cbl-3: a new mammalian cbl family protein

We have cloned a new human gene, cbl-3, which encodes a protein with marked homology to the cbl family of proteins. The predicted protein encoded by this gene retains the conserved phosphotyrosine binding domain (PTB) in the N-terminal and the zinc finger but is significantly shorter (MW 52.5 kDa) than the other mammalian cbl proteins. The protein lacks the extensive proline rich domain and leucine zipper seen in c-cbl and cbl-b and structurally most resembles the C. elegans and Drosophila cbl proteins. The gene is ubiquitously expressed with highest expression in the aerodigestive tract, prostate, adrenal gland, and salivary gland. The protein is phosphorylated and recruited to the EGFR upon EGF stimulation and inhibits EGF stimulated MAP kinase activation. In comparison to the other mammalian cbl proteins (e.g. cbl-b), cbl-3 interacts with a restricted range of proteins containing Src Homology 3 regions. An alternatively spliced form of the cbl-3 protein was also identified which deletes a critical region of the PTB domain and which does not interact with the EGFR nor inhibit EGF stimulated MAP kinase activation. These data demonstrate that cbl-3, a novel mammalian cbl protein, is a regulator of EGFR mediated signal transduction.

The 100-kDa proteolytic fragment of RB is retained predominantly within the nuclear compartment of apoptotic cells

The retinoblastoma tumor suppressor protein (RB) has been shown to play a role in regulating the eukaryotic cell cycle, promoting cellular differentiation, and modulating programmed cell death. Although regulation of RB tumor suppressor activity is mediated by reversible phosphorylation, an additional posttranslational modification involves the cleavage of 42 residues from the carboxy terminus of RB during the onset of drug-induced or receptor-mediated apoptosis. We now demonstrate that a recombinant p100cl RB species localizes to the nucleus where it may retain wildtype "pocket" protein binding activity. In addition, using immunocytochemistry, we show that cleavage of the endogenous RB protein occurs in vivo in human cells and that p100cl is predominantly retained within the nuclear compartment of cells during early apoptosis. We also show that the carboxy-terminal cleavage of RB is detected immediately following caspase-3 and PARP cleavage during FAS-mediated apoptosis of MCF10 cells. These findings suggest that this cleavage event may be a component of a downstream cascade during programmed cell death.

cbl-b inhibits epidermal growth factor receptor signaling

The role of cbl-b in signaling by the epidermal growth factor receptor (EGFR) was studied and compared with c-cbl. We demonstrate in vivo, that cbl-b, like c-cbl, is phosphorylated and recruited to the EGFR upon EGF stimulation and both cbl proteins can bind to the Grb2 adaptor protein. To investigate the functional role of cbl proteins in EGFR signaling, we transfected cbl-b or c-cbl into 32D cells overexpressing the EGFR (32D/EGFR). This cell line is absolutely dependent on exogenous IL-3 or EGF for sustained growth. 32D/EGFR cells overexpressing cbl-b showed markedly inhibited growth in EGF compared to c-cbl transfectants and vector controls. This growth inhibition by cbl-b was the result of a dramatic increase in the number of cells undergoing apoptosis. Consistent with this finding, cbl-b overexpression markedly decreased the amplitude and duration of AKT activation upon EGF stimulation compared to either vector controls or c-cbl overexpressing cells. In addition, the duration of EGF mediated MAP kinase and Jun kinase activation in cells overexpressing cbl-b is shortened. These data demonstrate that cbl-b inhibits EGF-induced cell growth and that cbl-b and c-cbl have distinct roles in EGF mediated signaling.

