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Departments of Physiology (J.V.S., P.C.S., S.M., Y.G., J.S., J.G.D., L.J.M.) and Internal Medicine (L.J.M.), University of Manitoba, Winnipeg, Canada R3E 3P4
Address all correspondence and requests for reprints to: Liam J. Murphy, Departments of Physiology and Internal Medicine, University of Manitoba, Winnipeg, Canada R3T 2N2.
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Introduction |
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Low-plasma IGFBP-3 levels have been reported to have predictive value in identifying individuals with advanced-stage prostate cancer (2). Low-plasma IGFBP-3 could increase the availability of free IGF-I and -II in the prostate and thereby favor the initiation and progression to prostate cancer. In addition, low IGFBP-3, by reducing the IGF-independent, antiproliferative, and proapoptotic effects of IGFBP-3 on prostate epithelium, could also potentially favor the development and progression of prostate cancer.
The epidemiological literature together with the in vitro observations provide strong support for the concept that the IGF system, in particular IGF-I and IGFBP-3, is important in prostate cancer. However a direct demonstration for a causal relationship to explain the associations between the IGF system and prostate cancer progression in patients is lacking. As yet there are few in vivo data to support the in vitro observations with cultured prostate cancer cells. Furthermore, to date, the IGF-independent effects of IGFBP-3 on prostate cancer have been demonstrated only in vitro.
The proapoptotic effects of IGFBP-3 are both dependent on and independent of p53 (10, 11). Impaired function of the tumor suppressor protein p53 is involved in the pathogenesis of prostate cancer (12), and increased IGFBP-3 expression is an important downstream mediator of p53 action in prostate and other cancer cells (11, 13). In mouse models of cancer that use the simian virus 40 (SV40) large T-antigen (Tag) as the oncogenic transgene, the cellular tumor suppressor p53 is inactivated. In the case of the long probasin promoter (LPB)-Tag mouse model of prostate cancer, transgene expression is targeted specifically to the prostate (14, 15).
The N-terminal domain of IGFBP-3 appears to be most important for binding to IGF-I and -II with high affinity. Mutations in the N terminal of IGFBP-3 result in molecules that do not bind IGF-I or -II (16). Six residues, Ile56, Tyr57, Arg75, Leu77, Leu80, and Leu81, have been identified as important in high-affinity binding of IGF to IGFBP-3. Of these, Ile56, Leu80, and Leu81 are most important and substitution with glycine or alanine results in a mutant IGFBP-3 that lacks the ability to bind IGF-I or IGF-II but retains the ability to bind plasma membranes (5) and promote apoptosis and inhibit proliferation in prostate and breast cancer cell lines (5, 17, 18).
We previously generated transgenic mice that overexpress human IGFBP-3 using the phosphoglycerate kinase (PGKBP-3) and cytomegalovirus (CMVBP-3) promoters (19). These mice demonstrate fetal and postnatal growth retardation. More recently we generated transgenic mice that overexpress the I56G/L80G/L81G-mutant IGFBP-3 (PGKmBP-3) (20). The PGKmBP-3 transgenic mice do not have a growth-retarded phenotype.
In this report we tested the hypothesis that IGFBP-3 inhibits prostate cancer growth by examining the progression from epithelial hyperplasia to dysplasia and carcinoma in F1 crosses of PGKBP-3, CMVBP-3, and PGKmBP-3 transgenic mice that ubiquitously overexpress IGFBP-3 or PGKmBP-3 with LPB-Tag mice (14).
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Materials and Methods |
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IGFBP-3 and IGF-I assays
Human IGFBP-3 was measured using an immunoradiometric assay from Diagnostic Systems Laboratories (Webster, TX). Total plasma IGF-I was measured by a sensitive rat IGF-I RIA kit (Linco Research, Inc., St. Charles, MO).
