Multidrug Resistance Genes and P-Glycoprotein in the Testis of the Rat, Mouse, Guinea Pig, and Human1

Abstract

Study of the multidrug resistance phenomenon in tumor cell lines has led to the discovery of the product of the multidrug resistance (MDR) type 1 genes, the plasma membrane P-glycoprotein (P-gp) that functions as an energy-dependent pump for the efflux of diverse anticancer drugs. P-gp was also recently identified in normal epithelial cells with secretory/excretory functions and in the endothelial cells of the capillary blood vessels in the brain and the testis. These endothelial cells are key elements of the blood-brain and blood-testis barriers, respectively. The aim of this study, in the rat, mouse, guinea pig, and human, was to determine whether testicular cells other than the capillary endothelial cells could express MDR type I genes. Immunohistochemistry on testicular sections revealed that P-gp is present in interstitial cells in the mouse, rat, and human testes, in early and late spermatids in guinea pig testis, and in late spermatids in the rat, mouse, and human. Reverse transcription-polymerase chain reaction analysis on isolated mouse, rat, and human cells showed that all somatic testicular cells (Leydig cells, macrophages, peritubular cells, and Sertoli cells) and the cytoplasmic lobes from rat late spermatids expressed MDR type I mRNAs, whereas spermatogonia, pachytene spermatocytes, and early spermatids did not. An ontogenesis study in the mouse reveals that type I MDR gene expression begins at 13.5 days postcoitum at the time when the seminiferous cords and the blood vessels appear and are maintained thereafter. Finally, two functional tests on isolated rat cells, the doxorubicin and rhodamine uptake assays, demonstrated that rat testicular macrophages, Leydig cells, peritubular cells, and Sertoli cells displayed a multidrug-resistance activity, whereas spermatogonia, pachytene spermatocytes, and early spermatids did not. Western blot experiments have revealed that a P-gp of 175 kDa is present in the human testis as well as in the rat Leydig cells, testicular macrophages, peritubular cells, and Sertoli cells, but is absent in spermatogonia, spermatocytes, and early spermatids. We conclude that P-gp is involved in the self-protection of the somatic cells and is most probably one of the molecules that confers its functionality to the blood-testis barrier. The absence of expression of MDR type I genes in mitotic and meiotic germ cells probably explains their particular vulnerability to various anticancer drugs. In contrast, expression of the P-gp in the haploid cells most likely reflects the ability of spermatozoa to assume their own antidrug defense.

Upregulation of P-Glycoprotein Activity in Porcine Oocytes and Granulosa Cells During In Vitro Maturation

“…In addition, its efflux was completely suppressed by verapamil, an inhibitor of Pgp that inhibits the efflux of rhodamine 6G in a competitive manner [23,24]. Our findings are very similar to those of a recent report using the testes of several species [14]. High expression of Pgp in the ovaries, testes, adrenal glands, and reproductive organs suggests a function closely associated with steroid hormone transport.…”

“…In addition, its efflux was completely suppressed by verapamil, an inhibitor of Pgp that inhibits the efflux of rhodamine 6G in a competitive manner [23,24]. Our findings are very similar to those of a recent report using the testes of several species [14]. …”

“…In contrast, it is known that Pgp is not expressed in spermatocytes of several species including the rat [14,21], mouse, guinea pig and human [14], whereas MDR1 transcript is detected in porcine oocytes by RT-PCR [22]. In our recent studies using RT-PCR with primer sets based on the human sequence [15], it was found that MDR1 is expressed in the porcine oocyte at least through the period of the first meiotic stage and that the cDNA sequence of the porcine MDR1 RT-PCR product is highly homologous to the human cDNA at nucleotide positions 2282-2783.…”

“…Expression of Pgp in trophoblasts may indicate the development of a protection system during embryogenesis. In contrast, studies using testicular cells from various species reported that few MDR type I genes such as human MDR1 and mouse mdr1a and mdr1b are expressed in the mitotic and meiotic germ cells [14]. More recently, we detected the MDR1 transcript in the germinal vesicle (GV) and second metaphase (MII) oocytes and granulosa cells of porcine ovaries by RT-PCR analysis using primer sets based on the human gene [15,16].…”

Breast cancer resistance protein (Bcrp) and the testis—an unexpected turn of events

“…20,21,48 Unlike P-glycoprotein, which is localized to the BTB and expressed by Sertoli cells, Leydig cells and late spermatids, 20,50,51 and Mrp1, which is also localized to Sertoli cells at the BTB in humans and mice, 20,52 , but not in endothelial cells in the microvessels of rat testes, 53 Bcrp is not found at the BTB in rat testes. 20,21,33 Recent studies have shown that Bcrp is also expressed by Sertoli cells and late spermatids (steps 17-18, but not step 19) in rat testes in a tightly stage-specific pattern at the Sertoli/spermatid interface at the apical ES, in stage VI-VIII tubules (Figure 3).…”