IGF-binding proteins.

Insulin-like growth factor-binding proteins (IGFBPs) 1-6 bind IGFs but not insulin with high affinity. They were initially identified as serum carriers and passive inhibitors of IGF actions. However, subsequent studies showed that, although IGFBPs inhibit IGF actions in many circumstances, they may also potentiate these actions. IGFBPs are widely expressed in most tissues, and they are flexible endocrine and autocrine/paracrine regulators of IGF activity, which is essential for this important physiological system. More recently, individual IGFBPs have been shown to have IGF-independent actions. Mechanisms underlying these actions include (i) interaction with non-IGF proteins in compartments including the extracellular space and matrix, the cell surface and intracellular space, (ii) interaction with and modulation of other growth factor pathways including EGF, TGF-ß and VEGF, and (iii) direct or indirect transcriptional effects following nuclear entry of IGFBPs. Through these IGF-dependent and IGF-independent actions, IGFBPs modulate essential cellular processes including proliferation, survival, migration, senescence, autophagy and angiogenesis. They have been implicated in a range of disorders including malignant, metabolic, neurological and immune diseases. A more complete understanding of their cellular roles may lead to the development of novel IGFBP-based therapeutic opportunities.

Scaling of the mean and variance of population dynamics under fluctuating regimes.

Theoretical ecologists have long sought to understand how the persistence of populations depends on the interactions between exogenous (biotic and abiotic) and endogenous (e.g., demographic and genetic) drivers of population dynamics. Recent work focuses on the autocorrelation structure of environmental perturbations and its effects on the persistence of populations. Accurate estimation of extinction times and especially determination of the mechanisms affecting extinction times is important for biodiversity conservation. Here we examine the interaction between environmental fluctuations and the scaling effect of the mean population size with its variance. We investigate how interactions between environmental and demographic stochasticity can affect the mean time to extinction, change optimal patch size dynamics, and how it can alter the often-assumed linear relationship between the census size and the effective population size. The importance of the correlation between environmental and demographic variation depends on the relative importance of the two types of variation. We found the correlation to be important when the two types of variation were approximately equal; however, the importance of the correlation diminishes as one source of variation dominates. The implications of these findings are discussed from a conservation and eco-evolutionary point of view.

Diabetes is a major risk factor for mortality after lung transplantation.

Survival following lung transplant (LTx) remains significantly lower than after other solid organ transplants. Diabetes mellitus (DM) is a mortality risk factor not comprehensively studied in LTx recipients. Notably, neither the relation of time of DM onset to survival nor the actual causes of DM-associated excess mortality have been described. We determined DM status, DM diagnosis date and all-cause mortality in 386 consecutive adults who underwent LTx at our institution from January 1, 2001 to July 31, 2010. The relationship of DM to survival both as a categorical and time-dependent variable was studied. Fifty-three percent of patients had DM. Overall median survival was 5.2 (95% CI 3.8-6.6) years. At study end, 52% of patients had died, of whom 64% had DM. Estimated median survival was 10 years in patients without DM, 5.0 (3.3-6.8) years in patients with DM pre- and post-LTx and 4.3 (3.1-5.5) years in patients with new onset DM. As a time-dependent covariate, DM was the strongest risk factor for mortality, hazard ratio 3.96 (2.85-5.51). Bronchiolitis obliterans syndrome was the main cause of death in all patients surviving >90 days, but its incidence was not increased in patients with DM. Further studies are warranted to determine whether improved glycemic control could improve outcomes in LTx recipients.

Stereotactic radiosurgery for treatment of Cushing disease: an Australian experience.

Stereotactic radiation therapy has emerged as an alternative to conventional radiotherapy for treatment of Cushing disease. The aim of this study was to investigate the efficacy and safety of this treatment. Records of patients with Cushing disease treated with stereotactic radiation were reviewed. Seventeen patients underwent stereotactic radiosurgery. Ten achieved remission after a mean of 23 (95% confidence interval, 15-31) months, and two developed hormone deficiencies.

