Transmembrane orientation of an early biosynthetic form of acetylcholine receptor delta subunit determined by proteolytic dissection in conjunction with monoclonal antibodies

The transmembrane topology of acetylcholine receptor (AChR) delta subunit, synthesized in vitro and co-translationally integrated into dog pancreas rough microsomal membranes, was studied using limited proteolysis and domain-specific immunoprecipitation. Forty-four kilodaltons (kd) of the 65-kd delta subunit comprise a single fragment that is inaccessible to exhaustive proteolytic digestion from the cytoplasmic surface of the membrane by trypsin, chymotrypsin, thermolysin, and pronase. Previously, we have shown that this 44-kd "protected" fragment contains the amino terminus of the intact molecule and all of the core oligosaccharides (Anderson, D.J., P. Walter, and G. Blobel (1982) J. Cell Biol. 93: 501-506). Here we demonstrate that this domain can be further dissected into a 26-kd fragment, together with low molecular weight material, when the membranes are rendered permeable to trypsin by low concentrations of deoxycholate (Kreibich, G., P. Debey, and D. D. Sabatini (1973) J. Cell Biol. 58: 436-462). This 26-kd fragment contains all of the core oligosaccharides present on the intact subunit and therefore constitutes at least part, if not all, of the extracellular domain. The remaining low molecular weight material may derive from the membrane-embedded domain; our data imply that as much as 18 kd may be internal to the lipid bilayer. On the other hand, part of the cytoplasmic pole of AChR-delta can be recovered as a discrete, 12-kd fragment upon mild trypsinization of intact vesicles. We have used this 12-kd fragment to identify anti-AChR-delta monoclonal antibodies (mAbs) that react with the cytoplasmic domain of this subunit. Partial proteolytic fragmentation of the AChR in vitro translation products, in topologically well defined rough microsomes, may be used as a general assay to characterize the domain specificity of anti-AChR mAbs. For example, in the case of AChR-beta, we were able to identify two mAbs that recognize extracellular and cytoplasmic fragments, respectively.

Identification of homo-oligomers as potential intermediates in acetylcholine receptor subunit assembly

We have examined the sedimentation behavior, on sucrose density gradients, of acetylcholine receptor (AcChoR) subunits synthesized in vitro and integrated into heterologous rough microsomal membranes. In media containing nondenaturing detergents such as Triton X-100 or deoxycholate, the subunits appear to self-associate although, as previously reported, no heterologous interactions were detected. The sedimentation profiles assume a broad distribution in the region of 7-13 S. However, the peak fractions occupy the same region of the gradient as does native AcChoR, run in parallel. Such large homo-oligomers were not observed for another membrane protein, opsin, studied in the same way. This indicated that the associations are indeed between the AcChoR subunits and not simply between all newly synthesized membrane proteins. The homologous associations are interpreted to suggest a mechanism for maintaining the ionophore surfaces of the subunits in an energetically preferred, but metastable, configuration during the lengthy period of post-translational assembly.

Spontaneous tumors in long-term--vasectomized mice. Increased incidence and association with antisperm immunity

In two independent studies the authors have observed a significantly higher incidence of spontaneous tumors in vasectomized BDF1 mice over the long term than in age-matched sham-vasectomized control mice. In the first study, necropsies were performed on the animals at 30 months of age (27 months after surgery), and 15 of 24 vasectomized versus 2 of 14 sham-vasectomized mice (P less than or equal to 0.025) had detectable tumors in various tissues. In a second study, necropsies were performed on the animals at a younger age (18 months, 15 months after surgery), and liver tumors predominated: 82 of 171 vasectomized versus 33 of 97 controls (48% versus 34%, P less than or equal to 0.037) had at least one hepatic tumor, and a significantly higher percentage of vasectomized animals had large (greater than or equal to 31 sq mm) hepatic tumor burdens (80% versus 49%; P less than or equal to 0.002) and multiple hepatic tumors (19% versus 5%; P less than or equal to 0.002). In combined data from both studies, the vasectomy group had a higher incidence of (1) at least one tumor (P less than or equal to 0.025), (2) multiple tumors (P less than or equal to 0.005), and (3) more than one type of tumor (P less than or equal to 0.05. Furthermore, in both studies tumor number and size were significantly associated with antisperm immunity detected by antibody or aspermatogenesis evaluation. It is speculated that sperm degradation products and/or the autoimmune response to sperm that commonly accompanies vasectomy may affect tumor induction or growth directly or indirectly by interfering with immunosurveillance mechanisms.

