Organ-specific requirements for cell adhesion molecules during lymphoma cell dissemination.
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Animals↗
Biomedical subjects
D Naor
Publications and source records attributed to D Naor.
Calcium- and calmodulin-dependent PMA-activation of the CD44 adhesion molecule.
The ability of the CD44 adhesion molecule to interact with its ligand hyaluronic acid (HA) is tightly regulated. CD44-positive mouse LB lymphoma cells are unable to bind HA unless activated by the tumor promoter phorbol 12-myristate 13-acetate (PMA). PMA causes a dose-dependent increase in both CD44 expression level and HA-binding capacity, with the binding of HA observed only above a threshold amount of CD44 molecules. This induction of HA-binding as well as the increase in CD44 expression are prevented by cycloheximide, suggesting a requirement for new additional CD44 molecules on the cell surface and/or cooperating proteins. In the present study, we have investigated which of the signal transduction pathways activated by PMA leads to the increased CD44 expression with subsequent acquisition of HA-binding capacity. By comparing the influence of each inhibitory agent on PMA-activated LB lymphoma cells versus that on a constitutive HA-binder cell line derived from LB cells (designated HA9 cells), we could distinguish between an effect on the PMA-activation phase and a one on the HA-binding phase. Our data show that the PMA-induced HA-binding could not be blocked by agents inhibiting protein kinase C (PKC) (staurosporine, sphingosine, polymyxin B, quercetin) or genestein, an inhibitor of tyrosine protein kinases. However, this PMA response was strongly inhibited by calmodulin antagonists (chlorpromazine, trifluoperazine, W-7) and the calcium blocker verapamil. The calmodulin antagonists inhibited the PMA-induced increase in CD44 expression on LB cells, but had no influence on the ability of the constitutive HA-binder HA9 cell line to interact with HA, indicating an effect on the PMA induction phase rather than on the binding itself. Verapamil also blocked the PMA-induced increase in CD44 expression on LB cells, but in addition it slightly reduced the ability of the HA9 cells to bind HA without affecting their CD44 expression level. In conclusion, our data suggest that CD44 activation by PMA is calcium and calmodulin dependent, rather than mediated by protein kinase C.
Animals↗
Hyaluronan-independent lodgment of CD44+ lymphoma cells in lymphoid organs.
We previously found that monoclonal antibodies (MAbs) directed against the constant region of the CD44 molecule block lymph node infiltration of a mouse LB T-cell lymphoma, suggesting a role for this glycoprotein in the LB cell dissemination process. In the present study, we investigated whether LB cells in the local tumor must undergo a change in the CD44 phenotype to be able to migrate to and invade the remote lymph nodes, and if hyaluronic acid (HA), the principal ligand of activated CD44, functions as a mediator in this process. We compared the in vivo behavior of a non-HA-binder LB cell line with that of a constitutive HA-binder HA9 subline. Our results show that the lymphoid organ-infiltrating LB cells express similar levels of pan-CD44 and V4- and V6-containing CD44 variants, as the corresponding cells in the local growth and the cultured LB cells. The tested CD44 phenotype of HA9 cells also remained unchanged during the metastatic process. Even after lymph node infiltration, LB cells remained incapable of binding HA, whereas the HA9 cells retained an efficient HA-binding capacity. The constitutive HA-binder HA9 cells that expressed an approximately 10-fold higher level of pan-CD44 than did the parental LB cells, as well as an elevated level of the V4 and V6 exon products formed a local tumor and invaded both lymph nodes and spleen, as did the parental LB cells, albeit at a much slower rate. Our finding indicates that there is no direct correlation between the amount of CD44 expressed on the cell surface, the HA-binding capacity and tumorigenicity. Moreover, interaction with HA is not obligatory for LB cell localization in the lymphoid organs, and a tight cell-HA interaction, as observed in HA9 cells, does not prevent tumor cell dissemination, although it may retard tumor spread.
Animals↗
Mitogenic properties of insulin and insulin analogues mediated by the insulin receptor.
