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Cell Differentiation↗
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Alterations in human colonic mucin occurring with cellular differentiation and malignant transformation.
The binding of fluorescein isothiocyanate (FITC)-conjugated lectins to mucin in the human colon was studied by using fluorescence microscopy. In normal mucosa, lectins that preferentially bind to exposed N-acetyl-galactosamine residues (Dolichos biflorus agglutinin and soybean agglutinin) bound selectively to the goblet cell mucin of well-differentiated cells in the upper colonic crypt. By contrast, lectins that require exposed non-reducing galactose residues for binding (Ricinus communis agglutinin1 and Bauhinia purpurea agglutinin) preferentially labeled the mucin of less-differentiated goblet cells located in the lower portion of the colonic crypt. The lectin derived from Arachis hypogaea (peanut agglutinin) has a high affinity for a carbohydrate structure not normally exposed in human tissues. This lectin did not label the goblet cell mucin in the normal colon. However, the mucin was labeled in all 21 colon cancer specimens examined. Additionally, the nonmalignant epithelium immediately adjacent to colon cancer (termed "transitional mucosa") also contained goblet cell mucin that was labeled by FITC-peanut agglutinin. Three conclusions may be drawn from the selective binding characteristics of FITC-lectins to colonic mucins. First, an alteration in the exposed, nonreducing carbohydrate residues occurs in human colonic mucin during the process of goblet cell differentiation. Second, an exposed carbohydrate structure that is not normally present in human tissues is expressed in the mucin produced by malignant colonic epithelium. Third, the presence of the cancer-associated carbohydrate structure in the mucin of transitional mucosa suggests that this tissue may be in the process of early malignant transformation.
Cell Differentiation↗
Intrahypothalamic injection of a cell line secreting gonadotropin-releasing hormone results in cellular differentiation and reversal of hypogonadism in mutant mice.
GT1 is an immortalized cell line that synthesizes and secretes the neurohormone gonadotropin-releasing hormone (GnRH). We have placed these cells into the brains of adult mutant hypogonadal (hpg) mice, which lack a functional GnRH gene, to determine whether such cells could differentiate in situ and support gonadal development. Immunocytochemical detection of GnRH revealed that these cells migrated widely in the central nervous system and elaborated axonal processes which on rare occasion projected to the normal target, the median eminence. Using a battery of antibodies, we demonstrated that these cells could cleave the GnRH precursor and that the amidated decapeptide as well as other cleavage products were present. The presence of biologically active material and its appropriate secretion were further documented by gonadal growth in both males and females. The morphological differentiation of the GT1 cells correlated with the density of cells injected. Those remaining within the injection site and/or forming a tumor retained a simple, rounded or fibroblastic appearance. Those cells that migrated into the host away from such tumors assumed the simple fusiform shape of normal GnRH neurons with dendrites extending from one or both poles. When cell density was drastically reduced a much more complex dendritic arbor was elaborated. These data suggest that such cell lines can be useful in reversing genetic defects and in studying such processes as GnRH neuronal migration, axonal targeting, and cytological differentiation.
Animals↗
Retinoic acid receptor/retinoid X receptor heterodimers can be activated through both subunits providing a basis for synergistic transactivation and cellular differentiation.
The receptor for 9-cis-retinoic acid, retinoid X receptor (RXR), forms heterodimers with several nuclear receptors, including the receptor for all-trans-retinoic acid, RAR. Previous studies have shown that retinoic acid receptor can be activated in RAR/RXR heterodimers, whereas RXR is believed to be a silent co-factor. In this report we show that efficient growth arrest and differentiation of the human monocytic cell line U-937 require activation of both RAR and RXR. Also, we demonstrate that the allosteric inhibition of RXR is not obligatory and that RXR can be activated in the RAR/RXR heterodimer in the presence of RAR ligands. Remarkably, RXR inhibition by RAR can also be relieved by an RAR antagonist. Moreover, the dose response of RXR agonists differ between RXR homodimers and RAR/RXR heterodimers, indicating that these complexes are pharmacologically distinct. Finally, the AF2 activation domain of both subunits contribute to activation even if only one of the receptors is associated with ligand. Our data emphasize the importance of signaling through both subunits of a heterodimer in the physiological response to retinoids and show that the activity of RXR is dependent on both the identity and the ligand binding state of its partner.
