Discovery of melanotransferrin as a serological marker of colorectal cancer by secretome analysis and quantitative proteomics

To discover serological colorectal cancer (CRC) markers, we analyzed cell line secretome to gather proteins of higher potential to be secreted from tissues into circulation. A total of 898 human proteins were identified, of which 62.2% were predicted to be released or shed from cells. The identified proteins were compared with tissue proteomes to find candidate proteins whose expressions were elevated in tumor tissues compared with normal tissues as revealed by (i) quantitative proteomic analysis based on cICAT and mTRAQ or (ii) data mining of immunohistochemical images piled in Human Protein Atlas database. By applying various stringent criteria, 11 candidate proteins were selected. Among these, we validated an significant increase (p = 0.0018) of melanotransferrin (TRFM) at the plasma level of CRC patients through Western blotting, using 130 plasma samples containing 30 healthy controls, 80 CRC patients, and 20 patients of other diseases. Finally, we measured the expression level of TRFM in 325 plasma samples containing 77 healthy controls and 228 CRC patients (34.6 ± 4.2 ng/mL and 67.0 ± 6.4 ng/mL, p < 0.0001) through ELISA and demonstrated the area under the receiver operating characteristic curve of 0.723 (p < 0.0001) with a 92.5% specificity, 48.2% sensitivity, and 95.7% positive predictive value. Furthermore, unlike CEA and PAI-1, up-regulation of TRFM in pathological stages I & II groups compared with stages III & IV groups lead us to expect the use TRFM for early-stage diagnosis of CRC. In this study, we suggest TRFM as a potential serological marker for CRC and expect our discovery strategy to help identify highly cancer-specific and body-fluid-accessible biomarkers.

Conjugation of melanotransferrin antibody on solid lipid nanoparticles for mediating brain cancer malignancy

Solid lipid nanoparticles (SLNs) comprising complex internal lipids were conjugated with melanotransferrin antibody (MA) to carry anticancer etoposide across the blood-brain barrier (BBB) for managing glioblastoma multiforme (GBM). MA was crosslinked on the surface of etoposide-loaded SLNs (ETP-SLNs) to target human brain-microvascular endothelial cells (HBMECs) and U87MG cells. The experimental evidences showed that an increase in the tripalmitin weight percentage in lipids enhanced the particle size and viability of U87MG cells, however decreased the etoposide loading efficiency, MA conjugation efficiency, and permeability coefficient for etoposide across the BBB. A high level of MA on the particle surface increased the atomic ratio of nitrogen to phosphorus and permeability coefficient for propidium iodide and etoposide across the BBB, however reduced the MA conjugation efficiency, transendothelial electrical resistance, and viability of U87MG cells. Based on immunochemical staining, we found that MA on ETP-SLNs triggered the melanotransferrin-mediated transcytosis and promoted the growth-inhibitory efficacy to U87MG cells. MA-conjugated ETP-SLNs can be a promising colloidal delivery system for malignant GBM pharmacotherapy. © 2015 American Institute of Chemical Engineers Biotechnol. Prog., 32:480-490, 2016.

Draft Genome of the Sea Cucumber Holothuria glaberrima, a Model for the Study of Regeneration

Regeneration is one of the most fascinating and yet least understood biological processes. Echinoderms, one of the closest related invertebrate groups to humans, can contribute to our understanding of the genetic basis of regenerative processes. Among echinoderms, sea cucumbers have the ability to grow back most of their body parts following injury, including the intestine and nervous tissue. The cellular and molecular events underlying these abilities in sea cucumbers have been most extensively studied in the species Holothuria glaberrima. However, research into the regenerative abilities of this species has been impeded due to the lack of adequate genomic resources. Here, we report the first draft genome assembly of H. glaberrima and demonstrate its value for future genetic studies. Using only short sequencing reads, we assembled the genome into 89,105 scaffolds totaling 1.1 gigabases with an N50 of 25 kilobases. Our BUSCO assessment of the genome resulted in 894 (91.4%) complete and partial genes from 978 genes queried. We incorporated transcriptomic data from several different life history stages to annotate 51,415 genes in our final assembly. To demonstrate the usefulness of the genome, we fully annotated the melanotransferrin (Mtf) gene family, which have a potential role in the regeneration of the sea cucumber intestine. Using these same data, we extracted the mitochondrial genome, which showed high conservation to that of other holothuroids. Thus, these data will be a critical resource for ongoing studies of regeneration and other studies in sea cucumbers.

Phylogenetic and sequence analyses of insect transferrins suggest that only transferrin 1 has a role in iron homeostasis

Iron is essential to life, but surprisingly little is known about how iron is managed in nonvertebrate animals. In mammals, the well-characterized transferrins bind iron and are involved in iron transport or immunity, whereas other members of the transferrin family do not have a role in iron homeostasis. In insects, the functions of transferrins are still poorly understood. The goals of this project were to identify the transferrin genes in a diverse set of insect species, resolve the evolutionary relationships among these genes, and predict which of the transferrins are likely to have a role in iron homeostasis. Our phylogenetic analysis of transferrins from 16 orders of insects and two orders of noninsect hexapods demonstrated that there are four orthologous groups of insect transferrins. Our analysis suggests that transferrin 2 arose prior to the origin of insects, and transferrins 1, 3, and 4 arose early in insect evolution. Primary sequence analysis of each of the insect transferrins was used to predict signal peptides, carboxyl-terminal transmembrane regions, GPI-anchors, and iron binding. Based on this analysis, we suggest that transferrins 2, 3, and 4 are unlikely to play a major role in iron homeostasis. In contrast, the transferrin 1 orthologs are predicted to be secreted, soluble, iron-binding proteins. We conclude that transferrin 1 orthologs are the most likely to play an important role in iron homeostasis. Interestingly, it appears that the louse, aphid, and thrips lineages have lost the transferrin 1 gene and, thus, have evolved to manage iron without transferrins.

