The protein phosphatase inhibitors okadaic acid and calyculin A induce apoptosis in human osteoblastic cells

To determine whether protein phosphorylation and dephosphorylation can affect apoptosis in osteoblastic cells, we examined the effects of okadaic acid (OA) and calyculin A (CA) on cultured human osteoblastic cells Saos-2 and MG63, and mouse osteoblastic MC3T3-E1 cells. After reaching confluence, these cells were exposed to varying concentrations of OA or CA. OA and CA induced cell death in all three cell lines in a dose- and time-dependent manner. Marked nuclear condensation and fragmentation of chromatin were also observed in these cells by using the Hoechst 33342 stain. DNA ladder formation, a hallmark of apoptosis, was detected in Saos-2 and MG63 cells, but not in MC3T3-E1 cells by treatment of OA or CA. In the Saos-2 cells, OA- and CA-induced DNA ladder formation was dose-dependent with maximal effect at concentrations of 10 and 2 nM, respectively, and was time-dependent from 14 to 48 h. DNA ladder formation in response to OA and CA was revealed by using conventional ethidium bromide staining of electrophoresed DNA without using autoradiography. Beyond the maximal effects at the respective concentrations, however, cell death did not indicate DNA laddering, suggesting that phosphatase activity may be required for ladder formation. Our results indicate that apoptosis in the cultured osteoblastic cells is induced by moderate inhibition of PP-1 or PP-2A based on the known selectivity of okadaic acid and of calyculin A.

Immunohistochemical and immunoblotting identification of protein phosphatase 1 gamma 1 in rat salivary glands

We have analyzed the distribution of the gamma 1 isotype of rat protein phosphatase type 1 catalytic subunit in rat salivary glands. Formaldehyde-fixed paraffin sections were reacted with the PP1 gamma 1 antibody using an immunohistochemical method. Positive staining occurred in striated ducts of parotid gland. However, the staining reaction was less intense in submandibular gland. Proteins were also prepared from rat salivary glands and subjected to SDS-PAGE, followed by Western blotting analysis with the PP1 gamma 1 antibody. The antibody interacted with protein corresponding to an estimated molecular mass of 36 kDa present in the parotid gland. The staining reaction was considerably weaker with the proteins from submandibular gland.

Transblot identification of avidin-interacting proteins in rat salivary glands

Blotting of rat parotid gland proteins separated by SDS-PAGE and transferred to Immobilon transfer membranes revealed that avidin-peroxidase conjugate interacted with bands having estimated molecular weights of 72, 74, and 120 kDa. Even at the lowest concentration of avidin-peroxidase used in the general ABC method (1:2000 dilution), three bands were clearly discernible. The staining reaction of parotid gland proteins was eliminated on preincubating the proteins with native avidin. The staining reaction was markedly reduced with the proteins obtained from submandibular/sublingual glands.

Identification of the Fas antigen in human gingiva

The Fas antigen is a cell-surface glycoprotein that mediates apoptosis from the cell surface into the cytoplasm. Polyclonal antibody (Fas D) was raised against a synthetic polypeptide selected from the extracellular part of the human Fas antigen (amino acid residues 104-114) and was used to detect the Fas antigen in human gingiva. Biopsy specimens of human gingiva were prepared, and the paraffin sections were reacted with the Fas D antibody by an immunohistochemical method. The antibody localized to the prickle-cell layer and to granular layer keratinocytes of human gingiva. Proteins were also prepared from human gingiva and subjected to SDS-PAGE, followed by Western-blotting analysis with the Fas D antibody. The antibody interacted with a band corresponding to an estimated molecular weight of 35 kDa. The incidence of the immunoreactive 35-kDa protein was detected in the gingiva of 90% of the 20 individuals examined. The Fas antigen detected in human gingiva may be related to the physiological turnover of oral mucosa.

