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PubMed1982

Assembly, glycosylation, and secretion of the oligomeric rat prostatic binding protein in Xenopus oocytes.

Prostatic binding protein (PBP), a hormonally controlled oligomeric glycoprotein secreted by the rat ventral prostate, is composed of three different polypeptide chains, C1, C2, and C3. Microinjection of prostate mRNA into Xenopus laevis oocytes results in the synthesis, processing, and correct assembly of these three components, and also in the export of PBP into the medium. The glycosylation of component C3--the only glycopeptide of PBP--by the oocyte enzymes does not lead to the same result as in the native prostate tissue. The intracellular oocyte component contains an incompletely processed oligomannosyl core unit. Upon secretion this sugar core is further processed, probably at random because the carbohydrate chains attached to the exported C3 molecules are heterogeneous; they are also different from the oligosaccharide unit of authentic C3. However, tunicamycin experiments show that glycosylation is neither a prerequisite for secretion nor for the assembly of PBP, at least in oocytes.

Androgen-Binding Protein↗
PubMed1982

[Lipid dependence of the activity of cytochrome P-450 from microsomes of rat liver by the phosphatidylcholine transfer protein from bovine liver].

The lipid dependence of hydroxylase and demethylase activities of microsomal cytochrome P-450 was studied, using purified phosphatidylcholine transfer protein from bovine liver. In the presence of this protein exogeneous phosphatidylcholine was shown to reactivate cytochrome P-450 inactivated earlier with lysophosphatidylcholine.

Androgen-Binding Protein↗
PubMed1982

[Transmembrane migration of phosphatidylcholine and peroxidation of lipids in rat liver microsomes].

The exchangeability of phosphatidylcholine in microsomes differing in the degree of lipid peroxidation was determined by incubation of microsomes labelled in vivo with [methyl-14C]choline chloride with an excess of phosphatidylcholine liposomes and phosphatidyl-exchange protein from beef liver. The phosphatidylcholine peroxidation products were shown to act as substrates for the phosphatidylcholine-exchange protein. The level of exchangeable microsomal phosphatidylcholine did not depend on the degree of lipid peroxidation in the microsomes. Stimulation of lipid peroxidation by Fe2+-ascorbate or inhibition of lipid peroxidation by alpha-tocopherol did not influence the exchange of microsomal phosphatidylcholine. However, with highly peroxidized phosphatidylcholine liposomes as acceptor particles the exchange of microsomal phosphatidylcholine in the presence of phosphatidylcholine-exchange protein was strongly inhibited. In all cases the percentage of microsomal phosphatidylcholine exchangeable within 1-2 hrs was 85-90%. It is concluded that lipid peroxidation is not responsible for the rapid translocation (flip-flop) of phosphatidylcholine in rat liver microsomes. A possible involvement of membrane proteins in this process is proposed.

Androgen-Binding Protein↗
PubMed1982

[Rapid transmembrane migration of phosphatidylcholine under the influence of cytochrome P-450].

The phosphatidylcholine exchange protein and bee venom phospholipase A2 were used to estimate the phosphatidylcholine accessibility in proteoliposome-containing cytochrome P-450. Without cytochrome P-450 phosphatidylcholine was only partly accessible for the both membrane probes. Incorporation of cytochrome P-450 into the liposomes resulted in a complete accessibility of phosphatidylcholine for the phosphatidylcholine exchange protein and phospholipase A2. On the other hand, phosphatidylcholine was only partly available for the membrane probes in cytochrome b5 containing proteoliposomes. It was concluded that cytochrome P-450 induces rapid transmembrane translocation of phosphatidylcholine with tau 1/2 less than 20 min. It is proposed that cytochrome P-450 may be responsible for rapid flip-flop of phosphatidylcholine in rat liver microsomes.

Androgen-Binding Protein↗
PubMed1982

Prostate alpha-protein. Isolation and characterization of the polypeptide components and cholesterol binding.

alpha-Protein, a major glycoprotein in the cytosol fraction of rat ventral prostate, has a molecular weight of about 50,000 and can be dissociated, by sodium dodecyl sulfate, into two different subunits (A and B). alpha-Protein has three different polypeptide components with apparent molecular weights of 10,000 (I), 14,000 (II), and 15,000 (III). These components were purified to homogeneity and their amino acid compositions were determined. Subunit A is composed of Components I and III, whereas subunit B is composed of Components II and III. Carbohydrate was detectable only on Component III. Component III isolated from subunit A and Component III isolated from subunit B appear to be identical. The purified alpha-protein contains 0.7-1 mol of cholesterol/mol of protein. If cholesterol was removed by acetone, about 1 mol of 5 alpha-dihydrotestosterone or pregnenolone could bind to 1 mol of alpha-protein. In the presence of 2 mM ZnCl2, alpha-protein can form dimers and tetramers. In cell-free systems, alpha-protein can inhibit binding of the androgen-receptor complex to nuclear chromatin and also can promote the release of the complex already bound to chromatin. This effect is due to polypeptide Component I.

