Sertoli cell tight junction dynamics: their regulation during spermatogenesis

FSH-sensitive murine sertoli cell lines immortalized by human telomerase gene hTERT express the androgen receptor in response to TNF-alpha stimulation

Sertoli cells are regulated by follicular stimulating hormone (FSH) and testosterone secreted by the pituitary gland and Leydig cells, respectively. However, the expression of the FSH receptor and androgen receptor were undetectable in both primary cultured Sertoli cells and Sertoli cell lines immortalized by SV40 large T antigen. Two Sertoli cell lines, B6Sc-2 and B6Sc-3, were established from the testis of 19-day-old C57BL/6 mice testis by immortalization with human telomere reverse transcriptase. These Sertoli cell lines expressed FSH receptors and the total phosphoprotein patterns were converted after FSH treatment. Additionally, immunological methods demonstrated that these cell lines expressed characteristic Sertoli cell proteins, such as tyrosine-tubulin, vimentin and stem cell factor (SCF). Reverse transcription-polymerase chain reaction (RT-PCR) also indicates that they express Sertoli specific mRNAs, such as Amh, claudin11 and ZO-1. The expression of the androgen receptor in both B6Sc-2 and B6Sc-3 cells could be induced by TNF-alpha treatment. The present results indicate that these Sertoli cell lines are more native than others and may thus provide useful tools for in vitro studies.

Inhibition of the urokinase-type plasminogen activator by triplex-forming oligonucleotides in rat Sertoli cells: a new contraceptive alternative?

Urokinase-type plasminogen activator (uPA), expressed in Sertoli cells in the testis, is closely related with tight junctions of blood-testis barrier (BTB), and it has been considered as a potential contraceptive target. In the present study, the antigene effects of triplex-forming oligodeoxynucleotides (TFO) targeting uPA in rat Sertoli cells were investigated in vitro. The stable triplexes, formed by uPA specific TFOs under physiological conditions, were tested by means of electrophoretic mobility shift assays (EMSA). Although tPA, another form of plasminogen activators (PAs), partially compensated the lose of PAs activities, uPA mRNA and protein were significantly reduced as demonstrated by real-time reverse transcription PCR and a chromogenic assay, after the treatment of Sertoli cells with uPA specific TFOs at a concentration of 330 nM. The capacity of TFOs resistance to nuclease degradation was enhanced by the phosphorothioated on the backbone of the oligonucleotides. Our results indicated that the TFOs can downregulate uPA expression and uPA might be an alternative contraceptive target.

Actin-based dynamics during spermatogenesis and its significance

Actin can be found in all kinds of eukaryotic cells, maintaining their shapes and motilities, while its dynamics in sperm cells is understood less than their nonmuscle somatic cell counterparts. Spermatogenesis is a complicated process, resulting in the production of mature sperm from primordial germ cell. Significant structural and biochemical changes take place in the seminiferous epithelium of the adult testis during spermatogenesis. It was proved that all mammalian sperm contain actin, and that F-actin may play an important role during spermatogenesis, especially in nuclear shaping. Recently a new model for sperm head elongation based on the acrosome-acroplaxome-manchette complex has been proposed. In Drosophila, F-actin assembly is supposed to be very crucial during individualization. In this mini-review, we provide an overview of the structure, function, and regulation characteristics of actin cytoskeleton, and a summary of the current status of research of actin-based structure and movement is also provided, with emphasis on the role of actins in sperm head shaping during spermiogenesis and the cell junction dynamics in the testis. Research of the Sertoli ectoplasmic specialization is in the spotlight, which is a testis-specific actin-based junction very important for the movement of germ cells across the epithelium. Study of the molecular architecture and the regulating mechanism of the Sertoli ectoplasmic specialization has become an intriguing field. All this may lead to a new strategy for male infertility and, at the same time, a novel idea may result in devising much safer contraception with high efficiency. It is hoped that the advances listed in this review would give developmental and morphological researchers a favorable investigating outline and could help to enlarge the view of new strategies and models for actin dynamics during spermatogenesis.

Immortalized Sertoli cell lines sk11 and sk9 and binding of spermatids in vitro

AIM

To determine the effectiveness of the sk11, sk9 and sk11 TNUA5 Sertoli cell lines in binding germ cells in vitro.

METHODS

The immortalized Sertoli cell lines sk9, sk11 and sk11 TNUA5 were used in co-culture experiments with germ cells in media with or without reproductive hormones and incubated for 44 h at 32 degrees . The number of germ cells bound to Sertoli cells was then determined and statistically analyzed. Western blot analysis and reverse transcriptase-polymerase chain reaction (RT-PCR) studies were employed to investigate the presence of cell adhesion proteins and follicle stimulating hormone (FSH) receptor, respectively.

RESULTS

No statistical difference between the number of bound step-8 spermatids and bound pre-step 8 spermatids on Sertoli cells from any of the cell lines existed. After the addition of germ cells, Sertoli cells showed more lipid accumulation in their cytoplasm, indicating active phagocytosis. Western blot analysis in the sk11 TNUA5 line indicated the expression of N-cadherin. FSH-only and testosterone-only treatments increased N-cadherin expression, regardless of germ cell addition. The addition of germ cells to the sk11 TNUA5 Sertoli cells increased the expression of espin, as did the addition of FSH with germ cells. RT-PCR studies of the sk11 TNUA5 cells indicated that the mRNA for FSH receptor decreased with successive passages.

CONCLUSION

In vitro binding between isolated germ cells and sk9, sk11 or sk11 TNUA5 Sertoli cells is not feasible, and therefore these cell lines are not useful for the in vitro investigation of Sertoli-germ cell interactions and primary Sertoli cell isolates must still be used.

Dual transcriptional control of claudin-11 via an overlapping GATA/NF-Y motif: positive regulation through the interaction of GATA, NF-YA, and CREB and negative regulation through the interaction of Smad, HDAC1, and mSin3A

The expression of claudin-11, a key integral tight junction protein, is tightly regulated to ensure that the integrity of the seminiferous epithelium could be maintained during the translocation of spermatocytes at the blood-testis barrier at stages VIII-IX. In this study, we elucidate how the overlapping GATA/NF-Y motif within the core promoter of claudin-11 gene is modulated by differential binding of various transcription factors, resulting in dual transcriptional control. Using electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) assay, we confirmed that GATA, nuclear factor YA (NF-YA), and cAMP response element-binding protein (CREB) form a complex in vivo and bind to the GATA/NF-Y region to promote claudin-11 gene transcription. Such gene activations were significantly reduced in the presence of siRNA specific to these transcription factors. GATA and CREB transactivation could be further modulated by the presence of Smad3 and Smad4 proteins. Binding of Smad proteins at the GATA/NF-Y motif could repress the GATA and CREB transactivation of claudin-11 gene. Such repression which required the recruitment and physical interactions of histone deacetylase 1 and its co-repressor, mSin3A with Smad proteins, was abolished by treatment with Trichostatin A, thus suggesting the involvement of histone deacetylation at the site of the promoter region. It is believed that cyclic changes in the ratio of positive regulators (GATA, NF-Y, and CREB) to negative regulators (Smads) in the seminiferous epithelium during the spermatogenic cycle might provide a precise control in claudin-11 gene transcription.

