Regulation of prostate cell growth by the insulin-like growth factor binding proteins and their proteases

IGFBPs mediate IGF-1's functions in retinal lamination and photoreceptor development during pluripotent stem cell differentiation to retinal organoids

Development of the retina is regulated by growth factors, such as insulin-like growth factors 1 and 2 (IGF-1/2), which coordinate proliferation, differentiation, and maturation of the neuroepithelial precursors cells. In the circulation, IGF-1/2 are transported by the insulin growth factor binding proteins (IGFBPs) family members. IGFBPs can impact positively and negatively on IGF-1, by making it available or sequestering IGF-1 to or from its receptor. In this study, we investigated the expression of IGFBPs and their role in the generation of human retinal organoids from human pluripotent stem cells, showing a dynamic expression pattern suggestive of different IGFBPs being used in a stage-specific manner to mediate IGF-1 functions. Our data show that IGF-1 addition to culture media facilitated the generation of retinal organoids displaying the typical laminated structure and photoreceptor maturation. The organoids cultured in the absence of IGF-1, lacked the typical laminated structure at the early stages of differentiation and contained significantly less photoreceptors and more retinal ganglion cells at the later stages of differentiation, confirming the positive effects of IGF-1 on retinal lamination and photoreceptor development. The organoids cultured with the IGFBP inhibitor (NBI-31772) and IGF-1 showed lack of retinal lamination at the early stages of differentiation, an increased propensity to generate horizontal cells at mid-stages of differentiation and reduced photoreceptor development at the later stages of differentiation. Together these data suggest that IGFBPs enable IGF-1's role in retinal lamination and photoreceptor development in a stage-specific manner.

Concentrations of IGF-I and IGFBP-3 and pancreatic cancer risk in the European Prospective Investigation into Cancer and Nutrition

Background:

Insulin-like growth factors (IGFs) and their binding proteins (BPs) regulate cell differentiation, proliferation and apoptosis, and may have a role in the aetiology of various cancers. Information on their role in pancreatic cancer is limited and was examined here in a case–control study nested within the European Prospective Investigation into Cancer and Nutrition.

Methods:

Serum concentrations of IGF-I and IGFBP-3 were measured using enzyme-linked immunosorbent assays in 422 cases and 422 controls matched on age, sex, study centre, recruitment date, and time since last meal. Conditional logistic regression was used to compute odds ratios (OR) and 95% confidence intervals (CI) adjusted for confounding variables.

Results:

Neither circulating levels of IGF-I (OR=1.21, 95% CI 0.75–1.93 for top vs bottom quartile, P-trend 0.301), IGFBP-3 (OR=1.00, 95% CI 0.66–1.51, P-trend 0.79), nor the molar IGF-I/IGFBP-3 ratio, an indicator of free IGF-I level (OR=1.22, 95% CI 0.75–1.97, P-trend 0.27), were statistically significantly associated with the risk of pancreatic cancer. In a cross-classification, however, a high concentration of IGF-I with concurrently low levels of IGFBP-3 was related to an increased risk of pancreatic cancer (OR=1.72, 95% CI 1.05–2.83; P-interaction=0.154).

Conclusion:

On the basis of these results, circulating levels of components of the IGF axis do not appear to be the risk factors for pancreatic cancer. However, on the basis of the results of a subanalysis, it cannot be excluded that a relatively large amount of IGF-1 together with very low levels of IGFBP-3 might still be associated with an increase in pancreatic cancer risk.

Inhibition of growth and increased expression of insulin-like growth factor-binding protein-3 (IGFBP-3) and -6 in prostate cancer cells stably transfected with antisense IGFBP-4 complementary deoxyribonucleic acid

Insulin-like growth factor-binding proteins (IGFBPs) both stimulate and inhibit IGF activity, and in the M12 prostate cancer cell line, overexpression of IGFBP-4 was shown to delay tumorigenesis while decreasing the production of IGFBP-2. We have performed the reverse experiment, inhibition of IGFBP-4 expression with antisense complementary DNA, in two prostate tumor cell lines, ALVA-31 and M12. Expression of antisense messenger RNA transcripts was verified by RNase protection assays, and inhibition of mature IGFBP-4 in cell medium was demonstrated by Western blotting. Both transfected lines (ALVA-31asBP4 and M12asBP4) proliferated more slowly in monolayer culture than parental controls. Colony formation in soft agar was strongly inhibited in both cases, and the rate of tumor formation and growth in male athymic nude mice injected with M12asBP4 was markedly reduced relative to that in mice receiving M12 control cells. Apoptosis induced by the topoisomerase inhibitor etoposide was also enhanced in transfected cells. The effects on colony formation in soft agar and tumor formation in mice were maintained for the duration of the experiments, in contrast to the delayed growth observed in the previous study of IGFBP-4 overexpression. A significant difference was found in the patterns of IGFBP expression; production of both messenger RNA and protein for IGFBP-3 and IGFBP-6 was greatly increased in the M12asBP4 and ALVA31asBP4 cell lines. Up-regulation of these binding proteins has been observed in association with actions of 1,25-dihydroxyvitamin D(3) in prostate cancer cells, and the data suggest a role for IGFBP-3 and IGFBP-6 in the suppression of prostate tumor cell growth.