Tyrosine phosphorylation and complex formation of Cbl-b upon T cell receptor stimulation

Cbl-b, a mammalian homolog of Cbl, consists of an N-terminal region (Cbl-b-N) highly homologous to oncogenic v-Cbl, a Ring finger, and a C-terminal region containing multiple proline-rich stretches and potential tyrosine phosphorylation sites. In the present study, we demonstrate that upon engagement of the T cell receptor (TCR), endogenous Cbl-b becomes rapidly tyrosine-phosphorylated. In heterogeneous COS-1 cells, Cbl-b was phosphorylated on tyrosine residues by both Syk- (Syk/Zap-70) and Src- (Fyn/Lck) family kinases, with Syk kinase inducing the most prominent effect. Syk associates and phosphorylates Cbl-b in Jurkat T cells. A Tyr-316 Cbl-binding site in Syk was required for the association with and for the maximal tyrosine phosphorylation of Cbl-b. Mutation at a loss-of-function site (Gly-298) in Cbl-b-N disrupts its interaction with Syk. Cbl-b constitutively binds Grb2 and becomes associated with Crk-L upon TCR stimulation. The Grb2- and the Crk-L-binding regions were mapped to the C-terminus of Cbl-b. The Crk-L-binding sites were further determined to be Y655DVP and Y709KIP, with the latter being the primary binding site. Taken together, these results implicate that Cbl-b is involved in TCR-mediated intracellular signaling pathways.

Chemotherapy augments TRAIL-induced apoptosis in breast cell lines

Expression and function of the TRAIL apoptotic pathway was investigated in normal and malignant breast epithelial cells. Glutathione-S-transferase (GST)-TRAIL extracellular domain fusion proteins were produced to analyze TRAIL-induced apoptosis. Only GST-TRAIL constructs containing regions homologous to the Fas self-association and ligand binding domains could induce apoptosis. GST-TRAIL induced significant (>90%) apoptosis in just one of eight normal and one of eight malignant breast cell lines. All other lines were relatively resistant to TRAIL-induced apoptosis. Activating TRAIL receptors DR4 and DR5 were expressed in all normal and malignant breast cell lines. The inhibitory receptor TRID was highly expressed in one of four normal and two of seven malignant breast cell lines. DR4, DR5, or TRID expression did not correlate with sensitivity to TRAIL-induced apoptosis. Incubation of cell lines with doxorubicin or 5-fluorouracil significantly augmented TRAIL-induced apoptosis in most breast cell lines. By fractional inhibition analysis, the toxicity of the combination of TRAIL and doxorubicin or 5-fluorouracil was synergistic compared with either agent alone. In contrast, melphalan and paclitaxel augmented TRAIL-induced apoptosis in few cell lines, and methotrexate did not augment it in any cell line. Augmentation of TRAIL-induced apoptosis by doxorubicin or 5-fluorouracil was mediated through caspase activation. This was evidenced by the fact that chemotherapy agents that synergized with TRAIL (e.g., doxorubicin) themselves caused cleavage of caspase-3 and poly(ADP-ribose) polymerase (PARP), and their toxicity was blocked by the caspase inhibitor Z-Val-Ala-Asp(OMe)-CH2 (ZVAD-fmk). The combination of TRAIL and doxorubicin caused significantly greater caspase-3 and PARP cleavage, and the combined toxicity also was inhibited by ZVAD-fmk. In contrast, chemotherapy agents that did not augment TRAIL-induced apoptosis (e.g., methotrexate) caused minimal caspase-3 and PARP cleavage by themselves, and their toxicity was not inhibited by ZVAD-fmk. These drugs also did not increase caspase-3 or PARP cleavage when combined with TRAIL. In summary, few breast cell lines are sensitive to TRAIL-induced apoptosis, and no difference in sensitivity is found between normal and malignant cell lines. Treatment with chemotherapy provides an approach to sensitize breast cancer cells to TRAIL-induced apoptosis.

Serine phosphorylation of Cbl induced by phorbol ester enhances its association with 14-3-3 proteins in T cells via a novel serine-rich 14-3-3-binding motif

