Keratin expression: a measure of phenotypic modulation of human prostatic epithelial cells by growth inhibitory factors

Intraductal prostate cancer: An aggressive subset of prostate cancers? Immunophenotypic evaluation

Introduction:

The presence of intraductal prostate cancer in a sample is often associated with large tumor volume, an advanced stage of the disease, a high Gleason score and an increased risk of recurrence, and resistance to androgen suppression and chemotherapy, which are also correlated with reduced progression-free survival and with postoperative, biochemical relapse.

Methods:

The aim of our study was to investigate whether carbonic anhydrase IX (CA IX) is upregulated in prostate cancer and to investigate ERG and EZH2 as potential markers for cancer aggression in aggressive acinar disease with intraductal component prostate cancer. The series consisted of 79 cases of prostate cancer. Immunohistochemical staining was performed for EZH2 ERG and CA IX.

Results:

The results of this study underline the fact that EZH2 protein expression is a powerful predictor of PSA relapse in prostate cancer and that this effect is stronger in ERG-positive cancers than in ERG-negative cancers. Evident EZH2 nuclear expression was found in prostatic tumor, proposing increased EZH2 expression important for the spread of prostate cancer.

Conclusions:

The relationship to tumor phenotype and prognosis was more considerable in ERG-positive tumors than in ERG-negative tumors. EZH2 has gained great interest as a target for epigenetic cancer therapy. Although prostate cancer is a hypoxic tumor, it does not express CA IX and cannot be used as an endogenous marker for hypoxia.

Ciliary neurotrophic factor (CNTF) and its receptor (CNTFRα) signal through MAPK/ERK pathway in human prostate tissues: a morphological and biomolecular study

Ciliary neurotrophic factor (CNTF) is a member of interleukin-6 type cytokine family. The CNTF receptor complex is a heterodimer including gp130 and CNTF receptor α (CNTFRα) proteins triggering the activation of multiple intracellular signaling pathways including AKT/PI3K, MAPK/ERK and Jak/STAT pathways. At present no data are available on the localization of CNTF and CNTFRα in prostate as well as on the role of CNTF in this organ. In this study we have analyzed the localization of CNTF and CNTFRα by immunohistochemistry and we have used PWR-1E cell line as a model for normal glandular cell to investigate the role of this cytokine. Our results show that CNTF and CNTFRa are expressed in the staminal compart of the prostate and that CNTF selectively inhibits ERK pathway. In conclusion, we suggest that CNTF could be considered as key molecule to maintenance epithelium homeostasis via pERK downregulation by an autocrine mechanism. Further CNTF studies in prostate cancer could be useful to verify the potential role of this cytokine in carcinogenesis.

LEADeR role of miR-205 host gene as long noncoding RNA in prostate basal cell differentiation

Though miR-205 function has been largely characterized, the nature of its host gene, MIR205HG, is still completely unknown. Here, we show that only lowly expressed alternatively spliced MIR205HG transcripts act as de facto pri-miRNAs, through a process that involves Drosha to prevent unfavorable splicing and directly mediate miR-205 excision. Notably, MIR205HG-specific processed transcripts revealed to be functional per se as nuclear long noncoding RNA capable of regulating differentiation of human prostate basal cells through control of the interferon pathway. At molecular level, MIR205HG directly binds the promoters of its target genes, which have an Alu element in proximity of the Interferon-Regulatory Factor (IRF) binding site, and represses their transcription likely buffering IRF1 activity, with the ultimate effect of preventing luminal differentiation. As MIR205HG functions autonomously from (albeit complementing) miR-205 in preserving the basal identity of prostate epithelial cells, it warrants reannotation as LEADeR (Long Epithelial Alu-interacting Differentiation-related RNA).

miR-205 is known to have context-dependent tumor suppressive or oncogenic roles. Here, the authors report the host gene of miR-205, MIR205HG as a nuclear lincRNA that maintains the basal identity of prostate cell and prevents luminal cell differentiation via the repression of interferon responsive genes.

Targeting phenotypic heterogeneity in benign prostatic hyperplasia

Benign prostatic hyperplasia and associated lower urinary tract symptoms remain difficult to treat medically, resulting in hundreds of thousands of surgeries performed annually in elderly males. New therapies have not improved clinical outcomes since alpha blockers and 5 alpha reductase inhibitors were introduced in the 1990s. An underappreciated confounder to identifying novel targets is pathological heterogeneity. Individual patients display unique phenotypes, composed of distinct cell types. We have yet to develop a cellular or molecular understanding of these unique phenotypes, which has led to failure in developing targeted therapies for personalized medicine. This review covers the strategic experimental approach to unraveling the cellular pathogenesis of discrete BPH phenotypes and discusses how to incorporate these findings into the clinic to improve outcomes.

Context dependent regulatory patterns of the androgen receptor and androgen receptor target genes

BACKGROUND

Expression of the androgen receptor (AR) is associated with androgen-dependent proliferation arrest and terminal differentiation of normal prostate epithelial cells. Additionally, activation of the AR is required for survival of benign luminal epithelial cells and primary cancer cells, thus androgen deprivation therapy (ADT) leads to apoptosis in both benign and cancerous tissue. Escape from ADT is known as castration-resistant prostate cancer (CRPC). In the course of CRPC development the AR typically switches from being a cell-intrinsic inhibitor of normal prostate epithelial cell proliferation to becoming an oncogene that is critical for prostate cancer cell proliferation. A clearer understanding of the context dependent activation of the AR and its target genes is therefore desirable.

METHODS

Immortalized human prostate basal epithelial EP156T cells and progeny cells that underwent epithelial to mesenchymal transition (EMT), primary prostate epithelial cells (PrECs) and prostate cancer cell lines LNCaP, VCaP and 22Rv1 were used to examine context dependent restriction and activation of the AR and classical target genes, such as KLK3. Genome-wide gene expression analyses and single cell protein analyses were applied to study the effect of different contexts.

RESULTS

A variety of growth conditions were tested and found unable to activate AR expression and transcription of classical androgen-dependent AR target genes, such as KLK3, in prostate epithelial cells with basal cell features or in mesenchymal type prostate cells. The restriction of androgen- and AR-dependent transcription of classical target genes in prostate basal epithelial cells was at the level of AR expression. Exogenous AR expression was sufficient for androgen-dependent transcription of AR target genes in prostate basal epithelial cells, but did not exert a positive feedback on endogenous AR expression. Treatment of basal prostate epithelial cells with inhibitors of epigenetic gene silencing was not efficient in inducing androgen-dependent transcription of AR target genes, suggesting the importance of missing cofactor(s).

