The antiapoptotic effect of IL-6 autocrine loop in a cellular model of advanced prostate cancer is mediated by Mcl-1

Levels of the proinflammatory cytokine interleukin-6 (IL-6) are increased in therapy-resistant prostate cancer. IL-6 has been considered a positive growth factor in late-stage prostate cancer cells and a potential target for therapeutic interference. Effects of inhibition of IL-6 on cell survival were studied in LNCaP-IL6+ cells, a model system for advanced prostate cancer, which produce IL-6. We show that the autocrine IL-6 loop is responsible for resistance to apoptosis and increased cellular levels of myeloid cell leukemia-1 (Mcl-1) protein, an antiapoptotic member of the Bcl-2 family. Treatment of cells with a chimeric anti-IL-6 antibody (CNTO 328) led to the induction of apoptosis and downregulation of Mcl-1 protein levels. Specific knockdown of Mcl-1 gene expression by small interfering RNA also yielded an increase in apoptosis of LNCaP-IL-6+ cells. Vice versa, inactivation of IL-6 autocrine loop had no influence on apoptosis levels in the absence of Mcl-1, thus suggesting this molecule as a mediator of the survival action of IL-6. Mcl-1 protein regulation by the endogenous cytokine directly involved the extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase pathway. Our data support the concept of anti-IL-6 targeted therapy in therapy-resistant prostate cancer.

Proliferation of prostate cancer cells in the bone marrow predicts recurrence in patients with localized prostate cancer

BACKGROUND

Reverse-transcription polymerase chain reaction (RT-PCR) amplification of prostate specific antigen (PSA) mRNA has been used to detect the presence of prostate cancer cells in the peripheral blood and bone marrow of patients with clinically localized disease. Some studies have demonstrated a correlation between detection of PSA-mRNA and disease recurrence. However, many RT-PCR-positive patients remain disease-free. We propose that phenotypic characterization of individual micrometastatic cells may provide more prognostic information than mere detection of such cells.

METHODS

We studied 58 patients undergoing radical prostatectomy for clinically localized disease whose bone marrow had been found to contain PSA-mRNA by RT-PCR. Immunohistochemical detection and phenotypic characterization of micrometastatic cells was performed using a two-color technique: cytokeratin antibody for detection and the MIB-1 antibody for proliferation. The clinical endpoint was disease recurrence.

RESULTS

One or more micrometastatic cells were proliferating in 36.2% of the patients; the disease-free survival rate was 76.2% in this group. In contrast, in the patients with non-proliferating cells, 97.3% remained disease-free (P = 0.025). Multivariate analysis demonstrated that the presence of proliferating cells was the only preoperative variable that correlated with disease-free survival (P = 0.05).

CONCLUSIONS

Determination of the phenotype of individual micrometastatic cells can contribute prognostic information above and beyond the mere determination of their presence or absence. Phenotypic characterization of individual micrometastatic cells may ultimately be used to select patients for systemic therapy given either alone or in combination with local therapy.

Differential regulation of matrix metalloproteinase-9, tissue inhibitor of metalloproteinase-1 (TIMP-1) and TIMP-2 expression in co-cultures of prostate cancer and stromal cells

Tumor-stromal interactions have been suggested to be a critical factor in both tumor invasion and tumor metastasis. Here, we examined the role of tumor-stromal interactions using co-cultures of prostate cancer (PC) cells derived from primary and metastatic tumors with primary or immortalized stromal (fibroblast and smooth muscle) cells and their effect on matrix metalloproteinase (MMP) and tissue inhibitor of metalloproteinase (TIMP) expression. Co-cultures of PC and stromal cells showed enhanced levels of pro-MMP-9 and reduced levels of TIMP-1 and TIMP-2. Whereas enhanced expression of pro-MMP-9 occurred in PC cells, the TIMPs were down-regulated in stromal cells. Induction of pro-MMP-9 and reduction of TIMP expression did not require cell-cell contact and were mediated by a soluble factor(s) present in the conditioned medium of the effector cell. Collagen I is a potent inducer of pro-MMP-9 in PC cells. Consistently, preliminary characterization of the soluble factor in the fibroblast conditioned medium revealed m.w. of approximately 100 to 250 kDa, and its effect on pro-MMP-9 expression was partly inhibited by an anti-alpha2 integrin antibody, a major collagen I receptor. Expression of pro-MMP-9 protein and mRNA was also induced in metastatic PC-3 cells grown in human fetal bone implants in SCID mice. Together, these findings demonstrate the importance of tumor-stromal interactions in the regulation of MMP and TIMP expression and their potential role in PC progression.

