Dominant-negative effect of truncated mannose 6-phosphate/insulin-like growth factor II receptor species in cancer

Impairing hydrolase transport machinery prevents human melanoma metastasis

Metastases are the major cause of cancer-related death, yet, molecular weaknesses that could be exploited to prevent tumor cells spreading are poorly known. Here, we found that perturbing hydrolase transport to lysosomes by blocking either the expression of IGF2R, the main receptor responsible for their trafficking, or GNPT, a transferase involved in the addition of the specific tag recognized by IGF2R, reduces melanoma invasiveness potential. Mechanistically, we demonstrate that the perturbation of this traffic, leads to a compensatory lysosome neo-biogenesis devoided of degradative enzymes. This regulatory loop relies on the stimulation of TFEB transcription factor expression. Interestingly, the inhibition of this transcription factor playing a key role of lysosome production, restores melanomas' invasive potential in the absence of hydrolase transport. These data implicate that targeting hydrolase transport in melanoma could serve to develop new therapies aiming to prevent metastasis by triggering a physiological response stimulating TFEB expression in melanoma.

Enhanced Thermal Stability of Polyphosphate-Dependent Glucomannokinase by Directed Evolution

Polyphosphate-dependent glucomannokinase (PPGMK) is able to utilize inorganic polyphosphate to synthesize mannose-6-phosphate (M6P) instead of highly costly ATP. This enzyme was modified and designed by combining error-prone PCR (EP-PCR) and site-directed saturation mutagenesis. Two mutants, H92L/A138V and E119V, were screened out from the random mutation library, and we used site-specific saturation mutations to find the optimal amino acid at each site. Finally, we found the optimal combination mutant, H92K/E119R. The thermal stability of H92K/E119R increased by 5.4 times at 50 °C, and the half-life at 50 °C increased to 243 min. Moreover, the enzyme activity of H92K/E119R increased to 16.6 U/mg, and its enzyme activity is twice that of WT. We analyzed the structure of the mutant using molecular dynamics simulation. We found that the shortening of the hydrogen bond distance and the formation of salt bridges can firmly connect the α-helix and β-sheet and improve the stability of the PPGMK structure.

Mutational Characterization of Colorectal Cancer from Korean Patients with Targeted Sequencing

Purpose: Effective treatment of colorectal cancer could benefit from understanding molecular characteristics including mutation profiles of important genes. This study aimed to explore the molecular characteristics of colorectal cancer based on next generation sequencing.

Methods: The mutational characteristics by targeted next generation sequencing in 172 colorectal tumor samples from Korean patients were evaluated to explore their associations with clinical features. Targeted sequencing of 375 genes was performed with an average target-depth of 800X.

Results: TP53 and APC showed higher mutation frequencies from the left-sided tumors, while CTNNB1 were more frequent from the right-sided tumors. The tumor suppressor NOTCH1 and the DNA strand break repair gene PALB2 were more frequently mutated in early onset tumors. KRAS and PTEN mutations were more frequent from patients with advanced cancers by cancer antigen markers. TP53 and BRAF mutations were more frequent from patients of T3 and T4 stages, where their variant allele fractions were generally higher in T4 tumors, implying that advanced tumors have higher fraction of cancer cells with TP53 and BRAF mutations. Mutational profiles of these patients were also assessed with other clinical features. Comparison of mutational characteristics with the Caucasian subjects from independent data showed that the identified mutational characteristics are largely Korean-specific except for a few key colorectal cancer genes.

Conclusion: Next generation sequencing-based targeted sequencing can provide valuable information on molecular characterization of colorectal cancer patients, and its clinically relevant information can provide benefits to better understand colorectal cancer.

Novel Regulators of the IGF System in Cancer

The insulin-like growth factor (IGF) system is a dynamic network of proteins, which includes cognate ligands, membrane receptors, ligand binding proteins and functional downstream effectors. It plays a critical role in regulating several important physiological processes including cell growth, metabolism and differentiation. Importantly, alterations in expression levels or activation of components of the IGF network are implicated in many pathological conditions including diabetes, obesity and cancer initiation and progression. In this review we will initially cover some general aspects of IGF action and regulation in cancer and then focus in particular on the role of transcriptional regulators and novel interacting proteins, which functionally contribute in fine tuning IGF1R signaling in several cancer models. A deeper understanding of the biological relevance of this network of IGF1R modulators might provide novel therapeutic opportunities to block this system in neoplasia.