CONCLUSIONS

Regulatory mechanisms of AR and androgen-dependent AR target gene transcription are insufficiently understood and may be critical for prostate cancer initiation, progression and escape from standard therapy. The present model is useful for the study of context dependent activation of the AR and its transcriptome.

Lemur Tyrosine Kinase 2, a novel target in prostate cancer therapy

Progression from early forms of prostate cancer to castration-resistant disease is associated with an increase in signal transduction activity. The majority of castration-resistance cancers persist in the expression of the androgen receptor (AR), as well as androgen-dependent genes. The AR is regulated not only by it associated steroid hormone, but also by manifold regulatory and signaling molecules, including several kinases. We undertook evaluation of the role of Lemur Tyrosine Kinase 2 (LMTK2) in modulating AR activity, as several Genome Wide Association Studies (GWAS) have shown a marked association of LMTK2 activity with the development of prostate cancer. We confirm that not only is LMTK2 mRNA reduced in prostate cancer tissue, but also LMTK2 protein levels are markedly diminished. Knockdown of LMTK2 protein in prostate cell lines greatly increased the transcription of androgen-responsive genes. In addition, LMTK2 knockdown led to an increase in prostate cancer stem cell populations in LNCaP cells, indicative of increased tumorogenicity. Using multiple approaches, we also demonstrate that LMTK2 interacts with the AR, thus putting LMTK2 as a component of a signaling complex modulating AR activity. Our finding that LMTK2 is a negative regulator of AR activity defines a novel cellular pathway for activation of AR-responsive genes in castrate resistant-prostate cancer. Moreover, pharmacologic manipulation of LMTK2 activity will provide a novel therapeutic target for more effective treatments for patients with castrate-resistant prostate cancer.

Reversal of the low-affinity neurotrophin receptor stromal-epithelial expression pattern between benign and malignant human prostate

Reduced expression of the low-affinity p75 neurotrophin receptor (p75(NTR)) occurs in prostate epithelial cells during malignant transformation. Recent studies indicating that the p75(NTR) can transduce signals that induce apoptosis suggest that diminished p75(NTR) in transformed prostate cells may contribute to immortalization. Mutations in the transmembrane domain of the p75(NTR) gene have been associated with decreased p75(NTR) protein expression and may block the ability of the p75(NTR) to induce apoptosis. Therefore, we used Western blot to analyze prostate cancer (PC) cell lines for p75(NTR) protein expression and gene single strand conformation polymorphism (SSCP) analysis and direct DNA sequencing to analyze mutations in the transmembrane domain of the p75(NTR). p75(NTR) Protein was present in all cell lines, and mutations in the p75(NTR) gene were not detected in cDNA derived from any cell line. To define the expression pattern of p75(NTR) in PCs in vivo, we used immunohistochemical techniques to examine tissue specimens from 20 benign, 19 malignant primary, and 14 metastatic prostate specimens. In benign prostate tissues, expression of p75(NTR) was universally detected in basal cells but not in secretory epithelial or stromal cells. In both primary and metastatic PC tissues, p75(NTR) immunoreactivity could not be detected in malignant prostate epithelial cells. However, in contrast to the benign prostate, p75(NTR) protein was expressed in stromal cells surrounding malignant epithelial cells. Stromal p75(NTR) expression was present in 84% (16 of 19) primary and in 86% (12 of 14) metastatic specimens. These data show that in the benign prostate p75(NTR) protein is expressed by basal cells and not stromal cells whereas in malignant prostate p75(NTR) protein is expressed by stromal cells but not prostatic carcinoma cells. Reversal of the p75(NTR) stromal-epithelial pattern of expression between benign and malignant prostate suggests that p75(NTR) may contribute to the development and maintenance of prostate cancer.

Effects of simulated microgravity on DU 145 human prostate carcinoma cells

The high aspect rotating-wall vessel (HARV) was recently designed by NASA to cultivate animal cells in an environment that simulates microgravity. This work examines the effects of HARV cultivation on DU 145 human prostate carcinoma cells. In the HARV, these prostate cells grew in suspension on Cytodex-3 microcarrier beads to form bead aggregates with extensive three-dimensional growth between beads and on the aggregate surface. HARV and spinner-flask control cultures of DU 145 cells had similar doubling times, but the former was characterized by a higher percentage of G(1)-phase cells, larger bead aggregates, enhanced development of filopodia and microvilli-like structures on the aggregate surface, and stronger staining for select cytoskeletal proteins (cytokeratins 8 and 18, actin, and vimentin). When compared with static controls grown in a T-flask and Transwell insert, HARV cultures grew more slowly and differences in the cell cycle and immunostaining became more pronounced. These results suggest that HARV cultivation produced a culture that was less aggressive from the perspective of proliferation, more differentiated and less pliant than any of the three control cultures examined in this work. Possible factors effecting this change are discussed including turbulence and three-dimensional growth.

E-cadherin-mediated survival of androgen-receptor-expressing secretory prostate epithelial cells derived from a stratified in vitro differentiation model

The androgen receptor (AR) is expressed in differentiated secretory prostate epithelial cells in vivo. However, in the human prostate, it is unclear whether androgens directly promote the survival of secretory cells, or whether secretory cells survive through androgen-dependent signals from the prostate stroma. Biochemical and mechanistic studies have been hampered by inadequate cell-culture models. In particular, large-scale differentiation of prostate epithelial cells in culture has been difficult to achieve. Here, we describe the development of a differentiation system that is amenable to functional and biochemical analysis and its application to deciphering the survival pathways in differentiated AR-expressing epithelial cells. Confluent prostate epithelial cell cultures were treated with keratinocyte growth factor (KGF) and dihydrotestosterone. After 2 weeks, a suprabasal cell layer was formed in which cells no longer expressed alpha2, alpha3, alpha6, alphav, beta1 or beta4 integrins or p63, K5, K14, EGFR, FGFR2IIIb or Bcl-2, but instead expressed AR and androgen-induced differentiation markers, including K18, K19, TMPRSS2, Nkx3.1, PMSA, KLK2 and secreted prostate-specific antigen (PSA). Differentiated prostate cell survival depended on E-cadherin and PI3K, but not KGF, androgen, AR or MAPK. Thus survival of differentiated prostate epithelial cells is mediated by cell-cell adhesion, and not through androgen activity or prostate stroma-derived KGF.

p63 in prostate biology and pathology

The identification of stem cells and differentiation programs regulating the development and maintenance of the normal prostate epithelium is essential for the identification of the cell type(s) and molecular alterations involved in the development and propagation of prostate cancer (CaP). The p53-homologue p63 is highly expressed in normal prostate basal cells and is a clinically useful biomarker for the diagnosis of CaP. Importantly, p63 has been shown to play a critical role in prostate development. Recent experimental evidence also suggests that this gene is essential for normal stem cell function in the prostate as well as other epithelial organs. Future studies aimed at better defining the role of p63 in the renewal of the adult prostate epithelium are likely to shed new light on the mechanisms involved in prostate carcinogenesis.