Advanced glycation end-products (AGEs) and functionality of reverse cholesterol transport in patients with type 2 diabetes and in mouse models.

AIMS/HYPOTHESIS: We investigated the contribution of AGEs to the impairment of reverse cholesterol transport (RCT) variables in diabetic individuals and in two animal models of diabetic obesity and of renal impairment. METHODS: The capacity of plasma and HDL from 26 individuals with moderately controlled type 2 diabetes to support cholesterol efflux was compared with 26 age- and sex-matched individuals without diabetes. We also compared the rates of RCT in vivo in two animal models: db/db mice and mice with chronic renal failure. RESULTS: Diabetic individuals had characteristic dyslipidaemia and higher levels of plasma AGEs. The capacity of whole plasma, ApoB-depleted plasma and isolated HDL to support cholesterol efflux was greater for diabetic patients compared with controls despite their lower HDL-cholesterol levels. The capacity of plasma to support cholesterol efflux correlated with plasma levels of cholesteryl ester transfer protein and levels of ApoB, but not with levels of AGE. RCT was severely impaired in db/db mice despite elevated HDL-cholesterol levels and no change in AGE concentration, whereas RCT in uraemic mice was unaffected despite elevated AGE levels. CONCLUSIONS/INTERPRETATION: AGEs are unlikely to contribute significantly to the impairment of RCT in type 2 diabetes.

Environmental fluctuations and level of density-compensation strongly affects the probability of fixation and fixation times.

The probability of, and time to, fixation of a mutation in a population has traditionally been studied by the classic Wright-Fisher model where population size is constant. Recent theoretical expansions have covered fluctuating populations in various ways but have not incorporated models of how the environment fluctuates in combination with different levels of density-compensation affecting fecundity. We tested the hypothesis that the probability of, and time to, fixation of neutral, advantageous and deleterious mutations is dependent on how the environment fluctuates over time, and on the level of density-compensation. We found that fixation probabilities and times were dependent on the pattern of autocorrelation of carrying capacity over time and interacted with density-compensation. The pattern found was most pronounced at small population sizes. The patterns differed greatly depending on whether the mutation was neutral, advantageous, or disadvantageous. The results indicate that the degree of mismatch between carrying capacity and population size is a key factor, rather than population size per se, and that effective population sizes can be very low also when the census population size is far above the carrying capacity. This study highlights the need for explicit population dynamic models and models for environmental fluctuations for the understanding of the dynamics of genes in populations.

Population viability analysis on domestic horse breeds (Equus caballus).

In this study, we performed a population viability analysis on 3 domestic horse breeds (Equus caballus) of Danish origin, namely, the Frederiksborg, the Knabstrupper, and the Jutland breeds. Because of their small population sizes, these breeds are considered endangered. The Vortex software simulation package was used for the population viability analysis. First, we investigated the future viability of these breeds based on present demographic and environmental parameters. Second, a sensitivity analysis revealed the most important variables for the viability of these breeds. Third, we examined management scenarios in which one of the studbooks was closed. According to the Vortex analysis, 2 of the breeds (Knabstrupper and Jutland) will persist for the next 200 yr, whereas the smaller breed (Frederiksborg) could become extinct within 40 yr. The sensitivity analyses indicated that the variables concerning reproduction of the mares had the greatest impact, with the number of mares actively breeding being the most influential on the population forecasts. The results suggest that closing the Knabstrupper studbooks can be done only if increasing the number of mares actively breeding counteracts the loss of genetic variation attributable to such a management strategy. It is recommended, based on these results, that the number of Frederiksborg and Knabstrupper mares actively breeding must be increased to approximately 30% in the 2 breeds that are presently using only 13%, while leaving the third (Frederiksborg ) at its present 30% level. Monitoring of the breeds in the future, however, may be exploited to adjust the breeding strategies. We suggest that the large amount of data required by Vortex makes it very useful for analyzing domestic animals because of the comprehensive data material often available. The results of this analysis accord with other studies on the Prezwalski horse, indicating robustness in the parameter sensitivity for horses.

