The specific and endogenous mitotic inhibitor of lymphocytes (chalone)

Novel lymphocyte growth-inhibiting tripeptide: N-acetyl-glu-ser-GlyNH(2)

The limited and predetermined number of cells that constitutes an organ or specialized cell population is to all appearances regulated according to a negative feedback principle involving growth inhibitors with sufficient tissue specificity. To find growth-inhibiting factors in lymphoid cells, we followed established purification procedures and assays. We found a single-peak fraction in water extracts of dog spleen homogenates that inhibited proliferation of Molt (T cell) lymphoma cells at low concentrations in vitro, with no significant effect on a B cell lymphoma cell line (Ramos). C-terminal amino acid sequencing and MS analysis showed the factor to be a tripeptide: N-acetyl-Glu-Ser-GlyNH(2). Treatment with a synthetic tripeptide with the structure N-acetyl-Glu-Ser-GlyNH(2) decreased the number of cell doublings of Molt cells. The peptide also delayed cell flux at the G(2)-M transition of the cell cycle, while incorporation of tritiated thymidine was not altered at the examined time points in this cell line. However, DNA synthesis in PPD-stimulated normal human lymphocytes was significantly inhibited and with a bell-shaped dose-response curve.

Serum proteins of mice with splenomegaly

Our earlier serum electrophoretic study in 'lethargic' mutant mice showed that the quantity of protein in 1 band is inversely related to the size of the spleen. In this study, we demonstrate that this protein band almost entirely disappears in mice with splenomegaly following spontaneous skin infection. The results suggest that this serum protein may play a role in regulating growth of lymphoid tissue.

Partial purification, physicochemical characterization and biological function of a rosette-decreasing factor (RDF) extracted from guinea pig thymus

A factor that decreases rosette formation between guinea pig T-cells and rabbit red blood cells (RRBC) was extracted from the thymus of the guinea pig. The active factor could be extracted from the spleen as well as the thymus, but not from the liver or kidney. The active factor of the thymic extract was found in the precipitates produced by 80% saturated ammonium sulfate and it was separated from the water-soluble fraction of the precipitates. The molecular weight of the partially purified substance was estimated to range between 10,000 and 30,000 by filtration through a diaflow membrane. From the studies on physicochemical characterization, it might be a heat-resistant basic peptide probably bound to a ribonucleotide moiety. This factor reduced rosette formation between RRBC and guinea pig T-cells, but did not reduce erythrocyte-antibody-complement rosette formation. This factor also inhibited mitogen (concanavalin A, phytohemagglutinin-P)- induced DNA synthesis of guinea pig lymphocytes and antigen-induced DNA synthesis of sensitized guinea pig lymphocytes.

Thymus derived inhibitor of lymphocyte proliferation. I. Isolation and assessment of tissue specificity

Preparations from bovine thymus tissue were analyzed for their inhibitory effects during in vitro lymphocyte proliferation. The results indicate that these preparations strongly inhibit DNA synthesis in stimulated human peripheral lymphocytes, bone marrow cells, thymocytes and lymphoblastoid cells. This inhibition was dose-dependent and not due to cytotoxicity of the preparations. No inhibition was found of the spontaneous proliferation of HeLa cells and human fibroblasts indicating that the inhibitory effect was specific for proliferating lymphocytes. Control preparations from bovine liver or kidney did not show any suppression in the test systems used.

Screening for specific calf thymus inhibitors (chalones) of T-lymphocyte proliferation

Using agar colony assays with truly proliferating stimulated human T-lymphocytes and mouse granulocytes, two ultrafiltrate fractions were obtained from calf thymus which preferentially inhibited lymphocyte colony growth: Fraction I in the molecular range 1000-10,000 proved to be stable upon heating, prolonged storage and lyophilization, whereas Fraction II in the molecular range 10,000-30,000, was found to be unstable. Fraction I was also extracted with Tween 80 and cetyltrimethylammonium bromide. Chromatography of Fraction I on Biogel P6 and DEAE-cellulose further increased its specificity of inhibition for lymphocyte colony growth and revealed an estimated molecular weight of below 1400. Its inhibitory activity was found to be reversible and unlikely to result from spermine. Thus the properties of fraction I meet the requirements of a T-lymphocyte chalone as an endogenous non-cytotoxic and reversible inhibitor of T-lymphocyte proliferation.

The relevance of growth control (chalones) to the aging process

A large amount of data suggests that a wide variety of cells and tissues contain cell-specific endogenous inhibitors of mitosis which are non species-specific. Increasingly, it appears that these chalone inhibitors are actually relatively small polypeptides capable of complexing with large molecular weight anionic molecules. The purification and chamical characterization of these inhibitors has been rendered extraordinarily difficult and the results have been very slow in forthcoming because of this ability to form complexes with anionic polyelectrolytes. Our recent understanding of this behavior should markedly accelerate our understanding and knowledge of chalone biochemistry in the future. If, in fact, chalones are ubiquitously important to the control of cell proliferation, then they will be important to our understanding of the development of post-mitotic cells and to our concepts of programmed senescence; both in turn might be important to our knowledge of the aging process.

