KLF4 as a rheostat of osteolysis and osteogenesis in prostate tumors in the bone

We previously found that KLF4, a gene highly expressed in adult prostate stem cells, blocks the progression of indolent intraepithelial prostatic lesions into aggressive and rapidly growing tumors. To test whether this anti-cancer effect of KLF4 can also prevent prostate cancer-induced damage to the bone, we ablated KLF4 in human PC3 prostate cancer cells using CRISPR/Cas9-mediated genome editing and compared their behavior to null cells transduced with a DOX inducible KLF4 expression system. KLF4 re-expression inhibited growth of PC3 null cells in monolayer and as colonies in soft agar in a dose-dependent manner. When injected into the mouse femurs, PC3 null cells proliferated rapidly, forming very large, invasive and osteolytic tumors. Induction of KLF4 expression in PC3 null cells immediately after their intra-femoral inoculation blocked the development of tumors while preserving the normal bone architecture. KLF4 re-expression in established PC3 bone tumors inhibited osteolytic effects of PC3 null cells, preventing bone fractures and inducing a significant osteogenic response with regions of new bone formation. Transcriptome analyses of PC3 cells with no or high KLF4 expression revealed KLF4-dependent osteolytic or osteogenic transcriptional programs, respectively. Importantly, these KLF4-dependent functions significantly overlapped with metastatic prostate cancers in patients. Uninfected PC3 KLF4 wild-type cells and uninfected PC3 KLF4 null cells were grown for 48 hours and collected for RNA extraction. Another cohort of PC3 KLF4 null cells was infected with lentiviruses expressing a DOX inducible KLF4 expression construct (BFP-T2A-hKLF4) or the control empty vector (BFP-T2A). After 48 hours, DOX (10 ng/ml) was added to the culture medium to induce KLF4 expression. Control and KLF4-overexpressing cells were collected for RNA extraction after a 48-hour incubation with DOX. Total RNA was extracted using the RNeasy kit (Qiagen, CA, USA). RNA-Seq libraries were prepared with the TruSeq sample preparation kit (Illumina, CA, USA).