Recombinant human thyroid-stimulating hormone (Thyrogen) in thyroid cancer follow up: experience at a single institution.

BACKGROUND: Recombinant human thyroid-stimulating hormone (Thyrogen; Genzyme Corporation, Cambridge, MA, USA) (rhTSH)-stimulated serum thyroglobulin (Tg) (stim-Tg) and (131)I whole-body scanning (WBS) have been reported to allow follow up of patients with thyroid cancer without the symptoms of thyroxine withdrawal and with equivalent diagnostic information to that obtained after thyroxine withdrawal. The aim of the study was to report results of rhTSH use at the Alfred Hospital, Melbourne, from 1999 to 2006 and in particular to examine the significance of detectable serum Tg after rhTSH in relation to thyroid cancer staging and to compare the sensitivity of rhTSH-stimulated serum Tg to whole-body (131)I scanning (WBS) in the detection of residual and recurrent thyroid cancer. METHODS: The study was a retrospective chart review. RESULTS: In 90 patients, rhTSH was used for 96 diagnostic episodes and 18 doses of rhTSH were used to facilitate treatment with (131)I. In stages I and II cancer (n = 42), of three patients with stim-Tg 1-2 microg/L, none had identifiable disease, and the three patients who had stim-Tg >2 microg/L did not experience recurrent disease during follow up. In contrast, in stages III and IV cancer (n = 43) 2 of 5 with stim-Tg 1-2 microg/L had identifiable disease and 7 of 10 with stim-Tg >2 microg/L had identifiable disease. In Tg-positive, WBS-negative disease, further imaging identified persistent/recurrent disease. CONCLUSION: rhTSH was effective and safe in the management of thyroid cancer follow up for diagnosis of persistent/recurrent cancer and to enable (131)I treatment. In no case did rhTSH-stimulated WBS identify the presence of disease not also identified by raised basal Tg or stim-Tg. Therefore, in low risk cancer WBS may be omitted.

The evolution of n-player cooperation-threshold games and ESS bifurcations.

An evolutionary game of individuals cooperating to obtain a collective benefit is here modelled as an n-player Prisoner's Dilemma game. With reference to biological situations, such as group foraging, we introduce a threshold condition in the number of cooperators required to obtain the collective benefit. In the simplest version, a three-player game, complex behaviour appears as the replicator dynamics exhibits a catastrophic event separating a parameter region allowing for coexistence of cooperators and defectors and a region of pure defection. Cooperation emerges through an ESS bifurcation, and cooperators only thrive beyond a critical point in cost-benefit space. Moreover, a repelling fixed point of the dynamics acts as a barrier to the introduction of cooperation in defecting populations. The results illustrate the qualitative difference between two-player games and multiple player games and thus the limitations to the generality of conclusions from two-player games. We present a procedure to find the evolutionarily stable strategies in any n-player game with cost and benefit depending on the number of cooperators. This was previously done by Motro [1991. Co-operation and defection: playing the field and the ESS. J. Theor. Biol. 151, 145-154] in the special cases of convex and concave benefit functions and constant cost.

Insulin-like growth factor binding protein-2 binding to extracellular matrix plays a critical role in neuroblastoma cell proliferation, migration, and invasion.

