835

CASP2

CASP-2|ICH1|NEDD-2|NEDD2|PPP1R57;caspase 2, apoptosis-related cysteine peptidase;CASP2;caspase 2, apoptosis-related cysteine peptidase

caspase-2|neural precursor cell expressed developmentally down-regulated protein 2|protease ICH-1|protein phosphatase 1, regulatory subunit 57

7q34-q35

protein-coding

One of the pivotal functions of endogenous tumor suppression is to oppose aberrant cell survival, but the molecular requirements of this process are not completely understood. Here, we show that caspase 2, a death effector with largely unknown functions, represses transcription of the survivin gene, a general regulator of cell division and cytoprotection in tumors. This pathway involves caspase 2 proteolytic cleavage of the nuclear factor kappaB (NFkappaB) activator, RIP1. In turn, loss of RIP1 abolishes transcription of NFkappaB target genes, including survivin, resulting in deregulated mitotic transitions, enhanced apoptosis and suppression of tumorigenicity in vivo. Therefore, caspase 2 functions as an endogenous inhibitor of NFkappaB-dependent cell survival and this mechanism may contribute to tumor suppression in humans.

The multifunctional caspase-2 protein is involved in apoptosis, NF-kappaB regulation, and tumor suppression in mice. However, the mechanisms of caspase-2 responsible for tumor suppression remain unclear. Here we identified two sites of caspase-2, the catalytic Cys-320 site and the Ser-139 site, to be important for suppression of cellular transformation and tumorigenesis. Using SV40- and K-Ras-transformed caspase-2 KO mouse embryonic fibroblast cells reconstituted with expression of wild-type, catalytic dead (C320A), or Ser-139 (S139A) mutant caspase-2, we demonstrated that similar to caspase-2 deficiency, when Cys-320 and Ser-139 were mutated, caspase-2 lost its ability to inhibit cellular transformation and tumorigenesis. These mutant cells exhibited enhanced cell proliferation, elevated clonogenic activity, accelerated anchorage-independent growth, and transformation and were highly tumorigenic, rapidly producing large tumors in athymic nude mice. Investigation into the underlying mechanism showed that these two residues are needed for caspase-2 to suppress NF-kappaB activity, promote apoptosis, and sustain the G(2)/M checkpoint following DNA damage induction. In addition, tumors in nude mice derived from the two mutant cell lines had higher constitutive NF-kappaB activity and elevated expression of NF-kappaB targets of antiapoptotic proteins Bcl-xL, XIAP, and cIAP2. A reduction in caspase-2 mRNA was associated with multiple types of cancers in patients. Together, these observations suggest the combined functions of caspase-2 in suppressing NF-kappaB activation, promoting apoptosis, and sustaining G(2)/M checkpoint contribute to caspase-2 tumor-suppressing function and that caspase-2 may also impact tumor suppression in humans. These findings provide insight into tumor suppression at the cross-roads of apoptosis, cell cycle checkpoint, and NF-kappaB pathways.

The PIDDosome, a multiprotein complex constituted of the p53-induced protein with a death domain (PIDD), receptor-interacting protein (RIP)-associated ICH-1/CED-3 homologous protein with a death domain (RAIDD) and pro-Caspase-2 has been defined as an activating platform for this apoptosis-related protease. PIDD has been implicated in p53-mediated cell death in response to DNA damage but also in DNA repair and nuclear factor kappa-light-chain enhancer (NF-kappaB) activation upon genotoxic stress, together with RIP-1 kinase and Nemo/IKKgamma. As all these cellular responses are critical for tumor suppression and deregulated expression of individual PIDDosome components has been noted in human cancer, we investigated their role in oncogenesis induced by DNA damage or oncogenic stress in gene-ablated mice. We observed that Pidd or Caspase-2 failed to suppress lymphoma formation triggered by gamma-irradiation or 3-methylcholanthrene-driven fibrosarcoma development. In contrast, Caspase-2 showed tumor suppressive capacity in response to aberrant c-Myc expression, which did not rely on PIDD, the BH3-only protein Bid (BH3 interacting domain death agonist) or the death receptor ligand Trail (TNF-related apoptosis-inducing ligand), but associated with reduced rates of p53 loss and increased extranodal dissemination of tumor cells. In contrast, Pidd deficiency associated with abnormal M-phase progression and delayed disease onset, indicating that both proteins are differentially engaged upon oncogenic stress triggered by c-Myc, leading to opposing effects on tumor-free survival.