Study Subjects
Available for analysis by immunohistochemistry were archival, formalin-fixed, and paraffin-embedded specimens of renal cell carcinoma (n = 64), hepatocellular carcinoma (n = 123), melanoma (n = 20), cholangiocarcinoma (n = 20), transitional cell carcinoma of the bladder (n = 24), ovarian epithelial carcinoma (n = 63), cervical squamous cell carcinoma (n = 49), and adrenocortical carcinoma (n = 48). Information on the presence of metastases, presence of nodal invasion, stage, and/or grade were available for the specimens studied except for those of adrenocortical carcinoma. An additional nine pairs of renal cell carcinoma and adjacent healthy kidney tissue specimens in the form of formalin-fixed tissue microarray mounted to standard salinized slides were purchased to compare expression of adiponectin receptors in malignant and benign tissues (Imgenex, San Diego, CA, USA).
For analysis by real-time quantitative polymerase chain reaction (RT-qPCR), a panel of prenormalized cDNA from 48 cancerous tissues involving the kidney was purchased as an independent confirmatory study in a different population (TissueScan Kidney Disease Tissue qPCR Array, OriGene Technologies, Rockville, MD, USA). Two of the samples were excluded as they were not of renal cell carcinoma, and one sample was used as a negative control.
Immunohistochemistry Analysis
The immunohistochemistry analysis was performed as previously described [7, 11, 12]. Five-micrometer paraffin tissue sections were deparaffinized, rehydrated, microwaved for 25 min in 10 mmol/l citrate buffer, and incubated for 30 min in methanol-containing 0.5% H2O2. After incubation in 16% normal goat serum for 1 h at room temperature, the slides were incubated with the primary antibodies at room temperature. The primary antibodies used were rabbit antihuman AdipoR1 antiserum, which was raised against amino acid residues 357–375, and rabbit antihuman AdipoR2 antiserum, which was raised against amino acid residues 374–386 (both from Phoenix Pharmaceuticals Inc., Belmont, CA, USA). The primary antibodies were diluted at 1:500 and 1:200, respectively. The secondary antibody used was a biotinylated antirabbit antibody at 1:400 dilution and was applied for 30 min at room temperature. Vectastain Elite ABC Reagent (Vector Laboratories, Burlingame, CA, USA) was added for 30 min. The horseradish peroxidase reaction was developed with diaminobenzidine. The slides were counterstained with hematoxylin. The immunostaining was evaluated semiquantitatively according to its extent and degree of intensity on a scale of “−,” “−/+,” “+,” “++,” to “+++” by two expert pathologists independently. The results were averaged. For each of the cancers studied, primary antibody was replaced with nonimmune goat serum for a slide to serve as negative control.
Real-Time Quantitative Polymerase Chain Reaction
Expression of AdipoR1 and AdipoR2 was studied in the human renal adenocarcinoma cell line 786-O (American Type Culture Collection, Manassas, VA, USA) with RT-qPCR by total RNA extraction with Trizol (Invitrogen, Carlsbad, CA, USA), cDNA synthesis using High-Capacity cDNA Reverse Transcription Kit (Applied Biosystems, Foster City, CA, USA), and qPCR with human-specific TaqMan® Gene Expression Assay (Assay ID: Hs00360422_m1 and Hs00226105_m1, Applied Biosystems, Foster City, CA) in 7500 Fast Real-Time PCR system using Standard Real-Time 7500 protocol (Applied Biosystems, Foster City, CA, USA). Expression of AdipoR1 and AdipoR2 was also studied in cDNA samples from 45 specimens of renal cell carcinoma, including five specimens of surrounding normal tissues (TissueScan Kidney Disease Tissue qPCR Array, OriGene Technologies, Rockville, MD, USA) according to the application guide. Prenormalized cDNA (2–3 ng, by β-actin) in 30-µl reaction volumes were amplified using TaqMan® Gene Expression system with the specific primers stated above. Data were analyzed using 7500 Real-Time PCR System software (Applied Biosystems, Foster City, CA, USA). Relative quantification was done using ΔΔCt method with Eukaryotic 18S rRNA (Applied Biosystems, Foster City, CA, USA) as the endogenous control and human subcutaneous fat biopsy specimen and the normal renal tissue samples as reference controls.
