title: Tumor-suppressing function of caspase-2 requires catalytic site Cys-320 and site Ser-139 in mice.
abstract: The multifunctional caspase-2 protein is involved in apoptosis, NF-κB 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-κB 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-κB activity and elevated expression of NF-κB 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-κB 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-κB pathways.
authors.affiliation: Department of Cancer and Cell Biology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267, USA.
authors.forename: Keqin
authors.initials: K
authors.lastname: Ren
authors.forename: Jing
authors.initials: J
authors.lastname: Lu
authors.forename: Aleksey
authors.initials: A
authors.lastname: Porollo
authors.forename: Chunying
authors.initials: C
authors.lastname: Du
mesh_terms: D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D053143:Caspase 2 / Q000235:genetics / Q000378:metabolism*; D020134:Catalytic Domain; D002455:Cell Division; D002461:Cell Line, Transformed; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000378:metabolism; D004622:Embryo, Mammalian / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D016195:G2 Phase; D006801:Humans; D051379:Mice; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D051017:Apoptosis Regulatory Proteins; D016328:NF-kappa B; D025521:Tumor Suppressor Proteins; C490360:CASP2 protein, human; C090208:Casp2 protein, mouse; D053143:Caspase 2; D003546:Cysteine Endopeptidases