Cell Differentiation↗
Regulation of a TATA-binding protein-associated factor during cellular differentiation.
RNA polymerase III transcription is down-regulated when F9 embryonal carcinoma cells differentiate into parietal endoderm. This reflects a decrease in the activity of TFIIIB, a multisubunit complex that is required for all class III gene expression. Two essential components of TFIIIB are the TATA-binding protein (TBP) and an associated polypeptide called BRF that is specific to this complex. The abundance of both TBP and BRF decreases during F9 cell differentiation. Whereas the amount of TBP assembled into TFIIIB is down-regulated, this is not the case for all TBP-containing complexes. BRF levels show a more dramatic decline that appears sufficient to account for the overall change in transcriptional activity. Developmental regulation of a specific class of genes may therefore be achieved through changes in the availability of a TBP-associated factor.
Blotting, Western↗
Role of multidrug resistance protein 1 (MRP1) and glutathione S-transferase A1-1 in alkylating agent resistance. Kinetics of glutathione conjugate formation and efflux govern differential cellular sensitivity to chlorambucil versus melphalan toxicity.
We investigated the role of phase II (conjugation) and phase III (efflux) detoxification of the anticancer drugs melphalan (MLP) and chlorambucil (CHB). Although both drugs are substrates of Alpha-class glutathione S-transferases (GST) and the monoglutathionyl conjugates formed in these enzymatic reactions are transported by MRP1, we found that GSTA1-1 and MRP1 acted in synergy to confer resistance to CHB but not to MLP (Morrow, C. S., Smitherman, P. K., Diah, S. K., Schneider, E., and Townsend, A. J. (1998) J. Biol. Chem. 273, 20114-20120). To explain this selectivity of MRP1/GST-mediated resistance, we report results of side-by-side experiments comparing the kinetics of MLP- versus CHB-glutathione conjugate: formation, product inhibition of GSTA1-1 catalysis, and transport by MRP1. The monoglutathionyl conjugate of CHB, CHB-SG, is a very strong competitive inhibitor of GSTA1-1 (K(i) 0.14 microM) that is >30-fold more potent than that of the corresponding conjugate of MLP, MLP-SG (K(i) 4.7 microM). The efficiency of GSTA1-1-mediated monoglutathionyl conjugate formation is more than 4-fold higher for CHB than MLP. Lastly, both CHB-SG and MLP-SG are efficiently transported by MRP1 with similar V(max) although the K(m) for CHB-SG (0.37 microm) is significantly lower than for MLP-SG (1.1 microM). These results indicate that MRP1 is required for GSTA1-1-mediated resistance to CHB in order to relieve potent product inhibition of the enzyme by intracellular CHB-SG formed. The kinetic properties of MRP1 are well suited to eliminate CHB-SG at pharmacologically relevant concentrations. For MLP detoxification, where product inhibition of GSTA1-1 is less important, GSTA1-1 does not confer resistance because of the relatively poorer catalytic efficiency of MLP-SG formation. Similar analyses can be useful for predicting the pharmacological and toxicological consequences of MRP and GST expression on cellular sensitivity to various other electrophilic xenobiotics.
ATP-Binding Cassette Transporters↗
Molecular determinants responsible for differential cellular distribution of G protein-gated inwardly rectifying K+ channels.
Activation of the heteromeric G protein-gated inwardly rectifying K(+) channel (GIRK) GIRK1 and GIRK4 subunits gives rise to I(KACh), which controls excitability in atrial tissue. Although homomeric GIRK4 channels localize to the plasma membrane and display moderate function, GIRK1 channels fail to localize to the cell surface and do not exhibit significant function as homomers. Using oocytes to express GFP-tagged GIRK1 and GIRK4 and chimeras between these two proteins, we have identified two regions, one in the proximal C terminus and another in the distal N terminus that are critical for their subcellular localization. Replacement of both of these regions in GIRK1 with corresponding regions from GIRK4 was required for efficient expression of GIRK1 on the plasma membrane. Replacement of either region by itself was ineffective. The distal N terminus and proximal C terminus have been previously suggested to play important roles in ER-export and subunit co-assembly respectively in this family of channels. Our data indicate for the first time that both of these regions need to work in concert to mediate efficient targeting of these channels to the plasma membrane.