Proteasome inhibition blocks caspase-8 degradation and sensitizes prostate cancer cells to death receptor-mediated apoptosis

BACKGROUND

Proteasome inhibition through the administration of Velcade is a viable chemotherapeutic strategy that is approved to treat multiple myeloma and is being evaluated for efficacy against prostate cancer. Currently, the apoptotic pathways that contribute to this anticancer response are poorly understood. Our goal is to test the extent to which proteasome inhibition modulates apoptosis through death receptor pathways.

METHODS

Several prostate cancer cell lines and primary prostate epithelial cells (PrECs) were used as models. The death receptor pathway was activated by the expression of Fas ligand (FasL) or addition of TNF-related apoptosis-inducing ligand (TRAIL) in the presence or absence of proteasome inhibitors. The apoptotic response was quantified by annexin V, TUNEL and nuclear condensation assays. Western blot analysis was conducted to quantify protein levels and enzyme assays were used to measure caspase activity.

RESULTS

Proteasome inhibition markedly sensitized prostate cancer cells to apoptosis initiated by Fas ligand (FasL) or TRAIL. In the presence of either death ligand, procaspase-8 processing occurred, but led to minimal amounts of active caspase-8. The addition of Velcade, however, led to robust active caspase-8 protein abundance and activity. In the presence of Velcade the caspase-8 p18 subunit half-life increased from 22 min to over 2 hr.

CONCLUSIONS

These findings demonstrate that proteasome inhibition can sensitize cells to apoptosis elicited by tumor necrosis factor ligands and retarding caspase-8 degradation provides one explanation for this activity. This study suggests that the clinical efficacy of Velcade may result, at least in part, from the activity of death ligands.

Anchorage-independent culture maintains prostate stem cells

Freshly isolated mouse prostate epithelial cells regenerate fully differentiated prostate tissue when combined with embryonic urogenital sinus mesenchyme and grafted in vivo. We show here that this regenerative capacity, which has been attributed to a small population of pleuripotential progenitor epithelial cells, is rapidly lost when the cells are placed in monolayer culture but can be maintained by culture in anchorage-independent conditions. Epithelial cells placed in anchorage-independent culture formed proliferating spheres that could be serially passaged and exhibited increased expression of putative stem cell markers as compared to cells grown in monolayer culture. Epithelial cells isolated from the fetal urogenital sinus, the newborn, and adult prostate formed spheres with similar efficiency, while cells isolated from the post-castration prostate exhibited significantly higher sphere-forming abilities. When passaged spheres were recombined with E17 rat urogenital sinus mesenchyme and grafted in vivo, they generated fully differentiated mouse prostate glandular epithelium containing both p63+ basal cells and p63- luminal cells and expressing a variety of prostate-specific and terminal differentiation markers.

Prostate stem cells: from development to cancer

The cell of origin of prostate cancer is still unknown. The identification of these cells depends on understanding prostate cell differentiation lineage during development as well as adult prostate epithelium renewal. Recent advances in the field have shed light on the hierarchical relationship between epithelial prostate cells. On the basis of this knowledge, the isolation and characterization of prostate cancer stem cells may now be possible and could provide an explanation for the known clinical and molecular heterogeneity of human prostate cancer.

Regulation of cell proliferation in a stratified culture system of epithelial cells from prostate tissue

Mechanisms controlling epithelial proliferation and differentiation in the prostate have been primarily investigated in mouse models. The regulation of proliferation and differentiation is poorly understood in human prostate epithelial cells. In vivo, the glandular prostate epithelium consists of a p63-positive proliferating basal cell layer and a post-mitotic p27-positive secretory cell layer. We have established an organized stratified culture system of human primary prostate epithelial cells to gain insight into mechanisms regulating proliferation and differentiation. In this system, expression of p63 is observed in the bottom layer. In addition, BrdU incorporation persists even though cells are confluent. In contrast, in the upper layer, p63 expression is greatly diminished, p27 is expressed, and the cells are growth arrested. Overexpression of cyclin D1 or knockdown of p27 does not increase proliferation. After inactivation of the nuclear phosphoprotein Rb, the cell layers remain organized and cell proliferation increases only in the bottom layer. Furthermore, the expression of p63 remains confined to the bottom layer after Rb inactivation. Altogether, this in vitro model recapitulates certain aspects of in vivo growth regulation and differentiation and suggests that the loss of Rb family proteins in human cells trigger hyperplasia but is not sufficient for transformation.

Growth, morphogenesis, and differentiation during mouse prostate development in situ, in renal grafts, and in vitro

BACKGROUND

In vitro organ culture and renal grafting of the urogenital sinus (UGS) have both been used as models of prostate development. However, neither has been rigorously examined for its fidelity to replicate the canonical process of prostate differentiation in situ.

METHODS

We assessed size, morphology, histology, and the mRNA expression of differentiation marker genes of the E14 male mouse UGS grown for 0-28 days as sub-renal capsule allografts in nude mice or in culture containing androgen and compared these to UGS development in situ.

RESULTS

Development of grafted tissues was morphologically and histologically similar to development in situ but differentiation occurred more rapidly. UGS growth in organ culture resulted in bud formation, but did not trigger cellular differentiation. However, the potential for differentiation was maintained and could be rescued by grafting tissues into nude mice.

CONCLUSIONS

In vitro organ culture and renal grafting of UGS tissues may be appropriate models for studying prostatic bud formation, but only grafting is an appropriate model for prostatic differentiation.

