Intrinsic, Pro-Apoptotic Effects of IGFBP-3 on Breast Cancer Cells are Reversible: Involvement of PKA, Rho, and Ceramide

Roles of IGFBP-3 in cell migration and growth in an endophytic tongue squamous cell carcinoma cell line

Insulin-like growth factor binding protein-3 (IGFBP-3) is a member of the IGFBP family that has high affinity for IGFs and functions as either an oncogene or tumor suppressor in various types of cancer. We previously found that IGFBP3 mRNA levels are higher in endophytic-type human tongue squamous cell carcinoma (TSCC) that is more invasive and more prone to metastasis than exophytic and superficial types. This finding prompted us to investigate the roles of IGFBP-3 in TSCC using SAS cells, which were originally derived from endophytic-type TSCC. Specifically, we used SAS cells that express a fluorescent ubiquitination-based cell-cycle indicator (Fucci). RNA-sequencing analysis indicated that IGFBP-3 is associated with cell migration and cell growth. In fact, IGFBP-3 knockdown downregulates cell migration and causes cells to arrest in G₁. This migratory potential appears to be cell cycle–independent. IGFBP-3 knockdown also reduced levels of secreted IGFBP-3; however, decreased migratory potential was not rescued by exogenous recombinant human IGFBP-3. Furthermore, ERK activity was downregulated by IGFBP-3 depletion, which suggests that MEK/ERK signaling may be involved in IGFBP-3-mediated cell migration. We therefore conclude that intracellular IGFBP-3 enhances cell migration independently of the cell cycle in TSCC with a higher metastatic potential.

Interaction between GRP78 and IGFBP-3 Affects Tumourigenesis and Prognosis in Breast Cancer Patients

Insulin-like growth factor binding protein 3 (IGFBP-3) plays a key role in breast cancer progression and was recently shown to bind to the chaperone protein glucose-regulated protein 78 (GRP78); however, the clinical significance of this association remains poorly investigated. Here we report a direct correlation between the expression of GRP78 and IGFBP-3 in breast cancer cell lines and tumour sections. Kaplan-Meier survival plots revealed that patients with low GRP78 expression that are positive for IGFBP-3 had poorer survival rates than those with low IGFBP-3 levels, and we observed a similar trend in the publicly available METABRIC gene expression database. With breast cancer cells, in vitro IGFBP-3 enhanced induced apoptosis, however when GRP78 expression was silenced the actions of IGFBP-3 were switched from increasing to inhibiting ceramide (C2)-induced cell death and promoted cell invasion. Using immunofluorescence and cell surface biotinylation, we showed that knock-down of GRP78 negated the entry of IGFBP-3 into the cells. Together, our clinical and experimental results suggest that loss of GRP78 reduces IGFBP-3 entry into cells switching its actions to promote tumorigenesis and predicts a poor prognosis in breast cancer patients.

Insulin-Like Growth Factor Binding Protein-3 (IGFBP-3): Unraveling the Role in Mediating IGF-Independent Effects Within the Cell

Insulin-like growth factor (IGF) binding protein-3 (IGFBP-3), one of the six members of the IGFBP family, is a key protein in the IGF pathway. IGFBP-3 can function in an IGF-dependent as well as in an IGF-independent manner. The IGF-dependent roles of IGFBP-3 include its endocrine role in the delivery of IGFs from the site of synthesis to the target cells that possess IGF receptors and the activation of associated downstream signaling. IGF-independent role of IGFBP-3 include its interactions with the proteins of the extracellular matrix and the proteins of the plasma membrane, its translocation through the plasma membrane into the cytoplasm and into the nucleus. The C-terminal domain of IGFBP-3 has the ability to undergo cell penetration therefore, generating a short 8-22-mer C-terminal domain peptides that can be conjugated to drugs or genes for effective intracellular delivery. This has opened doors for biotechnological applications of the molecule in molecular medicine. The aim of this this review is to summarize the complex roles of IGFBP-3 within the cell, including its mechanisms of cellular uptake and its translocation into the nucleus, various molecules with which it is capable of interacting, and its ability to regulate IGF-independent cell growth, survival and apoptosis. This would pave way into understanding the modus operandi of IGFBP-3 in regulating IGF-independent processes and its pleiotropic ability to bind with potential partners thus regulating several cellular functions implicated in metabolic diseases, including cancer.

Insulin-like growth factor-1, insulin-like growth factor-binding protein-3, and breast cancer risk: observational and Mendelian randomization analyses with ∼430 000 women

BACKGROUND

Epidemiological evidence supports a positive association between circulating insulin-like growth factor-1 (IGF-1) concentrations and breast cancer risk, but both the magnitude and causality of this relationship are uncertain. We conducted observational analyses with adjustment for regression dilution bias, and Mendelian randomization (MR) analyses allowed for causal inference.

