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Molecular and biochemical characterization of the human trk proto-oncogene
D Martin-Zanca1, R Oskam, G Mitra
1Section of Developmental Oncology, National Cancer Institute Frederick Cancer Research Facility, Maryland 21701.
Abstract:
Molecular analysis of the human trk oncogene, a transforming gene isolated from a colon carcinoma biopsy, revealed the existence of a novel member of the tyrosine kinase gene family. This locus, which we now designate the trk proto-oncogene, codes for a protein of 790 amino acid residues that has several features characteristic of cell surface receptors. They include (i) a 32-amino-acid-long putative signal peptide, (ii) an amino-terminal moiety (residues 33 to 407) rich in consensus sites for N-glycosylation, (iii) a transmembrane domain, (iv) a kinase catalytic region highly related to that of other tyrosine kinases, and (v) a very short (15 residue) carboxy-terminal tail. Residues 1 to 392 were absent in the trk oncogene, as they were replaced by tropomyosin sequences. However, no other differences were found between the transforming and nontransforming trk alleles (residues 392 to 790), suggesting that no additional mutations are required to activate the transforming potential of this gene. The human trk proto-oncogene codes for a 140,000-dalton glycoprotein, designated gp140proto-trk. However, its primary translational product is a 110,000-dalton glycoprotein which becomes immediately glycosylated, presumably during its translocation into the endoplasmic reticulum. This molecule, designated gp110proto-trk, is further glycosylated to yield the mature form, gp140proto-trk. Both gp110proto-trk and gp140proto-trk proteins possess in vitro kinase activity specific for tyrosine residues. Finally, iodination of intact NIH 3T3 cells expressing trk proto-oncogene products indicated that only the mature form, gp140proto-trk, cross the plasma membrane, becoming exposed to the outside of the cell. These results indicate that the product of the human trk locus is a novel tyrosine kinase cell surface receptor for an as yet unknown ligand.
Insights
Researchers identified a new tyrosine kinase gene, the trk proto-oncogene, in colon cancer. Its protein product is a cell surface receptor with kinase activity, suggesting a novel signaling pathway.
Area of Science:
- Molecular Biology
- Oncology
- Cell Signaling
Background:
- The trk oncogene was identified from a colon carcinoma biopsy.
- It represents a novel member of the tyrosine kinase gene family.
- Understanding oncogenes is crucial for cancer research and therapy development.
Purpose of the Study:
- To characterize the molecular structure and function of the human trk proto-oncogene.
- To determine the nature of the protein product encoded by the trk locus.
- To investigate the transforming potential and cellular localization of trk gene products.
Main Methods:
- Molecular analysis of the trk gene sequence and its encoded protein.
- Identification of protein domains characteristic of cell surface receptors.
- Analysis of glycosylation patterns and kinase activity of trk protein products.
- Cell surface iodination assays to determine protein localization.
Main Results:
- The trk proto-oncogene encodes a 790-amino acid protein with features of a cell surface receptor, including a signal peptide, N-glycosylation sites, and a transmembrane domain.
- The transforming trk oncogene differs from the proto-oncogene by the absence of N-terminal residues (1-392), replaced by tropomyosin sequences.
- The primary translational product, gp110proto-trk, is glycosylated to gp140proto-trk, both exhibiting tyrosine kinase activity. Only gp140proto-trk is exposed on the cell surface.
Conclusions:
- The human trk proto-oncogene codes for a novel tyrosine kinase cell surface receptor.
- The receptor is a glycoprotein (gp140proto-trk) with intrinsic kinase activity.
- The findings suggest a new signaling pathway involving an as yet unidentified ligand.