Aberrations of the p19^Arf-Mdm2-p53 pathway in Slp65-deficient leukemias. (A) Western blot analysis of total cell lysates from pre-B cell tumors from Slp65^−/− mice for the expression of p53, p19^Arf, Mdm2, and Syk (loading control). (B) Quantitative RT-PCR analyses of p21^Cip1 expression in Slp65^−/− pre-B cell tumors without or with detectable p53 protein, normalized to GAPDH. Values in sorted WT BM B220⁺ cells were set to 1. Horizontal lines represent mean values of the relative expression levels. (C) Western blot analysis of total cell lysates from pre-B cell tumors from Btk^−/−Slp65^−/− mice for the expression of p53, p19^Arf, Mdm2, and Syk (loading control). (D) Western blot analysis of total cell lysates from pre-B cell tumors from p53^−/−Slp65^−/− mice for the expression of p19^Arf, Mdm2, and Syk (loading control). Protein of p53 was not detected in p53^−/−Slp65^−/− tumors.