Manik Paul

Prostate epithelial cell fate.

Androgen receptor (AR) within prostatic mesenchymal cells, with the absence of AR in the epithelium, is still sufficient to induce prostate development. AR in the luminal epithelium is required to express the secretory markers associated with differentiation. Nkx3.1 is expressed in the epithelium in early prostatic embryonic development and expression is maintained in the adult. Induction of the mouse prostate gland by the embryonic mesenchymal cells results in the organization of a sparse basal layer below the luminal epithelium with rare neuroendocrine cells that are interdispersed within this basal layer. The human prostate shows similar glandular organization; however, the basal layer is continuous. The strong inductive nature of embryonic prostatic and bladder mesenchymal cells is demonstrated in grafts where embryonic stem (ES) cells are induced to differentiate and organize as a prostate and bladder, respectively. Further, the ES cells can be driven by the correct embryonic mesenchymal cells to form epithelium that differentiates into secretory prostate glands and differentiated bladders that produce uroplakin. This requires the ES cells to mature into endoderm that gives rise to differentiated epithelium. This process is control by transcription factors in both the inductive mesenchymal cells (AR) and the responding epithelium (FoxA1 and Nkx3.1) that allows for organ development and differentiation. In this review, we explore a molecular mechanism where the pattern of transcription factor expression controls cell determination, where the cell is assigned a developmental fate and subsequently cell differentiation, and where the assigned cell now emerges with its own unique character.

Transgenic Mouse Models of Prostate Cancer

The reproductive organs are not required for an individual’s survival but are required for survival of the species. As the individual approaches adulthood, the prostate undergoes developmental changes, resulting in maturation of this gland at puberty. At this stage, the prostate becomes a differentiated gland that produces proteins and other substances fundamental for reproduction and survival of the species. By the age of 50, as many as 30% of all men will harbor microscopic foci of prostate adenocarcinoma (CaP), and the incidence increases with age. In the United States, CaP is clinically diagnosed in approx 10% of men during their lifetime (189,000/yr), where it will claim 31,900 lives each year (13% of male cancer deaths) (1). The recent rising incidence of CaP (2) has plateaued (3), but the high prevalence of this disease and the aging of the US population still makes this a cancer that demands prompt attention.

The Role of Foxa Proteins in the Regulation of Androgen Receptor Activity

Activation of the androgen receptor is required for normal prostate physiology and in controlling the growth prostate cancer. However, the fact that multiple target organs express androgen receptor and are exposed to circulating androgens, yet fail to express prostate-specific markers and fail to develop androgen-dependent cancers, indicates that androgen receptor alone is not sufficient to dictate normal function and progression to cancer. Therefore, androgen action can be restricted in a given tissue by transcription factors that serve as co-regulators of androgen receptor. How androgen signaling acts in concert with other transcription factors, resulting in tissue-specific gene expression needs to be understood. The establishment of unique transcription factor regulatory networks is responsible, at least in part, to control androgen receptor action (1) in tissue-specific gene expression; (2) organ determination; and (3) cell differentiation. The identification of TF networks involved in these disparate events will allow researchers to elucidate the mechanisms that control prostate development, function, and pathology. Experimental evidence generated by our laboratory and others indicates that members of the Foxa subfamily of transcription factors play an important role in (1) normal prostate development; (2) the determination of prostatic cell fate; and (3) specific types of prostate pathology. This chapter reviews evidence generated by our laboratory and others regarding the important role of the Foxa transcription factors in the regulation of prostate-specific gene regulatory networks.

Mash1 expression is induced in neuroendocrine prostate cancer upon the loss of Foxa2

Neuroendocrine (NE) prostate tumors and neuroendocrine differentiation (NED) in prostatic adenocarcinomas have been associated with poor prognosis. In this study, we used the TRAMP mouse model that develops NE prostate tumors to identify key factors that can lead to NED. We have previously reported that NE tumors express the forkhead transcription factor, Foxa2, Mash1 (mouse achaete scute homolog‐1), as well as Synaptophysin. In TRAMP, the prostatic intraepithelial neoplasia (PIN) first expresses Foxa2 and Synaptophysin, which then progresses to NE cancer. In order to determine if Foxa2 is dispensable for development or maintenance of NE cancer, a conditional knock‐out of Foxa2 in TRAMP mice was generated by breeding mice with two floxed alleles of Foxa2 and one copy of Nkx3.1‐Cre. Nkx3.1‐Cre/Foxa2loxP/loxP mice showed loss of Foxa2 expression in embryonic prostatic buds. No expression of Foxa2 was seen in the adult prostate in either conditional null or control mice. Foxa2 is universally expressed in all wild type TRAMP NE tumors, but Mash1 expression is seen only in a few samples in a few cells. With the loss of Foxa2 in the NE tumors of the TRAMP/Nkx3.1‐Cre/Foxa2loxP/loxP mice, the expression of the pro‐neuronal gene Mash1 is upregulated. NE tumors from both the TRAMP control and Foxa2‐deficient TRAMP prostate express Synaptophysin and SV40 Large T‐antigen, and both show a loss of androgen receptor expression in NE cells. These studies suggest that the TRAMP NE tumors can form in the absence of Foxa2 by an up regulation of Mash1. Prostate 73: 582–589, 2013.

Fast Neutron r.b.e. for Lethality and Genotoxicity in a Wild-type and a Repair-deficient Strain of Yeast

The relative biological effectiveness (r.b.e.) of cyclotron-produced fast neutrons (11 MeV) in relation to 60Co gamma-rays, was studied in a wild-type and a DNA repair-deficient yeast strain for cell killing and genotoxicity. In the wild-type (D7) strain the r.b.e. varied from 2.7 to 4.1 for lethality, 2.8 to 7.1 for reverse mutation and 3.5 to 7.8 for mitotic gene conversion. At different survival levels, the repair deficient strain (D7 rad 52/rad 52) generally showed a lower r.b.e. for both cell killing and genotoxicity (25.2 to 37.2 per cent reduction for the cell death and 24.8 to 70.6 per cent for mutation and gene conversion) compared to the wild type. Except at very low dose levels, the r.b.e. values for cell killing and genotoxicity were similar within a given strain. At similar survival levels, neutrons were no more genotoxic than gamma-rays.

Repair of potentially lethal damage in yeast induced by fast neutrons

Survival curves of 3 diploid (D7) yeast strains: one wild-type, one deficient in excision of pyrimidine dimers (UV-sensitive) and one blocked in DNA double-strand-break repair (X-ray-sensitive), were compared after irradiation with cyclotron-produced fast neutrons. It was observed that both the UV-sensitive (rad3/rad3) and the X-ray-sensitive (rad52/rad52) mutants were more sensitive to neutrons than the wild-type. The role of DNA double-strand-breaks in neutron-induced cell death was further studied by comparing the relative sensitivity of the rad52/rad52 mutant to gamma-rays and fast neutrons. A comparison of the dose modification factors revealed that the deficiency in DNA double-strand-break repair did not make the yeast cells more sensitive to neutrons than to photons, which suggests that lesions of a different type may also be produced by neutrons. Survival curves obtained upon immediate plating and after delayed plating of neutron-irradiated cells showed that all 3 yeast strains were efficient in liquid holding recovery. The role of different repair pathways in cellular recovery from neutron-induced lethal damage is discussed.