Insulin-like growth factor binding protein 5 is associated with involution of the ventral prostate in castrated and finasteride-treated rats

Pappa2 deletion in mice affects male but not female fertility

BACKGROUND

Recent studies have found associations between the gene encoding pregnancy associated plasma protein-A2 (PAPP-A2), a protease of insulin-like growth factor binding protein -5 (IGFBP-5), and measures of female reproductive performance in cattle. The purpose of the present study was to test the effects of Pappa2 deletion on reproduction in mice.

FINDINGS

We measured the fertility and offspring growth of Pappa2 deletion females, and also performed reciprocal matings (i.e., deletion males mated to control females) to control for the effects of offspring genotype. Ovarian and testicular IGFBP-5 levels were measured by Western blotting. As expected, deletion of Pappa2 increased ovarian IGFBP-5 levels. However, Pappa2 deletion in females had no effect on the interval between pairing and the birth of the first litter, the interval between the births of the first and second litters, or litter size. Offspring weight was lower in the offspring of Pappa2 deletion females, but effects of similar magnitude were observed in the offspring of Pappa2 deletion males, suggesting that the effects were due to heterozygosity for the deletion in the offspring. Pappa2 deletion in males had no effect on litter size or the interval between pairing and the birth of the first litter. However, the interval between the births of the first and second litters was significantly longer in deletion males.

CONCLUSIONS

Pappa2 deletion had no effect on female reproductive performance. In contrast, Pappa2 deletion had subtle effects on male fertility, although the underlying mechanism remains to be elucidated.

Overexpression of insulin like growth factor binding protein 5 reduces liver fibrosis in chronic cholangiopathy

The ATP-binding cassette, sub-family B member 4 knock-out mouse (Abcb4(-/-)) is a relevant model for chronic cholangiopathy in man. Due to the lack of this P-glycoprotein in the canalicular membrane of hepatocytes, the secretion of phospholipids into bile is absent, resulting in increased bile toxicity. Expression of insulin like growth factor binding protein 5 (Igfbp5) increases in time in the livers of these mice. It is unclear whether this induction is a consequence of or plays a role in the progression of liver pathology. The aim of this study was therefore to investigate the effect of IGFBP5 induction on the progression of liver fibrosis caused by chronic cholangiopathy. IGFBP5 and, as a control, green fluorescent protein were overexpressed in the hepatocytes of Abcb4(-/-) mice, using an adeno-associated viral vector (AAV). Progression of liver fibrosis was studied 3, 6, and 12 weeks after vector injection by analyzing serum parameters, collagen deposition, expression of pro-fibrotic genes, inflammation and oxidative stress. A single administration of the AAV vectors provided prolonged expression of IGFBP5 and GFP in the livers of Abcb4(-/-) mice. Compared to GFP control, fractional liver weight, extracellular matrix deposition and amount of activated hepatic stellate cells significantly decreased in IGFBP5 overexpressing mice even 12 weeks after treatment. This effect was not due to a change in bile composition, but driven by reduced inflammation, oxidative stress, and proliferation. Overexpression of IGFBP5 seems to have a protective effect on liver pathology in this model for chronic cholangiopathy.

PPARγ: a molecular link between systemic metabolic disease and benign prostate hyperplasia

The emergent epidemic of metabolic syndrome and its complex list of sequelae mandate a more thorough understanding of benign prostatic hyperplasia and lower urinary tract symptoms (BPH/LUTS) in the context of systemic metabolic disease. Here we discuss the nature and origins of BPH, examine its role as a component of LUTS and review retrospective clinical studies that have drawn associations between BPH/LUTS and type II diabetes, inflammation and dyslipidemia. PPARγ signaling, which sits at the nexus of systemic metabolic disease and BPH/LUTS through its regulation of inflammation and insulin resistance, is proposed as a candidate for molecular manipulation in regard to BPH/LUTS. Finally, we introduce new cell and animal models that are being used to study the consequences of obesity, diabetes and inflammation on benign prostatic growth.