Sex steroids have differential effects on growth and gene expression in primary human prostatic epithelial cell cultures derived from the peripheral versus transition zones

The majority of human prostate cancers arise from the peripheral zone (PZ). Prostate epithelial stem cells have been localized to the basal epithelial cell compartment. In addition, basal cells have been shown to maintain luminal epithelial cell differentiation and may mediate signals between the stromal and luminal cell compartments. Therefore, the study of adult prostate basal cells derived from different prostate zones may give insights into the mechanisms underlying normal and abnormal prostate growth. We herein compare the basal and sex steroid-stimulated expression and activity of several genes/proteins that are known to be critical in prostate cancer development in primary cultures of basal cells derived from the transition zone (TZ) and PZ of prostatectomy specimens. Our results demonstrate that prostate basal cells derived from the PZ versus TZ are more viable in culture, particularly in response to sex steroid addition. PZ cells exhibit higher telomerase activity and increased expression levels of androgen receptor, the anti-apoptotic protein bcl-2, and the dominant-negative splice variant of Kruppel-like Factor 6. PZ cells have lower basal expression levels of estrogen receptor-beta, the pro-apoptotic protein Bax, and cell-cycle inhibitor proteins (p53, p21(waf1/Cip1)). Finally, we demonstrate divergent responses to sex hormones in the two basal cell populations. The gene expression pattern in the PZ cells may partially explain the predominance of prostate cancer development in this region.

Interaction of nuclear receptor ligands with the Vitamin D signaling pathway in prostate cancer

A number of hormonal ligands and/or the nuclear receptors that mediate their actions have been targeted for prostate cancer therapy. Androgens, the ligands for the androgen receptor (AR), are critical for the growth of prostate cancer. Inhibition of androgen production has been the mainstay of treatment for advanced prostate cancer for decades. Other more recently tested targets include retinoid receptors (RAR and RXR), glucocorticoid receptors (GR), estrogen receptors (ER) and peroxisome proliferator-activated receptors (PPAR). Calcitriol, acting through the Vitamin D receptor (VDR), has many tumor suppressive activities in the prostate, including inhibition of proliferation, induction of apoptosis and/or differentiation, and reduction of cellular invasion. Because of these properties, calcitriol and its less hypercalcemic analogs are being evaluated as agents to prevent or treat prostate cancer. Androgens, retinoids, glucocorticoids, estrogens and agonists of PPAR directly or indirectly impact Vitamin D signaling pathways, and vice versa. In order to design the most effective strategies to use calcitriol to prevent or treat prostate cancer, the interactions of other nuclear receptors and their ligands with the Vitamin D signaling pathway need to be considered.

Studies on the differentiation pathway and growth characteristics of epithelial culture cells of the human prostate

We established explant primary cultures in order to study the growth and hormone responsiveness, and the differentiation process of prostatic epithelial cells. Cell outgrowth was achieved from explant tissue by using a new DU145-cell-conditioned medium and special plastic coverslips. To define the present model, proliferation assays were tested by [3H]thymidine assay and planimetric analysis. Cells were analyzed using immunocytochemistry, light, phase contrast and electron microscopy, polymerase chain reaction, telomerase ELISA and immunoassay (PSA). Morphology and electron microscopy revealed typical epithelial differentiation. Immunocytochemistry showed the content of basal and secretory epithelial cells, endocrine paracrine cells and a high level of proliferation. With increasing culture time, mature epithelial differentiation (PSA) increases and the initial increase of alpha-smooth muscle actin (alpha-SMA) decreases again. After further passaging, alpha-SMA expression is no longer detected and PSA expression decreases. Furthermore, epithelial cells showed both androgen responsiveness and androgen receptor expression. These findings show the presence of epithelial cells in a process of differentiation with endocrine paracrine cells and a high level of proliferation. This model may maintain the cellular and functional properties more closely related to the human prostate and may provide a valuable tool for studying stem cells and differentiation characteristics.

Are primary cultures realistic models of prostate cancer?

Primary cultures fill a unique niche among the repertoire of in vitro model systems available to investigate the biology of the normal and malignant human prostate. This review summarizes some of the properties of primary cultures, with special emphasis on two questions: are primary cultures from adenocarcinomas really comprised of cancer rather than normal cells, and do primary cultures faithfully retain characteristics of cells of origin?

In vitro deregulation of markers characteristic of human prostate epithelial cells

We have screened primary cultures of human prostate for the expression of markers reported to be characteristic of specific cell lineages in vivo, in order to ascertain whether human prostate cells in vitro maintain and reflect their in vivo differentiated phenotypes and to evaluate the homogeneity of the populations of cells that can be derived from this tissue. Using single and dual stain immunofluorescent microscopy to analyse very early organoid and subsequently derived monolayer stage cultures, we have observed that expression of markers characteristic of human prostate epithelial cells in vivo is deregulated within 48h, indicating that dissociation of human prostate tissue and cultivation of prostate epithelial cells in culture can result in promiscuous expression of cell type specific markers of prostate epithelial cells. These observations have important implications for studies of cell lineage and differentiation of prostate cells in vitro.

IL-10 signaling via IL-10E1 is dependent on tyrosine phosphorylation in the IL-10R alpha chain in human primary prostate cancer cell lines

Interleukin 10 (IL-10) stimulates rapid nuclear translocation and binding of a 22 kDa protein, termed interleukin 10 enhancer 1 (IL-10E1), to a novel enhancer element (i.e. HTE-1) of the tissue inhibitor of metalloproteinase-1 (TIMP-1) gene to upregulate TIMP-1 expression. IL-10E1 signaling involves tyrosine phosphorylation of the IL-10R JAK1 (Janus kinase) and TYK2 (tyrosine kinase) receptor kinases and tyrosine phosphorylation of two tyrosine moieties (Y57 and Y62) of a LIM domain of the IL-10E1 protein. In this paper, the studies showed that two tyrosine residues (Tyr(446) and Tyr(496)) located in the cytoplasmic domain of the IL-10R alpha chain were required for receptor function, and for phosphorylation and activation of IL-10E1. Immunoprecipitation studies revealed that 12 amino-acid peptides encompassing either of these two tyrosine residues in phosphorylated form coprecipitated IL-10E1 and blocked ligand-dependent IL-10E1 phosphorylation in a cell-free system. In contrast, peptides containing serine substitutions for Tyr(446) and Tyr(496), and tyrosine-phosphorylated peptides containing Tyr(230) or Tyr(252/259) did not prevent IL-10E1 activation or signaling. To confirm these observations in vivo, fusion protein constructs were made between a modified form of green fluorescent protein or GFP and the intact IL-10E1 protein (IL-10E1-MmGFP) and n-terminal peptides of the IL-10E1 protein (i.e. nt-nls-MmGFP and mutant sequences identified as nt-nls mC61-MmGFP and nt-nls mY57/mY62-MmGFP peptides). Confocal microscopy revealed that IL-10 triggered transport to the nucleus of IL-10E1-MmGFP, nt-nls-MmGFP, and nt-nls mC61-MmGFP by 10-30 min in HPCA-10a (human prostrate cancer cells; derived from Gleason sum 10 tumor tissue) cells. IL-10 failed to induce nuclear translocation of the mY57/mY62-MmGFP peptides with point mutations of the two tyrosine groups. Coinjection of nt-nls-MmGFP with the IL-10R Tyr(446) and Tyr(496) amino-acid residues completely blocked ligand signaling. Coinjection of peptides containing either serine substitutions for Tyr(446) and Tyr(496) or Tyr(230) and Tyr(252/259) failed to block nt-nls-MmGFP signaling. The data demonstrate that IL-10E1 is directly recruited to the ligand-activated IL-10R by binding to specific phosphotyrosine groups which control tyrosine phosphorylation of the LIM domain of the IL-10E1 protein (i.e. Y57/Y62 groups) and IL-10E1 activation.

