Regulation of the proteinase B structural gene PRB1 in Saccharomyces cerevisiae

The expression of PRB1, the gene that encodes the precursor to the soluble vacuolar proteinase B (PrB) in Saccharomyces cerevisiae, is regulated by carbon and nitrogen sources and by growth phase. Little or no PRB1 mRNA is detectable during exponential growth on glucose as the carbon source; it begins to accumulate as cells exhaust the glucose. Previous work has shown that glucose repression of PRB1 transcription is not mediated by HXK2 or by the SNF1, SNF4, and SNF6 genes (C. M. Moehle and E. W. Jones, Genetics 124:39-55, 1990). We analyzed the effects of mutations in the MIG1, TUP1, and GRR1 genes on glucose repression of PRB1 and found that mutations in each partially alleviate glucose repression. tup1 and mig1 mutants fail to translocate all of the Prb1p into the lumen of the endoplasmic reticulum. A screen for new mutants revealed mutations in MIG1 and REG1, genes already known to regulate glucose repression, as well as in three new genes that we have named PBD1 to PBD3; all cause derepressed expression. Mutations that result in failure to completely derepress PRB1 were also identified in two new genes, named PND1 and PND2. Good nitrogen sources, like ammonia, repress PRB1 transcription; mutations in URE2 do not affect this response. Derepression upon transfer to a poor nitrogen source is dependent upon GLN3.

Serum antibodies reactive with eye muscle antigens and the TSH receptor in a euthyroid subject who developed ophthalmopathy and Graves' hyperthyroidism

Serum antibodies reactive with eye muscle autoantigens, in particular a 64-kDa protein that is also expressed in the thyroid, and the TSH receptor, are associated with the ophthalmopathy that occurs in about 50% of patients with Graves' hyperthyroidism. We have had the opportunity to study a euthyroid, apparently normal, 35-year-old woman with a family history of thyroid autoimmunity and "colitis" but no clinical or biochemical evidence for thyroid disease or ophthalmopathy, who developed Graves' hyperthyroidism and ophthalmopathy together 18 months later. Serum taken when the patient was first seen was positive for antibodies reactive with (i) 9 different eye muscle proteins ranging in size from 15 to 130 kDa, notably those of 64, 55, and 50 kDa, by immunoblotting with eye muscle membranes, (ii) eye muscle and Müller's muscle cell membrane antigens in antibody-dependent cell-mediated cytotoxicity (ADCC), (iii) an eye muscle cytoplasmic antigen in indirect immunofluorescence, and (iv) the TSH receptor as measured in a radioreceptor binding inhibition assay. When she developed Graves' disease, serum concentration of antibodies to the 55-kDa protein had decreased from +2 to +/-, those reactive with other eye muscle antigens had not changed significantly, and TSH receptor antibodies had increased 3-fold. This case report suggests that antibodies reactive with eye muscle antigens and the TSH receptor are markers of the ophthalmopathy and able to predict its development in predisposed subjects. The significance of these findings needs to be confirmed in a prospective study of first-degree relatives of patients with thyroid-associated ophthalmopathy and patients with Graves' hyperthyroidism without eye signs.

Antibody-dependent cell-mediated cytotoxicity against orbital target cells in thyroid-associated ophthalmopathy and related disorders; close relationship between serum cytotoxic antibodies and parameters of eye muscle dysfunction