Protein phosphatase inhibitors, okadaic acid and calyculin A, induce alkaline phosphatase activity in osteoblastic cells derived from newborn mouse calvaria

To determine whether protein phosphatases can affect bone regulation, we examined the effects of okadaic acid (OA) and calyculin A (CA), specific inhibitors of protein phosphatases type 1 and type 2A, on alkaline phosphatase activity of mouse osteoblastic cells. Clone MC3T3-E1 cells were cultured with varying concentrations of OA and CA. OA and CA stimulated alkaline phosphatase (ALP) activity in the cells in dose-dependent fashion with a maximal effect at concentrations of 5 nM and 2 nM, respectively. The properties of OA-induced and native ALP in the cells were the same and they were liver-bone-kidney type. These results show that protein phosphatase inhibitors stimulate bone formation in vitro and that phosphorylation and dephosphorylation of specific proteins in the cells may be involved in bone regulation in vivo as well.

Detection of endogenous avidin-binding proteins in rat liver cells by transblot and electron microscopy

Peroxidase-conjugated avidin was used to detect the endogenous avidin-binding proteins in rat tissues. By a transblot method, avidin-peroxidase interacted with proteins of mitochondrial fractions of rat liver with estimated molecular weights of 120,000 and 74,000. The proteins were identified as pyruvate carboxylase (120 kDa, pI 6.4) and methylcrotonyl-CoA carboxylase (74 kDa, pI 7.2) by two-dimensional gel electrophoresis and transblot method. The estimated molecular weight of an additional band (220,000) detected in the cytosolic fraction of rat liver was consistent with acetyl-CoA carboxylase. Intense staining also occurred with kidney, heart, ovary and adipose tissue, moderate with large and small intestine, cerebrum and cerebellum, and very faint with testis, lung and spleen. The sections of rat liver embedded in LR white were incubated with avidin-colloidal gold conjugate and examined under an electron microscope. The glutaraldehyde-perfused rat liver blocks were also incubated with streptavidin-ferritin conjugate and the ultrathin sections were cut and examined. The majority of gold and ferritin particles were found in the mitochondria of liver cells. No other cellular compartment was labeled except the cytosol which accounted for approximately 20% of the total labeling of the hepatocytes. The present procedure is a simple, rapid and inexpensive method for detecting the intracellular localization of endogenous avidin-binding proteins in the cells.

Protein phosphatase 1 gamma 2 is associated with nuclei of meiotic cells in rat testis

We have shown that there are at least 4 isotypes of the catalytic subunit of type 1 protein phosphatase (PP1), PP1 alpha, PP1 gamma 1, PP1 gamma 2 and PP1 delta by rat cDNA cloning. Among these, PP1 gamma 2 mRNA was found to be abundant in rat testis. To study the roles of PP1 gamma 2 in rat spermatogenesis, we raised an antibody against a synthetic 21 mer peptide corresponding to the predicted amino acid sequence of the C-terminal region of the PP1 gamma 2. The antibody interacted with a testicular protein of 39-kDa prepared from rats after puberty (25 days after birth). However, the antibody did not interact with proteins extracted from the immature testes or from other tissues examined. Indirect immunofluorescent staining of PP1 gamma 2 of the seminiferous tubules from rats of various ages and costaining with DNA showed that the protein is located in the nuclei of late spermatocytes and of early spermatids. We suggest that PP1 gamma 2 plays some role in meiotic division during spermatogenesis.

Testis-specific mak protein kinase is expressed specifically in the meiotic phase in spermatogenesis and is associated with a 210-kilodalton cellular phosphoprotein

