ER stress induces caspase-8 activation, stimulating cytochrome c release and caspase-9 activation

Excess ER stress induces caspase-12 activation and/or cytochrome c release, causing caspase-9 activation. Little is known about their relationship during ER stress-mediated cell death. Upon ER stress, P19 embryonal carcinoma (EC) cells showed activation of various caspases, including caspase-3, caspase-8, caspase-9, and caspase-12, and extensive DNA fragmentation. We examined the relationship between ER stress-mediated cytochrome c/caspase-9 and caspase-12 activation by using caspase-9- and caspase-8-deficient mouse embryonic fibroblasts and a P19 EC cell clone [P19-36/12 (-) cells] lacking expression of caspase-12. Caspase-9 and caspase-8 deficiency inhibited and delayed the onset of DNA fragmentation but did not inhibit caspase-12 processing induced by ER stress. P19-36/12 (-) cells underwent apoptosis upon ER stress, with cytochrome c release and caspase-8 and caspase-9 activation. The dominant negative form of FADD and z-VAD-fmk inhibited caspase-8, caspase-9, Bid processing, cytochrome c release, and DNA fragmentation induced by ER stress, suggesting that caspase-8 and caspase-9 are the main caspases involved in ER stress-mediated apoptosis of P19-36/12 (-) cells. Caspase-8 deficiency also inhibited the cytochrome c release induced by ER stress. Thus, in parallel with the caspase-12 activation, ER stress triggers caspase-8 activation, resulting in cytochrome c/caspase-9 activation via Bid processing.

Distinct downstream pathways of caspase-11 in regulating apoptosis and cytokine maturation during septic shock response

Caspase-11 is an essential mediator of septic shock response and caspase-11-deficient mice are resistant to LPS-induced shock. Here we report that LPS-induced caspase-11 regulates lymphocyte apoptosis by activating both caspase-3 and caspase-7. The activation of caspase-11 preceded that of caspase-1 and caspases-3/-7, and in the absence of caspase-11, the activation of caspases-3/-7 was significantly reduced. The early activation of caspases-3/-7 by caspase-11 was not affected by blocking of caspase-1 activity and IL-1beta release, implying that caspase-11 activates caspases-3/-7 independently of caspase-1 activation. Furthermore, we show that caspase-11-mediated apoptosis under septic condition is Bid-independent. Our work suggests that the human homologue of caspase-11 may be an effective therapeutic target for treatment of septic shock.

Caspase-2 is not required for thymocyte or neuronal apoptosis even though cleavage of caspase-2 is dependent on both Apaf-1 and caspase-9

We have generated rat monoclonal antibodies that specifically recognise caspase-2 from many species, including mouse, rat and humans. Using these antibodies, we have investigated caspase-2 expression, subcellular localisation and processing. We demonstrate that caspase-2 is expressed in most tissues and cell types. Cell fractionation and immunohistochemistry experiments show that caspase-2 is found in the nuclear and cytosolic fractions, including a significant portion present in the Golgi complex. We found that caspase-2 is processed in response to many apoptotic stimuli but experiments with caspase-2 deficient mice demonstrated that it is not required for apoptosis of thymocytes or dorsal root ganglia (DRG) neurons in response to a variety of cytotoxic stimuli. Caspase-2 processing does not occur in thymocytes lacking Apaf-1 or caspase-9, suggesting that in this cell type, activation of caspase-2 occurs downstream of apoptosome formation.

Caspase-9 processing by caspase-3 via a feedback amplification loop in vivo

In contrast to the autoprocessing of caspase-9, little is known about the biological significance of caspase-9 processing by caspase-3 via a feedback loop in vivo. We prepared antisera against mouse caspase-9 cleavage sites so that only the activated form of mouse caspase-9 was recognized. Using these antisera and caspase-9- and caspase-3-deficient mouse embryonic fibroblasts, we demonstrated that mouse caspase-9 is initially autoprocessed at D(353) and D(368) at low levels during staurosporine-induced apoptosis, whereupon the D(368) and D(168) sites are preferentially processed over D(353) by activated caspase-3 as part of a feedback amplification loop. Ac-DEVD-MCA (caspase-3-like) and Ac-LEHD-MCA (caspase-9-like) cleavage activities clearly showed that caspase-9 autoprocessing was necessary for the activation of caspase-3, whereas full activation of caspase-3 and caspase-9 was achieved only through the feedback amplification loop. This feedback amplification loop also played a predominant role during programmed cell death of dorsal root ganglia neurons at mouse embryonic day 11.5.

Caspase-3-deficiency induces hyperplasia of supporting cells and degeneration of sensory cells resulting in the hearing loss

Caspase-3 is one of the cystein proteases that play essential roles in programmed cell death. As such, brain development is profoundly affected by caspase-3-deficiency, resulting in hyperplasia and abnormal cell organization (Kuida et al., Nature 1996;384:368-372). In the present study, we used caspase-3 (-/-) mice to show that caspase-3 deficiency results in severe hearing loss, hyperplasia of supporting cells and degeneration of sensory hair cells. The greater epithelial ridge, a remnant of the primordial organ of Corti, persists throughout all of the turns of cochlea in 2-week-old caspase-3 (-/-) mice, which indicates that the morphology of the cochlea is immature. The number of border cells, that develop from the greater epithelial ridge and are one of the supporting cells of the inner hair cell, increase significantly in both 2- and 5-week-old caspase-3 (-/-) mice. On the other hand, abnormal fused stereocilia can be seen in both 2- and 5-week-old caspase-3 (-/-) mice, and disarrangement and loss of sensory hair cells are observed in 5-week-old caspase-3 (-/-) mice. Taken together, both hyperplasia and degeneration occur simultaneously in the inner ear of the caspase-3 (-/-) mice, suggesting that caspase-3-dependent apoptosis is necessary for the development and formation of a properly functioning auditory system in mammals.

Lipopolysaccharide-induced IL-18 secretion from murine Kupffer cells independently of myeloid differentiation factor 88 that is critically involved in induction of production of IL-12 and IL-1beta

IL-18, produced as biologically inactive precursor, is secreted from LPS-stimulated macrophages after cleavage by caspase-1. In this study, we investigated the mechanism underlying caspase-1-mediated IL-18 secretion. Kupffer cells constantly stored IL-18 and constitutively expressed caspase-1. Inhibition of new protein synthesis only slightly reduced IL-18 secretion, while it decreased and abrogated their IL-1beta and IL-12 secretion, respectively. Kupffer cells deficient in Toll-like receptor (TLR) 4, an LPS-signaling receptor, did not secrete IL-18, IL-1beta, and IL-12 upon LPS stimulation. In contrast, Kupffer cells lacking myeloid differentiation factor 88 (MyD88), an adaptor molecule for TLR-mediated-signaling, secreted IL-18 without IL-1beta and IL-12 production in a caspase-1-dependent and de novo synthesis-independent manner. These results indicate that MyD88 is essential for IL-12 and IL-1beta production from Kupffer cells while their IL-18 secretion is mediated via activation of endogenous caspase-1 without de novo protein synthesis in a MyD88-independent fashion after stimulation with LPS. In addition, infection with Listeria monocytogenes, products of which have the capacity to activate TLR, increased serum levels of IL-18 in wild-type and MyD88-deficient mice but not in caspase-1-deficient mice, whereas it induced elevation of serum levels of IL-12 in both wild-type and caspase-1-deficient mice but not in MyD88-deficient mice. Taken together, these results suggested caspase-1-dependent, MyD88-independent IL-18 release in bacterial infection.

