RESUMEN
The origin and phenotype of stem cells in human prostate cancer remains a subject of much conjecture. In this scenario, CD133 has been successfully used as a stem cell marker in both normal prostate and prostate cancer. However, cancer stem cells have been identified without the use of this marker, opening up the possibility of a CD133 negative cancer stem cell. In this chapter, we review the current literature regarding prostate cancer stem cells, with specific reference to the expression of CD133 as a stem cell marker to identify and purify stem cells in normal prostate epithelium and prostate cancer.
Asunto(s)
Células Madre Neoplásicas , Neoplasias de la Próstata , Biomarcadores/metabolismo , Humanos , Masculino , Células Madre Neoplásicas/metabolismo , Neoplasias de la Próstata/metabolismoRESUMEN
BACKGROUND: Epigenetic control is essential for maintenance of tissue hierarchy and correct differentiation. In cancer, this hierarchical structure is altered and epigenetic control deregulated, but the relationship between these two phenomena is still unclear. CD133 is a marker for adult stem cells in various tissues and tumour types. Stem cell specificity is maintained by tight regulation of CD133 expression at both transcriptional and post-translational levels. In this study we investigated the role of epigenetic regulation of CD133 in epithelial differentiation and cancer. METHODS: DNA methylation analysis of the CD133 promoter was done by pyrosequencing and methylation specific PCR; qRT-PCR was used to measure CD133 expression and chromatin structure was determined by ChIP. Cells were treated with DNA demethylating agents and HDAC inhibitors. All the experiments were carried out in both cell lines and primary samples. RESULTS: We found that CD133 expression is repressed by DNA methylation in the majority of prostate epithelial cell lines examined, where the promoter is heavily CpG hypermethylated, whereas in primary prostate cancer and benign prostatic hyperplasia, low levels of DNA methylation, accompanied by low levels of mRNA, were found. Moreover, differential methylation of CD133 was absent from both benign or malignant CD133+/α2ß1integrinhi prostate (stem) cells, when compared to CD133-/α2ß1integrinhi (transit amplifying) cells or CD133-/α2ß1integrinlow (basal committed) cells, selected from primary epithelial cultures. Condensed chromatin was associated with CD133 downregulation in all of the cell lines, and treatment with HDAC inhibitors resulted in CD133 re-expression in both cell lines and primary samples. CONCLUSIONS: CD133 is tightly regulated by DNA methylation only in cell lines, where promoter methylation and gene expression inversely correlate. This highlights the crucial choice of cell model systems when studying epigenetic control in cancer biology and stem cell biology. Significantly, in both benign and malignant prostate primary tissues, regulation of CD133 is independent of DNA methylation, but is under the dynamic control of chromatin condensation. This indicates that CD133 expression is not altered in prostate cancer and it is consistent with an important role for CD133 in the maintenance of the hierarchical cell differentiation patterns in cancer.
Asunto(s)
Células Madre Adultas/metabolismo , Antígenos CD/genética , Diferenciación Celular/genética , Células Epiteliales/fisiología , Glicoproteínas/genética , Neoplasias/genética , Péptidos/genética , Regiones Promotoras Genéticas , Antígeno AC133 , Células Madre Adultas/fisiología , Animales , Antígenos CD/metabolismo , Biomarcadores/análisis , Biomarcadores/metabolismo , Línea Celular Tumoral , Metilación de ADN/fisiología , Células Epiteliales/metabolismo , Regulación del Desarrollo de la Expresión Génica , Regulación Neoplásica de la Expresión Génica , Glicoproteínas/metabolismo , Humanos , Masculino , Ratones , Ratones Endogámicos BALB C , Ratones Desnudos , Ratones Transgénicos , Neoplasias/metabolismo , Neoplasias/patología , Péptidos/metabolismo , Hiperplasia Prostática/genética , Hiperplasia Prostática/metabolismo , Hiperplasia Prostática/patología , Neoplasias de la Próstata/genética , Neoplasias de la Próstata/metabolismo , Neoplasias de la Próstata/patología , Trasplante HeterólogoRESUMEN
The prostate gland is highly dependent on androgens for its development, growth and function. Consequently, the prostatic epithelium predominantly consists of androgen-dependent luminal cells, which express the androgen receptor at high levels. In contrast, androgens are not required for the survival of the androgen-responsive, but androgen-independent, basal compartment in which stem cells reside. Basal and luminal cells are linked in a hierarchical pathway, which most probably exists as a continuum with different stages of phenotypic change. Prostate cancer is also characterised by heterogeneity, which is reflected in its response to treatment. The putative androgen receptor negative cancer stem cell (CSC) is likely to form a resistant core after most androgen-based therapies, contributing to the evolution of castration-resistant disease. The development of CSC-targeted therapies is now of crucial importance and identifying the phenotypic differences between CSCs and both their progeny will be key in this process.