The prostate contains classes of epithelial cells with variable differentiation status that may serve as targets for tumor initiation (8-10). Androgen cycling experiments suggest that stem cell activity is present in the prostate (11). These cells are thought to reside in the basal layer of the prostate because these cells are androgen-independent and preferentially retained in castrated rodents. Stem cells in the basal layer give rise to transit-amplifying epithelial cells (TACs) that differentiate to produce terminally differentiated secretory luminal cells (12).The most common form of human prostate cancer expresses luminal cell-specific markers (cytokeratins 8 and 18 and prostate-specific antigen) but low levels of the basal cell marker (p63), suggesting that the disease originates in terminally differentiated luminal cells (12,13). Some studies suggest that the disease is derived from high-grade prostatic intraepithelial neoplasia (PIN), which is believed to arise from intermediate epithelial cells (14). Other studies demonstrate that the majority of androgen-independent tumors express genes such as bcl-2 that are characteristic of the basal͞stem cell compartment in normal prostate tissue (8). Prostate cancers may arise from stem cells that undergo aberrant proliferation and differentiation to produce a heterogeneous population of cells expressing luminal-, basal-, and intermediate cell-specific genes (14, 15).The tissue recombination procedure developed by Cunha and Lung (16) uses fragments dissected from rat or mouse urogenital sinus mesenchyme (UGSM) in combination with adult epithelial tissue to regenerate prostate-like tissues. We developed a dissociated cell system to facilitate the study of unique prostate cell subpopulations to demonstrate that a subpopulation of murine prostate cells possesses stem-like capacity for de novo tubule regeneration (17). We find that Sca-1 (stem cell antigen-1), a glycosylphosphatidylinositol-linked cell surface protein known to enrich for somatic stem cells in other tissues (18,19), can be used to enrich for prostate-regenerating cells (PRCs). Sca-1 ϩ cell fractions contain an increased percentage of cells with immature cell properties, including replication quiescence, androgen independence, and multilineage differentiation potential. Perturbations of the PTEN͞AKT signaling axis in these cells result in the initiation of prostate tumorigenesis, and cancer progression is associated with a concomitant increase in Sca-1 ϩ cells. These studies suggest that Sca-1-enriched PRCs possess multiple stem͞progenitor cell properties and can serve as targets for the initiation of prostate tumorigenesis.
Materials and Methods
Infection of Dissociated Prostate Cells with Lentivirus and ProstateRegeneration. -Actin GFP transgenic mice were purchased from The Jackson Laboratory [C57BL͞6-TgN(ACTbEGFP)1Osb]. Dissociated prostate cells were prepared from 6-to 10-week-old C57BL͞6 and -actin GFP transgenic mice as described in ref.