Insulin has traditionally been considered as a hormone essential for metabolic regulation, while the insulin-like growth factors (IGF-I and IGF-II) are postulated to be more specifically involved in growth regulation. The conventional wisdom is that they share each other's effects only at high concentrations, due to their weak affinity for the heterologous receptor. We discuss here the evidence that in the proper cellular context, insulin can be mitogenic at physiologic concentrations through its own receptor. We studied the insulin and IGF-I binding characteristics of a new model suitable for analysing insulin receptor mediated mitogenesis; that is, a T-cell lymphoma line that depends on insulin for growth, but is unresponsive to IGFs. The cells showed no specific binding of 125I-IGF-I and furthermore, no IGF-I receptor mRNA was detected by RNAse protection assay in the LB cells, in contrast with mouse brain and thymus. The cells bound at saturation about 3000 insulin molecules to receptors that had normal characteristics in terms of affinity, kinetics, pH dependence and negative co-operativity. A series of insulin analogues competed for 125I-insulin binding with relative potencies comparable to those observed in other insulin target cells. The full sequence of the insulin receptor cDNA was determined and found to be identical to the published sequence of the murine insulin receptor cDNA. The LB cell line is therefore an ideal model with which to investigate insulin mitogenic signalling without interference from the IGF-I receptor. Using this model, we have started approaching the molecular basis of insulin-induced mitogenesis, in particular the role of signalling kinetics in choosing between mitogenic and metabolic pathways.
Animals↗
CD44: structure, function, and association with the malignant process.
CD44 is a ubiquitous multistructural and multifunctional cells surface adhesion molecule involved in cell-cell and cell-matrix interactions. Twenty exons are involved in the genomic organization of this molecule. The first five and the last 5 exons are constant, whereas the 10 exons located between these regions are subjected to alternative splicing, resulting in the generation of a variable region. Differential utilization of the 10 variable region exons, as well as variations in N-glycosylation, O-glycosylation, and glycosaminoglycanation (by heparan sulfate or chondroitin sulfate), generate multiple isoforms (at least 20 are known) of different molecular sizes (85-230 kDa). The smallest CD44 molecule (85-95 kDa), which lacks the entire variable region, is standard CD44 (CD44s). As it is expressed mainly on cells of lymphohematopoietic origin, CD44s is also known as hematopoietic CD44 (CD44H). CD44s is a single-chain molecule composed of a distal extracellular domain (containing, the ligand-binding sites), a membrane-proximal region, a transmembrane-spanning domain, and a cytoplasmic tail. The molecular sequence (with the exception of the membrane-proximal region) displays high interspecies homology. After immunological activation, T lymphocytes and other leukocytes transiently upregulate CD44 isoforms expressing variant exons (designated CD44v). A CD44 isform containing the last 3 exon products of the variable region (CD44V8-10, also known as epithelial CD44 or CD44E), is preferentially expressed on epithelial cells. The longest CD44 isoform expressing in tandem eight exons of the variable region (CD44V3-10) was detected in keratinocytes. Hyaluronic acid (HA), an important component of the extracellular matrix (ECM), is the principal, but by no means the only, ligand of CD44. Other CD44 ligands include the ECM components collagen, fibronectin, laminin, and chondroitin sulfate. Mucosal addressin, serglycin, osteopontin, and the class II invariant chain (Ii) are additional, ECM-unrelated, ligands of the molecule. In many, but not in all cases, CD44 does not bind HA unless it is stimulated by phorbol esters, activated by agonistic anti-CD44 antibody, or deglycosylated (e.g., by tunicamycin). CD44 is a multifunctional receptor involved in cell-cell and cell-ECM interactions, cell traffic, lymph node homing, presentation of chemokines and growth factors to traveling cells, and transmission of growth signals. CD44 also participates in the uptake and intracellular degradation of HA, as well as in transmission of signals mediating hematopoiesis and apoptosis. Many cancer cell types as well as their metastases express high levels of CD44. Whereas some tumors, such as gliomas, exclusively express standard CD44, other neoplasms, including gastrointestinal cancer, bladder cancer, uterine cervical cancer, breast cancer and non-Hodgkin's lymphomas, also express CD44 variants. Hence CD44, particularly its variants, may be used as diagnostic or prognostic markers of at least some human malignant diseases. Furthermore, it has been shown in animal models that injection of reagents interfering with CD44-ligand interaction (e.g., CD44s- or CD44v-specific antibodies) inhibit local tumor growth and metastatic spread. These findings suggest that CD44 may confer a growth advantage on some neoplastic cells and, therefore, could be used as a target for cancer therapy. It is hoped that identification of CD44 variants expressed on cancer but not on normal cells will lead to the development of anti-CD44 reagents restricted to the neoplastic growth.
Alternative Splicing↗
Interchanges of spatially neighbouring residues in structurally conserved environments.