Purification of immunosuppressive factors extracted from bovine spleen (lymphoid chalone)

A low molecular weight immunosuppressive factor FA which is able to reduce the blastic transformation capacity of lymphoid cells from treated mice has been characterized. It was prepared from a bovine spleen acetone powder and found to be associated partly with high molecular weight carriers in the form of an active complex characterized previously as part of a 'lymphoid chalone' fraction. FA may be obtained by selective ultrafiltration of F followed by P-2 Biogel chromatography of the ultrafiltrate. Thymidine, deoxyinosine and deoxycytidine have been identified as the major constituents of FA by mass spectrometry, ultraviolet absorption data and thin layer chromatography. However, none of these nucleotides has the biological activity of FA.

The effects of fractions (chalones) obtained from lymphoid organs on lymphocyte proliferation in vitro

Aqueous extracts of lymphoid organs were prepared and fractionated by means of gel filtration, ion exchange chromatography, and isoelectric focusing. A protein-containing fraction with a molecular weight of approximately 80,000--90,000 and isoelectric points of 7.6 and 5.3--6.2 was isolated and shown to inhibit reproducibly both thymidine incorporation and proliferation of concanavalin A-stimulated mouse spleen lymphocytes in vitro. This effect appeared specific since proliferation of mastocytoma P-815 and leukemia L-1210 cells remained unaffected. A small molecular weight fraction (500 to 10,000 daltons) was also found to inhibit lymphocyte proliferation in vitro but was without apparent specificity for cell type.

Lymphocyte and fibroblast chalones: some chemical properties

Experiments with lymphocyte and fibroblast chalones indicate that they are complexed strongly with RNA in tissue extracts; have a molecular weight of less than 10,000 and more than 1,000 daltons, and probably about 5,000 daltons; are strongly cationically charged; and contain mannose and perhaps other carbohydrates.

Inhibition of agar colony formation by partially purified granulocyte extracts (chalone)

Granulocytic extracts (GE) of different sources, presumably containing the granulocytic chalone, were prepared in different laboratories and purified to some extent. They specifically inhibited the formation of granulocyte and macrophage colonies in agar. The effect was however most pronounced on granulocyte and mixed granulocyte-macrophage colonies, and less on macrophage types. Addition of GE to bone marrow cells at the time of plating in agar, as well as short incubation of the cells together with GE prior to plating, inhibited subsequent colony formation. The inhibitory effect could easily be reversed by washing the cells with an excess of medium prior to plating during the first hour of preincubation, but not after five hours. Increasing the doses of colony stimulating activity (CSA) (at low doses of GE) released the inhibitory effect, but not at high doses of GE. The inhibitory effect of GE on colony formation was dose dependent down to almost 100% inhibition. No apparent cytotoxic effect of GE on bone marrow cells could be found and lymphoblastic cells were not inhibited. Extracts containing a specific inhibitor of erythropoiesis (EIF) stimulated myelopoietic colony formation in agar.

Ehrlich ascites tumor (EAT) chalone effects on nascent DNA synthesis and DNA polymerase alpha and beta

EAT chalone effects on nascent DNA synthesis and DNA polymerase were examined. Concentration related inhibition of 3H-thymidine (3H-TdR) incorporation into EAT cell DNA was noted over a chalone range of 50-200 mug/ml. RNA synthesis was not affected, but protein synthesis decreased an average of 82% during 3 hr. Nascent DNA pulse-labeled for 2 min was normally incorporated into bulk DNA in the presence of chalone, but crude alpha- and beta-polymerase activities were inhibited. Crude DNA polymerase for C3H mouse kidney and spleen was also partially inhibited by EAT chalone, suggesting non-specific inhibition of DNA polymerase. Preincubation studies of chalone with crude EAT DNA polymerase or 'gapped' DNA primer had no effect on chalone activity. Chalone may control mitotic activity by inhibiting alpha- and beta-polymerase activity, thereby decreasing nascent DNA synthesis. Nascent DNA is incorporated normally into bulk DNA in the presence of chalone, indicating the DNA ligase is not inhibited.

[Tissue specific inhibition of lymphocyte proliferation by spleen extract (lymphocyte chalone) (author's transl)]

Aqueous spleen extracts were purified using acetone precipitation, membrane filtration, affinity chromatography, and dialysis. These extracts were able to inhibit thymidine incorporation into lymphoid cells (MKT-CH and PHA-stimulated lymphocyte cultures). They did not influence non lymphoid tissue (melanoma cells Mel Ei 78 and Ehrlich ascites cells). The inhibition was reversible and the purified extracts were not cytotoxic. The extracts correspond to a chalone. Their importance for prevention of graft versus host reaction and for treatment of lymphoproliferative diseases is discussed.

Cytotoxic effects on splenic ultrafiltrates upon leukaemic lymphocytes

Ultrafiltrates from spleen inhibited both DNA synthesis and the proliferation of normal lymphocytes stimulated inculture from both mouse and man without apparent cytotoxicity. However, the same doses of this spleen ultrafiltrate will kill up to two-thirds of the leukaemic lymphoblasts from both mouse and man after 24 h incubation. This unique lymphocytotoxic effect could also be demonstrated on fresh primary cultures of leukaemic lymphocytes and was highly effective on slowly growing established cell lines under crowd culture conditions. Furthermore. ultrafiltrated thymus extract did not affect the DNA synthesis rates of the viability of NC-37 lymphoblasts, which have B cell characteristic. Thymus extract was cytotoxic to Molt cells, which have T cell characteristics.