Persistence of human vascular endothelium in experimental human prostate cancer bone tumors

Using the SCID-human model, we recently found that human circulating prostate cancer cells formed tumors in human bone but not mouse bone (Nemeth et al. Cancer Res 1999; 59: 1987-93). It is possible that this tissue preference was mediated by interaction between human tumor cells and human endothelial cells within the implanted bone tissue. We sought to determine the relative amounts of human and mouse vasculature within human bone implants and resulting prostate cancer bone tumors in the SCID-human model. Paraffin sections of plain bone implants or PC3 or LNCaP human bone tumors were double stained for factor VIII (all vessels) and human CD31 (human vessels) followed by fluorescent secondary reagents. At 4 weeks post implantation (when cancer cells are typically introduced), the vasculature within human bone fragments remained primarily human (84.5%), and this pattern persisted to at least 10 weeks (91.6% human). Injection of PC3 cells into the bone resulted in an increase in mouse-derived vessels, however the majority (58%) of the vessels remained human even after the formation of large bone tumors. LNCaP bone tumors were highly angiogenic, and there was a sharp decline in the proportion of vessels which were antigenically human (36.8%), suggesting recruitment of mouse endothelial cells during the angiogenic process. Nonetheless, the persistence of human vasculature suggests the SCID-human model can be used to study the interaction between bone-seeking tumor cells, such as prostate cancer, and human bone endothelium in vivo, and to test potential therapeutic strategies which may depend on the presence of human vessels.

Six-pin halo fixation and the resulting prevalence of pin-site complications

BACKGROUND

In spite of the many advances in halo application technique, the prevalence of complications associated with the use of halo fixation remains high, particularly at the pin sites. Many practitioners do not use more than four pins for halo application in adults because they believe that it increases the risk of complications. The purpose of this study was to investigate the use of six pins in halo application, in order to determine if the extra pins increased fixation strength without increasing the overall pin-site complication rate.

METHODS

The first part of our study consisted of force-deflection tests conducted on models of the skull fitted with either a four or a six-pin halo to determine if the six-pin halo provided greater fixation strength. Each skull model was placed in a servocontrolled hydraulic test machine; an axial distraction force was then applied until failure occurred. The second part of the study was a retrospective analysis of sixty-three patient records to document the prevalence of pin-site complications in patients treated with a six-pin halo system; these findings were then compared with established complication rates associated with four-pin halos.

RESULTS

In the force-deflection tests, the mean load to failure of the six-pin halo construct (2879 N [647 lb]) showed the system to be significantly stronger (p = 0.0033) than the four-pin halo construct (1681 N [378 lb]). Of the sixty-three patient records reviewed, five (8% [95% confidence interval, 1% to 15%]) revealed pin-loosening; no infection was recorded for these five patients. One of the sixty-three patients had redness and erythema at "multiple sites," but these areas healed well. Another presented with infection at all six sites; this was recorded as an allergic reaction.

CONCLUSIONS

Six-pin halo fixation results in greater halo strength and cervical spine stabilization without increasing the risk of pin-site complications.

CLINICAL RELEVANCE

Our findings are relevant for current clinical practice as the high complication rates associated with halo application have deterred some practitioners from using this type of fixation. The use of six pins, along with an improved protocol for halo application and care, may contribute to a more successful treatment outcome with fewer complications.

Prostatic luminal cell differentiation and prostatic steroid-binding protein (PBP) gene expression are differentially affected by neonatal castration

BACKGROUND

Although normal prostatic development is androgen-dependent, the prostate continues to grow in the neonate despite castration. However, the manner in which neonatal growth of the prostate occurs, in the absence of the testis, remains largely unknown. The purpose of this study was to examine the differentiation of prostatic epithelial cells after neonatal castration.