Claudin-11 expression and localisation is regulated by androgens in rat Sertoli cells in vitro

Claudin-11 and occludin are protein components in tight junctions (TJs) between Sertoli cells which are important for the maintenance of the blood-testis barrier. Barrier formation occurs during puberty, with evidence suggesting hormonal regulation of both claudin-11 and occludin. This study aimed to investigate the regulation of claudin-11 and occludin mRNA expression by testosterone (T) and FSH and their immunolocalisation at rat Sertoli cell TJs in vitro, and to correlate any steroid regulation with the functional capacity of TJs. Sertoli cells formed functional TJs within 3 days as assessed by transepithelial electrical resistance (TER). Both T and dihydrotestosterone significantly (P < 0.01) increased TER twofold and claudin-11 mRNA two- to threefold within 3 days. FSH partially stimulated TER and claudin-11 mRNA, but estradiol had no effect. T also promoted claudin-11 localisation into extensive intercellular contacts. In contrast to claudin-11, Tand FSH did not change occludin mRNA expression, however, T promoted localisation of occludin at cell contacts in a similar manner to claudin-11. Addition of flutamide to T-stimulated cells caused a twofold decrease in both TER and claudin-11 mRNA expression, and resulted in the loss of both proteins from cell contacts. This effect was reversible following flutamide removal. It is concluded that androgens i) co-regulate claudin-11 mRNA expression and TER, implicating claudin-11 in TJ formation and ii) promote the localisation of claudin-11 and occludin at Sertoli cell contacts. Hence, the ability of androgens to maintain spermatogenesis in vivo is partly via their effects on TJ proteins and regulation of the blood-testis barrier.

Altered expression of ZO-1 and ZO-2 in Sertoli cells and loss of blood-testis barrier integrity in testicular carcinoma in situ

Carcinoma in situ (CIS) is the noninvasive precursor of most human testicular germ cell tumors. In normal seminiferous epithelium, specialized tight junctions between Sertoli cells constitute the major component of the blood-testis barrier. Sertoli cells associated with CIS exhibit impaired maturation status, but their functional significance remains unknown. The aim was to determine whether the blood-testis barrier is morphologically and/or functionally altered. We investigated the expression and distribution pattern of the tight junction proteins zonula occludens (ZO) 1 and 2 in normal seminiferous tubules compared to tubules showing CIS. In normal tubules, ZO-1 and ZO-2 immunostaining was observed at the blood-testis barrier region of adjacent Sertoli cells. Within CIS tubules, ZO-1 and ZO-2 immunoreactivity was reduced at the blood-testis barrier region, but spread to stain the Sertoli cell cytoplasm. Western blot analysis confirmed ZO-1 and ZO-2, and their respective mRNA were shown by RT-PCR. Additionally, we assessed the functional integrity of the blood-testis barrier by lanthanum tracer study. Lanthanum permeated tight junctions in CIS tubules, indicating disruption of the blood-testis barrier. In conclusion, Sertoli cells associated with CIS show an altered distribution of ZO-1 and ZO-2 and lose their blood-testis barrier function.

Multiple roles of the nuclear receptors for oxysterols liver X receptor to maintain male fertility

Oxysterol nuclear receptors liver X receptor (LXR)alpha and LXRbeta are known to regulate lipid homeostasis in cells exposed to high amounts of cholesterol and/or fatty acids. In order to elucidate the specific and redundant roles of the LXRs in the testis, we explored the reproductive phenotypes of mice deficient of LXRalpha, LXRbeta, and both, of which only the lxralpha;beta-/- mice are infertile by 5 months of age. We demonstrate that LXRalpha-deficient mice had lower levels of testicular testosterone that correlated with a higher apoptotic rate of the germ cells. LXRbeta-deficient mice showed increased lipid accumulation in the Sertoli cells and a lower proliferation rate of the germ cells. In lxralpha;beta-/- mice, fatty acid metabolism was affected through a decrease of srebp1c and increase in scd1 mRNA expression. The retinoid acid signaling pathway was also altered in lxralpha;beta-/- mice, with a higher accumulation of all-trans retinoid receptor alpha, all-trans retinoid receptor beta, and retinoic aldehyde dehydrogenase-2 mRNA. Combination of these alterations might explain the deleterious phenotype of infertility observed only in lxralpha;beta-/- mice, even though lipid homeostasis seemed to be first altered. Wild-type mice treated with a specific LXR agonist showed an increase of testosterone production involving both LXR isoforms. Altogether, these data identify new roles of each LXR, collaborating to maintain both integrity and functions of the testis.

Perturbation of spermatogenesis by androgen antagonists directly injected into seminiferous tubules of live mice

Natural and artificial substances present in the environment can affect our health. Testicular toxicants in particular are troublesome, because they disturb gonadal function of males. Translocation of substances into the seminiferous epithelium where sperm production proceeds is restricted due to the blood–testis barrier, but this permeability barrier temporarily disappears under physiological and sub-physiological conditions. This means that any substance could enter the seminiferous epithelium and disturb sperm production. To reduce the risk posed by such toxins, it is important to accurately determine which substances possess the toxicity. However, existing assay systems are not satisfactory in terms of both accuracy and sensitivity. Here, we report the establishment of such a system. We injected the androgen antagonists, flutamide and vinclozolin, directly into seminiferous tubules of live mice, which had been treated with busulfan for a temporal arrest of spermatogenesis, and the testes were histologically examined to see the effect of the injected materials on spermatogenesis that was in the process of recovery. The injection of either substance brought about a severe impairment of spermatogenesis at an amount over a million times smaller than that used in the previous assay systems where animals are administered with test substances outside of the testis. In contrast, these androgen antagonists at the same doses showed lesser effects when intratubularly or intraperitoneally administered into mice that had not been pretreated with busulfan. We propose that the method adopted in this study is a novel assay system to identify potential testicular toxicants.

Development of neonatal mouse and fetal human testicular tissue as ectopic grafts in immunodeficient mice

AIM

To investigate the stepwise development and germ cell gene expression in allografted neonatal mouse testes and the differentiation of immature human testicular cells in xenografted human testes.

METHODS

Immunodeficient nude mice were used as hosts for allografting of neonatal mouse testes and xenografting of human fetal testicular tissues. Stepwise development and stage-specific gene expression of germ cells in allografts were systematically evaluated and parallel compared with those in intact mice by periodically monitoring the graft status with measurement of graft weight, histological analysis and determination of five stage-specific genes. Human testicular tissues from 20 and 26 weeks fetuses were used for the xenografting study. Histological analysis of xenografts was performed 116 and 135 d after the grafting procedure.