PATIENTS AND METHODS

We investigated the associations between circulating IGF-1 concentrations and incident breast cancer risk in 206 263 women in the UK Biobank. Multivariable hazard ratios (HRs) and 95% confidence intervals (CI) were estimated using Cox proportional hazards models. HRs were corrected for regression dilution using repeat IGF-1 measures available in a subsample of 6711 women. For the MR analyses, genetic variants associated with circulating IGF-1 and IGF-binding protein-3 (IGFBP-3) levels were identified and their association with breast cancer was examined with two-sample MR methods using genome-wide data from 122 977 cases and 105 974 controls.

RESULTS

In the UK Biobank, after a median follow-up of 7.1 years, 4360 incident breast cancer cases occurred. In the multivariable-adjusted models corrected for regression dilution, higher IGF-1 concentrations were associated with a greater risk of breast cancer (HR per 5 nmol/l increment of IGF-1 = 1.11, 95% CI = 1.07-1.16). Similar positive associations were found by follow-up time, menopausal status, body mass index, and other risk factors. In the MR analyses, a 5 nmol/l increment in genetically-predicted IGF-1 concentration was associated with a greater breast cancer risk (odds ratio = 1.05, 95% CI = 1.01-1.10; P = 0.02), with a similar effect estimate for estrogen-positive (ER+) tumours, but no effect found for estrogen-negative (ER-) tumours. Genetically-predicted IGFBP-3 concentrations were not associated with breast cancer risk (odds ratio per 1-standard deviation increment = 1.00, 95% CI = 0.97-1.04; P = 0.98).

CONCLUSION

Our results support a probable causal relationship between circulating IGF-1 concentrations and breast cancer, suggesting that interventions targeting the IGF pathway may be beneficial in preventing breast tumorigenesis.

The insulin-like growth factor family and breast cancer prognosis: A prospective cohort study among postmenopausal women in Denmark

OBJECTIVE

Circulating levels of insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) have been associated with breast cancer (BC) risk. The evidence in relation to BC prognosis is limited. We aimed to evaluate the association between pre-diagnostic serum levels of IGF-I, IGF-II, IGFBP-2, IGFBP-3 and BC prognosis (i.e. recurrence, BC specific mortality and all-cause mortality) among women diagnosed with BC. We hypothesized that higher serum levels of IGFs and IGFBPs were associated with poor BC prognosis and that the associations were modified by estrogen receptor (ER) status.

DESIGN

From the Danish Diet, Cancer and Health cohort, 412 postmenopausal women diagnosed with incident BC within 5 years of cohort baseline (1993-1997) were identified. Baseline serum samples were analyzed for IGF-I, IGF-II, IGFBP-2 and IGFBP-3. Follow-up was carried out through 2014 by linkage to national Danish registries. Exposures were related to BC prognosis by Cox Proportional Hazard models; effect modification by ER status was investigated and sensitivity analyses by follow-up time were made.

RESULTS

During a median of 15 years, 106 women experienced recurrence and 172 died (118 due to BC). Overall, no associations were observed between IGF-I, IGF-II, IGFBP-2, IGFBP-3 and BC prognosis and no effect modification by ER status was observed. However, higher levels of IGF-II were associated with higher BC specific mortality [Hazard Ratio (HR) (95% Confidence Intervals (CI)): 1.43 (1.01-2.04)] within 10 years of follow-up. Likewise, higher levels of IGFBP-2 were associated with higher BC specific mortality [HR (95% CI): 1.87 (1.19-2.94)] within 5 years of follow-up. In contrast, higher levels of IGFBP-3 were associated with lower risk of recurrence [HR (95% CI): 0.76 (0.60-0.97)] at 5 years of follow-up and BC specific mortality [HR (95% CI): 0.80 (0.65-0.98)] within 10 years of follow-up.

CONCLUSIONS

The present study did not support an association between higher serum levels of IGFs, IGFBPs and adverse BC prognosis. However, it is possible that the role of the IGF family in the etiology of the 5-10 year BC prognosis is different from that of longer-term BC prognosis.

Involvement of insulin-like growth factor binding protein-3 in peroxisome proliferator-activated receptor gamma-mediated inhibition of breast cancer cell growth

We have previously reported that insulin-like growth factor binding protein-3 (IGFBP-3), a protein with dichotomous effects on both cell proliferation and cell survival, interacts with peroxisome proliferator-activated receptor gamma (PPARγ) and inhibits adipogenic PPARγ signaling. We now show that IGFBP-3 and PPARγ interact in breast cancer cells, through amino- and carboxyl-terminal residues of IGFBP-3. IGFBP-3 and the PPARγ ligands, rosiglitazone or 15-deoxy-Δ(12,14)-prostaglandin J2, separately inhibited the proliferation of MCF-7, MDA-MB-231 and MDA-MB-468 breast cancer cells. However, growth inhibition by IGFBP-3 and PPARγ ligand combined was greater than by either alone. Two IGFBP-3 mutants with reduced PPARγ binding caused no growth inhibition when used alone and abolished the inhibitory effect of rosiglitazone when used in combination with PPARγ ligand. Cell growth inhibition by PPARγ ligands was substantially blocked by IGFBP-3 siRNA and restored by exogenous IGFBP-3. We conclude that the interaction between IGFBP-3 and PPARγ is important for the growth-inhibitory effect of PPARγ ligands in human breast cancer cells, suggesting that IGFBP-3 expression by breast tumors may regulate their sensitivity toward PPARγ ligands.