The mak gene encodes a new protein kinase distantly related to cdc2 kinase, and its transcripts are expressed exclusively in testicular germ cells at and after meiosis (H. Matsushime, A. Jinno, N. Takagi, and M. Shibuya, Mol. Cell. Biol. 10:2261-2268, 1990). In this study, we prepared a series of antibodies against synthetic peptides and fusion products of the mak gene and characterized the subcellular localization, protein kinase activity, and association with other cellular proteins of Mak. Mak products were identified as 66- and 60-kDa proteins that specifically appeared in rat testes after puberty. Testicular germ cell fractionation revealed that Mak products were most abundant in the fraction of the late pachytene stage and that their levels were dramatically decreased in postmeiotic haploid cells. Mak products were localized mostly in the cytoplasm as a soluble form. [35S]methionine labelling demonstrated that Mak products were associated with a 210-kDa cellular protein; in an in vitro kinase assay with immunoprecipitates of Mak products, the 210-kDa cellular protein was efficiently phosphorylated on serine and threonine residues. Furthermore, in a testicular cell culture system with 32Pi, the 210-kDa molecule associated with Mak was phosphorylated in vivo on serine and threonine residues. These results strongly suggest that the Mak complex may play a role in meiosis during spermatogenesis and that a phosphorylated 210-kDa protein is one of the physiological substrates for this protein kinase.

Expression of PP2A B regulatory subunit beta isotype in rat testis

We isolated a rat cDNA encoding part of the beta-isotype of the B regulatory subunit (BR beta) of protein phosphatase 2A (PP2A). The isolated cDNA encoded the region corresponding to amino acids positions 8(R) to 177(N) of human BR beta. The identities of the nucleotide and amino acid sequences of the rat and human BR beta s were 95.7% and 100%, respectively. The BR beta mRNA was specifically expressed in rat brain and testis, the lengths of mRNAs in these two organs being different. In the testis, the BR beta mRNA was first detected 40 days after birth, increasing gradually thereafter, and was expressed specifically in elongated spermatids, while mRNA of the alpha-isotype (BR alpha) was expressed equally in all spermatogenic cells. After meiosis, round spermatids change morphologically to elongated spermatids. BR beta may regulate the activity of the PP2A catalytic subunit in spermatids, and be involved in spermatogenic maturation, especially spermatid elongation.

Identification of pyruvate carboxylase in 3T3-L1 cells by transblot and its correlation with differentiation into adipocytes

The 3T3-L1 preadipocytes treated with insulin, dexamethasone and 3-methyl-1-isobutylxanthine (IBMX) two days before reaching monolayer undergo differentiation into adipocytes. Cell lysates were prepared from these cells under various conditions and analyzed by SDS-PAGE and transblot. Peroxidase-conjugated avidin used to detect endogenous proteins interacted strongly with a protein with an estimated molecular weight of 120 kDa, corresponding to pyruvate carboxylase, in the differentiated 3T3-L1 cells. On the other hand, this protein was not detected in undifferentiated 3T3-L1 cells.

Identification and expression of boar sperm proteins in the reproductive tract that interact with antibodies in serum from an infertile woman

Serum designated as IS obtained from a young healthy infertile woman induced a head-to-head agglutination of ejaculated boar sperm. The immunoglobulin G (IgG) prepared from IS localized to the acrosomal region of the sperm head obtained from the corpus and cauda epididymis as determined by an indirect immunofluorescent method. The IgG interacted with a boar sperm protein with an estimated molecular weight of 45-kDa, determined by sodium dodecyl sulfate-polyacrylamide gel electrophoretic (SDS-PAGE) immunoblotting technique. However, the IgG did not interact with proteins extracted from sperm obtained from the testis and caput epididymis or from non-gonadal tissues including liver, kidney, spleen, muscle and serum. The IgG interacted with additional proteins of about 75- and 38-kDa present in the corpus and cauda epididymal fluids but not those in the caput epididymal fluid. The staining intensity of the 75-kDa band was reduced and that of the 38-kDa was nullified with ejaculated seminal plasma proteins. The interacting proteins were adsorbed when chromatographed on Concanavalin A Sepharose column, suggesting that they are glycoproteins.