Stimulation of the T cell antigen receptor (TCR).CD3 complex induces rapid tyrosine phosphorylation of Cbl, a protooncogene product which has been implicated in intracellular signaling pathways via its interaction with several signaling molecules. We found recently that Cbl associates directly with a member of the 14-3-3 protein family (14-3-3tau) in T cells and that the association is increased as a consequence of anti-CD3-mediated T cell activation. We report here that phorbol 12-myristate 13-acetate stimulation of T cells also enhanced the interaction between Cbl and two 14-3-3 isoforms (tau and zeta). Tyrosine phosphorylation of Cbl was not sufficient or required for this increased interaction. Thus, cotransfection of COS cells with Cbl plus Lck and/or Syk family protein-tyrosine kinases caused a marked increase in the phosphotyrosine content of Cbl without a concomitant enhancement of its association with 14-3-3. Phorbol 12-myristate 13-acetate stimulation induced serine phosphorylation of Cbl, and dephosphorylation of immunoprecipitated Cbl by a Ser/Thr phosphatase disrupted its interaction with 14-3-3. By using successive carboxyl-terminal deletion mutants of Cbl, the 14-3-3-binding domain was mapped to a serine-rich 30-amino acid region (residues 615-644) of Cbl. Mutation of serine residues in this region further defined a binding motif distinct from the consensus sequence RSXSXP, which was recently identified as a 14-3-3-binding motif. These results suggest that TCR stimulation induces both tyrosine and serine phosphorylation of Cbl. These phosphorylation events allow Cbl to recruit distinct signaling elements that participate in TCR-mediated signal transduction pathways.

Apoptosis is associated with cleavage of a 5 kDa fragment from RB which mimics dephosphorylation and modulates E2F binding

Dephosphorylation of the RB protein has been reported to be associated with apoptosis. In contrast, we show that treatment of HL60 cells with etoposide or cytosine arabinoside or treatment of breast epithelial cells with alpha-FAS is associated with the cleavage of a 5 kDa fragment from the C-terminus of RB, resulting in a truncated product that we have designated as p100cl. This cleavage event coincides with the activation of cysteine proteases at the onset of apoptosis, is blocked by the addition of iodoacetamide to cells prior to the onset of apoptosis, and results in the expression of faster migrating protein species which can mimic dephosphorylated RB. The free 5 kDa fragment is detected only during apoptosis, predicts a cleavage site that we have mapped to a unique CPP32-like recognition sequence which is present at the C-terminus of all reported RB homologues, and results in a truncated RB protein with enhanced E2F binding affinity. While the causality for this cleavage event in the apoptotic process is still under investigation, our findings suggest distinct post-translational pathways for the RB product between cells examined during growth arrest (p105 hypophosphorylated RB) or apoptosis (p100cl).

Fas expression and function in normal and malignant breast cell lines

Expression and function of the Fas apoptotic pathway was investigated in normal and malignant human breast epithelial cells. Nontransformed mammary epithelial cell lines all expressed high levels of Fas mRNA and protein, but only one of seven breast cancer cell lines (T47D) expressed high levels of Fas. Apoptosis was induced in the nontransformed lines when they were incubated with the anti-Fas antibody. However, all of the breast cancer cell lines tested, except T47D, were resistant to Fas-mediated apoptosis. Four of five Fas-resistant breast cancer cell lines became sensitive to Fas-mediated apoptosis upon treatment with IFN-gamma. Fas mRNA increased slightly in both cell lines that became sensitive and in the cell line that remained resistant to Fas-mediated apoptosis upon IFN-gamma treatment. However, the cell surface expression of Fas showed little or no increase in any of the cell lines tested upon IFN-gamma treatment. In contrast to Fas expression, interleukin-1beta-converting enzyme (ICE) expression increased only in the cell lines that became Fas sensitive after IFN-gamma treatment. The importance of ICE and/or ICE-like proteases in Fas-mediated apoptosis in these cells was confirmed by inhibition of Fas-mediated apoptosis by a specific ICE inhibitor, YVAD-cmk. Fas sensitivity was reconstituted in the IFN-gamma-resistant cell line by transfection of ICE into that cell line. Together, these data suggest that down-regulation of Fas and its pathway may be a step in tumor progression and that modulation of Fas expression may provide an approach to inducing apoptosis in breast cancer cells.