Immunophenotypic characterization of 225 prostate adenocarcinomas with intermediate or high Gleason scores

This study provides detailed staining results for 225 prostate adenocarcinomas, including 150 Gleason score 8, 9, and 10 adenocarcinomas with cytokeratins (CKs) 7, 20, 5/6, and 17, prostate-specific antigen (PSA), prostatic acid phosphatase (PAP), carcinoembryonic antigen (CEA), WT1, thyroid transcription factor-1 (TTF-1), and villin. CK7 was reactive in 112 adenocarcinomas (49.8%). The percentage of CK7-reactive adenocarcinomas and the percentage of CK7-stained cells increased in higher Gleason score adenocarcinomas; most reactive neoplasms had CK7 staining of fewer than 25% of cells. CK20 had similar results. The percentage of PSA- and PAP-reactive adenocarcinomas and the percentage of stained cells in reactive neoplasms decreased in higher Gleason score adenocarcinomas. CK5/6 and CK17, WT1, CA-125, TTF-1, and villin were nonreactive. The prostate can be the primary site of metastatic adenocarcinoma that is nonreactive for PAP and PSA and has CK7 or CK20 reactivity in fewer than 50% of the cells. The likelihood that a metastatic adenocarcinoma is from the prostate is low if reactivity with any of the cytokeratin antibodies, CEA, TTF-1, CA-125, WT1, or villin is extensive.

N-(4-hydroxyphenyl)retinamide (4-HPR) decreases neoplastic properties of human prostate cells: an agent for prevention

The development of prostate cancer through a multistep process of carcinogenesis may have a long latent period of 20-30 years. It is possible that progression to a malignant state could be blocked or reversed during this time. This study focuses on the ability of the synthetic retinoid, N-(4-hydroxyphenyl)-retinamide (4-HPR), to reverse changes associated with malignant transformation and tumor progression, towards a normal phenotype. To examine the responsiveness of cells at different steps of prostate carcinogenesis, three immortalized, but non-tumorigenic (RWPE-1, WPE1-7 and WPE1-10), and one human prostate carcinoma cell line (DU-145), were used. The effects of 4-HPR on cell proliferation, expression of intermediate filament proteins cytokeratin 18 and vimentin, and tumor suppressor proteins p53 and pRb were examined by immunostaining and compared. Results show that 4-HPR caused inhibition of growth in all cell lines in a dose-dependent manner. 4-HPR induced an increase in staining for cytokeratin 18, a marker of differentiation for prostate epithelial cells. While all cell lines showed strong immunostaining for vimentin, treatment with 4-HPR for 8 days caused a marked decrease in staining for vimentin in all cell lines. In an in vitro assay, 4-HPR also caused inhibition of invasion by DU-145 cells in a dose-dependent manner. Furthermore, 4-HPR treatment was effective in significantly decreasing the abnormal nuclear staining for the tumor suppressor proteins p53 and pRb. Because 4-HPR decreased invasion-associated vimentin expression, inhibited invasion, and normalized p53 and pRb immunostaining, we propose that 4-HPR may be an effective agent for secondary and tertiary prevention, i.e. promotion and progression stages, respectively, of prostate cancer.

The BMP family member Gdf7 is required for seminal vesicle growth, branching morphogenesis, and cytodifferentiation

Epithelial-mesenchymal interactions play an important role in the development of many different organs and tissues. The secretory glands of the male reproductive system, including the prostate and seminal vesicles, are derived from epithelial precursors. Signals from the underlying mesenchyme are required for normal growth, branching, and differentiation of the seminal vesicle epithelium. Here, we show that a member of the BMP family, Gdf7, is required for normal seminal vesicle development. Expression and tissue recombination experiments suggest that Gdf7 is a mesenchymal signal that acts in a paracrine fashion to control the differentiation of the seminal vesicle epithelium.

p63 is a prostate basal cell marker and is required for prostate development

The p53 homologue p63 encodes for different isotypes able to either transactivate p53 reporter genes (TAp63) or act as p53-dominant-negatives (DeltaNp63). p63 is expressed in the basal cells of many epithelial organs and its germline inactivation in the mouse results in agenesis of organs such as skin appendages and the breast. Here, we show that prostate basal cells, but not secretory or neuroendocrine cells, express p63. In addition, prostate basal cells in culture predominantly express the DeltaNp63alpha isotype. In contrast, p63 protein is not detected in human prostate adenocarcinomas. Finally, and most importantly, p63(-/-) mice do not develop the prostate. These results indicate that p63 is required for prostate development and support the hypothesis that basal cells represent and/or include prostate stem cells. Furthermore, our results show that p63 immunohistochemistry may be a valuable tool in the differential diagnosis of benign versus malignant prostatic lesions.

