Regulation of Mdmx and its role in the p53 pathway

The p53 protein is an important tumor suppressor that acts as a key regulator of the integrity of the genome. Two essential regulators of the p53 protein are Mdm2 and its homologue Mdmx. Like Mdm2, Mdmx represses p53-induced transcription. However, Mdmx cannot ubiquitinate or degrade p53 opposed to Mdm2. In chapter 2, studies aimed to better understand the functional differences between Mdmx and Mdm2. By generation of hybrid constructs between Mdmx and Mdm2, we found that in addition to a complete RING domain of Mdm2, also an internal acidic domain is required for p53 ubiquitination and degradation. In chapter 3 the role of Mdmx in human tumor formation is described. The results show that the mdmx gene can function as an oncogene and demonstrate that the transforming function of the Mdmx protein is dependent on its ability to interact with p53. In chapter 4, the regulation of Mdmx stability is described. We demonstrate that the stability of Mdmx is determined by a balance in de-ubiquitination by HAUSP and ubiquitination by Mdm2. Chapter 5 the results of initial studies on the role of SUMO conjugation in Mdmx function are shown.UBL - phd migration 201

Sumoylation inhibits α-synuclein aggregation and toxicity

Sumoylation of α-synuclein decreases its rate of aggregation and its deleterious effects in vitro and in vivo

Erratum: Correction for Danovi et al. "Amplification of Mdmx (or Mdm4) Directly Contributes to Tumor Formation by Inhibiting p53 Tumor Suppressor Activity" (Molecular and cellular biology (2004) 24 13 (5835-5843) PII: e00150-19)

SCOPUS: er.jDecretOANoAutActifinfo:eu-repo/semantics/publishe

Amplification of Mdmx (or Mdm4) Directly Contributes to Tumor Formation by Inhibiting p53 Tumor Suppressor Activity

Human tumors are believed to harbor a disabled p53 tumor suppressor pathway, either through direct mutation of the p53 gene or through aberrant expression of proteins acting in the p53 pathway, such as p14(ARF) or Mdm2. A role for Mdmx (or Mdm4) as a key negative regulator of p53 function in vivo has been established. However, a direct contribution of Mdmx to tumor formation remains to be demonstrated. Here we show that retrovirus-mediated Mdmx overexpression allows primary mouse embryonic fibroblast immortalization and leads to neoplastic transformation in combination with HRas(V12). Furthermore, the human Mdmx ortholog, Hdmx, was found to be overexpressed in a significant percentage of various human tumors and amplified in 5% of primary breast tumors, all of which retained wild-type p53. Hdmx was also amplified and highly expressed in MCF-7, a breast cancer cell line harboring wild-type p53, and interfering RNA-mediated reduction of Hdmx markedly inhibited the growth potential of these cells in a p53-dependent manner. Together, these results make Hdmx a new putative drug target for cancer therapy

Loss of HAUSP-mediated deubiquitination contributes to DNA damage-induced destabilization of Hdmx and Hdm2

The p53 tumor suppressor protein has a major role in protecting the integrity of the genome. In unstressed cells, p53 is maintained at low levels by the ubiquitin-proteasome pathway. A balance between ubiquitin ligase activity (Hdm2, COP1, and Pirh2) and the ubiquitin protease activity of the Herpes virus-associated ubiquitin-specific protease (HAUSP) determines the half-life of p53. HAUSP also modulates p53 stability indirectly by deubiquitination and stabilization of Hdm2. The Hdmx protein affects p53 stability as well through its interaction with and regulation of Hdm2. Vice versa, Hdmx is a target for Hdm2-mediated ubiquitination and degradation. Here, we show that HAUSP also interacts with Hdmx, resulting in its direct deubiquitination and stabilization. HAUSP activity is required to maintain normal Hdmx protein levels. Therefore, the balance between HAUSP and Hdm2 activity determines Hdmx protein stability. Importantly, impaired deubiquitination of Hdmx/Hdm2 by HAUSP contributes to the DNA damage-induced degradation of Hdmx and transient instability of Hdm2