Joan Bolt

REGULATION OF GROWTH OF LNCaP HUMAN PROSTATE TUMOR CELLS BY GROWTH FACTORS AND STEROID HORMONES

The mitogenic activity of several growth factors on androgen responsive LNCaP human prostate tumor cells was studied. A two-fold stimulation of cell proliferation was observed after a culture period of 6 days in 1 ng EGF/ml, 10 ng TGF-alpha/ml or 20 ng basic FGF/ml. TGF-beta (0.02 ng/ml), which did not affect cell proliferation when added alone to the culture medium, inhibited the EGF- and TGF-alpha-induced growth. The synthetic androgen R1881 (0.1 nM) stimulated cell proliferation three-fold and increased the number of EGF receptors from 11500 to 28500 sites/cell. One of the mechanisms involved in androgen action on these cells is therefore an increased EGF receptor expression and increased sensitivity to EGF. TGF-beta did not directly affect androgen-responsive growth but inhibited the synergistic effect of EGF. A considerable expression of TGF alpha (precursors) could be demonstrated on the cells by immunohistochemical staining. However the staining intensity was not affected by androgens. These results make it less likely that androgen-responsive growth is mediated by regulation of secretion of an EGF- or TGF alpha-like activity, which in turn acts in an autocrine manner to stimulate growth. Estrogens, progestagens and antiandrogens do not inhibit androgen responsive growth of LNCaP cells but have striking growth stimulatory effects, increase EGF receptor level and increase acid phosphatase secretion. LNCaP cells contain a modified androgen receptor system with respect to both steroid specificity and antiandrogen sensitivity. It has recently been shown that the stimulatory effects are due to a mutated amino acid in the steroid binding domain of the androgen receptor.

The human prostatic cancer cell line LNCaP and its derived sublines: An in vitro model for the study of androgen sensitivity

The LNCaP-FGC (fast growing colony) cell line, a subline derived from the LNCaP cell line, shares all the main characteristics, including its androgen sensitivity, described for the parental line. A number of sublines originating from the FGC line were characterized with respect to their response to steroid-depleted medium and to the synthetic androgen R1881. The growth of FGC cells in DCC medium with 0.1 nM R1881 was stimulated 2-3-fold compared to growth in DCC medium only. FGC cells that were continuously grown in DCC medium did not die, but their growth rate was clearly slowed down, and the cells remained responsive to androgen. These cells, therefore, have the androgen-sensitive, rather than the androgen-dependent phenotype. As cells of the subline FGC-JB could not be maintained in DCC medium, these cells better represent the androgen-dependent cell type. In contrast to the FGC line, cells of the R line, grew equally well in medium with complete or DCC serum. Under none of these culture conditions, R cells could significantly be stimulated further with R1881. Further analysis of the LNCaP-FGC sublines should provide valuable information concerning the development of androgen resistance in human prostate cancer.

Androgens and transforming growth factor β modulate the growth response to epidermal growth factor in human prostatic tumor cells (LNCaP)

UNLABELLED Treatment of LNCaP human prostatic cancer cells with 0.1 nM of the synthetic androgen, R1881, resulted in a three-fold stimulation of growth in 6 days. Of several growth factors tested (epidermal growth factor (EGF), platelet-derived growth factor, insulin-like growth factor, and insulin) only EGF (1 ng/ml) stimulated cell growth (two-fold). This stimulatory effect of EGF was inhibited for approximately 70% by 0.02 ng transforming growth factor beta (TGF beta)/ml. EGF (1 ng/ml) acted synergistically with R1881 (0.1 nM) on LNCaP cells to induce cell proliferation (seven-fold increase in cell growth). The synergistic effect of androgen and EGF was inhibited by TGF beta (0.05 ng/ml). IN CONCLUSION human prostatic LNCaP cells are sensitive to EGF. Androgen increases and TGF beta decreases the growth response to EGF. This effect of TGF beta on an androgen-responsive system has not been observed before.

