Abstract B23: Epigenetic control of prostate epithelial stem cell differentiation
Authors: Maitland Norman James , Packer John 
Published: May 2016

Introduction: Hormone manipulation offers an effective but short term and time-limited treatment for human prostate cancers, reducing both tumor bulk and serum levels of prostate-specific antigen. In normal prostate, castration results in a loss of luminal cells and persistence of a poorly differentiated basal-like population, which is responsible for repopulation after restoration of hormone levels. However in fetal prostate development, the hormonal stimulus is provided indirectly to the developing epithelial structures via androgen-sensitive stromal cells.

To study the drivers of prostate epithelial cell differentiation, we sought the epigenetic factors affecting cell fate in adult human normal, hyperplastic and malignant epithelium, to provide more precise targets for prostate cancer therapy, based on this developmental paradigm.

Methods: We have adopted a multiple model approach for the study of human prostate stem cells. Epithelial cell fractions are prepared from human tissues using multiparametric FACS with a Beckman Coulter Astrios, or adhesion-based separations from (i) MRI guided biopsies of prostate tissues (and patient matched non- tumor tissues) (ii) primary cultures in defined serum free medium from prostate tissues depleted of stromal cells and (iii) a novel set of near patient mouse xenografts of human tissues. In these systems the (normal) colony forming and (malignant) tumor-inducing capacity largely resides in a CD133+/ CD44+/a2B1 integrin Hi/CD49f population which comprises 1% and &lt;0.1% of the normal and malignant epithelium respectively. Cell populations were analyzed independently for their gene expression patterns, non-coding RNA expression, histone modifications and genome CpG methylation. Using a modified analysis algorithm we then related gene expression to both miRNA expression and genomic methylation/ chromatin condensation.

Results: At the chromosomal level, prostate SC display a unique pattern of CpG methylation compared to their more differentiated progeny, with distinct changes in cancer. The SC also have a characteristic bivalent chromatin pattern when probed for specific histone modifications. This bivalent chromatin pattern is also indicative, in embryonic systems, of monoallelic gene expression, which was confirmed in prostate SC populations by analysis of the prostate-specific TMPRSS2 gene, in both native and fused form (to ERG).

MicroRNA expression patterns are tightly linked to SC differentiation, rather than carcinogenesis, and the miRNAs expressed in prostate SC most closely resemble those in human embryonic SC, and intriguingly in the most malignant forms of prostate cancer. Since miRNAs can control expression of multiple genes, we have devised an algorithm to predict regulation of only those genes expressed in the prostate epithelium. Perhaps significantly for cancer treatment, the principal functions controlled by miRNA expression are both DNA damage repair and wnt signaling, manipulation of which can increase the radiation resistance resident in the SC population.

By studying genes which are tightly co-regulated during cell differentiation, we defined 4 non-overlapping sets of genes in which retinoic acid acts as a driver of primitive cell differentiation, an intermediate cell type expressing genes with a bivalent response to RA and androgens, and committed basal/luminal cells in which androgen control of cell fate dominates.

Discussion: By studying highly enriched cell populations in different model systems, all of which are derived from primary human tissues, we have built up a complex picture of epigenetic regulation of gene expression during differentiation of human prostate. Many of these essential functions are related to similar functions in developing prostate tissue, but are often characterized by phenotypic plasticity, where the differentiated products of asymmetric division (self-renewal) can revert to a stem-like state.

Citation Format: Norman James Maitland, John Packer. Epigenetic control of prostate epithelial stem cell differentiation. [abstract]. In: Proceedings of the AACR Special Conference: Developmental Biology and Cancer; Nov 30-Dec 3, 2015; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(4_Suppl):Abstract nr B23.