Polypeptides that comprise an approximately 100-amino acid residue region of a centrosomal P4.1-associated protein (CPAP) that possess microtubule-destabilizing activity, polynucleotides encoding such polypeptides, compositions comprising the polypeptides and polynucleotides, and methods of use thereof, are disclosed. The invention is useful for destabilizing microtubules in eukaryotic cells, including but not limited to cancer cells.