2.2 Clinical specimens
Shanghai Outdo Biotech Co. Ltd. selected 94 patients at random who underwent routine treatment in 2009 and paraffin-embedded COAD tissues meeting rigorous follow-up criteria. Clinical pathological parameters containing age, gender, tumor size, clinical stage, TNM stage and 5-year survival, were seriously inspected. Ages of patients ranged from 27 to 90, with an average age of 58.5 years. 48:46 was the ratio of male-to-female. In conformity with the seventh edition of the American Joint Committee on Cancer, 21 COAD specimens were staged as early stage (I-II) and 36 as late stage (III-IV). The median survival time was 48 months. In addition, 78 cases from adjoining non-tumor tissues were obtained from the margin of the cancer resection in these patients.
2.3 Cell culture and transfection
The COAD cell lines (SW620, SW480, HCT-116, HT-29 and Caco2) purchased from the ATCC were cultured in DMEM medium (Gibco, Gaithersburg, MD, USA) which supplemented with 10% FBS and appropriate antibiotics, and maintained in humidifies 5% CO2 at 37°C. Three kinds of SMC4 siRNAs (si-SMC4#1, si-SMC4#2 and si-SMC4#3) (RIBOBIO, China) were purchased. In the light of the knockdown effect, control siRNA, si-SMC4#1 and si-SMC4#3 were applied in this research. The sequence of si-SMC4#1 and si-SMC4#3 were 5′-CCACAAGAGTAGCATATCA-3′ and 5′-GAAAGTCCTTGATGCAATA-3′. COAD cells (SW480 and HCT-116) were transfected with 30nM of siRNA by adding Lipofectamine 3000 (Invitrogen, USA) as stated by the manufacturer’s protocol.
2.4 Western blots
Total protein was extracted with RIPA buffer containing a mixture of protease inhibitor and phosphatase inhibitor. Protein samples were separated on SDS-PAGE and transferred to 0.45 um PVDF membranes (Millipore). After blocking with 5% fat-free milk, incubated at 4°C with the primary antibody overnight and then with horseradish peroxydase-coupled secondary antibody (Millipore). Enhanced chemiluminescence (Millipore) was used to detect signal.
2.5 Reagents
Antibodies against β-Actin, E-cadherin, Vimentin, Snail and were purchased from Cell Signaling Technology (Boston, USA). Antibody against SMC4 was purchased from Proteintech (Wuhan, China), MMP-2, MMP-9, Beclin-1 and LC3-II were purchased from Cell Signaling Technology (Boston, USA).
2.6 Immunohistochemistry (IHC)
For immunohistochemical studies, tissues were deparaffinized using xylene, while rehydrated in graded alcohol washes. Antigen retrieval was performed by placing the slides in sodium citrate buffer at 80°C for 40 min. After rinsing with PBS three times, the endogenous peroxidase was blocked by 3% H2O2 for 15 min at room temperature (RT). The slides were subsequently incubated with the indicated antibody (1:200 dilution) at RT 4°C overnight followed by incubating with the secondary antibody at for 1 h, DAB was immunostained and hematoxylin was counterstained.
2.7 Evaluation of IHC staining
The SMC4 staining of COAD tissue sections was judged by a couple-scoring system, combined staining intensity and area extent. The intensity of staining was graded as below: 0 meant no obvious staining; 1 meant weak staining; 2 meant moderate staining; 3 meant strong staining. The area extent was graded as below (proportion of positive cells): none or < 5% positive cells: 0; 5%-25% positive cells: 1; 26%-50% positive cells: 2; >50% positive cells: 3. The total scores were divided into low or high expression groups via multiplying the intensity score and the ratio of positive cells score. 0 ~ 1 was negative (-), 2 ~ 4 was weak positive (+), 5 ~ 7 was moderate positive (++), and ≥ 8 was strong positive (+++). Tissue sections scored as ‘++’ and ‘+++’ were considered as strong positives (high-level expression) of SMC4. Two pathologists scored all the specimens in a blinded manner. Final score established for cases with discrepancies was determined by reassessment of both pathologists with a double-headed microscope.
2.9 Colony formation assay
Cells (2000 cells) were seeded in 6-well plates in triplicate and incubated. After 2 weeks, cells were fixed by 4% paraformaldehyde and stained with hematoxylin for 20 min. Then, stained cells were washed with PBS for 30 min. Colonies (containing > 50 cells) were counted directly and images were captured.
2.10 MTT assay
Approximately 2000 cells per well were seeded into 96-well plates, then added the MTT (100 µL per well) at 0, 24, 48 and 72 h respectively. Removed the MTT from the wells after 4 h and added 100 µL DMSO into each well. The relative number of viable cells was assessed by measuring absorbance.
2.11 Wound healing assay
Cells were seeded in a 6-well plate and cultured overnight. A sterile 200 µL pipette tips were used to create wounds through the monolayer, then used pre-warmed PBS washed plates to remove cellular debris. Cell migration was monitored at 0 h, 48 h respectively and images were captured using microscope.
2.12 Acridine 0range (AO) staining
Cells were stained with 1 µg/mL− 1 of AO (Macklin, Shanghai, China) for 15 min and washed with PBS at RT in the dark. The formation of acidic vesicular organelles (AVOs) was determined under a fluorescence microscope (AO, bright red fluorescence in acidic vesicles).
2.13 Immunofluorescence staining
Adherent cells in 6-well plates culture slides fixed with 4% paraformaldehyde for 15 min, 0.5% Triton X-100 (CWBIO, China) was used to permeabilize and blocked with 3% BSA for 2 h. Cells were incubated with primary antibody (Beclin-1 and LC3-II) in 3% BSA at 4°C overnight, PBS washed for three times, incubated with Alexa Fluor 488-labeled goat anti-rabbit IgG secondary antibody (Invitrogen) for 1 h, nuclei were stained with DAPI solution and then captured by fluorescence microscope (Leica SP5II).
2.14 Statistical analysis
The data analysis was performed by SPSS 25.0 software and GraphPad Prism 8.0 software. T-test for independent means were used for group comparisons. Kaplan-Meier analysis calculated the survival curves. Univariate and multivariate hazard ratios of study variables were examined by Cox proportional hazards regression model. Group comparisons for continuous data were done by Mann-Whitney U test or one-way ANOVA. Biochemical experiments were performed in triplicate and at least three independent experiments were evaluated. The value of P < 0.05 was considered statistically significant.