Insulin-like growth factor binding protein-6 activates programmed cell death in non-small cell lung cancer cells

Molecular cloning and expression profiling of insulin-like growth factor 2 and IGF-binding protein 6 in Clarias magur (Hamilton 1822)

Growth is an important trait in aquaculture and the major genes that regulate it are Insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs). In this study, the full-length coding sequences of IGF2 and IGFBP6 genes in the Indian catfish Clarias magur were cloned and characterized. The full-length cDNA sequences of IGF2 and IGFBP6 were 885 bp (ORF 642 bp) and 928 bp (ORF 600 bp), encoding 213 and 199 amino acids, respectively. Bioinformatics analyses revealed that the magur IGF2 and IGFBP6 proteins are hydrophilic and secretory in nature. Sequence alignment with other teleosts and mammalian orthologues shows conservation of the functional domains. Gene expression analysis in 6 individuals each of high (298 ± 5.0 g) and low (210 ± 6.0 g) growth performing families showed significantly (p < 0.05) higher expression (2.5-3 fold) of IGF2, and lower expression (∼2.5 fold) of IGFBP6 in liver and muscle of fast-growing fish. This study suggests that IGF2 could be playing a major role in the growth regulation of magur. These genes and their expression patterns could be developed into growth-associated markers for magur and other catfishes.

High-fat diet induces C-reactive protein secretion, promoting lung adenocarcinoma via immune microenvironment modulation

To understand the effects of a high-fat diet (HFD) on lung cancer progression and biomarkers, we here used an inducible mutant epidermal growth factor receptor (EGFR)-driven lung cancer transgenic mouse model fed a regular diet (RD) or HFD. The HFD lung cancer (LC-HFD) group exhibited significant tumor formation and deterioration, such as higher EGFR activity and proliferation marker expression, compared with the RD lung cancer (LC-RD) group. Transcriptomic analysis of the lung tissues revealed that the significantly changed genes in the LC-HFD group were highly enriched in immune-related signaling pathways, suggesting that an HFD alters the immune microenvironment to promote tumor growth. Cytokine and adipokine arrays combined with a comprehensive analysis using meta-database software indicated upregulation of C-reactive protein (CRP) in the LC-HFD group, which presented with increased lung cancer proliferation and metastasis; this was confirmed experimentally. Our results imply that an HFD can turn the tumor growth environment into an immune-related pro-tumorigenic microenvironment and demonstrate that CRP has a role in promoting lung cancer development in this microenvironment.

Identification and Characterization of Cancer-Associated Fibroblast Subpopulations in Lung Adenocarcinoma

Cancer-associated fibroblasts (CAFs) reside within the tumor microenvironment, facilitating cancer progression and metastasis via direct and indirect interactions with cancer cells and other stromal cell types. CAFs are composed of heterogeneous subpopulations of activated fibroblasts, including myofibroblastic, inflammatory, and immunosuppressive CAFs. In this study, we sought to identify subpopulations of CAFs isolated from human lung adenocarcinomas and describe their transcriptomic and functional characteristics through single-cell RNA sequencing (scRNA-seq) and subsequent bioinformatics analyses. Cell trajectory analysis of combined total and THY1 + CAFs revealed two branching points with five distinct branches. Based on Gene Ontology analysis, we denoted Branch 1 as "immunosuppressive", Branch 2 as "neoantigen presenting", Branch 4 as "myofibroblastic", and Branch 5 as "proliferative" CAFs. We selected representative branch-specific markers and measured their expression levels in total and THY1 + CAFs. We also investigated the effects of these markers on CAF activity under coculture with lung cancer cells. This study describes novel subpopulations of CAFs in lung adenocarcinoma, highlighting their potential value as therapeutic targets.

Gene expression and prognosis of insulin‑like growth factor‑binding protein family members in non‑small cell lung cancer

Lung cancer is the leading cause of cancer mortality worldwide. Approximately 85% of all lung cancer cases are classified as non-small cell lung cancer (NSCLC). Currently, there is no standard method to predict the survival of patients with NSCLC. Insulin-like growth factor-binding proteins (IGFBPs) function as modulators of IGF signaling and are attracting increasing attention for their role in NSCLC. However, the prognostic values of individual IGFBPs in NSCLC, particularly at the mRNA level, remain unknown. In the present study, the distinct expression patterns and prognostic values of IGFBP family members in patients with NSCLC through bioinformatics analysis were reported using a series of databases, including Gene Expression Profiling Interactive Analysis, Kaplan-Meier Plotter, cBioPortal, GeneMANIA, and the Database for Annotation, Visualization and Integrated Discovery. In patients with NSCLC, IGFBP2 and IGFBP3 were significantly upregulated, while IGFBP6 was downregulated. High IGFBP1/2/4 expression was correlated with poor overall survival (OS) in all NSCLC types, especially adenocarcinoma; however, high IGFBP2/5 expression was significantly correlated with favorable OS only in patients with squamous cell carcinoma. In addition, aberrant IGFBP1/2/3/4/5 mRNA levels were associated with the prognosis of subsets of NSCLC with different clinicopathological features. These results indicated that various IGFBPs can serve as useful prognostic biomarkers and as potential targets for NSCLC therapies.

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-β 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.

IGFBP6 is a novel nasopharyngeal carcinoma prognostic biomarker

Insulin-like growth factor binding proteins (IGFBPs) play critical roles in carcinogenesis. This study assessed the impact of IGFBP6 on the progression of nasopharyngeal carcinoma (NPC). Using immunohistochemical analysis, we found that IGFBP6 was differentially expressed in primary malignant NPC tissues. Clinical samples were divided into two groups: IGFBP6(+) and IGFBP6(−). Five years of follow-up revealed that overall survival and distant metastasis-free survival rates were significantly higher in the IGFBP6(+) than IGFBP6(−) group. We also used real-time PCR, ELISA and western blot assays to measure IGFBP6 levels in five NPC cell lines (CNE1, CNE2, HONE1, HK1 and SUNE1). All the cell lines expressed IGFBP6, but at different levels, reflecting disease heterogeneity. In addition, exogenous expression of IGFBP6 inhibited CNE2 cell proliferation and invasion in vitro. IGFBP6 knockdown activated the GSK3β/β-catenin/cyclin D1 pathway and enhanced CNE2 tumor cell growth and metastasis in a mouse model. These results suggest that IGFBP6 may be an independent prognostic biomarker for NPC.

Insulin-Like Growth Factor-Binding Proteins of Teleost Fishes

The insulin-like growth factor (Igf) binding protein (Igfbp) family has a broad range of physiological functions and a fascinating evolutionary history. This review focuses on the Igfbps of teleost fishes, where genome duplication events have diversified gene repertoire, function, and physiological regulation-with six core Igfbps expanded into a family of over twenty genes in some lineages. In addition to briefly summarizing the current state of knowledge on teleost Igfbp evolution, function, and expression-level regulation, we highlight gaps in our understanding and promising areas for future work.