The protein tyrosine phosphatase DEP-1 is induced during differentiation and inhibits growth of breast cancer cells

Sodium butyrate-induced differentiation of breast cancer cell lines was used to identify protein tyrosine phosphatases (PTPs) involved in differentiation and growth inhibition of breast cancer cells. Of 42 PTPs analyzed, 31 were expressed in the ZR75-1 breast cancer cell line. Expression of four PTPs (DEP-1, SAP, PTP gamma, and PAC) was regulated in ZR75-1 cells undergoing differentiation. Expression of two of these PTPs (DEP-1 and SAP) was also regulated in the SKBr-3 cell line undergoing differentiation. In view of its marked induction with differentiation in an estrogen receptor (ER)-positive and an ER-negative breast cancer cell line, DEP-1 was investigated for a role in growth inhibition or induction of differentiation in breast cancer cells. A DEP-1 cDNA construct under control of a constitutively active cytomegalovirus promoter was transfected into the ZR75-1, SKBR-3, and MCF-7 breast cancer cell lines, and resistant colonies were selected with G418. DEP-1 expression inhibited the development of resistant colonies by 3-5-fold in all three lines compared to transfection with vector alone. Three stable MCF-7 cell lines expressing DEP-1 under control of an inducible metallothionein promoter were then established. In these lines, induction of DEP-1 expression inhibited breast cancer cell growth by 5-10-fold. These data describe PTPs expressed and regulated in breast cancer cell lines during differentiation and identify one PTP, DEP-1, that inhibits the growth of breast cancer cells in vitro.

Cloning and characterization of cbl-b: a SH3 binding protein with homology to the c-cbl proto-oncogene

We have cloned a new gene, cbl-b, with homology to the c-cbl proto-oncogene. A large protein is predicted (approx. MW 108,000) that has a proline rich domain, a nuclear localization signal, a C3HC4 zinc finger and a putative leucine zipper. There is striking nucleotide and amino acid homology to the c-cbl proto-oncogene most notably in the structural motifs described above. Cbl-b is expressed in normal and malignant mammary epithelial cells, in a variety of normal tissues, and in hematopoietic tissue and cell lines. Cbl-b expressions is up-regulated with macrophage/monocyte differentiation of the HL60 and U937 cell lines. There is direct association of the cbl-b protein with the Src Homology 3 domains of several proteins including signaling, cytoskeletal and adaptor proteins. Our data suggest that cbl-b encodes a protein which can interact with signal transduction proteins to regulate their function or to be regulated by them. Together, cbl-b and c-cbl are members of a novel family of proto-oncogenes involved in signal transduction.

Two new Drosophila genes related to human hematopoietic and neurogenic transcription factors

We have identified two new basic domain helix-loop-helix (bHLH) genes in Drosophila melanogaster, DroSCL and DroNHLH. DroSCL was identified because of its homology to the mammalian hematopoietic transcription factor SCL. DroNHLH was similarly identified by homology to NHLH1 and NHLH2, two bHLH genes expressed in the developing mammalian nervous system. A partial DroSCL complementary DNA clone was obtained from an early pupal (5.5-7.5-day) Drosophila library. DroSCL is 73% identical to SCL within the 55-amino acid region of the bHLH domain. A DroNHLH complementary DNA clone was obtained from an early instar (I and II) Drosophila library. Its coding region consists of 162 amino acids and encodes a predicted protein of 18,312 daltons. DroNHLH is 87% identical to NHLH1 and NHLH2 within the bHLH domain. DroSCL and DroNHLH are located on the X chromosome. A 1.7-kilobase DroSCL transcript and a 1.5-kilobase DroNHLH transcript were detected by Northern analysis of total Drosophila RNA. Examination of Drosophila embryos by tissue in situ hybridization reveals restricted expression of both genes in a subset of cells in the developing central nervous system.

A comparative structural characterization of the human NSCL-1 and NSCL-2 genes. Two basic helix-loop-helix genes expressed in the developing nervous system

Human cDNA clones for NSCL-1 and NSCL-2, two basic domain helix-loop-helix (bHLH) genes expressed predominantly in the developing nervous system, were obtained from a fetal brain cDNA library. The full-length transcripts and the genomic structures were determined. The cDNAs for the two genes encode predicted proteins of similar size (133 and 135 amino acids for NSCL-1 and NSCL-2, respectively) and structure. The carboxyl-terminal 75 amino acids of the two proteins contain the bHLH motif and differ from each other by only three conservative amino acid changes, while the amino-terminal portions are markedly divergent from each other. In addition to the similar protein structure, the genes have a similar genomic organization, suggesting a close evolutionary relationship. The 5'-regulatory regions of the two genes share some features (i.e. potential TATA, CCAAT, and GATA binding sites) but also differ significantly in their G+C content. NSCL-1 is relatively G+C-rich (63%) in the sequences upstream of transcription initiation and has multiple potential binding sites for transcription factors that bind to G+C-rich sequences (e.g. AP-2). NSCL-2 is relatively A+T-rich (63%) in this region and has a potential binding site for AP1. Studies of expression in normal tissues demonstrated expression of NSCL-1 and NSCL-2 in the developing central and peripheral nervous system, most likely in developing neurons. Additional Northern analysis studies in cell lines revealed expression of these genes in some cell lines derived from tumors with neural or neuroendocrine features such as neuroblastoma, PNET, and small cell lung cancer. NSCL-1 is expressed in a larger number of these cell lines. The differences in expression may parallel differences in developmental regulation.

