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Biomedical subjects

L Sachs

Publications and source records attributed to L Sachs.

At least 181 records · Page 10Linked to original sources
PubMed1982

Regulation of growth and differentiation by phorbol esters and the mechanism of tumor promotion.

Our studies on the growth and differentiation of normal and malignant myeloid cells have shown that tumor-promoting, but not nonpromoting, phorbol esters can induce the production of an specifically increase cell susceptibility to the normal myeloid inducers of growth and differentiation, the macrophage- and granulocyte-inducing proteins MGI. In some clones of myeloid leukemic cells, the tumor promoters induced cell differentiation via the production of MGI. In other clones that were not inducible by adding only the tumor promoters or MGI, the tumor promoters induced differentiation by increasing cell susceptibility to externally added MGI. Normal myeloid progenitor cells, unlike leukemic cells, require MGI for cell viability and multiplication. Our studies with these normal cells have shown, that tumor promoters can also induce cell multiplication both by the induction of MGI and by increasing cell susceptibility to externally added MGI. We suggest that by the above mechanisms of inducing the production and increasing cell susceptibility to normal regulators of cell multiplication and differentiation, tumor-promoting phorbol esters can exert pleiotropic effects, the nature of these effects depending on which molecules are being regulated in the treated cells.

Animals↗
PubMed1982

Activation of normal differentiation and restoration of the normal phenotype in leukemia.

The origin and progression of cancer involves a sequence of genetic changes. However, evidence has been obtained with various types of tumors that malignant cells have not lost the genes that control normal growth and differentiation. Experiments are presented here on the induction of normal cell differentiation and restoration of the normal phenotype in myeloid leukemia by the physiological inducer of differentiation, i.e., the appropriate form of the macrophage and granulocyte that induces protein. The results of these studies can be therapeutically valuable. They have also been proposed as a general model for cell differentiation and the origin and progression of cancer.

Cell Differentiation↗
PubMed1982

Cell competence for industion of differentiation by insulin and other compounds in myeloid leukemic clones continuously cultured in serum-free medium.

Clones of myeloid leukemic cells varying in their competence for induction of differentiation have been continuously grown in serum-free medium. In the medium used, which contained transferrin, the growth rates of these cells were nearly similar to those found in serum-containing medium. The clones also maintained in this medium their competence for induction of differentiation by the normal macrophage and granulocyte differentiation-induction protein MGI-2, the steroid dexamethasone, and lipopolysaccharide. In contrast to the results with these inducters, some clones continuously cultured in a serum-free medium showed a gain of inducibility by insulin and another clone a gain of inducibility by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate in low serum and serum-free medium. Induction of differentiation by these two compounds was therefore inhibited in these clones by the presence of serum. It is suggested that serum-free medium may also show the existence of other inducers of differentiation not detected in serum-containing medium and that these results are relevant to the possible therapeutic use of compounds such as insulin for the induction of normal differentiation in leukemic cells in vivo.

Animals↗
PubMed1981

Regulation of gene expression by tumor promoters. III. Complementation of the developmental program in myeloid leukemic cells by regulating mRNA production and mRNA translation.

Regulation of gene expression has been analysed in different clones of mouse myeloid leukemic cells treated with the tumor promoter 12-0-tetradecanoyl-phorbol-13-acetate (TPA), the macrophage- and granulocyte-inducing protein MGI, and combined treatment with TPA and MGI. Two-dimensional gel electrophoresis was used to measure changes in the rate of synthesis of specific proteins and in the amount of corresponding translatable mRNAs assayed in the reticulocyte cell-free translation system. TPA induced different subsets of differentiation-associated protein changes in the different clones and the degree of response to TPA was not necessarily related to the degree of response to MGI. It is shown that TPA can induce protein changes either by inducing the synthesis of new mRNA, by increasing or decreasing the amount of pre-existing mRNA, or by modulating the translation of a constant amount of mRNA. Combined treatment with TPA and MGI resulted in an enhancement of protein changes induced by MGI or TPA alone and induced differentiation-associated protein changes not induced by either compound separately in differentiation-defective clones. This complementation of gene expression appeared to be due to each compound inducing functions not induced by the other, so that the combined treatment resulted in new gene expression. Complementation also occurred at the level both of mRNA production and of mRNA translation. It is suggested that the ability of TPA to regulate gene expression at the level of mRNA production and mRNA translation and to complement changes in gene expression induced by other compounds such as MGI are important functions for its role as a tumor promoter.

Animals↗
PubMed1981

Characterization of macrophage- and granulocyte-inducing proteins for normal and leukemic myeloid cells produced by the Krebs ascites tumor.