RESULTS

In the allografting study, progressive increase in tissue volume and weight as well as in tubule diameter in grafts was observed; the appearance time of various germ cells in seminiferous tubules, including spermatogonia, spermatocytes, round and elongate spermatids and sperm, was comparable with that in intact donors; the initiation of gene transcription in grafts showed a similar trend as in normal mice. Graft weight ceased to increase after 7-8 weeks and degradation of grafts was observed after 5 weeks with progressive damage to seminiferous epithelium. In the xenografting study using immature human testicular tissues, graft survival and development was indicated by increasing graft weight, Sertoli cells differentiation into advanced stage, germ cells migration and location to the basal lamina and formation of a niche-like structure.

CONCLUSION

The developmental course and gene expression pattern of germ cells in allografts were similar to those in intact mice. The best time point for retrieval of mouse sperm from grafts was 5-7 weeks after grafting procedure. An accelerated development of immature human testicular cells could be achieved by ectopic xenografting of human testes.

Pharmacological profile of inhibition of the chloride channels activated by extracellular acid in cultured rat Sertoli cells

Sertoli cells from mammalian testis are key cells involved in the development and maintenance of stem cell spermatogonia as well as in the secretion of a Cl(-) and K(+)-rich fluid into the lumen of seminiferous tubules. The pharmacology and contribution of Cl(-) channels to the physiology of Sertoli cells were investigated using whole-cell patch clamp and iodide efflux experiments applied to cultured rat Sertoli cells. We characterized an outwardly rectifying Cl(-) current stimulated by various acid species including the physiologically relevant lactic acid. Using the iodide efflux technique, the pharmacological properties of this Cl(-) current, noted ICl(acid), revealed Ca(2+)-independent inhibition by DIDS (IC(50) = 27 microM), glibenclamide (IC(50) = 31 microM) and DPC (IC(50) = 86 microM). ICl(acid) was neither affected by calix[4]arene nor by 9-AC. The order of potency for inhibition of ICl(acid) is DIDS approximately glibenclamide > DPC >> calix[4]arene, 9-AC. For comparison, the inhibitory profile of the swelling- and ATP-activated Cl(-) currents in Sertoli cells is DPC = DIDS >> glibenclamide = 9-AC for ICl(swell) and DPC = 9-AC = DIDS >> glibenclamide for ICl(ATP). This description provides new insights into the physiology and pharmacology of the endogenous Cl(-) channels expressed and potentially involved in fluid secretion in Sertoli cells.

Regulation of junction dynamics in the testis--transcriptional and post-translational regulations of cell junction proteins

Cell junctions are the sites at which cells attach to the neighboring cells. They do not only maintain tissue integrity, their turnover also plays a crucial role in cell development and morphogenesis. In the testis, tight junctions and adherens junctions are dynamically remodeled to allow the movement of post-meiotic germ cells across the seminiferous epithelium and the timely release of spermatids into the tubular lumen. There is growing evidence that this dynamic remodeling of cell junctions is mediated by several mechanisms at the transcriptional and post-translational levels. This review summarizes what is known about the transcriptional regulation, ubiquitination and endocytosis that are involved in modulating junction dynamics in epithelial cells. It also highlights the recent findings on the regulation of junction dynamics in the testis and the specific areas that require further research for a thorough understanding of the role of junction remodeling in spermatogenesis. Understanding the junction dynamics in the seminiferous epithelium may unfold new targets for non-hormonal male contraceptive development.

Characterization of novel Na+-dependent nucleobase transport systems at the blood-testis barrier

In the testis, nucleosides and nucleobases are important substrates of the salvage pathway for nucleotide biosynthesis, and one of the roles of Sertoli cells is to provide nutrients and metabolic precursors to spermatogenic cells located within the blood-testis barrier (BTB). We have already shown that concentrative and equilibrative nucleoside transporters are expressed and are functional in primary-cultured rat Sertoli cells as a BTB model, but little is known about nucleobase transport at the BTB or about the genes encoding specific nucleobase transporters in mammalian cells. In the present study, we examined the uptake of purine ([3H]guanine) and pyrimidine ([3H]uracil) nucleobases by primary-cultured rat Sertoli cells. The uptake of both nucleobases was time and concentration dependent. Kinetic analysis showed the involvement of three different transport systems in guanine uptake. In contrast, uracil uptake was mediated by a single Na+-dependent high-affinity transport system. Guanine uptake was inhibited by other purine nucleobases but not by pyrimidine nucleobases, whereas uracil uptake was inhibited only by pyrimidine nucleobases. In conclusion, it was suggested that there might be purine- or pyrimidine-selective nucleobase transporters in rat Sertoli cells.

Adult sertoli cells are not terminally differentiated in the Djungarian hamster: effect of FSH on proliferation and junction protein organization

Sertoli cell number is considered to be stable and unmodifiable by hormones after puberty in mammals, although recent data using the seasonal breeding adult Djungarian hamster (Phodopus sungorus) model challenged this assertion by demonstrating a decrease in Sertoli cell number after gonadotropin depletion and a return to control levels following 7 days of FSH replacement. The present study aimed to determine whether adult Sertoli cells are terminally differentiated using known characteristics of cellular differentiation, including proliferation, junction protein localization, and expression of particular maturational markers, in the Djungarian hamster model. Adult long-day (LD) photoperiod (16L:8D) hamsters were exposed to short-day (SD) photoperiod (8L:16D) for 11 wk to suppress gonadotropins and then received exogenous FSH for up to 10 days. Sertoli cell proliferation was assessed by immunofluorescence by the colocalization of GATA4 and proliferating cell nuclear antigen and quantified by stereology. Markers of Sertoli cell maturation (immature, cytokeratin 18 [KRT18]; mature, GATA1) and junction proteins (actin, espin, claudin 11 [CLDN11], and tight junction protein 1 [TJP1, also known as ZO-1]) also were localized using confocal immunofluorescence. In response to FSH treatment, proliferation was upregulated within 2 days compared with SD controls (90% vs. 0.2%, P < 0.001) and declined gradually thereafter. In LD hamsters, junction proteins colocalized at the basal aspect of Sertoli cells, consistent with inter-Sertoli cell junctions, and were disordered within the Sertoli cell cytoplasm in SD animals. Exogenous FSH treatment promptly restored localization of these junction markers to the LD phenotype. Protein markers of maturity remain consistent with those of adult Sertoli cells. It is concluded that adult Sertoli cells are not terminally differentiated in the Djungarian hamster and that FSH plays an important role in governing the differentiation process. It is proposed that Sertoli cells can enter a transitional state, exhibiting features common to both undifferentiated and differentiated Sertoli cells.

