In Vivo Application of CRISPR/Cas9 Revealed Implication of and in Prostate Cancer Proliferation and Epithelial Plasticity

Prostate cancer is the most common cancer in men in the Western world and the number is rising. Prostate cancer is notoriously heterogeneous, which makes it hard to generate and study in pre-clinical models. The family of Forkhead box (FOX) transcription factors are often altered in prostate cancer with especially high mutation burden in and . harbors loss or gain of function mutations in 8% of prostate cancer, which increases to 14% in metastatic samples. predominately occurs with loss of function mutations in 7% of primary tumors, and similar incidents are found in metastatic samples. Here, we applied in vivo CRISPR editing, to study the loss of functions of these two FOX transcription factors, in murine prostate in combination with loss of . Deficiency of Foxp1 increased proliferation in combination with loss of Pten. In contrast, proliferation was unchanged when androgen was deprived. The expression of was increased when Foxp1 was mutated in vivo, showing that Foxp1 is a repressor for this androgen-regulated target. Furthermore, analysis of and expression in a human prostate cancer data set revealed a negative correlation. Mutation of in the murine prostate induces cell plasticity to luminal cells. Here, epithelial cells with loss of were transdifferentiated to cells with expression of the basal markers Ck5 and p63. Interestingly, these cells were located in the lumen and did not co-express Ck8. Overall, this study reveals that loss of increases cell proliferation, whereas loss of induces epithelial plasticity in prostate cancer.