Bcl-X(L)-caspase-9 interactions in the developing nervous system: evidence for multiple death pathways

Programmed cell death is critical for normal nervous system development and is regulated by Bcl-2 and Caspase family members. Targeted disruption of bcl-x(L), an antiapoptotic bcl-2 gene family member, causes massive death of immature neurons in the developing nervous system whereas disruption of caspase-9, a proapoptotic caspase gene family member, leads to decreased neuronal apoptosis and neurodevelopmental abnormalities. To determine whether Bcl-X(L) and Caspase-9 interact in an obligate pathway of neuronal apoptosis, bcl-x/caspase-9 double homozygous mutants were generated. The increased apoptosis of immature neurons observed in Bcl-X(L)-deficient embryos was completely prevented by concomitant Caspase-9 deficiency. In contrast, bcl-x(-/-)/caspase-9(-/-) embryonic mice exhibited an expanded ventricular zone and neuronal malformations identical to that observed in mice lacking only Caspase-9. These results indicate both epistatic and independent actions of Bcl-X(L) and Caspase-9 in neuronal programmed cell death. To examine Bcl-2 and Caspase family-dependent apoptotic pathways in telencephalic neurons, we compared the effects of cytosine arabinoside (AraC), a known neuronal apoptosis inducer, on wild-type, Bcl-X(L)-, Bax-, Caspase-9-, Caspase-3-, and p53-deficient telencephalic neurons in vitro. AraC caused extensive apoptosis of wild-type and Bcl-X(L)-deficient neurons. p53- and Bax-deficient neurons showed marked protection from AraC-induced death, whereas Caspase-9- and Caspase-3-deficient neurons showed minimal or no protection, respectively. These findings contrast with our previous investigation of AraC-induced apoptosis of telencephalic neural precursor cells in which death was completely blocked by p53 or Caspase-9 deficiency but not Bax deficiency. In total, these results indicate a transition from Caspase-9- to Bax- and Bcl-X(L)-mediated neuronal apoptosis.

DNA damage-induced neural precursor cell apoptosis requires p53 and caspase 9 but neither Bax nor caspase 3

Programmed cell death (apoptosis) is critical for normal brain morphogenesis and may be triggered by neurotrophic factor deprivation or irreparable DNA damage. Members of the Bcl2 and caspase families regulate neuronal responsiveness to trophic factor withdrawal; however, their involvement in DNA damage-induced neuronal apoptosis is less clear. To define the molecular pathway regulating DNA damage-induced neural precursor cell apoptosis, we have examined the effects of drug and gamma-irradiation-induced DNA damage on telencephalic neural precursor cells derived from wild-type embryos and mice with targeted disruptions of apoptosis-associated genes. We found that DNA damage-induced neural precursor cell apoptosis, both in vitro and in vivo, was critically dependent on p53 and caspase 9, but neither Bax nor caspase 3 expression. Neural precursor cell apoptosis was also unaffected by targeted disruptions of Bclx and Bcl2, and unlike neurotrophic factor-deprivation-induced neuronal apoptosis, was not associated with a detectable loss of cytochrome c from mitochondria. The apoptotic pathway regulating DNA damage-induced neural precursor cell death is different from that required for normal brain morphogenesis, which involves both caspase 9 and caspase 3 but not p53, indicating that additional apoptotic stimuli regulate neural precursor cell numbers during telencephalic development.

Deficiency in caspase-9 or caspase-3 induces compensatory caspase activation

Dysregulation of apoptosis contributes to the pathogenesis of many human diseases. As effectors of the apoptotic machinery, caspases are considered potential therapeutic targets. Using an established in vivo model of Fas-mediated apoptosis, we demonstrate here that elimination of certain caspases was compensated in vivo by the activation of other caspases. Hepatocyte apoptosis and mouse death induced by the Fas agonistic antibody Jo2 required proapoptotic Bcl-2 family member Bid and used a Bid-mediated mitochondrial pathway of caspase activation; deficiency in caspases essential for this pathway, caspase-9 or caspase-3, unexpectedly resulted in rapid activation of alternate caspases after injection of Jo2, and therefore failed to protect mice against Jo2 toxicity. Moreover, both ultraviolet and gamma irradiation, two established inducers of the mitochondrial caspase-activation pathway, also elicited compensatory activation of caspases in cultured caspase-3(-/-) hepatocytes, indicating that the compensatory caspase activation was mediated through the mitochondria. Our findings provide direct experimental evidence for compensatory pathways of caspase activation. This issue should therefore be considered in developing caspase inhibitors for therapeutic applications.

Detection of caspase-9 activation in the cell death of the Bcl-x-deficient mouse embryo nervous system by cleavage sites-directed antisera

Caspases, which play crucial roles during apoptosis, are activated from their inactive proforms in a sequential cascade of cleavage by other members of the caspase family. Caspase-9 is autoprocessed by the Apaf-1/cytochrome c pathway and acts at an early point in this cascade, whereas Bcl-xL, an antiapoptotic member of the Bcl-2 family, prevents activation of caspases in vitro. Little is known, however, about the relation between caspase-9 and Bcl-xL during development of the mammalian nervous system. We used antisera against two cleavage sites in mouse caspase-9 that recognize only the activated form of mouse caspase-9, and we examined immunohistochemically the activation of mouse caspase-9 in the nervous system of Bcl-x-deficient mouse embryos. Mouse caspase-9 is processed at both D(353) and D(368), but it is processed preferentially at D(368) during apoptosis of cultured cells induced by various stimuli and in the nervous system of Bcl-x-deficient mouse embryos. We show that Bcl-xL protects against caspase-9- and/or caspase-3-dependent apoptosis in the caudal portion of the ventral hindbrain, anterior horn cells, and dorsal root ganglia neurons of the normal mouse embryos and against caspase-9/caspase-3-independent apoptosis in the dorsal region of the nervous system including the dorsal spinal cord. Furthermore, we demonstrate that Bcl-xL blocks cytochrome c release from mitochondria, causing activation of caspase-9 in anterior horn cells and dorsal root ganglia neurons in mouse embryos at embryonic day 11.5.