Decreased expression of insulin-like growth factor binding protein 6 is associated with gastric adenocarcinoma prognosis

The present study aimed to investigate the expression and prognostic significance of insulin-like growth factor binding protein 6 (IGFBP-6) in gastric adenocarcinoma. The expression of IGFBP-6 was examined in 263 specimens from gastric adenocarcinoma patients using reverse transcription-quantitative polymerase chain reaction (RT-qPCR), western blotting and immunohistochemical (IHC) staining. The association between IGFBP-6 expression, clinicopathological factors and clinical outcomes was investigated. Akaike information criterion (AIC) and Harrell's concordance index (c-index) were used to evaluate the accuracy of the predictive prognosis. RT-qPCR and western blotting results showed that IGFBP-6 mRNA expression was lower in the tumors compared with that in adjacent non-tumor tissues. IGFBP-6 showed significantly decreased expression in 170 out of 263 patients based on IHC data and this was associated with a larger tumor size (P<0.001) and poorly-differentiated adenocarcinoma (P=0.001), as well as with palliative gastrectomy (P=0.015). Additionally, decreased expression of IGFBP-6 was associated with stage T3/4a/4b disease and lymph node-positive metastasis (P<0.001). The association between decreased expression and a poor prognosis was revealed by Kaplan-Meier curves. Cox regression model identified IGFBP-6 as an independent prognostic factor. The prognostic value of the model with IGFBP-6 expression (AIC, 924.881; c-index, 0.878) was superior to that without IGFBP-6 expression (AIC, 947.164; c-index, 0.825). In conclusion, IGFBP-6 involves the development and progression of gastric adenocarcinoma, and its decreased expression predicts poor clinical outcomes.

The Expression of IGFBP6 after Spinal Cord Injury: Implications for Neuronal Apoptosis

IGFBP6, a member of the insulin-like growth factor-binding proteins family that contains six high affinity IGFBPs, modulates insulin-like growth factor (IGF) activity and also showed an independent effect of IGF, such as growth inhibition and apoptosis. However, the role of IGFBP6 in spinal cord injury (SCI) remains largely elusive. In this study, we have performed an acute SCI model in adult rats and investigated the dynamic changes of IGFBP6 expression in the spinal cord. Our results showed that IGFBP6 was upregulated significantly after SCI, which was paralleled with the levels of apoptotic proteins p53 and active caspase-3. Immunofluorescent labeling showed that IGFBP6 was co-localizated with active caspase-3 and p53 in neurons. To further investigate the function of IGFBP6, an apoptosis model was established in primary neuronal cells. When IGFBP6 was knocked down by specific short interfering RNA (siRNA), the protein levels of active caspase-3 and Bax as well as the number of apoptotic primary neurons were significantly decreased in our study. Taken together, our findings suggest that the change of IGFBP6 protein expression plays a key role in neuronal apoptosis after SCI.

Current ideas on the biology of IGFBP-6: More than an IGF-II inhibitor?

IGFBP-6 binds IGF-II with higher affinity than IGF-I and it is a relatively specific inhibitor of IGF-II actions. More recently, IGFBP-6 has also been reported to have IGF-independent effects on cell proliferation, survival, differentiation and migration. IGFBP-6 binds to several ligands in the extracellular space, cytoplasm and nucleus. These interactions, together with activation of distinct intracellular signaling pathways, may contribute to its IGF-independent actions; for example, IGF-independent migration induced by IGFBP-6 involves interaction with prohibitin-2 and activation of MAP kinase pathways. A major challenge for the future is delineating the relative roles of the IGF-dependent and -independent actions of IGFBP-6, which may lead to the development of therapeutic approaches for diseases including cancer.

Insulin-like growth factor binding proteins 4-6

Insulin-like growth factor binding proteins (IGFBPs) 4-6 have important roles as modulators of IGF actions. IGFBP-4 and IGFBP-6 predominantly inhibit IGF actions, whereas IGFBP-5 may enhance these actions under some circumstances. IGFBP-6 is unique among the IGFBPs for its marked IGF-II binding preference. IGFBPs 4-6 are found in the circulation as binary complexes with IGFs that can enter tissues. Additionally, about half of the circulating IGFBP-5 is found in ternary complexes with IGFs and an acid labile subunit; this high molecular complex cannot leave the circulation and acts as an IGF reservoir. IGFBPs 4-6 also have IGF-independent actions. These IGFBPs are regulated in a cell-specific manner and their dysregulation may play a role in a range of diseases including cancer. However, there is no clear clinical indication for measuring serum levels of these IGFBPs at present.

Interaction of AIM with insulin-like growth factor-binding protein-4

Apoptosis inhibitor of macrophages (AIM/cluster of differentiation 5 antigen-like/soluble protein α) has been shown to inhibit cellular apoptosis; however, the underlying molecular mechanism has not been elucidated. Using yeast two-hybrid screening, the present study uncovered that AIM binds to insulin-like growth factor binding protein-4 (IGFBP-4). AIM interaction with IGFBP-4, as well as IGFBP-2 and -3, but not with IGFBP-1, -5 and -6, was further confirmed by co-immunoprecipitation (co-IP) using 293 cells. The binding activity and affinity between AIM and IGFBP-4 in vitro were analyzed by co-IP and biolayer interferometry. Serum depletion-induced cellular apoptosis was attenuated by insulin-like growth factor-I (IGF-I), and this effect was abrogated by IGFBP-4. Of note, in the presence of AIM, the inhibitory effect of IGFBP-4 on the anti-apoptosis function of IGF-I was attenuated, possibly through binding of AIM with IGFBP-4. In conclusion, to the best of our knowledge, the present study provides the first evidence that AIM binds to IGFBP-2, -3 and -4. The data suggest that this interaction may contribute to the mechanism of AIM-mediated anti-apoptosis function.

Recent insights into the actions of IGFBP-6

IGFBP-6 is an O-linked glycoprotein that preferentially binds IGF-II over IGF-I. It is a relatively selective inhibitor of IGF-II actions including proliferation, survival and differentiation of a wide range of cells. IGFBP-6 has recently been shown to have a number of IGF-independent actions, including promotion of apoptosis in some cells and inhibition of angiogenesis. IGFBP-6 also induces migration of tumour cells including rhabdomyosarcomas by an IGF-independent mechanism. This chemotactic effect is mediated by MAP kinases. IGFBP-6 binds to prohibitin-2 on the cell surface and the latter is required for IGFBP-6-induced migration by a mechanism that is independent of MAP kinases. IGFBP-6 may enter the nucleus and modulate cell survival and differentiation. IGFBP-6 expression is decreased in a number of cancer cells and it has been postulated to act as a tumour suppressor. IGFBP-6 expression is increased in a smaller number of cancers, which may reflect a compensatory mechanism to control IGF-II actions or IGF-independent actions. The relative balance of IGF-dependent and IGF-independent actions of IGFBP-6 in vivo together with the related question regarding the roles of IGFBP-6 binding to IGF and non-IGF ligands are keys to understanding the physiological role of this protein.

Downregulation of Insulin-like growth factor binding protein 6 is associated with ACTH-secreting pituitary adenoma growth

BACKGROUND

Adrenocorticotrophic hormone (ACTH)-dependent Cushing's syndrome, called Cushing disease, is caused by a corticotroph tumor of the pituitary gland. Insulin-like growth factor binding protein 6 (IGFBP6), which regulates insulin-like growth factor (IGF) activity and inhibits several IGF2-dependent cancer growths, plays a pivotal role in the tumorigenesis of malignancy, but its roles in ACTH-secreting pituitary adenomas remain unclear.

OBJECTIVE

To investigate IGFBP6 expression in ACTH-secreting pituitary adenomas, and its involvement in tumor growth.

METHODS

Sporadic ACTH-secreting pituitary adenomas specimens (n = 41) and adjacent non-tumorous pituitary tissues (n = 9) were collected by transphenoidal surgery. IGFBP6 expression was assessed by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and validated by Western blotting. Associations of IGFBP6 expression with maximum tumor diameter or Ki-67 labeling index were evaluated in ACTH-secreting pituitary adenomas.

RESULTS

IGFBP6 mRNA and protein expression were both decreased in ACTH-secreting pituitary adenomas, compared to adjacent non-tumorous pituitary tissues (P < 0.01). IGFBP6 expression was correlated inversely with maximum tumor diameter (Rho = -0.53, P < 0.0001) and Ki-67 levels (Rho = -0.52, P < 0.05). Moreover, IGFBP6 downregulation activated PI3 K-AKT-mTOR pathway in ACTH-secreting pituitary adenomas.

