Protein degradation in human disease

In-Silico and In-Vitro Analysis of Human SOS1 Protein Causing Noonan Syndrome - A Novel Approach to Explore the Molecular Pathways

Aims

Perform in-silico analysis of human SOS1 mutations to elucidate their pathogenic role in Noonan syndrome (NS).

Background

NS is an autosomal dominant genetic disorder caused by single nucleotide mutation in PTPN11, SOS1, RAF1, and KRAS genes. NS is thought to affect approximately 1 in 1000. NS patients suffer different pathogenic effects depending on the mutations they carry. Analysis of the mutations would be a promising predictor in identifying the pathogenic effect of NS.

Methods

We performed computational analysis of the SOS1 gene to identify the pathogenic nonsynonymous single nucleotide polymorphisms (nsSNPs) th a t cause NS. SOS1 variants were retrieved from the SNP database (dbSNP) and analyzed by in-silico tools I-Mutant, iPTREESTAB, and MutPred to elucidate their structural and functional characteristics.

Results

We found that 11 nsSNPs of SOS1 that were linked to NS. 3D modeling of the wild-type and the 11 nsSNPs of SOS1 showed that SOS1 interacts with cardiac proteins GATA4, TNNT2, and ACTN2. We also found that GRB2 and HRAS act as intermediate molecules between SOS1 and cardiac proteins. Our in-silico analysis findings were further validated using induced cardiomyocytes (iCMCs) derived from NS patients carrying SOS1 gene variant c.1654A>G (NSiCMCs) and compared to control human skin fibroblast-derived iCMCs (C-iCMCs). Our in vitro data confirmed that the SOS1, GRB2 and HRAS gene expressions as well as the activated ERK protein, were significantly decreased in NS-iCMCs when compared to C-iCMCs.

Conclusion

This is the first in-silico and in vitro study demonstrating that 11 nsSNPs of SOS1 play deleterious pathogenic roles in causing NS.

La dégradation protéasomique : De l’adressage des protéins aux nouvelles perspectives thérapeutiques

The proteasome is the main intracellular proteolytic machinery. It is involved in all major cellular functions and decisions. It has long been thought that prior ubiquitinylation of almost all of its substrates was necessary for degradation. It has also long been considered that ubiquitinylation and degradation were two uncoupled mechanisms and that the recruitment of ubiquitinylated species was only performed by specialized subunits of the proteasome. The recent literature questions this simplified view. It also suggests that, on the one hand, the fraction of proteins hydrolyzed by the proteasome independently of their ubiquitinylation has largely been underestimated and, on the other hand, that the recognition of ubiquitinylated proteins involves complex addressing systems. Furthermore, it indicates a higher order structuration of the ubiquitin/proteasome pathway, a fraction of the proteasome and of ubiquitinylation enzymes being engaged in supramolecular complexes. Finally, proteasomal degradation is altered in a number of pathological situations. It, thus, constitutes a therapeutic target and the first applications are emerging.

A phase II study of bortezomib in the treatment of metastatic malignant melanoma

BACKGROUND

Bortezomib is a proteasome inhibitor with manageable clinical toxicity and laboratory evidence of anti-melanoma activity. Therefore, it was considered for clinical testing in patients with metastatic melanoma.

METHODS

Patients with metastatic melanoma and adequate hematologic, renal, and hepatic function were treated with bortezomib (a 1.5-mg/m2 intravenous bolus twice weekly for 2 of every 3 weeks). Eligible patients were age > or = 18 years with an Eastern Cooperative Oncology Group performance status of 0-1. The primary goal of the current study was to evaluate the 18-week disease progression-free survival rate and tolerability of bortezomib in these patients.

RESULTS

The current study was intended to treat 45 patients. It was closed at the planned interim analysis due to early evidence of insufficient clinical efficacy. Twenty-seven patients with a median age of 56 years (range, 32-77 years)were accrued. There were no major clinical responses to treatment. Only 6 patients (22%) achieved stable disease. Of these 6 patients, 4 were still stable after 4 cycles of treatment, but were removed from the study due to toxicity. The median time to disease progression was 1.5 months (95% confidence interval [95% CI], 1.4-1.6) with a median overall survival of 14.5 months (95% CI, 9-22). Having failed bortezomib, most patients proceeded to other clinical trials. Twenty-six patients were evaluable for toxicity. One patient was removed from the study for other reasons and could not return for the cycle evaluation and thus was never evaluated. Of the 26 patients, no Grade 4/5 treatment-related toxicities (using the National Cancer Institute Common Toxicity Criteria [version 2.0]) were reported. Eleven patients (42%) had Grade 3 toxicities (believed to be at least possibly related to treatment), including sensory neuropathy, thrombocytopenia, constipation, fatigue, ileus, abdominal pain, and infection without neutropenia. The median number of treatment cycles patients received was two (range, one to six treatment cycles). Two patients (7%) had 1 dose delay and 6 patients (22%) had dose reductions during 1 treatment cycle due to adverse events.

CONCLUSIONS

Single-agent bortezomib, administered twice weekly x 2 weeks, every 3 weeks at a dose of 1.5 mg/m2, was not found to be effective in the treatment of patients with metastatic melanoma.

Expression of protein gene product 9.5 (PGP9.5)/ubiquitin-C-terminal hydrolase 1 (UCHL-1) in human myeloma cells

The neuron cytoplasmic protein gene product 9.5 (PGP9.5)/ubiquitin-C-terminal hydrolase 1 (UCHL-1) protein is a thiol protease that recognizes and hydrolyzes a peptide bond at the C-terminal of ubiquitin, and is involved in the processing of ubiquitin precursors and ubiquinated proteins. Although this molecule is known as a specific tissue marker for the neuroendocrine system, many reports have indicated that PGP9.5 is a marker for certain tumour types, such as cancer of the lung, colon, and pancreas. The expression of PGP9.5 in myeloma cells was examined. PGP9.5 seemed to be expressed specifically in myeloma cells as compared with other haematological malignant cells. In addition, in myeloma cells subjected to growth-factor starvation, the upregulation of PGP9.5 was observed in association with that of p27(Kip1), a cyclin-dependent-kinase inhibitor, although the upregulation caused by irradiation was milder. In contrast, the hypoxic culture of myeloma cells induced down-regulation of PGP9.5. These results suggested that PGP9.5 may be a good marker for myeloma among haematological malignancies. In addition, it may indicate certain cellular features of myeloma cells, such as sensitivity to proteasome inhibitors.