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Suppression of tubulin tyrosine ligase during tumor growth
L Lafanechère1, C Courtay-Cahen, T Kawakami
1Laboratoire du Cytosquelette, INSERM U366, DBMS, Commisariat a l'Energie Atomique/Grenoble, Grenoble, France.
Abstract:
The C terminus of the tubulin alpha-subunit of most eukaryotic cells undergoes a cycle of tyrosination and detyrosination using two specific enzymes, a tubulin tyrosine ligase (TTL) and a tubulin carboxypeptidase. Although this enzyme cycle is conserved in evolution and exhibits rapid turnover, the meaning of this modification has remained elusive. We have isolated several NIH-3T3 derived clonal cell lines that lack TTL (TTL-). TTL- cells contain a unique tubulin isotype (delta2-tubulin) that can be detected with specific antibodies. When injected into nude mice, both TTL- cells and TTL- cells stably transfected with TTL cDNA form sarcomas. But in tumors formed from TTL rescued cells, TTL is systematically lost during tumor growth. A strong selection process has thus acted during tumor growth to suppress TTL activity. In accord with this result, we find suppression of TTL activity in the majority of human tumors assayed with delta2-tubulin antibody. We conclude there is a widespread loss of TTL activity during tumor growth in situ, suggesting that TTL activity may play a role in tumor cell regulation.
Insights
Tubulin tyrosine ligase (TTL) activity is lost during tumor growth, suggesting a role in regulating tumor cells. This loss is observed in both mouse and human tumors, indicating a conserved mechanism.
Area of Science:
- Cell Biology
- Biochemistry
- Oncology
Background:
- The C terminus of the alpha-tubulin subunit undergoes tyrosination/detyrosination via tubulin tyrosine ligase (TTL) and carboxypeptidase.
- The functional significance of this conserved tubulin modification cycle remains largely unknown.
Purpose of the Study:
- To investigate the role of tubulin tyrosine ligase (TTL) activity in cellular regulation and tumor development.
- To characterize tubulin modifications in TTL-deficient cells and tumors.
Main Methods:
- Isolation and characterization of TTL-deficient NIH-3T3 cell lines (TTL-).
- Detection of delta2-tubulin isotype using specific antibodies.
- Tumorigenicity assays in nude mice with TTL-deficient and TTL-rescued cells.
- Analysis of TTL activity and delta2-tubulin in human tumors.
Main Results:
- TTL- cells exhibit a unique delta2-tubulin isotype.
- TTL- cells form sarcomas in nude mice, and TTL activity is lost during tumor growth.
- Suppression of TTL activity and presence of delta2-tubulin are prevalent in human tumors.
Conclusions:
- TTL activity is systematically suppressed during tumor growth in vivo.
- Loss of TTL activity may be a significant factor in tumor cell regulation.
- Delta2-tubulin serves as a marker for suppressed TTL activity in tumors.