CONCLUSIONS

IGFBP6 attenuation in ACTH-secreting pituitary adenomas is associated with tumor growth, through activation of PI3K-AKT-mTOR pathway. The finding underlies IGFBP6 roles in Cushing disease and would potentially provide a novel target of medical therapies.

Expression and clinical significance of IGF-1, IGFBP-3, and IGFBP-7 in serum and lung cancer tissues from patients with non-small cell lung cancer

The expression and clinical significance of insulin-like growth factor 1 (IGF-1), insulin-like growth factor binding protein 3 (IGFBP-3), and insulin-like growth factor binding protein 7 (IGFBP-7) were investigated in serum and lung cancer tissues from 57 patients with non-small cell lung cancer (NSCLC). Lung cancer tissues at different pathologic stages (27 patients at stages I–II and 30 patients at stages III–IV), normal lung tissues from 17 patients with benign pulmonary disease, and serum samples from both lung cancer and benign pulmonary disease patients were collected during surgery. Enzyme-linked immunosorbent assay and avidin-biotin-peroxidase complex immunohistochemical staining were used to detect IGF-1, IGFBP-3, and IGFBP-7 expression in serum and tissues, respectively. The results show that expression of IGF-1 in lung cancer tissues and serum from NSCLC patients were significantly higher than in the control (P < 0.05). However, expression of IGFBP-3 and IGFBP-7 in cancer tissues and serum from NSCLC patients was significantly lower than in the control (P < 0.05). These results suggest that upregulation of IGF-1 and downregulation of IGFBP-3 and IGFBP-7 may be potential diagnostic biomarkers for NSCLC.

Kininogen 1 and insulin-like growth factor binding protein 6: candidate serum biomarkers of proliferative vitreoretinopathy

BACKGROUND

The aim was to validate whether kininogen 1 (KNG1) or insulin-like growth factor binding protein 6 (IGFBP-6) are serum biomarkers of proliferative vitreoretinopathy (PVR).

METHODS

Samples from vitreous and corresponding serum samples were collected from patients with PVR. The donor vitreous samples and serum samples from healthy volunteers and volunteers who had undergone vitrectomies for other conditions were used as controls. The samples were subsequently analysed using Western blotting (WB) and enzyme-linked immunosorbent assay.

RESULTS

The Western blotting outcomes indicated both IGFBP-6 and KNG1 could be specifically detected in the vitreous and serum samples of patients with PVR. The concentrations of KNG1 and IGFBP-6 were significantly higher in both vitreous and serum samples from patients with severe PVR than in the samples from patients with moderate PVR. The serum concentrations of KNG1 or IGFBP-6 had decreased by the post-vitrectomy examinations. The receiver operating characteristic (ROC) analyses when the concentrations of IGFBP-6 or KNG1 were greater than 181.4 pg/ml or 441.75 ng/ml, respectively, predicted severe PVR with both a sensitivity and specificity of over 70 per cent. When the concentrations of IGFBP-6 or KNG1 were greater than 98.5 pg/ml or 88.5 ng/ml, respectively, they predicted the PVR prognosis with both a sensitivity and specificity of 80 per cent.

CONCLUSIONS

KNG1 and IGFBP-6 may be candidate serum biomarkers of PVR.

Insulin-like growth factor-binding protein-6 and cancer

The IGF (insulin-like growth factor) system is essential for physiological growth and it is also implicated in a number of diseases including cancer. IGF activity is modulated by a family of high-affinity IGF-binding proteins, and IGFBP-6 is distinctive because of its marked binding preference for IGF-II over IGF-I. A principal role for IGFBP-6 is inhibition of IGF-II actions, but recent studies have indicated that IGFBP-6 also has IGF-independent effects, including inhibition of angiogenesis and promotion of cancer cell migration. The present review briefly summarizes the IGF system in physiology and disease before focusing on recent studies on the regulation and actions of IGFBP-6, and its potential roles in cancer cells. Given the widespread interest in IGF inhibition in cancer therapeutics, increasing our understanding of the mechanisms underlying the actions of the IGF ligands, receptors and binding proteins, including IGFBP-6, will enhance our ability to develop optimal treatments that can be targeted to the most appropriate patients.

Highly synergistic effect of sequential treatment with epigenetic and anticancer drugs to overcome drug resistance in breast cancer cells is mediated via activation of p21 gene expression leading to G2/M cycle arrest

Epigenetic alterations such as aberrant DNA methylation and histone modifications contribute substantially to both the cause and maintenance of drug resistance. These epigenetic changes lead to silencing of tumor suppressor genes involved in key DNA damage-response pathways, making drug-resistant cancer cells nonresponsive to conventional anticancer drug therapies. Our hypothesis is that treating drug-resistant cells with epigenetic drugs could restore the sensitivity to anticancer drugs by reactivating previously silenced genes. To test our hypothesis, we used drug-resistant breast cancer cells (MCF-7/ADR) and two epigenetic drugs that act via different mechanisms--5-aza-2'-deoxycytidine (decitabine, DAC), a demethylating agent, and suberoylanilide hydroxamic acid (SAHA), a histone deacetylase inhibitor--in combination with doxorubicin. We show that the sequential treatment of resistant cells, first with an epigenetic drug (DAC), and then with doxorubicin, induces a highly synergistic effect, thus reducing the IC(50) of doxorubicin by several thousand fold. The sequential treatment caused over 90% resistant cells to undergo G2/M cell cycle arrest, determined to be due to upregulation of p21(WAF1/CIP1) expression, which is responsible for cell-cycle regulation. The induction of p21(WAF1/CIP1) correlated well with the depletion of DNA methyltransferase1 (DNMT1), an enzyme that promotes methylation of DNA, suggesting that the p21(WAF1/CIP1) gene may have been methylated and hence is inactive in MCF-7/ADR cells. Microarray analysis shows expression of several tumor suppressor genes and downregulation of tumor promoter genes, particularly in sequentially treated resistant cells. Sequential treatment was found to be significantly more effective than simultaneous treatment, and DAC was more effective than SAHA in overcoming doxorubicin resistance. Synergistic effect with sequential treatment was also seen in drug-sensitive breast cancer cells, but the effect was significantly more pronounced in resistant cells. In conclusion, the sequential treatment of an epigenetic drug in combination with doxorubicin induces a highly synergistic effect that overcomes doxorubicin resistance in breast cancer cells.

Patterns of deregulation of insulin growth factor signalling pathway in paediatric and adult gastrointestinal stromal tumours

BACKGROUND

Data regarding the patterns and the mechanisms of deregulation of the insulin growth factor (IGF) pathway in adult and paediatric gastrointestinal stromal tumours (GISTs) are limited.

METHODS

We investigated the expression profiling of the genes encoding the main components of the IGF signalling pathway in 131 GISTs (106 adults, 21 paediatric and four young adults) and 25 other soft-tissue sarcomas (STS) using an Affymetrix U133A platform. IGF2 was investigated for loss of imprinting (LOI) whereas IGF1R was analysed for copy number aberration and mutation.

RESULTS

IGF2 was the most highly overexpressed gene of the IGF pathway in GIST. IGF2 expression was also significantly higher than in other STS. IGF2 expression was correlated to the age onset and mutational status of GIST. Indeed, IGF2 expression was significantly higher in the 'adult' group than in the 'paediatric' and 'young adult' groups. Among adult GIST, IGF2 expression was higher in tumours lacking Homo sapiens v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog (KIT) or alpha-type platelet-derived growth factor receptor (PDGFRA) mutations in comparison with mutated cases. A trend for a higher expression of IGF2 in resistant GIST in comparison to responsive GIST was also found. Overexpression of IGF2 was not related to LOI. Conversely, the expression of the IGF1R gene was significantly higher in the paediatric group than in the adult group. No copy number gains or mutations of IGF1R were observed.