RNA extraction and RNase protection assays
Total RNA was extracted from prostate tissue and tumors using TRizol reagent (Invitrogen, Carlsbad, CA). The concentration of RNA was determined spectrophotometrically, and the integrity of the RNA in all samples was documented by visualization of the 18 and 28S ribosomal RNA bands after electrophoresis through a 0.8% formaldehyde/agarose gel. Maxiscript SP6/T7 and RPAIII kits (Ambion, Austin TX) were used for the RNase protection assay. A 267-bp fragment containing the sequence corresponding to the 3'-end of the human IGFBP-3 cDNA and the bovine GH polyadenylation signal was used as a template as previously described (19). A mouse cyclophilin riboprobe was used as the internal standard, and century RNA markers (Ambion) were used to determine the size of the protected fragment. The protected sizes for the transgene-derived RNA and cyclophilin fragments were 267 and 103 bp, respectively.
Immunoblotting
Analysis of proteins was performed using approximately 20 µg of protein extracted from prostate tissue samples and separated on 10% SDS-PAGE. Proteins were transferred to nitrocellulose or polyvinyl difluoride membranes followed by blocking with 5% nonfat milk and incubation with the primary antibody. After incubation, membranes were washed three times (5 min each) in 10 mM Tris, 150 mM NaCl, 0.05% Tween 20 (pH 8.0) and incubated with a 1:5000 dilution of antirabbit horseradish peroxidase-conjugate (Santa Cruz Biotechnology, Santa Cruz, CA) for 1 h at room temperature (RT). After washing (3 x 5 min) in 10 mM Tris, 150 mM NaCl, 0.05% Tween 20 (pH 8.0), membranes were analyzed with enhanced chemiluminescence detection system. Primary antibodies were used as follows: IGFBP-3, 1:500 dilution of rabbit polyclonal antihuman IGFBP-3 (Santa Cruz Biotechnology) antibody for 2 h at RT; p53 and epidermal growth factor receptor (EGF-R), rabbit polyclonal antibodies (Santa Cruz Biotechnology) at a 1:400 dilution; IGF receptor (IGF-IR), rabbit polyclonal antibody against the C terminus of the ß-chain of the IGF-IR (Santa Cruz Biotechnology) at a dilution of 1:1,000; pAkt, rabbit polyclonal antibody phospho-AKT (Ser473) antibody (Cell Signaling, Beverly, MA) at a dilution of 1:1,000; dorsolateral proteins (DLP), rabbit polyclonal antibody against dorsolateral proteins (gift from Dr. G. Cunha, University of California, San Francisco, San Francisco, CA) at a dilution of 1:40,000. This antibody recognizes androgen-dependent dorsolateral prostate secretory products and is a marker of differentiated function of the rodent prostate (21).
Ligand blotting
For ligand blotting 20 µg protein samples (without dithiothreitol) were separated by SDS-PAGE on a 10% gel and transferred to the nitrocellulose membrane as mentioned above. After blocking with 5% nonfat milk, membranes were incubated in 10 mM Tris-HCl buffer (pH 7.4), 150 mM NaCl, 3% Nonidet P-40 containing 400,000 cpm 125I-IGF-I for 3 h at RT. After washing (3 x 15 min each) with the same buffer without radioligand, the membranes were exposed to MR film (Kodak, Rochester, NY) at –70 C.
Immunohistochemistry
Formalin-fixed, paraffin-embedded prostate tissue was assessed by immunohistochemistry for the expression of androgen receptor, DLP, Tag, or proliferating cell nuclear antigen (PCNA). Antigen retrieval on 4-µm sections was achieved by microwave treatment in either citrate buffer [0.01 M (pH 6.0)] or urea (1 M). Endogenous peroxidase was quenched using hydrogen peroxide (1% in PBS) for 30 min and blocked with normal goat serum. Primary antibodies were applied overnight at the following dilutions: rabbit anti-AR (5 µg/ml; Santa Cruz), rabbit anti-DLP (1:2500; kindly provided by G. Cunha), mouse anti-Tag (1:20; Oncogene Science, La Jolla, CA) or mouse anti-PCNA (2.5 µg/ml; Oncogene Science). After washes in PBS, secondary antibodies were applied: either goat antirabbit or goat antimouse (1:100) followed by either rabbit peroxidase-antiperoxidase or mouse clono-peroxidase-antiperoxidase (1:500; Sternberger Monoclonals Inc., Berkeley, CA). The peroxidase complex was detected with 3,3'-diaminobenzidine tetrahydrochloride. Sections were counterstained with hematoxylin.
