Relationship between cell surface protease activity and doubling time in various normal and transformed cells.

A sensitive method for measuring cell surface and secreted protease activity utilizing 3H-labelled casein is described. The method is based upon proteolytic degradation of the casein substrate into trichloracetic acid soluble 3H-labelled peptides. Utilizing the radioassay we found that all cultured cell lines examined contain cell surface proteolytic activity which is not secreted into the media. The protease activity was found to be due to protease(s) other than plasminogen activator or plasmin. A comparison of surface protease activity of normal and transformed mouse epidermal cells indicated that the transformed cells contained approximately 3--1 times more proteolytic activity than the normal cells. Surface protease activity was also correlated with the doubling times of various cultured cells. The results indicated that cultured cells with doubling times of greater than three days possess less surface protease activity than cells with shorter doubling times. In order to determine changes in the levels of surface protease activity during the cell cycle several cell lines were synchronized. In synchronized rabbit aortic fibroblasts, mouse transformed epidermal cells and human melanoma cells, a marked increase in surface protease activity was observed during or before mitosis. The protease levels decreased following mitosis. The results suggest that in culture, cell surface protease(s) may be important factor in regulating the rate of cell growth.     

Enzymic hydrolysis of myelin basic protein and other proteins in central nervous system and lymphoid tissues from normal and demyelinating rats.

Proteolytic activity of central-nervous-system tissue of the normal rat was examined over the pH range 2-9 with casein, haemoglobin and myelin basic protein as substrates. With casein as a substrate, brain and spinal cord homogenates showed very similar activity profiles with increasing pH, with the main peaks of proteolytic activity at pH 3-4 and 5-6. When haemoglobin was used, one broad main peak of activity from pH 3 to 5 was demonstrated. There was no optimum pH, however, for proteolytic activity with myelin basic protein as a substrate, and considerable hydrolysis were observed from pH 3.5 up to pH8. Proteolytic activity at the various pH values was compared by using homogenates of spinal cords from rats with acute experimental allergic encephalomyelitis and those from rats injected with Freund's adjuvant alone. The profiles of activity were similar with peaks at pH 3.5 and 5.5 with casein as a substrate, but the specific activity was significantly higher at most pH values in the spinal-cord homogenates from rats with experimental allergic encephalomyelitis. Similarly the spinal-cord homogenates from these latter rats contained much more proteolytic activity toward myelin basic protein throughout the pH range than was present in the control spinal cords. Homogenates from lymph nodes of rats with experimental allergic encephalomyelitis and from those of the controls contained two to three times as much proteolytic activity as that of the central-nervous-system tissue and had a different proteolytic activity profile form that of the central-nervous system, with higher activity at the neutral than at acid pH. The results are discussed with regard to the probability that inflammatory cells such as lymphocytes may be the cause of the increased proteolytic activity in the central nervous system of animals with experimental allergic encephalomyelitis, and that enzymes from these cells possess the capability of digesting myelin basic protein.     

Immunofluorescence on avian sarcoma virus-transformed cells: localization of the src gene product.