CONCLUSION

The IGF pathway is deregulated in GIST with distinct patterns according to age onset and mutational status. The IGF pathway may represent a therapeutic target in patients with primary or secondary resistance to imatinib.

A novel interaction between insulin-like growth factor binding protein-6 and the vitamin D receptor inhibits the role of vitamin D3 in osteoblast differentiation

Insulin-like growth factor binding protein-6 (IGFBP-6) is a secreted glycoprotein that reduces the bioavailability of IGFs. It has both IGF-dependent and -independent effects on cell growth, however the mechanisms responsible for its IGF-independent actions of IGFBP-6 are not fully understood. In previous studies, we have shown that recombinant IGFBP-6 can be internalized and translocated to the nucleus. The present study shows that IGFBP-6 interacts with the vitamin D receptor (VDR). Physical interactions between IGFBP-6 and the VDR were confirmed by GST pulldown and co-immunoprecipitation assays. We also determined that the interaction binding sites were on the C-terminal region of the VDR. This interaction can influence retinoid X receptor (RXR):VDR heterodimerization. Furthermore, immunofluorescence colocalization studies showed that IGFBP-6 colocalized with the VDR predominantly in the cell's nucleus. Inductions of osteocalcin and growth hormone promoter activities by 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) were significantly decreased when cells were co-transfected with IGFBP-6 and the VDR compared with cells transfected with the VDR only. Moreover, we found that alkaline phosphatase activity (ALP, a general marker of osteoblast differentiation) was significantly decreased in osteoblast-like cells when they were transfected with IGFBP-6 in the presence of 1,25(OH)(2)D(3). No obvious difference in ALP activity was observed when cells were transfected with IGFBP-6 and endogenous VDR was knocked down by siRNA. These results demonstrate that IGFBP-6 inhibits osteoblastic differentiation mediated by 1,25(OH)(2)D(3) and the VDR through interacting with the VDR and inhibiting its function. This is a novel mechanism for IGFBP-6.

Purification and characterization of native human insulin-like growth factor binding protein-6

Insulin-like growth factor binding proteins (IGFBPs) are key regulators of insulin-like growth factor (IGF) mediated signal transduction and thereby can profoundly influence cellular phenotypes and cell fate. Whereas IGFBPs are extracellular proteins, intracellular activities were described for several IGFBP family members, such as IGFBP-3, which can be reinternalized by endocytosis and reaches the nucleus through routes that remain to be fully established. Within the family of IGFBPs, IGFBP-6 is unique for its specific binding to IGF-II. IGFBP-6 was described to possess additional IGF-independent activities, which have in part been attributed to its translocation to the nucleus; however, cellular uptake of IGFBP-6 was not described. To further explore IGFBP-6 functions, we developed a new method for the purification of native human IGFBP-6 from cell culture supernatants, involving a four-step affinity purification procedure, which yields highly enriched IGFBP-6. Whereas protein purified in this way retained the capacity to interact with IGF-II and modulate IGF-dependent signal transduction, our data suggest that, unlike IGFBP-3, human IGFBP-6 is not readily internalized by human tumor cells. To summarize, this work describes a novel and efficient method for the purification of native human insulin-like growth factor binding protein 6 (IGFBP-6) from human cell culture supernatants, applying a four-step chromatography procedure. Intactness of purified IGFBP-6 was confirmed by IGF ligand Western blot and ability to modulate IGF-dependent signal transduction. Cellular uptake studies were performed to further characterize the purified protein, showing no short-term uptake of IGFBP-6, in contrast to IGFBP-3.

Cross-talk between MAP kinase pathways is involved in IGF-independent, IGFBP-6-induced Rh30 rhabdomyosarcoma cell migration

Insulin-like growth factor binding protein-6 (IGFBP-6) inhibits the tumorigenic properties of IGF-II-dependent cancer cells by directly inhibiting IGF-II actions. However, in some cases, IGFBP-6 is associated with increased cancer cell tumorigenicity, which is unlikely to be due to IGF-II inhibition. The mechanisms underlying the contradictory actions of IGFBP-6 remain unclear. We recently generated an IGFBP-6 mutant that does not bind IGFs (mIGFBP-6) to address this issue. Although RD rhabdomyosarcoma cells express IGF-II, we previously showed that mIGFBP-6 promoted migration through an IGF-independent, p38-dependent pathway. We further studied the role of MAP kinases in IGFBP-6-induced migration of Rh30 rhabdomyosarcoma cells, which also express IGF-II. In these cells, mIGFBP-6 induced chemotaxis rather than chemokinesis. Both wild-type (wt) and mIGFBP-6 transiently induced phosphorylation of ERK1/2 and JNK1, but not p38. Inhibition of ERK1/2 phosphorylation completely prevented mIGFBP-6-induced ERK1/2 activation and cell migration, whereas a JNK inhibitor partially prevented migration. Interestingly, p38 pathway inhibition completely prevented mIGFBP-6-induced ERK1/2 and JNK1 activation and migration despite mIGFBP-6 not activating p38. Furthermore, blocking the ERK1/2 pathway also inhibited mIGFBP-6-induced JNK1 activation. In contrast, IGFBP-6 had no effect on Akt phosphorylation and an Akt inhibitor had no effect on migration. These results indicate that IGFBP-6 promotes Rh30 rhabdomyosarcoma chemotaxis in an IGF-independent manner, and that MAPK signaling pathways and their cross-talk play an important role in this process. Therefore, besides decreasing Rh30 cell proliferation by inhibiting IGF-II, IGFBP-6 promotes their migration via a distinct pathway. Understanding these disparate actions of IGFBP-6 may lead to the development of novel cancer therapeutics.

Transcriptional activation of insulin-like growth factor binding protein 6 by 17beta-estradiol in SaOS-2 cells

Osteoblasts can synthesize the insulin-like growth factors (IGFs) and the IGF-binding proteins (IGFBPs), which may either enhance or attenuate IGF-stimulated bone cell proliferation. Since estrogen induced osteoblastic differentiation and proliferation through an estrogen-responsive gene in target cells, we investigated the effects of estrogen on IGFBP-6 expression in the human osteoblastic-like cell line SaOS-2. Expressions of IGFBP-6 protein and mRNA increased 2.8 and 2-fold, respectively, in the presence of 17-beta-estradiol (E2) (0.01 to 1 micronM) and estrogen receptor (ER) in SaOS-2 cells. On the other hand, E2 induced a 2-fold increase in SaOS-2 cell proliferation. To identify genomic sequences associated with estrogen responsiveness, the 5'-promoter region (-44 to +118) of the IGFBP-6 gene was cloned into a chloramphenicol acetyltransferase (CAT) reporter vector. E2 induced a 3-fold increase in CAT activity in SaOS-2 cells transiently transfected with this construct. Identification of the estrogen-responsive element (ERE) [5-CCTTCA CCTG-3] (-9 to +1) in this IGFBP-6 gene promoter region was confirmed using electromobility shift assays and deletion analysis. This functional ERE was important for E2-induced trans-activation of the IGFBP-6 gene. These results demonstrate that E2 exhibits a positive effect on IGFBP-6 gene transcription through estrogen-liganded ER binding to the functional ERE in the IGFBP-6 gene promoter in SaOS-2 cells.