The question of whether interchanges of spatially neighboring residues are coupled, or whether they change independently of each other, has been addressed repeatedly over the last few years. Utilizing a residue order-independent structural comparison tool, we investigated interchanges of spatially adjacent residue pairs in conserved 3D environments in globally dissimilar protein structures. We define spatially adjacent pairs to be non-local neighboring residues which are in spatial contact, though separated along the backbone, to exclude backbone effects. A dataset of unrelated structures is extensively compared, constructing a matrix of all 400x400 interchanges of residue pairs. Our study indicates that (i) interchanges of residues which are spatial neighbors are independent of each other. With the exception of a few pairs, the pattern of interchanges of pairs of adjacent residues resembles that expected from interchanges of single residues. However, clustering residues of similar characteristics, serves to enhance secondary trends. Hence, (ii) clustering the hydrophobic, aliphatic and, separately, the aromatic, and comparing them with the charged, and the polar, indicates that hydrophobic pairs are favorably replaced by hydrophobic, and charged/ polar by charged/polar. The most strongly conserved are the charged. Interestingly, the type of charge (like or opposite) plays no role. Interchanges between the hydrophobic and hydrophilic classes are unfavorable. (iii) Clustering by volume indicates that the most highly conserved are the (Small, Small) pairs. The least favorable are interchanges of the type (Small, Small) <--> (Large, Large). Interchanges of the type (Large, Small) <--> (Large, Large) are less favorable than (Large, Small) <--> (Small, Small). Compensatory interchanges of the type (Large, Small) <--> (Small, Large) are unfavorable. (iv) Inspection of the trends in the interchanges of the clustered small residues versus clustered large rigid, and separately versus clustered large flexible, illustrates clear differences. Consistently, within all hydrophobic, large and small, the flexible aliphatic differ from the more rigid aromatic. The flexible aliphatic residue pairs are unfavorably replaced by other residue types. Furthermore, (v) the unique properties of the aromatics, conferred by the electronic configuration of their benzene rings, are transformed into clear trends. Replacements of polar residues by aromatics, while unfavorable, are nevertheless consistently more favorable than into aliphatics. We address these issues and their direct implications to protein design and to fold recognition.
Amino Acids↗
Predominant role of alpha 4-integrins for distinct steps of lymphoma metastasis.
To analyze the role of alpha4-integrins in lymphoma metastasis, sublines of the T-cell lymphoma LB were generated by retrovirus-mediated gene transfer that differ exclusively in the expression of alpha4-integrins. Using LB-alpha4 and control LB-NTK cells, we demonstrate that expression of alpha4-integrins strongly suppresses metastasis formation of LB lymphoma cells in secondary lymphoid organs such as spleen, mesenteric and peripheral lymph nodes, or Peyer's patches after i.v. injection into syngeneic BALB/c mice. Moreover, alpha4-integrin expression inhibited development of metastatic tumors in liver, lung, and kidney. Expansion of LB lymphoma cells in bone marrow was not affected by alpha4-integrin expression. In vivo migration assays using 51Cr-labeled lymphoma cells demonstrated that low-metastatic LB-alpha4 cells accumulated with the same efficiency as high-metastatic LB-NTK cells in all target organs examined and were even enriched in mucosal lymphoid organs. Collectively, these results indicate that alpha4-integrins inhibit metastasis formation of lymphoma cells at a stage subsequent to the invasion of target organs.
Animals↗
Amino acid pair interchanges at spatially conserved locations.
Here we study the pattern of amino acid interchanges at spatially, locally conserved regions in globally dissimilar and unrelated proteins. By using a method which completely separates the amino acid sequence from its respective structure, this work addresses the question of which properties of the amino acids are the most crucial for the stability of conserved structural motifs. The proteins are taken from a structurally non-redundant dataset. The spatially conserved substructural motifs are defined as consisting of a "large enough" number of Calpha atoms found to provide a geometric match between two proteins, regardless of the order of the Calpha atoms in the sequence, or of the sequence composition of the substructures. This approach can apply to proteins with little or no sequence similarity but with sufficient structural similarity, and is unique in its ability to handle local, non-topological matches between pairs of dissimilar proteins. The method uses a computer-version based algorithm, the Geometric Hashing. Since the Geometric Hashing ignores sequence information it lends itself to answer the question posed above. The interchanges at geometrically similar positions that have been obtained with our method demonstrate the expected behaviour. Yet, a closer inspection reveals some distant characteristics, as compared with interchanges based upon sequence-order based techniques, or from energy-contact-based considerations. First, a pronounced division of the amino acids into two classes is displayed: Lys, Glu, Arg, Gln, Asp, Asn, Pro, Gly, Thr, Ser and His on the one hand, and Ile, Val, Leu, Phe, Met, Tyr, Trp, Cys and Ala on the other. These groups further cluster into subgroups: Lys, Glu, Arg, Gln; Asp Asn; Pro, Gly; Ile, Val, Leu, Phe. The other amino acids stand alone. Analysis of the conservation among amino acids indicates proline to be consistently, by far, the most conserved. Next are Asp, Glu, Lys and Gly. Cys is also highly conserved. Interestingly, oppositely charged amino acids are interchanged roughly as frequently as those of the same charge. These observations can be explained in terms of the three-dimensional structures of the proteins. Most of all, there is a clear distinction between residues which prefer to be on the protein surfaces, compared to those frequently buried in the interiors. Analysis of the interchanges indicates their low information content. This, together with the separation into two groups, suggest that the predictive value of the spatial positions of the Calpha+ atoms is not much greater than the sequence alone, aside from their hydrophobicity/hydrophillicity classification.