Execution of apoptosis signal-regulating kinase 1 (ASK1)-induced apoptosis by the mitochondria-dependent caspase activation

ASK1 activates JNK and p38 mitogen-activated protein kinases and constitutes a pivotal signaling pathway in cytokine- and stress-induced apoptosis. However, little is known about the mechanism of how ASK1 executes apoptosis. Here we investigated the roles of caspases and mitochondria in ASK1-induced apoptosis. We found that benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (zVAD-fmk), a broad-spectrum caspase inhibitor, mostly inhibited ASK1-induced cell death, suggesting that caspases are required for ASK1-induced apoptosis. Overexpression of ASK1DeltaN, a constitutively active mutant of ASK1, induced cytochrome c release from mitochondria and activation of caspase-9 and caspase-3 but not of caspase-8-like proteases. Consistently, caspase-8-deficient (Casp8 (-/-)) cells were sensitive to ASK1-induced caspase-3 activation and apoptosis, suggesting that caspase-8 is dispensable for ASK1-induced apoptosis, whereas ASK1 failed to activate caspase-3 in caspase-9-dificient (Casp9 (-/-)) cells. Moreover, mitochondrial cytochrome c release, which was not inhibited by zVAD-fmk, preceded the onset of caspase-3 activation and cell death induced by ASK1. ASK1 thus appears to execute apoptosis mainly by the mitochondria-dependent caspase activation.

Deficiency of a STE20/PAK family kinase LOK leads to the acceleration of LFA-1 clustering and cell adhesion of activated lymphocytes

Lymphocyte-oriented kinase (LOK) is a member of the STE20/p21-activated kinase (PAK) family and expressed predominantly in lymphoid organs. Generation of LOK-deficient mice revealed that the leukocyte-function-associated antigen (LFA-1)/intercellular adhesion molecules (ICAM)-mediated aggregation of mitogen-stimulated T cells was greatly enhanced in the absence of LOK. Though levels of total LFA-1 and ICAMs as well as the active form of LFA-1 on T cell blasts were comparable in the presence and absence of LOK, clustering of active LFA-1 detected by binding of soluble ICAM-1 was accelerated in the absence of LOK. These results suggest that LOK is potentially involved in the regulation of LFA-1-mediated lymphocyte adhesion.

Caspase-9

Caspase-9 is a member of caspase family of cysteine proteases that have been implicated in apoptosis and cytokine processing. When cells receive apoptotic stimuli, mitochondria releases cytochrome c which then binds to Apaf-1, the mammalian Ced-4 homologue, together with dATP. The resultant complex recruits Caspase-9 leading to its activation. Activated Caspase-9 cleaves downstream caspases such as Caspase-3, -6 and -7 initiating the caspase cascade. The majority of homozygous Caspase-9 null mice die perinatally with a markedly enlarged and malformed cerebrum caused by a reduction of apoptosis during early brain development. Thus, Caspase-9 function is essential for apoptosis during normal development of the central nervous system. These data suggest that inhibition of Caspase-9 activity would render opportunity to treat patients suffering from neurological diseases such as stroke, neurodegenerative diseases or brain injury caused by hypoxia.

Epistatic and independent functions of caspase-3 and Bcl-X(L) in developmental programmed cell death

The number of neurons in the mammalian brain is determined by a balance between cell proliferation and programmed cell death. Recent studies indicated that Bcl-X(L) prevents, whereas Caspase-3 mediates, cell death in the developing nervous system, but whether Bcl-X(L) directly blocks the apoptotic function of Caspase-3 in vivo is not known. To examine this question, we generated bcl-x/caspase-3 double mutants and found that caspase-3 deficiency abrogated the increased apoptosis of postmitotic neurons but not the increased hematopoietic cell death and embryonic lethality caused by the bcl-x mutation. In contrast, caspase-3, but not bcl-x, deficiency changed the normal incidence of neuronal progenitor cell apoptosis, consistent with the lack of expression of Bcl-X(L) in the proliferative population of the embryonic cortex. Thus, although Caspase-3 is epistatically downstream to Bcl-X(L) in postmitotic neurons, it independently regulates apoptosis of neuronal founder cells. Taken together, these results establish a role of programmed cell death in regulating the size of progenitor population in the central nervous system, a function that is distinct from the classic role of cell death in matching postmitotic neuronal population with postsynaptic targets.

Caspase knockouts: matters of life and death

Apoptosis, the seemingly counter-intuitive act of physiological cell suicide, is accomplished by an evolutionarily conserved death program that is centered on the activation of a group of intracellular cysteine proteases known as caspases. It is now clear that both extra- and intra-cellular stimuli induce apoptosis by triggering the activation of these otherwise latent proteases in a process that culminates in caspase-mediated disintegration of cellular contents and their subsequent absorption by neighboring cells. While many elegant in vitro studies have demonstrated the requirement of caspase activities for the execution of most, if not all, apoptosis, the precise contribution of individual caspases in vivo and how they functionally relate to each other remain poorly elucidated. Fortunately, the generation of various caspase deficient mice through gene targeting has provided a unique window of opportunity to definitely examine the physiological function of these caspases in vivo. As the list of caspase knockouts grows, we considered it was time to review what we have been learned, from these studies about the exact role of individual caspases in mediating apoptotic events. We will also provide our prediction on the direction of future studies in this ever-growing field of caspases.

Caspase-1-independent, Fas/Fas ligand-mediated IL-18 secretion from macrophages causes acute liver injury in mice

IL-18, produced as a biologically inactive precursor, is processed by caspase-1 in LPS-activated macrophages. Here, we investigated caspase-1-independent processing of IL-18 in Fas ligand (FasL)-stimulated macrophages and its involvement in liver injury. Administration of Propionibacterium acnes (P. acnes) upregulated functional Fas expression on macrophages in an IFNgamma-dependent manner, and these macrophages became competent to secrete mature IL-18 upon stimulation with FasL. This was also the case for caspase-1-deficient mice. Administration of recombinant soluble FasL (rFasL) after P. acnes priming induced comparable elevation of serum IL-18 in parallel with elevated serum liver enzyme levels. However, liver injury was not induced in IL-18-deficient mice after rFasL administration. These results indicate a caspase-1-independent pathway of IL-18 secretion from FasL-stimulated macrophages and its critical involvement in FasL-induced liver injury.