Other novel agents: Rationale and current status as chemopreventive agents

Several novel targets are currently being evaluated both preclinically and clinically for the prevention of prostate cancer. Four divergent and novel approaches were discussed at the National Cancer Institute-sponsored workshop entitled, "New Clinical Strategies in Prostate Cancer Prevention." These interventions are further categorized into soy protein-based serine-protease inhibitors that reduce superoxide-induced DNA damage, and molecularly targeted approaches that are directed toward endothelin-1 expression/overexpression, peroxisome proliferator-activated receptor ligands, and insulinlike growth factors. Understanding each of these approaches has offered insights into the process of malignant transformation of prostatic epithelium, and further illustrates the difficulties of developing new agents in the treatment and prevention of prostate cancer. Close scrutiny of the clinical data emerging with these approaches, including validation of biologic endpoints, is required before large-scale prevention studies with these novel agents and targets can be considered.

Does the GH-IGF axis play a role in cancer pathogenesis?

Recent case-controlled studies have found increases in the serum levels of insulin-like growth factor-I (IGF-I) in subjects who had, or who eventually developed, prostate or premenopausal breast cancers. Since growth hormone (GH) increases IGF-I levels, concern has been raised regarding its potential role as a cancer initiation factor. The epidemiological studies, which indicate an association between serum IGF-I levels and cancer risk, have not established causality. In fact, several alternative explanations for the elevated serum IGF-I levels in cancer patients may be proposed based on human and animal models. First, an effect of IGF-I causing symptomatic benign tissue hyperplasia may result in an ascertainment bias leading to an initiation of procedures resulting in the diagnosis of asymptomatic cancers. Second, elevated serum IGF-I in cancer patients may originate within the tumor (as suggested by some animal studies). Thirdly, serum IGF-I may actually be a surrogate marker of tissue IGF-I levels or of nutritional factors, which are not under GH control and may be involved in cancer initiation. The role of GH in cancer initiation is further negated by the fact that in acromegaly, the incidence of cancer, other than possibly colonic neoplasia does not appear to be significantly increased. Furthermore, GH transgenic mice, with high IGF-I levels, do not develop breast, prostate, or colonic malignancies. It is known that IGFBP-3 can inhibit IGF action on cancer cells in vitro and also can induce apoptosis via an IGF-independent mechanism. Importantly, in addition to increasing IGF-I levels, GH also increases the serum levels of IGFBP-3 and serum IGFBP-3 levels have been shown to be negatively correlated with the risk of cancer in the above mentioned epidemiological studies and in a similar study on colon cancer. These studies suggest that cancer risk is increased in individuals in whom both high IGF-I levels and low IGFBP-3 levels are present. In subjects treated with GH, IGF-I and IGFBP-3 levels both rise together and are not within the elevated cancer-risk range, based on published studies. Long-term studies are needed to assess the potential risks, including the long-term cancer risk associated with GH therapy. These should take into account several factors, including the duration of exposure, the risk magnitude associated with the degree of serum IGF-I elevation, and the adjusted risk based on a concomitant increase in IGFBP-3 levels. Since GH treated patients often have sub-normal IGF-I serum levels, which normalize on therapy, one might predict that their cancer risk on GH therapy should not increase above the normal population. Until further research in the area dictates otherwise, on-going cancer surveillance and routine monitoring of serum IGF-I and IGFBP-3 levels in GH-recipients should be the standard of care. At present, the data that are available do not warrant a change in our current management of approved indications for GH therapy.

Hormone therapy failure in human prostate cancer: analysis by complementary DNA and tissue microarrays

BACKGROUND

The molecular mechanisms underlying the progression of prostate cancer during hormonal therapy have remained poorly understood. In this study, we developed a new strategy for the identification of differentially expressed genes in hormone-refractory human prostate cancer by use of a combination of complementary DNA (cDNA) and tissue microarray technologies.

METHODS

Differences in gene expression between hormone-refractory CWR22R prostate cancer xenografts (human prostate cancer transplanted into nude mice) and a xenograft of the parental, hormone-sensitive CWR22 strain were analyzed by use of cDNA microarray technology. To validate the data from cDNA microarrays on clinical prostate cancer specimens, a tissue microarray of specimens from 26 prostates with benign prostatic hyperplasia, 208 primary prostate cancers, and 30 hormone-refractory local recurrences was constructed and used for immunohistochemical detection of protein expression.

