Transforming growth factor beta 1 enhances expression of 50 kDa protein related to 2'-5' oligoadenylate synthetase in human sperm cells

Vaccine for human contraception targeting sperm Izumo protein and YLP12 dodecamer peptide

There is an urgent need to develop a better method of contraception which is non-steroidal and reversible to control world population explosion and unintended pregnancies. Contraceptive vaccines (CV), especially targeting sperm-specific proteins, can provide an ideal contraceptive modality. Sperm-specific proteins can induce an immune response in women as well as men, thus can be used for CV development in both sexes. In this article, we will review two sperm-specific proteins, namely Izumo protein and YLP12 dodecamer peptide. Gene-knockout studies indicate that Izumo protein is essential for sperm-egg membrane fusion. Vaccination with Izumo protein or its cDNA causes a significant reduction in fertility of female mice. The antibodies to human Izumo inhibit human sperm penetration assay. Recently, our laboratory found that a significant percentage of infertile women have antibodies to Izumo protein. The second sperm-specific protein is YLP12 , a peptide mimetic sequence present on human sperm involved in recognition and binding to the human oocyte zona pellucida. Vaccination with YLP12 or its cDNA causes long-term, reversible contraception, without side effects, in female mice. Infertile, but not fertile, men and women have antibodies to YLP12 peptide. Our laboratory has isolated, cloned, and sequenced cDNA encoding human single chain variable fragment (scFv) antibody from infertile men which reacts with YLP12 peptide. The human YLP12 scFv antibody may provide a novel passive immunocontraceptive, the first of its kind. In conclusion, sperm-specific Izumo protein and YLP12 peptide can provide exciting candidates for antisperm CV development.

Head and flagella subcompartmental proteomic analysis of human spermatozoa

Subcellular proteomics not only deepens our knowledge of what proteins are present within cells, but also opens our understanding as to where those proteins reside. Given the highly differentiated, cross-linked state of spermatozoa, such studies have proven difficult to perform. In this study we have fractionated spermatozoa into two components, consisting of either the head or flagellar region. Following SDS-PAGE, 1 mm slices were digested and used for LC-MS/MS analysis. In total, 1429 proteins were identified with 721 proteins being exclusively found in the tail and 521 exclusively in the head. Not only is this the largest reported proteomic analysis of human spermatozoa, but also it has provided novel insights into the compartmentalization of proteins, particularly receptors, never previously reported to be present in this cell type.

Effect of sperm DNA vaccine on fertility of female mice

Our laboratory has identified a sperm-specific dodecamer peptide sequence, designated as YLP(12), vaccination with which causes a long-term reversible immunocontraceptive effect in female mice. In the present study, the effects of YLP(12) DNA vaccine were examined. YLP(12) 36 bp cDNA was cloned into pVAX1 vector to prepare the DNA vaccine. Two additional vaccine constructs were made by in frame cloning of one and two CpG repeats in the YLP(12)-cDNA vaccine. Five groups of female mice were immunized intradermally by using gene gun with YLP(12)-cDNA, YLP(12)-cDNA-CpG, YLP(12)-cDNA-CpG-CpG, YLP(12)-cDNA mixed with exogenous synthetic CpG oligodeoxynucleotide (ODN), or vector DNA alone, respectively. Vaccination with all three constructs and the YLP(12) vaccine mixed with exogenous ODN raised antibody response both in the sera as well as locally in the vaginal tract. There was no antibody response in the mice injected with the vector alone. In sera, the highest titers were obtained for the IgG class for all constructs and formulation followed by IgA class. In vaginal washings the highest titers were obtained for the IgA class followed by IgG class. Within the IgG class, the titers for the IgG2a subclass were significantly greater than the IgG1 subclass. Immunization with all constructs and formulation caused a significant (P < 0.05 to <0.001) reduction (20-43%) in fertility of female mice. The highest reductions were seen in mice immunized with YLP(12)-cDNA-CpG-CpG (two repeats) (43% reduction) and with the YLP(12) vaccine administered with exogenous CpG ODN (42% reduction). T lymphocytes obtained from DNA-vaccinated mice showed clearly distinguished comparative RT-PCR analysis of cytokine mRNA expression for Th1 and Th2 immune responses compared to T lymphocytes obtained from control animals injected with vector DNA. Expression of both Th1 cytokines (IL-2 and IFN-gamma) and Th2 cytokines (IL-4 and IL-10) was enhanced after DNA vaccination as compared to controls, with a bias towards Th1 response. The immunocontraceptive effects were long-lasting observed up to 1.3 years of the observation period and increased with time. These novel findings indicate that the intradermal immunization with a sperm-specific DNA vaccine causes a long-term circulating and local immune response resulting in immunocontraceptive effects in female mice.