The localization of the avian sarcoma virus src gene product (termed p60src) was examined by indirect immunofluorescence in cells transformed by the Schmidt-Ruppin strain of Rous sarcoma virus, subgroup D (SR-RSV-D). Antiserum to p60src was obtained from rabbits bearing SR-RSV-D-induced tumors, and immunofluorescence was performed on chicken embryo fibroblasts (CEF) transformed with SR-RSV-D, as well as normal rat kidney (NRK) cells transformed by the same virus (termed SR-RK cells). Both acetone and formaldehyde fixation were used for the immunofluorescence tests. The specificity of the anti-tumor serum was first demonstrated in both cell systems by gel electrophoresis of immunoprecipitates prepared from 35S--methionine-labeled cells. Anti-tumor serum precipitated p60src from SR-RSV-D-transformed CEF but not from CEF infected with a transformation-defective mutant of SR-RSV-D. All viral structural proteins and precursors contained in these immunoprecipitates could be eliminated by competition with unlabeled virus. Similar experiments on SR-RK cells indicated that no viral proteins other than p60src were expressed in these cells, and this observation was supported by immunofluorescence tests using antiserum to whole virus. For immunofluorescence localization of p60src, reactions with viral structural proteins were blocked with unlabeled virus. This presaturation step, obligatory for p60src detection in the SR-RSV-D-transformed CEF, was unnecessary when antitumor serum was tested on SR-RK cells, since p60src was the only viral protein detectable in these cells. With acetone-fixed cells, p60src-specific immunofluorescence revealed a characteristic fluorescence pattern which was similar in both cell systems. The principal pattern was diffuse and situated in the cytoplasm. A clear nuclear fluorescence was never observed. Immunofluorescence on formaldehyde-fixed cells also indicated the cytoplasmic location of p60src and revealed a specific subcytoplasmic concentration of the fluorescence. With both fixation methods, an additional fluorescence pattern was seen between cells in contact, and was also found in both SR-RK cells and SR-RSV-D-transformed CEF. Immunofluorescence on viable cells suggested that p60src was not on the surface of these transformed cells. The fluorescence patterns were specific for avian sarcoma virus-transformed cells and were not found in uninfected cells, cells infected with a transformation-defective mutant of SR-RSV-D or cells transformed by an antigenically unrelated murine sarcoma virus. Furthermore, anti-tumor serum did not contain antibodies to proteins of the microtubules or intermediate filaments.     

Relationship between cell surface protease activity and doubling time in various normal and transformed cells

A sensitive method for measuring cell surface and secreted protease activity utilizing ³H-labelled casein is described. The method is based upon proteolytic degradation of the casein substrate into trichloroacetic acid soluble ³H-labelled peptides. Utilizing the radioassay we found that all cultured cell lines examined contain cell surface proteolytic activity which is not secreted into the media. The protease activity was found to be due to protease(s) other than plasminogen activator or plasmin. A comparison of surface protease activity of normal and transformed mouse epidermal cells indicated that the transformed cells contained approximately 3–4 times more proteolytic activity than the normal cells.Surface protease activity was also correlated with the doubling times of various cultured cells. The results indicated that cultured cells with doubling times of greater than three days possess less surface protease activity than cells with shorter doubling times. In order to determine changes in the levels of surface protease activity during the cell cycle several cell lines were synchronized. In synchronized rabbit aortic fibroblasts, mouse transformed epidermal cells and human melanoma cells, a marked increase in surface protease activity was observed during or before mitosis. The protease levels decreased following mitosis. The results suggest that in culture, cell surface protease(s) may be important factor in regulating the rate of cell growth.     

Cell surface changes accompanying viral transformation: N-acetylneuraminic acid ectotransferase system activity.

The activity of the sialyl ectotransferase system of normal chick embryo fibroblasts (CEF) and chick embryo fibroblasts transformed with the Schmidt-Ruppin strain of Rous sarcoma virus (SR-RSV) have been compared. Neuraminidase treatment of the intact cells increased the sialyl ectotransferase system activity of control and transformed cells two to three times. The ectotransferase system activity increased as the pH was decreased from 7.8 to 6.0. The temperature optimum for both systems was 40 degrees C. Approximately 60% of the 14C-sialic acid incorporated at pH 6.5 or above could be removed with neuraminidase. The activity of the transformed cell system with or without neuraminidase treatment was more stimulated by addition of Mn2+ ions, particularly above pH 7.0. This difference in ion sensitivity indicates that a different cell surface phenomenon is being studied after transformation.     

Immunological and structural properties of Rous sarcoma virus-transformed and tumor cells]

We compared the capacity of both normal and Rous sarcoma virus (RSV)-transformed chicken embryo fibroblast (CEF) cells as well as Rous sarcoma (RS) tumor cells to serve as targets in anti-tumor immunity assays. These studies showed that sera from tumor-bearing donors were able to stain transformed CEF more efficiently than RS cells as detected by immunofluorescence. In contrast, antiserum against the major viral glycoprotein, gp 85, stained a higher percentage of RS than transformed cells. Normal CEF cells, which served as controls, were essentially non-reactive with the immune system as judged by this type of assay. We observed that RS cells are considerably larger and contain far higher levels of protein than either normal or transformed CEF. Scanning electron microscopy revealed both the RS cells and transformed CEF to be rich in surface ruffles, blebs and microvilli as distinguished from the flattened, fusiform appearance of normal CEF cells.     