IGF binding proteins (IGFBPs) modulate IGF cellular bioavailability and may directly regulate tumor growth and invasion. We have previously shown that IGFBP-2 binds and localizes IGF-I to the pericellular matrix and have provided some evidence suggesting that the heparin binding domain (HBD) or the arginine-glycine-aspartic acid (RGD) integrin binding motif may be involved in these interactions. However, the precise mechanisms involved remain to be elucidated. We therefore mutated the HBD or RGD sequence of IGFBP-2 and investigated consequent effects on extracellular matrix (ECM) binding, IGF-induced proliferation, and migration of neuroblastoma cells. IGFBP-2 and its arginine-glycine-glutamic acid (RGE) mutant similarly bound ECM components, whereas binding of mutant HBD-IGFBP-2 to each of the ECM substrates was markedly reduced by 70-80% (P < 0.05). IGF-I (100 ng/ml) increased incorporation of 3H-thymidine in neuroblastoma SK-N-SHEP cells by approximately 30%, an effect blunted by exogenously added native or either mutant IGFBP-2. Overexpression of IGFBP-2 and its RGE mutant potently promoted SHEP cell proliferation (5-fold), whereas SHEP cell proliferation was negligible when HBD-IGFBP-2 was overexpressed. Addition or overexpression of IGFBP-2 and its RGE mutant potently (P < 0.05) enhanced SHEP cell migration/invasion through the ECM. However, overexpression of the HBD-IGFBP-2 mutant potently inhibited (50-60%) SHEP cell invasion through ECM. Thus, IGFBP-2, which binds to the ECM, enhances proliferation and metastatic behavior of neuroblastoma cells, functions that directly or indirectly use the HBD but not the integrin binding sequence. Our novel findings thus point to a key role for the HBD of IGFBP-2 in the control and regulation of neuroblastoma growth and invasion.

Fibroblast growth factor-2 over-rides insulin-like growth factor-I induced proliferation and cell survival in human neuroblastoma cells.

The insulin-like growth factor (IGF) system is a key regulator of cell growth, survival and differentiation, and these functions are co-modulated by other growth factors including fibroblast growth factor-2 (FGF-2). To investigate IGF/FGF interactions in neuronal cells, we employed neuroblastoma cells (SK-N-MC). In serum free conditions proliferation of the SK-N-MC cells was promoted by IGF-I (25 ng/ml), but blunted by FGF-2 (50 ng/ml). IGF-I-induced proliferation was abolished in the presence of FGF-2 even when IGF-I was used at 100 ng/ml. In addition to our previously described FGF-2 induced proteolytic cleavage of IGFBP-2, we found that FGF-2 increased IGFBP-6 levels in conditioned medium (CM) without affecting IGFBP-6 mRNA abundance. Modulation of IGFBP-2 and -6 levels were not significant mechanisms involved in the blockade of IGF-I action since the potent IGF-I analogues [QAYL]IGF-I and des(1-3)IGF-I (minimal IGFBP affinity) were unable to overcome FGF-2 inhibition of cell proliferation. FGF-2 treated cells showed morphological differentiation expressing the TUJ1 neuronal marker while cells treated with IGF-I alone showed no morphological change. When IGF-I was combined with FGF-2, however, cell morphology was indistinguishable from that seen with FGF-2 alone. FGF-2 inhibited proliferation and enhanced differentiation was also associated with a 70% increase in cell death. Although IGF-I alone was potently anti-apoptotic (60% decreased), IGF-I was unable to prevent apoptosis when administrated in combination with FGF-2. Gene-array analysis confirmed FGF-2 activation of the intrinsic and extrinsic apoptotic pathways and blockade of IGF anti-apoptotic signaling. FGF-2, directly and indirectly, overcomes the proliferative and anti-apoptotic activity of IGF-I by complex mechanisms, including enhancement of differentiation and apoptotic pathways, and inhibition of IGF-I induced anti-apoptotic signalling. Modulation of IGF binding protein abundance by FGF-2 does not play a significant role in inhibition of IGF-I induced mitogenesis.

Single and serial measurements of cardiac troponin I in asymptomatic patients on chronic hemodialysis.

AIMS: Coronary artery disease is the major cause of death in patients with end-stage renal failure on dialysis. This study aimed to assess the predictive value of a single cardiac troponin I (cTnI), and also the kinetics of serial values. METHODS: Since cTnI is a potential biomarker of cardiac outcome, the present study examined single cTnI measurements (n = 88 patients) and its predictive value for future cardiac events, and a kinetic substudy of serial weekly cTnI measured for 8 weeks (n = 57) in a group of patients on hemodialysis. RESULTS: Single cTnI measurements: 9 patients (10.2%) had a detectable cTnI at baseline and 79 patients (89.8%) had a negative baseline cTnI. There were no significant differences in age, sex, history of ischemic heart disease, diabetes, smoking or dyslipidemia between patients with detectable and negative cTnI. At the end of 9 months, the rate of combined primary endpoints, which included myocardial infarction, cardiac death and cardiac revascularization, was significantly higher in the patients with a detectable baseline cTnI (55.6%), compared to patients with a negative cTnI (6.3%) (p = 0.0007). Serial weekly cTnI measurements: significant fluctuations in cTnI were noted over time; 27% of patients with an undetectable cTnI measured at baseline had subsequent detectable levels in the serial follow-up. CONCLUSION: A single detectable cTnI in asymptomatic patients on hemodialysis defines patients at high risk of future cardiac events. However, the incidence of detectable cTnI levels is markedly increased when serial weekly measurements are performed. The clinical significance of detectable serial measurements of cTnI is the focus of ongoing studies.