Distinct effects of Jak3 signaling on alphabeta and gammadelta thymocyte development

Janus kinase 3 (Jak3) plays a central role in the transduction of signals mediated by the IL-2 family of cytokine receptors. Targeted deletion of the murine Jak3 gene results in severe reduction of alphabeta and complete elimination of gammadelta lineage thymocytes and NK cells. The developmental blockade appears to be imposed on early thymocyte differentiation and/or expansion. In this study, we show that bcl-2 expression and in vivo survival of immature thymocytes are greatly compromised in Jak3-/- mice. There is no gross deficiency in rearrangements of the TCRdelta and certain gamma loci in pre-T cells, and a functional gammadelta TCR transgene cannot rescue gammadelta lineage differentiation in Jak3-/- mice. In contrast, a TCRbeta transgene is partially able to restore alphabeta thymocyte development. These data suggest that the signals mediated by Jak3 are critical for survival of all thymocyte precursors particularly during TCRbeta-chain gene rearrangement, and are continuously required in the gammadelta lineage. The results also emphasize the fundamentally different requirements for differentiation of the alphabeta and gammadelta T cell lineages.

Flow cytometric diagnosis of the cell lineage and developmental stage of acute lymphoblastic leukemia by novel monoclonal antibodies specific to human pre-B-cell receptor

Three novel monoclonal antibodies (MoAbs) have been established that recognize distinct epitopes of a human pre-B-cell receptor (pre-BCR) composed of a mu heavy (muH) chain and a lambda5/VpreB surrogate light (SL) chain. HSL11 reacts with lambda5 whereas HSL96 reacts with VpreB. Intriguingly, HSL2 does not bind to each component of the pre-BCR but does bind to the completely assembled pre-BCR complex. Flow cytometric analyses with cytoplasmic staining of a panel of human cell lines showed that HSL11 and HSL96 specifically stained cell lines derived from the pro-B and pre-B-cell stages of B-cell development. In contrast, HSL2 stained exclusively cell lines derived from the pre-B-cell stage. These results prompted us to explore the possibility of clinical application of these MoAbs for the determination of the cell lineage and developmental stage of acute lymphoblastic leukemia (ALL). Whereas none of mature B-lineage ALLs (B-ALLs), T-lineage ALLs (T-ALLs), and acute myeloid leukemias analyzed were stained in the cytoplasm with these three MoAbs, the vast majority of non-B- and non-T-ALLs (53 out of 56 cases) were found positive for either lambda5, Vpre-B, or both in their cytoplasm. Among these 53 cytoplasmic SL chain-positive ALLs, 19 cases were also positive for cytoplasmic muH chain, indicative of pre-B-cell origin. Interestingly, 6 out of these 19 pre-B-ALL cases were found negative for cytoplasmic staining with HSL2. From these results, we propose a novel classification of B-ALL in which five subtypes are defined on the basis of the differential expression of SL chain, muH chain, pre-BCR, and light chain along the B-cell development.

Reduced apoptosis and cytochrome c-mediated caspase activation in mice lacking caspase 9

Caspases are essential components of the mammalian cell death machinery. Here we test the hypothesis that Caspase 9 (Casp9) is a critical upstream activator of caspases through gene targeting in mice. The majority of Casp9 knockout mice die perinatally with a markedly enlarged and malformed cerebrum caused by reduced apoptosis during brain development. Casp9 deletion prevents activation of Casp3 in embryonic brains in vivo, and Casp9-deficient thymocytes show resistance to a subset of apoptotic stimuli, including absence of Casp3-like cleavage and delayed DNA fragmentation. Moreover, the cytochrome c-mediated cleavage of Casp3 is absent in the cytosolic extracts of Casp9-deficient cells but is restored after addition of in vitro-translated Casp9. Together, these results indicate that Casp9 is a critical upstream activator of the caspase cascade in vivo.

High levels of expression and nuclear localization of interleukin-1 beta converting enzyme (ICE) and CPP32 in favorable human neuroblastomas

Neuroblastomas frequently show spontaneous regression and differentiation, which may at least partly be regulated by signaling through nerve growth factor and its receptors, TRK-A and p75LNTR. We studied 52 neuroblastic tumors to test whether the cell death-related proteases, interleukin-1 beta converting enzyme (ICE), CPP32, and Ich-1, were involved in the regression of the tumors. High levels of expression of ICE and CPP32 were significantly correlated with a high level of TRK-A expression, single copy of N-myc, younger age, lower stages, and better prognosis. The immunohistochemical studies and Western analyses as well as the terminal dUTP-biotin nick end labeling (TUNEL) method revealed that both ICE and CPP32 were translocated from the cytoplasm into the nuclei in regressing, apoptotic tumor cells. Our results suggest that ICE and CPP32 cysteine proteases may play an important role in regulating the apoptotic process of the favorable neuroblastomas.

Interleukin-1 beta converting enzyme (ICE) is preferentially expressed in neuroblastomas with favourable prognosis

To determine whether interleukin-1 beta converting enzyme (ICE) plays a role in the programmed cell death of neuroblastoma, we studied ICE expression in primary tumours. In patients in stages I, II and IVS, ICE mRNA was detected in 22 of 32 (69%) tumours, while only 5 of 26 (19%) tumours expressed ICE in stages III and IV (P < 0.001). ICE mRNA was expressed in 27 of 47 (57%) tumours without MYCN amplification, but it was not detected in any tumours with MYCN amplification (P < 0.01). Immunohistochemically, the cytoplasm was stained in all 15 neuroblastomas examined. The nuclei were stained in 12 neuroblastomas without MYCN amplification, whereas only 1 of 3 tumours with MYCN amplification had positive staining in the nuclei. In ganglioneuromas, high levels of ICE mRNA were expressed, but immunostaining showed that the protease expression was confined to the cytoplasm. These observations suggest that ICE may be associated with the spontaneous regression often seen in favourable neuroblastomas and that localisation of ICE protease in the cell may be important for the cell death pathway. Double staining for ICE and TUNEL showed that they were co-localised in some nuclei, but the distribution of ICE protease expression was not necessarily the same as that of DNA fragmentation, suggesting that the protease expression probably preceded DNA fragmentation during the apoptotic process. ICE may play an important role in regulating the apoptotic process of neuroblastoma.

LOK is a novel mouse STE20-like protein kinase that is expressed predominantly in lymphocytes

We have identified a new gene, designated lok (lymphocyte-oriented kinase), that encodes a 966-amino acid protein kinase whose catalytic domain at the N terminus shows homology to that of the STE20 family members involved in mitogen-activated protein (MAP) kinase cascades. The non-catalytic domain of LOK does not have any similarity to that of other known members of the family. There is a proline-rich motif with Src homology region 3 binding potential, followed by a long coiled-coil structure at the C terminus. LOK is expressed as a 130-kDa protein, which was detected predominantly in lymphoid organs such as spleen, thymus, and bone marrow, in contrast to other mammalian members of the STE20 family. LOK phosphorylated itself as well as substrates such as myelin basic protein and histone IIA on serine and threonine residues but not on tyrosine residues, establishing LOK as a novel serine/threonine kinase. When coexpressed in COS7 cells with the known MAP kinase isoforms (ERK, JNK, and p38), LOK activated none of them in contrast to PAK- and GCK-related kinases. These results suggest that LOK could be involved in a novel signaling pathway in lymphocytes, which is distinct from the known MAP kinase cascades.