Amino Acid Sequence↗
Dynamic expression changes in vivo of adhesion and costimulatory molecules determine load and pattern of lymphoma liver metastasis.
Although intradermal primary tumor growth and spontaneous liver metastasis of ESbL-lacZ lymphoma in syngeneic DBA/2 mice are progressive and malignant, they are characterized by a transient plateau period with a constant tumor diameter and a low number of metastasized cells in the liver. This period, which was shown to be immune dependent, was followed by a second expansion phase characterized by a preferential localization of tumor cells in the periportal areas of liver lobules (mosaic phenotype). To elucidate possible mechanisms leading to the plateau period as well as for the mosaic-like metastasis pattern, we investigated, using flow cytometry analysis, alterations in costimulatory and adhesion molecule expression in liver sinusoidal cells as well as in tumor cells isolated directly ex vivo throughout the kinetics of metastasis. In tumor and sinusoidal cells, we found up-regulation in the expression of MHC class II and B7 molecules during the plateau period. These molecules, which facilitate cell-mediated immune responses, were again down-regulated during the final exponential tumor growth and metastasis. In the final expansion phase, in which the mosaic phenotype of liver metastasis is seen, we detected a significant increase of leukocyte function-associated antigen-1/intercellular adhesion molecule-1 expression in both tumor and sinusoidal cells, suggesting tumor cell-sinusoidal cell interactions. vascular cell adhesion molecule-1/very late activated antigen-4 did not show any modification during the whole metastatic process. In vivo application of monoclonal antibodies directed to leukocyte function-associated antigen-1 and intercellular adhesion molecule-1 appeared to block the spread of metastasis, while no effect was seen with monoclonal antibodies directed to vascular cell adhesion molecule-1 and very late activated antigen-4. This study reveals in situ expression changes of cell surface molecules in tumor and host cells during metastasis. The changes seen during the plateau phase and during the second expansion phase differ, suggesting associations with mechanisms of immune control and tumor immune evasion, respectively.
Animals↗
Mitogenic potential of insulin on lymphoma cells lacking IGF-1 receptor.
We have characterized an insulin-dependent T-cell lymphoma, LB, devoid of IGF-I receptor, which undergoes insulin stimulation and cell proliferation both in vitro and in vivo. In these cells, the mitogenic response can be evoked only through binding of insulin to its own receptor. This lymphoma is thus a good model for studying the molecular mechanisms involved in insulin mitogenicity. The high level of activated Ras in LB cells, even under nonproliferative conditions, shows that activation of Ras is insufficient for mitogenicity. It has been suggested earlier that separate pathways of signal transduction may emerge from Ras. The decision to activate a certain signaling pathway may depend on the activation state of other signaling routes in the cell. This may be the case in LB cells, where a signaling component activated by insulin works in concert with the Ras signaling pathway to induce mitogenesis. Yet it is still unclear whether activated Ras is a prerequisite for the insulin-induced response in LB cells.
Animals↗
Lymph node (but not spleen) invasion by murine lymphoma is both CD44- and hyaluronate-dependent.
