ΔNp73β expressed at a physiological level is capable of suppressing cell growth. (A to D) The ΔNp73β expression level in the presence of 0.2 or 0.02 μg of tetracycline/ml is comparable to a physiological level of endogenous ΔNp73β in LS174T, DLD-1, SW480, and U251 cells. H1299-ΔNp73β-4 cells were seeded on 10-cm-diameter dishes in the presence of 0.02, 0.2, or 2 μg of tetracycline/ml to regulate ΔNp73β expression. LS174T, DLD-1, SW480, and U251 cells were treated with CPT (1 μM), DOX (1 μg/ml), or 5-FU (400 μM) for 24 h. Cell extracts were collected for Western blot analysis. ΔNp73β was detected by using anti-p73 (Ab2 and Ab3) monoclonal antibodies. (E) ΔNp73β expressed at a physiological level is capable of suppressing cell growth. Approximately 2 × 104 H1299-ΔNp73β-4 cells were seeded in the absence or presence of 0.02, 0.2, or 2 μg of tetracycline/ml to regulate ΔNp73β expression.