Activation of the STAT signaling pathway can cause expression of caspase 1 and apoptosis

Protein tyrosine kinases activate the STAT (signal transducer and activator of transcription) signaling pathway, which can play essential roles in cell differentiation, cell cycle control, and development. However, the potential role of the STAT signaling pathway in the induction of apoptosis remains unexplored. Here we show that gamma interferon (IFN-gamma) activated STAT1 and induced apoptosis in both A431 and HeLa cells, whereas epidermal growth factor (EGF) activated STAT proteins and induced apoptosis in A431 but not in HeLa cells. EGF receptor autophosphorylation and mitogen-activated protein kinase activation in response to EGF were similar in both cell lines. The breast cancer cell line MDA-MB-468 exhibited a similar response to A431 cells, i.e., STAT activation and apoptosis correlatively resulted from EGF or IFN-gamma treatment. In addition, in a mutant A431 cell line in which STAT activation was abolished, no apoptosis was induced by either EGF or IFN-gamma. We further demonstrated that both EGF and IFN-gamma induced caspase 1 (interleukin-1beta converting enzyme [ICE]) gene expression in a STAT-dependent manner. IFN-gamma was unable to induce ICE gene expression and apoptosis in either JAK1-deficient HeLa cells (E2A4) or STAT1-deficient cells (U3A). However, ICE gene expression and apoptosis were induced by IFN-gamma in U3A cells into which STAT1 had been reintroduced. Moreover, both EGF-induced apoptosis and IFN-gamma-induced apoptosis were effectively blocked by Z-Val-Ala-Asp-fluoromethylketone (ZVAD) in all the cells tested, and studies from ICE-deficient cells indicated that ICE gene expression was necessary for IFN-gamma-induced apoptosis. We conclude that activation of the STAT signaling pathway can induce apoptosis through the induction of ICE gene expression.

The roles of preB cell receptor in early B cell development and its signal transduction

The preB cell receptor is expressed for a short period after mu heavy chain is produced, that is, at the large preB cell stage in B cell development. The severe impairment of B cell differentiation observed in mice deficient for the preB cell receptor clearly demonstrated the importance of the preB cell receptor in B cell development. Analyses of bone marrow precursor B cells in normal and B cell-deficient mutant mice indicated the preB cell receptor transduced signals to drive cell cycle and to induce allelic exclusion. The proliferation of the preB cell receptor-expressing cells leads to the selective expansion of cells which have succeeded in the productive rearrangement of mu heavy chain gene. This process builds up a preB cell pool large enough to generate sufficient numbers of mature B cells. The preB cell receptor appears to induce allelic exclusion by shutting off the expression of recombinase activation gene (RAG). In order to analyse the signal transduction pathway downstream of the preB cell receptor, we have developed a new system in which cross-linking of Ig beta expressed on bone marrow proB cells mimics the signalling through the preB cell receptor to induce differentiation from proB to small preB cells.

Response to local inflammation of IL-1 beta-converting enzyme- deficient mice

IL-1 beta-converting enzyme (ICE) cleaves pro-IL-1 beta to the mature, released form. Although other proteases can process pro-IL-1 beta, ICE-deficient (ICE -/-) mice do not release mature IL-1 beta in response to endotoxin. The purpose of our study was to investigate the response of ICE -/- mice in two models of local inflammation, turpentine-induced tissue damage and zymosan-induced peritonitis. No differences were observed in the development of the systemic acute phase response after turpentine administration between wild-type and ICE -/- mice, but this response was completely impaired in IL-1 beta -/- mice. Accordingly, the levels of mature IL-1 beta produced in response to turpentine did not differ between wild-type and ICE -/- mice. In contrast, following zymosan-induced peritonitis, the levels of mature IL-1 beta were significantly lower in ICE -/- mice. This was associated with a 50% decrease in cellular infiltrate in ICE -/- mice compared with that in wild-type controls. The reduced production of zymosan-induced mature IL-1 beta in ICE -/- mice was also observed from cultured peritoneal or spleen cells. Our results demonstrate that in turpentine-induced tissue necrosis, precursor IL-1 beta is processed by non-ICE proteases, but in complement-mediated inflammation, ICE participates in the processing of the IL-1 beta precursor.

Response to local inflammation of IL-1 beta-converting enzyme- deficient mice

IL-1 beta-converting enzyme (ICE) cleaves pro-IL-1 beta to the mature, released form. Although other proteases can process pro-IL-1 beta, ICE-deficient (ICE -/-) mice do not release mature IL-1 beta in response to endotoxin. The purpose of our study was to investigate the response of ICE -/- mice in two models of local inflammation, turpentine-induced tissue damage and zymosan-induced peritonitis. No differences were observed in the development of the systemic acute phase response after turpentine administration between wild-type and ICE -/- mice, but this response was completely impaired in IL-1 beta -/- mice. Accordingly, the levels of mature IL-1 beta produced in response to turpentine did not differ between wild-type and ICE -/- mice. In contrast, following zymosan-induced peritonitis, the levels of mature IL-1 beta were significantly lower in ICE -/- mice. This was associated with a 50% decrease in cellular infiltrate in ICE -/- mice compared with that in wild-type controls. The reduced production of zymosan-induced mature IL-1 beta in ICE -/- mice was also observed from cultured peritoneal or spleen cells. Our results demonstrate that in turpentine-induced tissue necrosis, precursor IL-1 beta is processed by non-ICE proteases, but in complement-mediated inflammation, ICE participates in the processing of the IL-1 beta precursor.

Bcl-2 lies downstream of parathyroid hormone-related peptide in a signaling pathway that regulates chondrocyte maturation during skeletal development

Parathyroid hormone-related peptide (PTHrP) appears to play a major role in skeletal development. Targeted disruption of the PTHrP gene in mice causes skeletal dysplasia with accelerated chondrocyte maturation (Amizuka, N., H. Warshawsky, J.E. Henderson, D. Goltzman, and A.C. Karaplis. 1994. J. Cell Biol. 126:1611-1623; Karaplis, A.C., A. Luz, J. Glowacki, R.T. Bronson, V.L.J. Tybulewicz, H.M. Kronenberg, and R.C. Mulligan. 1994. Genes Dev. 8: 277-289). A constitutively active mutant PTH/PTHrP receptor has been found in Jansen-type human metaphyseal chondrodysplasia, a disease characterized by delayed skeletal maturation (Schipani, E., K. Kruse, and H. Jüppner. 1995. Science (Wash. DC). 268:98-100). The molecular mechanisms by which PTHrP affects this developmental program remain, however, poorly understood. We report here that PTHrP increases the expression of Bcl-2, a protein that controls programmed cell death in several cell types, in growth plate chondrocytes both in vitro and in vivo, leading to delays in their maturation towards hypertrophy and apoptotic cell death. Consequently, overexpression of PTHrP under the control of the collagen II promoter in transgenic mice resulted in marked delays in skeletal development. As anticipated from these results, deletion of the gene encoding Bcl-2 leads to accelerated maturation of chondrocytes and shortening of long bones. Thus, Bcl-2 lies downstream of PTHrP in a pathway that controls chondrocyte maturation and skeletal development.