A measure of genomic instability and its relevance to lymphomagenesis

A recent pilot study that we performed on 12 individuals who are involved in the cultivation and processing of grains and legumes suggests to us that we may have in hand a relatively quick, inexpensive, and highly sensitive assay that identifies individuals at increased risk for the development of lymphoid malignancy. The generation of this assay evolved from our interest in the causes and consequences of lymphocyte-specific chromosomal aberration.

Interlocus V-J recombination measures genomic instability in agriculture workers at risk for lymphoid malignancies

V(D)J [variable-(diversity)-joining] rearrangements occur between, as well as within, immune receptor loci, resulting in the generation of hybrid antigen-receptor genes and the formation of a variety of lymphocyte-specific chromosomal aberrations. Such hybrid genes occur at a low frequency in the peripheral blood lymphocytes (PBL) of normal individuals but show a markedly increased incidence in the PBL of individuals with the autosomal recessive disease ataxia-telangiectasia. In this manuscript we demonstrate that the frequency of hybrid antigen-receptor genes is 10- to 20-fold increased in the PBL of an occupational group, agriculture workers, with related environmental exposures. Both ataxia-telangiectasia patients and this population of agriculture workers are at increased risk for lymphoid malignancy. This result suggests that the measurement of hybrid antigen receptor-genes in PBL may be a sensitive assay for a type of lymphocyte-specific genomic instability. As a corollary, this assay may identify populations at risk of developing common types of lymphoid malignancy.

NSCL-2: a basic domain helix-loop-helix gene expressed in early neurogenesis

We have identified a new basic domain helix-loop-helix (bHLH) gene, NSCL-2, which was cloned because of its homology to the previously described putative hematopoietic transcription factor, SCL. NSCL-2 has been identified in both human and murine DNA. NSCL-2 complementary DNA clones were obtained from an 11.5-day murine embryo library. The coding region is 405 base pairs and encodes a predicted protein of 15.6 kilodaltons. There is 74% homology at the nucleotide level with the coding region of the murine SCL and 27% protein homology. Unlike the majority of previously described bHLH genes, the NSCL-2 coding region ends only six amino acids beyond the second amphipathic helix of the HLH domain. The NSCL-2 gene shows a markedly restricted pattern of expression predominantly confined to murine embryos at days 11-13 of development, although low level expression can be detected in murine embryos flanking this time point. Examination of 11- and 12-day mouse embryos by tissue in situ hybridization reveals expression of NSCL-2 in the developing nervous system, most likely in developing neurons. The NSCL-2 gene maps to murine chromosome 3. The temporally and tissue restricted pattern of expression of this gene and its identification as a member of a family of transcription factors relevant to growth and development in a wide variety of species suggest a role for NSCL-2 in the development of the eukaryotic nervous system.

Molecular characterization of NSCL, a gene encoding a helix-loop-helix protein expressed in the developing nervous system

We report here the molecular cloning and chromosomal localization of an additional member of the helix-loop-helix (HLH) family of transcription factors, NSCL. The NSCL gene was identified based on its hybridization to the previously described hemopoietic HLH gene, SCL. Murine NSCL cDNA clones were obtained from a day 11.5 mouse embryo cDNA library. The coding region is 399 base pairs and encodes a predicted protein of 14.8 kDa. The nucleotide sequence shows 71% identity and the amino acid sequence shows 61% identity to murine SCL in the HLH domain. The NSCL protein-coding region terminates six amino acids beyond the second amphipathic helix of the HLH domain. Expression of NSCL was detected in RNA from mouse embryos between 9.5 and 14.5 days postcoitus, with maximum levels of expression at 10.5-12 days. Examination of 12- and 13-day mouse embryos by in situ hybridization revealed expression of NSCL in the developing nervous system. The NSCL gene was mapped to murine chromosome 1. The very restricted pattern of NSCL expression suggests an important role for this HLH protein in neurological development.