METHODS

Immunohistochemistry was utilized to detect the expression of differentiation products: basal-cell cytokeratin (CK 5), luminal-cell cytokeratin (CK 18), and prostatic steroid-binding protein (PBP), a ventral prostate-specific marker indicative of secretory function in luminal cells. The reverse transcription-polymerase chain reaction was used to detect transcription products of the three polypeptide subunits of PBP, designated C1, C2, and C3. Rats were castrated on day 5 after birth, and ventral prostates were collected on day 14. Dihydrotestosterone was injected (100 microg/animal every 2 days) in castrated animals to determine if PBP expression could be initiated by androgen.

RESULTS

Although no major effects of castration were detected on the differentiation of stromal or basal cells (which differentiate prior to day 5), castration had a pronounced effect on luminal-cell differentiation. Castration inhibited PBP protein expression, but did not affect the expression of luminal-cell cytokeratin (CK 18) protein. Furthermore, castration reduced C1, C2, and C3 transcription. Androgen replacement to castrated animals allowed for the initiation of PBP expression, although its onset was delayed.

CONCLUSIONS

These observations indicate that the testis is not necessary for prostatic luminal-cell differentiation, but is necessary for full expression of luminal-cell secretory phenotype. Furthermore, our study suggests that factors of testicular origin, in addition to androgen, are needed for proper timing of PBP expression. This investigation establishes that the cytological and the physiological differentiation of the rat prostate are differentially regulated.

Prostatic ductal system in rats: changes in regional distribution of extracellular matrix proteins during castration-induced regression

BACKGROUND

The extracellular matrix (ECM) is an intricate network composed of an array of molecules that play an integral role in the regulation of cell function, differentiation, and tissue-specific gene expression in various epithelia. In the present study, we examined the distribution of collagen type IV and laminin along the rat ventral prostatic duct before and after castration.

METHODS

Mature Sprague-Dawley rats were castrated and their prostates processed for immunocytochemistry of ECM proteins, laminin, and collagen type IV. Tissue sections were also processed for apoptosis staining, using the 3' end-labeling technique. To examine the effect of ECM proteins on epithelial growth, rat ventral epithelial cells were cultured on ECM-coated surfaces.

RESULTS

In the intact rat, laminin was localized in the basement membrane along all regions of the ventral prostate ductal system. Collagen type IV was found to be distributed evenly in the basement membrane of the distal and intermediate regions but was absent or poorly organized in the proximal region, where apoptosis in the epithelium occurs at a high rate. In the regressing prostate after castration, there was a shift in apoptosis from the proximal region to the distal intermediate regions of the prostatic duct. Associated with the shift was a remodeling of basement membrane proteins due to the specific loss of collagen type IV in the distal and intermediate regions. Collagen type IV reappeared underneath the epithelium 7 days after castration, when apoptosis in the epithelium stopped. In vitro, collagen type IV enhanced the growth of ventral prostatic epithelial cells, as assessed by cell number.

CONCLUSIONS

Collagen basement membrane type IV mediates growth of rat ventral prostate epithelium, and its loss during tissue remodeling after castration is associated with cell death.

Membrane type 1-matrix metalloproteinase (MT1-MMP) and MMP-2 immunolocalization in human prostate: change in cellular localization associated with high-grade prostatic intraepithelial neoplasia

Membrane type 1-matrix metalloproteinase (MT1-MMP) is a known activator of latent MMP-2 (pro-MMP-2), and increased MMP-2 expression has been associated with tumor aggressiveness in prostate cancer. However, expression of MT1-MMP in human prostate tissue has not been described. We investigated the expression and immunolocalization of MT1-MMP and MMP-2 in the epithelial components of benign prostate epithelium, high-grade prostatic intraepithelial neoplasia (HGPIN), and prostate cancer. Tissue sections from the peripheral zone of 50 prostates (radical prostatectomy specimens) were chosen based on their containing benign glands, HGPIN, and prostate cancer glands. All 50 sections were immunostained for MT1-MMP and MMP-2 and were evaluated for staining pattern, uniformity, and intensity. Western blotting and gelatin zymography were done to confirm expression of MT1-MMP and activity of MMP-2, respectively. Comparisons were made between benign epithelium, HGPIN, and cancer. In benign glands, basal cells (BCs) uniformly stained intensely for MT1-MMP, whereas secretory cells (SCs) were rarely positive (P < 0.0001). Conversely in HGPIN, SCs showed consistent cytoplasmic staining (P < 0.0001). In cancer cells, staining was heterogeneous and varied from no staining to very intense staining in select glands. MMP-2 in normal tissue stained both BCs and the apical region of SCs, whereas in HGPIN, staining was observed in the SC in a predominantly cytoplasmic pattern. Similar to MT1-MMP, staining in cancer tissue for MMP-2 was heterogeneous; however, there was a significant association between the pattern of MMP-2 and MT1-MMP staining within the epithelial components of the cancer glands in individual specimens (P < 0.001). Finally, MMP-2 and MT1-MMP were confirmed to be expressed in the prostate tissues by gelatin zymography and Western blotting. In conclusion, we found that consistent changes in localization and intracellular distribution of MMP-2 and MT1-MMP were associated with the transition from benign prostate epithelium to HGPIN, suggesting that regulation of these enzymes is altered during the earliest stages of prostate cancer.

