The cytotoxic lymphocyte protease, granzyme B, targets the cytoskeleton and perturbs microtubule polymerization dynamics.

Granzyme B, a serine protease derived from cytotoxic T lymphocyte (CTL) and Natural Killer (NK) cell granules, plays an important role in coordinating apoptosis of CTL and NK target cells. Here, we report that granzyme B targets the cytoskeleton by cleaving and removing the acidic C-terminal tail of alpha-tubulin. Consistent with this, Granzyme B markedly enhanced rates of microtubule polymerization in vitro, most likely by removal of an autoinhibitory domain within the tubulin C terminus. Moreover, delivery of Granzyme B into HeLa target cells promoted dramatic reorganization of the microtubule network in a caspase-independent manner. These data reveal that granzyme B directly attacks a major component of the cell cytoskeleton, which may contribute to the incapacitation of target cells during CTL/NK-mediated killing.