Protein phosphorylation at tyrosine is induced by the v-erbB gene product in vivo and in vitro

The v-erbB gene product of avian erythroblastosis virus (AEV) has extensive homology with the receptor for epidermal growth factor (EGF). We report here that chicken embryo fibroblasts (CEF) transformed by AEV show enhanced tyrosine phosphorylation of a number of cellular polypeptides, including the 36 kd protein, which is phosphorylated in avian sarcoma virus-transformed fibroblasts, and the 42 kd protein, which is phosphorylated in mitogen-stimulated cells. CEF infected by AEV mutants with deletions in v-erbA showed enhanced tyrosine phosphorylation, whereas CEF infected by mutants with deletions in v-erbB did not. When membranes from AEV-transformed cells were incubated with gamma-32P-ATP, both the v-erbB gene product and the 36 kd cellular protein became phosphorylated at tyrosine. These results indicate that the v-erbB protein induces tyrosine phosphorylation in vivo and in vitro, and suggest that, like the EGF receptor, it possesses tyrosine-specific protein kinase activity.     

Transformation of chicken embryo fibroblast cells by avian retroviruses containing the human Fyn gene and its mutated genes.

The transforming activity of the human fyn protein, p59fyn, which is a kinase of the src family, was investigated by testing the effect of recombinant avian retrovirus (Fyn virus) expressing p59fyn on chickens or cultured chicken embryo fibroblast (CEF) cells. The Fyn virus did not induce transformed foci. After several passages of the virus stock on CEF cells, however, a few foci were detected in the presence of dimethyl sulfoxide. Chickens inoculated with Fyn virus at the stage of 12-day-old embryos developed fibrosarcomas 3 to 6 weeks after hatching. The viruses obtained from these foci and from one of the tumor tissues showed high transforming activity in the presence of dimethyl sulfoxide, suggesting that these viruses carry spontaneous mutations of the fyn gene. Four fyn genes from CEF DNAs infected with transforming viruses were molecularly cloned, and their products were confirmed to possess transforming activity. DNA sequence analysis of the fyn genes showed that two of the four mutants have Thr instead of Ile at position 338 in the kinase domain. The other two mutants carry deletions of 78 and 108 base pairs, respectively, which result in complete loss of region C of SH2. The overall level of proteins containing phosphotyrosine was significantly higher in transformed cells than in normal CEF cells. Our data indicate that when expressed at high levels in a retrovirus, normal p59fyn cannot cause cellular transformation, but that mutant p59fyn with either a single amino acid substitution in the kinase domain or a deletion including region C produces a transforming protein, perhaps due to enhanced tyrosine kinase activity. This is the first observation that deletion of region C can unmask the potential transforming activity of a src family kinase.     

Modulation of arachidonic acid metabolism by Rous sarcoma virus

Arachidonic acid (C20:4) metabolites were released constitutively from wild-type Rous sarcoma virus-transformed chicken embryo fibroblasts (CEF). 3H-labeled C20:4 and its metabolites were released from unstimulated and uninfected CEF only in response to stimuli such as serum, phorbol ester, or the calcium ionophore A23187. High-pressure liquid chromatography analysis showed that the radioactivity released from [3H]arachidonate-labeled transformed cells was contained in free arachidonate and in the cyclooxygenase products prostaglandin E2 and prostaglandin F2 alpha; no lipoxygenase products were identified. The release of C20:4 and its metabolites from CEF infected with pp60src deletion mutants was correlated with serum-independent DNA synthesis and with the expression of the mRNA for 9E3, a gene expressed in Rous sarcoma virus-transformed cells which has homology with several mitogenic and inflammatory peptides. 3H-labeled C20:4 release was not correlated with p36 phosphorylation, which argues against a role for this protein as a phospholipase A2 inhibitor. CEF infected with other oncogenic viruses encoding a tyrosine kinase also released C20:4, as did CEF infected with viruses that contained mos and ras; however, infection with a crk-containing virus did not result in stimulation of 3H-labeled C20:4 release, suggesting that utilization of this signaling pathway is specific for particular transformation stimuli.     