Maternal transmission of an Igf2r domain 11: IGF2 binding mutant allele (Igf2rI1565A) results in partial lethality, overgrowth and intestinal adenoma progression

The cation-independent mannose 6-phosphate/insulin-like growth factor-2 receptor (M6P/IGF2R or IGF2R) traffics IGF2 and M6P ligands between pre-lysosomal and extra-cellular compartments. Specific IGF2 and M6P high-affinity binding occurs via domain-11 and domains-3-5-9, respectively. Mammalian maternal Igf2r allele expression exceeds the paternal allele due to imprinting (silencing). Igf2r null-allele maternal transmission results in placenta and heart over-growth and perinatal lethality (>90%) due to raised extra-cellular IGF2 secondary to impaired ligand clearance. It remains unknown if the phenotype is due to either ligand alone, or to both ligands. Here, we evaluate Igf2r specific loss-of-function of the domain-11 IGF2 binding site by replacing isoleucine with alanine in the CD loop (exon 34, I1565A), a mutation also detected in cancers. Igf2rI1565A/+p maternal transmission (heterozygote), resulted in placental and embryonic over-growth with reduced neonatal lethality (<60%), and long-term survival. The perinatal mortality (>80%) observed in homozygotes (Igf2rI1565A/I1565A) suggested that wild-type paternal allele expression attenuates the heterozygote phenotype. To evaluate Igf2r tumour suppressor function, we utilised intestinal adenoma models known to be Igf2 dependent. Bi-allelic Igf2r expression suppressed intestinal adenoma (ApcMin). Igf2rI1565A/+p in a conditional model (Lgr5-Cre, Apcloxp/loxp) resulted in worse survival and increased adenoma proliferation. Growth, survival and intestinal adenoma appear dependent on IGF2R-domain-11 IGF2 binding.

Inhibition of insulin-like growth factor II (IGF-II)-dependent cell growth by multidentate pentamannosyl 6-phosphate-based ligands targeting the mannose 6-phosphate/IGF-II receptor

The mannose 6-phosphate/insulin-like growth factor II receptor (M6P/IGF2R) binds M6P-capped ligands and IGF-II at different binding sites within the ectodomain and mediates ligand internalization and trafficking to the lysosome. Multivalent M6P-based ligands can cross-bridge the M6P/IGF2R, which increases the rate of receptor internalization, permitting IGF-II binding as a passenger ligand and subsequent trafficking to the lysosome, where the IGF-II is degraded. This unique feature of the receptor may be exploited to design novel therapeutic agents against IGF-II-dependent cancers that will lead to decreased bioavailable IGF-II within the tumor microenvironment. We have designed a panel of M6P-based ligands that bind to the M6P/IGF2R with high affinity in a bivalent manner and cause decreased cell viability. We present evidence that our ligands bind through the M6P-binding sites of the receptor and facilitate internalization and degradation of IGF-II from conditioned medium to mediate this cellular response. To our knowledge, this is the first panel of synthetic bivalent ligands for the M6P/IGF2R that can take advantage of the ligand-receptor interactions of the M6P/IGF2R to provide proof-of-principle evidence for the feasibility of novel chemotherapeutic agents that decrease IGF-II-dependent growth of cancer cells.