Antisperm Vaccine for Contraception

PROBLEM

This study is a review of antisperm contraceptive vaccine (CV) development with the main focus on research going on in our laboratory.

METHOD OF STUDY

Various methods of proteomics and genomics, hybridoma technology, substractive libraries, differential display method, and phage display technology were used to obtain sperm-specific genes and proteins. The present study will primarily focus on the sequences obtained by using the phage display technology and their role in CV development and human immunoinfertility.

RESULT

Four novel peptides, delineated by using the phage display technology, were found to be involved in human immunoinfertility. The vaccine based on one of these peptides, designated as YLP(12), caused a reversible contraception in female mice.

CONCLUSIONS

The vaccine targeting sperm is a feasible and exciting approach to contraception. The phage display technology is a powerful tool to delineate sperm-specific peptide sequences that can be used for the CV development and in the diagnosis and treatment of infertility mediated through antisperm antibodies.

Presence of interleukin-8 and the IL-1 receptor antagonist in the cervical mucus of fertile and infertile women

Background. Cytokines are involved in almost every aspect of reproduction and recent studies suggested a relationship between cytokines and male/female infertility. In the present study, the levels of interleukin-8 (IL-8) and interleukin-1 receptor antagonist (IL-1Ra) were determined in the cervical mucus of fertile and infertile women. Methods. Groups of patients were formed according to the results of the standard procedure for infertility investigation, including postcoital test and the presence of antispermatozoid antibodies in the sera of both partners and in seminal plasma, by mixed antiglobulin reaction (MAR) test and Kibrick agglutination test. IL-8 and IL-1Ra levels were determined in solubilized (ultrasonographic sonicaton) cervical mucus sampled in the midcycle by commercial ELISA kits and expressed as pg/mg proteins. Results. The groups were designated as fertile (n=20) and infertile (n=48). The latter was divided into two subgroups, one consisting of infertile women with positive postcoital test and without antispermatozoid antibodies (n=30), and the other designated as infertile women with negative postcoital test (n=18). This subgroup was composed of women with negative postcoital test and without antibodies (n=10) and the women with negative postcoital test with antibodies (n=8). Similar levels of IL-8 and IL-1 Ra were noted in the cervical mucus of in fertile women and women with positive postcoital test and without antispermatozoid antibodies. A tendency of decrease (p=0,052) and significant decrease in IL-8 levels (p<0.05) was noted in negative postcoital test group and negative postcoital test group without antibodies respectively, compared to the levels in the fertile examinees. A significant rise in IL-1Ra levels (p<0,05) was detected in the mucus of negative postcoital test group with further increase in negative postcoital test group with antibodies (p<0.02). Conclusion. Changes in IL-8 and IL-1 Ra levels in the cervical mucus of infertile patients with negative postcoital test suggested the existence of the relatinship between cervical cytokines and infertility in these women.

Expression of alpha and gamma interferon receptors in the sperm cell

The present study was conducted to examine whether or not the sperm cell has the expression of receptors for interferon (IFN) -alpha and -gamma. This was investigated using specific antibodies. Antibody to IFN-alpha receptor reacted with the acrosomal and tail regions of the murine sperm cell in the indirect immunofluorescence technique (IFT) and immunoscanning electron microscopic procedure (ISEP). In the immunoprecipitation and Western blot procedures, this antibody specifically recognized a protein band of approximately 100 kD, which corresponds to the molecular weight of IFN-alpha receptor present in other cell types. Antibody to IFN-gamma receptor specifically reacted with the posterior head, midpiece, and tail regions of sperm cell in IFT and ISEP, and recognized a band of approximately 85 kD in the immunoprecipitation and Western blot procedures, corresponding to the IFN-alpha receptor. Similar bands of approximately 100 kD and approximately 85 kD molecular identities were also detected in the testes extracts and sperm extracts of other mammalian species namely human, rabbit, and pig, the species tested. These findings indicate that the mammalian sperm cell has expression of IFN-alpha and IFN-gamma receptors, which seem to develop during spermatogenesis in the testes. These findings may have implications in male infertility and antisperm contraceptive vaccine development.