Insulin-like growth factor-binding protein-5 (IGFBP-5): a critical member of the IGF axis

The six members of the insulin-like growth factor-binding protein family (IGFBP-1-6) are important components of the IGF (insulin-like growth factor) axis. In this capacity, they serve to regulate the activity of both IGF-I and -II polypeptide growth factors. The IGFBPs are able to enhance or inhibit the activity of IGFs in a cell- and tissue-specific manner. One of these proteins, IGFBP-5, also has an important role in controlling cell survival, differentiation and apoptosis. In this review, we report on the structural and functional features of the protein which are important for these effects. We also examine the regulation of IGFBP-5 expression and comment on its potential role in tumour biology, with special reference to work with breast cancer cells.

Insulin-Like Growth Factor (IGF) family and prostate cancer

There is abundant in vitro, animal and epidemiologic evidence to suggest that the Insulin-Like Growth Factor (IGF) family is a multi-component network of molecules which is involved in the regulation of both physiological and pathological growth processes in prostate. The IGF family plays a key role in cellular metabolism, differentiation, proliferation, transformation and apoptosis, during normal development and malignant growth. This family also seem essential in prostate cancer bone metastases, angiogenesis and androgen-independent progression. Therapeutic alternatives in men with progressive prostate cancer after androgen ablation are very limited. More effective therapies are needed for these patients. Pharmacologic interventions targeting the IGF family are being devised. Such strategies include reduction of IGF-I levels (growth hormone-releasing hormone antagonists, somatostatin analogs), reduction of functional IGF-I receptor levels (antisense oligonucleotides, small interfering RNA), inhibition of IGF-IR and its signalling (monoclonal antibodies, small-molecule tyrosine kinase inhibitors) and Insulin-Like Growth Factor Binding Proteins.

Insulin-like growth factor binding proteins in development

IGFBPs regulate growth and development by regulating IGF transport to tissues and IGF bioavailability to IGF receptors at cell membrane level. IGFBP excess leads predominantly to inhibition of IGF action and growth retardation with impaired organogenesis. Absence of human and also mouse ALS leads to decreased IGF-I levels in circulation and causes mild growth retardation. Although IGFBP KO mice demonstrate relatively minor phenotypes, the possibility of compensatory mechanisms that mask the phenotypic manifestation of lack of individual binding proteins needs to be further investigated. Recent studies of hepatic regeneration in IGFBP-1 KO mice and also with mutant IGFBP-3 Tg mice provide some limited support for the existence of IGF-independent mechanism of action in vivo.

Insulin-like growth factor binding protein-5 (IGFBP-5) interacts with thrombospondin-1 to induce negative regulatory effects on IGF-I actions

Insulin-like growth factor binding protein-5 (IGFBP-5) and thrombospondin-1 (TS-1) are both present in extracellular matrix (ECM). Both proteins have been shown to bind to one another with high affinity. The purpose of these studies was to determine how the interaction between IGFBP-5 and TS-1 modulates IGF-I actions in porcine aortic smooth muscle cells (pSMC) in culture. The addition of increasing concentrations of TS-1 to pSMC cultures enhanced the protein synthesis and cell migration responses to IGF-I; whereas the addition of IGFBP-5 alone resulted in minimal changes. In contrast, the addition of IGFBP-5 to cultures that were also exposed to IGF-I and TS-1 resulted in inhibition of protein synthesis. When the cell migration response was assessed, the response to IGF-I plus TS-1 was also significantly inhibited by the addition of IGFBP-5, whereas 1.0 microg/ml of IGFBP-5 alone had no effect on the response to IGF-I. To determine the molecular mechanism by which this inhibition occurred, a mutant form of IGFBP-5 that does not bind to IGF-I was tested. This mutant was equipotent compared to native IGFBP-5 in its ability to inhibit both protein synthesis and cell migration responses to IGF-I plus TS-1 thus excluding the possibility that IGFBP-5 was inhibiting the response to TS-1 and IGF-I by inhibiting IGF-I binding to the IGF-I receptor. To determine if an interaction between TS-1 and IGFBP-5 was the primary determinant of the inhibitory effect of IGFBP-5, an IGFBP-5 mutant that bound poorly to TS-1 was utilized. The addition of 1.0 microg/ml of this mutant did not inhibit the protein synthesis or cell migration responses to IGF-I plus TS-1. To determine the mechanism by which IGFBP-5 binding to TS-1 inhibited cellular responses to TS-1 plus IGF-I, TS-1 binding to integrin associated protein (IAP) was assessed. The addition of IGFBP-5 (1.0 microg/ml) inhibited TS-1-IAP association. In contrast, a mutant form of IGFBP-5 that bound poorly to TS-1 had a minimal effect on TS-1 binding to IAP. Further analysis showed that IGFBP-5 addition altered the ability of TS-1 to modulate the SHPS-1/IAP interaction. When the IGFBP-5 mutant that did not bind to IGF-I was incubated with TS-1 and IGF-I, it inhibited the capacity of TS-1 to enhance the IGF-I receptor phosphorylation and MAP kinase activation in response to IGF-I. In contrast, the IGFBP-5 mutant that did not bind to TS-1 had no effect on IGF-I stimulated IGF-I receptor phosphorylation or MAP kinase activation. These results indicate that IGFBP-5 inhibits the binding of TS-1 to IAP, and this results in an alteration of the ability of TS-1 to modulate the disruption of the IAP/SHPS-1 interaction which leads to attenuation of the ability of TS-1 to enhance cellular responsiveness to IGF-I.

