Lorella Bonaccorsi

Androgen Receptor Expression in Prostate Carcinoma Cells Suppresses α6β4 Integrin-Mediated Invasive Phenotype1

Prostate cancer cells may lose androgen-sensitivity after androgen ablation therapy, becoming highly invasive and metastatic. The biological mechanisms responsible for higher tumurogenicity of androgen-independent prostate carcinomas are not entirely known. We demonstrate that androgen receptor regulation of adhesion and invasion of prostate cancer cells through modulation of α6β4 integrin expression may be one of the molecular mechanisms responsible of this phenomenon. We found that protein and gene expressions of α6 and β4 subunits were strongly reduced in the androgen-sensitive cell line LNCaP respect to the androgen-independent PC3 and that transfection of PC3 cells with a full-length androgen receptor expression vector resulted in a decreased expression of α6β4 integrin, reduced adhesion on laminin, and suppressed Matrigel invasion. Growth in soft agar was also suppressed in androgen receptor-positive PC3 clones. Treatment of androgen receptor positive clones with the synthetic androgen R1881 further...

HUMAN SPERM ACTIVATION DURING CAPACITATION AND ACROSOME REACTION: ROLE OF CALCIUM, PROTEIN PHOSPHORYLATION AND LIPID REMODELLING PATHWAYS.

Two processes, namely capacitation and acrosome reaction, are of fundamental importance in the fertilization of oocyte by spermatozoon. Physiologically occurring in the female genital tract, capacitation is a complex process, which renders the sperm cell capable for specific interaction with the oocyte. During capacitation, modification of membrane characteristics, enzyme activity and motility property of spermatozoa render these cells responsive to stimuli that induce acrosome reaction prior to fertilization. Physiological acrosome reaction occurs upon interaction of the spermatozoon with the zona pellucida protein ZP3. This is followed by liberation of several acrosomal enzymes and other constituents that facilitate penetration of the zona and exposes molecules on the sperm equatorial segment that allows fusion of sperm membrane with the oolemma. The molecular mechanisms and the signal transduction pathways mediating the processes of capacitation and acrosome reaction are only partially defined, and appear to involve modifications of intracellular calcium and other ions, lipid transfer and phospholipid remodelling in sperm plasma membrane as well as changes in protein phosphorylation. The human and mouse sperm receptor for ZP3 has been recently sequenced and cloned. This receptor exhibits sequence homology with proto-oncogenes that mediate proliferation and differentiation in somatic cells. This review summarizes the main signal transduction pathways involved in capacitation and acrosome reaction.

Tyrosine kinase inhibition reduces the plateau phase of the calcium increase in response to progesterone in human sperm.

Progesterone (P) has previously been shown to induce a rapid increase in [Ca2+]i as well as tyrosine phosphorylation of proteins in human spermatozoa. Both these effects are essential for induction of the acrosome reaction by P. We investigated a possible relationship between the P‐induced calcium increase and tyrosine kinase activation, by evaluating the effect of the tyrosine kinase inhibitor genistein on these two effects. We found that preincubation with genistein abolished P‐induced tyrosine phosphorylation of two sperm proteins of 97 and 75 kDa molecular weight and significantly inhibited the plateau phase of P‐induced [Ca2+]i increase without affecting the peak phase. Conversely, the plateau phase was enhanced by the tyrosine phosphatase inhibitor Na3VO4. The effect of genistein was specific for P, since no inhibition was observed on the [Ca2+]i increase induced by thapsigargin, an inhibitor of endoplasmic Ca2+‐ATPase previously shown to mobilize Ca2+ in spermatozoa. These results indicate that tyrosine kinase activation is involved in the generation of the plateau phase of Ca2+ influx induced by P, and suggest the possibility that two different pathways are involved in the induction of Ca2+ entry by P in human sperm.

EGF receptor (EGFR) signaling promoting invasion is disrupted in androgen‐sensitive prostate cancer cells by an interaction between EGFR and androgen receptor (AR)

We previously demonstrated that expression of androgen receptor (AR) by transfection of the androgen‐independent prostate cancer cell line PC3 decreases invasion and adhesion of these cells (PC3‐AR) through modulation of α6β4 integrin expression. The treatment with androgens further reduced invasion of the cells without modifying α6β4 expression, suggesting an interference with the invasion process by androgens. Here, we investigated EGF‐mediated signal transduction processes that lead to invasion in PC3‐AR cells. We show that EGF‐induced EGFR autotransphosphorylation is reduced in PC3‐AR cells compared to PC3 cells transfected only with the vector (PC3‐Neo). EGF‐stimulated PI3K activity, a key signaling pathway for invasion of these cells, and EGF‐PI3K interaction are also decreased in PC3‐AR cells and further reduced by treatment with androgen. Finally, we show that EGFR internalization process was reduced in PC3‐AR and LNCaP cells compared to PC3‐Neo. Investigations on the location of AR in PC3‐AR transfected cells were also conducted. Immunoconfocal microscopy and coimminoprecipitation studies demonstrated the presence of an interaction between EGFR and AR at membrane level in PC3‐AR and LNCaP cells. In conclusion, our results suggest that the expression of AR by transfection in PC3 cells confers a less‐malignant phenotype by interfering with EGFR signaling leading to invasion through a mechanism involving an interaction between AR and EGFR.