Demonstration of intermediate cells during human prostate epithelial differentiation in situ and in vitro using triple-staining confocal scanning microscopy

In human prostate epithelium, morphologically basal and luminal cells can be discriminated. The basal cell layer that putatively contains progenitor cells of the secretory epithelium is characterized by the expression of keratins (K) 5 and 14. Luminal cells represent the secretory compartment of the epithelium and express K8 and 18. We developed a technique for the simultaneous analysis of K5, 14, and 18 to identify intermediate cell stages in the prostate epithelium and to study the dynamic aspects of its differentiation in vitro. Nonmalignant prostate tissue and primary epithelial cultures were immunohistochemically characterized using triple staining with antibodies for K5, K14, and K18. Antibodies for K18 and K5 were conjugated directly with fluorochromes Alexa 488 and 546. K14 was visualized indirectly with streptavidin-Cy5. Keratin expression was analyzed by confocal scanning microscopy. The occurrence of exocrine and neuroendocrine differentiation in culture was determined via antibodies to prostate-specific antigen (PSA), chromogranin A, and serotonin. We found that basal cells expressed either K5(++)/14(++)/18+ or K5(++)/18+. The majority of luminal cells expressed K18(++), but colocalization of K5+/18(++) were recognized. Epithelial monolayer cultures predominantly revealed the basal cell phenotype K5(++)/14(++)/18+, whereas intermediate subpopulations expressing K5+/14+/18(++) and K5+/18(++) were also identified. On confluence, differentiation was induced as multicellular gland-like buds, and extensions became evident on top of the monolayer. These structures were composed of K18(++)- and K5+/18(+)-positive cell clusters surrounded by phenotypically basal cells. Few multicellular structures and cells in the monolayer showed exocrine differentiation (PSA+), but expression of chromogranin A and serotonin was absent. We conclude that simultaneous evaluation of keratin expression is useful for analyzing epithelial differentiation in the prostate. During this process, putative stem cells phenotypically resembling K5(++)/14(++)/18+ differentiate toward luminal cells (K18(++)) via intermediate cell stages, as identified by up-regulation of K18 and down-regulation of K5 and 14.

Generation of active TGF-beta by prostatic cell cocultures using novel basal and luminal prostatic epithelial cell lines

Two prostatic epithelial lines, one of basal origin and one of luminal origin, were established from the dorsolateral prostates of p53 null mice. The cell lines are nontumorigenic when inoculated subcutaneously under the renal capsule or intraprostatically in syngeneic mice. The luminal cell line (PE-L-1) expresses cytokeratins 8 and 18 and the basal cell line (PE-B-1) expresses cytokeratins 5 and 14. The basal cells require serum for growth, whereas the luminal cells grow only in serum-free medium. Both cell lines require the presence of growth factors for optimal growth in culture, with EGF and FGF-2 having the greatest effect on the growth rate. Both lines express androgen receptor (AR) mRNA and protein. Androgen stimulates growth of the basal cell line, indicating that the ARs are functional, whereas growth of the luminal cells is unaffected by androgens. The luminal line is significantly inhibited by exogenous TGF-beta and produces low levels of endogenous TGF-beta. In contrast, the basal cell line produces significant amounts of TGF-beta and its growth is not influenced by this cytokine. Coculture of luminal cells with prostatic smooth muscle cells results in the generation of increased levels of biologically active TGF-beta, indicating a paracrine mechanism of TGF-beta activation that may be involved in the maintenance of normal prostatic function. To our knowledge this is the first report describing both basal and luminal prostatic cell lines from a single inbred animal species and the first indication that prostatic epithelial and stromal cells interact to generate the biologically active form of TGF-beta. These lines will provide an important model for determining basal/luminal interactions in both in vitro and in vivo assays.

Comparison of marker protein expression in benign prostatic hyperplasia in vivo and in vitro

OBJECTIVE

To use multiple immunofluorescence to compare the in vivo and in vitro expression of tissue-specific proteins in BPH. Materials and methods Pure populations of prostate epithelial and stromal cells were produced using standard methods. Serum-free media for epithelial cells were compared. Co-localization of proteins was compared in frozen-tissue sections and cultured cells by simultaneous multiple immunofluorescence, and recorded using a high-resolution charge-coupled device camera.

RESULTS

In contrast to the other serum-free media tested, epithelial cells grew without squamous differentiation or vacuolation in prostate epithelial growth medium (PrEGM, Clonetics, BioWhittaker UK Ltd., Berks, UK). These cells were predominantly of a basal phenotype, with some cells showing a luminal phenotype. Most of the stromal cells had features of myofibroblasts, but smooth muscle cells and fibroblasts also were present.

CONCLUSION

PrEGM is a commercially available serum-free medium in which primary cultures of prostate epithelial cells can be propagated reproducibly. This study provides a comprehensive description of tissue-specific protein expression in BPH in vivo and in vitro. The use of simultaneous multiple immunofluorescence to study co-localization has resulted in a more precise definition of phenotype than has previously been possible, thereby establishing the relevance of the in vitro model system BPH.

Amphiregulin is coordinately expressed with heparin-binding epidermal growth factor-like growth factor in the interstitial smooth muscle of the human prostate

Peptide growth factors have been proposed as mediators of smooth muscle-epithelial cell interactions in the human prostate; however, the identity of these molecules has not been established. In this study, we compared expression levels of messenger RNAs (mRNAs) encoding the epidermal growth factor (EGF) receptor-related receptor tyrosine kinases (ErbB1 through 4), the six EGF receptor ligands, EGF, transforming growth factor (TGF)-alpha, amphiregulin (ARG), HB-EGF, betacellulin, and epiregulin, and the related molecule heregulin-alpha, in a series of 10 prostate tissue specimens. Only EGF showed a disease-specific association, with increased mRNA levels in four of five PCa specimens in comparison to matched normal tissue from the same subject. In contrast, ARG and HB-EGF mRNAs showed a coordinate pattern of expression in 7/10 specimens that was distinct from all other growth factor or receptor genes examined and from mRNAs for prostate specific antigen, the androgen receptor and GAPDH, a house-keeping enzyme. Analysis of an additional series of benign prostatic hyperplasia and prostate cancer specimens from 60 individuals confirmed that ARG and HB-EGF mRNA levels varied in a highly coordinate manner (r = 0.93; P < 0.0001) but showed no association with disease. ARG was immunolocalized largely to interstitial smooth muscle cells (SMC), previously identified as the site of synthesis of HB-EGF in the prostate, while the cognate ARG and HB-EGF receptor, ErbB1, was localized exclusively to ductal epithelial cells and carcinoma cells. Although ARG was a relatively poor mitogen for Balb/c3T3 cells in comparison to HB-EGF, it was similar in potency to HB-EGF in stimulating human prostate epithelial cell growth, suggesting that prostate epithelia may be a physiologic target for ARG in vivo. Expression of both ARG and HB-EGF mRNAs was induced in cultured prostate SMC by fibroblast growth factor-2, a human prostate SMC mitogen linked to prostate disease. These findings indicate that ARG and HB-EGF are likely to be key mediators of directional signaling between SMC and epithelial cells in the human prostate and appear to be coordinately regulated.

