Tamoxifen treatment of CreERT2-p53^F/F mice before, during, and after IR demonstrates the role of p53 in suppressing carcinogen-induced tumorigenesis.

<p>(A) Deletion of p53 prior to irradiation prevents robust apoptotic response in CreERT2-p53^F/F mice. Three month old CreERT2-p53^F/F mice were injected with tamoxifen or vehicle (corn oil) two weeks prior to treatment with 5 Gray ionizing radiation. Five hours after IR treatment, spleens were harvested and tissue sections subjected to TUNEL assays for apoptotic cells. Note strong apoptotic response in vehicle treated mice and greatly reduced apoptotic response in tamoxifen-treated mice. Panel to the right shows percentage of TUNEL positive cells in spleens from untreated mice (No Tx), corn oil injected and non-irradiated mice (vehicle, No IR), corn oil injected and irradiated mice (vehicle, IR), and tamoxifen injected and irradiated mice (TAM, IR). (B) The p53 damage response is abrogated in tamoxifen injected CreERT2-p53^F/F mice subjected to IR. Spleens were harvested from non-irradiated (-IR) and irradiated (+IR), non-injected (-INJ) and injected (+INJ 0 or 2 weeks post-injection) CreERT2-p53^F/F (+Cre) and p53^F/F (-Cre) mice and Western blots performed on tissue lysates using p53, p21, and actin antibodies. Note that robust p53 and p21 expression indicative of a robust p53 response occurs only in irradiated but non-Cre expressing or non-injected mice. (C) Six week old CreERT2-p53^F/F mice were subjected to 2.5 Gy ionizing radiation and were injected with tamoxifen either 2 weeks prior (n = 10), simultaneous with (n = 14), 2 weeks after (n = 11), or 4 weeks after (n = 13) IR exposure. Non-irradiated tamoxifen treated mice CreERT2-p53^F/F are included as controls (n = 62). (D) Kaplan-Meier tumor-free survival curves of IR-treated CreERT2-p53^F/F mice show similar lymphoma latency of lymphomas post injection while non-IR treated tamoxifen-injected mice showed more delayed tumorigenesis. (E) Natural logarithm of mortality rates fitted using the T4253H smoothing algorithm comparing Gompertz variables from CreERT2-p53^F/F mice injected with tamoxifen at 2 weeks prior and 4 weeks after IR treatment and non-IR treated tamoxifen-treated CreERT2-p53^F/F mice (x-axis in days). Note that the IR-treated mice exhibit high mortality whether or not p53 is present at the time of radiation.