IGFBP-3: a cell fate pivot in cancer and disease

One of the hallmarks in the advancement of cancer cells is an ability to overcome and acquire resistance to adverse conditions. There has been a large amount of cancer research on IGFBP-3 as a pro-apoptotic molecule in vitro. These pro-apoptotic properties, however, do not correlate with several studies linking high IGFBP-3 levels in breast cancer tissue to rapid growth and poor prognosis. Evidence is emerging that IGFBP-3 also exhibits pro-survival and growth-promoting properties in vitro. How IGFBP-3 pivots cell fate to either death or survival, it seems, comes down to a complex interplay between cells' microenvironments and the presence of cellular IGFBP-3 binding partners and growth factor receptors. The cytoprotective actions of IGFBP-3 are not restricted to cancer but are also observed in other disease states, such as retinopathy and brain ischaemia. Here we review the literature on this paradoxical nature of IGFBP-3, its pro-apoptotic and growth-inhibitory actions versus its cytoprotective and growth-potentiating properties, and discuss the implications of targeting IGFBP-3 for treatment of disease.

IGFBP-3 inhibits TNF-α production and TNFR-2 signaling to protect against retinal endothelial cell apoptosis

In models of diabetic retinopathy, insulin-like growth factor binding protein-3 (IGFBP-3) protects against tumor necrosis factors-alpha (TNF-α)-mediated apoptosis of retinal microvascular endothelial cells (REC), but the underlying mechanisms are unclear. Our current findings suggest that at least two discrete but complimentary pathways contribute to the protective effects of IGFBP-3; 1) IGFBP-3 directly activates the c-Jun kinase/tissue inhibitor of metalloproteinase-3/TNF-α converting enzyme (c-Jun/TIMP-3/TACE), pathway, which in turn inhibits TNF-α production; 2) IGFBP-3 acts through the IGFBP-3 receptor, low-density lipoprotein receptor-related protein 1 (LRP1), to inhibit signaling of TNF-α receptor 2 (TNFR2). Combined, these two IGFBP-3 pathways substantially reduce REC apoptosis and offer potential targets for the treatment of diabetic retinopathy.

IGF binding proteins in cancer: mechanistic and clinical insights

The six members of the family of insulin-like growth factor (IGF) binding proteins (IGFBPs) were originally characterized as passive reservoirs of circulating IGFs, but they are now understood to have many actions beyond their endocrine role in IGF transport. IGFBPs also function in the pericellular and intracellular compartments to regulate cell growth and survival - they interact with many proteins, in addition to their canonical ligands IGF-I and IGF-II. Intranuclear roles of IGFBPs in transcriptional regulation, induction of apoptosis and DNA damage repair point to their intimate involvement in tumour development, progression and resistance to treatment. Tissue or circulating IGFBPs might also be useful as prognostic biomarkers.

Insulin-like growth factor binding protein-3 (IGFBP-3): Novel ligands mediate unexpected functions

In addition to its important role in the regulation of somatic growth by acting as the major circulating transport protein for the insulin-like growth factors (IGFs), IGF binding protein-3 (IGFBP-3) has a variety of intracellular ligands that point to its function within major signaling pathways. The discovery of its interaction with the retinoid X receptor has led to the elucidation of roles in regulating the function of several nuclear hormone receptors including retinoic acid receptor-α, Nur77 and vitamin D receptor. Its interaction with the nuclear hormone receptor peroxisome proliferator-activated receptor-γ is believed to be involved in regulating adipocyte differentiation, which is also modulated by IGFBP-3 through an interaction with TGFβ/Smad signaling. IGFBP-3 can induce apoptosis alone or in conjunction with other agents, and in different systems can activate caspases -8 and -9. At least two unrelated proteins (LRP1 and TMEM219) have been designated as receptors for IGFBP-3, the latter with a demonstrated role in inducing caspase-8-dependent apoptosis. In contrast, IGFBP-3 also has demonstrated roles in survival-related functions, including the repair of DNA double-strand breaks through interaction with the epidermal growth factor receptor and DNA-dependent protein kinase, and the induction of autophagy through interaction with GRP78. The ability of IGFBP-3 to modulate the balance between pro-apoptotic and pro-survival sphingolipids by regulating sphingosine kinase 1 and sphingomyelinases may be integral to its role at the crossroads between cell death and survival in response to a variety of stimuli. The pleiotropic nature of IGFBP-3 activity supports the idea that IGFBP-3 itself, or pathways with which it interacts, should be investigated as targets of therapy for a variety of diseases.