Effects of a non-IGF binding mutant of IGFBP-5 on cell death in human breast cancer cells

We have demonstrated previously that IGFBP-5 alone had no effect on cell death but modulated ceramide-induced apoptosis in Hs578T IGF non-responsive cells. To investigate if IGFBP-5 maintains its intrinsic ability to modulate apoptosis in IGF-responsive cells, we used a non-IGF binding mutant of IGFBP-5. In Hs578T cells, non-glycosylated, glycosylated or mutant IGFBP-5 alone each had no effect on cell death, whereas all forms inhibited ceramide-induced apoptosis. In IGF-responsive MCF-7 cells, each wild type form reduced ceramide-induced cell death but mutant IGFBP-5 was without effect. In the presence of mutant IGFBP-5, however, IGF-I no longer conferred survival and in the presence of wild type IGFBP-5, long R3 IGF-I was also unable to confer survival. In summary, all forms of IGFBP-5 modulated ceramide-induced apoptosis in Hs578T cells. In MCF-7 cells, IGF-I-induced survival could be facilitated by IGFBP-5, but also blocked by IGFBP-5 if association with IGFBP-5 was prevented.

Signalling pathways involved in the direct effects of IGFBP-5 on breast epithelial cell attachment and survival

We have demonstrated previously that IGFBP-5 can confer survival against apoptosis induced by ceramide, C2, or a small synthetic arginine-glycine-aspartic acid (RGD)-containing peptide in a direct manner. The endogenous ceramide-induced pathway is normally counter-balanced by survival signals mediated by sphingosine kinase (SK) and protein kinase C (PKC). In order to investigate whether these pathways are involved in the IGFBP-5 survival effect, we have used inhibitors of SK (N, N-di-methyl sphingosine, DMS) and PKC (chelerythrine chloride, CC). The effect of pre-incubating Hs578T breast cancer cells with IGFBP-5 on cell adhesion or on subsequent cell death induced by C2 or RGD was investigated with and without the presence of DMS or CC. Cell death was determined by trypan blue cell counts and apoptosis confirmed by morphological assessment and flow cytometry. Cell attachment was determined by a cell adhesion assay. The presence of IGFBP-5 significantly inhibited cell death induced by C2 or RGD, compared to the triggers of apoptosis alone (P<0.01 in both cases). In the presence of either IGFBP-5, CC or DMS, there was no significant effect on cell death compared to the control. IGFBP-5 in the presence of either inhibitor resulted in a significant increase in cell death; IGFBP-5 also lost its ability to confer survival on C2 and RGD-induced apoptosis and in contrast significantly increased cell death. In the cell adhesion assay, IGFBP-5 significantly increased cell attachment over basal levels. In the presence of either inhibitor the IGFBP-5 effect on cell adhesion was reversed and cell attachment was reduced to below basal levels. These data suggest that IGFBP-5 promotes the attachment and survival of Hs578T cells by modulating the balance between ceramide and opposing survival signals.