Activation of interferon-gamma inducing factor mediated by interleukin-1beta converting enzyme

The interleukin-1beta (IL-1beta) converting enzyme (ICE) processes the inactive IL-1beta precursor to the proinflammatory cytokine. ICE was also shown to cleave the precursor of interferon-gamma inducing factor (IGIF) at the authentic processing site with high efficiency, thereby activating IGIF and facilitating its export. Lipopolysaccharide-activated ICE-deficient (ICE-/-) Kupffer cells synthesized the IGIF precursor but failed to process it into the active form. Interferon-gamma and IGIF were diminished in the sera of ICE-/- mice exposed to Propionibacterium acnes and lipopolysaccharide. The lack of multiple proinflammatory cytokines in ICE-/- mice may account for their protection from septic shock.

Decreased apoptosis in the brain and premature lethality in CPP32-deficient mice

Programmed cell death (apoptosis) is a prominent feature of the development of the immune and nervous systems. The identification of the Caenorhabditis elegans cell death gene, ced-3, as a prototype of the interleukin-1beta converting enzyme (ICE) protease family has led to extensive evidence implicating these enzymes in apoptosis. Among the ten or more members of the ICE protease family, CPP32/yama/apopain exhibits the highest similarity to CED-3 in both sequence homology and substrate specificity. To analyse its function in vivo, we generated CPP32-deficient mice by homologous recombination. These mice, born at a frequency lower than expected by mendelian genetics, were smaller than their littermates and died at 1-3 weeks of age. Although their thymocytes retained normal susceptibility to various apoptotic stimuli, brain development in CPP32-deficient mice was profoundly affected, and discernible by embryonic day 12, resulting in a variety of hyperplasias and disorganized cell deployment. These supernumerary cells were postmitotic and terminally differentiated by the postnatal stage. Pyknotic clusters at sites of major morphogenetic change during normal brain development were not observed in the mutant embryos, indicating decreased apoptosis in the absence of CPP32. Thus CPP32 is shown to play a critical role during morphogenetic cell death in the mammalian brain.

Dysregulated expression of the IL-2 receptor beta-chain abrogates development of NK cells and Thy-1+ dendritic epidermal cells in transgenic mice

The IL-2 receptor beta-chain (IL-2R beta), a specificity-determining subunit in the IL-2R complex with a restricted tissue distribution pattern, is essential for signal transduction. Our previous studies demonstrate that the continuous treatment of mice with anti-IL-2R beta resulted in the complete disappearance of NK cells and Thy-1+ dendritic epidermal cells (Thy-1+ dEC), suggesting that signals through IL-2R beta are critically involved in development of these lymphocyte subsets. However, these lymphocyte subsets are reported to be apparently unaffected in the IL-2-deficient mice. To further examine the biological roles of the IL-2R beta, transgenic mice carrying the IL-2R beta transgene were generated. In these mice, high levels of the cell surface expression of the IL-2R beta were observed in essentially all hematopoietic lineage cells, and CD4+ T cells as well as CD8+ T cells showed vigorous cell proliferation upon IL-2 stimulation. Surprisingly, NK cells marked with a high expression of NK1.1 in the spleen and Thy-1+ dEC in the skin were completely absent in transgenic mice. However, the development of other lymphocyte subsets including conventional alpha beta TCR+ cells, gamma delta TCR+ cells and B cells remained apparently intact. From these observations together with previous data on IL-2-deficient mice, we speculate that factors, other than IL-2 that utilizes the IL-2R beta as its functional receptor subunit, may have a vital role in the development of NK cells and Thy-1+ dEC. Implications for possible in vivo functions of over-expressed IL-2R beta are discussed.

Altered cytokine export and apoptosis in mice deficient in interleukin-1 beta converting enzyme

The interleukin-1 beta (IL-1 beta) converting enzyme (ICE) processes the inactive IL-1 beta precursor to the proinflammatory cytokine. Adherent monocytes from mice harboring a disrupted ICE gene (ICE-/-) did not export IL-1 beta or interleukin-1 alpha (IL-1 alpha) after stimulation with lipopolysaccharide. Export of tumor necrosis factor-alpha and interleukin-6 (IL-6) from these cells was also diminished. Thymocytes from ICE-/- mice were sensitive to apoptosis induced by dexamethasone or ionizing radiation, but were resistant to apoptosis induced by Fas antibody. Despite this defect in apoptosis, ICE-/- mice proceed normally through development.

Targeted disruption of Bcl-2 alpha beta in mice: occurrence of gray hair, polycystic kidney disease, and lymphocytopenia

Mice carrying ablated coding regions of the bcl-2 alpha and bcl-2 beta transcripts have been made. bcl-2-/- mutants are smaller but viable, although about half of them die by 6 weeks of age. As shown earlier with somatic bcl-2 gene-targeted mice, the number of lymphocytes markedly decreased within few weeks after birth while other hematopoietic lineages remained unaffected. Among lymphocytes, CD8+ T cells disappeared most quickly followed by CD4+ T cells, whereas B cells were least affected. bcl-2-/- lymphocytes, however, could respond normally to various stimuli including anti-CD3, Con A, phorbol 12-myristate 13-acetate plus ionomycin, interleukin 2, lipopolysaccharide, and anti-IgM antibody. Abnormalities among nonlymphoid organs include smaller auricles, hair color turning gray at 4-5 weeks of age, and polycystic kidney disease-like change of renal tubules. These results suggest that Bcl-2 may be involved during morphogenesis where inductive interactions between epithelium and mesenchyme are important such as in the kidneys, hair follicles, and perichondrium of auricles. Surprisingly, the nervous system, intestines, and skin appear normal despite the fact that these organs show high levels of endogenous Bcl-2 expression in normal mice.

Requirement for CD8 beta chain in positive selection of CD8-lineage T cells

CD8 is either an alpha alpha homodimer or an alpha beta heterodimer, although most peripheral CD8-lineage T cells express only the CD8 alpha beta heterodimer. The physiological function of CD8 beta was elucidated with mice that were chimeric for the homozygous disruption of the CD8 beta gene. The CD8 beta-1- T cells developed normally to CD4+CD8+ stage, but did not efficiently differentiate further, which resulted in few peripheral CD8+ T cells. The number of peripheral CD8+ T cells was restored by transfer of an exogenous CD8 beta gene into CD8 beta-deficient T cells. Thus, CD8 beta is necessary for the maturation of CD8+ T cells.