Identification of IGFBP-6 as an effector of the tumor suppressor activity of SEMA3B

SEMA3B, a member of class 3 semaphorins, is a tumor suppressor. Competition with vascular endothelial growth factor (VEGF)165 explains a portion of the activity, whereas the VEGF-independent mechanism was not elucidated. We employed a microarray and screened for the genes whose expression was increased by SEMA3B in NCI-H1299 cells. Insulin-like growth factor-binding protein-6 (IGFBP-6), a tumor suppressor, showed greatest difference in the expression level. Introduction of IGFBP-6 cDNA reduced colony formation both on the dish surface and in soft agar. Insulin-like growth factor II, which antagonizes IGFBP-6, partly abrogated the effect. Inhibition of IGFBP-6 by small interfering RNA diminished the sub-G0/G1 population that was induced by SEMA3B and abrogated the growth suppressive effect of SEMA3B. We concluded that IGFBP-6 is the effector of tumor suppressor activity of SEMA3B in NCI-H1299 cells. It has been reported that beta-catenin suppresses the expression of IGFBP-6. Introduction of beta-catenin into the cells partly abrogated the growth suppressive effect of SEMA3B. Our result indicates that semaphorin signaling and beta-catenin signaling converge on IGFBP-6 and antithetically affect their functions.

A functional nuclear localization signal in insulin-like growth factor binding protein-6 mediates its nuclear import

IGF binding protein (IGFBP)-6 is a member of the IGFBP family that regulates the actions of IGFs. Although IGFBPs exert their functions extracellularly in an autocrine/paracrine manner, several members of the family, such as IGFBP-3 and -5, possess nuclear localization signals (NLS). To date, no NLS has been described for IGFBP-6, an IGFBP that binds preferentially to IGF-II. We report here that both exogenous and endogenous IGFBP-6 could be imported into the nuclei of rhabdomyosarcoma and HEK-293 cells. Nuclear import of IGFBP-6 was mediated by a NLS sequence that bears limited homology to those found in IGFBP-3 and -5. IGFBP-6 nuclear translocation was an active process that required importins. A peptide corresponding to the IGFBP-6 NLS bound preferentially to importin-alpha. A comprehensive peptide array study revealed that, in addition to positively charged residues such as Arg and Lys, amino acids, notably Gly and Pro, within the NLS, played an important part in binding to importins. Overexpression of wild-type IGFBP-6 increased apoptosis, and the addition of IGF-II did not negate this effect. Only the deletion of the NLS segment abolished the apoptosis effect. Taken together, these results suggest that IGFBP-6 is translocated to the nucleus with functional consequences and that different members of the IGFBP family have specific nuclear import mechanisms.

Growth inhibition of non-small cell lung cancer cells by AP-1 blockade using a cJun dominant-negative mutant

cJun, a major constituent of AP-1 transcription factor transducing multiple mitogen growth signals, is frequently overexpressed in non-small cell lung cancers (NSCLCs). The purpose of this study is to determine the effects of AP-1 blockade on the growth of NSCLC cells using a cJun dominant-negative mutant, TAM67. Transiently transfected TAM67 inhibited AP-1 transcriptional activity in NSCLC cell lines, NCI-H1299 (H1299), A549 and NCI-H520 (H520). The colony-forming efficiency of H1299 and A549 was reduced by TAM67, while that of H520 was not. To elucidate the effects of TAM67 on the growth of H1299, we established H1299 clone cells that expressed TAM67 under the control of a doxycycline-inducible promoter. In the H1299 clone cells, the induced TAM67 inhibited anchorage-dependent growth by promoting G1 cell-cycle block, but not by apoptosis. The induced TAM67 decreased the expression of a cell-cycle regulatory protein, cyclin A. TAM67 also inhibited anchorage-independent growth of these cells. Furthermore, TAM67 reduced growth of established xenograft tumours from these cells in nude mice. These results suggest that AP-1 plays an essential role in the growth of at least some of NSCLC cells.

Promotion of cancer cell migration: an insulin-like growth factor (IGF)-independent action of IGF-binding protein-6

A family of six high affinity IGF-binding proteins (IGFBPs 1-6) plays an important role in modulating IGF activities. Recent studies suggest that some IGFBPs may have IGF-independent effects, including induction of apoptosis and modulation of cell migration. However, very little is known about possible IGF-independent actions of IGFBP-6. We have generated a non-IGF-binding IGFBP-6 mutant by substituting Ala for four amino acid residues (Pro(93)/Leu(94)/Leu(97)/Leu(98)) in its N-domain IGF-binding site. A >10,000-fold loss of binding affinity for IGF-I and IGF-II was observed using charcoal solution binding assay, BIAcore biosensor, and ligand blotting. Wild-type and mutant IGFBP-6, as well as IGF-II, induced cell migration in RD rhabdomyosarcoma and LIM 1215 colon cancer cells. Cell migration was mediated by the C-domain of IGFBP-6. Transient p38 phosphorylation was observed in RD cells after treatment with IGFBP-6, whereas no change was seen in phospho-ERK1/2 levels. Phospho-JNK was not detected. IGFBP-6-induced cell migration was inhibited by SB203580, an inhibitor of p38 MAPK, and PD98059, an inhibitor of ERK1/2 MAPK activation. In contrast, SP600125, a JNK MAPK inhibitor, had no effect on migration. Knockdown of p38 MAPK using short interfering RNA blocked IGFBP-6-induced migration of RD cells. These results indicate that p38 MAPK is involved in IGFBP-6-induced IGF-independent RD cell migration.

Expression, purification, and characterization of secreted recombinant human insulin-like growth factor-binding protein-6 in methylotrophic yeast Pichia pastoris

The mitogenic and metabolic activities of insulin-like growth factors (IGF) are modulated by a family of six high-affinity IGF-binding proteins (IGFBPs). This study describes the secretion and purification of the recombinant human IGFBP-6 expressed in methylotrophic yeast Pichia pastoris. In this research, a multicopy expression plasmid pA-O815/3xIGFBP-6 containing 3 copies of human IGFBP-6 expression cassette was constructed and transformed into P. pastoris GS115. The encoding sequence of alpha-factor leading peptide fused in-frame at the 5' end of human IGFBP-6 open reading frame and led expressed IGFBP-6 into the secretory pathway. After transformed cells were induced with methanol, medium supernatant was analyzed by SDS-PAGE and Western blotting. The two major protein bands of approximately 30 and approximately 18kDa were detected. The protein of approximately 30kDa was confirmed to be the glycosylated recombinant human IGFBP-6 (rhIGFBP-6), which was partially proteolyzed by protease Kex2 to produce a approximately 18kDa fragment. Approximately 95% homogeneity of the soluble form of 30kDa rhIGFBP-6 were achieved by two-step purification procedure using ion-exchange chromatography and then hydrophobic-interaction chromatography. The rhIGFBP-6 could be distributed to all of the cell body when cultured MDA-MB-231 cell with rhIGFBP-6 and the activities of rhIGFBP-6 were assayed by [(3)H]thymidine incorporation, which revealed that rhIGFBP-6 inhibited IGF-II-stimulated cell proliferation. Our results demonstrated that functional rhIGFBP-6 can be produced in sufficient quantities by using P. pastoris for further structural and functional studies.