We have carried out tests for antibody-dependent cell-mediated cytotoxicity (ADCC) against extra ocular muscle (EOM), Müller's muscle, orbital fibroblasts and skeletal muscle in patients with thyroid-associated ophthalmopathy (TAO) and related eye disorders. Cytotoxicity was measured as lactate dehydrogenase (LDH) release and results expressed as % cytotoxicity. Tests were positive, with EOM cells, in 65% of patients with TAO, 75% with ocular myopathy, a variant of TAO in which periorbital inflammation is minimal, 50% with euthyroid Graves' disease defined as ophthalmopathy associated with subclinical thyroiditis and in 50% of patients with stable lid lag and retraction but no other signs of progressive ophthalmopathy, but in only 13% of patients with Graves' hyperthyroidism without ophthalmopathy, 10% with Hashimoto's thyroiditis and 14% of patients with other thyroid disorders. Tests were positive, with Müller's muscle cells, in 40% of patients with TAO, 25% with ocular myopathy, 40% with euthyroid Graves' disease, 44% with lid lag, 19% with Graves'hyperthyroidism, 50% with Hashimoto's thyroiditis and in 37.5% of patients with other thyroid disorders. When skeletal muscle cells were used as target, tests were positive in 13% of patients with TAO, 31% with lid lag, 25% with Graves' hyperthyroidism and in 29% of patients with Hashimoto's thyroiditis, but in no patient with euthyroid Graves' disease or other thyroid disorders. Tests were negative in all patients and normals tested when EOM-derived fibroblasts were used as targets in ADCC. A significant positive correlation between % cytotoxicity against EOM cells and the severity of the eye muscle dysfunction expressed as an eye muscle index, was observed in patients with TAO. There was a significant negative correlation between the duration of eye disease and % cytotoxicity against EOM cells, suggesting higher titers of cytotoxic antibodies in the early stages of TAO. There was no correlation between % cytotoxicity and serum level of anti-TSH receptor antibodies, measured in a radioreceptor assay. These findings suggest that autoimmunity against Müller's muscle may play a role in the pathogenesis of persistent lid lag and retraction. The nature of the EOM and Müller's muscle autoantigens recognized by cytotoxic antibodies in the serum of patients with TAO and related eye disorders is unknown.

Significance of tissue specific and tissue non specific autoimmune reactions of Graves' disease

The relationship between the many immunologic abnormalities demonstrated in the peripheral blood of patients with Graves' disease (GD) and the broad spectrum of clinical features with which patients may present has not yet been addressed in detail. In this review we examine the evidence to support the notion that GD could be considered a multi-system autoimmune disorder in which tissue damage is restricted to the thyroid gland, connective tissue of the skin and orbit, extra-ocular and other skeletal muscles and, possibly, the lacrimal glands. Apart from the well recognized reactions of autoantibodies and sensitized T lymphocytes with epitopes on the thyroid specific TSH receptor, thyroid peroxidase and thyroglobulin, in patients with hyperthyroidism, there is also good evidence for autoantibody and, to a lesser extent, T lymphocyte reactivity with several eye muscle, other skeletal muscle and connective tissue, antigens in patients with ophthalmopathy, systemic myopathy, dermopathy and acropachy. There is also some evidence for immunoreactivity against lacrimal gland antigens in patients with ophthalmopathy associated with other features of GD. There are, in addition, a variety of organ non-specific reactions in GD; antinuclear antibodies are detected in serum from about one-third of patients with hyperthyroidism and ophthalmopathy, while from 5% to 10% have antibodies reactive with several other ubiquitous tissue proteins. Cloned proteins which are autoantigenic in some patients with hyperthyroidism or Hashimoto's thyroiditis and ophthalmopathy include collagen XIII, nebulin, the calcium binding protein calmitine, and the Mac-II antigen. All antibodies reactive with eye muscle antigens, except the 64 kDa protein which is also expressed in the thyroid, cross react with the same, or a related, protein in other skeletal muscle. Future research should focus on the underlying mechanisms for this broad loss of tolerance to self antigens and the effect of environmental factors such as stress, radioiodine and viral infection of the thyroid gland and other target tissues, in precipitating disease.