Chicken embryo fibroblasts exposed to weak,time-varying magnetic fields share cell proliferation,adenosine deaminase activity,and membrane characteristics of transformed cells

Chicken embryo fibroblasts (CEF) exposed to a sinusoidally varying magnetic field (SVMF) (100 Hz, 700 μT, for 24 h) showed a remarkable rise of segmental rotational relaxation rate of adenosine deaminase (ADA, EC 3.5.4.4) as determined by multifrequency phase fluorometry. Pyrene-labeled, small subunit ADA was applied to cultured (normal) CEF, which have available and abundant ADA complexing protein (ADCP) on their plasma membranes. Sine-wave-modulated fluorometry of the pyrene yielded a profile of phase angle vs. modulation frequency. In SVMF-treated cells and in Rous-sarcoma-virus (RSV) transformed cells the differential phase values at low modulation frequencies of the excitation are remarkably reduced. This effect is magnetic rather than thermal, because the temperature was carefully controlled and monitored; nevertheless to further check this matter we studied CEF, infected by the RSV-Ts68 temperature-sensitive mutant (36°C transformed, 41°C “revertant”). When grown at 36°C in the SVMF, cells did not show the slightest trend towards reversion, as would be expected had there been local heating. Concomitant with the increased segmental rotational relaxation rate of ADA, there was a decrease in fluorescence lifetime and a slight, yet significant, increase in membrane lipid “microfluidity.” These biophysical observations prompted us to examine the effect of SVMF on cell proliferation and ADA activity (a malignancy marker): higher rates of cell proliferation and reduced specific activity of ADA were observed. © 1993 Wiley-Liss, Inc.     

Modulation by the src oncogene of the effect of inhibitory diffusible factor IDF45

Density-dependent inhibition of growth has been assumed to be under the control of inhibitory molecules diffusing from dense cell cultures. Growth inhibitory factors have been fractionated or purified from medium conditioned by different cell types. In the present work, it was shown that IDF45 (inhibitory factor diffusing from 3T3 cells) decreased DNA synthesis in chick embryo fibroblasts (CEF) and was an inhibitor of CEF growth; this inhibition was reversible. Since similitudes between oncogene products and growth factors have been observed, it was of interest to compare the inhibitory effect of IDF45 upon the stimulation of DNA synthesis induced either by serum or by pp60-src. CEF infected by Ny68 virus (a mutant of Rous sarcoma virus ts for the expression of transformation) were density-inhibited at 41 degrees C, but were stimulated at this temperature by addition of 1% serum. This stimulation was 94% inhibited by IDF45. The same Ny68-infected cells could also be stimulated by transfer to 37 degrees C, the permissive temperature (in the absence of serum). The stimulation of DNA synthesis by src expression was poorly inhibited by IDF45. From our results, it appears that oncogene expression in CEF induces a loss in their sensitivity to IDF45. This would explain why transformed cells escape DDI of growth.     

The effect of the tumor promoter, phorbol myristate acetate (PMA), on hyaluronic acid (HA) synthesis by chicken embryo fibroblasts

Treatment of chicken embryo frbroblasts (CEF) with the tumor promoter, phorbol myristate accetate (PMA), resulted in a rapid increase in their ability to synthesize the glycosaminoglycan, hyaluronic acid (HA), whereas the parent compound, phorbol, had no effect. CEF cultures incubated with PMA (100 ng/ml) for 6 h resulted in a 15-fold increase in HA synthetase activity compared with phorbol-treated control cultures. The incorporation of [³H]acetate into HA and chemical determination of this polymer also demonstrated increased synthesis of HA by cells treated with PMA. We have previously shown that CEF infected with a temperature-sensitive mutant of Rous sarcoma virus, LA24, exhibit increased synthesis of HA upon transformation. PMA treatment of cells transformed with RSV-LA24 results in a further 1.5-fold stimulation of HA synthesis. These data indicate that PMA causes an increased synthesis of HA in CEF which is analogous to the increased synthesis of HA found in virally transformed CEF.     

