Tripeptidyl-peptidase II Controls DNA Damage Responses and In vivo γ-Irradiation Resistance of Tumors

Abstract

Cellular responses to ;-irradiation exposure are controlled by phosphatidylinositol 3-kinase-related kinases (PIKK) in the nucleus, and in addition, cytosolic PIKKs may have a role in such responses. Here, we show that the expression of tripeptidyl-peptidase II (TPPII), a high molecular weight cytosolic peptidase, required PIKK signaling and that TPPII was rapidly translocated into the nucleus of ;-irradiated cells. These events were dependent on mammalian target of rapamycin, a cytosolic/mitochondrial PIKK that is activated by ;-irradiation. Lymphoma cells with inhibited expression of TPPII failed to efficiently stabilize p53 and had reduced ability to arrest proliferation in response to ;-irradiation. We observed that TPPII contains a BRCA COOH-terminal-like motif, contained within sequences of several proteins involved in DNA damage signaling pathways, and this motif was important for nuclear translocation of TPPII and stabilization of p53. Novel tripeptide-based inhibitors of TPPII caused complete in vivo tumor regression in mice in response to relatively low doses of ;-irradiation (3-4 Gy/wk). This was observed with established mouse and human tumors of diverse tissue backgrounds, with no tumor regrowth after cancellation of treatment. These TPPII inhibitors had minor effects on tumor growth as single agent and had low cellular toxicity. Our data indicated that TPPII connects signaling by cytosolic/mitochondrial and nuclear PIKK-dependent pathways and that TPPII can be targeted for inhibition of tumor therapy resistance. [Cancer Res 2007; 67(15):7165-74]

Post-proteasomal and proteasome-independent generation of MHC class I ligands

“…A similar phenotype was observed in some tumors displaying resistance to apoptosis due to the compromised degradation of IAP (inhibitor of apoptosis) proteins [24]. Other reports described that TPP II induces genetic instability by overriding mitotic checkpoints [25] and that TPP is required for a normal response to DNA damage, although the latter point is controversial [26,27]. Mice with a genetic deletion of TPP II are viable but display degenerative alterations such as a decreased life span, premature immuno-hematopoietic senescence, and aggravated apoptosis [28].…”

Tripeptidyl Peptidase II Plays a Role in the Radiation Response of Selected Primary Cell Types but not Based on Nuclear Translocation and p53 Stabilization

“…Although we could not confirm the lack of radiation-induced p53 stabilization in the absence of TPPII, we nevertheless wanted to study other potential DNA damage response alterations. We therefore repeated the experiment described by Hong and colleagues (12) showing translocation of TPPII to the nucleus in EL4 cells within 1 hour after g-irradiation with 5 Gy. Like Hong and colleagues, we used immunofluorescence microscopy.…”

“…Major findings were (a) up-regulation and translocation of TPPII to the nucleus on g-irradiation; (b) failure of TPPII-siRNA-expressing lymphoma cells to stabilize p53 and consequently to halt the cell cycle in the G 1 phase on g-irradiation; and (c) complete remission of subcutaneous murine EL4 lymphomas on low-dose total body irradiation combined with either intratumoral expression of TPPII-specific siRNA or systemic administration of a subtilase inhibitor, which was reported by Hong and colleagues (12) to inhibit TPPII. These findings suggested not only an unexpected role of TPPII in the DNA damage response but also a potential suitability of TPPII inhibitors as radiosensitizers for clinical use in the radiotherapy of tumors.…”

“…Recently, a role of TPPII in the cellular response to g-irradiation and in the in vivo radiation response of tumors was reported by Hong and colleagues (12). Major findings were (a) up-regulation and translocation of TPPII to the nucleus on g-irradiation; (b) failure of TPPII-siRNA-expressing lymphoma cells to stabilize p53 and consequently to halt the cell cycle in the G 1 phase on g-irradiation; and (c) complete remission of subcutaneous murine EL4 lymphomas on low-dose total body irradiation combined with either intratumoral expression of TPPII-specific siRNA or systemic administration of a subtilase inhibitor, which was reported by Hong and colleagues (12) to inhibit TPPII.…”

Tripeptidyl Peptidase II Mediates Levels of Nuclear Phosphorylated ERK1 and ERK2

“…However, expressional changes of TPP2 interaction partners can also be suggested since both inhibitors alter TPP2 complex assembly and/or stability as well as localization. This may cause a shielding or exposure of domains, for instance the C-terminal BRCT-domain, that might interfere with a potential protein-stabilizing or destabilizing interaction of TPP2 (3,19,24,69). TPP2 inhibition can also change protein expression indirectly via mediator proteins.…”