Prostate stem cells: the niche and cell markers

Immunohistochemistry for Cancer Stem Cell Detection: Principles and Methods

Cancer stem cells (CSCs) are rare immortal cells within tumors with capabilities of self-renewal, differentiation, and tumorigenicity. CSCs play a pivotal role in the tumor development, progression, relapse, and resistance of anticancer therapy. The technique of choice to detect CSCs in formalin-fixed and paraffin-embedded (FFPE) samples is immunohistochemistry (IHC) since it is inexpensive and widespread in most laboratories. The main aims of this chapter are the description of the protocols and the automated immunohistochemical systems used for the identification of CSCs. Furthermore, a focus on the most common troubleshooting in CSC IHC is provided. Finally, an overview of the main markers of cancer stem cells in several cancer types will be provided.

The influence of prostatic anatomy and neurotrophins on basal prostate epithelial progenitor cells

BACKGROUND

Based on findings of surface marker, protein screens as well as the postulated near-urethral location of the prostate stem cell niche, we were interested whether androgen ablation, distinct anatomic regions within the prostate or neurotrophins have an influence on basal prostate epithelial progenitor cells (PESCs).

METHODS

Microdissection of the prostate, enzymatic digestion, and preparation of single cells was performed from murine and human prostates. Adult PESC marker expressions were compared between a group of C57BL/6 mice and a separate group of castrated C57BL/6 mice. Surface markers CD13/CD271 on human prostate epithelial progenitor cells were evaluated by FACS analyses in cells cultured under novel stem cell conditions. The effect of neurotrophins NGF, NT3, and BDNF were evaluated with respect to their influence on proliferation and activation of human basal PESCs in vitro.

RESULTS

We demonstrate the highest percentage of CD49f+ and Trop2+ expressing cells in the urethra near prostatic regions of WT mice (Trop2+ proximal: 10% vs. distal to the urethra: 3%, P < 0.001). While a marked increase of Trop2 expressing cells can be measured both in the proximal and distal prostatic regions after castration, the most prominent increase in Trop2+ cells can be measured in the prostatic tissue distant to the urethra. Furthermore, we demonstrate that the proportion of syndecan-1 expressing cells greatly increases in the regions proximal to the urethra after castration (WT: 5% vs. castrated: 40%). We identified heterogeneous CD13 and nerve growth factor receptor (p75(NGFR), CD271) expression on CD49f(+)/TROP2(high) human basal PESCs. Addition of the neurotrophins NT3, BDNF, and NGF to the stem cell media led to a marked temporary increase in the proliferation of human basal PESCs.

CONCLUSIONS

Our results in mice support the model, in which the proximal urethral region contains the prostate stem cell niche while a stronger androgen-dependent regulation of adult prostate stem cells can be found in the peripheral prostatic tissue. Neutrophin signaling via nerve growth factor receptor is possibly involved in human prostate stem cell homeostasis.

Prostate stem cells in the development of benign prostate hyperplasia and prostate cancer: emerging role and concepts

Benign Prostate hyperplasia (BPH) and prostate cancer (PCa) are the most common prostatic disorders affecting elderly men. Multiple factors including hormonal imbalance, disruption of cell proliferation, apoptosis, chronic inflammation, and aging are thought to be responsible for the pathophysiology of these diseases. Both BPH and PCa are considered to be arisen from aberrant proliferation of prostate stem cells. Recent studies on BPH and PCa have provided significant evidence for the origin of these diseases from stem cells that share characteristics with normal prostate stem cells. Aberrant changes in prostate stem cell regulatory factors may contribute to the development of BPH or PCa. Understanding these regulatory factors may provide insight into the mechanisms that convert quiescent adult prostate cells into proliferating compartments and lead to BPH or carcinoma. Ultimately, the knowledge of the unique prostate stem or stem-like cells in the pathogenesis and development of hyperplasia will facilitate the development of new therapeutic targets for BPH and PCa. In this review, we address recent progress towards understanding the putative role and complexities of stem cells in the development of BPH and PCa.

Cancer-associated fibroblasts enhance the gland-forming capability of prostate cancer stem cells

Signals originating from cancer-associated fibroblasts (CAF) may positively regulate proliferation and tumorigenicity in prostate cancer. In this study, we investigated whether CAFs may regulate the biology of prostate cancer stem cells (CSC) by using a conditional Pten deletion mouse model of prostate adenocarcinoma to isolate both CAF cultures and CSC-enriched cell fractions from the tumors. CSCs that were isolated possessed self-renewal, spheroid-forming, and multipotential differentiation activities in tissue culture, segregating with a cell fraction exhibiting a signature expression phenotype, including SCA-1 (high), CD49f (high), CK5 (high), p63 (high), Survivin (high), RUNX2 (high), CD44 (low), CD133 (low), CK18 (low), and Androgen Receptor (low). CSC spheroid-forming efficiency was differentially influenced by the nature of fibroblasts in a coculture system: Compared with mouse urogenital sinus mesenchyme or normal prostate fibroblasts, CAFs enhanced spheroid formation, with the spheroids displaying generally larger sizes and more complex histology. Graft experiments showed that CSCs admixed with CAFs produced prostatic glandular structures with more numerous lesions, high proliferative index, and tumor-like histopathologies, compared with those formed in the presence of normal prostate fibroblasts. Together, our findings underscore a significant role of CAFs in CSC biology.

