Bone marrow stromal proteoglycan heterogeneity: phenotypic variability between cell lines and the effects of glucocorticoid

Hematopoiesis in vivo is dependent upon the interaction of hematopoietic stem cells with a complex microenvironment, of which stromal proteoglycans are an important functional component. Certain bone marrow stromal cell lines provide a microenvironment that supports hematopoiesis in vitro, a function that is dependent upon glucocorticoid supplementation. Proteoglycan synthesis in the hematopoietic-supportive D2XRII, Bl6 and 14F1 bone marrow stromal cell lines was studied by 35S-sulfate precursor labelling and ion-exchange separation, followed by isopyknic CsCl density centrifugation and gel filtration HPLC. The effects of glucocorticoid were also investigated. A similar pattern of proteoglycan heterogeneity was observed in all three cell lines, although there was considerable quantitative variation. All cultures synthesized three species of chondroitin/dermatan sulfate (CS/DS) proteoglycans: DS1, excluded from a Bio-Sil TSK-400 HPLC column, and DS2, eluting at Kd = 0.31, were present mainly in the culture media. The smallest (DS3) eluted at Kd = 0.63 and was present mainly in the cell layers. CS/DS species were the major proteoglycans in all cultures. Hydrocortisone-free cultures also synthesized heparan sulfate (HS) proteoglycans, including a cell-associated form (HS1), partially excluded from the TSK-400 column, and a secretory form (HS2), eluting at Kd = 0.15. D2XRII cells also secreted an apparently-unique, high-density proteoglycan, Kd = 0.65, into the culture medium. Hydrocortisone at 10(-6) M virtually abolished HS proteoglycan synthesis in all three cell lines, and altered the pattern of CS/DS proteoglycans in the culture media, increasing the quantity of DS1 and DS3, and reducing the quantity of DS2.     

Phylogenetic distribution in the genus Mus of t-complex-specific DNA and protein markers: inferences on the origin of t-haplotypes

We have examined the phylogenetic distribution of two t-specific markers among representatives of various taxa belonging to the genus Mus. The centromeric TCP-1a marker (a testicular protein variant specific for all t-haplotypes so far studied) has also been apparently detected in several non-t representatives of the Mus IVA, Mus IVB, and probably M. cervicolor species. By contrast, a t-specific restriction- fragment-length polymorphism allele (RFLP) of the telomeric alpha- globin pseudogene DNA marker alpha-psi-4 was found only in animals belonging to the M. musculus-complex species either bearing genuine t- haplotypes or, like the M. m. bactrianus specimen studied here, likely to do so. This t-specific alpha-psi-4 RFLP allele was found to be as divergent from the RFLP alleles of the latter, non-t, taxonomical groups as it is from Mus 4A, Mus 4B, or M. spretus ones. These results suggest the presence of t-haplotypes and of t-specific markers in populations other than those belonging to the M. m. domesticus and M. m. musculus subspecies, implying a possible origin for t-haplotypes prior to the radiation of the most recent offshoot of the Mus genus (i.e., the spretus/domesticus divergence), some 1-3 Myr ago.      

Radiosensitivity of human bone marrow granulocyte-macrophage progenitor cells and stromal colony-forming cells: effect of dose rate

Study of the radiation biology of human bone marrow hematopoietic cells has been difficult since unseparated bone marrow cell preparations also contain other nonhematopoietic stromal cells. We tested the clonogenic survival after 0.05 or 2 Gy/min X irradiation using as target cells either fresh human bone marrow or nonadherent hematopoietic cells separated from stromal cells by the method of long-term bone marrow culture (LTBMC). Sequential nonadherent cell populations removed from LTBMC were enriched for hematopoietic progenitors forming granulocyte-macrophage colony-forming unit culture (GM-CFUc) that form colonies at Day 7, termed GM-CFUc7, or Day 14 termed GM-CFUc14. The results demonstrated no effect of dose rate on the D0 or n of fresh marrow GM-CFUc (colonies greater than or equal to 50 cells) after plating in a source of their obligatory growth factor, colony-stimulating factor (CSF) (GM-CFUc7 irradiated at 2 Gy/min, D0 = 1.02 +/- 0.05, n = 1.59 +/- 0.21; at 0.05 Gy/min, D0 = 1.07 +/- 0.03, n = 1.50 +/- 0.04; GM-CFUc14 at 2 Gy/min, D0 = 1.13 +/- 0.03, n = 1.43 +/- 0.03; at 0.05 Gy/min, D0 = 1.16 +/- 0.04, n = 1.34 +/- 0.05). There was a decrease in the radiosensitivity of GM-CFUc7 and GM-CFUc14 derived from nonadherent cells of long-term bone marrow cultures compared to fresh marrow that was observed at both dose rates. In contrast, adherent stromal cells irradiated at low compared to high dose rate showed a significantly greater radioresistance (Day 19 colonies of greater than or equal to 50 cells; at 2 Gy/min, D0 = 0.99 Gy, n = 1.03; at 0.05 Gy/min D0 = 1.46 Gy, n = 2.00). These data provide strong evidence for a difference in the radiosensitivity of human marrow hematopoietic progenitor compared to adherent stromal cells.     