Apoptosis
Apoptosis in comparable areas of high-grade PIN in prostate tumors from LPB-Tag/wild-type (Wt), LPB-Tag/PGKBP-3, LPB-Tag/CMVBP-3, and LPB-Tag/PGKmBP-3 mice was quantified using the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling assay (ApopTag peroxidase in situ apoptosis detection kit, Chemicon, Temecula, CA), at 9, 13, and 17 wk of age. Three to five sections from three or four mice per transgenic strain were analyzed. Approximately 360 cells per section, or approximately 4300 cells per Tg strain, were scored.
Statistical analysis
All data are expressed as the mean ± SEM. Statistical analysis was initially performed using an ANOVA and followed by the either Tukey honestly significant difference test, in which multiple comparisons were made between groups, or Dunnett’s t test in which comparisons were made between multiple groups and a single control group, using online statistical software (http://faculty.vassar.edu/lowry/VassarStats.html). Comparison was made between LPB-Tag/Wt mice and the other groups of mice for both the whole data set and data from each time point. Prostate weight was log transformed, and least squares regression analysis was used to determine the lines of best fit and their confidence limits. The statistical significance of the difference in the slope and intercept was then determined.
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Results |
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. There was no significant difference in prostate weights in Wt/Wt, CMVBP-3/Wt, and PGKBP-3/Wt mice. For the purpose of clarity, only a single curve is shown for Wt/Wt, CMVBP-3/Wt, and PGKBP-3/Wt mice in Fig. 1. Prostate tumorigenesis, as assessed by prostate weight, was markedly attenuated by overexpression of IGFBP-3 under either the CMV or PGK promoters (P < 0.001 by ANOVA). This attenuation was more marked in LPB-Tag/CMVBP-3 mice, compared with LPB-Tag/PGKBP-3 mice (P < 0.05). Once initiated, prostate tumors grew at a slightly slower rate in LPB-Tag/CMVBP-3 and LPB-Tag/PGKBP-3 mice than LPB-Tag/Wt mice (Fig. 1). Prostate tumor weight was log transformed, and least squares regression analysis was used to obtain the line of best fit for the relationship between prostate weight and time. The slope of this relationship was significantly less in LPB-Tag/CMVBP-3, compared with LPB-Tag/Wt mice (P < 0.001), and similar trend was apparent in LPB-Tag/PGKBP-3 mice (Table 1). In LPB-Tag/Wt mice, a prostate weight of 10 g was achieved at approximately 17 wk of age. This weight was achieved after a further delay of approximately 2.5 and approximately 5 wk in LPB-Tag/PGKBP-3 and LPB-Tag/CMVBP-3 mice, respectively. Although the PGKBP-3 and CMVBP-3 mice were approximately 10% smaller than Wt mice (19), differences in body weight did not account for the apparent reduction in prostate tumor growth. A significant reduction in relative weight of the prostate gland was still apparent when expressed as a percentage of total body weight. Examination of the different lobes of the prostate gland in various transgenic strains gave similar results to that seen when the whole prostate gland was considered (data not shown).