Effect of actinomycin D and cycloheximide on human sperm function

The effects of actinomycin D and cycloheximide on human spermatozoal function were examined to investigate the potential transcriptional and translational activities of human sperm cell during capacitation/acrosome reaction. Treatment with actinomycin D significantly increased and treatment with cycloheximide decreased the acrosome reaction, and the penetration rates in the human sperm penetration of zona-free hamster oocytes assay (SPA). [35(S)]Methionine got incorporated into 3-9 de novo synthesized proteins present in the head and midpiece regions of the swim-up population of human sperm. Treatment with actinomycin D completely blocked and treatment with cycloheximide slightly reduced the synthesis of proteins. There seem to be some transcriptional and translational activities in the head and midpiece regions of human sperm during capacitation/acrosome reaction.

Sertoli cell-germ cell interactions and TGF beta 1 expression and secretion in vitro

Transforming growth factor beta 1 (TGF beta 1) has been reported to be secreted and to act within the somatic cells of the testis. We examined whether the TGF beta 1 expression is present at mRNA and protein levels in purified rat Sertoli cells (SC), purified pachytene spermatocytes (SPC), and early spermatids (SPT) cultured alone or together. SC expressed a single TGF beta 1 transcript of 2.5 kb, but no TGF beta 1 protein could be detected in SC conditioned medium indicating that, if at all, SC secreted less than 10 pg/10(6) cells/24 h. Neither TGF beta 1 mRNA nor protein could be detected in either SPC or SPT. Coculture of SC with either SPC or SPT resulted in a 2-fold increase of TGF beta 1 mRNA and more importantly in the secretion of TGF beta 1 protein. These findings demonstrate that Sertoli cell-germ cell interactions regulate TGF beta 1 expression and secretion and indicate that TGF beta 1 may be involved in spermatogenesis.

Reproductive effects of chronic administration of murine interferon-gamma

Daily subcutaneous doses of 0.02, 0.2, or 2 mg/kg/d of recombinant murine interferon-gamma (rmuIFN-gamma) were given to mice on postnatal days 8 through 60 to determine effects on maturation, behavioral/ functional development, and reproductive capacity. Male mice receiving 2 mg/kg/d rmuIFN-gamma had delayed sexual maturation, reduced epididymal and testes weights, reduced sperm count and concentration, and sperm abnormalities (crimped flagellum). Mating performance and fertility were also reduced in the absence of altered histopathology of the testes. Males given 0.2 and 2 mg/kg/d had swelling and ulcerative dermatitis around the urogenital area, which were observed after sexual contact and attributed to a bacterial infection. Motor activity (time spent in movement) was decreased in all mice receiving 2 mg/kg/d. No microscopic changes observed in any organs were attributed to rmuIFN-gamma administration.

Effects of products of activated immune cells and recombinant cytokines on spontaneous and ionophore-induced acrosome reaction

PROBLEM

The purpose of this study was to examine whether the products of activated immune cells influence spontaneous and ionophore-induced sperm acrosome reaction.

METHOD

The spontaneous and ionophore-induced acrosome reaction were evaluated by staining with fluorescein isothiocyanate (FITC) Pisum sativam agglutinin after incubation in capacitating media supplemented with either supernatants from Con-A activated leukocyte cultures or human recombinant (r) IL-1 beta, TNF-alpha, and INF-gamma.

RESULTS

The supernatants from Con A-activated peripheral blood leukocyte cultures at 1:1 and 1:10 dilution significantly increased the rate of spontaneous acrosome reaction (P < 0.001 and P < 0.01). Along with displayed abnormally elevated levels of spontaneous acrosome loss, sperm cells showed an insufficient ability to undergo acrosome reaction in response to the ionophore treatment. Recombinant IL-1 beta at increasing concentrations from 30 to 3 x 10(4) U/ml did not have an effect on spontaneous and ionophore-induced acrosome reaction. In contrast, spermatozoa that underwent capacitation in media with 7 x 10(3), 7 x 10(4), and 7 x 10(5) U/ml of rINF-gamma showed a significant increase in spontaneous and induced acrosome reaction compared to the control (P < 0.001). Recombinant TNF-alpha at concentrations of 3.5 x 10(3) U/ml and 3.5 x 10(4) U/ml significantly inhibited ionophore-induced acrosome reaction (P < 0.001). Both rINF-gamma and rTNF-alpha together revealed an effect on the acrosome reaction similar to Con-A generated supernatants (1:1 and 1:10 dilution) only at the highest concentrations.