Stimulatory effects of antiandrogens on LNCaP human prostate tumor cell growth, EGF-receptor level and acid phosphatase secretion

LNCaP cells (derived from a lymph node carcinoma of the human prostate) show androgen responsive growth. Progestagens, estradiol and antiandrogens competed with androgens for binding to the androgen receptor in the cells to a higher extent than in other androgen-sensitive systems. Optimal growth (3-4 fold increase in DNA content of 6 day cell cultures vs controls) was observed after addition of the synthetic androgen R1881 (0.1 nM). Both steroidal and non-steroidal antiandrogens did not suppress the androgen responsive growth. At a concentration of 10 nM cyproterone acetate or 100 nM RU 23908, growth was even stimulated to an extent comparable to that observed after addition of androgen. Cyproterone acetate and RU 23908 also increased the number of epidermal growth factor receptors expressed at the cell surface to a comparable level as did the androgen. Like androgens, cyproterone acetate, RU 23908 or estradiol stimulated the secretion per cell of prostate specific acid phosphatase in the culture fluid. In conclusion, antiandrogens can exert striking stimulatory effects on the proliferation of LNCaP cells probably due to a defective androgen receptor system. It is discussed that comparable changes in the specificity of the androgen receptor in prostate cancer cells may give these cells an advantage in growth rate and may contribute to development of tumors characterized as hormone independent.

Antiproliferative effects of suramin on androgen responsive tumour cells

UNLABELLED The effect of the polyanionic drug suramin on two androgen responsive tumour cell lines was studied. Human prostate tumour (LNCaP) cell growth is stimulated two- to three-fold by the synthetic androgen R1881 (0.1 nM) or EGF (1 ng/ml). Suramin (0.01-1.0 mM) inhibited the growth of LNCaP cells in a dose dependent way, both in the presence and absence of androgen or EGF. Growth was arrested in the G0/G1 phase of the cell cycle, but was resumed after removal of suramin. DDT-1 hamster ductus deferens tumour cells are stimulated by PDGF (25 ng/ml), b-FGF (10 ng/ml) and testosterone (10 nM). Suramin inhibited PDGF and b-FGF stimulated cell growth. However in the presence of testosterone, suramin showed a biphasic effect: stimulatory at low dose (0.01 mM) and inhibitory above 0.01 mM. Suramin decreased the apparent affinity of EGF binding sites on LNCaP cells with a two- to eight-fold increase in Kd at 0.1 and 1.0 mM suramin, respectively. IN CONCLUSION suramin counteracts the growth stimulatory effects of both androgens and growth factors on androgen sensitive tumour cells. The effects are reversible after withdrawal of suramin.

The human prostatic carcinoma cell line LNCaP and its derivatives

SummaryThe FGC (fast growing colony) line, a derivative of the LNCaP cell line shares all the main characteristics, including its androgen dependence, described for the original LNCaP cultures. A number of sublines originated from the FGC line which were characterized with respect to their response to steroiddepleted serum and to the synthetic androgen, R1881. After subcloning the FGC line a series of clones was isolated with distinct patterns of androgen-responsiveness. Among the sublines and clones studied, the FGC, FGC-JB and FGC clone-9 were androgen-dependent, whereas subline LNO, R and presumably also FGC clone-22 were androgen-independent. Distinct morphological differences were observed between the cells of the various sublines and between clone-9 and 22. The LNCaP cell line, its descending sublines and clonal derivatives provide a suitable in vitro model for studying different aspects of androgen-responsiveness of human prostate cancer.

Mechanism of androgen action: Recent observations on the domain structure of androgen receptors and the induction of EGF-receptors by androgens in prostate tumor cells☆

In this paper two different aspects of androgen action are reviewed. Polyacrylamide gel electrophoresis of androgen receptors, photoaffinity labeled with R1881 showed that receptors isolated from both human prostate cells and calf uterine cytosol cells are proteins with a molecular mass of approx 110 kD. Purification to homogeneity of this form of the receptor from calf uterus also yielded a 110 kD protein. A molecular model for the DNA-binding form of the receptor is presented in which one polypeptide comprises three active domains: one for ligand binding, one for interaction with nuclear acceptor sites, and a third domain which modulates nuclear interaction. Mild digestion with chymotrypsin or a protease from rat prostates removes the modulating domain and leaves the ligand binding and nuclear interaction domain intact. Trypsin treatment yields a fragment of lower molecular mass containing the ligand binding domain with some affinity for RNA, but not DNA. In vitro studies with a human prostate tumor cell line (LNCaP), suggest that androgens not only directly effect cell growth, but also act indirectly. Both epidermal growth factor (EGF) and androgens stimulate cell growth. In addition androgens stimulate synthesis of receptors for EGF. Thus androgens effect tumor cell growth by autocrine or paracrine mechanisms by making the cells more sensitive for growth factor mediated stimuli.