Basal cells are progenitors of luminal cells in primary cultures of differentiating human prostatic epithelium

BACKGROUND

Human prostatic epithelium consists mainly of basal and secretory luminal cells: the origin of these phenotypes from a common stem cell, within the basal compartment, has been proposed but not yet demonstrated.

METHODS

Analyses by light and electron microscopy, immunocytochemistry, and flow cytometry were used to determine lineage. The criteria for identifying the different phenotypes were characteristic morphology, and organization and expression of luminal- and basal-specific markers.

RESULTS

After organoids attached, outgrowths appeared with cells maintaining close cell-to-cell associations. The dividing cell compartment contained a subpopulation of cells with stem-cell characteristics and a major population that may correspond to amplifying cells. The characteristics of the stem-cell phenotype included reactivity with antibodies CKbasal, CK14, and Ki67. The amplifying cells were characterized as an intermediate phenotype between basal and luminal, as reactivity was demonstrated with CKbasal, CK14, and CK18. As outgrowths eventually merged, multilayering was apparent and cells on the uppermost layer had numerous secretory vacuoles and reacted strongly with antibodies CK18 and CK19, androgen receptor, and prostate-specific antigen, which is characteristic of secretory luminal cells in vivo. In passaged cultures, loss of reactivity with CKbasal was detected; we postulate that this population contains the stem-cell fraction.

CONCLUSIONS

These findings demonstrate that basal and luminal cells are of the same lineage and are derived from a common stem cell. Moreover, the progenitor stem cells reside within the basal compartment.

Expression of cytokeratin-19 as a marker of neoplastic progression of human prostate epithelial cells

BACKGROUND

Our earlier studies demonstrated neoplastic transformation of SV40-immortalized neonatal human prostate epithelial cells (267B1) by fractionated doses of ionizing radiation or by introduction of v-ki-ras oncogene. X-ray-treated 267B1 cells represent three different stages of neoplastic progression: nontumorigenic F3-SAC cells that acquired morphological changes and anchorage independence when treated with 2 x 2 Gy of X-rays; malignantly transformed 267B1-XR and 267B1-SXR cells that received 2-Gy doses to a total of 30 Gy. We also reported alterations in cell size, morphology, actin stress fibers, and levels of actin-binding proteins in these transformed human prostate cells.

METHODS

We analyzed intermediate filament-nuclear matrix (IF-NM) protein expression in the various 267B1 cells as a consequence of neoplastic progression by two-dimensional gel electrophoresis and immunofluorescence.

RESULTS

Our present study revealed that the 267B1 cells experienced progressive changes in their intermediate filament protein composition during the process of neoplastic conversion, achieved either by X-rays or by ras-oncogene. In particular, we observed a stepwise downregulation of cytokeratin-19 in these in vitro transformed 267B1 cells.

CONCLUSIONS

Our data suggest that loss of expression of cytokeratin-19 accompanied the morphological alterations associated with in vitro neoplastic transformation of SV40-immortalized prostate epithelial cells.

Neuroendocrine differentiation in prostatic carcinoma during hormonal treatment

OBJECTIVES

Neuroendocrine differentiation (NED) is a common feature in adenocarcinoma of the prostate. Several studies suggest that NED may have a major impact on cancer progression as neuroendocrine (NE) secretory products have been shown to possess growth stimulatory effects. NED has also been proposed to constitute part of the mechanism by which a prostate cancer cell progresses toward androgen independence as NE tumor cells have been demonstrated to be devoid of androgen receptor immunoreactivity. In this retrospective study, we evaluated NED status in prostate cancer specimens from patients undergoing androgen ablation therapy.

METHODS

The degree of NED in transurethral resection of the prostate (TURP) samples from 53 patients with prostate cancer was investigated by immunocytochemistry using polyclonal rabbit immunoglobin G (IgG) against chromogranin A (CgA). Changes in NED with time were determined by a manual semiquantitative cell counting method.

RESULTS

During androgen withdrawal therapy, 21 tumors (40%) displayed increased NED concomitant with histopathologic tumor progression, whereas 29 carcinomas (55%) showed no change in NED status. However, a majority of the histopathologically unchanged tumors displayed marked NED at the first TURP and an increase in NED was by definition not possible. In only 3 cases (5%) was a decrease in NED observed with time.

CONCLUSIONS

Androgen ablation therapy may be a contributing factor to the increase in NED of prostatic adenocarcinoma with time, and our findings imply that androgen withdrawal therapy enhances the selection and progression of NED, androgen-independent tumor cells.

Prostatic ductal system in rats: tissue-specific expression and regional variation in stromal distribution of transforming growth factor-beta 1

BACKGROUND

Regional variations in stromal-epithelial interactions, mediated through soluble growth factors, may be responsible for differences in epithelial growth and death observed between regions of the rat prostatic ductal system. Since transforming growth factor-beta 1 (TGF-beta 1) can induce prostatic epithelial cell death in vitro and in vivo, we examined the localization and production of TGF-beta 1 with respect to the functional regions of the rat prostatic ductal system.

METHODS

The distribution of TGF-beta 1 in the rat ventral prostate was examined by immunohistochemistry. Cell type-specific expression of TGF-beta 1 was determined using RT-PCR analysis of prostate epithelial and stromal cell fractions separated by Percoll gradient centrifugation.

RESULTS

Immunohistochemical staining of normal prostate revealed regional variations in stromal TGF-beta 1 protein, which was most abundant in the stroma surrounding the degenerative proximal ducts. TGF-beta 1 staining was also tightly associated with the prostatic smooth muscle. Results of RT-PCR experiments confirmed the major source of TGF-beta 1 mRNA in normal rat prostate to be the stroma, with lesser expression by the epithelium.

CONCLUSIONS

Stromal TGF-beta 1 was associated with cell death in the adjacent epithelial cell compartment in the prostatic ductal system, and alpha-smooth muscle actin-positive stromal cells may play a negative growth-regulatory role in the rat ventral prostate through production of TGF-beta 1.

Identification of K1/K10 and K5/K14 keratin pairs in human melanoma cell lines

Keratin expression in cultured malignant melanoma cells has been studied only rarely. Moreover, no studies have reported of universality of keratin expression in human malignant melanoma cells. In this study, therefore, we analyzed keratin expression in eight cell lines. Using a low-salt aqueous solution without high salt and Triton X-100, as a washing buffer for keratin extraction, followed by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and immunological analysis, we demonstrated keratin expression in all eight human malignant melanoma cell lines. The keratin polypeptide expressions common to all melanoma cells were K1, K5, K10 and K14. In addition, K8, K13, K17 and K18, respectively, were detected in individual cells. A measure of keratin expression universality in malignant melanoma cells may have implications regarding their invasive and metastatic behaviors, co-expressed with vimentin.

