Protein and Peptide Letters - Current Issue

Resistance to anti-tumor agents targeting the epidermal growth factor receptor (EGFR) reduces treatment response and requires the development of novel EGFR antagonists. Mutant epidermal growth factor (EGF) forms with reduced agonistic activity could be promising agents in cancer treatment.

EGF D46G affinity to EGFR domain III was assessed with affinity chromatography. EGF D46G acute toxicity in Af albino mice at 320 and 3200 μg/kg subcutaneous doses was evaluated. EGF D46G activity in human epidermoid carcinoma cells at 10 ng/mL concentration in serum-free medium and in subcutaneous Ehrlich ascites carcinoma mice model at 320 μg/kg dose was studied.

The D46G substitution decreases the thermal stability of EGF complexes with EGFR domain III by decreasing the ability of the C-terminus to be released from the intermolecular β-sheet. However, with remaining binding sites for EGFR domain I, EGF D46G effectively competes with other EGF-like growth factors for binding to EGFR and does not demonstrate toxic effects in mice. EGF D46G inhibits the proliferation of human epidermoid carcinoma cells compared to native EGF. A single subcutaneous administration of EGF D46G along with Ehrlich carcinoma cells injection inhibits the proliferation of these cells and delays tumor formation for up to seven days.

EGF D46G can be defined as a partial EGFR agonist as this mutant form demonstrates reduced agonistic activity compared to native EGF. The study emphasizes the role of the EGF C-terminus in establishing interactions with EGFR domain III, which are necessary for EGFR activation and subsequent proliferation of cells.

Glycogen Storage Disease type III (GSD III) is a metabolic disorder resulting from a deficiency of the Glycogen Debranching Enzyme (GDE), a large monomeric protein (approximately 170 kDa) with cytoplasmic localization and two distinct enzymatic activities: 4-α-glucantransferase and amylo-α-1,6-glucosidase. Mutations in the Agl gene, with consequent deficiency in GDE, lead to the accumulation of abnormal/toxic glycogen with shorter chains (phosphorylase limit dextrin, PLD) in skeletal and/or heart muscle and/or in the liver. Currently, there is no targeted therapy, and available treatments are symptomatic, relying on specific diets.

Enzyme Replacement Therapy (ERT) might represent a potential therapeutic strategy for GSD III. Moreover, the single-gene nature of GSD III, the subcellular localization of GDE, and the type of affected tissues represent ideal conditions for exploring gene therapy approaches. Toward this direction, we designed a synthetic, codon-optimized cDNA encoding the human GDE.

This gene yielded high amounts of soluble, enzymatically active protein in Escherichia coli. Moreover, when transfected in Human Embryonic Kidney cells (HEK-293), it successfully encoded a functional GDE.

These results suggest that our gene or protein might complement the missing function in GSD III patients, opening the door to further exploration of therapeutic approaches for this disease.

Peptide drugs are advantageous because they are subject to rational design and exhibit highly diverse structures and broad biological activities. The NS2B-NS3 protein is a particularly promising flavivirus therapeutic target, with extensive research on the development of inhibitors as therapeutic candidates, and was used as a model in this work to determine the mechanism by which GA-Hecate inhibits ZIKV replication.

The present study aimed to evaluate the potential of GA-Hecate, a new antiviral developed by our group, against the Brazilian Zika virus and to evaluate the mechanism of action of this compound on the flavivirus NS2B-NS3 protein.

Solid-phase peptide Synthesis, High-Performance Liquid Chromatography, and Mass Spectrometry were used to obtain, purify, and characterize the synthesized compound. Real-time and enzymatic assays were used to determine the antiviral potential of GA-Hecate against ZIKV.

The RT-qPCR results showed that GA-Hecate decreased the number of ZIKV RNA copies in the virucidal, pre-treatment, and post-entry assays, with 5- to 6-fold fewer RNA copies at the higher nontoxic concentration in Vero cells (HNTC: 10 μM) than in the control cells. Enzymatic and kinetic assays indicated that GA-Hecate acts as a competitive ZIKV NS2B-NS3 protease inhibitor with an IC50 of 32 nM and has activity against the yellow fever virus protease.