Promising tumor-associated antigens for future prostate cancer therapy

Prostate cancer (CaP) is one of the most prevalent malignant diseases among men in Western countries. There is currently no cure for metastatic castrate-resistant CaP, and median survival for these patients is about 18 months; the high mortality rate seen is associated with widespread metastases. Progression of CaP from primary to metastatic disease is associated with several molecular and genetic changes that can affect the expression of specific tumor-associated antigens (TAAs) or receptors on the cell surface. Targeting TAAs is emerging as an area of promise for controlling late-stage and recurrent CaP. Several reviews have summarized the progress made in targeting signaling pathways for CaP but will not be discussed here. We describe some important CaP TAAs. These include prostate stem-cell antigen, prostate-specific membrane antigen, MUC1, epidermal growth factor receptor, platelet-derived growth factor and its receptor, urokinase plasminogen activator and its receptor, and extracellular matrix metalloproteinase inducer. We summarize recent advancements in our understanding of their role in CaP metastasis, as well as potential therapeutic options for targeting CaP TAAs. We also discuss the origin, identification, and characterization of prostate cancer stem cells (CSCs) and the potential benefits of targeting prostate CSCs to overcome chemoresistance and CaP recurrence.

Retinoid metabolism and ALDH1A2 (RALDH2) expression are altered in the transgenic adenocarcinoma mouse prostate model

Retinoids, which include vitamin A (retinol) and metabolites such as retinoic acid, can inhibit tumor growth and reverse carcinogenesis in animal models of prostate cancer. We analyzed retinoid signaling and metabolism in the TRAMP (transgenic adenocarcinoma mouse prostate) model. We detected increased retinol and retinyl esters in prostates pooled from 24 to 36 week TRAMP transgenic positive mice compared to nontransgenic littermates by HPLC. We used quantitative RT-PCR to measure transcripts for genes involved in retinoid signaling and metabolism, including ALDH1A1, ALDH1A2, ALDH1A3, CYP26A1, LRAT, and RARbeta(2), in prostate tissue from TRAMP positive (+) and age-matched littermate control mice ranging from 18 to 36 weeks. Transcript levels of ALDH1A1, a putative stem cell marker, were decreased in ventral and lateral lobes of prostates from TRAMP mice compared to age-matched, nontransgenic mice. ALDH1A2 (RALDH2) mRNA levels in dorsal and anterior lobes of TRAMP+ mice were lower than in age-matched (24 week) nontransgenic mice. We detected lower RARbeta(2) mRNA levels in dorsal prostate lobes of 36 week TRAMP mice relative to nontransgenic mice. We detected high levels of ALDH1A2 protein in the cytoplasm and nucleus in nontransgenic murine prostate paraffin sections, and lower ALDH1A2 protein levels in all prostate lobes of TRAMP mice compared to nontransgenic mice by immunohistochemistry. We also detected much lower cytoplasmic ALDH1A2 protein levels in all human prostate cancer paraffin sections stained (19 total) relative to normal human prostate tissue on the same sections. Our data indicate that this reduction in ALDH1A2 protein is an early event in human prostate cancer.

Lower urinary tract symptoms after hormone replacement therapy in Japanese patients with late-onset hypogonadism: a preliminary report

Hormone replacement therapy (HRT) is performed for the treatment for patients with late onset hypogonadism (LOH). One of the main concerns about HRT is the influence of lower urinary tract including prostate. This study examined whether HRT for Japanese patients of LOH affected lower urinary tract symptoms. A total of 21 patients with LOH were included in this study. Changes of International prostate symptom score (IPSS), IPSS quality of life (QOL) index and King's health questionnaire (KHQ), before HRT and 3 months after HRT, were evaluated. Statistical comparisons were made using the Wilcoxon signed rank test, P < 0.05 was considered statistically significant. Total IPSS and QOL index were not significantly different from 7.43 +/- 6.56, 2.71 +/- 1.74 at baseline to 8.29 +/- 6.24, 2.91 +/- 1.13 after 3 months. There were no significant differences in any of the nine categories of KHQ. In this preliminary study, the results suggested that HRT for LOH had no short-term effects on patients with lower urinary symptoms.