FIG. 1.

Is Atm required for p53-dependent apoptosis and tumor suppression in the TgT₁₂₁ brain tumor model? (A) Transgenic expression of T₁₂₁ in CP inactivates pRb family proteins (pRb-f) (including pRb, p107, and p130), resulting in abnormal proliferation and tumorigenesis. As a result, p53 is activated, causing apoptosis and attenuation of tumor growth (34). (B) Atm is expressed in T₁₂₁ CP. Western immunoblotting was performed on tissue extracts by using a monoclonal antibody specific for ATM, 2C6. Lane 1, Atm^−/− spleen (negative control); lanes 2 and 3, thymus and spleen tissues, respectively, of a wild-type mouse (positive control); lane 4, TgT₁₂₁ CP. Two resolvable Atm-specific bands the size of mouse Atm are detectable in lanes 2 through 4 and are absent from the negative control. The position of a 175-kDa molecular mass marker is shown on the right.