Hybrid T cell receptor genes formed by interlocus recombination in normal and ataxia-telangiectasis lymphocytes

In this paper, using polymerase chain reaction (PCR), we demonstrated the occurrence of hybrid genes formed by interlocus recombination between T cell receptor gamma (TCR-gamma) variable (V) regions and TCR-beta joining (J) regions in the peripheral blood lymphocytes (PBL) from normal individuals and patients with ataxia-telangiectasia (AT). Sequence analysis of the PCR-derived hybrid genes confirmed that site-specific V gamma-J beta recombination had occurred and showed that 10 of 23 genomic hybrid genes maintained a correct open reading frame. By dilution analysis, the frequency of these hybrid genes was 8 +/- 1/10(5) cells in normal PBL and 587 +/- 195/10(5) cells in AT PBL. These frequencies and the approximately 70-fold difference between the normal and AT samples are consistent with previous cytogenetic data examining the occurrence of an inversion of chromosome 7 in normal and AT PBL. We also demonstrated expression of these hybrid genes by PCR analysis of first-strand cDNA prepared from both normal and AT PBL. Sequence analysis of the PCR-amplified transcripts showed that, in contrast to the genomic hybrid genes, 19 of 22 expressed genes maintained a correct open reading frame at the V-J junction and correctly spliced the hybrid V-J exon to a TCR-beta constant region, thus allowing translation into a potentially functional hybrid TCR protein. Another type of hybrid TCR transcript was found in a which a rearranged TCR-gamma V-J exon was correctly spliced to a TCR-beta constant region. This form of hybrid gene may be formed by trans-splicing. These hybrid TCR genes may serve to increase the repertoire of the immune response. In addition, studies of their mechanism of formation and its misregulation in AT may provide insight into the nature of the chromosomal instability syndrome associated with AT. The mechanism underlying hybrid gene formation may be analogous to the mechanism underlying rearrangements between putative growth-affecting genes and the antigen receptor loci, which are associated with AT lymphocyte clones and lymphoid malignancies.

Inversion of chromosome 7 in ataxia telangiectasia is generated by a rearrangement between T-cell receptor beta and T-cell receptor gamma genes

Specific and recurrent chromosomal rearrangements are often observed in the karyotypes of phytohemagglutinin-stimulated lymphocytes. The percentage of cells demonstrating these rearrangements is dramatically increased in the genetic disease ataxia telangiectasia. Inversion of chromosome 7 represents approximately half of the chromosomal rearrangements in this disease. Because the chromosomal locations of the inv(7) breakpoints coincide precisely with those of the T-cell antigen receptor (TCR) beta and gamma genes, it has been hypothesized that this rearrangement may occur by recombination between those two loci. Here, we present direct evidence that inversion of chromosome 7 in ataxia telangiectasia is generated by site-specific recombination between a TCR gamma variable segment and a TCR beta joining segment.

Human B lymphoblastoid cell lines provide an interleukin 1-like signal for mitogen-treated T lymphocytes via direct cell contact

The B lymphoblastoid cell lines (B-LCL) 8392, SB, 1788, and Daudi provide accessory cell activity for mitogen-treated T cells, whereas the T lines MOLT-4, 8402, CEM, and HSB do not provide this function. Direct cell contact is required for the accessory cell activity, and active lymphocyte growth factors could not be detected in the supernatants of the B-LCL. The B-LCL also present alloantigens to responding T cells, and this response is independent of additional accessory cells. The target for the B-LCL is the responding T cell itself, rather than a minor contaminating population of endogenous accessory cells. This conclusion is based on the finding that, under culture conditions in which T cells do not proliferate in response to PHA, accessory cell activity of the B-LCL is maintained. Paraformaldehyde- or glutaraldehyde-treated B-LCL retain their accessory cell activity at levels of these agents that completely eliminate metabolic activity of the B-LCL, as determined by incorporation of leucine, thymidine, and uridine into macromolecules. This treatment eliminates alloantigen presentation by the B-LCL. T cells treated with IO-4 or with monoclonal anti-T3 antibodies fail to respond to highly purified IL 1, and respond minimally to supra-optimal concentrations of IL 2. Nevertheless, these cells respond maximally to the accessory cell activity of the B-LCL. The IO-4 treated cells or cells exposed to anti-T3 also proliferate in response to TPA. Together, our data suggest that the B-LCL provide an IL 1-like signal for mitogen-treated T cells via direct cell contact, in the absence of detectable soluble IL 1.