Transformation-defective virus mutants in a class of morphologic revertants of sarcoma virus transformed nonproducer cells

In studies of the viral and cellular functions involved in expression of transformation by murine sarcoma virus, selective methods have led to the isolation of morphologic revertants following mitomycin C mutagenization of nonproductively transformed mouse cells. The revertants exhibit normal growth properties, yet still contain the sarcoma virus. Further, they are as susceptible as normal cells to exogenous sarcoma virus infection. In the present studies, these revertants are shown to contain levels of sarcoma viral RNA quantitatively and qualitatively indistinguishable from that present in the parental transformed clone. Following rescue with helper leukemia virus, they release low levels of wild-type transforming virus and a large excess of transformation-defective sarcoma virus as measured by molecular hybridization. The defective viruses can be transmitted to new cells in the absence of morphologic alteration. These results provide strong evidence that the revertants contain mutant viruses defective in transforming functions. The release of wild-type sarcoma virus by cells in a revertant culture appears to occur concomitantly with the spontaneous appearance of retransformed cells. This suggests that the reversion of mutant virus to wild-type within the cell occurs as a result of reversion of a point mutation in the integrated sarcoma viral genome. The present sarcoma virus mutants appear to be the first obtained by spontaneous or chemically-induced genetic alteration of stably integrated virus in eucaryotic cells.     

Biochemical and functional characterization of proteoglycans produced by Sl/Sld murine bone marrow stromal cell lines

The Steel anemia of mice results from an inherited defect in the hematopoietic microenvironment. Proteoglycans synthesized by bone marrow stromal cells are an important functional component of the hematopoietic microenvironment in normal animals. It is thus possible that Steel anemia results from a molecular abnormality involving bone marrow stromal proteoglycans. To investigate this possibility, we studied proteoglycan synthesis in three stromal cell lines from Steel anemic (Sl/Sld) animals and two control stromal cell lines, one (+/+2.4) from a non-anemic littermate, and one (GBl/6) from a normal mouse. Proteoglycans were precursor labelled with 35S sulfate and separated by ion exchange HPLC, CsCl density gradient centrifugation, and molecular sieve HPLC. Glycosaminoglycan (GAG) moieties were characterized by molecular sieve HPLC and enzyme sensitivity. There were no consistent differences in total proteoglycan synthesis, proteoglycan heterogeneity, GAG hydrodynamic size, or enzyme sensitivity among the cell lines studied. Growth factor binding to stromal extracellular matrix (ECM) was studied by co-culture of an IL-3-dependent cell line (FDC-P1) with cell-free ECM preparations from an Sl/Sld and a control (GBl/6) stromal cell line, with and without pre-incubation with IL-3. Cell-free ECM preparations from Sl/Sld and control cell lines supported FDC-P1 growth to an approximately equal extent after pre-incubation with IL-3. FDC-P1 growth support by ECM preparations from both cell lines was also observed without IL-3 pre-incubation, although to a lesser extent, suggesting ECM binding of endogenous growth factors synthesized by the stromal cells.     

Progesterone interacts with P-glycoprotein in multidrug-resistant cells and in the endometrium of gravid uterus

P-Glycoprotein (P-GP) plays a pivotal role in maintaining the multidrug-resistant (MDR) phenotype. This membrane glycoprotein is overproduced in MDR cells and the endometrium of the mouse gravid uterus (Arceci, R.J., Croop, J.M., Horwitz, S.B., and Housman, D. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 4350-4354). This latter observation and an interest in endogenous substrates for P-GP led to a study of the interaction of steroids with P-GP found in the endometrium of the mouse gravid uterus and in MDR cells derived from the murine macrophage-like cell J774.2. [3H]Azidopine labeling of P-GP from these two sources was inhibited by various steroids, particularly progesterone. Progesterone also markedly inhibited [3H]vinblastine binding to membrane vesicles prepared from MDR cells, enhanced vinblastine accumulation in MDR cells, and increased the sensitivity of MDR cells to vinblastine. In addition, we have demonstrated that the hydrophobicity of a steroid is important in determining its effect on inhibition of drug binding to P-GP. It is concluded that progesterone, a relatively nontoxic endogenous steroid, interacts with P-GP and is capable of reversing drug resistance in MDR cells.     