Cellular proliferation and prevalence of micrometastatic cells in the bone marrow of patients with clinically localized prostate cancer

The presence of prostate cancer cells in the bone marrow (BM) of patients with clinically localized disease is associated with an increased chance of disease recurrence; however, not all patients develop recurrence. We therefore sought to determine the phenotype of individual micrometastatic cells as a potential method to better predict disease outcome. Immunostaining was performed on BM cells from 46 patients whose BM RNA fraction had been identified to contain prostate-specific antigen mRNA. The prevalence of micrometastatic cells among BM mononuclear cells was determined using an anticytokeratin antibody. Mib-1 antibody was used to determine the percentage of micrometastatic cells that were proliferating. Micrometastatic cells were found in 96% of patient samples, with a 30-fold variation in prevalence ranging from 0.1-3.26/10(5) BM cells. Prior androgen ablation was associated with a reduced prevalence of micrometastatic cells (P = 0.010). In 68% of patients, some micrometastatic cells were judged to be proliferating at proportions ranging from 1 of 11 (9%) to 4 of 4 (100%). Higher Gleason score of the primary tumor was associated with a higher proliferative proportion of micrometastatic cells (P = 0.038). We conclude that, in patients with clinically localized disease, there is wide variability in the prevalence of micrometastatic cells and the proportion which are proliferating. Long-term follow-up will determine whether the development of clinically obvious metastatic disease is related to higher prevalence of micrometastatic cells in the marrow or the proportion that are proliferating.

Severe combined immunodeficient-hu model of human prostate cancer metastasis to human bone

Commonly used in vivo models of prostate cancer metastasis include syngeneic rodent cancers and xenografts of human cancer in immunodeficient mice. However, the occurrence of osseous metastases in these models is rare, and in xenograft models, species-specific factors may limit the ability of human cells to metastasize to rodent bones. We have modified the severe combined immunodeficient (SCID)-human model to test the ability of circulating human prostate cancer cells to home to macroscopic fragments of human bone and other organs previously implanted into SCID mice. We have also compared the growth of human prostate cancer cells in various human and mouse tissue microenvironments in vivo. Macroscopic fragments of human fetal bone, lung, or intestine (16-22 weeks gestation) or mouse bone were implanted s.c. into male CB.17 SCID mice. Four weeks later, human prostate cancer cells were injected either i.v. via the tail vein (circulating cell colonization assay) or directly into the implanted tissue fragments transdermally (end organ growth assay). Tumor growth was followed for 6 weeks by palpation and magnetic resonance imaging. After 6 weeks, tumors were enumerated in implanted human and mouse organ fragments and native mouse tissue. Tumors were characterized by histology, immunohistochemistry, and chromosomal analysis. After i.v. injection, circulating PC3 cells successfully colonized implanted human bone fragments in 5 of 19 mice. Tumors were easily followed by palpation and imaging and had an average volume of 258 mm3 at autopsy. Histological examination revealed osteolysis and a strong desmoplastic stromal response, which indicated intense stromal-epithelial interaction. Bone tumors were subcultured, and chromosomal analysis demonstrated that the tumors were derived from the parental prostate cancer cell line. Microscopic tumor colonies were also found in a few mouse lungs after i.v. injection of PC3, DU145, and LNCaP cells, however the volume of the lung nodules was less than 1 mm3 in all of the cases. No colonization of human lung or intestine implants, the mouse skeleton, or other mouse organs was detected, demonstrating a species- and tissue-specific colonization of human bone by PC3 cells. Direct injection of 10(4) prostate cancer cells into human bone implants resulted in large tumors in 75-100% of mice. PC3 and DU145 bone tumors were primarily osteolytic, whereas LNCaP bone tumors were both osteoblastic and osteolytic. PC3 and LNCaP bone tumors showed a desmoplastic stromal response, which indicated intense stromal-epithelial interaction. All three of the cell lines formed tumors in implanted human lung tissue; however, the tumors were all < or = 10 mm3 in volume and showed minimal stromal involvement. No tumors formed after either s.c. injection or injection of cells into implanted mouse bone demonstrating both species- and tissue-specific enhancement of growth of human prostate cancer cells by human bone. The severe combined immunodeficient-human model provides a useful system to study species-specific mechanisms involved in the homing of human prostate cancer cells to human bone and the growth of human prostate cancer cells in human bone.