CONCLUSIONS

Some cases of infertility may result from a defective acrosome reaction (premature acrosome loss or insufficient acrosome response to the stimulants) caused by products of activated lymphocytes and macrophages that are released into the male and female reproductive tracts.

Interleukins-6 and -8 levels in sera and cervical mucus of fertile, idiopathic infertile, and immunoinfertile women: implication in infertility

PROBLEM

The purpose of this study was to investigate the levels of interleukin-6 and -8 (IL-6 and IL-8) in sera and cervical mucus of infertile (idiopathic and immunoinfertile) women and to compare the levels with those in age-matched normally cycling fertile women.

METHODS

Levels of IL-6 and IL-8 were measured in the sera and cervical mucus of fertile and infertile women by the enzyme-linked immunosorbent assay (ELISA). A non-parametric Mann-Whitney test was used to evaluate significance between the means. Linear regression analysis of IL-6 and IL-8 concentrations in serum versus cervical mucus and with antisperm antibody titers was performed by condition as well as all groups together. P < 0.05 was considered significant.

RESULTS

Both IL-6 and IL-8 were detected in sera and cervical mucus of fertile as well as infertile groups. Although serum levels of IL-6 and IL-8 were significantly different between fertile and infertile groups, the differences were more pronounced in the cervical mucus samples. Cervical mucus of idiopathic and immunoinfertile women demonstrated significantly (P = 0.002 to < 0.0001) greater concentrations of IL-6 and IL-8 compared to fertile controls. In general, there was no significant correlation between the serum and cervical mucus IL-6 and IL-8 levels, whether analyzed by condition or all groups together.

CONCLUSIONS

Elevated levels of IL-6 and IL-8 in cervical mucus of infertile groups may play a role in etiology of idiopathic and immunologic infertility. These findings suggest that the measurements of cytokines (especially IL-6 and IL-8) in cervical mucus may provide a tool for specific diagnosis and possibly treatment of infertility, especially idiopathic infertility.

Increased levels of interferon-gamma in seminal plasma of infertile men

The role of the cell-mediated immunity in male infertility is still far from clear. Interferon-gamma (INF-gamma), a secretory product of activated T cells and natural killer cells, has been hypothesized to have a toxic effect on sperm function. The presence of INF-gamma was investigated in seminal plasma of fertile and infertile subjects, using a specific enzyme-linked immunosorbent assay, in order to study its role in male infertility. Forty-one subjects were studied; 20 had proven fertility and normal semen quality (fertile group) and 21 showed male infertility for at least 2 years and poor semen quality (infertile group). INF-gamma was present in significantly higher levels in the seminal plasma of infertile subjects (6.36 +/- 0.72 fmol ml-1) compared to fertile subjects (3.68 +/- 0.30 fmol ml-1). Moreover, a significant negative correlation between INF-gamma levels and sperm count, motility and morphology was detected, whereas no correlation between INF-gamma levels and leukocyte count was found. These findings (i) confirm INF-gamma to be present in seminal plasma; (ii) show increased INF-gamma secretion in the infertile group; (iii) demonstrate negative correlations of INF-gamma with the main spermiogram parameters and (iv) no correlation with leukocyte count. INF-gamma may therefore play an important role in male infertility.

Thymosin alpha-1 and FA-1 monoclonal antibody affect murine preimplantation embryo development by modulating protein phosphorylation

