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The proteasome is a key regulator of cellular protein homeostasis and is a clinically validated anticancer target. The immunoproteasome, a subtype of proteasome expressed mainly in hematopoietic cells, was initially recognized for its role in antigen presentation during the immune response. Recently, the immunoproteasome has been implicated in several disease conditions including cancer and autoimmune disorders, but many of the factors contributing to these pathological processes remain unknown. In particular, the codon 60 polymorphism of the PSMB9 gene encoding the β1i immunoproteasome catalytic subunit has been investigated in the context of a variety of diseases. Despite this, previous studies have so far reported inconsistent findings regarding the impact of this polymorphism on proteasome activity. Thus, we set out to investigate the impact of the PSMB9 codon 60 polymorphism on the expression and activity of the β1i immunoproteasome subunit in a panel of human cancer cell lines. The β1i-selective fluorogenic substrate Acetyl-Pro-Ala-Leu-7-amino-4-methylcoumarin was used to specifically measure β1i catalytic activity. Our results indicate that the codon 60 Arg/His polymorphism does not significantly alter the expression and activity of β1i among the cell lines tested. Additionally, we also examined the expression of β1i in clinical samples from colon and pancreatic cancer patients. Our immunohistochemical analyses showed that ≈ 70% of clinical colon cancer samples and ≈ 53% of pancreatic cancer samples have detectable β1i expression. Taken together, our results indicate that the β1i subunit of the immunoproteasome is frequently expressed in colon and pancreatic cancers but that the codon 60 genetic variants of β1i display similar catalytic activities and are unlikely to contribute to the significant inter-cell-line and inter-individual variabilities in the immunoproteasome activity.

Prostate apoptosis response-4 (Par-4) is a tumor suppressor which protects against neoplastic transformation. Remarkably, Par-4 is capable of inducing apoptosis selectively in cancer cells without affecting the normal cells. In this study, we found that recombinant Par-4 protein had limited serum persistence in mice that may diminish its anti-tumor activity in vivo. To improve the in vivo performance of the short-lived Par-4 protein, we aimed to develop a novel, long-lasting form of Par-4 with extended sequence, denoted as Par-4Ex, without affecting the desirable molecular function of the natural Par-4. We demonstrate that the Par-4Ex protein entity, produced by using the Escherichia coli expression system suitable for large-scale production, fully retains the desirable pro-apoptotic activity of Par-4 protein, but with ~7-fold improved biological half-life. Further in vivo tests confirmed that, due to the prolonged biological half-life, the Par-4Ex protein is indeed more potent in suppressing metastatic tumor growth in mice. [ABSTRACT FROM AUTHOR]