Level of Melanotransferrin in Tissue and Sera Serves as a Prognostic Marker of Gastric Cancer

AIM

The aim of the study was to identify novel biomarkers that are vital for improving management of patients with gastric cancer (GC).

MATERIALS AND METHODS

An RNA-sequencing analysis was conducted using gastric tissue from patients with metastatic GC. In vitro cell functions were evaluated by siRNA-mediated knockdown assays. A total of 230 pairs of gastric tissue were subjected to expression analysis of mRNA and protein in situ. The serum levels of the candidate biomarker were determined by ELISA.

RESULTS

MELTF was identified as a candidate biomarker. Inhibition of MELTF expression suppressed the invasion ability of GC cells. Increased tissue MELTF mRNA expression was associated with shorter survival. Furthermore, staining intensity of tissue MELTF protein was linked to recurrence rates. Serum MELTF levels gradually were increased from healthy controls to advanced GC. Patients with high serum MELTF levels had poor prognosis.

CONCLUSION

Both tissue and serum MELTF levels may serve as biomarkers of GC progression.

Low Cerebrospinal Fluid Levels of Melanotransferrin Are Associated With Conversion of Mild Cognitively Impaired Subjects to Alzheimer's Disease

The disruption of iron metabolism and iron transport proteins have been implicated in the pathogenesis of Alzheimer's disease (AD). Serum melanotransferrin (MTf), a transferrin homolog capable of reversibly binding iron, has been proposed as a biochemical marker of AD. MTf has also been shown to be elevated in iron-rich reactive microglia near amyloid plaques in AD. We examined the association of CSF MTf to hippocampal volumes and cognitive tests in 86 cognitively normal, 135 mild cognitive impairment (MCI) and 66 AD subjects. CSF was collected at baseline for MTf, Aβ, total-tau and phosphorylated-tau measurements. Serial cognitive testing with ADAS-Cog13, Rey's auditory visual learning test (RAVLT), mini-mental state examination (MMSE) were performed alongside hippocampal MRI volumetric analysis for up to 10 years after baseline measurements. High levels of baseline CSF MTf were positively associated with baseline hippocampal volume (R ² = 22%, β = 0.202, and p = 0.017) and RAVLT scores (R ² = 7.30%, β = -0.178, and p = 0.043) and negatively correlated to ADAS-Cog13 (R ² = 17.3%, β = 0.247, and p = 0.003) scores in MCI subjects. Interestingly, MCI subjects that converted to AD demonstrated significantly lower levels of CSF MTf (p = 0.020) compared to MCI non-converters at baseline. We suggest the diminished CSF MTf observed in MCI-converters to AD may arise from impaired transport of MTf from blood into the brain tissue/CSF and/or increased MTf export from the CSF into the blood arising from attenuated competition with reduced levels of CSF Aβ. Further investigations are required to determine the source of CSF MTf and how brain MTf is regulated by cellular barriers, Aβ and activated microglia that surround plaques in AD pathophysiology. In conclusion, low CSF MTf may identify those MCI individuals at risk of converting to AD.

Discovery of a Highly Conserved Peptide in the Iron Transporter Melanotransferrin that Traverses an Intact Blood Brain Barrier and Localizes in Neural Cells

The blood-brain barrier (BBB) hinders the distribution of therapeutics intended for treatment of diseases of the brain. Our previous studies demonstrated that that a soluble form of melanotransferrin (MTf; Uniprot P08582; also known as p97, MFI2, and CD228), a mammalian iron-transport protein, is an effective carrier for delivery of drug conjugates across the BBB into the brain and was the first BBB targeting delivery system to demonstrate therapeutic efficacy within the brain. Here, we performed a screen to identify peptides from MTf capable of traversing the BBB. We identified a highly conserved 12-amino acid peptide, termed MTfp, that retains the ability to cross the intact BBB intact, distributes throughout the parenchyma, and enter endosomes and lysosomes within neurons, astrocytes and microglia in the brain. This peptide may provide a platform for the transport of therapeutics to the CNS, and thereby offers new avenues for potential treatments of neuropathologies that are currently refractory to existing therapies.

Unlocking the potential of melanotransferrin (CD228): implications for targeted drug development and novel therapeutic avenues

INTRODUCTION

Melanotransferrin (CD228), a cell membrane-anchored protein, has emerged as a significant cancer antigen due to its high expression in various solid tumors. This review synthesizes the current understanding and therapeutic potential of CD228.

AREAS COVERED

We conducted a literature search using PubMed, Web of Science, and ClinicalTrials.gov with the keywords 'melanotransferrin' and 'CD228.' Our comprehensive review examines CD228 and its isoforms, membrane-bound CD228 (mMFI2) and soluble CD228 (sMFI2), their roles in tumorigenesis, angiogenesis, endothelial cell migration, plasminogen activation, and transendothelial transport across the BBB, as well as the current state of drug development efforts targeting CD228.

EXPERT OPINION

Targeting CD228 represents a promising therapeutic strategy in oncology, with mMFI2 as a potential target for solid tumors and sMFI2 valuable for disease diagnosis in malignant tumors, Alzheimer's disease, and arthritis, and facilitating macromolecular drug delivery across the blood-brain barrier (BBB). Despite its potential to transform the treatment landscape for numerous solid cancers, further research into the precise mechanisms and clinical translation of CD228-directed treatments is needed to maximize its therapeutic utility.