RESULTS

Among 5184 genes surveyed with cDNA microarray technology, expression of 37 (0.7%) was increased more than twofold in the hormone-refractory CWR22R xenografts compared with the CWR22 xenograft; expression of 135 (2.6%) genes was reduced by more than 50%. The genes encoding insulin-like growth factor-binding protein 2 (IGFBP2) and 27-kd heat-shock protein (HSP27) were among the most consistently overexpressed genes in the CWR22R tumors. Immunohistochemical analysis of tissue microarrays demonstrated high expression of IGFBP2 protein in 100% of the hormone-refractory clinical tumors, in 36% of the primary tumors, and in 0% of the benign prostatic specimens (two-sided P =.0001). Overexpression of HSP27 protein was demonstrated in 31% of the hormone-refractory tumors, in 5% of the primary tumors, and in 0% of the benign prostatic specimens (two-sided P =.0001).

CONCLUSIONS

The combination of cDNA and tissue microarray technologies enables rapid identification of genes associated with progression of prostate cancer to the hormone-refractory state and may facilitate analysis of the role of the encoded gene products in the pathogenesis of human prostate cancer.

Novel aspects of the insulin-like growth factor binding proteins

The insulin-like growth factors (IGFs), IGF binding proteins (IGFBPs), and IGFBP proteases regulate somatic growth and cellular proliferation both in vivo and in vitro. IGFs are potent mitogens whose actions are determined by the availability of free IGFs to interact with IGF receptors. IGFBPs comprise a family of six proteins that bind IGFs with high affinity and specificity and thereby regulate IGF-dependent actions. IGFBPs have also recently emerged as IGF-independent regulators of cell growth. Several IGFBP association proteins have been discovered recently which can affect IGFBP action. Cleavage of IGFBPs by specific proteases modulates levels of free IGFs and IGFBPs and thereby their actions. IGFBP-related proteins (IGFBP-rPs) are an emerging group of proteins which bind IGFs with low affinity and also play important roles in cell growth and differentiation. The IGFBPs appear to have emerging roles in the mechanisms underlying human cancer. The GH-IGF-IGFBP axis is complex and powerful. Future research on its physiology promises exciting insights into cell biology as well as advancements in the treatment of a wide range of disease states including cancer, diabetes, vascular disease, asthma, and growth disorders.

Serum Insulin-like Growth Factors and Insulin-like Growth Factor-binding Proteins: Clinical Implications

The last decade has been characterized by a major investigative thrust into the physiology of two unique but ubiquitous peptides, insulin-like growth factor (IGF)-I and IGF-II. The regulatory systems that control the tissue bioactivity of the IGFs have been delineated, and subcellular signaling mechanisms have been clarified. Clearly, both tissue and circulating growth factor concentrations are important in defining the relationship between IGF-I and cell activity. Bone, liver, and circulatory IGF-I have received the most attention by investigators, in part because of the ease of measurement and the interaction with disease states such as osteoporosis. More recently, attention has focused on the role IGF-I plays in neoplastic transformation and growth. Two large prospective observational studies have demonstrated greater risk for prostate and breast cancer associated with high circulating concentrations of IGF-I. Animal models and in vitro studies confirm that there is a close, albeit complex, interaction between IGF-I signaling and bone turnover. This report will focus on: (a) IGF physiology, including IGF ligands, binding proteins, and proteases; (b) the relationship between IGF-I and bone mass in respect to risk for osteoporosis; (c) the heritable regulation of the IGF-I phenotype; and (d) the association between serum IGF-I and cancer risk. The IGFs remain a major area for basic and clinical investigations; future studies may define both diagnostic and therapeutic roles for these peptides or their related proteins in several disease states.

Circulating IGF-I: New Perspectives for a New Century

Insulin-like growth factor I (IGF-I) is a ubiquitous endocrine, paracrine and autocrine polypeptide, which influences cell proliferation and differentiation in many tissues. Classically, IGF-I has been tied to growth hormone (GH) and has often been considered a surrogate marker of overall GH status. The advent of recombinant technology has made possible studies of GH and IGF-I for the treatment of chronic diseases (such as diabetes mellitus, osteoporosis and muscle atrophy) as well as to forestall the aging process. Examples of currently active areas of research include efforts to define the involvement of IGF-I physiology in bone remodeling, atherosclerosis and neoplasia. Recent epidemiological evidence suggests that individuals with IGF-I levels in the 'high normal' range have increased risk of common cancers relative to individuals with levels in the 'low normal' range. These findings have focused renewed attention on the genetic and non-genetic determinants of serum IGF-I levels. It is unlikely that the serum IGF-I level itself is related directly to risk of neoplasia, but it may serve as a surrogate for a variable that is important in epithelial cell carcinogenesis, such as rate of epithelial cell proliferation. We review relatively new data suggesting that adult serum IGF-I levels are under the control of heritable factors apart from GH. Such factors may influence tissue expression of IGF-I as well as serum IGF-I levels, and influence a number of clinically important outcomes, including bone density and risk of neoplasia. The concept that there is little physiological importance in the heterogeneity between individuals regarding IGF-I levels within the broad 'normal' range may require re-assessment.