Role of prostatic basal cells in the regulation and suppression of human prostate cancer cells

Cytokeratin expression in normal and malignant prostatic tissue indicates a loss of basal epithelial cells in cancer. We investigated the ability of basal-like prostatic epithelial cells to inhibit the growth of prostatic cancer cells. Human prostate LNCaP cells were grown in medium with or without 10 nM dihydrotestosterone (DHT) on plastic culture dishes or on extracellular matrix derived from basal-like epithelial cells (primary cultures derived from normal peripheral zone of the prostate) that were grown with or without 10 nM DHT. Colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assays were used to assess the growth of LNCaP cells. On plastic dishes, growth of LNCaP cells was increased 5-10% by the presence of DHT in the medium. On matrix derived from basal-like cells that were grown in the absence of DHT, growth of LNCaP cells with or without DHT was similar to that on plastic. However, on matrix derived from basal-like cells that were grown with DHT, growth of LNCaP cells was suppressed when compared to all other culture conditions (P < 0.01). To determine whether basal-like cells could alter the function of LNCaP cells, we measured prostate-specific antigen (PSA) mRNA expression with the use of comparative RT-PCR. We found a significant decrease in the mature PSA transcript in cells grown on matrix derived from basal-like cells that were grown with DHT. The expression of PSA transcript was not altered in LNCaP cells that were grown on matrix derived from basal-like cells that were grown in the absence of DHT. Furthermore, using differential display of mRNA, we demonstrated that there were induction and suppression of multiple unique transcripts in the LNCaP cells when grown on the various culture conditions. To determine a possible mechanism for these observations. We used a dot blot immunoassay for several known inhibitory factors. We determined that DHT can induce the basal-like cells to secrete transforming growth factor-beta (TGF-beta 1), and that TGF-beta 1 can inhibit the proliferation of LNCaP cells in a dose dependent manner. We conclude that basal-like epithelial cells, in the presence of DHT, secrete an extracellular matrix o matrix associated factor(s), e.g. TGF-beta 1, that suppresses proliferation and function of prostate cancer cells. Our data suggest that the disappearance of the basal cell layer may be a prerequisite for the progression of prostatic neoplasia.

Parathyroid hormone--related protein (PTHrP) is an epidermal growth factor-regulated secretory product of human prostatic epithelial cells

Parathyroid hormone-related protein (PTHrP) has previously been shown to be expressed in human prostatic tissue and in prostatic cancer cell lines. In the present study, PTHrP immunoreactivity was detected in the glandular epithelium of normal prostate and benign prostatic hyperplasia (BPH), as well as in prostatic adenocarcinoma (CaP). Epithelial cell cultures derived from normal, BPH, and CaP tissues were also stained by antibodies against PTHrP, and northern analysis revealed multiple transcripts of PTHrP in the cellular RNA. PTHrP (1-34) was measurable by radioimmunoassay (RIA) in media conditioned by the prostatic epithelial cell cultures, and PTHrP accumulated in conditioned media during a 72 hr time course. Addition of complete growth medium to starved cells resulted in increased PTHrP mRNA levels by 1 hr, with maximal stimulation at 8-24 hr. Several individual factors contained in the complete growth medium were tested for their ability to regulate PTHrP expression. Epidermal growth factor (EGF) was the major inducer of PTHrP expression, while cholera toxin, bovine pituitary extract, hydrocortisone, and insulin had minimal or no effect on PTHrP transcript levels. Since each of these factors is growth stimulatory, the unique ability of EGF to induce PTHrP is apparently unrelated to mitogenicity. 1,25-Dihydroxyvitamin D3[1,25(OH)2D3], an inhibitor of PTHrP expression in several other cell types, had no effect on steady-state levels of PTHrP mRNA expressed by epithelial cells in complete growth medium, although prostate cells have vitamin D receptors and are responsive to 1,25(OH)2D3 in other ways. Our results indicate that PTHrP expression is not confined to the neuroendocrine cells of the human prostate and that our culture system can be used as a model to investigate the role of PTHrP in the prostate.

Upregulation of cytokeratins 8 and 18 in human breast cancer T47D cells is retinoid-specific and retinoic acid receptor-dependent

The mamary gland is chiefly composed of luminal epithelial cells expressing cytokeratins (K) 8, 18 and 19, and basal/myoepithelial cells expressing cytokeratins 5 and 14. Human breast cancer T47D cells have a luminal phenotype and are growth-inhibited by retinoids, a class of compounds known to regulate cytokeratin expression. To extend our knowledge of retinoid action in breast cancer, we have studied the retinoid regulation of cytokeratin expression in the T47D model. We found that retinoid inhibition of T47D cell growth was accompanied by increases in K8, K18 and K19 mRNA steady-state levels (Northern blot analysis). The effect on K8 was studied in greater detail. This effect was seen with as low as 1 nM all-trans retinoic acid (tRA) and was maximal (up to 7 fold over control) with 1 microM tRA (the highest dose tested). Time-course studies revealed a detectable effect at 1 h and a maximal effect at 8-24 h. Non-retinoidal growth inhibitors (tamoxifen, BrcAMP and genistein) did not modulate K8 expression, demonstrating that the effect of tRA was specific, K8 mRNA upregulation was blocked by actinomycin D and cycloheximide, suggesting, in accordance with other studies, that tRA exerted a transcriptional effect that was secondary to de novo protein synthesis. Five retinoids known to activate retinoic acid receptor (RAR) and/or retinoid X receptor (RXR) - tRA; 9-cis-retinoic acid, 9cRA; 13-cis RA, 13cRA; retinyl acetate; and N-(4-hydroxyphenyl) retinamide 4HPR - inhibited T47D cell growth and increased K8 expression, whereas an arotinoid (Ro-40-8757) that is not a RAR activator caused growth inhibition but did not upregulate K8. Activation of RAR alpha contributed to K8 upregulation, since this effect was partially blocked by the RAR alpha-selective antagonist Ro-41-5253. Analogous results were obtained throughout when blots were reprobed with K18 cDNA. Western blot and immunocytochemistry experiments demonstrated that protein levels of K8 and K18 increased by 2 days of treatment with 1 microM tRA. These results show that retinoids enhance the expression of cognate cytokeratin markers of luminal differentiation in T47D breast cancer cells.