In cells, stable microtubules (MTs) are covalently modified by a carboxypeptidase, which removes the C-terminal Tyr residue of α-tubulin. The significance of this selective detyrosination of MTs is not understood. In this study, we report that tubulin detyrosination in fibroblasts inhibits MT disassembly. This inhibition is relieved by overexpression of the depolymerizing motor mitotic centromere-associated kinesin (MCAK). Conversely, suppression of MCAK expression prevents disassembly of normal tyrosinated MTs in fibroblasts. Detyrosination of MTs suppresses the activity of MCAK in vitro, apparently as the result of a decreased affinity of the adenosine diphosphate (ADP)–inorganic phosphate- and ADP-bound forms of MCAK for the MT lattice. Detyrosination also impairs MT disassembly in neurons and inhibits the activity of the neuronal depolymerizing motor KIF2A in vitro. These results indicate that MT depolymerizing motors are directly inhibited by the detyrosination of tubulin, resulting in the stabilization of cellular MTs. Detyrosination of transiently stabilized MTs may give rise to persistent subpopulations of disassembly-resistant polymers to sustain subcellular cytoskeletal differentiation.

Tubulin-tyrosine ligase (TTL), the enzyme that catalyzes the addition of a C-terminal tyrosine residue to α-tubulin in the tubulin tyrosination cycle, is involved in tumor progression and has a vital role in neuronal organization. We show that in mammalian fibroblasts, cytoplasmic linker protein (CLIP) 170 and other microtubule plus-end tracking proteins comprising a cytoskeleton-associated protein glycine-rich (CAP-Gly) microtubule binding domain such as CLIP-115 and p150 Glued, localize to the ends of tyrosinated microtubules but not to the ends of detyrosinated microtubules. In vitro, the head domains of CLIP-170 and of p150 Glued bind more efficiently to tyrosinated microtubules than to detyrosinated polymers. In TTL-null fibroblasts, tubulin detyrosination and CAP-Gly protein mislocalization correlate with defects in both spindle positioning during mitosis and cell morphology during interphase. These results indicate that tubulin tyrosination regulates microtubule interactions with CAP-Gly microtubule plus-end tracking proteins and provide explanations for the involvement of TTL in tumor progression and in neuronal organization.

Tubulin carboxypeptidase identity revealed: Enzymes of the α-tubulin detyrosination/tyrosination cycle create landmarks on microtubules that are essential for their multiple cellular functions and are altered in disease. Tubulin carboxypeptidases (TCPs) responsible for detyrosination have remained elusive for 40 years (see the Perspective by Akhmanova and Maiato). Aillaud et al. identified vasohibins as enzymes that perform the TCP function and found that their small interacting partner SBVP was essential for their activity. Vasohibin/SVBP complexes were involved in neuron polarization and brain cortex development. The authors also developed an inhibitor targeting this family of enzymes. Using a completely different strategy, Nieuwenhuis et al. also showed that vasohibins can remove the C-terminal tyrosine of α-tubulin. Science , this issue p. 1448 , p. 1453 ; see also p. 1381

Purpose: To determine the prevalence and the prognostic value of microtubule component expression in tumors of patients with locally advanced or metastatic non–small cell lung cancer (NSCLC).Experimental Design: Expression of microtubular components was immunohistochemically examined in 93 tumor samples from untreated patients with stage III and IV NSCLC. All patients received vinorelbine-based chemotherapy. Response to chemotherapy, progression-free survival, and overall survival were correlated with the expression of microtubule proteins.Results: The response rate was 27.3% (21 partial responses among 77 valuable patients). Although expression of microtubule components was not associated with the response rate, high class III β-tubulin expression was correlated with resistance to vinorelbine, defined as disease progression under treatment. Patients whose tumors expressed high levels of class III β-tubulin isotype had shorter progression-free survival and overall survival (P = 0.002 and 0.001, respectively). High Δ2 α-tubulin expression was associated with a shorter overall survival (P = 0.018). Tubulin II levels were not found to be correlated with patient outcome. A multivariate analysis, taking into account sex, age, histology, stage, weight loss, and class II β-tubulin, class III β-tubulin, and Δ2 α-tubulin levels, confirmed that class III β-tubulin expression was independently correlated with progression-free survival (P = 0.04) and overall survival (P = 0.012).Conclusions: These findings suggest that a high level of expression of class III β-tubulin in tumor cells is associated with resistance to vinorelbine and a poor prognosis in patients with NSCLC receiving vinorelbine-based chemotherapy.