Provided are methods for modulating the proliferation of cells and tissues. In some embodiments, the methods include administering to a subject an effective amount of a modulator of a biological activity of a bone marrow X kinase (Bmx) gene product. Also provided are methods for increasing the radiosensitivity of a target cell or tissue, methods for suppressing tumor growth, methods for inhibiting tumor blood vessel growth, and compositions that include modulators of a biological activity of a bone marrow X kinase (Bmx) gene product.