Genes upregulated during castration-induced rat prostatic apoptosis: cloning and characterization of new cDNAs

OBJECTIVE

To isolate new cDNAs corresponding to genes whose expression is increased during castration-induced rat prostate apoptosis.

MATERIALS AND METHODS

Differential display of mRNAs from 3-day castrated and normal rat ventral prostates was used to identify differentially expressed clones. Northern blots were hybridized to confirm the positive regulation of the candidates and to follow the change in their expression in the involuting rat prostate, and in thymocytes of dexamethazone-treated rats.

RESULTS

Five cDNAs were cloned: one encoding ribosomal protein L7, one coding for the insulin-like growth factor binding protein-3 (IGFBP-3), and three whose products are unknown. After castration, all five genes had expression kinetics that closely paralleled the proportion of prostatic epithelial cells undergoing apoptosis. The gene encoding L7 and two of the unknown genes were also upregulated in glucocorticoid-induced programmed death in thymocytes. In addition to the IGFBP-3 gene, those coding for proteins IGFBP-4, -5 and -6 were also overexpressed in the involuting prostate of androgen-deprived rats.

CONCLUSION

Five new genes were identified that are up-regulated during castration-induced rat prostate apoptosis, three of which are potentially involved in the common intracellular pathway leading to programmed cell death.

Overexpression of insulin-like growth factor binding protein-5 helps accelerate progression to androgen-independence in the human prostate LNCaP tumor model through activation of phosphatidylinositol 3'-kinase pathway

Although insulin-like growth factor (IGF) binding protein-5 (IGFBP-5) is highly up-regulated in normal and malignant prostate tissues after androgen withdrawal, its functional role in castration-induced apoptosis and androgen-independent progression remains undefined. To analyze the functional significance of IGFBP-5 overexpression in IGF-I-mediated mitogenesis and progression to androgen-independence, IGFBP-5-overexpressing human androgen-dependent LNCaP prostate cancer cells were generated by stable transfection. The growth rates of IGFBP-5-transfected LNCaP cells were significantly faster, compared with either the parental or vector-only transfected LNCaP cells in both the presence and absence ofdihydrotestosterone. IGFBP-5-induced increases in LNCaP cell proliferation occurs through both IGF-I-dependent and -independent pathways, with corresponding increases in the cyclin D1 messenger RNA expression and the fraction of cells in S + G2/M phases of the cell cycle. Changes in Akt/protein kinase B, a downstream component of phosphatidylinositol 3'-kinase (PI3K) pathway, in the LNCaP sublines also paralleled changes in their growth rates. Although treatment with a PI3K inhibitor induced apoptosis in both control and IGFBP-5-overexpressing LNCaP cells, this PI3K inhibitor-induced apoptosis was prevented by exogenous IGF-I treatment only in IGFBP-5 transfectants, suggesting that IGFBP-5 overexpression can potentiate the antiapoptotic effects of IGF-I. Furthermore, tumor growth and serum prostate-specific antigen levels increased several fold faster in mice bearing IGFBP-5-transfected LNCaP tumors after castration, despite having similar tumor incidence and tumor growth rates with controls when grown in intact mice before castration. Collectively, these data suggest that IGFBP-5 overexpression in prostate cancer cells after castration is an adaptive cell survival mechanism that helps potentiate the antiapoptotic and mitogenic effects of IGF-I, thereby accelerating progression to androgen independence through activation of the PI3K-Akt/ protein kinase B signaling pathway.