Human B lymphoblastoid cell lines provide an interleukin 1-like signal for mitogen-treated T lymphocytes via direct cell contact

The B lymphoblastoid cell lines (B-LCL) 8392, SB, 1788, and Daudi provide accessory cell activity for mitogen-treated T cells, whereas the T lines MOLT-4, 8402, CEM, and HSB do not provide this function. Direct cell contact is required for the accessory cell activity, and active lymphocyte growth factors could not be detected in the supernatants of the B-LCL. The B-LCL also present alloantigens to responding T cells, and this response is independent of additional accessory cells. The target for the B-LCL is the responding T cell itself, rather than a minor contaminating population of endogenous accessory cells. This conclusion is based on the finding that, under culture conditions in which T cells do not proliferate in response to PHA, accessory cell activity of the B-LCL is maintained. Paraformaldehyde- or glutaraldehyde-treated B-LCL retain their accessory cell activity at levels of these agents that completely eliminate metabolic activity of the B-LCL, as determined by incorporation of leucine, thymidine, and uridine into macromolecules. This treatment eliminates alloantigen presentation by the B-LCL. T cells treated with IO-4 or with monoclonal anti-T3 antibodies fail to respond to highly purified IL 1, and respond minimally to supra-optimal concentrations of IL 2. Nevertheless, these cells respond maximally to the accessory cell activity of the B-LCL. The IO-4 treated cells or cells exposed to anti-T3 also proliferate in response to TPA. Together, our data suggest that the B-LCL provide an IL 1-like signal for mitogen-treated T cells via direct cell contact, in the absence of detectable soluble IL 1.

Expression of receptors for interleukin 2: Role in the commitment of T lymphocytes to proliferate

We examined the role of IL 2 and IL 2 receptors in human T lymphocyte proliferation induced by neuraminidase and galactose oxidase (NAGO)-treated autologous macrophages. T lymphocytes cultured with these aldehyde-bearing macrophages developed responsiveness to IL 2 after as few as 2 to 4 hr of activation and exhibited maximal responsiveness to IL 2 after 18 to 24 hr of activation. This early expression of IL 2 receptors was also shown by the direct binding of a monoclonal anti-IL 2 receptor antibody (anti-Tac) to the activated T lymphocytes. The production of IL 2 by T lymphocytes cultured with NAGO-treated macrophages closely paralleled the induction of IL 2 receptors on the T lymphocytes. IL 2 production began after 4 to 8 hr of activation and peaked at approximately 18 hr. Although the production of IL 2 is strictly dependent upon accessory cell function, the expression of receptors for IL 2 seems to be relatively independent of accessory cells. Despite early expression of receptors for IL 2 and early production of IL 2 by T lymphocytes during activation, T lymphocytes were not committed to proliferate in the absence of IL 2 until more than 24 hr of incubation with NAGO-treated macrophages had elapsed. The commitment to proliferate increased after 24 hr of activation until, after more than 40 hr of activation, the cells proliferated equally well in the presence or absence of IL 2. Proliferation of uncommitted, IL 2 receptor-bearing T lymphocytes was inhibited by interfering with IL 2 binding to its receptor by IL 2 receptor blockade with the anti-Tac antibody. In contrast, proliferation of T lymphocytes committed to proliferate was not affected by IL 2 receptor blockade with the anti-Tac antibody. Taken together, these data suggest three phases of T lymphocyte activation. The first phase requires mitogen (or antigen) to induce expression of IL 2 receptors and production of IL 2 by the T lymphocytes. Accessory cells are strictly required for IL 2 production during this activation phase, but they may not be necessary for expression of IL 2 receptors. The second phase is an IL 2-dependent phase that requires the interaction of IL 2 with the newly expressed IL 2 receptors. The third phase is a commitment of the activated T lymphocytes to proliferate that is independent of both mitogen and IL 2.