Effects of estrogenic compounds on human spermatozoa: evidence for interaction with a nongenomic receptor for estrogen on human sperm membrane

Estrogens play an important role in the development and regulation of the male reproductive system. We have earlier shown that a nongenomic receptor for estradiol present on sperm plasma membrane mediates the effects exerted by this hormone on sperm intracellular calcium concentrations ([Ca(2+)](i)), as well as on the biological response to progesterone (P). In particular, 17 beta-estradiol (17betaE(2)) shows an inhibitory effect on P-mediated calcium influx and acrosome reaction (AR). In the present study, the effects of different anti-estrogens and xenoestrogens on [Ca(2+)](i) and AR stimulated by P have been investigated in human spermatozoa in order to better define the pharmacological characteristics of the sperm membrane estrogen receptor. The anti-estrogens tamoxifen (Tx) and ICI 164384 (ICI) induce only a slight increase of [Ca(2+)](i), which, however, as in the case of 17betaE(2), results in a reduction of P-stimulated calcium influx. Moreover, both the compounds reduce the calcium response to 17betaE(2) without affecting 17betaE(2)-inhibition of calcium response to P. Concerning AR, Tx alone does not alter either spontaneous or P-stimulated AR but partially revert the inhibitory effect of 17betaE(2). These results indicate that the two estrogens act as pharmacological agonists of the membrane estrogen receptors of human spermatozoa. On the other hand, the xenoestrogens bisphenol A (BPA) and octyiphenol polyethoxilate (OP) do not exert any direct effect on calcium fluxes and AR in human spermatozoa either in basal conditions or in response to P challenge. Moreover, although these environmental estrogens have been suggested to mimic estrogen effects in the other cell types, probably acting through genomic receptors, in human spermatozoa they do not interfere with 17betaE(2) binding to its membrane receptor and with the short-term effects exerted by this steroid. In conclusion, our data indicate that the membrane receptor for estradiol in human spermatozoa shows both biochemical and pharmacological differences respect to the genomic receptor.

NONGENOMIC EFFECTS OF PROGESTERONE ON SPERMATOZOA: MECHANISMS OF SIGNAL TRANSDUCTION AND CLINICAL IMPLICATIONS

Progesterone (P) is one of the physiological stimuli of human sperm acrosome reaction. It is present in high levels at the site of fertilization (cumulus oophorus) and has been describe to affect several sperm functions including motility, capacitation and acrosome reaction. The effects of the steroid, which is present in high levels in the cumulus matrix that surrounds the oocyte, are mediated by an increase of intracellular calcium concentrations, efflux of chloride, stimulation of activity of phospholipases and phosphorylation of proteins. These effects are due to activation of a rapid/nongenomic pathway. Two different types of receptors for P, distinct from the genomic ones, have been recently identified on the surface of human spermatozoa. The affinities of P for these receptors are respectively in the nano- and in the micromolar range. Sperm responsiveness to progesterone is impaired in subfertile patients and is strictly correlated to the ability of fertilize the oocyte. In addition, the determination of sperm responsiveness is predictive of fertilizing ability with a positive predictive value of 90% and can be clinically useful for the preliminary assessment of the male partner to select the appropriate assisted reproductive technique.

Characterization of membrane nongenomic receptors for progesterone in human spermatozoa.

Rapid, nongenomic actions of steroid hormones have been characterized only recently. They may be mediated by interaction with a poorly characterized membrane receptor, by classic receptor located to the plasma membrane, or by interaction of the classic receptor with other signaling effectors. Among these, rapid effects of progesterone on human spermatozoa have been shown to be mediated by interaction with one or more membrane receptors. Two proteins, respectively of 57 and 28 kDa, representing the possible surface progesterone receptors in human spermatozoa, have been identified by our group employing an antibody (c-262) directed against the progesterone binding domain of the genomic receptor. The two proteins have been immunoprecipitated using c-262, isolated by 2D gel electrophoresis and analyzed by Maldi-Tof. Preliminary results of the analysis in data bank of the obtained masses suggest that the two proteins represent previously unidentified ones since they do not match with any protein in the database. We have also performed RT-PCR analysis with RNA extracted from human spermatozoa, utilizing various oligoprimers in different regions of the human progesterone genomic receptor. Results indicate the presence of transcripts for the complete genomic receptor. However, several previously published studies in the literature indicate the absence of expression of the genomic receptor in human spermatozoa. In this light posttranscriptional/posttraductional modifications of the receptor can be hypothesized. Interestingly, with primers amplifying in the DNA-binding domain of the progesterone receptor gene, we detected a higher molecular weight transcript when compared to the placenta. Further studies are needed to determine whether the sequences of the transcripts obtained by RT-PCR analysis of human sperm RNA match exactly with the human genomic receptor gene and to define the sequence of the higher molecular weight transcript detected in the DNA-binding region.

