For quantification of band intensities, images from different sets of experiments were analyzed using the Image J software. was ubiquitinated in the absence of SMU1 and then subjected to proteolysis through the 26S proteasome. To prevent the proteolytic degradation of IK, a deubiquitinating enzyme, USP47, directly interacted with IK and stabilized it through deubiquitination. Collectively, our results suggest that IK is required for proper splicing of the pre-mRNA and USP47 contributes toward the stabilization of IK. pre-mRNA by spliceosome is not yet clearly understood. In the present study, we observed that the depletion of the splicing factor IK leads to intron 1 retention in ATM, but not 3-deazaneplanocin A HCl (DZNep HCl) in ATR, indicating that IK stabilization is very important for the proper splicing Rabbit Polyclonal to DDX55 of ATM. In addition, we demonstrate that the stability of spliceosomal protein IK is regulated by ubiqutination-mediated proteolysis. USP47, 3-deazaneplanocin A HCl (DZNep HCl) which belongs to the ubiquitin-specific protease (USP) family of deubiquitinating enzymes (DUBs), prevents the proteolysis of IK through deubiquitination. Materials and methods Cell culture HeLa and HEK 293T cells obtained from the ATCC were maintained in Dulbeccos modified Eagles medium (DMEM, Hyclone) supplemented with 10% heat-inactivated fetal bovine serum at 37?C in a humidified 5% CO2 incubator, as described previously13. The cells were treated with the following DNA-damaging reagents: thymidine (Thy), mitomycin C (MMC), neocarzinostatin (NCS), camptothecin (CPT), etoposide (ETP), and hydroxyurea (HU). The cells were also treated with the protein synthesis inhibitor cycloheximide (CHX), the lysosomes inhibitor bafilomycin (Baf), the autophagy inhibitor wortmannin (Wor), and the proteasome inhibitor bortezomib (BTZ) or MG132. Plasmids Full-length human IK and USP47 cDNAs were purchased from OriGene (OriGene Technologies, Inc., Rockville, MD) and cloned into pcDNA 3.1, pcDNA 3.0, and pCMV-tag-2B vectors. In the restoration assay, IK cloned into pCMV-tag-2B vector was used. The full-length mouse IK cDNA was purchased from Origene and cloned into pcDNA 3.1 vector. Plasmid transfection was performed using a polyethylenimine (PEI) solution, X-tremeGENE HP DNA Transfection Reagent, and jetPRIME (Polyplus) reagent, according to the manufacturers instructions. Antibodies Primary antibodies used for immunoblotting and immunofluorescence analyses were as follows: rabbit polyclonal anti-IK (Santa Cruz, sc-1335485), rabbit polyclonal anti-IK (Bethyl Laboratories, A301-708A), mouse monoclonal anti-USP47 (Santa Cruz, sc-100633), mouse monoclonal anti–actin (Santa Cruz, sc-47778), rabbit monoclonal anti-pATM S1981 (Cell Signaling, #5883), rabbit monoclonal anti-ATM (Cell Signaling, #2873), rabbit polyclonal anti-pATR S428 (Cell Signaling, #2853), rabbit 3-deazaneplanocin A HCl (DZNep HCl) monoclonal ATR (Cell Signaling, #13934), rabbit monoclonal anti-pCHK1 S345 (Cell Signaling, #2348), rabbit polyclonal anti-pCHK1 S317 (Cell Signaling, #2344), rabbit polyclonal anti-pCHK2 T68 (Cell Signaling, #2661), mouse monoclonal anti-SMU1 (Santa Cruz, sc-100896), mouse monoclonal anti-Ub (Santa Cruz, sc-8017), mouse monoclonal anti-cleaved PARP (Cell Signaling, #9546), rabbit polyclonal anti-Cleaved Caspase-3 (Asp175) (Cell Signaling, 3-deazaneplanocin A HCl (DZNep HCl) #9661), rabbit monoclonal anti-Cleaved Caspase-9 (Asp315) (Cell Signaling, #20750), rabbit monoclonal anti-Mre11(Cell Signaling, #4847), rabbit polyclonal anti-pMre11(Ser676) (Cell Signaling, #4859), rabbit polyclonal anti-Rad50 (Cell Signaling, #3427), rabbit polyclonal anti-phospho p95 (Cell Signaling, #3001), rabbit monoclonal anti-p95 (Cell Signaling, #14956), rabbit monoclonal anti-phospho-Histone H2A.X (Ser139) (Cell Signaling, #9718), mouse monoclonal anti-HA (Santa Cruz, sc-7392), mouse monoclonal anti-FLAG (Sigma, F1804), mouse monoclonal anti-GFP (Santa Cruz, sc-9996), mouse monoclonal anti-SC-35 (Santa Cruz, sc-53518), and mouse monoclonal anti-BrdU (Cell Signaling, #5292) antibodies. The HRP-conjugated goat anti-mouse or anti-rabbit IgG (Fab) secondary antibodies were purchased from Enzo Life Sciences. RNAi For RNA interference assays, IK siRNA duplexes were designed to repress IK (#1, 5-CAAAGGUUGCAAGAUGUUU-3; #2, 5-CUACCAAGGAGUUGAUCAA-3; #3, 5-GCAUUCCAGUAUGGUAUCA-3; #4, 5-AGACCACACUGACCACAAA-3; #5, 5-AGCUGAGAUUGCCAGCAAA-3) and were used at a concentration of 20?nM10. The SMU1 siRNA duplexes (5-ACCACAGAAUGUUCAAAUA-3) and USP47 siRNA duplexes (#1, 5-GACUCUGAUAGUGUAGCAU-3; #2, 5-GCUCAGAUCCCUUUGGCUATT-3; #3, 5-GGCGUCAAGUCAACAUAUATT-3) were also designed. The siRNAs were synthesized by Bioneer. For DUB siRNA screening, the.