Tumor necrosis factor-alpha-induced apoptosis is associated with suppression of insulin-like growth factor binding protein-5 secretion in differentiating murine skeletal myoblasts

Wasting of muscle and fat during cachexia exceeds that explained by reduced food intake alone. This wasting may result from an imbalanced cytokine environment, which could lead to increased protein catabolism. Supporting this, tumor necrosis factor-alpha (TNF-alpha) is raised in several animal models of cachectic muscle wasting. Therefore, we assessed the effects of TNF-alpha and its second messenger, ceramide, on the proliferation, differentiation, and survival of murine C2 skeletal myoblasts. Because insulin-like growth factor binding protein-5 (IGFBP-5) and insulin-like growth factor-II (IGF-II) are potent regulators of myoblast proliferation and differentiation, we monitored the ability of exogenous TNF-alpha to manipulate this system. Fibroblast growth factor (FGF) ceramide, or TNF-alpha suppressed differentiation of C2 cells compared with controls. All treatments suppressed IGF-II production but only TNF-alpha blocked IGFBP-5 secretion. TNF-alpha increased apoptotic cell death, which otherwise remained basal (low serum differentiation medium (LSM), FGF) or low (ceramide). Suppression of both IGFBP-5 and IGF-II secretion may explain why of all triggers tested, only TNF-alpha not only blocked differentiation, but also promoted cell death. This suggests a fundamental role of IGFBP-5 for maintaining muscle survival. Supporting this hypothesis, no increase in apoptosis was seen in IGFBP-5 cDNA tranfected C2 cells after TNF-alpha treatment. In summary, the IGF system is essential for maintaining skeletal muscle cell survival and differentiation, and its suppression by TNF-alpha is fundamental regarding muscle wasting, and may be associated in vivo with cancer cachexia.

Prostatic involution in men taking finasteride is associated with elevated levels of insulin-like growth factor-binding proteins (IGFBPs)-2, -4, and -5

BACKGROUND

Insulin-like growth factor-binding proteins (IGFBPs)-2, -4, and -5 are associated with upregulation of apoptosis in the ovary. The purpose of this study was to assess the roles of IGF-I and IGFBPs during involution of the prostate. Frozen and fixed tissue was collected by transurethral prostatectomy from Caucasian men, aged 52-82 years, scheduled for prostatectomy for benign prostatic hyperplasia, who took either placebo (n = 7) or the 5alpha-reductase inhibitor finasteride for 6 days to 6 years (n = 15) prior to surgery.

METHODS

Intraprostatic androgen levels were measured by radioimmunoassay. Tissues were immunostained for IGF-I and IGFBP-2, -3, -4, and -5, and staining was quantitated by computerized image analysis. Serial sections were stained for markers of apoptosis (TUNEL and tissue transglutaminase) and IGFBP-2, -4, or -5.

RESULTS

IGF-I staining was significantly decreased in the medium-term (18-43 days) treatment group and remained so for the duration of the study (P = 0.026). IGFBP-3 staining was unchanged in the early and medium-term treatment groups; however, a transient earlier rise in the level of this proapoptotic protein cannot be ruled out. The percentage of epithelial cell area staining positively for IGFBP-2 increased significantly, from 1.6 +/- 0.5 in the placebo group to 12.0 +/- 2.0 (P < 0.0001), and 7.6 +/- 1.9 (P = 0.003) in the short (6-13 days) and medium-term treatment groups, respectively. IGFBP-4 staining increased from 2.2 +/- 0.6 to 9.8 +/- 1.9 (P < 0.0001) and 7.4 +/- 1.2 (P = 0.004) in the short and medium-term groups, respectively, and IGFBP-5 staining increased from 0.2 +/- 0.1 to 3.8 +/- 2.0 (P = 0.004) in the medium-term group. The results from serial sections showed that IGFBP-2 and -4 costained with markers of apoptosis, while IGFBP-5 did not.

CONCLUSIONS

These results indicate that IGFBP-2, -4, and -5 are associated with prostatic involution. Because of the timing and distribution of expression, we hypothesize that IGFBP-2 and -4 have a role as signals for apoptosis, but that IGFBP-5 likely does not.

The prostate: development and physiology

The development of the prostate is controlled by steroid hormones that in turn induce and maintain a complex and little understood cross talk between the various cell types making up the gland. The result of this intercellular communication can be either new growth or growth quiescence, depending upon the differentiation state of the cell type being stimulated. Secretory function of the prostate is dependent upon direct stimulation of fully differentiated prostatic epithelial cells by androgens. The prostate thus seems to be regulated in a similar manner to other organs of the male and female genital tract with proliferative control mediated by cell-cell interactions, whereas differentiated function is determined by direct steroid action on the parenchymal cells.