Similar to activated T cells, LB T cell lymphoma expresses the CD44 cell surface Ag. In addition, the vast majority of LB cells also express the beta 2 (CD18) and alpha L (CD11a) chains of LFA-1 integrin. In view of the finding that anti-CD18 mAb blocked spleen, but not lymph node invasion by LB cells inoculated s.c. into BALB/c mice, we tested the ability of anti-CD44 mAb (IM 7.8.1) to block the infiltration of LB cells into the lymph nodes. We found that, as opposed to anti-CD18 mAb, anti-CD44 mAb, as well as its F(ab')2 or Fab fragment, prevented lymph node infiltration but had no effect on spleen invasion. This conclusion was based on histologic examination and [3H]thymidine incorporation into proliferating LB cells invading the lymphoid organs. Histologic analysis further demonstrated that LB cells invade the lymph node via the afferent lymphatics. The surface expression of CD44 molecules on LB cells was enhanced after PMA activation. PMA activation also enabled in vitro binding of the lymphoma to hyaluronic acid (HA), a known ligand of CD44. Because anti-CD44 mAb, its F(ab')2 or Fab fragment, and hyaluronidase blocked this binding, we also tested the ability of the enzyme to inhibit lymph node invasion by LB cells. We established through histologic examination and [3H]thymidine incorporation that hyaluronidase protected the lymph node, but not the spleen, from invasion by the lymphoma.
Animals↗
Induction of an autoimmune response against syngeneic lymphoma cells by immunogenic 64-kDa protein isolated from normal blast cells of BALB/c mice.
Immunogenic proteins with identical molecular mass (64 kDa) were purified from a syngeneic spontaneous T cell leukaemia line, designated LB3, and lymphoblast extracts both derived from BALB/c mice. The 64-kDa protein was purified by a sequence of biochemical steps from cell extracts containing protease inhibitors. The following steps were included in the purification pathway: Sephadex G-100 gel filtration, anion-exchange chromatography, concanavalin A (ConA) affinity chromatography, and preparative gel electrophoresis. The immunogenic fraction isolated in each step was subjected to the next step along the purification pathway. The immunogenicity of the separated fractions was measured by a lymph-node proliferation assay, which is indicative of delayed-type hypersensitivity. The final 64-kDa isolated protein of blast cells induced in BALB/c mice an efficient lymph-node proliferation response, which was detected in the regional lymph node after challenge with the final isolated protein of LB3 cells and vice versa. In addition to their identical molecular mass, both proteins were eluted from an anion-exchange column with the same NaCl concentration (0.57 M) and both expressed affinity to the ConA-Sepharose column, suggesting that they are glycosylated. The specificity of the immunological responses induced or elicited with the various isolated proteins was also shown. The implications of these findings are discussed.
Animals↗
On near-optimal alignments of biological sequences.
A near-optimal alignment between a pair of sequences is an alignment whose score lies within the neighborhood of the optimal score. We present an efficient method for representing all alignments whose score is within any given delta from the optimal score. The representation is a compact graph that makes it easy to impose additional biological constraints and select one desirable alignment from the large set of alignments. We study the combinatorial nature of near-optimal alignments, and define a set of "canonical" near-optimal alignments. We then show how to enumerate near-optimal alignments efficiently in order of their score, and count their number. When applied to comparisons of two distantly related proteins, near-optimal alignments reveal that the most conserved regions among the near-optimal alignments are the highly structured regions in the proteins. We also show that by counting the number of near optimal alignments as a function of the distance from the optimal score, we can select a good set of parameters that best constraints the biologically relevant alignments.
Algorithms↗
Beta 2-integrin dependent aggregate formation between LB T cell lymphoma and spleen cells: assessment of correlation with spleen invasiveness.
LB is an aggressive T cell lymphoma which rapidly invades the spleen and lymph nodes of BALB/c mice after s.c. inoculation. We previously reported that mAb directed against the beta 2 chain of the leukocyte function-associated antigen-1 (LFA-1) adhesion molecule (CD18) blocked the invasion of LB cells into the spleen but not into the lymph nodes. The same antibody also blocked in vitro aggregate formation between normal spleen cells and LB cells. However, aggregate formation between normal lymph node cells and LB cells was not detected, regardless of ratio. In an attempt to evaluate the association between aggregate formation and tumor invasion of the lymphoid organs, we have now extended the study. Intravenous injection of anti-CD18 mAb, which blocked spleen invasion by LB cells, also blocked the formation of ex vivo aggregates, spontaneously generated in spleen, but not in lymph node, cell suspensions of BALB/c mice s.c. inoculated with LB cells. In contrast, mAbs unable to block spleen invasion were ineffective inhibitors of both in vitro and ex vivo aggregate formation between spleen and LB cells. Spleens of nude mice that did not provide a supportive environment for lymphoma invasion, were also deficient in target cells forming aggregates with LB cells. In line with this observation, enriched T cells formed more aggregates with LB cells than did enriched non-T cells, indicating the lymphoma's preferential binding to splenic T cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Blocking lymphoma invasiveness with a monoclonal antibody directed against the beta-chain of the leukocyte adhesion molecule (CD18).