Transformed lepidopteran cells expressing a protein of the silkmoth fat body display enhanced susceptibility to baculovirus infection and produce high titers of budded virus in serum-free media

Baculovirus vectors constitute important tools for therapeutic protein production and mammalian cell transduction for gene therapy applications. A prerequisite for such applications is that the cell lines in which baculoviruses are propagated be maintained in serum-free media that are devoid of potential human pathogens. However, in serum-free media, the performance of baculovirus-based systems can be significantly reduced. In this report, we show that silkmoth-derived host cell lines for the Bombyx mori-nuclear polyhedrosis virus (BmNPV) that are transformed with the gene for the promoting protein (PP), a silkmoth-derived secreted factor containing a lipid-binding domain, display enhanced susceptibility to BmNPV infection and enhanced budded virus productivity in serum-free media. For transformed silkmoth cells maintained in serum-free media, the rate of BmNPV entry is enhanced by two orders of magnitude relative to the untransformed cells, while the rate of budded virus production is increased five-fold. The infectivity-enhancing effect can be also conferred to normal cells grown in serum-free media by addition of conditioned media from the transformed cells, which contain the secreted recombinant PP. Thus, PP substitutes for serum factors whose presence facilitates baculovirus entry into the cells. However, the effects of silkmoth-derived PP may be specific to the BmNPV-silkmoth system since little or no changes in viral infectivity are obtained by PP expression in Trichoplusia ni-derived High-Fivetrade mark cells grown in serum-free media and infected with a different baculovirus (AcNPV).     

Phosphoprotein phosphatase activity at the outer surface of intact normal and transformed 3T3 fibroblasts.

Using 32P-labeled phosphocasein or phosphohistones as exogenous substrates it was possible to detect a phosphoprotein phosphatase activity on the outer surface of intact normal and transformed 3T3 fibroblasts. Incubation of monolayers of intact cells in buffered salt solution with the radioactively labeled substrate resulted in the release of alkali-labile 32P counts into the surrounding medium. The reaction was: (a) linear with time (at least up to 20 min); (b) proportional to the cell density; (c) dependent on the temperature and pH of the incubation medium; (d) stimulated by K+; and (e) inhibited by sodium fluoride, inorganic pyrophosphate, zinc chloride and relatively impermeant sulfhydryl reagents. Less than 2% of the externally located phosphoprotein phosphatase activity was detectable in pooled cell-free washings of the intact cell monolayer. Phosphocasein did not cause any detectable leakage of intracellular lactate dehydrogenase or soluble phosphoprotein phosphatase activity into the external medium; incubation of the cells with phosphohistones, on the other hand, resulted in appreciable leakage of both these cytoplasmic activities. Neoplastic transformation was associated with a nearly two-fold decrease in the activity of the surface phosphoprotein phosphatase. Addition of serum to either non-transformed 3T3 or spontaneously transformed 3T6 cells resulted in a rapid and remarkeable drop in the cell surface dephosphorylating activity. Acrylamide gel electrophoresis of the dephosphorylated casein or histone substrate revealed no proteolytic degradation or change in electrophoretic mobility. The intact cells showed no damage upon microscopic examination as a result of exposure to phosphocasein or phosphohistones.     