LIM kinase 2 is widely expressed in all tissues

The LIM kinase family includes two proteins: LIMK1 and LIMK2. These proteins have identical genomic structure and overall amino acid identity of 50%. Both proteins regulate actin polymerization via phosphorylation and inactivation of the actin depolymerizing factors ADF/cofilin. Although the function of endogenous LIMK1 is well established, little is known about the function of the endogenous LIMK2 protein. To understand the specific role of endogenous LIMK2 protein, we examined its expression in embryonic and adult mice using a rat monoclonal antibody, which recognizes specifically the PDZ domain of LIMK2 but not that of LIMK1. Immunoblotting and immunoprecipitation analyses of mouse tissues and human and mouse cell lines revealed widespread expression of the 75-kDa LIMK2 protein. Immunofluorescence analysis demonstrated that the cellular localization of LIMK2 is different from that of LIMK1. LIMK2 protein is found in the cytoplasm localized to punctae and is not enriched within focal adhesions like LIMK1. Immunohistochemical studies revealed that LIMK2 is widely expressed in embryonic and adult mouse tissues and that its expression pattern is similar to that of LIMK1 except in the testes. We have also demonstrated that endogenous LIMK1 and LIMK2 form heterodimers, and that LIMK2 does not always interact with the same proteins as LIMK1.

Oligo-astheno-teratozoospermia in mice lacking RA175/TSLC1/SynCAM/IGSF4A, a cell adhesion molecule in the immunoglobulin superfamily

RA175/TSLC1/SynCAM/IGSF4A (RA175), a member of the immunoglobulin superfamily with Ca2+-independent homophilic trans-cell adhesion activity, participates in synaptic and epithelial cell junctions. To clarify the biological function of RA175, we disrupted the mouse Igsf4a (Ra175/Tslc1/SynCam/Igsf4a Ra175) gene. Male mice lacking both alleles of Ra175 (Ra175-/-) were infertile and showed oligo-astheno-teratozoospermia; almost no mature motile spermatozoa were found in the epididymis. Heterozygous males and females and homozygous null females were fertile and had no overt developmental defects. RA175 was mainly expressed on the cell junction of spermatocytes, elongating and elongated spermatids (steps 9 to 15) in wild-type testes; the RA175 expression was restricted to the distal site (tail side) but not to the proximal site (head side) in elongated spermatids. In Ra175-/- testes, elongated and mature spermatids (steps 13 to 16) were almost undetectable; round spermatids were morphologically normal, but elongating spermatids (steps 9 to 12) failed to mature further and to translocate to the adluminal surface. The remaining elongating spermatids at improper positions were finally phagocytosed by Sertoli cells. Furthermore, undifferentiated and abnormal spermatids exfoliated into the tubular lumen from adluminal surfaces. Thus, RA175-based cell junction is necessary for retaining elongating spermatids in the invagination of Sertoli cells for their maturation and translocation to the adluminal surface for timely release.

Spermatogenic cells distal to the blood-testis barrier in rats lack C3 convertase regulators and may be at risk of complement-mediated injury

On most tissues, multiple membrane complement regulators (CReg) protect self-cells from damage by complement. An exception is the brain, where the blood-brain barrier provides a protected environment within which cells survive with little or no protection from complement. The testis has a functionally similar structure, the blood-testis barrier (BTB). Here, we have investigated the expression of C3/C5 convertase CReg and C3 in the normal rat testis at different ages and different spermatogenetic stages, as well as in rats in which spermatogenesis and the BTB were impaired due to a developmental deficit. Immature testis, prior to BTB formation at puberty, displayed broad expression of the ubiquitous rodent CReg Crry on all elements and no expression of CD46 or CD55. Within days of BTB formation, CReg expression was dramatically altered; Crry was expressed only in the spermatogenetic cells external to the BTB in basal layers of adult seminal epithelium. Spermatogenic cells immediately distal to the BTB at first expressed no C3/C5 convertase regulators but later acquired expression of CD46 and CD55. Staining for C3 was widespread pre-puberty, but absent distal to the BTB in mature rats. In rats with defects in spermatogenesis and BTB integrity, expression patterns of CReg and C3 resembled those in pre-pubertal normals. The relative paucity of CReg and absence of C3 synthesis distal to the BTB suggest the presence of a complement-protected environment analogous to that described in the brain, and suggest also that cells enclosed by the BTB may be susceptible to complement damage when the barrier is breached.

Androgens regulate the permeability of the blood-testis barrier

Within the mammalian testis, specialized tight junctions between somatic Sertoli cells create basal and apical polarity within the cells, restrict movement of molecules between cells, and separate the seminiferous epithelium into basal and adluminal compartments. These tight junctions form the basis of the blood-testis barrier, a structure whose function and dynamic regulation is poorly understood. In this study, we used microarray gene expression profiling to identify genes with altered transcript levels in a mouse model for conditional androgen insensitivity. We show that testosterone, acting through its receptor expressed in Sertoli cells, regulates the expression of claudin 3, which encodes a transient component of newly formed tight junctions. Sertoli cell-specific ablation of androgen receptor results in increased permeability of the blood-testis barrier to biotin, suggesting claudin 3 regulates the movement of small molecules across the Sertoli cell tight junctions. These results suggest that androgen action in Sertoli cells regulates germ cell differentiation, in part by controlling the microenvironment of the seminiferous epithelium. Our studies also indicate that hormonal strategies for male contraception may interfere with the blood-testis barrier.

TESTICULAR MICROLITHIASIS AND ANTISPERM ANTIBODIES FOLLOWING TESTICULAR BIOPSY IN BOYS WITH CRYPTORCHIDISM

PURPOSE

Testicular biopsy (TBx) performed during orchiopexy in boys with cryptorchidism can help to predict future semen analyses and possibly identify patients at risk for testicular cancer. It has been theorized that TBx can be detrimental to the long-term health of the testis. We examined testicular microlithiasis (TM) and antisperm antibody (ASA) production in cryptorchid TBx.

MATERIALS AND METHODS

A total of 112 males underwent fertility evaluation. These patients had previously undergone orchiopexy and bilateral TBx (mean age 8.6 years) for unilateral or bilateral undescended testis. At a mean age of 19.6 years all patients underwent physical examination and scrotal ultrasound for evaluation of testis size, echotexture and abnormalities. Of 112 patients 57 also underwent direct Immunobead(R) assay with positive controls. Moving sperm free and/or bound to IgG bead complex were counted in the preparation.

RESULTS

A total of 29 patients had bilateral and 83 had unilateral undescended testis. Of the 112 patients 26 were black and 86 were white. Four black patients (15.4%) and 4 white patients (4.7%) had testicular microlithiasis. Three patients had bilateral and 5 had unilateral diffuse TM. No tunica albuginea scars or testis masses were noted. In the 57 patients who underwent direct Immunobead assay no semen sample demonstrated evidence of forming bead-sperm complex, ie none had direct ASA.