The primary culture of rat prostate basal cells

The objective of this study was to identify the cells from rat prostate epithelium that attach and proliferate in primary culture. Minced ventral prostate was dissociated by DNAse/collagenase digestion, suspended in RPMI-1640 containing 10% fetal bovine serum, and subjected to Percoll centrifugation to separate the epithelial cells from stromal cells. With the use of lectins, it became possible to identify and monitor the fate of the dissociated epithelial cells held in suspension at 37 degrees C for several hours. In tissue sections of the rat prostate, Griffonia simplicifolia I-isolectin B4 (GSI-B4) specifically bound to basal cells, while Glycine maximus (soybean agglutinin [SBA]) was specific for secretory cells. Double staining with lectins and propidium iodide of dissociated cells revealed a preponderance of GSI-B4-positive live cells. The cells were plated in WAJC-404 medium supplemented with various factors, including insulin (5 ng/ml), transferrin (5 ng/ml), EGF (10 ng/ml), and bovine pituitary extract (30 microg/ml). Epithelial colonies that formed and proliferated from these cells also stained positively for GSI-B4 marker and for cytokeratins specific for basal cells as assessed by immunocytochemical staining. Proliferation was greater in cells grown on a collagen Type I matrix. These findings suggest that the epithelial cells that survived in suspension and proliferated in culture originated from basal cells of the rat prostate epithelium.

Keratinocyte growth factor in the rat ventral prostate: androgen-independent expression

Keratinocyte growth factor (KGF/FGF-7) is a stromally derived factor which exerts proliferative and differentiating effects on a variety of epithelial cells. Results of recent studies utilizing in vitro methods such as tissue culture and organ culture have suggested that KGF may act as a paracrine mediator of androgen-induced growth and development of the prostate and seminal vesicle. We undertook the present study to determine the distribution of KGF in relation to the functional regions of the rat prostatic ductal system, and whether KGF expression is influenced by androgen in vivo. Immunohistochemical staining revealed KGF to be present in the stroma throughout the prostate, regardless of the functional region, and staining for KGF remained high through 21 days post-castration. Message for KGF could also be detected by reverse transcriptase-PCR analysis of prostate stromal cells isolated from 4- and 21-day castrated animals, and no gross change in message level was observed following castration. Furthermore, no significant change in either stromal staining or message for KGF was observed in newborn rat prostates 10 days after castration, suggesting a similar regulatory mechanism for KGF in the adult and immature prostate. Epithelial staining for KGF decreased following castration, and greatly increased upon androgen replacement, possibly indicating a change in KGF internalization. These observations suggest that the presence of KGF protein is not related to functional differences in the prostate epithelium, and that expression of KGF in vivo is not greatly influenced by androgen.

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.

Loss of expression of transforming growth factor beta type I and type II receptors correlates with tumor grade in human prostate cancer tissues

Transforming growth factor beta1 (TGF-beta1) is a potential regulator of prostate cancer cell growth that signals through a heteromeric complex composed of type I and type II receptors. In the present study, an attempt was made to establish a correlation between expression of TGF-beta receptors and tumor grade in archival human prostate cancer tissues. To this end, immunohistochemical studies for TGF-beta receptors were carried out on 32 cases of human prostate cancer and 8 samples of benign human prostate. In both benign and malignant human prostate tissues, immunoreactivity for both type I and type II receptors was detected predominantly in epithelial cells. In addition, there was an inverse correlation between the loss of expression of TGF-beta1 type I and type II receptors and the tumor grade. Of the 32 prostate cancer cases screened, staining was completely absent in four samples for type II receptor (P < 0.05) and eight samples for type I receptor (P < 0.025). In contrast, all eight samples of benign prostate tissues investigated in this study showed strong staining for both type I and type II receptors. These results, taken together, indicate that human prostate cancer cells frequently have loss of expression of TGF-beta type I and/or type II receptors. Furthermore, these observations provide a potential mechanism for prostate cancer cells to escape the growth-inhibitory effect of TGF-beta.