Bicalutamide (Casodex)-induced prostate regression involves increased expression of genes encoding insulin-like growth factor binding proteins

OBJECTIVES

To examine the effects of bicalutamide (Casodex), a pure antiandrogen with high specificity for the androgen receptor, on insulin-like growth factor binding protein (IGFBP) expression and apoptotic regression of the rat ventral prostate.

METHODS

Rats were treated daily with 10 mg/kg body weight bicalutamide or vehicle alone. Ventral prostates were collected at various days of treatment. Northern blot analysis was performed to quantitate expression of genes encoding IGFBPs, and the TUNEL method was used to determine the extent of apoptosis in ventral prostate.

RESULTS

In rats treated daily with bicalutamide, increases in mRNA levels of IGFBP-2, -3, -4, and -5 were detectable by Northern blotting by 6 hours and reached 6 to 10-fold of control levels after 5 days of treatment. The time-course of induction of apoptosis in the ventral prostate by bicalutamide, as detected in situ by the TUNEL method, corresponded to the time-course of induction of IGFBP expression.

CONCLUSIONS

We demonstrate that apoptotic regression of the ventral prostate during bicalutamide treatment is accompanied by increased expression of IGFBP-2, -3, -4, and -5. Rapid induction of IGFBPs, which can limit access of insulin-like growth factors (IGFs) to the IGF-I receptor, may play a role in the induction of apoptosis by antiandrogens, particularly in view of the increasing evidence that IGF-I inhibits apoptosis. These results document a previously unrecognized effect of antiandrogens and extend our previous studies relating IGF physiology to prostate biology. Together with evidence that a strong positive correlation exists between plasma IGF-I levels and prostate cancer risk, our data suggest that IGF physiology may play a key role in prostate cancer biology and is strongly influenced by androgen-targeting therapies.

Insulin-like growth factors and IGF-binding proteins in bovine seminal plasma

Insulin-like growth factor-I (IGF-I) is an important factor for germ cell development and maturation of spermatozoa. Actions of IGFs are modulated by IGF-binding proteins (IGFBPs) that may, depending on their concentration and site of expression, inhibit or enhance effects of IGF-I. We characterized IGFs and IGFBPs in seminal plasma from bulls routinely used for artificial insemination (AI) and from bulls producing poor-quality semen (low mass and individual motility of spermatozoa). IGFs were measured by specific radioimmunoassay in 22 samples of seminal plasma from nine different AI bulls with high (> 76.8%), average (72.8-73.4%), or low (< 69.5%) nonreturn rate (NRR). IGF-I and IGF-II levels were 144 +/- 9 ng/ml (mean +/- SE; range, 79-238 ng/ml) and 144 +/- 10 ng/ml (range, 55-221 ng/ml), respectively, and did not correlate with NRRs. IGF-I concentrations in seminal plasma from bulls producing poor-quality semen (n = 10) were significantly (P < 0.05) greater (194 +/- 26 ng/ml; range, 94-370 ng/ml), whereas IGF-II levels were significantly (P < 0.05) lower (93 +/- 17 ng/ml; range, 38-183 ng/ml) than in AI bulls. Ligand blot analysis of seminal plasma for IGFBPs revealed the presence of a 38-/45-kDa doublet band and a 30-kDa IGFBP. These IGFBPs were identified as IGFBP-3 and IGFBP-5, respectively, by immunoprecipitation using specific antibodies. In addition, a low amount of IGFBP-4 was detected in bovine seminal plasma by immunoprecipitation. There was a marked difference in the activity of IGFBPs between individual bulls, with a relatively small within-bull variance. The differences in IGFBP activities did not correlate with the fertilization capacity of the bulls in vivo or in vitro nor with immunoreactive IGF-I and IGF-II levels in seminal plasma. Our results demonstrate the presence of IGFBPs in bovine seminal plasma. In contrast to human seminal plasma, high activity of IGFBP-3 was detected in seminal plasma of some bulls, suggesting species-specific regulation of IGFBP activity by proteases.