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). The same was true for IGF-I, which was significantly increased in CMVBP-3/Wt, PGKBP-3/Wt, and LPB-Tag/PGKBP-3 mice, compared with Wt/Wt control mice of similar age, reflecting the increased IGF-I binding capacity in the serum. We have previously shown that the presence of the transgene derived human IGFBP-3 has negligible effects on the abundance of murine IGFBP-3 or other IGFBPs in CMVBP-3, PGKBP-3, and LPB-Tag/PGKBP-3 mice (19, 20). However, transgene expression was markedly increased in prostate tissue from CMVBP-3/Wt, compared with PGKBP-3/Wt mice (Fig. 2B). The RNase protection assay is specific for the transgene and does not detect murine IGFBP-3 (20), hence the absence of signal in the lanes containing prostate RNA from Wt/Wt mice. The abundance of human (h)IGFBP-3 mRNA in prostate tissue from CMVBP-3/Wt mice was increased 5.6 ± 0.9-fold, compared with PGKBP-3/Wt mice (P < 0.001).
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). However, a marked reduction in tumor growth was observed in LPB-Tag/PGKmBP-3 mice after 15 wk of age, and at subsequent time points, there was no significant difference in prostate tumor size in LPB-Tag/PGKmBP-3 and double-transgenic mice expressing the intact IGFBP-3 driven by the same promoter. A total of 43 LPB-Tag/PGKmBP-3 mice were examined from three different PGKmBP-3 stud male mice. Because the different stud males contributed different numbers of offspring to each point, we investigated whether there was any difference in prostate weight in offspring of different stud males at 15 and 17 wk in which there was adequate representation of offspring from all three. When prostate weight for individual mice was expressed as a percentage of mean prostate weight for the whole group at each time point, there was no significant difference in prostate weight of the offspring of different PGKmBP-3 stud males.
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). Both intact hIGFBP-3 of approximately 40 kDa and a less abundant approximately 19 kDa IGFBP-3 proteolytic fragment, previously reported in other tissue extracts (22), were apparent. hIGFBP-3 was also detected, but less abundant, in prostate extracts from LPB-Tag/PGKBP-3 mice. As anticipated, no signal was observed in extracts from LPB-Tag/Wt or Wt/Wt mice. Weak immunoreactivity was apparent in lanes containing extracts from LPB-Tag/PGKmBP-3 mice (Figs. 4A and 5A). In extracts from these mice, the approximately 40-kDa hIGFBP-3 immunoreactivity was present as a smear and the approximately 19-kDa fragment was not seen, suggesting the possibility of extensive degradation of the non-IGF binding mutant IGFBP-3 consistent with our previous report (20).
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). No binding was observed in lanes containing prostate extract from LPB-Tag/PGKmBP-3 mice because this mutant IGFBP-3 does not bind IGF-I (20). Radioactivity was also not detected in lanes containing extracts from LPB-Tag/Wt and Wt/Wt mice, probably because of the low sensitivity of this technique in detecting endogenous murine IGFBPs in prostate tissue extracts under these conditions. The data shown in Fig. 4B are from prostate tissue obtained at 15 wk of age. To ensure that the LPB-Tag/PGKmBP-3 continued to carry a mutant IGFBP-3 at the later time points, we used Western ligand blotting to analyze samples collected at 21 wk of age. Similar results were obtained with these tissues (Fig. 4C). 125I-IGF-I binding was observed in lanes containing extracts from LPB-Tag/CMVBP-3 and LPB-Tag/PGKBP-3 mice but not in lanes with extracts from LPB-Tag/PGKmBP-3 mice. The difference in signal intensity between Fig. 4B and Fig. 4C results from differences in decay in radiolabel and autoradiography exposure time, and no meaningful conclusions can be drawn concerning the abundance of transgene expression at the two time points.
The presence of immunoreactive p53 was assessed in prostate tissue in various mouse strains at 15 wk of age. In LPB-Tag/Wt mice, the SV40 large Tag stabilizes p53, and p53 immunoreactivity was easily detected in prostate extracts from these mice (Fig. 5). A lower level of p53 protein was also detected in extracts from LPB-Tag/PGKmBP-3 mice. No p53 was apparent in lanes containing extracts from Wt/Wt, LPB-Tag/PGKBP-3 or LPB-Tag/CMVBP-3 mice. Expression of dorsolateral proteins, a marker of differentiated function (21), was lost in prostate tissue from LPB-Tag/Wt and LPB-Tag/PGKmBP-3 mice but relatively preserved in LPB-Tag/CMVBP-3 and LPB-Tag/PGKBP-3 mice (Fig. 5C).