Animals↗
The adaptive response to dietary zinc in mice involves the differential cellular localization and zinc regulation of the zinc transporters ZIP4 and ZIP5.
The ZIP5 gene encodes a protein closely related to ZIP4, a zinc transporter mutated in the human genetic disorder acrodermatitis enteropathica. Herein, we demonstrate that mouse ZIP5 and ZIP4 genes are co-expressed in several tissues involved in zinc homeostasis (intestine, pancreas, embryonic yolk sac). However, unlike expression of the ZIP4 gene, which is induced during periods of zinc deficiency, ZIP5 gene expression is unaltered by dietary zinc. Immunohistochemistry localizes ZIP5 to the basolateral surfaces of enterocytes, acinar cells, and visceral endoderm cells in mice fed a zinc-adequate diet. However, this protein is removed from these cell surfaces and internalized during dietary zinc deficiency. In contrast, ZIP4 is induced and recruited to the apical surface of enterocytes and endoderm cells during zinc deficiency. In the pancreas, ZIP4 is expressed in beta-cells, whereas ZIP5 is expressed in acinar cells. These results suggest that the function of ZIP5 is antagonistic to that of ZIP4 in the control of zinc homeostasis; rather than functioning in the acquisition of dietary zinc, as does ZIP4, ZIP5 may function in the removal of zinc from the body. Thus, during periods when dietary zinc is replete, ZIP5 may function to remove zinc from the blood via the pancreas and intestine, the major sites of zinc excretion in mammals, whereas the acquisition of dietary zinc by intestinal ZIP4 would be minimal. In contrast, during periods of dietary zinc deficiency when secretion of zinc by the pancreas and intestine is minimized, ZIP5 is removed from the cell surface, and the intestinal uptake of zinc is augmented by induction of ZIP4.
Amino Acid Sequence↗
Mesenchymal chondrosarcoma: an immunohistochemical study of 10 cases examining prognostic significance of proliferative activity and cellular differentiation.
AIMS: Mesenchymal chondrosarcoma is a rare malignant chondrogenic neoplasm that tends to affect young adults and teenagers. The prognosis is unpredictable, and the identification of prognostic markers that could aid in determining the behaviour of this tumour would be helpful. There are few studies in the literature that have attempted to address this issue. METHODS AND RESULTS: In this study, we explored the prognostic significance of three different parameters: (1) tissue morphology of small cell areas, (2) the expression of tumour differentiation marker genes, and (3) the proliferation rate. Our results did not show a correlation of prognosis with the histological features of the neoplastic small cell areas or the expression of tumour differentiation genes. However, the proliferative activity of the tumour cells appeared to have some prognostic significance as related to patient survival. CONCLUSION: Mesenchymal chondrosarcoma is a rare tumour with a wide clinical range of behaviour. Therefore, it is difficult to obtain reliable prognostic parameters. Nevertheless, our study suggests that proliferative activity may be a useful prognostic parameter for mesenchymal chondrosarcomas.
Adolescent↗
Bryostatin induces protein kinase C modulation, Mcl-1 up-regulation and phosphorylation of Bcl-2 resulting in cellular differentiation and resistance to drug-induced apoptosis in B-cell chronic lymphocytic leukemia cells.