Unravelling novel functions of the endosomal transporter mannose 6-phosphate/insulin-like growth factor receptor (CD222) in health and disease: An emerging regulator of the immune system

Properly balanced cellular responses require both the mutual interactions of soluble factors with cell surface receptors and the crosstalk of intracellular molecules. In particular, immune cells exposed unceasingly to an array of positive and negative stimuli must distinguish between what has to be tolerated and attacked. Protein trafficking is one of crucial pathways involved in this labour. The approximately >270-kDa protein transporter called mannose 6- phosphate/insulin-like growth factor 2 receptor (M6P/IGF2R, CD222) is a type I transmembrane glycoprotein present largely intracellularly in the Golgi apparatus and endosomal compartments, but also at the cell surface. It is expressed ubiquitously in a vast majority of higher eukaryotic cell types. Through binding and trafficking multiple unrelated extracellular and intracellular ligands, CD222 is involved in the regulation of a plethora of functions, and thus implicated in many physiological but also pathophysiological conditions. This review describes, first, general features of CD222, such as its evolution, genomic structure and regulation, protein structure and ligands; and second, its specific functions with a special focus on the immune system.

Critical Functions of the Lysosome in Cancer Biology

Lysosomes (or lytic bodies) were so named because they contain high levels of hydrolytic enzymes. Lysosome function and dysfunction have been found to play important roles in human disease, including cancer; however, the ways in which lysosomes contribute to tumorigenesis and cancer progression are still being uncovered. Beyond serving as a cellular recycling center, recent evidence suggests that the lysosome is involved in energy homeostasis, generating building blocks for cell growth, mitogenic signaling, priming tissues for angiogenesis and metastasis formation, and activating transcriptional programs. This review examines emerging knowledge of how lysosomal processes contribute to the hallmarks of cancer and highlights vulnerabilities that might be exploited for cancer therapy.

MicroRNA-19a/b mediates grape seed procyanidin extract-induced anti-neoplastic effects against lung cancer

Oncomirs are microRNAs (miRNA) associated with carcinogenesis and malignant transformation. They have emerged as potential molecular targets for anti-cancer therapy. We hypothesize that grape seed procyanidin extract (GSE) exerts antineoplastic effects through modulations of oncomirs and their downstream targets. We found that GSE significantly down-regulated oncomirs miR-19a and -19b in a variety of lung neoplastic cells. GSE also increased mRNA and protein levels of insulin-like growth factor II receptor (IGF-2R) and phosphatase and tensin homolog (PTEN), both predicted targets of miR-19a and -19b. Furthermore, GSE significantly increased PTEN activity and decreased AKT phosphorylation in A549 cells. Transfection of miR-19a and -19b mimics reversed the up-regulations of IGF2R and PTEN gene expression and abrogated the GSE induced anti-proliferative response. Additionally, oral administration of leucoselect phytosome, comprised of standardized grape seed oligomeric procyanidins complexed with soy phospholipids, to athymic nude mice via gavage, significantly down-regulated miR-19a, -19b and the miR-17-92 cluster host gene (MIR17HG) expressions, increased IGF-2R, PTEN, decreased phosphorylated-AKT in A549 xenograft tumors, and markedly inhibited tumor growth. To confirm the absorption of orally administered GSE, plasma procyanidin B1 levels, between 60 and 90 min after gavage of leucoselect phytosome (400 mg/kg), were measured by LC/MS at week 2 and 8 of treatment; the estimated concentration that was associated with 50% growth inhibition (IC50) (1.3 μg/mL) in vitro was much higher than the IC50 (0.032-0.13 μg/ml) observed in vivo. Our findings reveal novel antineoplastic mechanisms by GSE and support the clinical translation of leucoselect phytosome as an anti-neoplastic and chemopreventive agent for lung cancer.

Soluble M6P/IGFIIR in the circulation

Soluble M6P/IGFIIR has the potential to be a significant carrier of IGF-II and mannose 6-P proteins in the circulation and play an important role as an antagonist to the cellular receptor. Evidence suggests that soluble receptor plays a role in fetal and childhood growth by opposing the growth stimulatory effects of IGF-II. Maternal serum levels of M6P/IGFIIR are elevated in late pregnancy and the IGF-II:soluble M6P/IGFIIR ratio in cord blood correlates strongly with weight at birth and placental weight suggesting an important role in fetal growth and development. However, elevated soluble receptor levels may also be indicative of disease in later life, such as liver cirrhosis and some tumor types and may be a useful marker for monitoring treatment and progression of the disease. Further investigation of the regulation of this soluble receptor in health and disease is required to fully elucidate its role in the circulation.