Expression of both EGF-R and IGF-IR were up-regulated in the prostate tumors (Fig. 6). EGF-R was most abundant in LPB-Tag/Wt and LPB-Tag/PGKmBP-3 mice, and the lowest levels of expression were apparent in tissue from LPB-Tag/CMVBP-3 mice. In contrast, IGF-IR was significantly elevated in all transgenic mice carrying the LPB-Tag transgene, compared with Wt mice, and there was no significant difference between those expressing intact or mutant IGFBP-3. Despite increased levels of IGF-IR in LPB-Tag/CMVBP-3 and LPB-Tag/PGKBP-3 mice, the abundance of phospho pAkt(Ser 473) was reduced in these mice, compared with LPB-Tag/Wt and LPB-Tag/PGKmBP-3 mice (Fig. 6, lower panel), suggesting that signaling at the IGF-IR was attenuated in the double-transgenic mice expressing intact IGFBP-3.
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, upper panel). Tissue from LPB-Tag/CMVBP-3 at 9 wk was similar to that from LPB-Tag/PGKBP-3 mice (data not shown). At later time points, prostate tissue from LPB-Tag/CMVBP-3 and LPB-Tag/PGKBP-3 mice resembled early time points in LBP-Tag/Wt mice with high-grade PIN throughout the entire gland. In general, high-grade PIN was associated with loss of DLP staining, increased nuclear localization of androgen receptor staining, and positive staining for PCNA and Tag (Fig 7, lower panel). There was no obvious difference in immunostaining or histology between tissues from LPB-Tag/PGKBP-3 and LPB-Tag/PGKmBP-3 mice.
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). In LPB-Tag/Wt, LPB-Tag/PGKBP-3, and LPB-Tag/CMVBP-3 mice, the percentage of apoptotic cells was relatively constant from 9 through 17 wk. In contrast, in LPB-Tag/PGKmBP-3 mice, the percentage of apoptotic cells was low at 9 and 13 wk but increased significantly at 17 wk (Fig. 8).
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Discussion |
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In this manuscript, we report the attenuation of prostate tumor growth in mice that overexpress IGFBP-3. These experiments were performed by generating double-transgenic mice. Both the IGFBP-3 and the LPB-Tag mice were generated in the same CD1 strain, thereby eliminating the potential confounding effects of different genetic backgrounds. These observations represent the first demonstration of attenuated prostate tumor growth in vivo by IGFBP-3 overexpression.
The marked reduction of tumor growth seen in both LPB-Tag/PGKBP-3 and LPB-Tag/CMVBP-3 mice was predominantly due to paracrine/autocrine effects in the prostate rather than the result of systemic IGFBP-3 because the effect was more marked in LPB-Tag/CMVBP-3 mice that have higher levels of transgene expression in the prostate but similar levels of circulating IGFBP-3 to LPB-Tag/PGKBP-3 mice. Furthermore, attenuation of prostate tumorigenesis was apparent despite significantly increased levels of IGF-I in the circulation in both these strains of double-transgenic mice (19).
After 15 wk of age, the tumors in LPB-Tag/PGKBP-3 and LPB-Tag/CMVBP-3 grew rapidly, although at a slightly slower rate than that seen in LPB-Tag/Wt mice, suggesting that the predominant effect of overexpression of IGFBP-3 was at the early stages of tumor development. The mechanisms involved in tumor development in LPB-Tag mice are not fully understood, but tumor development is delayed until after sexual maturation in this model and is clearly androgen dependent (14). Both PGKBP-3 and CMVBP-3 male mice are fertile and testosterone levels are not markedly different in these mice and Wt mice (Ref.19 ; and Silha, J., and L. J. Murphy, unpublished observations). Although not studied in this LPB-Tag model, prostate cancer development is thought to be IGF-I dependent in the early stages, whereas the tumor progression may be less dependent on IGF-I as the disease progresses (23), possibly as a result of amplification of the IGF-IR and/or downstream signal transduction pathways (24). Our observations in LPB-Tag/PGKBP-3 and LPB-Tag/CMVBP-3 mice would be consistent with this notion. In these mice tumor development was delayed, but once well established, the tumor appeared to grow at a rate approaching that seen in LPB-Tag/Wt mice. Furthermore, prostate histology in LPB-Tag/PGKBP-3, LPB-Tag/CMVBP-3, and LPB-Tag/Wt mice appeared similar.