The same integrin adhesion molecules used by normal leukocytes for traffic and localization in inflammation sites may be used by malignant cells for dissemination. Identifying the adhesion molecules and then blocking them with appropriate antibody may therefore prove useful for controlling tumor spread. This prediction was tested on a spontaneous murine T cell lymphoma (LB) that expresses LFA-1 adhesion molecules. The adhesion molecules were identified by fluorocytometry and immunoprecipitation with anti-CD18 mAb (M18/2). Subcutaneously inoculated LB lymphoma rapidly infiltrated the spleen and the lymph nodes, as indicated by histologic examination and [3H]thymidine incorporation assay of proliferating LB cells derived from the invaded organs. The normal organization of the lymphoid organs was totally effaced by the infiltrating LB cells. Intravenous injection of anti-CD18 mAb, protein G-purified anti-CD18 mAb, or its F(ab')2 fragments (but not irrelevant control mAb) blocked the invasion of the s.c. inoculated lymphoma into the spleen. Whereas i.v. injected anti-CD18 mAb could not block the infiltration of LB cells into the lymph nodes, local s.c. injection of this antibody near the lymph nodes partially inhibited lymphoma invasion into these organs. It was further found that LB cells form aggregates with spleen cells but not with lymph node cells. In addition, spleen-infiltrating LB cells invade both the spleen and the lymph nodes after s.c. injection. On the other hand, lymph node-infiltrating LB cells invade mainly the lymph nodes under similar circumstances.
Animals↗
Insulin dependence of murine T-cell lymphoma. II. Insulin-deficient diabetic mice and mice fed low-energy diet develop resistance to lymphoma growth.
Physiological concentrations of insulin support the in vitro growth of LB T-cell lymphoma. We could not detect similar insulin dependence in other tumor cell lines. This study reports that insulin also enhances the growth of LB cells in vivo. Mice treated with Streptozotocin (SZ) developed partial resistance to LB lymphoma growth and they survived longer (p < 0.0025) than non-diabetic mice after LB-cell inoculation. A few diabetic mice developed complete tumor resistance, manifested by total regression of the lymphoma. SZ-treated diabetic mice reconstituted with external insulin died as fast as non-diabetic mice when both were inoculated with the same number of LB cells. The SZ-treated diabetic mice did not develop resistance to the growth of BCLI B-cell leukemia, which demonstrated only a marginal proliferative response to insulin in vitro. Mice fed a low-energy diet exhibited low insulin levels and also developed resistance to lymphoma growth (50% survival 21 days vs. 15 days; p < 0.0005), supporting the concept that insulin enhances LB T-cell tumor development in mice.
Animals↗
Insulin dependence of murine lymphoid T-cell leukemia.
The in vitro proliferation of the spontaneous lymphoid T-cell leukemia designated LB was enhanced by physiological, intermediate and supraphysiological concentrations of insulin. The enhancing effect was observed in both serum-free medium (SFM) and medium containing low concentrations of serum. Guinea-pig anti-insulin serum, but not guinea-pig normal serum, inhibited the proliferation of LB cells incubated either in medium containing serum alone or in medium containing serum and supplemented with insulin. This finding suggests that LB cells use serum insulin as a growth factor. Insulin-like growth factors I (IGF-I) and II (IGF-II) failed to stimulate an appreciable proliferation in LB cells, whereas in the same experiment insulin markedly enhanced the proliferation of this lymphoid leukemia. Furthermore, the concentration of unlabelled insulin required to displace 50% of 125I-insulin bound to LB cells was 3 orders of magnitude lower than the concentration of IGF-I required to achieve the same displacement. Our findings indicate that interaction of insulin with its own receptor, and not with IGF-I receptor, triggers the proliferation of LB cells. Radio-receptor assays revealed that LB cells express approximately 3,200 molecules of high affinity (Kd = 10(-9) M) insulin receptor per cell. None of 7 other tumor cell lines tested responded to insulin. The proliferation of insulin-stimulated LB cells was also inhibited with tyrphostin, a tyrosine kinase blocker analogous to tyrosine, which perhaps blocks the tyrosine kinase activity of the insulin receptor beta-chain.
Animals↗
A different outlook at the phenotype-function relationships of T cell subpopulations: fundamental and clinical implications.
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Humans↗