Medium from serum-free cultures of Krebs ascites tumor cells contains two macrophage and granulocyte inducing (MGI) activities that can act on the myeloid precursors of these hematopoietic cells. One activity, MGI-1, induced the formation of macrophage and granulocyte colonies from normal myeloid precursors. The second activity, MGI-2, induced macrophage and granulocyte differentiation in myeloid leukemic cells that no longer required MGI-1 for colony formation. The medium contained one species of MGI-1 and two species of MGI-2. One species of MGI-2, MGI-2A, copurified through five stages of purification with MGI-1, but separated from the other MGI-2 species, MGI-2B, at an early stage in purification. MGI-1, MGI-2A and MGI-2B were purified 1490, 1140 and 678-fold, respectively. When bands with biological activity gel from non-denaturing polyacrylamide gels were run on SDS-polyacrylamide gel electrophoresis, MGI-1 and MGI-2A activities were associated with similar Mr and each activity showed two bands, one of 23 000 and the other 25 000. MGI-2B activity showed one band with a Mr of 45 000. Secretion did not appear to involve glycosylation, none of the species bound to concanavalin A, soybean agglutinin, or wheat germ agglutinin agarose columns and they did not appear to contain carbohydrates. The assays for MGI-1 and MGI-2 activities were not affected by adding protease inhibitors. But MGI-2 was more readily destroyed by treatment with proteases and was more labile at high temperature and low pH than MGI-1. It is suggested that the level of cellular proteases may play a role in regulating the relative amounts of MGI-1 and MGI-2 that are present in vivo.

Animals↗
PubMed1981

Conversion of Met-enkephalin-Arg6-Phe7 by a purified brain carboxypeptidase (cathepsin A).

A carboxypeptidase A-like enzyme known as cathepsin A was purified from rat brain by extraction with Triton X-100, followed by chromatography on DEAE-Sephadex A-50 and gel-filtration. Purified enzyme was devoid of contamination of tryptic-like enzymes, by dipeptidyl carboxypeptidase (angiotensin converting enzyme) and of enkephalinnases cleaving the Tyr-Gly and Gly-Phe bonds of Met-enkephalin. Incubation of purified enzyme with Met-enkephalin-Arg6-Phe7, a naturally occurring enkephalin surrogate, was accompanied by the release of three products as detected by reverse phase HPLC. Subsequent amino acid analysis identified these as Phe, Met-enkephalin-Arg6, and Met-enkephalin, indicating cleavage at the Arg6-Phe7 and Met5-Phe6 bonds. Breakdown followed a precursor-product-relationship with the hexapeptide appearing as an intermediate and the pentapeptide as the final product. The Km for cleavage of the Arg-Phe site was 0.09 mM. Rates of cleavage of hexa- and heptapeptide accord with those found for synthetic N-protected dipeptide substrates. Cathepsin A does not act as an enkephalinase in the accepted sense, since no breakdown of Met-enkephalin was observed.

Amino Acid Sequence↗
PubMed1981

Constitutive gene expression in myeloid leukemia and cell competence for induction of differentiation by the steroid dexamethasone.

Regulation of the cytoplasmic protein changes during myeloid cell differentiation has been analyzed with two-dimensional gel electrophoresis and differentiation-defective cell mutants. The cells studied include a clone of myeloid leukemia cells (clone 11) that can be induced to differentiate to macrophages by the protein inducer MGI and the steroid dexamethasone (Dex) and mutant clones that were inducible for differentiation to macrophages by MGI but not by Dex. The mutants were not defective in the specific binding of [3H]Dex to cytoplasmic receptors or in the transport and nuclear binding of the receptor--steroid complex. The protein patterns in the mutants showed both specific constitutive protein changes and nonresponding proteins. Twenty-one percent of the Dex-induced protein changes and 2% of the MGI-induced protein changes in clone 11 were constitutively expressed in the mutants. In addition, 28% of the proteins that responded to Dex in clone 11 did not respond to Dex in the mutants, whereas only 4% of the proteins that responded to MGI in clone 11 did not respond to MGI. The higher percentage of constitutive changes was thus associated with a larger defect in induction. The proteins with an abnormal response to Dex still showed a normal response to MGI, and the constitutive changes and nonresponding proteins were different for the two inducers. It is suggested that specific constitutive protein changes expressed by the mutants produced an asynchrony in the developmental program, resulting in a defective response to Dex and to MGI, and that this may apply to other inducers and developmental programs.

Cell Differentiation↗
PubMed1981

Constitutive gene expression and restoration of the normal phenotype in malignant cells: a model for the origin and evolution of leukemia.