Not unexpectedly prostate tumor development and growth in LPB-Tag/PGKmBP-3 was similar to LPB-Tag/Wt mice during the first 15 wk. Because mutant IGFBP-3 does not bind IGF-I (20), it would be unable to inhibit IGF-I action during the critical early stages of prostate tumorigenesis. We have previously shown that PGKmBP-3 transgenic mice have low levels of human IGFBP-3 in the circulation (
0.5 µg/ml), compared with PGKBP-3 transgenic mice (5 µg/ml), despite identical transgene promoters and similar levels of tissue transgene mRNA (19, 20). We speculated that the mutant IGFBP-3 was more rapidly cleared from the circulation and degraded because mutant IGFBP-3 is unable to bind IGF-I, which appears to be necessary for the formation of stable ternary complexes with the acid-labile subunit (25). Western blotting of prostrate extracts confirmed that mutant IGFBP-3 was more degraded than native IGFBP-3. Human prostate tissue contains prostate-specific antigen that can proteolyze IGFBP-3 (26). It is likely that mouse prostate tissue contains similar kallikreins that can degrade IGFBP-3. Immunohistochemical analysis indicated that regions of the prostate demonstrating high-grade PIN had low levels of expression of dorsolateral proteins. We speculate that in these regions IGFBP-3 proteolysis may be reduced.
The unexpected finding in this report was the decline in tumor growth in LPB-Tag/PGKmBP-3 after 15 wk of age. Whereas this most likely represents an IGF-independent effect of IGFBP-3 similar to those reported by other investigators using in vitro cultures of prostate and breast cancer cells (5, 11, 17, 18, 22), it is unclear why these IGF-independent effects were not manifested earlier. We carefully excluded the possibility that this was artifactual by reviewing the parentage of each of the mice and also analyzing the tumor extracts from 21-wk-old mice by Western ligand blotting (Fig. 4). The LPB-Tag/PGKmBP-3 offspring used for the age 19- and 21-wk data points were from the same stud PGKmBP-3 male that contributed offspring to earlier time points, and thus, the data from the later time points are not the result of a specific stud male. Consistent with this apparent delayed effect of mutant IGFBP-3 expression, we demonstrate a significant increase in the percentage of apoptotic cells in the high-grade PIN lesion with time in LPB-Tag/PGKmBP-3 mice.
Under in vitro conditions, it is possible to demonstrate multiple and opposing effects of IGFBP-3 on cell proliferation and apoptosis. IGFBP-3 has IGF-dependent antiproliferative, proapoptotic effects related to binding IGF-I and restriction of access of IGF-I to the IGF-IR. Under certain conditions, IGF-dependent effects of enhancing cell survival and proliferation, possibly by enhancing delivery of IGF-I to the cell membrane receptor, can also be demonstrated with IGFBP-3 (27). In addition, as discussed above, IGFBP-3 has IGF-independent antiproliferative, proapoptotic effects actions that have been reported in vitro in the past. Various potential mechanisms have been proposed to explain these IGF-independent effects of IGFBP-3. These include the interaction of IGFBP-3 with various cell membrane-associated proteins such as the type V TGFß receptor (28) and autocrine motility factor (29) as well as other as-yet-unidentified proteins (30, 31). In addition, IGFBP-3 has been shown to interact with nuclear transcription factors such as the retinoid X receptor-
and stimulate apoptosis via this interaction (32).