The contractile basis of amoeboid movement: V. The control of gelation, solation, and contraction in extracts from dictyostelium discoideum

Motile extracts have been prepared from Dictyostelium discoideum by homogenization and differential centrifugation at 4 degrees C in a stabilization solution (60). These extracts gelled on warming to 25 degrees Celsius and contracted in response to micromolar Ca++ or a pH in excess of 7.0. Optimal gelation occurred in a solution containing 2.5 mM ethylene glycol-bis (β-aminoethyl ether)N,N,N',N'-tetraacetate (EGTA), 2.5 mM piperazine-N-N'-bis [2-ethane sulfonic acid] (PIPES), 1 mM MgC1(2), 1 mM ATP, and 20 mM KCI at ph 7.0 (relaxation solution), while micromolar levels of Ca++ inhibited gelation. Conditions that solated the gel elicited contraction of extracts containing myosin. This was true regardless of whether chemical (micromolar Ca++, pH >7.0, cytochalasin B, elevated concentrations of KCI, MgC1(2), and sucrose) or physical (pressure, mechanical stress, and cold) means were used to induce solation. Myosin was definitely required for contraction. During Ca++-or pH-elicited contraction: (a) actin, myosin, and a 95,000-dalton polypeptide were concentrated in the contracted extract; (b) the gelation activity was recovered in the material sqeezed out the contracting extract;(c) electron microscopy demonstrated that the number of free, recognizable F-actin filaments increased; (d) the actomyosin MgATPase activity was stimulated by 4- to 10-fold. In the absense of myosin the Dictyostelium extract did not contract, while gelation proceeded normally. During solation of the gel in the absense of myosin: (a) electron microscopy demonstrated that the number of free, recognizable F- actin filaments increased; (b) solation-dependent contraction of the extract and the Ca++-stimulated MgATPase activity were reconstituted by adding puried Dictyostelium myosin. Actin purified from the Dictyostelium extract did not gel (at 2 mg/ml), while low concentrations of actin (0.7-2 mg/ml) that contained several contaminating components underwent rapid Ca++ regulated gelation. These results indicated : (a) gelation in Dictyostelium extracts involves a specific Ca++-sensitive interaction between actin and several other components; (b) myosin is an absolute requirement for contraction of the extract; (c) actin-myosin interactions capable of producing force for movement are prevented in the gel, while solation of the gel by either physical or chemical means results in the release of F-actin capable of interaction with myosin and subsequent contraction. The effectiveness of physical agents in producting contraction suggests that the regulation of contraction by the gel is structural in nature.     

The v-src oncogene may not be responsible for the increased radioresistance of hematopoietic progenitor cells expressing v-src.

Infection of the IL-3-dependent, myeloid progenitor cell line 32D cl 3 with murine retroviruses that contain either the wild-type or a temperature-sensitive mutant v-src can render these cells growth-factor independent. These cells also became resistant to gamma irradiation administered at the low-dose rate of 0.05 Gy/min, which is used clinically. The v-src-dependent nature of resistance to gamma irradiation was examined by studying four clones of 32D cl 3 cells that had been infected with a retrovirus carrying the tsLA31A mutant of v-src. The tyrosine-specific kinase activity of this mutant is dramatically reduced at the nonpermissive temperature of 39 degrees C. Cells transformed by v-src and grown at either 34 or 39 degrees C, in the presence or absence of IL-3, demonstrated a significantly higher D0 compared to parental cells examined under identical conditions. In addition, expression of v-src abrogated the synergistic killing effect of heat and gamma irradiation. The D0 of parental 32D cl 3 cells kept at 39 degrees C after gamma irradiation was reduced significantly compared to the D0 of these cells kept at 34 degrees C. This contrasts with data from 32D cl 3 cells infected with either the wild-type v-src or the temperature-sensitive mutant, neither exhibited a synergistic effect in the D0 at either 34 or 39 degrees C. Therefore, while continuous expression of a v-src gene product is required for maintenance of the growth-factor-independent state, v-src does not appear to be responsible for the increased gamma-radiation resistance of these cells at low dose rate.     

Roles of creatine in the regulation of cardiac protein synthesis

The observation that increased muscular activity leads to muscle hypertrophy is well known, but identification of the biochemical and physiological mechanisms by which this occurs remains an important problem. Experiments have been described (5, 6) which suggest that creatine, an end product of contraction, is involved in the control of contractile protein synthesis in differentiating skeletal muscle cells and may be the chemical signal coupling increased muscular activity and the increased muscular mass. During contraction, the creatine concentration in muscle transiently increases as creatine phosphate is hydrolyzed to regenerate ATP. In isometric contraction in skeletal muscle for example, Edwards and colleagues (3) have found that nearly all of the creatine phosphate is hydrolyzed. In this case, the creatine concentration is increased about twofold, and it is this transient change in creatine concentration which is postulated to lead to increased contractile protein synthesis. If creatine is found in several intracellular compartments, as suggested by Lee and Vissher (7), local changes in concentration may be greater then twofold. A specific effect on contractile protein synthesis seems reasonable in light of the work of Rabinowitz (13) and of Page et al. (11), among others, showing disproportionate accumulation of myofibrillar and mitochondrial proteins in response to work-induced hypertrophy and thyroxin-stimulated growth. Previous experiments (5, 6) have shown that skeletal muscles cells which have differentiated in vitro or in vivo synthesize myosin heavy-chain and actin, the major myofibrillar polypeptides, faster when supplied creatine in vitro. The stimulation is specific for contractile protein synthesis since neither the rate of myosin turnover nor the rates of synthesis of noncontractile protein and DNA are affected by creatine. The experiments reported in this communication were undertaken to test whether creatine selectively stimulates contractile protein synthesis in heart as it does in skeletal muscle.