Insulin-like growth factor binding protein-related protein 1 (IGFBP-rP1) has potential tumour-suppressive activity in human lung cancer

The expression of insulin-like growth factor binding protein-related protein 1 (IGFBP-rP1) is decreased in various tumours, but the role of IGFBP-rP1 in lung cancer is not yet clear. In this study, IGFBP-rP1 expression in lung cancer cell lines was evaluated and reduced expression of IGFBP-rP1 was found. In tissue microarrays containing 138 primary tumours and 20 normal lung tissues analysed by immunohistochemistry, 58 tumours (42%) exhibited no expression of IGFBP-rP1, while all 20 normal lung tissues showed high expression. In squamous cell lung cancer, low expression of IGFBP-rP1 was significantly linked to high-grade tumours. Treatment with 5-aza-2'-deoxycytidine restored the expression of IGFBP-rP1 in three of four lung cancer cell lines. Sequencing of PCR products of sodium bisulphite-treated genomic DNA from the three lung cancer cell lines revealed a heterogeneous methylation pattern in the region of exon 1 and intron 1. Stable transfection of IGFBP-rP1 full-length cDNA into the H2170 lung cancer cell line led to increased expression of IGFBP-rP1 protein. IGFBP-rP1-positive transfectants exhibited remarkably reduced colony-forming ability in soft agar, suppression of tumour growth rate in nude mice, and increased apoptotic cell number as well as activated caspase-3 expression level. The data suggest that IGFBP-rP1 is a tumour suppressor inactivated by DNA methylation in human lung cancer.

Expression profiling of p53-target genes in copper-mediated neuronal apoptosis

Copper toxicity associated with Wilson's disease is known to cause neuronal damage and death in the basal ganglia and frontal cortex leading to Parkinson-like symptoms and cognitive deficits. Our previous work in cultured human NTERA-2-N neurons showed that copper-induced neuronal apoptosis is dependent on the induction and nuclear translocation of the tumor suppressor protein, p53. Because p53 acts as a DNA-binding transcription factor, this work used an oligonucleotide array to identify p53 target genes that are differentially regulated in copper-loaded neurons. Arrays representing 145 human genes expressed downstream of p53 were hybridized with labeled mRNA from control and copper-treated neurons. Differentially regulated mRNAs included those involved in the regulation of the cell cycle, cytoprotective mechanisms, and apoptotic mechanisms. Transfection of cells with a dominant-negative p53 construct enabled us to determine which molecular events were dependent on p53 expression. Copper treatment resulted in the upregulation of p21, reprimo, stathmin, and Tp53INP1, all known to participate in cell cycle arrest. Protective mechanisms included the upregulation of stat-3, and the heat-shock proteins, heat-shock protein (Hsp) 70 and Hsp 27. Both p53-dependent and -independent mechanisms leading to apoptosis were identified including insulin-like growth factor binding protein-6, glutathione peroxidase, bcl-2, RB-1, PUMA, and several members of the redox active PIG family of proteins. Thus it appears that following copper-mediated neuronal DNA damage, the regulation of a variety of pro- and antiapoptotic genes are responsible for determining neuronal fate.

Sonic hedgehog signaling regulates the expression of insulin-like growth factor binding protein-6 during fetal prostate development

At the onset of ductal morphogenesis in the developing prostate, Shh expression condenses at evaginations of urogenital sinus epithelium and activates Gli transcription factors in the adjacent mesenchyme. Abrogation of Hedgehog signaling disrupts proper prostatic budding, ductal growth, and branching. We now show that Hedgehog signaling regulates the expression of insulin-like growth factor binding protein-6 (Igfbp-6) in the developing mouse prostate. Igfbp-6 is a secreted factor that specifically binds insulin-like growth factor-II (IGF-II), prevents its binding to the IGF-I receptor, and is thought to regulate the activity of IGF-II in growth and differentiation. Igfbp-6 is expressed in both the developing and adult prostate. In the urogenital sinus, Igfbp-6 mRNA colocalized with Ptc1 and Gli1 mRNA in the mesenchyme, while Igfbp-6 protein was found in both the mesenchymal and epithelial layers. Exogenous Shh peptide induced expression of Igfbp-6 in the developing prostate while the chemical inhibitor of Hedgehog signaling, cyclopamine, reduced its expression. These studies show that Igfbp-6 is an actual target of Shh signaling in the urogenital sinus and provide the first evidence for a linkage between the Hedgehog and IGF signaling pathways in prostate development.

Proteomic Identification of Insulin-like Growth Factor-binding Protein-6 Induced by Sublethal H2O2 Stress from Human Diploid Fibroblasts

Fibroblasts are the most ubiquitous cell types within our body. They produce various factors to maintain the texture and structure of a particular organ or tissue. To identify protein factors secreted by fibroblasts and alteration of these protein factors upon oxidative stress, HCA3 human skin diploid fibroblasts were exposed to a sublethal dose of H2O2, which induces a prematurely senescent phenotype. Conditioned media from prematurely senescent cells versus control cells were analyzed for proteins using an LC-MS/MS-based proteomic technique. Collagen alpha1(VI), collagen alpha2(I), fibronectin, lumican, and matrix metalloproteinase 2 were among the proteins consistently detected from control and H2O2-treated cells. Insulin-like growth factor-binding protein-6 (IGFBP-6) consistently showed up in the conditioned medium of H2O2-treated cells but not from untreated cells. Increased IGFBP-6 production due to H2O2 treatment was confirmed by RT-PCR and Western blot analyses. While H2O2 induced a dose-dependent elevation of IGFBP-6 mRNA, Western blot analyses detected elevated levels of IGFBP-6 protein in the conditioned medium of H2O2-treated cells. In comparison, fibronectin or matrix metalloproteinase 2 did not show changes at the mRNA level in cell lysates or at the protein level in the conditioned medium by H2O2 treatment. Using several types of toxins at sublethal doses, including cis-platin, hydroxyurea, colchicine, L-mimosine, rhodamine, dithiothreitol, or N-ethylmaleimide, we found that these agents induced increases of IGFBP-6 at mRNA and protein levels. An increased level of IGFBP-6 protein was detected in the plasma of aging mice and of young mice treated with doxorubicin. These data suggest that IGFBP-6 may serve as a sensitive biomarker of cell degeneration or injury in vitro and in vivo.

IGFBP-6 five years on; not so 'forgotten'?

Insulin-like growth factor binding protein (IGFBP)-6 is unique among IGFBPs for its IGF-II binding specificity. IGFBP-6 inhibits growth of a number of IGF-II-dependent cancers, including rhabdomyosarcoma, neuroblastoma and colon cancer. Although the major action of IGFBP-6 appears to be inhibition of IGF-II actions, a number of studies suggest that it may also have IGF-independent actions. Gene array studies show regulation of IGFBP-6 in many circumstances that are consistent with antiproliferative actions. However, other studies show the opposite, so that IGFBP-6 may be acting as a counter-regulator in these situations or it may have other as yet undetermined actions. Both the N-terminal and C-terminal domains of IGFBP-6 contribute to high affinity IGF binding, and the C-terminal domain appears to confer its IGF-II specificity. The three-dimensional structure of the C-domain of IGFBP-6 contains a thyroglobulin type 1 fold, and the IGF-II binding site is located in the proximal half of this domain adjacent to the glycosaminoglycan binding site. Future studies are needed to further delineate the putative IGF-independent actions of IGFBP-6 and to build on the structural information to enhance our understanding of this IGFBP. This is particularly significant since IGFBP-6 provides an attractive basis for therapy of IGF-II-dependent tumors.

Advances in the Biology of Lung Cancer Chemoprevention

The heavy burden of lung cancer, which includes the highest worldwide mortality of any cancer, and its resistance to standard approaches (smoking cessation, screening, and therapy), have motivated an intense interest in chemoprevention of this disease. Randomized controlled trials of agents (including retinoids, beta-carotene, and vitamin E) to prevent lung cancer have produced only disappointing clinical results to date. New, molecular-targeted approaches are advancing rapidly, however, with many promising targets and interactive signaling pathways for developing novel agents and combinatorial approaches in this setting. This promise is illustrated by recent studies of 15-hydroxyprostaglandin dehydrogenase, which plays a critical role in polyunsaturated fatty acid metabolism and (like another important target, prostacyclin) is downstream of cyclooxygenase-2. 15-hydroxyprostaglandin dehydrogenase degrades prostaglandin E2, appears to have tumor suppressor activity, and can be induced both by peroxisome proliferator-activated receptor-gamma ligands and an epidermal growth factor receptor inhibitor. Other important targets/pathways include the insulin-like growth factor axis, phosphoinositide 3-kinase pathway, cyclin D and E family members, and epigenetic events. Defining highest lung cancer risk (eg, establishing molecular risk models through long-term analyses of high-risk cohorts) will facilitate the clinical development of molecular-targeted prevention that will potentially reduce the enormous burden of lung cancer.