Differential effects of epidermal growth factor on the differentiation of type A spermatogonia in adult mouse cryptorchid testes in vitro

The effect of epidermal growth factor (EGF) on testicular germ cell differentiation was investigated. Testicular fragments from surgically prepared cryptorchid testes of adult mice were cultured for 9 days in serum-free media containing various concentrations of EGF. Histological sections of testis were examined under a light microscope and each type of germ cell and mitotic cell in the seminiferous tubules was counted per 1000 Sertoli cells. EGF at concentrations ranging from 100 to 200 ng/ml induced differentiation of type A spermatogonia. The observed maximal stimulatory activity of EGF at a concentration of 100 ng/ml was 30% of the positive control cultures treated with calf serum. EGF at concentrations ranging from 1 to 100 ng/ml significantly inhibited the mitotic activity of FSH, FSH plus retinol, or FSH plus fetuin on type A spermatogonia and their differentiation. The number of type A spermatogonia in testes cultured with FSH, FSH plus retinol, or FSH plus fetuin decreased when EGF was added. On the other hand, EGF stimulated the differentiation of type A spermatogonia induced with fetuin but did not influence retinol-induced differentiation. It is proposed that EGF inhibits testicular germ cell differentiation by blocking the proliferation of type A spermatogonia stimulated by FSH.

Identification of the sperm antigen interacting with antibodies in serum from an infertile woman

Serum (IS) obtained from an infertile woman induced head-to-head agglutination of human sperm. The immunoglobulin G (IgG) fraction of the IS was prepared by ammonium sulfate fractionation and DEAE cellulose chromatography. The IgG localized to the post-acrosomal region of the sperm, determined by indirect immunofluorescence and interacted with a human sperm protein with an estimated Mr of 80 kDa, determined by immunoblotting. The identity of the interacting sperm antigen was verified by isolating the 80 kDa sperm protein by affinity chromatography. The present results suggest that the anti-80 kDa antibodies may be responsible for the infertility.

Protein phosphorylation during 1-methyladenine-induced maturation of Asterias oocytes

Maturation was induced in Asterias oocytes with 1-methyladenine (1-MA) at a final concentration of 2 microM. At 5, 10, and 30 min of treatment, oocytes were homogenized and the cytosolic fraction was prepared. The cytosol was incubated with [gamma-32P]ATP and [gamma-32P]GTP. The phosphorylated proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the radioactivity in the gels was determined by autoradiography. The cytosol prepared from 1-MA-treated oocytes incubated with [gamma-32P]ATP showed a marked increase in the radiolabeling of proteins with estimated molecular weights of 70,000 and 62,000 Da. With [gamma-32P]GTP a 56,000-Da protein showed increased radiolabeling. The present finding suggests that an early biochemical event of 1-MA-induced oocyte maturation in Asterias is the stimulation of phosphorylation of specific proteins.

Transblot identification of biotin-containing proteins in rat liver

Peroxidase-conjugated avidin was used to detect biotin-containing carboxylases in rat liver. By a transblot method, avidin-peroxidase interacted with liver proteins with estimated molecular masses of 120 and 74 kDa. The proteins were identified as pyruvate carboxylase (120 kDa, 6.4 pI) and methylcrotonyl-CoA carboxylase (74 kDa, 7.2 pI) by two-dimensional gel electrophoresis and transblot method. An additional band with estimated molecular mass of 220 kDa was detected in the cytosol fraction of rat liver, compatible with acetyl-CoA carboxylase. Rat liver proteins were prepared and treated with avidin and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transblot with avidin-peroxidase. A 190-kDa band was found with a parallel decrease in the 120-kDa band determined by Coomassie blue staining; however, these proteins did not stain by the transblot avidin-peroxidase method. When the transblot of parallel proteins was incubated with biotin and subsequently with avidin-peroxidase, two additional bands, namely 190 and 145 kDa, were detected while the 74-kDa band disappeared correlated with decreased staining of the 120-kDa band. The present procedure is a simple, rapid, and inexpensive method for detecting biotin-containing proteins in various tissues and organs and in determining the occurrence of nonspecific staining with the avidin-biotin complex method of immunoblot.