Disappearance of the lymphoid system in Bcl-2 homozygous mutant chimeric mice

The bcl-2 proto-oncogene can prevent the death of many cell types. Mice were generated that were chimeric for the homozygous inactivation of bcl-2. Lymphocytes without Bcl-2 differentiated into phenotypically mature cells. However, in vitro, the mature T cells that lacked Bcl-2 had shorter life-spans and increased sensitivity to glucocorticoids and gamma-irradiation. In contrast, stimulation of CD3 inhibited the death of these cells. T and B cells with no Bcl-2 disappeared from the bone marrow, thymus, and periphery by 4 weeks of age. Thus, Bcl-2 was dispensable for lymphocyte maturation, but was required for a stable immune system after birth.

Characterization of rat LECAM-1 (L-selectin) by the use of monoclonal antibodies and evidence for the presence of soluble LECAM-1 in rat sera

We have characterized the rat LECAM-1 (L-selectin) by the use of newly generated hamster anti-rat LECAM-1 monoclonal antibodies (mAb) (HRL1, HRL2, HRL3, HRL4), with respect to the biochemistry, cellular distribution and function, and developed an ELISA system to detect the soluble form of rat LECAM-1. In the rat, lymphocyte and neutrophil LECAM-1 have apparent molecular masses of 65 and 62 kDa, respectively, and differential glycosylation may account for the molecular heterogeneity. Readily detectable levels of LECAM-1 are expressed on peripheral blood lymphocytes and neutrophils, but not on thymocytes. Lymphocyte LECAM-1 is rapidly shed from the cell surface upon cell activation with PMA, but not with interleukin (IL)-8. In contrast, neutrophil LECAM-1 showed rapid shedding upon stimulation with phorbol 12-myristate 13-acetate (PMA) or IL-8. Concomitantly there is up-regulated expression of Mac-1 in PMA- and IL-8-stimulated neutrophils. Neutrophil rolling in mesenteric venules was significantly inhibited by administration of function-blocking anti-rat LECAM-1 mAb HRL3, but not by non-blocking HRL4, indicating that LECAM-1 plays a significant role in leukocyte rolling. Given that LECAM-1 is rapidly shed from the cell surface, we attempted to develop an ELISA system for detecting LECAM-1 is soluble form, and measured the levels in experimental autoimmune uveitis. The circulating levels of LECAM-1 increased from day 4, which preceded the appearance of clinical signs of uveitis and remained high until uveitis subsided, suggesting that soluble LECAM-1 is potentially a useful parameter to monitor certain types of inflammatory or immune disorders.

Selective long-term elimination of natural killer cells in vivo by an anti-interleukin 2 receptor beta chain monoclonal antibody in mice

The interleukin 2 receptor beta chain (IL-2R beta) is preferentially expressed in natural killer (NK) cells, but is not detected in a majority of resting T and B cells. We recently established a novel monoclonal antibody (mAb) to murine IL-2R beta and examined in vivo the effect of the mAb in mice. We found that intraperitoneal injection of the anti-IL-2R beta mAb into adult mice resulted in a selective in vivo elimination of splenic NK function in various mouse strains. The reduction of NK cell function is associated with complete disappearance of NK1.1+ cells in C57BL/6 mice. Other lymphocyte subsets in the thymus and spleen were uncompromised. T cell function was not affected by the mAb treatment as judged by allogeneic cytotoxic T cell induction. The single injection of anti-IL-2R beta mAb caused a long-term elimination of splenic NK cells, lasting for at least 5 wk. We also found that NK and/or NK precursor cells become susceptible to the mAb treatment only after birth, suggesting that functional maturation of NK cells in terms of IL-2R beta expression is a later event in the course of NK cell development. The use of the anti-IL-2R beta mAb will be useful in defining the physiological role of NK cells in host defense as well as dissecting their developmental pathway in vivo.

The role of the interleukin-2 (IL-2)/IL-2 receptor pathway in MRL/lpr lymphadenopathy: the expanded CD4-8- T cell subset completely lacks functional IL-2 receptors

Autoimmune MRL/MP-lpr/lpr (MRL/lpr) mice spontaneously develop a systemic lupus erythematosus-like disease accompanied by a profound lymphadenopathy that consists of CD4-8-B220+ alpha beta T cells. By the use of cross-linking experiments with radiolabeled interleukin-2 (IL-2), these abnormal T cells have been reported to constitutively express the IL-2 receptor beta chain (IL-2R beta), a signal transducing component of IL-2R, in the absence of the alpha chain (IL-2R alpha). To critically reevaluate the role of the IL-2/IL-2R pathway in the pathogenesis of lymphadenopathy we examined expression of the IL-2R alpha and IL-2R beta in MRL/lpr mice by 125I-IL-2 binding analysis and also by flow cytometric analysis using monoclonal antibodies against each component of the receptor. We found that, contrary to the previous report, the CD4-8-B220+ alpha beta T cells in lymph node (LN) of MRL/lpr mice were negative for both IL-2R alpha and IL-2R beta expression. The lpr liver CD4-8-B220+ alpha beta T cells that had been implicated in the genesis of these abnormal LN T cells were also negative for IL-2R beta expression. Therefore, our results indicate that the IL-2/IL-2R system plays little role, if any, in the expansion of abnormal CD4-8-B220+ alpha beta T cells in MRL/lpr mice.

Molecular mechanisms underlying lymphocyte recirculation. III. Characterization of the LECAM-1 (L-selectin)-dependent adhesion pathway in rats

LECAM-1 (L-selectin) is thought to play an important role in the binding of lymphocytes to high endothelial venules (HEV) of peripheral lymph nodes (LN), which is an essential process in lymphocyte recirculation. Previously we cloned the rat LECAM-1 cDNA. In this study, by using this probe we have sought to characterize a LECAM-1-dependent adhesion pathway in the rat. We have constructed a cDNA for rat LECAM-1-IgG chimera (rLEC-IgG), expressed it, purified the secreted recombinant chimera molecules, and produced mAb reactive with the rat homologue of LECAM-1 by using the chimera molecules. The use of rLEC-IgG revealed that ligands for LECAM-1 are selectively accumulated in high endothelial (HE) cells in LN, the white matter, neurons, cerebellar Purkinje cells, and choroid plexus of the central nervous system and also distal tubules and capillary blood vessels of the kidney. Binding of lymphocytes to LN HEV on frozen sections was blocked by either rLEC-IgG or the anti-rat LECAM-1 mAb. An HEV-derived cell line, Ax, specifically bound to rLEC-IgG fixed on plastic plate. Consistent with the presence of a C-type lectin domain in the ligand-binding region of LECAM-1, the binding was Ca2+ dependent and inhibitable by either the mannose-6-phosphate-rich polysaccharide polyphosphomannan ester or the anti-rat LECAM-1 mAb. These results indicate that the specific ligand for rat LECAM-1 is expressed on the Ax cells. rLEC-IgG precipitated 55-, 65-, 120-, 190-, and > 250-kDa sulfated glycoproteins from LN lysates and 190-, > 250-, and > 500-kDa proteins from Ax cell lysate. The precipitation was Ca2+ dependent and LECAM-1 specific. These results suggest that a carbohydrate structure on HE cells recognized by LECAM-1 is borne possibly on a limited number of cell surface-sulfated glycoproteins. The ligands were also found to be secreted in LN culture supernatants. rLEC-IgG and Ax cells should prove valuable for studying further the role of LECAM-1 in dynamic interactions between lymphocytes and HE cells.