Expression of receptors for interleukin 2: Role in the commitment of T lymphocytes to proliferate

We examined the role of IL 2 and IL 2 receptors in human T lymphocyte proliferation induced by neuraminidase and galactose oxidase (NAGO)-treated autologous macrophages. T lymphocytes cultured with these aldehyde-bearing macrophages developed responsiveness to IL 2 after as few as 2 to 4 hr of activation and exhibited maximal responsiveness to IL 2 after 18 to 24 hr of activation. This early expression of IL 2 receptors was also shown by the direct binding of a monoclonal anti-IL 2 receptor antibody (anti-Tac) to the activated T lymphocytes. The production of IL 2 by T lymphocytes cultured with NAGO-treated macrophages closely paralleled the induction of IL 2 receptors on the T lymphocytes. IL 2 production began after 4 to 8 hr of activation and peaked at approximately 18 hr. Although the production of IL 2 is strictly dependent upon accessory cell function, the expression of receptors for IL 2 seems to be relatively independent of accessory cells. Despite early expression of receptors for IL 2 and early production of IL 2 by T lymphocytes during activation, T lymphocytes were not committed to proliferate in the absence of IL 2 until more than 24 hr of incubation with NAGO-treated macrophages had elapsed. The commitment to proliferate increased after 24 hr of activation until, after more than 40 hr of activation, the cells proliferated equally well in the presence or absence of IL 2. Proliferation of uncommitted, IL 2 receptor-bearing T lymphocytes was inhibited by interfering with IL 2 binding to its receptor by IL 2 receptor blockade with the anti-Tac antibody. In contrast, proliferation of T lymphocytes committed to proliferate was not affected by IL 2 receptor blockade with the anti-Tac antibody. Taken together, these data suggest three phases of T lymphocyte activation. The first phase requires mitogen (or antigen) to induce expression of IL 2 receptors and production of IL 2 by the T lymphocytes. Accessory cells are strictly required for IL 2 production during this activation phase, but they may not be necessary for expression of IL 2 receptors. The second phase is an IL 2-dependent phase that requires the interaction of IL 2 with the newly expressed IL 2 receptors. The third phase is a commitment of the activated T lymphocytes to proliferate that is independent of both mitogen and IL 2.

Cellular and growth factor requirements for activation of human T lymphocytes by neuraminidase and galactose oxidase-treated lymphoid cells

Proliferation of peripheral blood mononuclear leukocytes (PBL) can be stimulated by irradiated autologous PBL that have been treated with neuraminidase and galactose oxidase (NAGO). We determined the types of cells that stimulate and respond by isolating populations of cells enriched for macrophages, B lymphocytes, and T lymphocytes. With PBL as responding cells, proliferation was stimulated by irradiated, NAGO-treated cells with the following hierarchy: macrophage greater than PBL greater than B cells greater than T cells. Irradiated NAGO-treated macrophages and PBL induced proliferation of isolated T cells greater than or equal to the proliferation they stimulated in PBL, indicating that T cells are the predominant responding cell type. Irradiated, NAGO-treated B cells or T cells were weak stimulators of isolated T cell proliferation when compared to their ability to stimulate PBL. The ability of irradiated NAGO-treated B cells or T cells to stimulate isolated T cell proliferation was greatly enhanced by the addition of untreated macrophages or by the addition of conditioned media from mitogen-activated PBL. Biologic, biochemical, and biophysical characterization of the conditioned media revealed it contained both lymphocyte polypeptide growth factors, interleukin 1 and interleukin 2. Semipurified preparations of either of these growth factors were capable of enhancing T cell proliferation stimulated by irradiated NAGO-treated B or T cells. These data indicate T cell proliferation induced by irradiated, NAGO-treated cells requires the aldehyde-bearing cells for the induction of soluble growth factor production and for the induction of putative membrane receptors for these growth factors.