Bryostatin, a macrocyclic lactone and protein kinase C (PKC) modulator, has been shown to have differentiation and anti-tumor activity against several leukemia cell lines in vitro. In this study, we demonstrated Bryostatin-induced differentiation in B-cell chronic lymphocytic leukemia (B-CLL) cells, characterized by an increase in cell size and a marked up-regulation of CD11c expression. The specific inhibitors of the extracellular signal-regulated kinase (ERK) and protein kinase C pathways, PD98059 and GF 109203X respectively, each completely blocked Bryostatin-induced differentiation of B-CLL cells, suggesting that activation of the ERK pathway plays a direct role in this process in a PKC-dependent manner. Furthermore, Bryostatin reduced both spontaneous and drug-induced apoptosis with chlorambucil, fludarabine and 2-chloro-2'-deoxyadenosine (2-Cda) in B-CLL cells. This resistance was associated with an early up-regulation of the anti-apoptotic protein Mcl-1 and post-translational phosphorylation of Bcl-2 at serine 70. The anti-apoptotic effects of Bryostatin were abrogated by GF 109203X, and to a lesser extent by the phosphatidylinositol 3-kinase (PI3-kinase) inhibitor, LY294002. Interestingly, the ERK inhibitor, PD98059 inhibited Mcl-1 expression but had little effect on Bryostatin-induced survival suggesting that the ERK pathway predominantly affects differentiation. Taken together these results present an explanation for Bryostatin-induced B-CLL cell survival in which modulation of the PKC pathway couples differentiation with an increase in antiapoptotic protein expression and calls into question the rationale for its use in the treatment of B-CLL.
Apoptosis↗
Cellular differentiation markers in lymphoproliferative diseases.
Immunologic progress has resulted in precise definition of different lymphocyte populations that participate in normal immune responses. It has also led to an understanding of the nature of lymphomas and leukemias as malignant expansions of the various cell types. By using characteristic cell markers, it is now possible to classify many malignancies on the basis of the cell types involved.
Adult↗
Cellular differentiation in the kidneys of newborn mice studies with the electron microscope.
The structure of the kidney of the Swiss albino mouse changes progressively during the first 2 weeks after birth. Cells proliferate to form new nephrons, cells differentiate by acquiring specialized membranous components, and certain cytological features which are present at birth diminish in abundance or disappear. The differentiation of the cells of the cortical tubules has been studied using the light and electron microscopes. The tubules are partially and variably differentiated at birth. During the first 2 weeks after birth the brush border develops in the proximal tubules by the accumulation of numerous microvilli on the apical cell margins. Basal striations develop in proximal and distal tubules as an alignment of mitochondria, the result of what appears to be progressive interlocking of adjacent fluted cells. The mitochondria increase in number and size, accumulate homogeneous matrix, and acquire small, very dense granules. The collecting ducts develop tight pleating of the basal cell membranes, and dark cells containing numerous small cytoplasmic vesicles and microvilli appear. At birth there are dense irregular cytoplasmic inclusions presumed to be lipide in renal cells, the cytoplasmic granules of Palade are abundant, and there are large round bodies in the cells of the proximal tubules. The lipide inclusions disappear a few days after birth, and the cytoplasmic granules of Palade diminish in abundance as the cells differentiate. The large round bodies in the proximal tubules consist of an amorphous material and contain concentrically lamellar structures and mitochondria. They resemble the cytoplasmic droplets produced in the proximal tubules of adult rats and mice by the administration of proteins. The large round bodies disappear from the proximal tubules of infant mice during the first week after birth, but the concentric lamellar structures may be found in adult mice.
Animals↗
Specific protein synthesis in cellular differentiation. Production of eggshell proteins by silkmoth follicular cells.
Silkmoth follicles, arranged in a precise developmental sequence within the ovariole, yield pure and uniform populations of follicular epithelial cells highly differentiated for synthesis of the proteinaceous eggshell (chorion). These cells can be maintained and labeled efficiently in organ culture; their in vitro (and cell free) protein synthetic activity reflects their activity in vivo. During differentiation the cells undergo dramatic changes in protein synthesis. For 2 days the cells are devoted almost exclusively to production of distinctive chorion proteins of low molecular weight and of unusual amino acid composition. Each protein has its own characteristic developmental kinetics of synthesis. Each is synthesized as a separate polypeptide, apparently on monocistronic messenger RNA (mRNA), and thus reflects the expression of a distinct gene. The rapid changes in this tissue do not result from corresponding changes in translational efficiency. Thus, the peptide chain elongation rate is comparable for chorion and for proteins synthesized at earlier developmental stages (1.3-1.9 amino acids/sec); moreover, the spacing of ribosomes on chorion mRNA (30-37 codons per ribosome) is similar to that encountered in other eukaryotic systems.
