Elsevier

European Urology

Volume 56, Issue 4, October 2009, Pages 690-699
European Urology

Kidney Cancer
Expression of Aquaporin 1 in Primary Renal Tumors: A Prognostic Indicator for Clear-Cell Renal Cell Carcinoma

https://doi.org/10.1016/j.eururo.2008.10.014Get rights and content

Abstract

Background

Aquaporin 1 (AQP1) is a water channel expressed in many epithelial tissues and endothelium, including the proximal nephron of the kidney.

Objective

We measured AQP1 expression in primary renal cell carcinomas (RCCs) and evaluated its significance and prognostic utility.

Design, setting, and participants

We examined AQP1 expression in 559 sporadic renal tumors as well as in 43 normal kidney tissue samples and collected clinicopathologic and prognostic data.

Measurements

AQP1 expression was measured by using real-time quantitative polymerase chain reaction (PCR).

Results and limitations

All normal kidney samples presented substantial AQP1 expression. Among tumor subtypes, AQP1 expression was significantly higher in clear-cell and papillary RCCs, whereas it was lower in chromophobe RCCs, oncocytomas, and collecting-duct carcinomas. In clear-cell RCC, AQP1 was significantly higher in patients without symptomatic presentation or whose tumors were smaller, lower grade, or either lower stage or lacking in microvascular invasion. Von Hippel-Lindau (VHL) tumor suppressor gene mutational status did not affect expression level. Cox univariate and multivariate analyses strongly associated high AQP1 expression with better prognosis in cancer-specific and cancer-free survival tests in all patient cohorts, as well as in cancer-specific survival in a cohort of patients with advanced metastatic RCC. The time-dependent receiver operation characteristic (ROC) analyses, combined with logistic regression models, revealed that the addition of the AQP1 parameter to the University of California Los Angeles Integrated Staging System (UISS) prognostic score can improve the accuracy of predictions of both cancer death and recurrence for all patient cohorts as well as of cancer death for advanced cases within a 5-yr follow-up period in clear-cell RCC. High AQP1 expression was also associated with better outcome in a univariate cancer-specific survival test in papillary RCCs.

Conclusions

AQP1 shows RCC subtype-specific expression, and its expression level provides useful prognostic information for patients with clear-cell RCC.

Introduction

Renal cell carcinoma (RCC), the most common malignancy of the adult kidney, accounts for approximately 3% of all malignancies [1], [2]. The incidence of RCC is increasing worldwide [1], [2]. More than 40% of patients with RCC die from their cancer [3]. Until now, complete surgical resection has been considered the only effective treatment for patients with clinically localized RCC. However, the disease will recur postoperatively in 20–40% of patients who undergo potentially curative nephrectomy [3]. The principal prognostic factors are tumor stage and histological grade. New prognostic parameters, including clinical, laboratory, and biomolecular factors, have long been desired to provide additional predictive value in clinical practice [4].

Recent studies demonstrate that RCC is morphologically and genetically a mixture of heterogeneous tumors [3], [5], [6], [7]. The clear-cell subtype is the most common, constituting approximately 80% of all RCC and >90% of metastatic cases [3], [5], [6], [7]. Genetically, the Von Hippel-Lindau (VHL) tumor suppressor gene is exclusively and frequently mutated in this subtype [3], [6], [7]. Aberrations in mesenchymal–epithelial transition factor (MET), fumarate hydratase (FH), or transcription factor E (TFE) genes are found in the papillary subtype or its variants. In contrast, the Birt-Hogg-Dubé (BHD) gene is closely associated with the occurrence of distal nephron tumors, such as chromophobe RCC and oncocytoma [7]. Therefore, subtype-specific biomarkers or new molecules should be identified for the accurate diagnosis and evaluation of patients’ clinical courses [8].

Aquaporins are water-transporting proteins that are physiologically expressed in many epithelial tissues and endothelium [9], [10]. In the normal kidney, AQP1, the first member to be identified, is present in the glomerular capillary endothelium and proximal tubular segments [9], [10], [11], [12]. AQP1 expression was also detected in some malignancies, such as lung cancer and glioma [13], [14]. In RCC, Northern blot analysis associated high AQP1 expression with a good prognosis in patients with clear-cell RCC [11]. An immunohistochemistry study suggested that AQP1 is a possible expression marker for low-grade clear-cell RCC [12]. We previously examined microarray gene expression profiles for various renal epithelial tumors and found hundreds of genes differentially expressed in each subtype [15]. Among them, AQP1 is a potent indicator of outcome in patients with clear-cell RCC. However, these observations, including our own, were based on limited numbers of samples and/or relatively short follow-up periods. Neither the detailed relationship between AQP1 and renal tumor biology nor the clinical impact of AQP1 on RCC is well elucidated.

In this experiment, we used real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR), a rapid and sensitive gene-expression detection assay, to measure AQP1 expression levels in a larger RCC patient cohort. We then investigated the relationships between AQP1 expression and various clinicopathologic parameters, VHL gene mutational status, and AQP1’s clinical utilities.

Section snippets

Patients and tumor samples

Primary sporadic tumor samples were collected from 559 patients with sporadic RCC who had consecutively undergone nephrectomy at our university hospital or its affiliated hospitals between March 1986 and November 2004. Fresh tumor specimens without apparent necrosis and corresponding normal kidney tissue specimens were grossly cut out immediately after nephrectomy, snap-frozen with liquid nitrogen, and stored at −80 °C until nucleic acid extraction. The tumors were classified according to the

Upregulation of aquaporin 1 in clear-cell and papillary renal cell carcinomas

AQP1 expression in a total of 559 primary renal tumors was quantified by qRT-PCR. We initially tested the reproducibility of gene expression levels between the former microarray and the qRT-PCR assay. Consequently, we found that the reproducibility was quite high (Spearman rank correlation coefficient: ρ = 0.774, n = 33).

We next evaluated AQP1 expression according to histopathologic subtype-specific patterns. qRT-PCR demonstrated that all normal kidney samples presented substantial AQP1 expression.

Discussion

In the present study, we measured AQP1 expression in a total of 559 renal tumors of various subtypes by qRT-PCR assay and subsequently examined the detailed relationships between the expression levels and clinicopathologic factors as well as patient outcomes. We detected high AQP1 expression in clear-cell and papillary RCCs, both of which are closely connected with the proximal nephron system [5], [6], [7], whereas we found low levels in other distal nephron-related tumors, including

Conclusions

We demonstrated that AQP1 is expressed exclusively in clear-cell and papillary RCCs. The AQP1 expression level is inversely correlated with tumor differentiation, aggressiveness, and the acquisition of metastatic activity in clear-cell RCC and probably also in papillary RCC. The determination of the AQP1 expression level as a biomolecular marker can provide useful prognostic information for patients with clear-cell RCC, specifically for predicting cancer survival times for all tumor stages and

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