Immunomodulatory properties of slowly cycling and mesenchymal-like castration-resistant prostate cancer stem cells

Tumors are constituted by different subpopulations of cells; this heterogeneity has multiple dimensions -genetic, epigenetic, and level of differentiation- with several clinical implications. On this work we outline the hierarchical organization of the normal epithelial of the prostate gland, and we observe that this organization is co-opted by tumors arising from this tissue. We uncovered two subsets of normal and cancer stem cells in different mouse models of prostate cancer; one population is largely quiescent with an EMT phenotype, and the other more committed toward epithelial differentiation and poised for activation in response to androgen stimuli. Whole exome sequencing revealed common pathways to these cells; exposing the prominence of integrin signaling and focal adhesion kinase (FAK) on the stem/progenitor cells behavior. Also we start to unveil a previously unnoticed property of cancer stem cells, the ability to modulate the tumor immune microenvironment and we link this function to downstream FAK signaling. To examine the characteristics and relationships of the prospectively identified subpopulations of prostate cells, the five subpopulations of cells defined by b4, Sca-1, and EpCAM expression, were sorted to purity by FACS and were used for RNAseq. These populations are defined as follows: DPE- (Lin-, ItgB4 hi, Sca1 hi, EpCAM low); DPE+ (Lin-, ItgB4 hi, Sca1 hi, EpCAM hi), BS (Lin-, ItgB4 hi, Sca1 low, EpCAM hi), SS (Lin-, ItgB4 low, Sca1 hi), DNE- (Lin-, ItgB4 low, Sca1 low, EpCAM low); DPE+ (Lin-, ItgB4 low, Sca1 low, EpCAM hi). This was done with both, normal gland (C57BL/6J mice) and prostate tumors of transgenic mouse models (PB-Tag, Hi-Myc (ARR2-Pb-cMyc), Ptenpc/pc (Pb-Cre4; Ptenfl/fl), and PB-ERG Pten-/- (Pb-Cre4; Ptenflox/flox; Rosa26ERG/ERG)). Finally to explore the role of integrin signaling on cancer stem cells, PB-TAg mice bearing tumor were treated with a FAK inhibitor or with vehicle as control, and then subject to the same analysis as above.