Phosphoprotein phosphate activity at the outer surface of intact normal and transformed 3T3 fibroblasts

Using ³²P-labeled phosphocasein or phosphohistones as exogenous substrates it was possible to detect a phosphoprotein phosphate activity on the outer surface of intact normal and transformed 3T3 fibroblasts. Incubation of monolayers of intact cells in buffered salt solution with the radioactively labeled substrate resulted in the release of alkali-labile ³²P counts into the surrounding medium. The reaction was: (a) linear with time (at least up to 20 min); (b) proportional to the cell density; (c) dependent on the temperature and pH of the incubation medium; (d) stimulated by K⁺; and (e) inhibited by sodium fluoride, inorganic pyrophosphate, zinc chloride and relatively impermeant sulfhydryl reagents. Less than 2% of the externally located phosphoprotein phosphatase activity was detectable in pooled cell-free washings of the intact cell monolayer. Phosphocasein did not cause any detectable leakage of intracellular lactate dehydrogenase or soluble phosphoprotein phosphatase activity into the external medium; incubation of the cells with phosphohistones, on the other hand, resulted in appreaciable leakage of both these cytoplasmic activities. Neoplastic transformation was associated with a nearly two-fold decrease in the activity of the surface phosphoprotein phosphatase. Addition of serum to either non-transformed 3T3 or spontaneously transformed 3T6 cells resulted in a rapid and remarkable drop in the cell surface dephosphorylating activity. Acrylamide gel electrophoresis of the dephosphorylated casein or histone substrate revealed no proteolytic degradation or change in electrophoretic mobility. The intact cells showed no damage upon microscopic examination as a result of exposure to phosphocasein or phosphohistones.     

Neuraminidase activity and cell surface sialic acid turnover in Rous sarcoma virus transformed chick embryo fibroblasts

Neuraminidase activity of Rous sarcoma virus transformed chick embryo fibroblasts (RSV-CEF) was assayed using an exogenous substrate, neuraminlactitol-[3H], and endogenous, cell surface [14C]-N]-acetyl-neuraminic acid. RSV-CEF had higher neuraminidase activity toward both substrates than did chick embryo fibroblasts (CEF) or nontransformed, Rous associated virus infected CEF (RAV-CEF). The total sialic acid content of RSV-CEF was lower than CEF or RAV-CEF, and more of the total sialic acid was accessible to extracellular Clostridium perfringens neuraminidase. Activity of the enzymes synthesizing and degrading the substrate for sialyltransferase, cytidine-5'-monophosphate-N-acetyl-neuraminic acid (CMP-AcNeu) was measured in order to determine whether control of substrate levels for sialyltransferase might contribute to the decreased levels of glycoprotein bound sialic acid. No change in activity of these enzymes was found in RSV-CEF as compared to CEF or RAV-CEF.     

Regulation of the proliferative response in Rous sarcoma virus transformed chicken embryo fibroblasts by serum and multiplication-stimulating activity (MSA).

A temperature sensitive mutant of Rous sarcoma virus (tsNY68) was used to obtain cultures of quiescent virus-infected chicken embryo fibroblasts arrested by serum starvation at the non-permissive temperature. Upon shift to the permissive temperature, these cells enter the replicative cell cycle as evidenced by increases in 2-deoxyglucose uptake, 3H-thymidine incorporation and percent labeled nuclei. These changes occur in the absence of serum and the cells become morphologically transformed within eight to ten hours after the temperature shift. Entry into the S phase temporally resembles that of normal quiescent fibroblasts stimulated with serum. This experimental system was used to examine the proliferative response of transformed cells to serum and purified multiplication-stimulating activity (MSA) during the transition from the resting to the growing state. Data are presented which show that the presence of serum in the medium enhances the proliferative response of quiescent infected cells shifted to the permissive temperature over those shifted in the absence of serum. In contrast, the presence of MSA has no additional effect on the response exhibited by infected cells shifted to the permissive temperature in serum-free medium. Labeled MSA binding experiments show that this lack of response is not due to a loss of MSA receptors on the cell surface since transformed cells are still capable of binding MSA at the same level as normal cells. The results are consistent with the hypothesis that the set of biochemical events initiated by MSA in normal cells are turned on in infected cells shifted to the permissive temperature by the activation of the src gene product.     

