Adiponectin receptor expression in human malignant tissues

Abstract

Adiponectin has been proposed to be a mediator of obesity-associated malignancies and to have direct antineoplastic effects acting via adiponectin receptors AdipoR1 and AdipoR2. We describe herein the expression of AdipoR1 and AdipoR2 in several cancers not previously studied. We used immunohistochemistry to assess expression of adiponectin receptors in archival 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). To compare expression in malignant versus nonmalignant tissues, we also studied AdipoR1 and AdipoR2 expression in pairs of renal cell carcinoma and adjacent healthy kidney tissue specimens by immunohistochemistry. We also studied mRNA expression in 45 specimens of renal cell carcinoma by real-time polymerase chain reaction. Finally, we utilized Western blotting to confirm the presence of adiponectin receptors and subsequently studied cell signaling pathways of adiponectin in the renal cancer cell line 786-O. Cancers associated with obesity were significantly more likely to express AdipoR1 than cancers not associated with obesity. Of the specimens of renal cell carcinoma, which is strongly associated with obesity, 93.8% expressed AdipoR1 compared to 44.9% of the specimens of cervical cell carcinoma, which is not associated with obesity (p < 0.001). There was no difference in the expression of adiponectin receptors or their mRNA between malignant and benign kidney tissue specimens. Overall, there were no correlations between expression of adiponectin receptors or their mRNA and tumor prognostic factors. Finally, Western blotting confirmed the presence of AdipoR1 in the renal cancer cell line 786-O, and adiponectin activates in vitro several signaling pathways in this cell line. In summary, we report for the first time expression of AdipoR1 and AdipoR2 in the above cancers and that AdipoR1 is more ubiquitously expressed in obesity-associated cancers.

Fig. 1

Adiponectin receptor expression is higher in obesity-related cancers than in obesity-nonrelated cancers. Immunohistochemical staining for AdipoR1 (a) and AdipoR2 (b) in renal cell carcinoma, AdipoR1 (c) and AdipoR2 (d) in hepatocellular carcinoma, and AdipoR1 (e) and AdipoR2 (f) in cervical squamous cell carcinoma. Immunohistochemical staining of negative control with no primary antibody (g). All figures are at ×250 magnification.

Fig. 2

mRNA expression (means ± standard error) of AdipoR1 and AdipoR2 in relation to stage of renal cell cancer.

Fig. 3

Cell signaling molecules activated by adiponectin stimulation in the human renal cancer cell line 786-O. In vitro adiponectin administration to human renal cancer cells was performed. The cells were treated with adiponectin at the indicated concentrations for 40 min (a, c, e, and g). The cells were treated with 5 and 20 µg/ml of adiponectin for the indicated time periods (b, d, f, and h). All immunoblots shown are representative of an experiment performed three times. All density values for each protein band of interest are expressed as a fold increase. All data were analyzed using one-way ANOVA followed by post hoc test for multiple comparisons. Values are means ± standard deviation. Means with different letters are significantly different, p < 0.05.

Fig. 3

Cell signaling molecules activated by adiponectin stimulation in the human renal cancer cell line 786-O. In vitro adiponectin administration to human renal cancer cells was performed. The cells were treated with adiponectin at the indicated concentrations for 40 min (a, c, e, and g). The cells were treated with 5 and 20 µg/ml of adiponectin for the indicated time periods (b, d, f, and h). All immunoblots shown are representative of an experiment performed three times. All density values for each protein band of interest are expressed as a fold increase. All data were analyzed using one-way ANOVA followed by post hoc test for multiple comparisons. Values are means ± standard deviation. Means with different letters are significantly different, p < 0.05.