Insulin-like growth factor binding protein-6 and CCI-779, an ester analogue of rapamycin, additively inhibit rhabdomyosarcoma growth.

Rhabdomyosarcomas secrete high levels of insulin-like growth factor-II, suggesting this autocrine growth factor plays a major role in the unregulated growth of this childhood cancer. Treatment of Rh30 rhabdomyosarcoma cells with insulin-like growth factor binding protein-6 (IGFBP-6; 1000 ng/ml), which binds insulin-like growth factor-II with high affinity, inhibited growth in vitro (p < 0.001). Co-incubation of cells with rapamycin (1.56 ng/ml), an inhibitor of p70 S6 kinase, and IGFBP-6 (200 ng/ml) resulted in a significant reduction in Rh30 cell number compared to rapamycin or IGFBP-6 alone (p < 0.05 for both). Co-treatment of Rh30 cells with CCI-779 (5 and 50 ng/ml), an ester analogue of rapamycin, and IGFBP-6 (200 or 1000 ng/ml) also inhibited growth in vitro relative to CCI-779 alone (p < 0.01 and p < 0.001, respectively). In a nude mouse model, xenografts of Rh30 cells transfected with a recombinant vector encoding IGFBP-6 (phBP6-E3) showed delayed growth relative to vector control xenografts (27 days vs. 19 days to reach an average tumour volume of 0.5 cm (3); p < 0.001). Treatment with CCI-779 (10 mg/kg) of mice inoculated with vector control xenografts, also delayed growth (to 31 days; p = 0.0055) relative to untreated mice with vector control xenografts. Co-treatment with CCI-779 (10 mg/kg) reduced phBP6-E3 transfected xenograft growth even further (to 45 days) compared to vector control xenografts (p < 0.001, day 33). CCI-779 thus acts additively with IGFBP-6 to reduce rhabdomyosarcoma growth both in vitro and in vivo.

Insulin-like growth factors decrease catecholamine content in PC12 rat pheochromocytoma cells.

Insulin-like growth factors (IGFs) stimulate proliferation and differentiation of PC12 rat pheochromocytoma cells and modulate catecholamine release in bovine adrenal medullary cells. Dexamethasone increases catecholamine synthesis in PC12 cells. We therefore studied the effects of IGFs and dexamethasone on catecholamine content in PC12 cells. Dopamine (DA) and norepinephrine (NE) content of PC12 cells were measured after incubation for 72 h with IGFs (100 ng/ml) and/or dexamethasone (500 nM). IGF-I (100 ng/ml) and IGF-II (100 ng/ml) decreased DA and NE content to approximately 35% and approximately 25% of control, respectively. [Leu27]IGF-II, which binds to the IGF-I receptor with markedly decreased affinity, did not reduce catecholamine levels, indicating that the effect is likely to be mediated by the IGF-I receptor. Dexamethasone (500 nM) increased levels of DA and NE to 173 +/- 20% and 331 +/- 48% of controls, respectively. Coincubation with IGFs did not significantly affect the stimulation of DA by dexamethasone, but abolished the rise in NE. Levels of tyrosine hydroxylase mRNA, protein and activity were increased following incubation with dexamethasone, but were unchanged by IGFs. These results indicate that IGFs decrease catecholamine content in PC12 cells via the IGF-I receptor. Complex regulation involving multiple synthetic and/or degradative steps is implicated in this process.