Western Blotting
Western blotting was performed on the renal cancer cell line 786-O (American Type Culture Collection, Manassas, VA, USA) to confirm the presence of AdipoR1 and AdipoR2. Fifty micrograms of protein were loaded. After SDS–polyacrylamide gel electrophoresis, proteins were blotted onto nitrocellulose membranes (Schleicher & Schuell, Inc., Keene, NH, USA). The membranes were blocked for 1 h in Tris-buffered saline (TBS) containing 5% nonfat dry milk and 0.1% Tween-20. Incubation with primary antibodies at a dilution of 1:1,000 was performed in TBS containing 5% nonfat dry milk overnight, which was followed by incubation with horseradish-peroxidase-labeled secondary antibodies at a dilution of 1:2,000 for 2 h. After incubation with the antibodies, membranes were washed with TBS containing 0.1% Tween-20. Enhanced chemiluminescence was used for detection. Measurement of signal intensity on nitrocellulose membranes after Western blotting was performed using Image J processing and analysis software (US National Institutes of Health, Bethesda, MD, USA).
Cell Signaling Studies
The renal cancer cell line 786-O (American Type Culture Collection, Manassas, VA, USA) was seeded in six-well tissue culture plates and grown in RPMI medium with 100 U/ml of penicillin, 100 mg/ml of streptomycin, and 1 mM of sodium pyruvate, supplemented with 10% fetal bovine serum. After 2 days of cell culture, 60% confluency was reached (referred to as day 0). The cells were then serum-starved overnight and treated with adiponectin (R&D systems, Minneapolis, MN, USA) in a time- and dose-dependent manner.
Western blotting was performed to assess for phosphorylation of signal transducer and activator of transcription 3 (STAT3), ribosomal S6 kinase (S6), extracellular signal-regulated kinases 1 and 2 (ERK1/2), and the serine/threonine kinase Akt. All cell lysates were examined by Western blotting with primary p-STAT3 (Santa Cruz Biotechnology, Inc., San Francisco, CA, USA), STAT3 (Santa Cruz Biotechnology, Inc., San Francisco, CA, USA), p-S6 (Cell Signaling Technology, Inc., Danvers, MA, USA), S6 (Cell Signaling Technology, Inc., Danvers, MA, USA), p-ERK1/2 (Santa Cruz Biotechnology, Inc., San Francisco, CA, USA), ERK1/2 (Santa Cruz Biotechnology, Inc., San Francisco, CA, USA), p-Akt (Santa Cruz Biotechnology, Inc., San Francisco, CA, USA), and Akt (Santa Cruz Biotechnology, Inc., San Francisco, CA, USA) antibodies diluted with TBS with 0.1% Tween-20 at 1:500. The secondary antibodies used were horseradish-peroxidase-conjugated antimouse, antirabbit, or antigoat antibodies and were diluted at 1:750. Measurement of signal intensity on nitrocellulose membranes was performed using Image J processing and analysis software (US National Institutes of Health, Bethesda, MD, USA). All experiments were performed in triplicate.
Statistical Analysis
For the immunohistochemistry studies, descriptive characteristics are presented as proportions and mean values ± standard deviations. Comparisons of categorical variables were conducted using Fisher’s exact test. Comparison of cases and controls on expression of adiponectin receptors were conducted using McNemar's test. Analyses were performed using SPSS version 11.5 (SPSS Inc., Chicago, IL, USA).
Statistics for the RT-qPCR data were performed using general linear models, and individual differences between groups were identified by one-way analysis of variance (ANOVA) followed by the protected least significant differences technique (SAS version 9.1; SAS Institute, Cary, NC, USA). Data are presented as means ± standard error.
For the cell signaling studies by Western blotting, all data were analyzed using one-way ANOVA followed by post hoc test for multiple comparisons with SPSS version 11.5 (SPSS Inc., Chicago, IL, USA). Values are expressed as means ± standard deviation.
For all studies, a two-sided level of α = 0.05 was used to determine statistical significance.