CONCLUSIONS

No patient exhibited evidence of direct ASA. Prepubertal open TBx does not increase the rate of TM. We found no evidence of additive testicular damage associated with TBx at the time of orchiopexy.

Myotubularin phosphoinositide phosphatases, protein phosphatases, and kinases: their roles in junction dynamics and spermatogenesis

Spermatogenesis in the seminiferous epithelium of the mammalian testis is a dynamic cellular event. It involves extensive restructuring at the Sertoli-germ cell interface, permitting germ cells to traverse the epithelium from basal to adluminal compartment. As such, Sertoli-germ cell actin-based adherens junctions (AJ), such as ectoplasmic specializations (ES), must disassemble and reassemble to facilitate this event. Recent studies have shown that AJ dynamics are regulated by intricate interactions between AJ integral membrane proteins (e.g., cadherins, alpha6beta1 integrins and nectins), phosphatases, kinases, adaptors, and the underlying cytoskeleton network. For instance, the myotubularin (MTM) phosphoinositide (PI) phosphatases, such as MTM related protein 2 (MTMR2), can form a functional complex with c-Src (a non-receptor protein tyrosine kinase). In turn, this phosphatase/kinase complex associates with beta-catenin, a constituent of the N-cadherin/beta-catenin functional unit at the AJ site. This MTMR2-c-Src-beta-catenin complex apparently regulates the phosphorylation status of beta-catenin, which determines cell adhesive function conferred by the cadherin-catenin protein complex in the seminiferous epithelium. In this review, we discuss the current status of research on selected phosphatases and kinases, and how these proteins potentially interact with adaptors at AJ in the seminiferous epithelium to regulate cell adhesion in the testis. Specific research areas that are open for further investigation are also highlighted.

Cytokines and junction restructuring during spermatogenesis—a lesson to learn from the testis

In the mammalian testis, preleptotene and leptotene spermatocytes residing in the basal compartment of the seminiferous epithelium must traverse the blood-testis barrier (BTB) at late stage VIII through early stage IX of the epithelial cycle during spermatogenesis, entering the adluminal compartment for further development. However, until recently the regulatory mechanisms that regulate BTB dynamics remained largely unknown. We provide a critical review regarding the significance of cytokines in regulating the 'opening' and 'closing' of the BTB. We also discuss how cytokines may be working in concert with adaptors that selectively govern the downstream signaling pathways. This process, in turn, regulates the dynamics of either Sertoli-Sertoli tight junction (TJ), Sertoli-germ cell adherens junction (AJ), or both junction types in the epithelium, thereby permitting TJ opening without compromising AJs, and vice versa. We also discuss how adaptors alter their protein-protein association with the integral membrane proteins at the cell-cell interface via changes in their phosphorylation status, thereby altering adhesion function at AJ. These findings illustrate that the testis is a novel in vivo model to study the biology of junction restructuring. Furthermore, a molecular model is presented regarding how cytokines selectively regulate TJ/AJ restructuring in the epithelium during spermatogenesis.

cAMP perturbs inter-Sertoli tight junction permeability barrier in vitro via its effect on proteasome-sensitive ubiquitination of occludin

Throughout spermatogenesis, inter-Sertoli tight junctions (TJs) that constitute the blood-testis barrier must be disassembled and reassembled to permit the timely movement of preleptotene and leptotene spermatocytes from the basal to the adluminal compartment of the seminiferous epithelium. However, the mechanism and the participating molecules that regulate the bioavailability of TJ proteins are entirely unknown. Using Sertoli cell culture, it was shown that there was an increase in occludin level, concomitant with a reduction of an E3 ubiquitin ligase, Itch, at the time when inter-Sertoli TJs were assembled. By co-immunoprecipitation, occludin was shown to associate with Itch at the TJs. A novel interaction between Itch and UBC4 (an ubiquitin-conjugating enzyme) was identified. When TJs were disrupted by dibutyryl-cAMP (db-cAMP), an increase in protein levels of Itch and UBC4 along with a significant reduction in endogenous occludin was detected. These results seemingly suggest that the interaction of Itch and UBC4 on occludin is potentially involved in regulating Sertoli TJ dynamics. Addition of a proteasome inhibitor, MG-132, into Sertoli cells cultured with db-cAMP blocked the db-cAMP-induced occludin loss in vitro. Accumulations of ubiquitin-conjugated and Itch-conjugated occludin were detected in Sertoli cells cultured in the presence of both MG-132 and db-cAMP. These results suggest that MG-132 prevented db-cAMP-induced TJ disruption by altering the rate of occludin degradation. Taken collectively, the results reported herein support the notion that db-cAMP-induced TJ disruption was mediated by an induction of Itch protein expression, which in turn triggered the ubiquitination of occludin resulting in TJ disruption.

Sertoli-germ cell anchoring junction dynamics in the testis are regulated by an interplay of lipid and protein kinases

When Sertoli and germ cells were co-cultured in vitro in serum-free chemically defined medium, functional anchoring junctions such as cell-cell intermediate filament-based desmosome-like junctions and cell-cell actin-based adherens junctions (e.g. ectoplasmic specialization (ES)) were formed within 1-2 days. This event was marked by the induction of several protein kinases such as phosphatidylinositol 3-kinase (PI3K), phosphorylated protein kinase B (PKB; also known as Akt), p21-activated kinase-2 (PAK-2), and their downstream effector (ERK) as well as an increase in PKB intrinsic activity. PI3K, phospho (p)-PKB, and PAK were co-localized to the site of apical ES in the seminiferous epithelium of the rat testis in immunohistochemistry studies. Furthermore, PI3K also co-localized with p-PKB to the same site in the epithelium as determined by fluorescence microscopy, consistent with their localization at the ES. These kinases were shown to associate with ES-associated proteins such as beta1-integrin, phosphorylated focal adhesion kinase, and c-Src by co-immunoprecipitation, suggesting that the integrin.laminin protein complex at the apical ES likely utilizes these protein kinases as regulatory proteins to modulate Sertoli-germ cell adherens junction dynamics via the ERK signaling pathway. To validate this hypothesis further, an in vivo model using AF-2364 (1-(2,4-dichlorobenzyl)-1H-indazole-3-carbohydrazide) to perturb Sertoli-germ cell anchoring junction function, inducing germ cell loss from the epithelium in adult rats, was used in conjunction with specific inhibitors. Interestingly, the event of germ cell loss induced by AF-2364 in vivo was also associated with induction of PI3K, p-PKB, PAK-2, and p-ERK as well as a surge in intrinsic PKB activity. Perhaps the most important of all, pretreatment of rats with wortmannin (a PI3K inhibitor) or anti-beta1-integrin antibody via intratesticular injection indeed delayed AF-2364-induced spermatid loss from the epithelium. In summary, these results illustrate that Sertoli-germ cell anchoring junction dynamics in the testis are regulated, at least in part, via the beta1-integrin/PI3K/PKB/ERK signaling pathway.