The change from normal to malignant cells involves a sequence of changes including specific chromosome changes. After this sequence, some leukemias can still be induced to revert with a high frequency from a malignant to a non-malignant phenotype. Results obtained from the analysis of regulation of growth and differentiation in normal and leukemic myeloid cells, restoration of the normal phenotype by induction of normal differentiation in myeloid leukemia, and the blocks in differentiation defective leukemic cell mutants have been used to propose a general model for the origin and evolution of leukemia. The model states that leukemia originates by changing specific pathways of gene expression required for growth from inducible to constitutive, in cells that can still be induced to differentiate normally by the physiological inducer of differentiation. The malignant, unlike the normal cells, then no longer require the physiological inducer for growth. This changes the requirements for growth and uncouples growth from differentiation. Constitutive expression of other specific pathways of gene expression can uncouple other controls, which then causes blocks in differentiation and the further evolution of leukemia. The existence of specific constitutive pathways of gene expression that uncouple controls in malignant cells, can also explain the origin and evolution of other types of malignancies.

Animals↗
PubMed1980

Clonal regulation of the induction of macrophage-and granulocyte-inducing proteins for normal and leukemic myeloid cells.

A cloned line of myeloid leukemic cells can be induced by the alkylating agent nitrosoguanidine for two macrophage- and granulocyte-inducing (MGI) activities. One activity, MGI-I, induced the formation of macrophage and granulocyte colonies from normal myeloblasts. Another activity, MGI-2, induced differentiation of MGI+D+ myeloid leukemic cells to macrophages and granulocytes. Experiments on the time course of induction of the two activities have shown that MGI-I was induced before MGI-2, MGI-1 was first detected in cell extracts and this was followed by detection of both activities in culture supernatants (conditioned medium). After induction with bacterial lipopolysaccharide, another inducer of both MGI activities in this clone, MGI-I was also detected before MGI-2 in cell extracts. The steroid dexamethasone, which is an effective inducer of some differentiation-associated properties in this clone, did not induce either MGI-1 or MGI-2. Studies with different clones of myeloid leukemic cells have shown a clonal variation in the induction of MGI-1 and MGI-2. Different clones were induced by nitrosoguanidine either for MGI-1 and MGI-2, for MGI-1 without MGI-2, or for neither MGI-1 nor MGI-2. None of the clones were induced for MGI-2 without MGI-1. The results indicate that the induction of MGI-1 and MGI-2 is differently regulated in the same clone, and that there is a clonal and thus presumably genetic variation in inducibility for these two activities of MGI.

Animals↗
PubMed1980

Separation of different molecular forms of macrophage- and granulocyte-inducing proteins for normal and leukemic myeloid cells.

It is shown that serum of mice treated with endotoxin (ES) contains three separable and functionally distinct forms of macrophage- and granulocyte-inducing (MGI) proteins. One form (MGI-1M) induced the formation of macrophage colonies from normal bone-marrow cells and showed on gel filtration an apparent molecular weight of 300,000; a second form (MGI-1G) induced the formation of granulocyte colonies from normal bone-marrow cells and had an apparent molecular weight of 45-100,000; and the third form (MGI-2) induced the normal differentiation of MGI+D+ myeloid leukemic cells to macrophages and granulocytes and had an apparent molecular weight of 28,000. Studies on the time course of the decrease of these three activities in ES have indicated that MGI-2 was more readily inactivated in vivo than MGI-1M and MGI-1G. The MGI-1M in ES isolated after gel filtration was completely neutralized by an antiserum to MGI-1 from mouse L-cells, whereas the isolated MGI-1G and MGI-2 were not affected by this antiserum. Gel filtration under dissociating conditions (6 M guanidinium chloride) resulted in a reduction of the apparent molecular weights of MGI-1M from 300,000 to 42,000, and of MGI-1G from 45-100,000 to 28,000, while it produced no change in the 28,000 apparent molecular weight of MGI-2. Similar studies with conditioned medium produced in vitro from mouse lung and peritoneal macrophages showed that in these conditioned media, MGI-1 (both G and M) in the native form had an apparent molecular weight of 41,000 and MGI-2 of 24,000, and that both MGI-1 and 2 had an apparent molecular weight of 24,000 under dissociating conditions. The results indicate that MGI-1 exists in serum in vivo and in these conditioned media as aggregated proteins, whereas MGI-2 does not, and that macrophages and lung tissue are not the only source of the MGI proteins found in ES. It is suggested that all three forms of MGI activity are derived from one precursor protein; that only the MGI-2 form assayed on leukemic cells should be used for treatment based on the induction of normal cell differentiation in myeloid leukemia; and that MGI-2 may serve as a survey mechanism for inducing differentiation in myeloid leukemic cells that have lost their responsiveness to the MGI-1 molecules that control the viability, proliferation and differentiation of normal myeloblasts.

Animals↗