Cell culture
The MDA-MB-231 cell line was cultured in RPMI 1640 medium supplemented with 10% fetal bovine serum. The cells were maintained at 37 ℃ in a 5% CO2 humidified incubator.
Lentivirus Vector Construction And Infection
For the construction of shRNA expression plasmids, CCT3-siRNA was designed based on the targeted sequence 5’- CAAGTCCATGATCGAAATT-3’, as described in a previous study [12]. In brief, the ligated products were transfected into Escherichia coli cells. The positive recombinants were identified for sequencing verification and plasmid extraction. Lentiviral vector DNA and packaging vectors were transfected into 293T cells, and the empty GV115 lentiviral vector was used as the shRNA control (shCtrl). After 48 h of culture, supernatants containing lentiviruses were harvested, and the lentiviruses were purified. Lentivirus infection was performed on cells at 80% confluence. Seventy-two hours after infection, the cells were used for downstream assays or transplantation.
Qrt-pcr
Total RNA was isolated by TRIzol method. The cDNA was reverse-transcribed and amplified using the following primer sets: CCT3: forward,5’- TCA GTC GGT GGT CAT CTT TGG-3’; reverse, 5’- CCT CCA GGT ATC TTT TCC ACT CT-3’; GAPDH: forward, 5’- TGA CTT CAA CAG CGA CAC CCA − 3’; reverse, 5’- CAC CCT GTT GCT GTA GCC AAA-3’. Real-time PCR using the SYBR Green PCR Master Mix kit was performed with an ABI Prisma 7000 Sequence Detection System (Applied Biosystems, Foster City, CA, USA). The data were normalized to the respective GAPDH expression values. The value of cells infected with shCtrl was considered 100 in each run.
Rna-sequencing
Total RNA was extracted from MDA-MB-231 cells transfected with or without CCT3-siRNA by a TRIzol Reagent Kit (Invitrogen, Carlsbad, CA, USA). RNA purity was evaluated using the NanoPhotometer® spectrophotometer (IMPLEN, CA, USA), and RNA integrity was assessed using the RNA Nano 6000 Assay Kit of the Bioanalyzer 2100 system (Agilent Technologies, CA, USA). A total amount of 1 µg RNA per sample was used as input material for the RNA sample preparations. Sequencing libraries were generated using the NEBNext® UltraTM RNA Library Prep Kit for Illumina® (NEB, USA) following the manufacturer’s recommendations and index codes were added to attribute sequences to each sample. Differentially expressed RNAs were selected according to fold change > 2 or fold change < 0.5 and p value < 0.05 by R package edgeR or DESeq2. The differentially expressed genes (DEGs) were subjected to Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis.
Tandem Mass Tag Proteomics (Tmt) Analysis
Sample Preparation
SDT buffer (4% SDS, 100mM Tris-HCl, pH 7.6) was added to the samples. The lysates were sonicated (this step can be skipped for protein solution) and then boiled for 15 min. After centrifugation at 14000 × g for 15 min, the protein concentrations of the supernatants were measured with the BCA Protein Assay Kit (P0012, Beyotime, Shanghai, China). The samples were stored at -80°C.
Filter-aided Sample Preparation (Fasp Digestion)
A total of 150–200 µg of protein from each sample was reduced with 100 mM DTT for 5 min at 100°C. Then the detergent, DTT and other low-molecular-weight components were removed using UA buffer (8 M urea, 150 mM Tris-HCl pH 8.5) and repeated ultrafiltration (Sartorius, 30 kD). Then 100 µl iodoacetamide (100 mM IAA in UA buffer) was added to block reduced cysteine residues and the samples were incubated for 30 min in the dark. The filters were washed with 100 µl UA buffer three times and then 100 µl 0.1 M TEAB buffer twice. Finally, the protein suspensions were digested with 4 µg trypsin (Promega) in 40 µl 0.1 M TEAB buffer overnight at 37°C, and the resulting peptides were collected as a filtrate. The peptide content was estimated by UV light spectral density at 280 nm using an extinction coefficient of 1.1 of 0.1% (g/l) solution, which was calculated on the basis of the frequency of tryptophan and tyrosine in vertebrate proteins.
Tmt Labeling
A 100 µg peptide mixture of each sample was labeled using TMT reagent according to the manufacturer’s instructions (Thermo Fisher Scientific).