TIMP-2 growth-stimulatory activity: a concentration- and cell type-specific response in the presence of insulin

In addition to proteinase-inhibitory activities, growth-stimulatory activities have been described for all three known members of the tissue inhibitors of the metalloproteinase (TIMP) family, TIMP-1, TIMP-2, and ChIMP-3, believed to be the chicken homologue of TIMP-3. However, the mechanism by which the TIMPs stimulate cell growth is unclear. In this report we have demonstrated that rTIMP-2 was growth-stimulatory for human foreskin fibroblasts (HSF4, HSF43, HS68), lung adenocarcinoma cells (A549), human melanoma cells (WM115), and the Burkitt's lymphoma cell line RAMOS, and this stimulatory response was concentration-dependent, with the greatest stimulation occurring a 10-30 pM rTIMP-2 in [3H]thymidine incorporation assays and at 20-100 pM in cell growth assays. Normal human colon (18Co) and lung (37Lu) fibroblasts showed no response to rTIMP-2. [3H]Thymidine incorporation was inhibited by rTIMP-2 treatment in the nonadherent cell line HL60. These studies also demonstrated that for the cell types tested, TIMP-2 alone was insufficient for a growth stimulatory response requiring, at a minimum, the presence of insulin. In the absence of any "co-factor(s)," such as insulin, TIMP-2 treatment was inhibitory.

Prostatic ductal system in rats: regional variation in stromal organization

The rat prostate is composed of a complex system of branching ducts which terminate proximally at the urethra. It has been recognized that epithelial cells lining the ducts respond differently to androgen in various regions of the ducts, with responses ranging from proliferation to apoptosis, but the cellular mechanisms underlying these effects are unclear. Interaction between prostatic stroma and epithelium is essential to normal prostate growth and development, and the prostatic stroma is thought to be the first site of androgen action. Therefore we have examined the organization and distribution of stromal cell types along the rat prostatic ductal system. Using immunohistochemical techniques, we observed abundant fibrous tissue surrounding the distal region of the ducts, with a sparse, discontinuous smooth muscle layer. The intermediate region was surrounded by a continuous layers of smooth muscle one to two cells thick, which increased to greater than four layers thick at the proximal region. Fibrous tissue was located in interductal spaces and occasionally interspersed within the muscle layers in both regions. These observations indicate that regional variations in the distribution of stromal cell types exist and suggest that their corresponding secretory products could be responsible for the various effects of androgen on the epithelium in the rat prostatic ductal system.

TIMP-2, a growth-stimulatory protein from SV40-transformed human fibroblasts

The mechanisms by which the early genes of simian virus 40 (SV40) transform human cells are unclear; however, this is clearly a multistep process involving a number of cellular and genetic changes. An early change following expression of the SV40 genes is growth under reduced serum conditions, which could be consistent with the production of autocrine/paracrine growth factors. HSF4-T12 is a human fibroblast cell line produced by transfection of primary cells with the genes for large T and small t antigens. A progressive stepwise transformation was observed with in vitro culture, eventually resulting in a tumorigenic cell line. Serum-free defined medium conditioned by HSF4-T12 was able to stimulate growth of normal human fibroblasts as determined by growth curve and [3H]-thymidine incorporation assays. Purification of this activity by heparin affinity chromatography and nondenaturing polyacrylamide gel electrophoresis resulted in a single band of approximately 21 kDa on a nonreducing, denaturing gel. A partial 14-amino acid sequence was found to share 100% homology with a region of tissue inhibitor of metalloproteinases-2 (TIMP-2). Western blot analysis with anti-TIMP-2 antiserum confirmed this identification, and addition of this same antiserum to HSF4-T12-conditioned medium resulted in inhibition of stimulatory activity.