To determine the effect of Trim28 deletion on ERV expression, we used the NPp53T (Nkx3.1-CreERT2/+; Ptenf/f; p53f/f; Trim28f/f) mouse model of prostate cancer with deletion of Pten, p53 and Trim28 (Fig. 1A [18]),. Here, TP53 is linked to prostate cancer.