Differential effects of estrogen and raloxifene on messenger RNA and matrix metalloproteinase 2 activity in the rat uterus

A detailed analysis of the differential effects of estrogen (E) compared to raloxifene (Ral), a selective estrogen receptor modulator (SERM), following estrogen receptor (ER) binding in gynecological tissues was conducted using gene microarrays, Northern blot analysis, and matrix metalloproteinase (MMP) 2 activity studies. We profiled gene expression in the uterus following acute (1 day) and prolonged daily (5 wk) treatment of E and Ral in ovariectomized rats. Estrogen regulated twice as many genes as Ral, largely those associated with catalysis and metabolism, whereas Ral induced genes associated with cell death and negative cell regulation. Follow-up studies confirmed that genes associated with matrix integrity were differentially regulated by Ral and E at various time points in uterine and vaginal tissues. Additional experiments were conducted to determine the levels of MMP2 activity in uterus explants from ovariectomized rats following 2 wk of treatment with E, Ral, or one of two additional SERMs: lasofoxifene, and levormeloxifene. Both E and lasofoxifene stimulated uterine MMP2 activity to a level twofold that of Ral, whereas levormeloxifene elevated MMP2 activity to a level 12-fold that of Ral. These data show that one of the significant differences between E and Ral signaling in the uterus is the regulation of genes and proteins associated with matrix integrity. This may be a potential key difference between the action of SERMs in the uterus of postmenopausal women.

Effect of an insulin-like growth factor binding protein fusion protein on thymidine incorporation in neuroblastoma and rhabdomyosarcoma cell lines

A fusion protein, FP 6/3, composed of IGF binding protein (IGFBP)-6 and IGFBP-3 was synthesized where the complete sequences of each binding protein were fused together into a single chimeric protein. The orientation of this fusion protein's structure has the N terminus of IGFBP-3 fused to the C terminus of IGFBP-6, leaving the key binding areas of each open. FP 6/3 bound to cells via its IGFBP-3 component and retained the increased affinity for IGF-II via its IGFBP-6 component. The effect of FP 6/3 on growth was determined in cell lines from both neuroblastoma and rhabdomyosarcoma, where IGF-II is an autocrine growth factor. In studies using FP 6/3, IGFBP-3, or IGFBP-6, a growth inhibition effect was shown for all when present under coincubation conditions with IGF-II. However, with transient exposure, FP 6/3 was the only IGFBP that retained this growth-inhibition property. Under transient exposure conditions, FP 6/3 was found to be effective when exposure was limited to as few as 10 min and concentrations were as low as 1 nm. These findings with FP 6/3 suggest that it potentially could lead be used as therapy against cancers in which IGF-II is an autocrine growth factor because it brings an inhibition action directly to tumor cells.

Lung cancer. 9: Molecular biology of lung cancer: clinical implications

It has been hypothesised that clinically evident lung cancers have accumulated many different genetic or epigenetic abnormalities in oncogenes and/or tumour suppressor genes. This notion has important clinical ramifications. Recent developments in our knowledge of the molecular biology of lung cancer are reviewed, with particular reference to genetic abnormalities in tumour suppressor gene inactivation and overactivity of growth promoting oncogenes. These changes lead to the "hallmarks of lung cancer". These hallmarks are the new rational targets for early detection, prevention, and treatment of lung cancer.

Microarray analysis uncovers retinoid targets in human bronchial epithelial cells

Retinoids, the natural and synthetic derivatives of vitamin A, have a role in cancer treatment and prevention. There is a need to reveal mechanisms that account for retinoid response or resistance. This study identified candidate all-trans-retinoic acid (RA) target genes linked to growth suppression in BEAS-2B human bronchial epithelial cells. Microarray analyses were performed using Affymetrix arrays. A total of 11 RA-induced species were validated by reverse transcription polymerase chain reaction (RT-PCR), Western or Northern analyses. Three of these species were novel candidate RA-target genes in human bronchial epithelial cells. These included: placental bone morphogenetic protein (PLAB), polyamine oxidase isoform 1 (PAOh1) and E74-like factor 3 (ELF3). Expression patterns were studied in RA-resistant BEAS-2B-R1 cells. In BEAS-2B-R1 cells, RA dysregulated the expression of the putative lymphocyte G0/G1 switch gene (G0S2), heme oxygenase 1 (HMOX1), tumor necrosis factor-alpha-induced protein 2 (TNFAIP2), inhibitor of DNA binding 1(Id1), fos-like antigen 1 (FOSL1), transglutaminase 2 (TGM2), asparagine synthetase (ASNS), PLAB, PAOh1 and ELF3, while prominent induction of insulin-like growth-factor-binding protein 6 (IGFBP6) still occurred. In summary, this study identified 11 candidate RA-target genes in human bronchial epithelial cells including three novel species. Expression studies in BEAS-2B-R1 cells indicated that several were directly implicated in RA signaling, since their aberrant expression was linked to RA resistance of human bronchial epithelial cells.

C-terminal-binding protein corepresses epithelial and proapoptotic gene expression programs

The genesis of carcinoma cells often involves epithelial-to-mesenchymal transitions and the acquisition of apoptosis resistance, but it is unclear whether these alterations are controlled coordinately or independently. Our previously reported effects of adenovirus E1a in human tumor cells raised the possibility that the E1a-interacting corepressor protein C-terminal-binding protein (CtBP) might selectively repress epithelial cell adhesion and proapoptotic genes. Here, we report that CtBP-knockout cells were hypersensitive to apoptosis. Correspondingly, microarray analysis of CtBP-knockout vs. CtBP-rescued mouse embryo fibroblasts revealed that many epithelial-specific and proapoptotic genes were indeed regulated by CtBP. Neither the apoptosis nor the repression activities of CtBP required histidine-315, suggesting that the proposed dehydrogenase activity is not essential for CtBP function. The results presented herein establish two functional roles of CtBP: to corepress epithelial genes, thus permitting epithelial-to-mesenchymal transitions, and to modulate the cellular threshold for apoptotic responses.

Free insulin-like growth factor (IGF)-I and IGF binding proteins 2, 5, and 6 in spinal motor neurons in amyotrophic lateral sclerosis

BACKGROUND

Insulin-like growth factor-I (IGF-I) is a potent survival factor for motor neurons and is being investigated as possible therapeutic agent for amyotrophic lateral sclerosis. However, very little information is available on the components of the IGF-I system in this disease. Insulin-like growth factor binding proteins (IGFBPs) play an important part in regulating the bioavailability of IGF-I.

METHODS

We investigated the components of the IGF-I system in spinal cord sections of ten patients with amyotrophic lateral sclerosis and in ten controls without neurological disease. IGF-I was studied by western immunoblotting. IGFBPs and IGF-I receptors were investigated by immunohistochemistry and Western immunoblotting.

FINDINGS

Total IGF-I in ventral horn homogenates did not differ between patients and controls. However, free IGF-I was 53% lower in patients than in controls. Compared with controls, immunoreactivity in the spinal motor neurons of patients with amyotrophic lateral sclerosis was 64% higher for IGFBP2, 46% higher for IGFBP5, and 33% higher for IGFBP6, with upregulation of IGF-I receptors. Immunoreactivity for IGFBPs1, 3, and 4 did not differ between patients and controls.

