β3 accelerates microtubule plus end maturation through a divergent lateral interface.

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Biology

Background:

• Beta-tubulin isotypes share similar sequences but possess distinct functions.
• The TUBB3/β3 isotype is implicated in aggressive cancers and chemotherapy resistance.
• Functional significance of minor sequence variations between tubulin isotypes is not fully understood.

Purpose of the Study:

• To investigate the functional importance of sequence divergence in TUBB3/β3.
• To identify specific residues and regions in β3 tubulin responsible for its unique activity.
• To elucidate the mechanistic basis of β3 tubulin's role in microtubule dynamics and drug resistance.

Main Methods:

• Creation of mutant yeast strains expressing β-tubulin alleles mimicking β3 variant residues.
• Analysis of microtubule dynamics in yeast and HeLa cells overexpressing β3.
• Assessment of microtubule response to microtubule-targeting agents, including paclitaxel.
• Examination of EB binding at microtubule plus ends and lattice maturation rates.

Main Results:

• Residues at the lateral interface of β3 tubulin are sufficient to alter microtubule dynamics and response to drugs.
• Overexpression of β3 in HeLa cells shortens microtubule growth lifetime and reduces EB binding duration.
• β3-containing microtubules exhibit faster lattice maturation and resist paclitaxel stabilization.
• Specific regions (H1-S2 and H2-S3) at the β3 lateral interface are critical for paclitaxel resistance.

Conclusions:

• Sequence variations at the lateral interface of β3 tubulin mechanistically explain its distinct activity.
• Tubulin isotype expression can modulate the rate of microtubule lattice maturation at growing plus ends.
• Findings provide insights into the role of β3 tubulin in cancer progression and chemoresistance.