Stimulation of clonal growth of normal fibroblasts with substrata coated with basic polymers

Improved media have reduced the amount of serum protein required for clonal growth of normal human and chicken fibroblast-like cells. In the presence of limiting amounts of serum protein, attachment of colonies to tissue culture plastic surfaces is weak. Treatment of the culture surface with polylysine or other basic polymers causes the cells to adhere much more tightly. Growth is also improved on the surfaces treated with basic polymers, and further reductions in the concentration of serum as possible. At sufficiently low protein concentrations, growth of some types of cells is totally dependent on the use of a treated surface. Several different types of normal human and chicken fibroblast-like cells show improved growth on polylysine- coated surfaces, but no improvement was obtained in growth of a line of SV-40 transformed WI-38 cells. Acidic and neutral polymers are generally inactive. Collagen and gelatin improve growth slightly, but the effect is much less than that obtained with basic polymers. Both natural and synthetic polymers with an excess of basic groups are active, including histone, polyarginine, polyhistidine, polylysine, polyornithine, and protamine. The only critical requirement appears to be a polymer that carries a positive charge at a physiological pH.     

Acid-activated insulin-like growth factor binding protein protease activity of Cathepsin D in normal and malignant prostatic epithelial cells and seminal plasma

In this study, we demonstrate insulin-like growth factor binding protein (IGFBP) acid proteolysis in conditioned media (CM) from normal and malignant primary cultures of prostatic epithelial cells, prostatic cell lines, and in seminal plasma. We further demonstrate the absence of such activity in CM from prostatic stromal cells. Radio-labeled IGFBPs (1–6) were incubated with various acidified CM and seminal plasma. None of these media showed IGFBP proteolytic activity at neutral pH, but all CM from prostatic epithelial cells (PC-E) demonstrated strong IGFBP proteolysis at acidic pH. No acid-activated proteolysis was observed in the CM from stromal cell cultures. In order to ascertain the role of cathepsin D, anti-cathepsin antibodies were used to immunodeplete the media of the selected enzymes prior to incubation with IGFBPs. Depletion of cathepsin D greatly reduced the proteolytic activity of the PC-E CM. Additionally, purified cathepsin D yielded a digestion pattern identical to that produced by prostatic cell CM and seminal plasma, following acidic incubation with IGFBP-3. Remarkably, the proteolytic pattern generated by seminal plasma, when incubated with IGFBP-3 at neutral pH, corresponded to that produced by prostate-specific antigen (PSA), demonstrating the interpolation of both neutral and acid proteases from prostate cells into seminal plasma. In conclusion, prostatic epithelial cells secrete acid-specific IGFBP protease(s) related to cathepsin D. Although no significant statistical difference was observed in the degree of acid-specific proteolysis in the media from normal versus malignant primary epithelial cell cultures, physiologicalcharacteristics of the malignant state might facilitate increased cathepsin D activity. We suspect this proteolysis may play a role in prostatic cell proliferationand invasive tumor growth. J. Cell. Physiol. 171:196–204, 1997. © 1997 Wiley-Liss, Inc.     

Different localization of the product of the v-rel oncogene in chicken fibroblasts and spleen cells correlates with transformation by REV-T

Reticuloendotheliosis virus strain T (REV-T) is a highly oncogenic avian retrovirus that transforms early lymphoid cells in vivo and in vitro, but REV-T does not transform chicken embryo fibroblasts (CEF). Using antisera to p59v-rel, the v-rel oncogene product of REV-T, we show that p59v-rel is expressed at equal levels and is a phosphoprotein in REV-T infected spleen cells and CEF. Biochemical fractionation and immunofluorescence of REV-T infected nontransformed CEF show that p59v-rel is loosely associated with the nucleus. However, in REV-T transformed spleen cells p59v-rel is primarily a cytoplasmic protein. MSB-1 cells, a Marek's disease virus transformed T cell leukemic line, and E26 virus transformed myeloid cells show nuclear staining of p59v-rel when they are infected by REV-T. Our results indicate that there is a correlation between a cytoplasmic localization of p59v-rel and transformation by REV-T, and they suggest that p59v-rel cannot transform cells in which it assumes solely a nuclear location.