INTERPRETATION

In the ventral horns of patients, free IGF-I is reduced, which could be because of specific increases in IGFBPs 2, 5, and 6 in spinal motor neurons. This abnormality might have an important role in the processes leading to motor neuron death, and should be taken into account when developing treatments aimed to stimulate IGF-I receptors in motor neurons.

Massive hepatic apoptosis associated with TGF-beta1 activation after Fas ligand treatment of IGF binding protein-1-deficient mice

Acute liver failure caused by viral hepatitis or toxic damage involves both apoptotic and necrotic pathways. IGF binding protein-1 (IGFBP-1), a hepatocyte-derived secreted protein, is required for normal liver regeneration. To determine whether IGFBP-1 could prevent liver injury that entails direct stimulation of hepatocyte apoptosis, IGFBP-1(-/-) mice, IGFBP-1(+/+) mice, and mice pretreated with Ab's against IGFBP-1 were treated with a normally sublethal dose of Fas agonist. IGFBP-1 deficiency was associated with massive hepatocyte apoptosis and caspase activation within 3 hours of Fas agonist treatment, which could be corrected by pretreatment with IGFBP-1. IGFBP-1-deficient livers had enhanced signaling via the integrin receptor at early times (0.5 to 1 hour) after Fas agonist treatment accompanied by elevated activated matrix metalloproteinase-9 (MMP-9), a known target of fibronectin signaling and activator of TGF-beta. Within 3 hours of Fas agonist treatment, elevated expression of active TGF-beta1, a hepatocyte apoptogen, was observed in IGFBP-1-deficient livers that correlated with the appearance of the apoptotic process. Both MMP-9 and TGF-beta1 expression were suppressed by IGFBP-1 treatment, supporting their role in the apoptotic process. IGFBP-1(-/-) mice also displayed increased injury in a toxic hepatic injury model caused by CCl(4). These findings indicate that IGFBP-1 functions as a critical hepatic survival factor in the liver by reducing the level of proapoptotic signals.

Massive hepatic apoptosis associated with TGF-beta1 activation after Fas ligand treatment of IGF binding protein-1-deficient mice

Acute liver failure caused by viral hepatitis or toxic damage involves both apoptotic and necrotic pathways. IGF binding protein-1 (IGFBP-1), a hepatocyte-derived secreted protein, is required for normal liver regeneration. To determine whether IGFBP-1 could prevent liver injury that entails direct stimulation of hepatocyte apoptosis, IGFBP-1(-/-) mice, IGFBP-1(+/+) mice, and mice pretreated with Ab's against IGFBP-1 were treated with a normally sublethal dose of Fas agonist. IGFBP-1 deficiency was associated with massive hepatocyte apoptosis and caspase activation within 3 hours of Fas agonist treatment, which could be corrected by pretreatment with IGFBP-1. IGFBP-1-deficient livers had enhanced signaling via the integrin receptor at early times (0.5 to 1 hour) after Fas agonist treatment accompanied by elevated activated matrix metalloproteinase-9 (MMP-9), a known target of fibronectin signaling and activator of TGF-beta. Within 3 hours of Fas agonist treatment, elevated expression of active TGF-beta1, a hepatocyte apoptogen, was observed in IGFBP-1-deficient livers that correlated with the appearance of the apoptotic process. Both MMP-9 and TGF-beta1 expression were suppressed by IGFBP-1 treatment, supporting their role in the apoptotic process. IGFBP-1(-/-) mice also displayed increased injury in a toxic hepatic injury model caused by CCl(4). These findings indicate that IGFBP-1 functions as a critical hepatic survival factor in the liver by reducing the level of proapoptotic signals.

Cellular actions of the insulin-like growth factor binding proteins

In addition to their roles in IGF transport, the six IGF-binding proteins (IGFBPs) regulate cell activity in various ways. By sequestering IGFs away from the type I IGF receptor, they may inhibit mitogenesis, differentiation, survival, and other IGF-stimulated events. IGFBP proteolysis can reverse this inhibition or generate IGFBP fragments with novel bioactivity. Alternatively, IGFBP interaction with cell or matrix components may concentrate IGFs near their receptor, enhancing IGF activity. IGF receptor-independent IGFBP actions are also increasingly recognized. IGFBP-1 interacts with alpha(5)beta(1) integrin, influencing cell adhesion and migration. IGFBP-2, -3, -5, and -6 have heparin-binding domains and can bind glycosaminoglycans. IGFBP-3 and -5 have carboxyl-terminal basic motifs incorporating heparin-binding and additional basic residues that interact with the cell surface and matrix, the nuclear transporter importin-beta, and other proteins. Serine/threonine kinase receptors are proposed for IGFBP-3 and -5, but their signaling functions are poorly understood. Other cell surface IGFBP-interacting proteins are uncharacterized as functional receptors. However, IGFBP-3 binds and modulates the retinoid X receptor-alpha, interacts with TGFbeta signaling through Smad proteins, and influences other signaling pathways. These interactions can modulate cell cycle and apoptosis. Because IGFBPs regulate cell functions by diverse mechanisms, manipulation of IGFBP-regulated pathways is speculated to offer therapeutic opportunities in cancer and other diseases.

Insulin-like growth factor binding protein-6 inhibits neuroblastoma cell proliferation and tumour development

In neuroblastoma cells, survival and proliferation are dependent upon the insulin-like growth factor (IGF) system. IGFs actively participate in cell growth, whereas IGFBP-6, is associated with the arrest of growth. With a view to blocking IGF-II action, we produced recombinant human IGFBP-6 capable of binding IGFs with affinities between 1.23 and 6.36 x 10(9) M(-1). Ex vivo mitogenic activities were tested on two human neuroblastoma cell lines, in which 100 ng/ml IGFBP-6 completely abolished the effects of both endogenous and exogenous IGF-II. In vivo, nude mice previously injected with neuroblastoma cells were submitted to either 15 daily injections of 4-20 microg IGFBP-6 or implantation of mini-pumps diffusing 20-100 microg IGFBP-6 over 2 weeks. The result was an average 18% reduction in the incidence and development of tumours. Delivery of the IGFBP-6 via mini-pumps also delayed tumour appearance by 6-15 days. Our results therefore show the involvement of IGFBP-6 in neuroblastoma cell growth, both ex vivo in terms of proliferation and in vivo in terms of tumour development.

Differentially expressed genes associated with mouse lung tumor progression

To detect altered gene expression associated with mouse lung tumor progression, we compared the gene expression profile of lung adenocarcinomas with that of lung adenomas and normal lungs. Autoradiographic analysis showed that among the 588 genes surveyed, 152 genes were detected and the remaining 436 genes did not give any signals. A gene-specific semiquantitative reverse transcription polymerase chain reaction method was used to confirm the expression profile. A total of 29 genes was found to be differentially expressed in mouse lung tumors when compared to normal lungs. The pattern of expression, either underexpression or overexpression, was the same for 10 genes between adenocarcinomas and adenomas. Among them, seven genes were overexpressed, two genes were underexpressed and one gene was lost. Interestingly, 19 genes showed differential expression or increased incidence or difference in level of change between lung adenomas and adenocarcinomas, including Stat1, ADAP, IGFBP-6, PDGF-A, TGF-beta2, Int-3, VEGFR2, BAX, BAG-1, c-Jun, FasL, TRAIL, YB-1, CD31, Cdc42, B-raf, Rab-2, Abi-1, and ACE. These genes can be designated as candidate 'lung tumor progression' (LTP) genes because their expression changes may specifically affect lung tumor progression in mice. Further analyses of these candidate LTP genes may provide new leads for elucidation of lung tumor progression in mice.