Protein phosphorylation during 5-hydroxytryptamine-induced maturation of Spisula oocytes

Maturation was induced in Spisula oocytes with 5-hydroxytryptamine (5-HT) creatinine sulfate at a final concentration of 5 microM. After 10 and 30 min of treatment, oocytes were homogenized and the cytosolic and particulate fractions were prepared. The fractions were incubated with [gamma-32P]GTP and [gamma-32P]ATP. The phosphorylated proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The radioactivity in the gels was determined by autoradiography. With [gamma-32P]GTP a marked increase in the radiolabeling of proteins with an estimated Mr of 47,000 and 20,000 in the cytosolic and particulate fractions, respectively, was demonstrated with the 5-HT-treated oocytes, whereas no stimulation was demonstrable with the use of [gamma-32P]ATP. A significant increase in GTP-mediated protein phosphorylation occurred within 10 min after 5-HT treatment before the occurrence of germinal vesicle breakdown, suggesting that this post-translation modification of proteins is an early action of the neurotransmitter in the induction of meiotic reinitiation in oocytes.

Identification of cell types in Sertoli cell-enriched cultures by immunocytochemistry and DNA-specific fluorochrome Hoechst 33342

The cell types in Sertoli cell-enriched cultures can be identified by using the DNA-specific fluorochrome Hoechst 33342 staining. This simple, rapid and reproducible procedure can be used with fixed and living cells. The peritubular myoid cells can be distinguished from the Sertoli cells in Sertoli cell-enriched cultures by the characteristic staining pattern obtained using Hoechst 33342 dye. Those cells identified as peritubular myoid cells by the characteristic DNA staining also interacted with the anti-fibronectin antibody determined by an immunocytochemical method while the Sertoli cells did not. The described staining method is valuable in assessing the presence of peritubular myoid cells in Sertoli cell-enriched cultures.

The antibody from an infertile woman that induces sperm agglutination interacts with rat testicular cells and sperm

The serum obtained from an infertile woman induced a specific head-to-head agglutination of human and rat sperm. The immunoglobulin G (IgG) fraction of the serum was obtained and found to interact with the proteins of rat sperm in testis and epididymis. Using an indirect immunofluorescent method with rat sperm from vas deferens, we determined that the antibody recognized the protein on the convex and concave regions of the acrosome and over the entire tail. However, with testicular spermatozoa, the antibody recognized only the distal end of the tails. In paraffin sections of adult rat testis, sperm tails located at the luminal region of the seminiferous tubules stained intensely. Weak but significant staining also occurred on late spermatids. In the epididymal sections, staining was restricted to spermatozoa in the lumen. On the other hand, sections of testes from 25-day-old rats containing spermatogonia and early spermatocytes had a completely negative reaction. Testicular somatic cells, including Sertoli cells, peritubular myoid cells and interstitial cells, did not stain. To identify the testicular protein interacting with the antibody, adult rat testis proteins were prepared and analyzed by a sodium dodecyl sulfate-polyacrylamide gel electrophoretic (SDS-PAGE) immunoblot technique. The antibody interacted with a protein with an estimated molecular weight of 82,000 in the testicular homogenate and particulate fraction, whereas the reaction was considerably weaker with the testicular cytosol fraction.

Identification of antigen in rat spermatogenic cells interacting with an anti-human sperm monoclonal antibody

A monoclonal antibody (MAb) raised against human sperm protein, designated YWK-II, was used to determine the distribution of antigens in rat spermatozoa and rat testicular germ cells. By an indirect immunofluorescent method, the antibody localized over the rat spermatozoal head, except for the postacrosomal region. In paraffin sections of adult and immature rat testis, germ cells, at every developmental stage, and Sertoli cells stained, while interstitial cells and peritubular myoid cells remained unstained. When cocultures of Sertoli and germ cells were tested, only the germ cells stained intensely. Sertoli cells and peritubular myoid cells in cultures did not stain. In the epididymal sections, strong staining occurred with spermatozoa in the lumen and epididymal epithelial cells, with moderate staining in the myoid layers of epididymis. To determine the sperm antigen interacting with the YWK-II antibody, rat spermatozoa proteins were prepared and analyzed by an immunoblot technique. The monoclonal antibody interacted with a single protein, with an estimated molecular weight of 115,000, present in the cauda epididymal spermatozoa. Among the proteins of the caput epididymal spermatozoa, however, the antibody interacted with a major and a minor band with molecular weights of 115,000 and 88,000, respectively. On the other hand, with proteins prepared from the membrane fraction of adult and immature rat testis, the antibody reacted with two bands with estimated molecular weights of 88,000 and 115,000. In the lysate prepared from germ cells dissociated from Sertoli-germ cell cocultures, the antibody recognized only the 88,000 protein. The present results show that the YWK-II MAb interacts with two proteins with different molecular weights. The amount of the interacting proteins in spermatozoa varied with their location within the epididymis.