Animals↗
Inhibition of cellular differentiation by phospholipase C. I. Effects of the enzyme on myogenesis and chondrogenesis in vitro.
In cell culture, a partially purified commercial preparation of phospholipase C (PLC) from Clostridium welchii inhibited fusion of myoblasts at concentrations of 12-50 microg per ml. At lower concentrations, PLC-treated cultures were indistinguishable from controls, and at concentrations above 100 microg per ml, PLC-treated cells detached from their substrates. The effect was reversible and fusion resumed approximately one cell cycle time after removal of the enzyme. Neither the percent of cells in the mitotic cycle nor the duration of the different phases of the cycle were altered by PLC at concentrations which inhibited fusion. Cell motility was not reduced by the enzyme. Unfused, PLC-treated myoblasts were virtually indistinguishable in ultrastructure from untreated cells just before fusion. In the presence of PLC, mononucleated myogenic cells did not synthesize thick (150 A) filaments. Treatment of culture medium with insolubilized commercial PLC did not abolish the capacity of the medium to support myogenesis. Chondrocytes treated with PLC divided repeatedly but failed to synthesize metachromatic matrix and failed to incorporate labeled sulfate into chondroitin sulfate. PLC was further purified by chromatography on Sephadex G-100. The resulting preparation was free of detectable protease, yielded one band on SDS-acrylamide gel electrophoresis, and displayed all of the biological activities of the less pure material.
Animals↗
Cellular differentiation of the immune system of mice. I. Separate splenic antigen-sensitive units for different types of anti-sheep antibody-forming cells.
Spleen cell suspensions of unprimed donor mice containing precursors of immunocytes have been transplanted into X-irradiated recipient mice. In the presence of antigen (sheep erythrocytes) these precursors, called antigen-sensitive units, gave rise to progeny cells secreting specific antibody. We studied quantitatively the production of cells releasing IgM hemolysins (direct plaque-forming cells), IgG hemolysins (indirect plaque-forming cells), and hemagglutinins (cluster-forming cells). We found that each of these immunocyte populations was distinct, i.e., that cells releasing agglutinins did not, as a rule, release hemolysins, and vice versa. We also found that cell populations secreting IgM hemolysins did not shift, under certain experimental conditions, to the production of IgG hemolysins during the primary immune response. By transplanting graded numbers of spleen cells, we succeeded in limiting to one or a few the number of antigen-sensitive units that reached the recipient spleen. We estimated thereby the frequency of antigen-sensitive units in donor cell suspensions and tested their potential for production of immunocytes of more than one type. Our results indicated that antigen-sensitive units were unipotent for they displayed in the spleens of unprimed donors the same restrictions of function and heterogeneity (antibody-specificity differentiation, antibody-class differentiation) found among antibody-forming cells. Furthermore, antigen-sensitive precursors for direct plaque-forming cells, indirect plaque-forming cells, and cluster-forming cells were detected in the spleens of unprimed mice in different frequencies, i.e., 1 in approximately 10(6), 1 in approximately 7 x 10(6), and 1 in approximately 19 x 10(6) spleen cells, respectively. We concluded that relatively advanced differentiation of potentially competent cells occurs before sheep erythrocyte administration. The relevance of this finding for the broad spectrum of immunologic reactivities and for the heterogeneity of antibody responses to given antigens was discussed.
Animals↗
Cellular differentiation of the immune system of mice. II. Frequency of unipotent splenic antigen-sensitive units after immunization with sheep erythrocytes.
