Stefan Bodmer

Complementary DNA for human glioblastoma-derived T cell suppressor factor, a novel member of the transforming growth factor-beta gene family.

Human glioblastoma cells secrete a peptide, termed glioblastoma‐derived T cell suppressor factor (G‐TsF), which has suppressive effects on interleukin‐2‐dependent T cell growth. As shown here, complementary DNA for G‐TsF reveals that G‐TsF shares 71% amino acid homology with transforming growth factor‐beta (TGF‐beta). In analogy to TGF‐beta it is apparently synthesized as the carboxy‐terminal end of a precursor polypeptide which undergoes proteolytic cleavage to yield the 112 amino‐acid‐long mature form of G‐TsF. Comparison of the amino‐terminal sequence of G‐TsF with that of porcine TGF‐beta 2 and bovine cartilage‐inducing factor B shows complete homology, which indicates that we have cloned the human analogue of these factors. It is tempting to consider a role for G‐TsF in tumor growth where it may enhance tumor cell proliferation in an autocrine way and/or reduce immunosurveillance of tumor development.

T cell suppressor factor from human glioblastoma cells is a 12.5-kd protein closely related to transforming growth factor-beta.

T cell suppressor factor produced by human glioblastoma cells inhibits T cell proliferation in vitro and more specifically interferes with interleukin‐2 (IL‐2)‐dependent T cell growth. Here we report the purification of this factor from conditioned medium of the human glioblastoma cell line 308. Amino‐terminal sequence analysis of the 12.5‐kd protein demonstrates that eight out of the first 20 amino acids are identical to human transforming growth factor‐beta. Purified glioblastoma‐derived T cell suppressor factor and transforming growth factor‐beta from porcine platelets inhibit both IL‐2‐induced proliferation of ovalbumin‐specific T helper cells and lectin‐induced thymocyte proliferation with similar specific activities. If released by glioblastoma cells in vivo, the factor may contribute to impaired immunosurveillance and to the cellular immunodeficiency state detected in the patients.

Transforming growth factor-beta bound to soluble derivatives of the beta amyloid precursor protein of Alzheimer's disease.

Transforming growth factors beta (TGF beta) are multifunctional polypeptides that participate in regulation of growth, differentiation and function of many cell types. The mature TGF beta molecule is a 25 kDa protein composed of two 12.5 kDa monomers linked by disulfide bonds. Human glioblastoma cells secrete biologically active TGF beta 2. Here we report that in addition to the free form of TGF beta 2, a stable complex between a approximately 110 kDa binding protein and TGF beta 2 was isolated from glioblastoma cell supernatant. This binding protein was purified and was found to show sequence identity to part of the beta amyloid precursor protein (beta APP), to be specifically labeled by several different antisera to beta APP, and to be affinity labeled with TGF beta by crosslinking. The complex formation between TGF beta and beta APP may have important implications in regulation of biological activity of the two proteins and in delivery or clearance of TGF beta and beta APP in the brain and other compartments.

Human glioblastoma cell derived transforming growth factor-β2: evidence for secretion of both high and low molecular weight biologically active forms

Transforming growth factors beta (TGF-beta) form a family of multifunctional polypeptides which in the active dimeric forms have a molecular weight of 25 kDa. Human glioblastoma cells secrete immunosuppressive TGF-beta consisting mostly of TGF-beta 2 rather than TGF-beta 1. The results shown here demonstrate that in addition to the mature 25 kDa form of TGF-beta 2, glioblastoma cells release a biologically active high molecular weight form of TGF-beta 2 which suppresses the interleukin-2-dependent growth of a T helper cell line. The high and low molecular weight forms of TGF-beta 2, separated by polyacrylamide gel electrophoresis under non-reducing conditions, can be eluted from the gel retaining their immunosuppressive activity. Similar results were obtained when analyzing supernatants of Chinese hamster ovary (CHO) cells transfected with a cDNA for TGF-beta 2. Both the high molecular weight form (90-120 kDa) and the 25 kDa form can be immunoprecipitated with a monoclonal antibody against mature native TGF-beta 2 and are detectable in tumor cyst fluid from glioblastoma patients. Taken together, the data provide evidence that in addition to the well-characterized 25 kDa form of TGF-beta 2 glioblastoma cells also secrete a high molecular weight form (90-120 kDa) with the biological characteristics of TGF-beta 2.

Analysis of nucleotides bound to the ATP synthetase from spinach chloroplasts isolated under different conditions

The total amount of bound adenine nucleotides in the coupling factor isolated from spinach chloroplasts and its distribution on AMP, ADP and ATP was analyzed after various incubation conditions. During purification of the coupling factor, the distribution of AMP, ADP and ATP is not altered. The coupling factor from deenergized membranes contains approximately 1 ADP, less than 1 ATP, and small amounts of AMP. During phosphorylation the pattern is changed and ATP becomes the dominant species. When exogenous ADP is lacking, phosphate is readily incorporated into ATP. Inhibition of adenylate kinase by AP5A does not change the distribution pattern of the adenine nucleotides. The distribution pattern shows no integer numbers for the different nucleotides, suggesting that the coupling factor is present in different states in a statistical distribution.

The glioblastoma cell derived T cell suppressor factor (G-TsF): Sequence analysis and biological mechanism of G-TsF

Some patients with motor neuron disease (MND) have plasma cell dyscrasi~ (PCD). It is not known whether the M-proteins are responsible for the neurological disorder. However IgM M-proteins from two of these patients immunoreact specifically with epitopes shared by the gangliosides GM 1 and GDIb. Although these gangliosides are widely distributed in the nervous system, GM 1 is concentrated at the external surface of the synaptlc terminals, and GDIb binds tetanus toxin, which is selectively taken up and retrogradely transported by motor nerves. Therefore M-proteins binding to this epitope could preferentially affect motor neurons.

Studies on the Iron-Binding Site of Bacterial Reaction Centers

Most reaction center preparations from photosynthetic bacteria are usually isolated as a complex of three polypeptides (H, H and L) and contain, besides other cofactors, nonheme iron in stoichiometric quantities. The exact structural arrangement of the various components of the reaction center is not yet established. However subunit H could be separated from the M-L complex without loss of photochemical activity (Okamura et al., 1974). Marinetti et al. (1979) showed that the primary quinone binding site is located on or close to the M subunit, whereas Gimenez-Gallego et al. (1982) found that even subunit L alone retains the characteristic absorption spectrum and the photochemical activity. We found no report so far on the binding site of the nonheme iron and therefore decided to study the iron binding site of the reaction center of Rho do spirillum rubrum using radioactive labeling and electrophoretic techniques.