Diabetic ketoacidosis secondary to dento-alveolar infection.

Diabetic ketoacidosis (DKA) is a medical emergency with a potentially fatal outcome if not recognized and treated appropriately. Infective processes are a common precipitant of DKA. We report two cases of dentoalveolar infections in patients with type I diabetes mellitus who presented with DKA. The management of such cases requires both specialist surgical and medical intervention.

Overexpression of insulin-like growth factor binding protein-6 inhibits rhabdomyosarcoma growth in vivo.

Rhabdomyosarcoma is the most common soft-tissue sarcoma of childhood. Rhabdomyosarcoma cell lines overexpress insulin-like growth factor-II (IGF-II), an autocrine growth factor that is inhibited by insulin-like growth factor binding protein-6 (IGFBP-6). IGFBP-6 is associated with myoblast quiescence, and expression in rhabdomyosarcoma cells is low. The effect of IGFBP-6 on 2 rhabdomyosarcoma cell lines, RD and Rh30, was studied. IGFBP-6 inhibited anchorage-dependent growth of RD and Rh30 cells in a dose-dependent manner (p < 0.0001). IGFBP-6 also inhibited anchorage-independent growth of RD cells in soft agar in a dose-dependent manner (p < 0.01). Anchorage-independent growth of RD cells on polyhydroxyethylmethacrylate-coated plates was decreased to a minimum of 48% of control after treatment with IGFBP-6 (p < 0.001). In this system, IGFBP-6 increased apoptosis 4-fold (p < 0.001). IGF-II partially reversed the IGFBP-6-induced decrease in growth and increase in apoptosis. Rh30 cells were stably transfected with an IGFBP-6 cDNA and subcutaneous xenografts established in BALB/c nude mice. After 18 days, sizes of 2 independent clones of IGFBP-6-overexpressing Rh30 cells were reduced to 12% and 26% of vector control-transfected tumors (p = 0.0006 and 0.002, respectively). IGFBP-6 therefore inhibits proliferation and promotes apoptosis of rhabdomyosarcoma in vitro and dramatically inhibits xenograft growth in vivo, at least in part by inhibiting IGF-II. Low expression of IGFBP-6 may therefore contribute to rhabdomyosarcoma growth and metastasis.

Advanced glycation end products cause epithelial-myofibroblast transdifferentiation via the receptor for advanced glycation end products (RAGE).

Tubulointerstitial disease, a prominent phenomenon in diabetic nephropathy, correlates with decline in renal function. The underlying pathogenic link between chronic hyperglycemia and the development of tubulointerstitial injury has not been fully elucidated, but myofibroblast formation represents a key step in the development of tubulointerstitial fibrosis. RAGE, the receptor for advanced glycation end products (AGEs), induces the expression of TGF-beta and other cytokines that are proposed to mediate the transdifferentiation of epithelial cells to form myofibroblasts. Here we report specific binding of (125)I-AGE-BSA to cell membranes prepared from a rat proximal tubule cell line and show that the binding site was RAGE. AGE exposure induced dose-dependent epithelial-myofibroblast transdifferentiation determined by morphological changes, de novo alpha smooth-muscle actin expression, and loss of epithelial E-cadherin staining. These effects could be blocked with neutralizing Ab's to RAGE or to TGF-beta. Transdifferentiation was also apparent in the proximal tubules of diabetic rats and in a renal biopsy from a patient with type 1 diabetes. The AGE cross-link breaker, phenyl-4,5-dimethylthiazolium bromide (ALT 711) reduced transdifferentiation in diabetic rats in association with reduced tubular AGE and TGF-beta expression. This study provides a novel mechanism to explain the development of tubulointerstitial disease in diabetic nephropathy and provides a new treatment target.

An evolutionary-game model of tumour-cell interactions: possible relevance to gene therapy.