The effects of thymosin alpha 1 (T alpha 1) and FA-1 monoclonal antibody (anti-FA-1 mAb) on murine preimplantation embryonic development were investigated by performing 2-cell embryo bioassay and by studying ova/embryos protein phosphorylation pattern (by 32P metabolic labeling and by in vitro kinase assay) and protein synthesis (by in vitro [35S]methionine labeling). T alpha 1 treatment (0.1, 0.5 and 5 ng/100 microliters) significantly increased blastulation rates (P < 0.01), blastocyst hatching rate (P < 0.0001), blastocyst diameter (P < 0.001) and number of cells per blastocyst (P < 0.0001) of the in vitro cultured 2-cell stage embryos. Anti-FA-1 mAb reduced blastulation rates (P < 0.001) primarily due to an arrest of development at morula stage. In vitro metabolic labeling of murine ova/embryos showed 32P incorporation into 4 major protein bands of murine ova (M(r) 125, 90, 68 and 31 kDa, respectively), 7 protein bands of 2-cell (M(r) 90, 68 and 31; and 145, 52, 38 and 32 kDa, respectively), 10 protein bands of morula (M(r) 150, 110, 92, 82, 70, 54, 39, 34, 30 and 29 kDa, respectively), and 15 protein bands of blastocyst (150, 110, 92, 70, 68, 54, 39, 34 and 30; and 131, 105, 52, 44, 43 and 33 kDa, respectively) stage embryos. T alpha 1 treatment (0.1-0.5 ng/100 microliters) resulted in a general increase in 32P labeling in all proteins of 2-cell, morula and blastocyst stage embryos. Anti-FA-1 mAb completely blocked 32P labeling of various proteins of murine ova, 2-cell, morula and blastocyst stage embryos, whereas control mouse myeloma IgG did not affect phosphorylation of these proteins. In vitro kinase assay performed directly on various ova/embryos extracts revealed 6 phosphoproteins (M(r) 105, 82, 55, 38, 34 and 33 kDa, respectively) that were common to ova and 2-cell embryos, besides a 43 kDa protein detected only in the ova extract. Of these phosphoproteins, T alpha 1 treatment specifically enhanced whereas anti-FA-1 mAb inhibited autophosphorylation of a 55 kDa protein of 2-cell embryos.(ABSTRACT TRUNCATED AT 250 WORDS)

Levels of interferon-gamma and tumor necrosis factor-alpha in sera and cervical mucus of fertile and infertile women: implication in infertility

Concentrations of two immune cytokines, namely interferon-gamma (INF-gamma) and tumor necrosis factor-alpha (TNF-alpha), were determined in the sera and cervical mucus samples of fertile (n = 16), idiopathic infertile (n = 44), and immunoinfertile women (n = 45) to investigate their role, if any, in female infertility. Sera of idiopathic infertile women demonstrated significantly (P < 0.0001) higher levels of INF-gamma compared to those in fertile controls, whether expressed as pg/ml or pg/mg serum protein. Similarly, sera of immunoinfertile women demonstrated significantly (P = 0.0008) higher levels of INF-gamma compared to fertile controls and idiopathic infertile women. Cervical mucus of idiopathic infertile women also demonstrated significantly (P < 0.0001) higher concentrations of INF-gamma compared to those in fertile controls. Cervical mucus of immunoinfertile women demonstrated significantly (P < 0.0001) higher concentrations of INF-gamma compared to those in fertile controls and idiopathic infertile women. INF-gamma levels in serum did not significantly (P > 0.05) correlate (r = 0.12-0.43) with the concentrations in cervical mucus, when all the three groups were compared together. However, when the serum levels were compared with the cervical mucus concentrations by condition, only the idiopathic infertile group showed a significant (P = 0.005) correlation (r = 0.70). Serum levels of TNF-alpha did not differ significantly (P > 0.05) among three groups of women. Cervical mucus concentrations of TNF-alpha, however, varied among groups with levels being significantly (P = 0.04) higher-in idiopathic infertile women compared with fertile controls and in immunoinfertile women significantly (P = 0.0007) higher than in fertile controls as well as idiopathic infertile women. TNF-alpha levels in serum correlated (r = 0.65) significantly (P < 0.001) with the concentrations in cervical mucus when all the three groups were compared together or individually by infertility condition. These findings suggest the involvement of cytokines in infertility, and thus may have potential applications in diagnosis and treatment of female infertility.

Enhanced levels of colony stimulating factor-1 (CSF-1) in sera and seminal plasma of antisperm antibody-positive infertile men

This investigation was carried out to examine the levels of CSF-1 in sera and seminal plasma of fertile, immunoinfertile, and male factor-infertile men in order to study the role of CSF-1 in human infertility. Sera, sperm, and seminal plasma were analyzed for antisperm antibodies by the sperm immobilization technique, tray agglutination technique, and immunobead binding technique. Sperm motility and fertilizing capacity were analyzed by sperm motion analysis and sperm penetration assay, respectively. CSF-1 concentration was estimated by the competitive radioimmunoassay. CSF-1 was detected in sera of both fertile and immunoinfertile men (mean +/- SD; fertile men: 52.9 +/- 10.3 pg/mg protein; immunoinfertile: 58.2 +/- 19.5 pg/mg protein; p > .05). CSF-1 was also detected in the seminal plasma of fertile, immunoinfertile, and male factor-infertile men (mean +/- SD; normal fertile men: 1.7 +/- 3.5 ng/mg; immunoinfertile men: 10.9 +/- 15.6 ng/mg; male factor-infertile men: 0.85 +/- 0.25 ng/mg). The levels of CSF-1 were highest in the immunoinfertile men, followed by those in fertile and male factor-infertile men. The average level in immunoinfertile men was significantly different from the average level in fertile or male factor-infertile men (p < .0001). Interestingly, the concentrations of CSF-1 per milliliter of seminal plasma was in general approximately 5 times greater than those in serum. These findings indicate that elevated seminal plasma CSF-1 concentration is correlated with male infertility.

