Towards an understanding of C9orf82 protein/CAAP1 function

Abstract

C9orf82 protein, or conserved anti-apoptotic protein 1 or caspase activity and apoptosis inhibitor 1 (CAAP1) has been implicated as a negative regulator of the intrinsic apoptosis pathway by modulating caspase expression and activity. In contrast, an independent genome wide screen for factors capable of driving drug resistance to the topoisomerase II (Topo II) poisons doxorubicin and etoposide, implicated a role for the nuclear protein C9orf82 in delaying DSBs repair downstream of Topo II, hereby sensitizing cells to DSB induced apoptosis. To determine its function in a genetically defined setting in vivo and ex vivo, we here employed CRISPR/Cas9 technology in zygotes to generate a C9orf82 knockout mouse model. C9orf82ko/ko mice were born at a Mendelian ratio and did not display any overt macroscopic or histological abnormalities. DSBs repair dependent processes like lymphocyte development and class switch recombination (CSR) appeared normal, arguing against a link between the C9orf82 encoded protein and V(D)J recombination or CSR. Most relevant, primary pre-B cell cultures and Tp53 transformed mouse embryo fibroblasts (MEFs) derived from C9orf82ko/ko E14.5 and wild type embryos displayed comparable sensitivity to a number of DNA lesions, including DSBs breaks induced by the topoisomerase II inhibitors, etoposide and doxorubicin. Likewise, the kinetics of γH2AX formation and resolution in response to etoposide of C9orf82 protein proficient, deficient and overexpressing MEFs were indistinguishable. These data argue against a direct role of C9orf82 protein in delaying repair of Topo II generated DSBs and regulating apoptosis. The genetically defined systems generated in this study will be of value to determine the actual function of C9orf82 protein.

Identification and Molecular Analysis of m6A-circRNAs from Cashmere Goat Reveal Their Integrated Regulatory Network and Putative Functions in Secondary Hair Follicle during Anagen Stage

“…Although its role in hair follicle cells remains undiscovered, this protein is essentially involved in the proliferation and cell cycle of gastric cancer cells through regulating the JAK2/STAT3 signaling pathway [59]. Additionally, CAAP1 was identified as a negative regulator of intrinsic cell apoptosis through regulating the expression and activity of the caspase protein [60], and CAAP1 was found to promote the proliferation, migration and invasion of SMMC-7721 cells by an apoptotic inhibition of the cells [61]. Taken together with our results, it seems reasonable that CAT, STAM2, and CAAP1 along with their corresponding m 6 A-circRNAs (m 6 A-circRNA-CAT, -STAM2, and -CAAP1) may establish a m 6 A dependent regulatory pathway in the proliferation and growth of cashmere goat SHF cells during the anagen stage.…”

Single-cell characterization of step-wise acquisition of carboplatin resistance in ovarian cancer

“…Neither total mutation burden nor gene-specific mutational burden was significantly associated with the resistant phenotype, albeit with limited statistical power (Supplementary Table 2 ). Interestingly, CAAP1 T103P, was identified in all 8 R clones and 1 S clone, and while the mutation is predicted to be deleterious (CADD score = 22 14 ), a role for CAAP1 in apoptosis signaling has not been validated 15 , 16 . Thus, these clonal populations derived from a single cell showed small genetic differences, unlikely to be the result of the treatment, but due to the small number of clones studied as well as the lack of functional information for most variants, a genetic cause to the resistance cannot be fully ruled out.…”

Single-cell characterization of step-wise acquisition of carboplatin resistance in ovarian cancer

“…Neither total mutation burden nor gene-specific mutational burden was significantly associated with the resistant phenotype, albeit with limited statistical power (Table S2). Interestingly, CAAP1 T103P, was identified in all 8 R clones and 1 S clone, and while the mutation is predicted to be deleterious (CADD score =22 14 ), a role for CAAP1 in apoptosis signaling has not been validated 15,16 . Thus, these clonal populations derived from a single cell were genetically homogeneous and the small numbers of genetic changes observed were unlikely to be causally associated with the resistant phenotype.…”