Human USP28 blocking peptide

The transcription factor MYC, which is dysregulated in the majority of gliomas, is difficult to target directly. Deubiquitinase ubiquitin-specific protease 28 (USP28) stabilizes oncogenic factors, including MYC. However, the contribution of USP28 in tumorigenesis, particularly in glioma, is unknown. Here, we determined the expression of USP28 and assessed its clinical significance in human glioma. We found that USP28 is overexpressed in human glioma but not in normal brain tissue. The level of USP28 protein expression in human glioma tissues was directly correlated with glioma grade. Meanwhile, the level of USP28 protein expression in human glioblastoma tissues was inversely correlated with patient survival. Enforced USP28 expression promotes SW1783 glioma cell proliferation. Moreover, gliomas that arose from USP28-transfected SW1783 cells displayed tumorigenicity in nude mouse model systems. Inhibition of USP28 expression in glioblastoma U373 cells suppressed anchorage-independent growth invitro and tumorigenicity invivo. Furthermore, USP28 regulates the expression of MYC protein, which is essential in USP28-induced cell growth in glioma cells. These results showed that USP28 is overexpressed in human glioblastomas and it contributes to glioma tumorigenicity. Therefore, USP28 could be a new target of therapy for human malignant glioma.

Background: USP28 is a deubiquitinating enzyme implicated in the DNA damage response, Myc stabilization, and cancer progression. Results: USP28 activity is regulated by SUMO conjugation on the N-terminal region. Conclusion: The N-terminal ubiquitin-binding domains of USP28 are not required for polyubiquitin processing. Significance: Cross-talk exists between SUMO and ubiquitin in the regulation of USP28 enzymatic activity. USP28 (ubiquitin-specific protease 28) is a deubiquitinating enzyme that has been implicated in the DNA damage response, the regulation of Myc signaling, and cancer progression. The half-life stability of major regulators of critical cellular pathways depends on the activities of specific ubiquitin E3 ligases that target them for proteosomal degradation and deubiquitinating enzymes that promote their stabilization. One function of the post-translational small ubiquitin modifier (SUMO) is the regulation of enzymatic activity of protein targets. In this work, we demonstrate that the SUMO modification of the N-terminal domain of USP28 negatively regulates its deubiquitinating activity, revealing a role for the N-terminal region as a regulatory module in the control of USP28 activity. Despite the presence of ubiquitin-binding domains in the N-terminal domain, its truncation does not impair deubiquitinating activity on diubiquitin or polyubiquitin chain substrates. In contrast to other characterized USP deubiquitinases, our results indicate that USP28 has a chain preference activity for Lys(11), Lys(48), and Lys(63) diubiquitin linkages.