Failure to demonstrate cell-mediated immunity to orbital tissue antigens and epitopic fragments of a 64 kDa protein in the majority of patients with thyroid-associated ophthalmopathy

We have studied a possible role of T cell sensitization to eye muscle antigens in patients with thyroid-associated ophthalmology (TAO). Peripheral blood mononuclear cell (PBMC) proliferation in response to crude porcine orbital tissue antigens, partially purified porcine eye muscle membrane proteins and predicted epitopic fragments of the recombinant 64 kDa protein 1D, was determined in patients with TAO and thyroid autoimmunity without eye disease. When membrane and cytosol fractions were used as antigen PBMC from 43% of patients with TAO but only 12.5% of normal subjects were responsive to a crude orbital connective tissue membrane fraction, although this difference was not significant. We were unable to demonstrate specific recognition of partially purified eye muscle membrane fractions; although most of the fractions tested were occasionally recognized by T cells from patients with ophthalmopathy, this was also the case for patients with autoimmune thyroid disease without ophthalmopathy and normal subjects. We did not clearly identify epitopic sequences within the 1D protein, most of the predicted peptides tested being recognized not only by T cells from a small proportion of patients with TAO, but also by those from some patients with autoimmune thyroid disease without ophthalmopathy and normal subjects. It is noteworthy however that approximately 22% of TAO patients, but no normal subjects, were positive to one or more of three peptides, suggesting that reactivity to the 1D protein may play a role in the pathogenesis of the eye disorder in some patients with TAO. The inconsistent and generally low T cell responses to crude and purified antigens noted in a few patients with TAO could be explained by low numbers of specifically sensitized lymphocytes in peripheral blood.

Should Graves' disease be considered a collagen disorder of the thyroid, skeletal muscle and connective tissue?

Graves' disease comprises hyperthyroidism, ophthalmopathy, pretibial myxedema and acropachy, which occur separately or in various combinations. We have used the indirect immunofluorescence test to investigate reactivity of sera from patients with autoimmune thyroid disorders with and without ophthalmopathy, with porcine extra ocular muscle (EOM) and control tissue substrates. Sera from 75% of patients with Graves' hyperthyroidism (GH) and ophthalmopathy, which we call thyroid-associated opthalmopathy (TAO), contained one or more antibodies reactive with EOM compared to 32% of those with GH without the eye disorder, 41% of patients with Hashimoto's thyroiditis (HT), and 16% of normals. Antibodies reactive with an EOM connective tissue antigen(s), seen as fluorescence of the interstitium and endomysium, were found in sera from 10% of patients with TAO and 16% of those with GH, but not from any patient with HT or normal subject. Similar patterns of connective tissue reactivity were also found in lacrimal gland, skeletal muscle, kidney and salivary gland. Antinuclear antibodies were detected in sera from 31% of patients with TAO, but from only 8% with HT, in no patient with GH and in only 3% of normal subjects. The most common pattern was a fine speckled fluorescence, found in 45% of sera, consistent with reactivity against the Sm antigen or nuclear RNP. The finding of a high prevalence of ANA and, less often, anti-connective tissue antibodies in patients with thyroid autoimmunity and ophthalmopathy, is consistent with Graves' disease being a "collagen-like disorder". The reason why inflammation and resulting tissue damage is limited to the thyroid, connective tissue of the skin and orbit, skeletal muscle and, possibly, the lacrimal gland, is unclear. One possibility is cross reaction of ANA with tissue specific membrane proteins in these sites. The extent of immunologic abnormalities, and the resulting clinical features, in patients with Graves' disease may reflect the severity of a putative defect in immune regulation.

New assays for the measurement of serum antibodies reactive with eye muscle membrane antigens confirm their significance in thyroid-associated ophthalmopathy

Although sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting are widely used to detect serum antibodies in patients with autoimmune disorders, this procedure unfolds and denatures proteins and may alter antibody binding sites. We have used nondenaturing methods for the purification of a 64-kDa eye muscle (EM) membrane antigen associated with thyroid-associated ophthalmopathy (TAO). Pig EM membrane proteins were prepared from crude homogenates by high-speed centrifugation and solubilized by hand homogenization. The 64-kDa protein was further purified by isoelectric focusing performed in the absence of SDS, detergents, reducing agents, and urea. Sera from patients with active TAO of recent onset and thyroid autoimmunity without ophthalmopathy were tested for reactivity against purified native 64-kDa protein in immunoblotting. Tests were positive in 64% of patients with TAO, in 37.5% of those with Graves' hyperthyroidism without eye disease, in 11% of patients with Hashimoto's thyroiditis without eye disease, and in 13% of normal subjects. Many of the same sera were also tested for cytotoxic activity against human EM cells in an antibody-dependent cell-mediated cytotoxicity (ADCC) assay. ADCC tests were positive in 69% of patients with TAO but in no normal subject. The specificity and sensitivity of these two tests in TAO surpass those for all other published results for orbital tissue reactive autoantibodies. Although there was a tendency for a relationship between reactivity to the 64-kDa protein and cytotoxic activity against EM cells in ADCC there were many exceptions and overall the relationship between the two tests was not significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Native gel electrophoresis and isoelectric focusing of a 64-kilodalton eye muscle protein shows that it is an important target for serum autoantibodies in patients with thyroid-associated ophthalmopathy and not expressed in other skeletal muscle