Immunoprecipitation of proteins from cell-free translations

A typical procedure for immunoprecipitating a protein (abundance ca 0.5%) synthesized in the wheat germ cell-free system is summarized below. 1. Two microliters of 25% SDS are added to 48 microliters of translation reaction mixture, and the sample is heated to 100 degrees for 4 min. 2. Four volumes (i.e., 200 microliters) of dilution buffer at 4 degrees are added to the above sample. Dilution buffer is 1.25% Triton X-100, 190 mM NaCl, 60 mM Tris-HCl, pH 7.4, 6 mM EDTA, 10 units of Trasylol per milliliter. 3. Five microliters of appropriate antisera are added, and the sample is incubated for at least 12 hr at 4 degrees. 4. The sample is spun for 2 min in a microcentrifuge, and the supernatant is transferred to a fresh tube. 5. Thirty microliters of a 1 : 1 suspension of protein A-Sepharose CL-4B (15 microliters of packed beads) are added, and the sample is incubated with end-over-end mixing at room temperature for 2 hr. 6. The Sepharose beads are pelleted by a 10-sec centrifugation in the microcentrifuge, and the supernatant is aspirated. 7. The beads are washed four times in 1 ml, per wash, of 0.1% Triton X-100, 0.02% SDS, 150 mM NaCl, 50 mM Tris-HCl, pH 7.5, 5 mM EDTA, 10 units of Trasylol per milliliter at room temperature with vortexing at each wash. 8. The beads are given a final wash with the above solution not containing detergent, and the supernatant is aspirated as completely as possible with a drawn-out Pasteur pipette. 9. Forty microliters of SDS-gel electrophoresis sample buffer containing 50 mM DTT are added to the beads, and the sample is heated for 4 min in a boiling water bath. 10. Free--SH groups are blocked by adding 10 microliters of 1.0 M iodoacetamide in sample buffer and incubating for 45 min at 37 degrees. 11. The beads are centrifuged out, and the supernatant is applied to an SDS-polyacrylamide slab gel.

Biosynthesis of acetylcholine receptor in vitro

Torpedo acetylcholine receptor is accessible to analysis by cell-free protein synthesis, like other membrane proteins studied previously. The factors deserving particular attention in this system are the small amounts of messenger RNA contained in electroplax tissue, the inherent complexity of an oligomeric membrane protein (necessitating the use of subunit-specific antibodies), the anomalous electrophoretic behavior of the primary translation products (attributable in part to the high--SH content of sAChRs), and the multiple glycosylated forms that appear upon processing by microsomal membranes. Although not all these complexities can be satisfactorily explained, they have been empirically characterized and can be well controlled if the appropriate procedures are followed.

Immunity to tumor-associated antigens in vasectomized men

Leukocytes from 49 vasectomized and 57 age-matched nonvasectomized men were tested in the leukocyte adherence inhibition (LAI) assay for reactivity to sperm and various 3-M KCl human tumor extracts. Forty-four percent of the vasectomized men and 15% of the control group were reactive to the sperm antigen preparation (P less than or equal to 0.03). Similarly, a significantly higher percentage of vasectomized men responded to 3 of 5 tumor extracts tested: melanoma I (34.7 vs. 15.8%, P less than or equal to 0.04), squamous cell carcinoma (48.8 vs. 26.0%, P less than or equal to 0.04), and breast carcinoma (19.5 vs. 4%, P less than or equal to 0.04). Thirty percent of vasectomized versus 4% of the control group responded to more than two tumor antigens (P less than or equal to 0.03). The degree of LAI reactivity to each tumor extract was highly correlated with degree of antisperm LAI reactivity, and the degree of LAI responsiveness to one of the melanoma extracts was significantly correlated with antisperm antibody titer as measured by the sperm-immobilization assay. Furthermore, nonresponsive leukocytes from the control population converted to tumor antigen-responsive when incubated with sera from vasectomized LaI-positive men. Data from this study indicated that a large percentage of vasectomized men with sperm immunity were responsive to tumor-associated antigens in the LAI test and that antisperm antibodies or other serum factors played a role in this response. These results and the evidence that most tumor antigen-responsive cancer patients also have serum antibodies that reacted with sperm suggested that vasectomized men and cancer patients frequently responded to immunologically cross-reactive antigenic determinants present on both sperm and tumor cells.