Evolutionary games have been applied as simple mathematical models of populations where interactions between individuals control the dynamics. Recently, it has been proposed to use this type of model to describe the evolution of tumour cell populations with interactions between cells. We extent the analysis to allow for synergistic effects between cells. A mathematical model of a tumour cell population is presented in which population-level synergy is assumed to originate through the interaction of triplets of cells. A threshold of two cooperating cells is assumed to be required to produce a proliferative advantage. The mathematical behaviour of this model is explored. Even this simple synergism (minor clustering effect) is sufficient to generate qualitatively different cell-population dynamics from the models published previously. The most notable feature of the model is the existence of an unstable internal equilibrium separating two stable equilibria. Thus, cells of a malignant phenotype can exist in a stable polymorphism, but may be driven to extinction by relatively modest perturbations of their relative frequency. The proposed model has some features that may be of interest to biological interpretations of gene therapy. Two prototypical strategies for gene therapy are suggested, both of them leading to extinction of the malignant phenotype: one approach would be to reduce the relative proportion of the cooperating malignant cell type below a certain critical value. Another approach would be to increase the critical threshold value without reducing the relative frequency of cells of the malignant phenotype.

Insulin-like growth factor-II renders LIM 2405 human colon cancer cells resistant to butyrate-induced apoptosis: a potential mechanism for colon cancer cell survival in vivo.

Butyrate has potent anti-tumorigenic effects on many colon cancer cell lines, including inhibition of growth and promotion of apoptosis in vitro. Nevertheless, despite the butyrate concentration in the colonic lumen being sufficient to result in the death of almost all cells in vitro, colon cancers still develop and grow in vivo, suggesting that cancer cells must develop mechanisms by which they escape the effects of butyrate observed in vitro. Insulin-like growth factor-II (IGF-II) is an autocrine growth factor in many colon cancer cells. The aim of this study was to determine whether IGF-II influences butyrate-mediated apoptosis in LIM 2405 human colon cancer cells. Butyrate and trichostatin A, both of which are histone deacetylase inhibitors although the latter is more specific, induced apoptosis as determined by floating cell counting, Hoechst 33258 staining, DNA laddering and a cell death detection ELISA. IGF-II inhibited the effects of both agents. Butyrate but not trichostatin A also induced LIM 2405 cell migration. In contrast to the above results, IGF-II enhanced butyrate-induced cell migration. Levels of IGF binding protein-3 (IGFBP-3), which may induce apoptosis by IGF-dependent or -independent mechanisms, were increased by butyrate and trichostatin A; IGF-II augmented this effect. It is therefore unlikely that IGFBP-3 mediates butyrate-induced apoptosis. We suggest that IGF-II inhibits the pro-apoptotic effect of butyrate downstream of histone deacetylase inhibition. In contrast, IGF-II promotes histone deacetylase-dependent IGFBP-3 expression and histone deacetylase-independent migration. IGF-II may promote tumour growth by mediating the development of resistance to the pro-apoptotic effects of butyrate.

Insulin-like growth factor (IGF)-binding protein-6 inhibits IGF-II-induced but not basal proliferation and adhesion of LIM 1215 colon cancer cells.

IGF-II is an autocrine growth factor for many colon cancer cells. This study aimed to determine the role of IGF-II in proliferation and adhesion of LIM 1215 colon cancer cells. RT-PCR demonstrated expression of IGF-I and IGF-II mRNA. Addition of IGF-I or -II increased monolayer proliferation in a dose-dependent manner. Although addition of IGFBP-6 had no effect on basal proliferation, coincubation of IGFBP-6 decreased IGF-II but not IGF-I-induced proliferation. Colony formation in agar was increased by IGF-II, an effect inhibited by coincubation with IGFBP-6. IGFBP-6 alone significantly decreased colony formation. Preincubation of cells with IGF-II increased adhesion to type IV collagen, fibronectin and laminin. IGFBP-6 had no effect on basal cell adhesion but completely inhibited the effects of IGF-II. LIM 1215 colon cancer cells are therefore IGF-responsive but IGF-II is not a major autocrine factor for these cells in monolayer, suggesting heterogeneity between colon carcinoma cell lines with respect to the role of the IGF system.