Regulation of mitotic spindle orientation by phosphorylation of end binding protein 1.

End binding protein 1 (EB1) is a key regulator of microtubule dynamics that orchestrates hierarchical interaction networks at microtubule plus ends to control proper cell division. EB1 activity is known to be regulated by serine/threonine phosphorylation; however, how tyrosine phosphorylation affects EB1 activity remains poorly understood. In this study, we mapped the tyrosine phosphorylation pattern of EB1 in synchronized cells and identified two tyrosine phosphorylation sites (Y217 and Y247) in mitotic cells. Using phospho-deficient (Y/F) and phospho-mimic (Y/D) mutants, we revealed that Y247, but not Y217, is critical for astral microtubule stability. The Y247D mutant contributed to increased spindle angle, indicative of defects in spindle orientation. Time-lapse microscopy revealed that the Y247D mutant significantly delayed mitotic progression by increasing the duration times of prometaphase and metaphase. Structural analysis suggests that Y247 mutants lead to instability of the hydrophobic cavity in the EB homology (EBH) domain, thereby affecting its interactions with p150glued, a protein essential for Gαi/LGN/NuMA complex capture. These findings uncover a crucial role for EB1 phosphorylation in the regulation of mitotic spindle orientation and cell division.