Nucleoside transport at the blood-testis barrier studied with primary-cultured sertoli cells

Nucleosides are essential for nucleotide synthesis in testicular spermatogenesis. In the present study, the mechanism of the supply of nucleosides to the testicular system across the blood-testis barrier was studied using primary-cultured Sertoli cells from rats and TM4 cells from mice. Uptake of uridine by these cells was time- and concentration-dependent. Uridine uptake was decreased under Na(+)-free conditions, and the system was presumed to be high affinity, indicating an Na(+)-dependent concentrative nucleoside transporter (CNT) is involved. On the other hand, nitrobenzylthioinosine, a potent inhibitor of Na(+)-independent equilibrative nucleoside transporters (ENTs), inhibited uridine uptake by the Sertoli cells in a concentration-dependent manner. Expression of nucleoside transporters ENT1, ENT2, ENT3, CNT1, CNT2, and CNT3 was detected in Sertoli cells by reverse transcriptase-polymerase chain reaction analysis. Inhibition studies of the uptake of uridine by various nucleosides both in the presence and absence of Na(+) indicated that the most of those expressed nucleoside transporters, ENTs and CNTs, are involved functionally. These results demonstrated that Sertoli cells are equipped with multiple nucleoside transport systems, including ENT1, ENT2, and CNTs, to provide nucleosides for spermatogenesis.

Rat Sertoli cells express epithelial but also mesenchymal genes after immortalization with SV40

A new immortal Sertoli cell line from pubertal rat testis was established and characterized. We have generated the clonal line SCIT-C8 expressing established markers for Sertoli cells (SC) like transferrin, clusterin and steel factor/stem cell factor (SCF). Additionally, the immortalized cells express afadin, a protein which is a member of tight and adherens junctions, therefore the cells may be useful for studies of the blood-testis barrier (BTB) in vitro. In contrast to primary SC, the immortalized cells lost expression of androgen receptor and responsiveness to androgens and follicle-stimulating hormone. Surprisingly, we found mRNA expression and protein secretion of the mesenchymal markers, fibronectin and entactin-1, which we also observed for the immortalized SC lines, ASC-17D and 93RS2. In comparison to primary SC, the immortalized cells demonstrated enhanced adhesion in vitro. This correlated with the expression of entactin-1 because adhesion was strongly reduced by antibody perturbation experiments. Additionally, we found the alternatively spliced and primarily muscle cell-specific long variant of TGF-beta2 not only in peritubular cells (PC), but also in the primary and immortalized SC. Furthermore, all immortalized cell lines secreted higher amounts of TGF-beta2 than primary SC. In conclusion, the immortalized SC lines from different developmental stages showed a similar pattern of epithelial and mesenchymal markers.

A close correlation in the expression patterns of Af-6 and Usp9x in Sertoli and granulosa cells of mouse testis and ovary

Usp9x, an X-linked deubiquitylating enzyme, is stage dependently expressed in the supporting cells (i.e. Sertoli cells and granulosa cells) and germ cells during mouse gametogenesis. Af-6, a cell junction protein, has been identified as a substrate of Usp9x, suggesting a possible association between Usp9x and Af-6 in spermatogenesis and oogenesis. In this study, we examined the expression pattern of Af-6 and Usp9x and their intracellular localization in testes and ovaries of mice treated with or without pregnant mare serum gonadotropin (PMSG), an FSH-like hormone. In both testes and ovaries, Af-6 expression was predominantly observed in supporting cells, as well as in steroidogenic cells, but not in any germ cells. In Sertoli cells, Af-6 was continuously expressed throughout postnatal and adult stages, where both Af-6 and Usp9x were enriched at the sites of Sertoli–Sertoli and Sertoli–spermatid junctions especially at stages XI–VI. In the granulosa cells, Af-6, as well as Usp9x, was highly expressed in primordial and primary follicles, but its expression rapidly decreased after the late-secondary follicle stage. Interestingly, in PMSG-treated mice, the expression levels of Af-6 and Usp9x were synchronously enhanced, slightly in Sertoli cells and strongly in granulosa cells of the late-secondary and Graafian follicles. Such closely correlated expression patterns between Af-6 and Usp9x clearly suggest that Af-6 may be deubiquitylated by Usp9x in both Sertoli and granulosa cells. It further suggests that the post-translational regulation of Af-6 by Usp9x may be one potential pathway to control the cell adhesion dynamics in mammalian gametogenesis.

Sertoli-Sertoli and Sertoli-germ cell interactions and their significance in germ cell movement in the seminiferous epithelium during spermatogenesis

Spermatogenesis is the process by which a single spermatogonium develops into 256 spermatozoa, one of which will fertilize the ovum. Since the 1950s when the stages of the epithelial cycle were first described, reproductive biologists have been in pursuit of one question: How can a spermatogonium traverse the epithelium, while at the same time differentiating into elongate spermatids that remain attached to the Sertoli cell throughout their development? Although it was generally agreed upon that junction restructuring was involved, at that time the types of junctions present in the testis were not even discerned. Today, it is known that tight, anchoring, and gap junctions are found in the testis. The testis also has two unique anchoring junction types, the ectoplasmic specialization and tubulobulbar complex. However, attention has recently shifted on identifying the regulatory molecules that "open" and "close" junctions, because this information will be useful in elucidating the mechanism of germ cell movement. For instance, cytokines have been shown to induce Sertoli cell tight junction disassembly by shutting down the production of tight junction proteins. Other factors such as proteases, protease inhibitors, GTPases, kinases, and phosphatases also come into play. In this review, we focus on this cellular phenomenon, recapping recent developments in the field.

Spermatid differentiation requires the assembly of a cell polarity complex downstream of junctional adhesion molecule-C

During spermatogenesis in the mammalian testis, stem cells (spermatogonia) differentiate into spermatocytes, which subsequently undergo two consecutive meiotic divisions to give rise to haploid spermatids. These cells are initially round but progressively elongate, condense their nuclei, acquire flagellar and acrosomal structures, and shed a significant amount of their cytoplasm to form spermatozoa (the sperm cells) in a developmental cascade termed spermiogenesis. Defects in these processes will lead to a lack of mature sperm cells (azoospermia), which is a major cause of male infertility in the human population. Here we report that a cell-surface protein of the immunoglobulin superfamily, junctional adhesion molecule-C (JAM-C), is critically required for the differentiation of round spermatids into spermatozoa in mice. We found that Jam-C is essential for the polarization of round spermatids, a function that we attribute to its role in the assembly of a cell polarity complex.