Androgen Receptor-Mediated Growth and Epidermal Growth Factor Receptor Induction in the Human Prostate Cell Line LNCaP

Human prostate tumor cells, LNCaP, contain androgen receptors and respond to androgens with increased growth rate. Although other steroid hormone receptors are not detectable in LNCaP cells, progesterone and estradiol stimulate the growth of these cells. The androgen receptor shows considerable cross binding activity with progesterone and estradiol but not with the glucocorticoid triamcinolone acetonide. The latter steroid does not have any effect on cell proliferation. LNCaP cells respond to epidermal growth factor (EGF) with an increased growth rate. Steroids that stimulate LNCaP cell proliferation also increase the number of EGF receptors per cell. In conclusion, LNCaP cells are sensitive to EGF. Different steroids bind to the androgen receptor and stimulate the proliferation of human prostate tumor cells. This stimulation of growth is preceded by an increase in EGF receptor number per cell.

Analysis of steroid- and DNA-binding domains of the calf uterine androgen receptor by limited proteolysis

The DNA-binding form of the calf uterine androgen receptor (AR) was subjected to limited protease digestion using chymotrypsin, trypsin and a rat prostate cytosol protease. The properties of the generated polypeptide fragments were identified and compared with those of the intact AR. Physicochemical characterization was achieved through sedimentation analysis, gel filtration chromatography and DEAE anion exchange chromatography. Intactness of functional binding domains was evaluated by measuring the retention of steroid- and DNA-binding capacity. Under non-denaturing conditions the intact AR is a highly asymmetrical molecule with a Stokes radius (RS) of 45A, a sedimentation coefficient of 4.3S and a relative molecular mass of 80,000 daltons. This form of AR has an intrinsic binding affinity for DNA and was eluted from DNA-cellulose with 9 mM MgCl2. Chymotrypsin produced a more globular polypeptide (RS: 31A; 3.1S; 41,000 daltons) with a decreased net negative charge. This fragment also displayed DNA-binding affinity but required a higher concentration of MgCl2 (14 mM) for DNA-cellulose elution, indicating an increased affinity for DNA. The observed reduction in molecular size upon chymotrypsin treatment was confirmed when analysed by SDS-polyacrylamide gel electrophoresis after covalently labelling of the AR with [3H]R1881. Rat prostate cytosol contains a protease which is very active in generating an AR polypeptide with an increased affinity for DNA, without changing the AR net negative charge (RS: 33A; 3.7S; 51,000 daltons). The specificity of this protease remained unknown since none of a large number of inhibitors was able to inactivate this enzyme. The fragment generated is different from that obtained with chymotrypsin since significant differences in size as well as in charge were measured. Trypsin treatment generated a much smaller polypeptide (RS: 25A; 2.9S; 30,000 daltons) which had lost its DNA-binding capacity, but not its steroid binding site. This form probably represents the so-called meroreceptor. When intact AR was treated sequentially with prostate cytosol and trypsin, a polypeptide fragment with identical properties was obtained, indicating the spatial separation of two of the proteolytic cleavage sites. These studies provide evidence for the distinct nature of the molecular domains for androgen and DNA interaction on the calf uterine AR.

Differential effects of molybdate on the hydrodynamic and DNA-binding properties of the non-activated and activated forms of the androgen receptor in calf uterus

Calf uterine cytosol contains an androgen receptor with a relative molecular mass of approx. 90,000. In this study we have analysed the structure and aggregation properties of the androgen receptor, using sucrose density gradient centrifugation on a vertical rotor (VTi65). In the presence of 10 mM NaCl the androgen receptor in whole cytosol sedimented at 8 S irrespective of the presence of molybdate. In 400 mM NaCl the receptor dissociated to a 4.3 S entity. In whole cytosol molybdate promoted a partial shift of the 4.3 S receptor into the aggregated 8 S state. The time of exposure of the receptor to molybdate and NaCl determined the proportion of receptor sedimentating at 8 S and 4.3 S. The DNA-binding form of the uterine androgen receptor when analysed under the conditions of the DNA-cellulose binding assay, sedimented at 6.5 S. Increasing concentrations of molybdate shifted its sedimentation coefficient gradually from 6.5 S to 4.5 S and in parallel reduced the DNA-binding capacity. Molybdate added to a partially purified, DNA-binding form of the androgen receptor did not promote receptor aggregation to faster sedimentating forms. This suggests that such preparations are devoid of an androgen receptor-aggregation factor. Indirect evidence for such a factor was obtained from reconstitution experiments with whole cytosol. Our results indicate that the DNA-binding form of the androgen receptor interacts with a cytosol factor to form the 8 S receptor complex. Molybdate has diverse effects: in the presence of the cytosol factor it stabilizes the 8S complex; in its absence molybdate prevents in a concentration-dependent way DNA-binding as well as reaggregation of the monomeric 4.3 S form.