lpr mice.