The results highlight the antiviral potential of the GA-Hecate bioconjugate and open the door for the development of new antivirals.

Colorectal cancer remains to be the third leading cause of cancer mortality rates. Despite the diverse effects of the miRNA cluster located in PVT1 of 8q24.21 across various tumors, the specific biological function in colorectal cancer has not been clarified.

The amplification of the miR-1204 cluster was analyzed with the cBioPortal database, while the expression and survival analysis of the miRNAs in the cluster were obtained from several GEO databases of colorectal cancer. To investigate the functional role of miR-1204 in colorectal cancer, overexpression and silencing experiments were performed by miR-1204 mimic and inhibitor transfection in colorectal cancer cell lines, respectively. Then, the effects of miR-1204 on cell proliferation were assessed through CCK-8, colony formation, and Edu assay. In addition, cell migration was evaluated using wound healing and Transwell assay. Moreover, candidate genes identified through RNA sequencing and predicted databases were identified and validated using PCR and western blot. A Dual-luciferase reporter experiment was conducted to identify MASPIN as the target gene of miR-1204.

In colorectal cancer, the miR-1204 cluster exhibited high amplification, and the expression levels of several cluster miRNAs were also significantly increased. Furthermore, miR-1204 was found to be significantly associated with disease-specific survival according to the analysis of GSE17536. Functional experiments demonstrated that transfection of miR-1204 mimic or inhibitor could enhance or decrease cancer cell proliferation and migration. MASPIN was identified as a target of miR-1204. Additionally, the overexpression of MASPIN partially rescued the effect of miR-1204 mimics on tumorigenic abilities in LOVO cells.

miR-1204 positioning in 8q24.21 promotes the proliferation and migration of colorectal cancer cells by targeting MASPIN.

Osteosarcoma (OS) is the leading cancer-associated mortality in childhood and adolescence. Increasing evidence has demonstrated the key function of microRNAs (miRNAs) in OS development and chemoresistance. Among them, miRNA-605-3p acted as an important tumor suppressor and was frequently down-regulated in multiple cancers. However, the function of miR-650-3p in OS has not been reported.

The aim of this work is to explore the novel role of miR-605-3p in osteosarcoma and its possible involvement in OS chemotherapy resistance.

The expression levels of miR-605-3p in OS tissues and cells were assessed by reverse transcription quantitative PCR (RT-qPCR). The relevance of miR-605-3p with the prognosis of OS patients was determined by the Kaplan-Meier analysis. Additionally, the influence of miR-605-3p on OS cell growth was analyzed using the cell counting kit-8, colony formation assay, and flow cytometry. The mRNA and protein expression of RAF1 were detected by RT-qPCR and western blot. The binding of miR-605-3p with the 3’-UTR of RAF1 was confirmed by dual-luciferase reporter assay.

Our results showed that miR-605-3p was markedly decreased in OS tissues and cells. A lower level of miR-605-3p was strongly correlated with lymph node metastasis and poor 5-year overall survival rate of OS patients. In vitro assay found that miR-605-3p suppressed OS cell proliferation and promoted cell apoptosis. Mechanistically, the proto-oncogene RAF1 was seen as a target of miR-605-3p and strongly suppressed by miR-605-3p in OS cells. Restoration of RAF1 markedly eliminated the inhibitory effect of miR-605-3p on OS progression, suggesting RAF1 as a key mediator of miR-605-3p. Consistent with the decreased level of RAF1, miR-605-3p suppressed the activation of both MEK and ERK in OS cells, which are the targets of RAF1. Moreover, lower levels of miR-605-3p were found in chemoresistant OS patients, and down-regulated miR-605-3p increased the resistance of OS cells to therapeutic agents.

Our data revealed that miR-605-3p serves as a tumor suppressor gene by regulating RAF1 and increasing the chemosensitivity of OS cells, which provided the novel working mechanism of miR-605-3p in OS. Engineering stable nanovesicles that could efficiently deliver miR-605-3p with therapeutic activity into tumors could be a promising therapeutic approach for the treatment of OS.