Amino Acids↗
PubMed1982

Prostate alpha-protein. Complete amino acid sequence of the component that inhibits nuclear retention of the androgen-receptor complex.

The amino acid sequence of Component I of alpha-protein, a glutamic acid-rich protein, is presented. Component I is a single chain polypeptide which consists of 88 amino acid residues with a molecular weight of 10,191. Component I has the amino acid composition Lys6, His, Arg2, Cys3, Asp5, Asn2, Thr3, Ser4, Glu13, Gln3, Pro3, Gly2, Ala6, Val9, Met4, Ile4, Leu8, Tyr6, Phe3, Trp, with serine and asparagine as NH2(-) and COOH-terminal amino acids, respectively. Automated sequences analysis of the whole protein, as well as characterization of the peptides obtained from trypsin, chymotrypsin, and staphylococcal protease digestion and cyanogen bromide treatment, led to the elucidation of the complete primary structure of this protein.

Amino Acid Sequence↗
PubMed1982

Study of a proline-rich polypeptide bound to the prostatic binding protein of rat ventral prostate.

A proline-rich polypeptide is associated with prostatic binding protein, a major androgen-dependent protein described previously in the rat ventral prostate. This polypeptide has been purified. Its molecular weight estimated by gel filtration is about 8500, but a markedly lower value (3300) is obtained by sodium dodecyl sulfate-urea polyacrylamide gel electrophoresis. Isoelectric focusing on thin layer polyacrylamide gels yields two major forms with isoelectric points of, respectively, 7.75 and 7.05. The amino acid composition of proline-rich polypeptide is characterized by a high (19.5%) proline content and its NH2-terminal amino acid is glycine. Like prostatic binding protein, proline-rich polypeptide is a characteristic component of the rat ventral prostate and localized primarily in the intraluminal secretion of this gland. In intact adult male rats the cytosol of a whole gland contains 0.70 +/- 0.15 (S.D.) mg of the polypeptide, as measured by radial immunodiffusion or 2.6 +/- 0.5% of (S.D.) of the total protein. This amount decreases gradually after castration and becomes undetectable after 8 days. Androgen treatment, on the other hand, results in a rapid stimulation, while estradiol and progesterone are ineffective. Proline-rich polypeptide is markedly more androgen-dependent than prostatic binding protein, and promises to be an interesting end point for studies on the mechanism of action of androgens.

Amino Acids↗
PubMedDate not supplied

Thanatogen expression during involution of the rat ventral prostate after castration.

After castration the rat ventral prostate undergoes regression. This process occurs due to the induction of apoptosis, or active cell death, in the epithelial cells of the gland. Several genes, including TRPM-2, (testosterone repressed prostate message), RVP.1, fos, and myc, have been shown to be induced in the prostate during this process. We have investigated the expression of several other genes that may be associated with apoptosis, including tissue transglutaminase (TGase), poly(ADP)ribose polymerase (PARP), and heat shock protein 27 (Hsp27). Northern hybridization has been used to determine the steady-state mRNA levels of these genes in the ventral prostate after castration, and the time course of induction has been compared to the changes in the steady-state levels of prostate steroid binding protein (PSBP), alpha-tubulin, and TRPM-2 mRNAs. The results show that the mRNAs for PARP, transglutaminase, and Hsp27, in addition to TRPM-2, are induced by androgen ablation in the rat ventral prostate and reach maximum levels between days 3 and 4 after castration. Using in situ hybridization we have established that these genes are expressed in the epithelial cells of the prostate that are known to undergo active cell death; this result suggests that their gene products may be required in the dying cells to ensure that the biochemical and morphological processes of apoptosis are completed appropriately.

Androgen-Binding Protein↗
PubMed1996

Mammaglobin, a mammary-specific member of the uteroglobin gene family, is overexpressed in human breast cancer.