Adaptors, Junction Dynamics, and Spermatogenesis1

Adaptors are component proteins of junctional complexes in all epithelia, including the seminiferous epithelium of the mammalian testis. They recruit other regulatory and structural proteins to the site of both anchoring junctions (such as cell-cell actin-based adherens junctions [AJs], e.g., ectoplasmic specialization [ES] and tubulobulbar complex, which are both testis-specific cell-cell actin-based AJ types, and cell-cell intermediate filament-based desmosome-like junctions) and tight junctions (TJ). Furthermore, adaptors per se can be substrates and/or activators of kinases or phosphatases. As such, the integrity of cell junctions and the regulation of junction dynamics during spermatogenesis rely on adaptors for their ability to recruit and link different junctional components to the same site and to tether transmembrane proteins at both anchoring and TJ sites to the underlying cytoskeletons, such as the actin filaments, intermediate filaments, and microtubules. These protein-protein interactions are possible because adaptors are composed of conserved protein binding domains, which allow them to link to more than one structural or signaling protein, recruiting multi-protein complexes to the same site. Herein, we provide a timely review of adaptors recently found at the sites of AJ (e.g., ES) and TJ. In addition, several in vivo models that can be used to delineate the function of adaptors in the testis are described, and the role of adaptors in regulating junction dynamics pertinent to spermatogenesis is discussed.

Testicular phenotype in luteinizing hormone receptor knockout animals and the effect of testosterone replacement therapy

The LH receptor knockout model, developed in our laboratory, was used in determining what FSH alone can do in the absence of LH signaling and whether any of the testicular LH actions are not mediated by androgens. The results revealed that null animals contained smaller seminiferous tubules, which contained the same number of Sertoli cells, spermatogonia, and early spermatocytes as wild-type siblings. The number of late spermatocytes, on the other hand, was moderately decreased, the number of round spermatids was dramatically decreased, and elongated spermatids were completely absent. These changes appear to be due to an increase in apoptosis in spermatocytes. While the number of Leydig cells progressively increased from birth to 60 days of age in wild-type animals, they remained unchanged in null animals. Consequently, 60-day-old null animals contained only a few Leydig cells of fetal type. The age-dependent increase in testicular macrophages lagged behind in null animals compared with wild-type siblings. Orchidopexy indicated that -/- testicular phenotype was not due to abdominal location. Rather, it was mostly due to androgen deficiency, as 21-day testosterone replacement therapy stimulated the growth of seminiferous tubules, decreased apoptosis, and increased the number of late spermatocytes and round spermatids and their subsequent differentiation into mature sperm. The therapy, however, failed to restore adult-type Leydig cells and testicular macrophage numbers to the wild-type levels. In summary, our data support the concept that FSH signaling alone can maintain the proliferation and development of Sertoli cells, spermatogonia, and early spermatocytes. LH actions mediated by testosterone are required for completion of spermatogenesis, and finally, androgen-independent actions of LH are required for the formation of adult-type Leydig cells and recruitment of macrophages into the testes.

Phorbol myristate acetate induces changes on F-actin and vinculin content in immature rat Sertoli cells

Actin and vinculin are two of the most abundant cytoskeletal proteins, widely expressed in nearly all types of eukaryotic cells. It has been well established that long-term exposure to the tumor promoter phorbol myristate acetate (PMA) affects Sertoli cell morphology, as well as F-actin and vinculin organization in vitro. To analyze in a quantitative manner the F-actin and vinculin content of rat immature Sertoli cells in vitro in response to PMA exposure, cytoskeletal fractions were prepared following extraction with Triton X-100. Analysis of the isolated cytoskeletal fractions by immunoblotting showed that exposure of immature rat Sertoli cells to PMA for 8h has an appreciable effect on the cellular level of both the actin and vinculin. Interestingly, as revealed by using calphostin C, a specific protein kinase C inhibitor, the observed F-actin and vinculin changes are most probably mediated by a mechanism that depends on protein kinase activity. A discussion is made concerning PKC modulation by PMA and the subsequent actin and vinculin quantitative changes and reorganization, phenomena that have been closely related to cell transformation.

Expression of Occludin in Canine Testis and Epididymis

Tight junctions (TJ) in inter-Sertoli junctional areas and epididymal epithelia are important for the formation of blood-testis barrier (BTB) and blood-epididymal barrier (BEB). In this study, the expression of occludin, an integral member of the TJ, was verified in canine testis and epididymis. Both low molecular weight (MW) (25-28 kDa) forms as well as high MW (68-72 kDa) forms of occludin were detected in the testis and epididymis using Western blot. The relative amount of the high MW forms of occludin vs low MW forms was higher in the testis than in the epididymis. Some difference in the composition of different MW forms of occludin was found along the segments of epididymis, suggesting the possible correlation between cellular composition of occludin proteins and paracellular permeability of epithelia along the epididymal tubule. In the testis, intense occludin immunoreactivity was found in the basally located inter-Sertoli junctional area. Diffused immunoreactivity of occludin was also found in the cytoplasm of Sertoli cells. A similar pattern of zonula occludens-1 immunoreactivity was found in the cytoplasm of Sertoli cells, suggesting that occludin was not confined to the inter-Sertoli junctional areas and that subcellular localization of occludin in the Sertoli cells was dynamically regulated during spermatogenesis in canine testis. In the epididymis weak immunoreactivity was found in the apical sides and cytoplasm of epithelial cells.

Nitric Oxide/Nitric Oxide Synthase, Spermatogenesis, and Tight Junction Dynamics1

During spermatogenesis, preleptotene and leptotene spermatocytes, residing in the basal compartment of the seminiferous epithelium, must traverse the blood-testis barrier (BTB) to gain entry to the adluminal compartment for further development at late stage VIII and early stage IX of the epithelial cycle. As such, the timely opening and closing of the BTB is crucial to spermatogenesis. A compromise in this process can lead to infertility. Moreover, the BTB is unique in its relative localization in the seminiferous epithelium compared to the tight junctions (TJs) found in other epithelia. Sertoli cell TJs are situated near the basal lamina in the testis, closest to the basement membrane (a modified form of extracellular matrix [ECM]), unlike TJs found in other epithelia, which are found nearest the apical portion of an epithelium, farthest away from ECM. Needless to say, BTB function in the testis is maintained by intricate regulatory mechanisms. In addition to hormones and cytokines, nitric oxide (NO) was recently shown to be a putative TJ regulator in the testis. Perhaps equally important, TJ dynamics in the testis were shown to be regulated, at least in part, by occludin, a TJ-integral membrane protein, via the NO/soluble guanylate cyclase/cGMP/protein kinase G signaling pathway. This minireview summarizes recent advances in the field regarding the role of NO in testicular function, with special emphasis regarding its role in TJ dynamics and the likely implications of these studies for male contraceptive development.

