Exploring the proteasome system: A novel concept of proteasome inhibition and regulation

The proteasome is a well-identified therapeutic target for cancer treatment. It acts as the main protein degradation system in the cell and degrades key mediators of cell growth, survival and function. The term "proteasome" embraces a whole family of distinct complexes, which share a common proteolytic core, the 20S proteasome, but differ by their attached proteasome activators. Each of these proteasome complexes plays specific roles in the control of cellular function. In addition, distinct proteasome interacting proteins regulate proteasome activity in subcellular compartments and in response to cellular signals. Proteasome activators and regulators may thus serve as building blocks to fine-tune proteasome function in the cell according to cellular needs. Inhibitors of the proteasome, e.g. the FDA approved drugs Velcade™, Kyprolis™, Ninlaro™, inactivate the catalytic 20S core and effectively block protein degradation of all proteasome complexes in the cell resulting in inhibition of cell growth and induction of apoptosis. Efficacy of these inhibitors, however, is hampered by their pronounced cytotoxic side-effects as well as by the emerging development of resistance to catalytic proteasome inhibitors. Targeted inhibition of distinct buiding blocks of the proteasome system, i.e. proteasome activators or regulators, represents an alternative strategy to overcome these limitations. In this review, we stress the importance of the diversity of the proteasome complexes constituting an entire proteasome system. Our building block concept provides a rationale for the defined targeting of distinct proteasome super-complexes in disease. We thereby aim to stimulate the development of innovative therapeutic approaches beyond broad catalytic proteasome inhibition.

Overexpression of proteasomal activator PA28α serves as a prognostic factor in oral squamous cell carcinoma

Background

Despite recent advances in oral squamous cell carcinoma (OSCC) diagnosis and therapy, disease recurrence remains common and is strongly associated with mortality. It is therefore critical to identify new targets for both treatment and diagnostic purposes. We aimed at investigating the role of PA28α, a proteasomal activator in OSCC.

Methods

The expression of PA28α was examined in a panel of OSCC cell lines and tissues, associated with oncomine analysis. In a large OSCC patient cohort, the prognostic value of PA28α expression was evaluated. Primary clinical end points were recurrence-free and overall survival rate. Functional involvement of PA28α in OSCC was examined in both in vitro and in vivo models upon specific siRNA knockdown.

Results

PA28α was found to be overexpressed in OSCC cell lines and tumor tissues. High expression of PA28α was significantly associated with recurrence and poorer overall survival. Specific knockdown of PA28α inhibited OSCC cell proliferation, migration, invasion in vitro and reduced the growth of OSCC xenografts in vivo. Multivariate Cox regression analyses revealed PA28α as independent prognostic predictors.

Conclusions

These results suggest that PA28α is involved in OSCC oncogenesis and may serve as a potential prognostic factor.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-016-0309-z) contains supplementary material, which is available to authorized users.

Prognostic role of serum cytokines in patients with nasopharyngeal carcinoma

BACKGROUND

Th1/Th2 cytokine network imbalance plays a major role in cancer development and progression. In this study, we aim to evaluate the relationship between those cytokines and clinical outcome in patients with nasopharyngeal carcinoma (NPC).

PATIENTS AND METHODS

The concentrations of Th1 cytokines (IL-2, TNF-α, IFN-γ) and Th2 cytokines (IL-4, IL-5, IL-10) in the serum were examined by Cytometric Bead Array in a total of 80 nasopharyngeal carcinoma patients pre and post treatment. Associations of those cytokines with clinical pathological factors, treatment response, and overall survival were analyzed.

RESULTS

Pretreatment serum levels of IL-2 and TNF-α were closely associated with overall survival. Compared to patients with low IL-2 expression, those with high expression had less risk of death (hazard ratio (HR) = 0.31, 95% confidence interval (CI) 0.13-0.75, p = 0.009). In contrast, TNF-α showed opposite effects on overall survival in patients with NPC. Patients with high TNF-α expression had a more than 2-fold increase in risk of death than those with low TNF-α (HR = 2.66, 95% CI 1.04-6.78, p = 0.041). All HRs were adjusted for age, sex, stage, histology, and treatment. Kaplan-Meier survival analysis showed similar survival differences between the 2 groups.

CONCLUSION

Lower serum IL-2 or elevated serum TNF-α concentrations predict an unfavorable prognosis for patients with NPC.