Overexpression of the Insulin-Like Growth Factor II Receptor Increases β-Amyloid Production and Affects Cell Viability

Amyloid β (Aβ) peptides originating from amyloid precursor protein (APP) in the endosomal-lysosomal compartments play a critical role in the development of Alzheimer's disease (AD), the most common type of senile dementia affecting the elderly. Since insulin-like growth factor II (IGF-II) receptors facilitate the delivery of nascent lysosomal enzymes from the trans-Golgi network to endosomes, we evaluated their role in APP metabolism and cell viability using mouse fibroblast MS cells deficient in the murine IGF-II receptor and corresponding MS9II cells overexpressing the human IGF-II receptors. Our results show that IGF-II receptor overexpression increases the protein levels of APP. This is accompanied by an increase of β-site APP-cleaving enzyme 1 levels and an increase of β- and γ-secretase enzyme activities, leading to enhanced Aβ production. At the cellular level, IGF-II receptor overexpression causes localization of APP in perinuclear tubular structures, an increase of lipid raft components, and increased lipid raft partitioning of APP. Finally, MS9II cells are more susceptible to staurosporine-induced cytotoxicity, which can be attenuated by β-secretase inhibitor. Together, these results highlight the potential contribution of IGF-II receptor to AD pathology not only by regulating expression/processing of APP but also by its role in cellular vulnerability.

Targeting the insulin-like growth factor pathway in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related deaths worldwide. Only 30%-40% of the patients with HCC are eligible for curative treatments, which include surgical resection as the first option, liver transplantation and percutaneous ablation. Unfortunately, there is a high frequency of tumor recurrence after surgical resection and most HCC seem resistant to conventional chemotherapy and radiotherapy. Sorafenib, a multi-tyrosine kinase inhibitor, is the only chemotherapeutic option for patients with advanced hepatocellular carcinoma. Patients treated with Sorafenib have a significant increase in overall survival of about three months. Therefore, there is an urgent need to develop alternative treatments. Due to its role in cell growth and development, the insulin-like growth factor system is commonly deregulated in many cancers. Indeed, the insulin-like growth factor (IGF) axis has recently emerged as a potential target for hepatocellular carcinoma treatment. To this aim, several inhibitors of the pathway have been developed such as monoclonal antibodies, small molecules, antisense oligonucleotides or small interfering RNAs. However recent studies suggest that, unlike most tumors, HCC development requires increased signaling through insulin growth factor II rather than insulin growth factor I. This may have great implications in the future treatment of HCC. This review summarizes the role of the IGF axis in liver carcinogenesis and the current status of the strategies designed to target the IGF-I signaling pathway for hepatocellular carcinoma treatment.

Insulin resistance and cancer: the role of insulin and IGFs

Insulin, IGF1, and IGF2 are the most studied insulin-like peptides (ILPs). These are evolutionary conserved factors well known as key regulators of energy metabolism and growth, with crucial roles in insulin resistance-related metabolic disorders such as obesity, diseases like type 2 diabetes mellitus, as well as associated immune deregulations. A growing body of evidence suggests that insulin and IGF1 receptors mediate their effects on regulating cell proliferation, differentiation, apoptosis, glucose transport, and energy metabolism by signaling downstream through insulin receptor substrate molecules and thus play a pivotal role in cell fate determination. Despite the emerging evidence from epidemiological studies on the possible relationship between insulin resistance and cancer, our understanding on the cellular and molecular mechanisms that might account for this relationship remains incompletely understood. The involvement of IGFs in carcinogenesis is attributed to their role in linking high energy intake, increased cell proliferation, and suppression of apoptosis to cancer risks, which has been proposed as the key mechanism bridging insulin resistance and cancer. The present review summarizes and discusses evidence highlighting recent advances in our understanding on the role of ILPs as the link between insulin resistance and cancer and between immune deregulation and cancer in obesity, as well as those areas where there remains a paucity of data. It is anticipated that issues discussed in this paper will also recover new therapeutic targets that can assist in diagnostic screening and novel approaches to controlling tumor development.