This report represents the first demonstration of the IGF-independent antiproliferative effects of IGFBP-3 in vivo. IGF-independent effects of IGFBP-3 demonstrated in vitro are apparent only under conditions in which IGF-I is absent (5, 11, 16) or in cell lines that are not dependent on IGF-I for growth because they lack IGF-IR (3, 4). It is possible that the IGF-independent effects of IGFBP-3 are inhibited by IGF-I or not apparent in cells in which the IGF-I signal transduction pathway is activated. Thus, early in prostate tumorigenesis in LPB-Tag/PGKmBP-3 mice in which the tumors are growing in response to IGF-I, these IGF-independent effects of IGFBP-3 may be blocked or masked by IGF-I stimulated mitogenesis.
An alternative explanation for the apparent lack of effect of mutant IGFBP-3 during early prostate cancer growth in this model may be related to the enhanced degradation of mutant IGFBP-3 in prostate tissue. With the loss of markers of differentiation, such as dorsolateral protein as the tumors progress, there may also be a loss of IGFBP-3 protease activity and consequently enhanced levels of mutant IGFBP-3 that could exert a progressively more marked effect with increasing tumor mass. Lack of sufficient quantities of recombinant mutant IGFBP-3 precluded us from directly testing this hypothesis.
Whereas the exact mechanism whereby overexpression of mutant IGFBP-3 exerts its antiproliferative effect requires further investigation, our data clearly demonstrate that local overexpression of IGFBP-3 attenuates prostate tumorigenesis. Recently Majeed et al. (33) reported that development and progression of the transgenic adenocarcinoma of mouse prostate (TRAMP) model of prostate cancer is delayed in the lit/lit mouse, which has low IGF-I and GH levels as a result of an inactivating mutation in the GH releasing factor receptor. Their data suggest that IGF-I, GH, or both are important in prostate cancer development and progression. Wang et al. (34) used a slightly different model in which the GH receptor gene was disrupted to demonstrate the importance of GH/IGF-I signaling for prostate carcinogenesis in the C3(1)/T-antigen mice. Our observations, using a slightly different model of prostate cancer, support an important role of local IGF-I levels in prostate tumor progression. Furthermore, our data also suggest the use of IGFBP-3 and its mutant may be a useful therapeutic strategy in the treatment of prostate cancer.
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Footnotes |
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Present address for Y.G.: Center of Reproductive Medicine, Shenzhen Hospital of Peking University, Shenzhen 518036, People’s Republic of China.
The content of this manuscript does not necessarily reflect the position or the policy of the Government, and no official endorsement should be inferred. The paper is part of United States Provisional Patent US60/710,893, filed on August 25, 2005, "Methods of attenuating prostate tumour growth by insulin-like growth factor binding protein 3." Applicants were Josef V. Silha, Janice G. Dodd, and Liam J. Murphy. There is no commercial involvement in the research or the patent prosecution at this time. P.C.S., S.M., Y.G., and J.Sc. have nothing to declare.
First Published Online February 9, 2006
Abbreviations: CMVBP-3, LPB-Tag mice crossed with cytomegalovirus BP-3 mice; DLP, dorsolateral protein; EGF-R, epidermal growth factor receptor; h, human; IGFBP, IGF binding protein; IGF-IR, IGF receptor; LPB, long probasin promoter; PCNA, proliferating cell nuclear antigen; PGKBP-3, LPB-Tag mice crossed with phosphoglycerate kinase BP-3 mice; PGKmBP-3, I56G/L80G/L81G-mutant IGFBP-3; PIN, prostatic intraepithelial neoplasia; RT, room temperature; SV40, simian virus 40; Tag, T-antigen; Wt, wild type.
Received October 6, 2005.
Accepted for publication February 2, 2006.
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regulate transcriptional signaling and apoptosis. J Biol Chem 275:33607–33613This article has been cited by other articles:
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