Spleen cell suspensions of primed donor mice containing precursors of immunocytes have been transplanted into X-irradiated recipient mice 122-138 days after immunization. Following secondary stimulation with antigen (sheep erythrocytes), these precursors, called antigen-sensitive units (ASU), gave rise to progeny cells secreting specific antibody in the spleens of recipients. Single cells releasing IgM hemolysins (direct plaque-forming cells or PFC), IgG hemolysins (indirect PFC), and hemagglutinins (cluster-forming cells or CFC) were enumerated. By transplanting graded and limiting numbers of primed spleen cells, inocula were found which contained one or a few ASU reaching the recipient spleens. We estimated, thereby, the frequency of ASU detectable by our procedures in donor cell suspensions. The values obtained from direct and in-indirect plaque assays, and from cluster assays were 1 in approximately 8.0 x 10(5), 1 in approximately 4.4 x 10(5), and 1 in approximately 5.9 x 10(5) nucleated spleen cells, respectively. The number of splenic ASU for direct PFC was not greater than that of unimmunized mice; however, immunization greatly increased the number of splenic ASU for indirect PFC and for CFC. By applying to each recipient spleen direct and indirect plaque tests and cluster tests, we found that positivity for each type of immunocyte was independent from that of the other two types. These results confirm the unipotent nature of splenic ASU in general, and document the commitment of ASU primed with SRBC to generate progeny cells secreting antibody of a single molecular (IgM or IgG) or functional (lysin or agglutinin) class. We concluded that splenic ASU are composed of relatively differentiated cells of the immune system of mice. With respect to specificity and class differentiation, ASU appear to be as specialized as antibody-producing cells themselves. Our results did not support the view that ASU-derived clonal populations shift from IgM to IgG antibody production.
Animals↗
Cellular differentiation of the immune system of mice. 3. Separate antigen-sensitive units for different types of anti-sheep immunocytes formed by marrow-thymus cell mixtures.
Marrow cell suspensions of unprimed donor mice have been transplanted into X-irradiated syngeneic hosts. 5-46 days later, bone cavities and spleens contained regenerated cells of the immune system which required interaction with thymocytes (from intact donors) and antigen (SRBC) to form antigen-sensitive units (ASU) and to generate mature immunocytes. These cells were capable of differentiating either into direct or indirect hemolytic plaque-forming cells (PFC). The precursors of PFC regenerated earlier than the other cell type necessary for immunocompetence, the antigen-reactive cell (ARC). The latter was not found until 10 or more days after transplantation. Availability of ARC was inferred from PFC responses elicited by grafted mice challenged with SRBC at varying intervals. In a second series of experiments, graded numbers of marrow cells (ranging from 10(7) to 5 x 10(7)) were transplanted with 5 x 10(7) or 10(8) thymocytes into irradiated mice, and SRBC were given 18 hr later. After 9-12 days the recipient spleens contained all or some of the following immunocytes: direct and indirect PFC, and hemagglutinating cluster-forming cells. The frequency of each immune response varied independently of the others, but in relation to the number of marrow cells grafted. This was interpreted to indicate that ASU formed in irradiated mice by interaction of marrow and thymus cells were similar to those of intact mice. In particular, they were specialized for the molecular class (IgM or IgG) and function (lysis or agglutination) of the antibody to be secreted by their descendent immunocytes. Hence, class-differentiation appeared to be conferred upon ASU by their marrow-derived components.
Animals↗
Cellular differentiation of the immune system of mice. IV. Lack of class differentiation in thymic antigen-reactive cells.
Thymocytes and marrow cells of unprimed donor mice were mixed in vitro and transplanted into X-irradiated syngeneic mice. 18 hr later, sheep erythrocytes were injected to induce immune responses. Splenic plaque-forming cells (PFC) secreting IgM (direct PFC) or IgG (indirect PFC) hemolytic antibody were enumerated at the time of peak responses. By transplanting graded and limiting numbers of thymocytes with 4 x 10(7) marrow cells, inocula were found which contained one or a few thymic antigen-reactive cells (ARC) reaching the recipient spleens, interacting with marrow cells, and inducing PFC formation. The frequency values of ARC inferred from direct and indirect plaque assays were very similar, 1 in approximately 10(7) thymocytes. Furthermore, statistical analysis indicated that the formation of direct PFC was not independent of the formation of indirect PFC. This was interpreted to mean that ARC were not specialized themselves and did not determine the molecular class of antibody to be secreted after interaction with marrow cells. Spleens of thymus-marrow grafted mice containing one or two ARC and non-limiting numbers of marrow precursors of PFC (P-PFC), had direct and indirect PFC clustered in several focal areas. Assuming that each focal area represented the progeny of one P-PFC that had interacted with ARC, these results confirmed the statistical evidence for lack of class differentiation in thymic ARC, and also indicated that each ARC or its progeny cells interacted with more than one P-PFC of either class.
Animals↗