Regulation of phosphorylation of the c-erbB-2/HER2 gene product by a monoclonal antibody and serum growth factor(s) in human mammary carcinoma cells

Monoclonal antibody (MAb) 4D5 was used to analyze the phosphorylation of p185HER2, the gene product of c-erbB-2/HER2, in SK-BR-3 cells. Culture in the continuous presence of 4D5 reduced the in vivo steady-state levels of p185HER2 phosphorylation by 80% in a dose-dependent manner, suggesting that MAb 4D5 may have interfered with the activation of phosphorylation of p185HER2. The observed MAb-mediated reduction of p185HER2 phosphorylation could not be completely accounted for by down-regulation. When cultures were grown under serum-free conditions, the steady-state levels of p185HER2 phosphorylation were reduced by 56%, and addition of 4D5 further inhibited phosphorylation to 20% of steady-state levels. With continuous exposure to increasing concentrations of newborn calf serum in these cultures, there was a linear increase in tyrosine-specific phosphorylation of p185HER2, reaching a 5.4-fold increase with 10% newborn calf serum. Phosphorylation of p185HER2 in the presence of newborn calf serum was not attributable to stimulation of the epidermal growth factor receptor by epidermal growth factor or by transforming growth factor-alpha. Extension of these observations to two other mammary carcinoma cell lines. MDA-MB-453 and BT-474, also demonstrated a significant capacity of serum to induce p185HER2 phosphorylation. The demonstration of antibody-mediated partial inhibition of phosphorylation under serum-free conditions suggests that mammary carcinoma cells may also produce and secrete a factor or factors which may activate p185HER2. Our observation that growth-inhibitory MAb 4D5 is able to reduce the phosphorylation of p185HER2 by newborn calf serum and by a cellular-derived factor(s) suggests the existence of a growth factor(s) which uses phosphorylation of p185HER2 as a signal transduction pathway to regulate cell proliferation.

Regulation of phosphorylation of the c-erbB-2/HER2 gene product by a monoclonal antibody and serum growth factor(s) in human mammary carcinoma cells

Monoclonal antibody (MAb) 4D5 was used to analyze the phosphorylation of p185HER2, the gene product of c-erbB-2/HER2, in SK-BR-3 cells. Culture in the continuous presence of 4D5 reduced the in vivo steady-state levels of p185HER2 phosphorylation by 80% in a dose-dependent manner, suggesting that MAb 4D5 may have interfered with the activation of phosphorylation of p185HER2. The observed MAb-mediated reduction of p185HER2 phosphorylation could not be completely accounted for by down-regulation. When cultures were grown under serum-free conditions, the steady-state levels of p185HER2 phosphorylation were reduced by 56%, and addition of 4D5 further inhibited phosphorylation to 20% of steady-state levels. With continuous exposure to increasing concentrations of newborn calf serum in these cultures, there was a linear increase in tyrosine-specific phosphorylation of p185HER2, reaching a 5.4-fold increase with 10% newborn calf serum. Phosphorylation of p185HER2 in the presence of newborn calf serum was not attributable to stimulation of the epidermal growth factor receptor by epidermal growth factor or by transforming growth factor-alpha. Extension of these observations to two other mammary carcinoma cell lines. MDA-MB-453 and BT-474, also demonstrated a significant capacity of serum to induce p185HER2 phosphorylation. The demonstration of antibody-mediated partial inhibition of phosphorylation under serum-free conditions suggests that mammary carcinoma cells may also produce and secrete a factor or factors which may activate p185HER2. Our observation that growth-inhibitory MAb 4D5 is able to reduce the phosphorylation of p185HER2 by newborn calf serum and by a cellular-derived factor(s) suggests the existence of a growth factor(s) which uses phosphorylation of p185HER2 as a signal transduction pathway to regulate cell proliferation.