Antibodies to antigens on teratocarcinoma cells are associated with parity in mice

Previous studies have demonstrated that the maternal host responds immunologically to antigens of the fetus, including oncofetal antigens (OFA). However, until now, the OFA that have been studied are those associated with the postimplantation embryo. In this paper we provide evidence that the maternal host also responds immunologically to antigens associated with the mouse teratocarcinoma (TC) cell lines F9 and PYS-2, which have been established as models for the preimplantation embryo. In a solid-phase radioimmunoassay using cell membrane extracts as antigen and 125I-protein A to detect binding antibodies, sera from parous C57BL/6 mice had a significantly greater reactivity than sera from age-matched virgin animals to F9 but not PYS-2, splenocyte or fibroblast antigen extracts. This finding was confirmed by surface immunofluorescence (IF) with fluorescein-labeled anti-mouse IgG. IF also detected a small number of multiparous mice with antibodies to PSY-2. Positive serum reactivity did not correlate directly with the number of previous litters. These TC cell lines express at least 2 OFA, F9 and Endo, which are found on preimplantation embryos and sperm, and preimmunization of female mice with F9 cells has been shown to reduce fertility. The parity-induced antibodies detected in this study could react with embryos at early stages of development and contribute to the natural decrease in litter size which occurs in mice after the second litter.

Urinary tract infection due to coagulase-negative staphylococcus

One hundred and fifty-six urine specimens with a pure culture of coagulase-negative Staphylococcus were studied. One hundred and eighteen charts were reviewed for clinical evidence of urinary tract infections. Twenty-four cases of urinary tract infection were found. The younger females in the study tended to have infection due to novobiocin resistant Staphylococcus in contrast to males and older females.

Signal recognition protein is required for the integration of acetylcholine receptor delta subunit, a transmembrane glycoprotein, into the endoplasmic reticulum membrane

Purified Signal Recognition Protein (SRP) has previously been shown to be required for the translocation of secretory proteins across the microsomal membrane (Walter and Blobel, 1980. Proc. Natl. Acad. Sci. U. S. A. 77:7, 112-7, 116) and to function in the early events of this process (Walter and Blobel, 1981. J. Cell Biol. 91:557-561). We demonstrate here that the delta subunit of acetylcholine receptor (AChR-delta), a transmembrane glycoprotein, likewise requires SRP for its asymmetric integration into microsomal membranes. We further demonstrate by partial sequence analysis that AChR-delta is synthesized with a transient NH2-terminal signal sequence of 21 residues that is cleaved off during integration into microsomal membranes. Integration of AChR-delta into the microsomal membrane vesicles proceeded asymmetrically, yielding a large (44 kdalton) core-glycosylated domain, inaccessible to externally added proteolytic enzymes and a smaller (approximately 16 kdalton) domain exposed on the outside of the vesicles and accessible to externally added proteolytic enzymes. The NH2 terminus of the molecule is contained in the 44-kdalton domain.

A specific estrogen receptor in the mouse spleen. Characterization and evidence of physiological regulation

We have used the synthetic estrogen [3H]-R2858 (11 beta-methoxy-17-ethnyl-1,3,5(10)-estratriene-3,17-diol) to characterize a cytoplasmic estrogen receptor in the mouse spleen. This receptor is specific for estrogens and binds to the steroids with high affinity. The binding is abolished by pronase or 37 C treatment, and the 8S peak is shifted to the 4S region on sucrose gradients under conditions of high salt. The concentration of spleen receptor increased significantly during pregnancy, and decreased after immunization with foreign protein. Estrogen receptors may be confined to certain subpopulations of spleen cells that change in numbers during pregnancy or after immunization.

Intraocular penetration of topically applied [14C]fosfonet sodium in rabbits

The intraocular penetration of [14C]fosfonet was studied following topical application of 25 mg of an ointment containing 5% [14C]fosfonet sodium onto the intact and abraded eyes of New Zealand white rabbits. Radioactivity penetrated rapidly through the abraded cornea and entered the anterior chamber. The concentration of fosfonet in the aqueous humor peaked at 7.2 microgram/ml by 90 min. Assuming an aqueous humor volume of 300 microliter, this level would correspond to approximately 0.2% of the applied dose. The highest concentration of fosfonet found in the abraded cornea was 0.3 microgram/mg, or 0.4% of the applied dose. The half-lives for the elimination of fosfonet from the aqueous humor and cornea were about 2.5 and 2.7 hr, respectively. The fosfonet levels in the iris were extremely low throughout the 6-hr period. The penetration of [14C]fosfonet through the intact cornea was considerably less than that found in the abraded eye. The peak concentrations of fosfonet in the aqueous humor and cornea of the intact eye were 0.26 microgram/ml and 0.02 microgram/mg, respectively, and occurred within 10 min of application of ointment.