Angiotensin-2 receptors (AT1-R and AT2-R), new prognostic factors for renal clear-cell carcinoma?

Abstract

Background: The growth factor Angiotensin-2 signals through Angiotensin receptor type 1 (AT1-R) in a broad range of cell types and tumours and through the type-2 receptor (AT2-R) in a more restricted group of cell types. Although numerous forms of cancer have been shown to overexpress AT1-R, expression of AT1-R and AT2-R by human renal clear-cell carcinoma (RCCC) is not well understood. In this study, the expression of both angiotensin receptors was quantified in a retrospective series of RCCC and correlated with prognostic factors.

Methods: Angiotensin receptor type 1 and AT2-R expressions were quantified on tumour tissues by immunohistochemistry (IHC), western blot and quantitative reverse transcriptase PCR (qRT-PCR). IHC results were correlated to Fuhrman's grade and patient progression-free survival (PFS).

Results: A total of 84 RCCC were analysed. By IHC, AT1-R and AT2-R were expressed to a greater level in high-grade tumours (AT1-R: P<0.001, AT2-R: P<0.001). Univariate analysis showed a correlation between PFS and AT1-R or AT2-R expression (P=0.001). By multivariate analysis, only AT2-R expression correlated with PFS (HR 1.021, P=0.006) and cancer stage (P<0.001). By western blot, AT1-R and AT1-R were also found to be overexpressed in higher Fuhrman's grade (P<0.01 and P=0.001 respectively). By qRT-PCR, AT1-R but not AT2-R mRNA were downregulated (P=0.001 and P=0.118, respectively).

Conclusion: Our results show that AT1-R and AT2-R proteins are overexpressed in the most aggressive forms of RCCC and that AT2-R expression correlates with PFS. AT1-R or AT2-R blockage could, therefore, offer novel directions for anti-RCCC therapy.

Figure 1

Staining by IHC on non-tumorous kidney tissue and renal cell carcinoma. Top panel, AT1-R IHC: (A) negative control, (B) staining of non-tumorous renal tissue, positive on tubular and Bowman's capsule cells, (C) Fuhrman's grade 1 renal carcinoma with no staining, (D) Fuhrman's grade 4 renal carcinoma with positive staining. Bottom panel, AT2-R IHC: (E) negative control, (F) staining of non-tumorous renal tissue on tubular cells, (G) Fuhrman's grade 1 renal carcinoma with no staining, (H) Fuhrman's grade 4 renal carcinoma with intense staining. × 200 magnification for all images.

Figure 2

Angiotensin receptor type 1 (A) and AT2-R (B) expression by IHC according to Fuhrman's grade. Results are expressed as percentage of AT1-R/AT2-R-positive tumour cells. Median expression is 12.5% for AT1-R and 10% for AT2-R. Angiotensin receptor type 1 (n=82 tumours) and AT2-R (n=76 tumours) are overexpressed by the most aggressive tumours (P<0.001 for both).

Figure 3

Quantification by western blot of AT1-R/Actin ratio (A, C) and AT2-R/Actin ratio (B, D). Angiotensin receptor type 1 is over expressed by the higher Fuhrman's grades tumours (P<0.001, n=47), as well as AT2-R (P=0.001, n=51). F for Fuhrman grade.

Figure 4

Reverse transcription–PCR of AT1-R and AT2-R according to Fuhrman's grade. Angiotensin receptor type 1 expression is significantly decreased according to the Fuhrman's grade (panel A, P=0.001, n=55). Angiotensin type 2 receptor is not differentially expressed between different Fuhrman's grades (panel B; P=0.118, n=44).

Figure 5

Patient progression-free survival curves according to AT1-R (A) and AT2-R (B) level, assessed by IHC. (A) AT1-R⩽median (plain line) or >median (dash) P=0.006; (B) AT1-R⩽median (plain line) or >median (dash) P=0.001 (log-rank test).