Nongenomic progesterone receptor on human spermatozoa: biochemical aspects and clinical implications.

Progesterone (P) is a physiological stimulus of human sperm functions. It is present in high levels at the site of fertilization (cumulus oophorus) and has been described to affect several sperm functions, including motility, capacitation, acrosome reaction, and the ability to bind and to respond to zona proteins. The effects of the steroid are mediated essentially by an increase of intracellular calcium concentrations, stimulation of activity of phospholipases, phosphorylation of proteins, efflux of chloride. These effects are due to activation of a rapid, nongenomic pathway. Whether the effects of progesterone are mediated or not by specific interactions with sperm membrane proteins is questioned. By using an antibody directed against the C-terminal region (P-binding region) of the genomic receptor, we have recently identified two sperm proteins with molecular weights distinct from the classic genomic receptors. In addition, ligand blot analysis with peroxidase-conjugated P demonstrated that P specifically binds these two proteins. Classical ligand binding experiments demonstrated the presence of two specific binding sites with affinity in the nanomolar and in the micromolar range, respectively. The involvement of progesterone in the physiological process leading to fertilization of the oocyte is suggested by several studies. In particular, the demonstration that sperm responsiveness to progesterone is impaired in subfertile patients and that is strictly correlated to the ability of fertilizing the oocyte represents a further indication of the participation of the steroid in this process. In addition, the determination of sperm responsiveness may be predictive of fertilizing ability with a positive predictive value of 90% and can be clinically useful for the preliminary assessment of the male partner to select the appropriate assisted reproductive technique.

Nongenomic effects of progesterone on spermatozoa mechanisms of signal transduction and clinical implications

: Progesterone (P) is one of the physiological stimuli of human sperm acrosome reaction. It is present in high levels at the site of fertilization (cumulus oophorus) and has been describe to affect several sperm functions including motility, capacitation and acrosome reaction. The effects of the steroid, which is present in high levels in the cumulus matrix that surrounds the oocyte, are mediated by an increase of intracellular calcium concentrations, efflux of chloride, stimulation of activity of phospholipases and phosphorylation of proteins. These effects are due to activation of a rapid/nongenomic pathway. Two different types of receptors for P, distinct from the genomic ones, have been recently identified on the surface of human spermatozoa. The affinities of P for these receptors are respectively in the nano- and in the micromolar range. Sperm responsiveness to progesterone is impaired in subfertile patients and is strictly correlated to the ability of fertilize the oocyte. In addition, the determination of sperm responsiveness is predictive of fertilizing ability with a positive predictive value of 90% and can be clinically useful for the preliminary assessment of the male partner to select the appropriate assisted reproductive technique.

The androgen receptor associates with the epidermal growth factor receptor in androgen-sensitive prostate cancer cells.

Many recent evidences indicate that androgen-sensitive prostate cancer cells have a lower malignant phenotype that is in particular characterized by a reduced migration and invasion. We previously demonstrated that expression of androgen receptor (AR) by transfection of the androgen-independent prostate cancer cell line PC3 decreases invasion and adhesion of these cells (PC3-AR) through modulation of alpha6beta4 integrin expression. The treatment with the synthetic androgen R1881 further reduced invasion of the cells without, however, modifying alpha6beta4 expression on the cell surface, suggesting an interference with the invasion process in response to EGF. We investigated whether the presence of the AR could affect EGF receptor (EGFR)-mediated signaling in response to EGF by evaluating autotransphosphorylation of the receptor as well as activation of downstream signalling pathways. Immunoprecipitation studies demonstrated a reduction of EGF-induced tyrosine phosphorylation of EGFR in PC3-AR cells. In addition, EGF-stimulated PI3K activity, a key signalling pathway for invasion of these cells, was decreased in PC3-AR cells and further reduced by treatment with R1881, indicating decreased functionality of EGFR. An interaction between EGFR and AR has been demonstrated by immunoconfocal and co-immunoprecipitation analysis in PC3-AR cells, suggesting a possible interference of AR on EGFR signalling by interaction of the two proteins. In conclusion, our results suggest that the expression of AR by transfection in PC3 cells confers a less malignant phenotype by interfering with EGFR autophosphorylation and signalling in response to EGF leading to invasion through a mechanism involving an interaction between AR and EGFR.