In this report, we describe a novel cDNA isolated from a primary human breast adenocarcinoma and differentially expressed in several breast carcinoma cell lines. The protein encoded by this cDNA, which we have named mammaglobin, is homologous to a family of secreted proteins that includes rat prostatic steroid-binding protein subunit C3, human Clara cell 10-kilodalton protein, and rabbit uteroglobin. Expression of the mammaglobin gene is restricted to the adult mammary gland. More significantly, in an analysis of 35 breast tumor biopsies, mammaglobin mRNA levels were increased at least 10-fold relative to normal breast tissue in 23% of cases. The breast-specific expression of this potentially secreted protein and its frequent overexpression in primary human breast tumors suggest that mammaglobin may be a novel marker for the management of breast cancer.

Adult↗
PubMed1996

p53-independent apoptosis during mammary tumor progression in C3(1)/SV40 large T antigen transgenic mice: suppression of apoptosis during the transition from preneoplasia to carcinoma.

Alterations in apoptosis and associated mechanisms during mammary tumor progression were investigated in transgenic mice expressing the SV40 large T antigen (T(AG)) driven by the rat prostatic steroid-binding protein C3(1) 5'-flanking region. Apoptosis levels, assessed by in situ end labeling, were low in normal mammary epithelial cells, highest in atypical hyperplasias (preneoplastic lesions), and less pronounced in adenocarcinomas. Preneoplastic cells maintain the ability to undergo apoptosis as a mechanism of tumor growth suppression, but this critical control of apoptosis is lost as these lesions progress to carcinomas. These alterations in apoptosis occur during mammary tumor progression in mice containing wild-type p53+/+ genotype as well as in mice with the p53-/- genotype. Thus, apoptosis in this tumor model occurs through a p53-independent mechanism. Because other studies have demonstrated p53-dependent apoptosis in T(AG)-induced choroid plexus tumors of transgenic mice, we propose that the role of p53 in apoptosis may be tissue-specific. In addition, bcl-2 protein was not expressed in any mammary lesions. SV40 T(AG) expression, which correlated with the nuclear p53 protein at all stages of tumor progression, was low in normal mammary epithelial cells, moderately high in atypical hyperplasias, and strongly expressed in adenocarcinomas. No p53 mutations were found at any stage of mammary adenocarcinoma development, suggesting that tumor progression does not require a dominantly acting p53 mutation in this transgenic model. p2l(Waf1/Cip1), a cyclin-dependent kinase inhibitor, was expressed in normal mammary tissue but was not detected in the mammary carcinomas, despite high nuclear accumulation of wild-type p53 protein, suggesting functional loss of p53 due to binding of SV40 T(AG), to p53. These findings suggest that suppression of apoptosis during the transition from atypical hyperplasia to adenocarcinoma appears to be a critical event for mammary cancer development in C3(1)/T(AG) transgenic mice and occurs by p53- and bcl-2-independent pathways.

Androgen-Binding Protein↗
PubMed1998

Baculovirus-mediated expression of recombinant rat phosphatidylcholine transfer protein.

Phosphatidylcholine transfer protein catalyzes intermembrane transfer of phosphatidylcholines exclusive of all other phospholipid classes. Although postulated to participate in phosphatidylcholine biosynthesis and biliary trafficking in liver, the molecular basis underlying the substrate specificity of phosphatidylcholine transfer protein remains to be elucidated. Having demonstrated the inability of Escherichia coli to express recombinant phosphatidylcholine transfer protein, we infected Spodoptera frugiperda (Sf9) cells with recombinant baculovirus. When assayed in vitro, cytosol of recombinant but not control infected cells demonstrated high levels of intermembrane phosphatidylcholine transfer activity and no transfer activity for phosphatidylethanolamine. A two-step purification protocol in which 10 mg of cytosolic protein was subjected to anion exchange chromatography followed by hydroxylapatite chromatography yielded 0.1 mg active protein which was >92% pure. The identity of purified protein was confirmed by matrix-assisted laser desorption-ionization mass spectrometry and by amino acid sequencing. Based on the recovery of 30% of PC transfer activity after purification, we estimate that recombinant rat phosphatidylcholine transfer protein accounted for approximately 3-6% of cytosolic protein mass of infected cells. These results demonstrate the utility of baculovirus for expressing recombinant phosphatidylcholine transfer protein and should facilitate studies designed to elucidate the structural biology and physiological functions of this uniquely specific phospholipid transfer protein.

Amino Acid Sequence↗