Although sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting are widely used to detect serum antibodies in patients with autoimmune disorders, this procedure unfolds and denatures proteins and may alter antibody-binding sites. We have used a gentle protocol for the preparation and purification of a 64-kilodalton (kDa) eye muscle (EM) membrane antigen associated with thyroid-associated ophthalmopathy (TAO) for use as antigen in immunoblotting. Pig EM membrane proteins were prepared from crude homogenates by high speed centrifugation and solubilized by hand homogenization. These native membrane proteins (NMprot) were then electrophoresed on an 8.5% polyacrylamide gel in the absence of SDS, reducing agents, or urea, and proteins from individual bands were eluted, applied to standard SDS-PAGE, and immunoblotted with selected TAO patient sera. A prominent 64-kDa protein, present in most of the bands, was recognized by autoantibodies in sera from 35% of the patients with TAO and 47% of those with Graves' hyperthyroidism without evident ophthalmopathy, but in only 4% of normal subjects. To further purify the 64-kDa protein and increase the sensitivity of immunoblotting, NMprot were separated by isoelectric focusing (IEF) in the absence of SDS, reducing agent, and urea. The 64-kDa protein appeared mainly in IEF fraction 7 and had an isoelectric point of 6.1-6.2. Similar results were found for a human EM protein of 64 kDa. Sera from groups of patients and normal subjects were tested in immunoblotting against a pig EM 64-kDa protein prepared from NMprot and purified in IEF. Tests were positive in 67% of patients with TAO, in 37.5% of those with Graves' hyperthyroidism without eye disease, in 11% of patients with Hashimoto's thyroiditis without eye disease, and in 9% of normal subjects. The 64-kDa protein was not found in other skeletal muscle. The demonstration that a native 64-kDa protein that is specifically targeted by autoantibodies in the serum of patients with TAO is expressed in EM, but not other skeletal muscle, greatly enhances its possible significance in the pathogenesis of this eye disorder.

The ocular muscle cell is a target of the immune system in endocrine ophthalmopathy

The exact pathogenic mechanism of thyroid-associated ophthalmopathy (TAO) remains unclear, and extensive studies on this disorder have resulted in often conflicting data. Well-known technical difficulties including the limited access to orbital tissues from patients with active and early disease, lack of an animal model and poor reproducibility of some of the immunological techniques used are in part responsible for this confusing situation. Despite this there is considerable evidence for eye muscle (EM) tissue involvement in the autoimmune reactions of TAO. Although the primary EM antigen(s) recognized by immunocompetent cells and autoantibodies has not been definitely identified, some good candidates, among them a membrane antigen of 64 kD which is also expressed in the thyroid, have been partially characterized. While it is unclear which component of the autoimmune reaction against EM-humoral or cell mediated-plays the more important role, autoantibodies seem to be responsible at least in part for the clinical features of the eye disorder. On the other hand, the orbital connective tissue (OCT) cells, especially the fibroblasts surrounding the EM fibers, seem to be extremely sensitive to stimulation by cytokines and other soluble proteins and immunoglobulins released in the course of an immune reaction in the muscle cells. Fibroblasts secrete large amounts of glycosaminoglycans and also participate in maintaining the autoimmune reaction. It seems likely that the EM is the main and primary target of the orbital autoimmune process whereas inflammation of the OCT is probably secondary.