Dibutyryl adenosine cyclic monophosphate regulates differentiation of type A spermatogonia with vitamin A in adult mouse cryptorchid testis in vitro

Surgically prepared cryptorchid mouse testes containing only type A spermatogonia were cultured with (Bu)2cAMP in combination with vitamin A (retinol). Treatment with (Bu)2cAMP and retinol for 12-24 h and with basal medium for an additional 8 days stimulated mitotic activity in type A spermatogonia and induced differentiation of germ cells. However, (Bu)2cAMP alone did not induce differentiation of type A spermatogonia. Moreover, when cryptorchid testes were treated with (Bu)2cAMP for longer than 3 days in the presence or absence of retinol, differentiation of type A spermatogonia did not take place; disintegration of the seminiferous tubules occurred instead. When the cryptorchid testes were cultured for 24 h in a medium containing a fixed concentration of retinol and varying concentrations of (Bu)2cAMP from 0.001-0.4 mM, there was a dose-dependent increase in the number of differentiated and mitotic germ cells and type A spermatogonia. Likewise, at a fixed dose of (Bu)2cAMP and increasing concentrations of retinol, a dose-dependent increase in the number of differentiated and mitotic germ cells occurred. However, the number of type A spermatogonia was decreased. The addition of puromycin, cycloheximide, and actinomycin D to the medium completely blocked retinol-(Bu)2cAMP-induced differentiation of the germ cells. The present results suggest that cAMP and retinol trigger biochemical events promoting the synthesis of specific macromolecules involved in the proliferation and differentiation of type A spermatogonia.

Effect of duration of cryptorchidism on ability of mouse germ cells to regenerate and differentiate

When 2-month-old mice were made cryptorchid for periods of up to 19 months, testicular weight fell between 0 and 10 days, remained steady until 7 months, fell rapidly until 12 months, and then remained low. The recovery of weight gain of the testes after surgical reversal of the cryptorchidism was related to the duration of cryptorchidism. After 8 months very little change in testicular weight or specific activity of lactate dehydrogenase X was obtained.

Effects of steel mutation on spermatogenesis stimulated by fetuin

The effect of the steel mutation on spermatogenesis was investigated using organ culture. Cultured cryptorchid testes from WB-+/+ mice showed an effective differentiation of type A spermatogonia in response to Pedersen type III fetuin. In contrast, the cryptorchid testes from WB-S1/+ showed neither differentiation nor division of type A spermatogonia. The findings reported here are the first demonstration of retarded response of steel mutation on a well-known agent, fetuin.

Vitamin A and follicle-stimulating hormone synergistically induce differentiation of type A spermatogonia in adult mouse cryptorchid testes in vitro

To study the mechanism of vitamin A and FSH action on testicular germ cell differentiation, artificially induced cryptorchid testes of adult mice were cultured in vitro, because such testes contain only type A spermatogonia and Sertoli cells in their seminiferous tubules. A synergistic effect of vitamin A compounds with FSH, but not with LH, on testicular germ cell differentiation was observed. Our data suggested that FSH stimulated the proliferation of type A spermatogonia, whereas retinoids induce spermatogenesis from type A spermatogonia into intermediate or type B spermatogonia. Possible mechanisms of action of retinoids and FSH on testicular germ cell differentiation are discussed.