Peptide Fractionation With Reversed-phase (Rp) Chromatography
TMT labeled peptides were fractionated by RP chromatography using Agilent 1260 infinity II HPLC. The peptide mixture was diluted with buffer A (10 mM HCOONH4, 5% ACN, pH 10.0) and loaded onto an XBridge Peptide BEH C18 Column (130 Å, 5 µm, 4.6 mm X 100 mm). The peptides were eluted at a flow rate of 1 ml/min with a gradient of 0% buffer B (10 mM HCOONH4, 85% ACN, pH 10.0) from 0–25 min, 0–7% buffer B from 25–30 min., 7–40% buffer B from 30–58 min, 40–100% buffer B from 58–70 min, 100% buffer B from 70–80 min. 100-0% buffer B from 80–85 min. 0-100% buffer B from 85–90 min. The elution was monitored at 214 nm based on the UV light trace, and fractions were collected every 1 min from 31–65 min. The collected fractions were combined into 34 fractions. The samples were freeze-dried, reconstituted with 0.1% FA, and combined into 10 parts.
Mass Spectrometry Analysis
Easy nLC
Each fraction was injected for nano LC-MS/MS analysis. The peptide mixture was loaded onto a C18-reversed phase analytical column (Thermo Fisher Scientific, Acclaim PepMap RSLC 50 um X 15 cm, nano viper,P/N164943) in buffer A (0.1% formic acid) and separated with a linear gradient of buffer B (80% acetonitrile and 0.1% formic acid) at a flow rate of 300 nl/min. The linear gradient was set as follows: 6% buffer B for 5 min, 6–28% buffer B for 40 min, 28–38% buffer B for 5min, 38–100% buffer B for 5 min, hold in 100% buffer B for 5 min.
Lc-ms/ms Analysis
LC-MS/MS analysis was performed on a Q Exactive mass spectrometer (Thermo Fisher Scientific) that was coupled to Easy nLC (Thermo Fisher Scientific) for 60 min. The mass spectrometer was operated in positive ion mode. MS data were acquired from the survey scan (350–1800 m/z) for HCD fragmentation. Survey scans were acquired at a resolution of 70000 at m/z 200 with an AGC target of 3e6 and a maxIT of 50 ms. MS2 scans were acquired at a resolution of 17500 or 35000 for HCD spectra at m/z 200 with an AGC target of 2e5 and a maxIT of 45 ms, and the isolation width was 2.0 m/z. Only ions with a charge state between 2–7 and a minimum intensity of 2e3 were selected for fragmentation. Dynamic exclusion for selected ions was 30 s. The normalized collision energy was 30 eV.
Data Analysis
MS/MS raw files were processed using the MASCOT engine (Matrix Science, London, UK; version 2.6) embedded into Proteome Discoverer 2.2, and searched against the database. The search parameters included trypsin as the enzyme used to generate peptides with a maximum of 2 missed cleavages permitted. A precursor mass tolerance of 10 ppm was specified and 0.05 Da tolerance for MS2 fragments. Except for TMT labels, carbamidomethyl (C) was set as a fixed modification. Variable modifications were Oxidation(M) and Acetyl (Protein N-term). A peptide and protein false discovery rate of 1% was enforced using a reverse database search strategy. Proteins with a fold change > 1.2 and p value (Student’s t test) < 0.05 were considered to be differentially expressed proteins.
Bioinformatics Analysis
First, all the protein sequences were aligned to the database downloaded from NCBI (ncbi-blast-2.2.28+-win32.exe), and only the top 10 sequences with and E-value < = 1e-3 were retained. Second, the GO term (database version: go_201504.obo) of the sequence with the top bit score by Blast2GO was selected. Then, the annotation from GO terms to proteins was completed by Blast2GO Command Line. After the elementary annotation, InterProScan was used to search the EBI database by motif and then add the functional information of the motif to proteins to improve annotation. Pathway analysis was performed using the KEGG database. Fisher's exact test was used to identify the significant Go terms and enriched pathways. For protein-protein interactions (PPIs), target proteins were searched in String(https://www.string-db.org/), and the interaction network with the target protein was directly or indirectly searched in the database. Echart software was used to generate the interaction network analysis results.
Conjoint Analysis
The DEGs/DEPs that were identified in transcriptomic and proteomic analyses were analysis, and the genes with the same up- or downregulated trends in both the transcriptome and proteome were identified.
Statistical analysis
The data are expressed as the mean ± standard error (S.E) and were analyzed using the Statistical Program for Social Sciences (SPSS) 10.0 software (IBM, Armonk, NY, USA). Differences between groups were analyzed using analysis of variance (ANOVA) or Student’s t test.