Regulation of blood-testis barrier dynamics: an in vivo study

An in vivo model was used to investigate the regulation of tight junction (TJ) dynamics in the testis when adult rats were treated with CdCl(2). It was shown that the CdCl(2)-induced disruption of the blood-testis barrier (BTB) associated with a transient induction in testicular TGF-beta2 and TGF-beta3 (but not TGF-beta1) and the phosphorylated p38 mitogen activated protein (MAP) kinase, concomitant with a loss of occludin and zonula occludens-1 (ZO-1) from the BTB site in the seminiferous epithelium. These results suggest that BTB dynamics in vivo are regulated by TGF-beta2/-beta3 via the p38 MAP kinase pathway. Indeed, SB202190, a specific p38 MAP kinase inhibitor, blocked the CdCl(2)-induced occludin and ZO-1 loss from the BTB. This result clearly illustrates that CdCl(2) mediates its BTB disruptive effects via the TGF-beta3/p38 MAP kinase signaling pathway. Besides, this CdCl(2)-induced occludin and ZO-1 loss from the BTB also associated with a significant loss of the cadherin/catenin and the nectin/afadin protein complexes at the site of cell-cell actin-based adherens junctions (AJs). An induction of alpha(2)-macroglobulin (a non-specific protease inhibitor) was also observed during BTB damage and when the seminiferous epithelium was being depleted of germ cells. These data illustrate that a primary disruption of the BTB can lead to a secondary loss of cell adhesion function at the site of AJs, concomitant with an induction in protease inhibitor, which apparently is used to protect the epithelium from unwanted proteolysis. alpha(2)-Macroglobulin was also shown to associate physically with TGF-beta3, afadin and nectin 3, but not occludin, E-cadherin or N-cadherin, indicating its possible role in junction restructuring in vivo. Additionally, the use of SB202190 to block the TGF-beta3/p-38 MAP kinase pathway also prevented the CdCl(2)-induced loss of cadherin/catenin and nectin/afadin protein complexes from the AJ sites, yet it had no apparent effect on alpha(2)-macroglobulin. These results demonstrate for the first time that the TGF-beta3/p38 MAP kinase signaling pathway is being used to regulate both TJ and AJ dynamics in the testis, mediated by the effects of TGF-beta3 on TJ- and AJ-integral membrane proteins and adaptors, but not protease inhibitors.

Genomic Organization, Incidence, and Localization of the SPAN-X Family of Cancer-Testis Antigens in Melanoma Tumors and Cell Lines

PURPOSE

Members of the SPAN-X (sperm protein associated with the nucleus mapped to the X chromosome) family of cancer-testis antigens are promising targets for tumor immunotherapy because they are normally expressed exclusively during spermiogenesis on the adluminal side of the blood-testis barrier, an immune privileged compartment.

EXPERIMENTAL DESIGN AND RESULTS

This study analyzed the human SPANX genomic organization, as well as SPAN-X mRNA and protein expression in somatic and cancer cells. The SPANX family consists of five genes, one of which is duplicated, all located in a gene cluster at Xq27.1. From the centromere, the arrangement of the five SPANX genes mapped on one contiguous sequence is SPANXB, -C, -A1, -A2, and -D. Reverse transcription-PCR analyses demonstrated expression of SPAN-X mRNA in melanoma and ovarian cell lines, and virtual Northern analysis established SPANX gene expression in numerous cancer cell lines. Immunoblot analysis using polyclonal antisera raised against recombinant SPAN-X confirmed the translation of SPAN-X proteins in melanoma and ovarian tumor cell lines. The immunoreactive proteins migrated between M(r) 15,000 and M(r) 20,000 similar to those observed in spermatozoa. Immunoperoxidase labeling of melanoma cells and tissue sections demonstrated SPAN-X protein localization in the nucleus, cytoplasm, or both. Ultrastructurally, in melanoma cells with nuclear SPAN-X, the protein was associated with the nuclear envelope, a localization similar to that observed in human spermatids and spermatozoa. Significantly, the incidence of SPAN-X-positive immunostaining was greatest in the more aggressive skin tumors, particularly in distant, nonlymphatic metastatic melanomas.

CONCLUSIONS

The data herein suggest that the SPAN-X protein may be a useful target in cancer immunotherapy.

Interactions of proteases, protease inhibitors, and the beta1 integrin/laminin gamma3 protein complex in the regulation of ectoplasmic specialization dynamics in the rat testis

During spermatogenesis, developing germ cells migrate progressively across the seminiferous epithelium. This event requires extensive restructuring of cell-cell actin-based adherens junctions (AJs), such as the ectoplasmic specialization (ES, a testis-specific AJ type), between Sertoli cells and elongating/elongate spermatids. It was postulated that proteases and protease inhibitors worked in a yin-yang relationship to regulate these events. If this is true, then it is anticipated that both proteases and protease inhibitors are found at the ES. Indeed, matrix metalloprotease (MMP)-2, membrane-type 1 (MT1)-MMP and their inhibitor, tissue-inhibitor of metalloproteases (TIMP)-2, were shown to localize at the apical ES. In order to identify the putative MMP substrate as well as the unknown binding ligand for alpha6beta1 integrin in the ES, immunofluorescent microscopy coupled with immunoprecipitation techniques were used to demonstrate that laminin gamma3, largely a germ cell product, was present at the apical ES and could form a bona fide complex with beta1-integrin. Furthermore, the structural interactions of MMP-2 and MT1-MMP with laminin gamma3 and beta1-integrin, but not with N-cadherin or nectin-3, have implicated the crucial role of MMP-2/MT1-MMP in the regulation of integrin/laminin-based ES dynamics. Using an in vivo model to study AJ dynamics where adult rats were treated with 1-(2,4-dichlorobenzyl)-indazole-3-carbohydrazide (AF-2364) to disrupt Sertoli-germ cell adhesive function, an induction of active MMP-2, active MT1-MMP and TIMP-2 but not active MMP-9 was detected between 0.5 and 8 h after AF-2364 treatment. This time frame coincided with the depletion of elongating/elongate spermatids from the epithelium, illustrating the synergistic relationships between MMP-2, MT1-MMP, and TIMP-2 in AJ disassembly. Perhaps the most important of all, the use of a specific MMP-2 and MMP-9 inhibitor, (2R)-2-[(4-biphenylylsulfonyl)amino]-3-phenylpropionic acid, could effectively delay the AF-2364-induced elongating/elongate spermatid loss from the epithelium, demonstrating the pivotal role of MMP-2 activation in ES disassembly. Collectively, these studies illustrate that the beta1-integrin/laminin gamma3 complex is a putative ES-structural protein complex, which is regulated, at least in part, by the activation of MMP-2 involving MT1-MMP and TIMP-2 at the apical ES. The net result of this interaction likely regulates germ cell movement in the seminiferous epithelium.