Controlled Access of p53 to the Nucleus Regulates Its Proteasomal Degradation by MDM2

Abstract

The tumor suppressor p53 can be sent to the proteasome for degradation by placing its nucleo-cytoplasmic shuttling under ligand control. Endogenous p53 is ubiquitinated by MDM2 in the nucleus, and controlling the access of p53 to the nuclear compartment regulates its ubiquitination and proteasomal degradation. This was accomplished by the use of a “protein switch” that places nuclear translocation under the control of externally applied dexamethasone. Fluorescence microscopy revealed that sending protein switch p53 (PS-p53) to the nucleus produces a distinct punctate distribution in both the cytoplasm and nucleus. The nuclear role in accessing the proteasome was investigated by inhibiting classical nuclear export with leptomycin B. Trapping PS-p53 in the nucleus only allows this punctate staining in that compartment, suggesting that PS-p53 must translocate first to the nuclear compartment for cytoplasmic punctate staining to occur. The role of MDM2 binding was explored by inhibiting MDM2/p53 binding with nutlin-3. Inhibition of this interaction blocked both nuclear export and cytoplasmic and nuclear punctate staining, providing evidence that any change in localization after nuclear translocation is due to MDM2 binding. Further, blocking the proteolytic activity of the proteasome maintained the nuclear localization of the construct. Truncations of p53 were made to determine smaller constructs still capable of interacting with MDM2, and their subcellular localization and degradation potential was observed. PS-p53 and a smaller construct, construct containing the two MDM2 binding regions of p53 (Box I+V) were indeed degraded by the proteasome as measured by loss of enhanced green fluorescent protein that was also fused to the construct. The influence of these constructs on p53 gene transactivation function was assessed, and revealed that PS-p53 decreased gene transactivation, while PS-p53(BoxI+V) did not significantly change baseline gene transactivation.

Preclinical Optimization of MDM2 Antagonist Scheduling for Cancer Treatment by Using a Model-Based Approach

“…The loss of MDM2 and p21 protein levels could be the result of changes in protein half-life on p53 activation as evidenced in published results where accelerated MDM2 autodegradation was reported during p53-mediated DNA damage response (17). However, p53 function and stability may also be tightly controlled by its subcellular localization (18,19). Therefore, it is possible that in a cell triggered into apoptosis, nuclear or mitochondrial localized p53 remains fairly stable following RG7388 washout, whereas MDM2 and p21 are accessible to be targeted by the cytoplasmic ubiquitin proteasome pathway.…”

Protein phosphatase Mg2+/Mn2+ dependent 1F promotes smoking-induced breast cancer by inactivating phosphorylated-p53-induced signals

“…For example, DNA damage induces the phosphorylation of p53 at Ser-15, Ser-20 and Ser-37, thereby weakening its binding to the oncogenic protein MDM2, which would otherwise promote the ubiquitination and proteasomal degradation of p53 [13]. Immunoprecipitation was performed to test whether PPM1F and p53 would form a complex after nicotine treatment.…”

“…The protein stability of p53 depends on the time required for its intracellular degradation. It has been reported that MDM2, an intracellular protein, binds to p53 [12] and exports it from the nucleus for ubiquitin-dependent proteolysis [13]. In response to DNA-damaging agents, posttranslational modifications such as the phosphorylation of Ser-15 [14, 15], Thr-18 [16], and Ser-20 [17] weaken the binding between p53 and MDM2.…”

Delivery of a Monomeric p53 Subdomain with Mitochondrial Targeting Signals from Pro-Apoptotic Bak or Bax

“…Under normal conditions, the E3 ligase murine double minute 2 (MDM2) binds to the MDM2 binding domain (MBD) of p53 prompting polyubiquitination of terminal lysines on the C-terminus of p53, which marks p53 for proteasomal degradation (2). Upon stress induction, such as DNA damage or ER stress, cytoplasmic p53 translocates either to the nucleus (3) or to the mitochondria (4).…”