Tissue distribution of human AKR1C3 and rat homolog in the adult genitourinary system

Abstract

Human aldo-keto reductase (AKR) 1C3 (type 2 3alpha-hydroxysteroid dehydrogenase/type 5 17beta-hydroxysteroid dehydrogenase) catalyzes androgen, estrogen, and prostaglandin metabolism. AKR1C3 is therefore implicated in regulating ligand access to the androgen receptor, estrogen receptor, and peroxisome proliferator activating receptor gamma in hormone target tissues. Recent reports on close relationships between ARK1C3 and various cancers including breast and prostate cancers implicate the involvement of AKR1C3 in cancer development or progression. We previously described the characterization of an isoform-specific monoclonal antibody against AKR1C3 that does not cross-react with related, >86% sequence identity, human AKR1C1, AKR1C2, or AKR1C4, human aldehyde reductase AKR1A1, or rat 3alpha-hydroxysteroid dehydrogenase (AKR1C9). In this study, a clone of murine monoclonal antibody raised against AKR1C3 was identified and characterized for its recognition of rat homolog. Tissue distribution of human AKR1C3 and its rat homolog in adult genitourinary systems including kidney, bladder, prostate, and testis was studied by IHC. A strong immunoreactivity was detected not only in classically hormone-associated tissues such as prostate and testis but also in non-hormone-associated tissues such as kidney and bladder in humans and rats. The distribution of these two enzymes was comparable but not identical between the two species. These features warrant future studies of AKR1C3 in both hormone- and non-hormone-associated tissues and identification of the rodent homolog for establishing animal models.

Figure 1

Specificity of a monoclonal antibody for a rat aldo-keto reductase (AKR)1C3 homolog. Total cellular proteins were extracted from rat tissues, electrophoresed on a Tris-HCl gel, and transferred to polyvinylidene difluoride (PVDF) membranes for immunoblot analysis. Detection of a rat homolog of human AKR1C3 in rat protein was performed by incubating the membranes with clone R9F9.H1. The immunoblot analysis shows that R9F9.H1 only reacts with one species of protein with ∼37 kDa prepared from rat tissue lysates in all samples except the kidney. In the kidney, a second band of ∼74–75 kDa is seen. This band corresponds to about double the molecular mass of the low molecular mass band.

Figure 2

Distribution of AKR1C3 and rat homolog in the prostate. IHC with antibody NP6G6.A6 against human AKR1C3 on human prostate (A,C) and antibody R9F9.H1 against rat homolog of human AKR1C3 in rat prostate (B,D). In human prostate, there is moderate positive immunoreactivity in the stromal cells (arrow in C) and basal cells (arrowhead in C) and no immunoreactivity in the epithelial cells (A,C). In contrast, the pattern is reversed in rat prostate. There is strong immunoreactivity in the epithelial cells (arrow in D) but not in the stromal cells (curved arrow in D). In contrast to human tissues, endothelial cells in rat tissue are non-reactive (arrowhead in D).

Figure 3

Distribution of AKR1C3 and rat homolog in the kidney and bladder. IHC with antibody NP6G6.A6 against human AKR1C3 on human kidney (A,C) and antibody R9F9.H1 against rat homolog of human AKR1C3 in rat kidney (B,D); human urothelium in renal pelvis (E) and rat urothelium in urinary bladder (F). In renal cortex, the endothelial cells in glomeruli have no immunoreactivity in both human and rat tissues (A,B). Bowman's capsule is strongly immunoreactive in humans (arrow in A) but not in rats (arrow in B). The mesangial cells are immunoreactive in humans (arrowhead in A) but not in rats. The proximal convoluted tubules are immunoreactive in renal cortex in both humans (curved arrow in A) and rats (curved arrow in B), but other tubules show weak or no immunoreactivity. In the medulla, the staining pattern is similar. Some of the tubules, presumably the proximal convoluted tubules are positive but other tubules are negative (C,D). Urothelial epithelium (transitional cell epithelium) possesses both nuclear and cytoplasmic immunoreactivities in both humans (arrow in E) and rats (arrow in F); enlarged images are in the insets. Note that endothelial cells of blood vessels are strongly immunoreactive in humans (arrowhead in C and E) but not in rats.

Figure 4

Distribution of AKR1C3 and rat homolog in the testis. Immunohistochemistry with antibody NP6G6.A6 against human AKR1C3 on human testis (A) and epididymis (C) and antibody R9F9.H1 against rat homolog of human AKR1C3 in rat testis (B) and epididymis (D). There is strong immunoreactivity in Leydig cells (thick arrow in A), fibromyocytes (curved arrow in A) around seminiferous tubules, and endothelial cells (thin arrow in A) of human testis (A). Germ cells and Sertoli cells are negative or at the most minimally reactive (arrowhead in A). In rat testis, the pattern of expression is reversed. Germ cells and Sertoli cells show strongly nuclear and cytoplasmic reactivity (arrowhead in B), whereas Leydig cells are only weakly reactive (arrow in B). In human epididymis, a scant number of epithelial cells are immunoreactive, and the nuclei of these cells tend to be close to the lumen (arrowhead and inset in C). The endothelial cells are strongly reactive (arrow in C). In rat epididymis, the epithelial cells possess diffuse but weak positive immunoreactivity (arrow and inset in D). The stromal cells and endothelial cells are non-reactive.