Molecular mechanisms underlying lymphocyte recirculation. III. Characterization of the LECAM-1 (L-selectin)-dependent adhesion pathway in rats

LECAM-1 (L-selectin) is thought to play an important role in the binding of lymphocytes to high endothelial venules (HEV) of peripheral lymph nodes (LN), which is an essential process in lymphocyte recirculation. Previously we cloned the rat LECAM-1 cDNA. In this study, by using this probe we have sought to characterize a LECAM-1-dependent adhesion pathway in the rat. We have constructed a cDNA for rat LECAM-1-IgG chimera (rLEC-IgG), expressed it, purified the secreted recombinant chimera molecules, and produced mAb reactive with the rat homologue of LECAM-1 by using the chimera molecules. The use of rLEC-IgG revealed that ligands for LECAM-1 are selectively accumulated in high endothelial (HE) cells in LN, the white matter, neurons, cerebellar Purkinje cells, and choroid plexus of the central nervous system and also distal tubules and capillary blood vessels of the kidney. Binding of lymphocytes to LN HEV on frozen sections was blocked by either rLEC-IgG or the anti-rat LECAM-1 mAb. An HEV-derived cell line, Ax, specifically bound to rLEC-IgG fixed on plastic plate. Consistent with the presence of a C-type lectin domain in the ligand-binding region of LECAM-1, the binding was Ca2+ dependent and inhibitable by either the mannose-6-phosphate-rich polysaccharide polyphosphomannan ester or the anti-rat LECAM-1 mAb. These results indicate that the specific ligand for rat LECAM-1 is expressed on the Ax cells. rLEC-IgG precipitated 55-, 65-, 120-, 190-, and &gt; 250-kDa sulfated glycoproteins from LN lysates and 190-, &gt; 250-, and &gt; 500-kDa proteins from Ax cell lysate. The precipitation was Ca2+ dependent and LECAM-1 specific. These results suggest that a carbohydrate structure on HE cells recognized by LECAM-1 is borne possibly on a limited number of cell surface-sulfated glycoproteins. The ligands were also found to be secreted in LN culture supernatants. rLEC-IgG and Ax cells should prove valuable for studying further the role of LECAM-1 in dynamic interactions between lymphocytes and HE cells.

Reconstitution of the intermediate-affinity interleukin-2 receptor by cell fusion

Although IL-2 receptor beta chain (IL-2R beta) expressed in various lymphoid cell lines binds IL-2 with an intermediate affinity, IL-2R beta expressed in fibroblasts is unable to bind IL-2, suggesting that IL-2R beta is on its own not sufficient for generating the intermediate-affinity receptor and that lymphoid-specific regulatory control may be operated to allow IL-2R beta to bind IL-2. In the present study, we observed that human IL-2R beta expressed in a mouse myeloma X63-Ag8.653 (X63) by cDNA transfection did not bind IL-2, while the same IL-2R beta expressed in an IL-6-dependent mouse B cell hybridoma F12-28, which was obtained by cell fusion between X63 and lipopolysaccharide (LPS)-induced lymphoblasts, bound IL-2 with the intermediate affinity. Interestingly, when the human IL-2R beta cDNA-transfected X63 clone, which by itself manifests no IL-2 binding, was fused with LPS-induced lymphoblasts, the resultant hybridomas manifested intermediate-affinity IL-2 binding. The IL-2 binding was specifically inhibited by addition of antihuman IL-2R beta mAb (Mik-beta 1) but not by mAb against mouse IL-2R subunits, indicating that human IL-2R beta was responsible for the IL-2 binding, i.e. non-functional human IL-2R beta in X63 was converted to competent IL-2R beta by complementation with a mouse spleen cell-derived factor(s) through the cell fusion. Cross-linking experiments with [125I]IL-2 revealed the presence of a 61 kDa protein other than IL-2R beta in cells expressing the intermediate-affinity IL-2R.(ABSTRACT TRUNCATED AT 250 WORDS)

Sequence and expression of a rat cDNA for LECAM-1

A rat cDNA clone encoding an adhesion molecule, LECAM-1, has been isolated from the SD rat and the partial nucleotide sequence was determined. It encodes a peptide of 372 amino acids (aa), including a signal peptide of 38 aa. The protein has three tandem domains: a lectin domain, an EGF-like domain and two repeats of complement regulatory proteins (CR domain). The lectin binding domain has 93.2% and 81.4% and the EGF-like domain has 85.3% and 76.5% aa identity with those of mouse and human, respectively. In the CR repeat domain, the amino acid identity was 72.6% between human and rat and 71.8% between mouse and rat. Northern blot analysis detects the main transcript of about 3 kb in peripheral blood mononuclear cells (PBMC), spleen and thymus. The expression was down-regulated by mitogen stimulation of PBMC and spleen T cells. The protein encoded by this cDNA interacted with PPME when it was expressed on gp90MEL-14 negative mouse EL-4 cells.

Post-translational attainment of allelic exclusion of the T cell receptor alpha chain in a T cell clone

Two in-frame rearranged mouse TCR alpha chain genes from a single CD4+ T cell clone, MS202, specific for self-class II MHC antigen were transfected into a TCR-negative T cell hybridoma together with a beta chain gene derived from the same T cell clone. Both alpha chain genes were efficiently transcribed and translated in the cytoplasm of host cells, but only one alpha chain (V alpha 5) was expressed on the cell surface in association with the partner beta chain (V beta 4). The other alpha chain gene (V alpha 4) was translated into a mature form of the alpha chain but was unable to make a pair with the beta chain, being prohibited from the surface expression. The supertransfection of the CD4 gene into the alpha beta transfectants did not alter the transcription and expression of both combinations of TCR alpha and beta genes. The original self-class II reactivity was, however, reconstituted only in the cells expressing V alpha 5 and V beta 4 genes supertransfected with CD4. These results indicate that the allelic exclusion of MS202 was achieved by a post-translational mechanism where the product of an in-frame rearranged alpha chain was unable to be expressed on the cell surface, allowing further rearrangement and expression of the other alpha chain gene. The self-class II reactivity of TCR was dependent on the co-expression of CD4 molecules.