Identification of an ataxia telangiectasia-mutated protein mediated surveillance system to regulate Bcl-2 overexpression

Bcl-2 can both promote and attenuate tumorigenesis. Although the former function is relatively well characterized, the mechanism of the latter remains elusive. We report here that enforced Bcl-2 expression in MCF7 cells stabilizes p53, induces phosphorylation of p53 serine 15 (p53pSer15) and inhibits MCF7 cell growth. Consistent with p53 Ser15 being a target of ataxia telangiectasia mutated protein(ATM)/ATR (ATM- and rad3-related) in the DNA damage response, Bcl-2 activates ATM by inducing ATM Ser1981 phosphorylation, which is accompanied with the phosphorylaton of two additional ATM substrates, Chk2 Thr68 and H2AX Ser139. Downregulation of ATM using a specific small interference RNA fragment (ATMRNAi) abolished Bcl-2-induced p53pSer15 and Bcl-2-mediated growth inhibition of MCF7 cells. Ectopic expression of a dominant-negative p53 mutant, p53175H, partially rescued this growth inhibition. Taken together, these observations demonstrate the contribution of ATM-p53 function to Bcl-2-mediated inhibition of MCF7 cell growth, indicating an ATM-mediated surveillance system for regulating Bcl-2 overexpression. Consistent with this concept, we found that MCF7 cells express Bcl-2 heterogeneously with 34.5% of cells being Bcl-2 negative. In general, Bcl-2-positive MCF7 cells proliferate slower than those of Bcl-2 negative. Thus, we provide evidence suggesting that activation of ATM suppresses Bcl-2-induced tumorigenesis, and that attenuation of ATM function may be an important event in breast cancer progression.

Mutant p53 cooperates with ETS and selectively up-regulates human MDR1 not MRP1

The most frequently expressed drug resistance genes, MDR1 and MRP1, occur in human tumors with mutant p53. However, it was unknown if mutant p53 transcriptionally regulated both MDR1 and MRP1. We demonstrated that mutant p53 did not activate either the MRP1 promoter or the endogenous gene. In contrast, mutant p53 strongly up-regulated the MDR1 promoter and expression of the endogenous MDR1 gene. Notably, cells that expressed either a transcriptionally inactive mutant p53 or the empty vector showed no endogenous MDR1 up-regulation. Transcriptional activation of the MDR1 promoter by mutant p53 required an Ets binding site, and mutant p53 and Ets-1 synergistically activated MDR1 transcription. Biochemical analysis revealed that Ets-1 interacted exclusively with mutant p53s in vivo but not with wild-type p53. These findings are the first to demonstrate the induction of endogenous MDR1 by mutant p53 and provide insight into the mechanism.

A Fas-associated death domain protein-dependent mechanism mediates the apoptotic action of non-steroidal anti-inflammatory drugs in the human leukemic Jurkat cell line

Non-steroidal anti-inflammatory drugs (NSAIDs) are inhibitors of cyclooxygenase-1 and -2 and are useful for prevention and cure of cancers, especially colon and rectal cancers. The NSAIDs indomethacin and sulindac sulfide have been shown to induce apoptosis of colon epithelial cancer cells by a Bax-dependent mechanism that involves mitochondria-mediated activation of a caspase-9-dependent pathway. In this report, we demonstrate that indomethacin and sulindac sulfide induce apoptosis of human leukemic Jurkat cells by a mechanism that requires the Fas-associated Death Domain Protein-mediated activation of a caspase-8-dependent pathway. Therefore, NSAIDs induce apoptosis by different mechanisms depending on the cell type.

Aggressive childhood neuroblastomas do not express caspase-8: an important component of programmed cell death

Neuroblastomas that overexpress N-Myc due to amplification of the MYCN oncogene are aggressive tumors that become very resistant to treatment by chemotherapy and irradiation. to identify tumor suppressor genes in this group of neuroblastomas we analyzed the expression and function of both apoptosis-related cell cycle regulatory genes in cell lines and patient tumor samples. We found that in a high percentage of neuroblastoma cell lines and patient samples with amplified MYCN, caspase-8 mRNA is not expressed. The caspase-8 gene, CASP8, was deleted or silenced by methylation in the neuroblastoma cell lines while methylation of its promoter region was the predominant mechanism for its inactivation in the patient tumor samples. Reintroduction of caspase-8 into the neuroblastoma cell lines resensitized these cells to drug-induced and survival factor dependent apoptosis. Subsequently others have also shown that caspase-8 is silenced by methylation in neuroblastoma and peripheral neural ectodermal tumors, and that the caspase-9 regulator Apaf-1 is silenced by methylation in melanoma cell lines and patient samples. We conclude that caspase-8 acts as a tumor suppressor gene in neuroblastomas, that its silencing provides a permissive environment for MYCN gene amplification once the tumors are treated with chemotherapeutic drugs/irradiation, and that expression of this gene in these tumor cells may be of clinical benefit. We also discuss the possible significance of the neural crest cell progenitor cell origin and the silencing of important apoptotic regulators via methylation in both neuroblastoma and melanoma tumors.

Dopaminergic cell death induced by MPP(+), oxidant and specific neurotoxicants shares the common molecular mechanism

Recent etiological study in twins (Tanner et al. 1999) strongly suggests that environmental factors play an important role in typical, non-familial Parkinson's disease (PD), beginning after age 50. Epidemiological risk factor analyses of typical PD cases have identified several neurotoxicants, including MPP(+) (the active metabolite of MPTP), paraquat, dieldrin, manganese and salsolinol. Here, we tested the hypothesis that these neurotoxic agents might induce cell death in our nigral dopaminergic cell line, SN4741 (Son et al. 1999) through a common molecular mechanism. Our initial experiments revealed that treatment with both MPP(+) and the other PD-related neurotoxicants induced apoptotic cell death in SN4741 cells, following initial increases of H(2)O(2)-related ROS activity and subsequent activation of JNK1/2 MAP kinases. Moreover, we have demonstrated that during dopaminergic cell death cascades, MPP(+), the neurotoxicants and an oxidant, H(2)O(2) equally induce the ROS-dependent events. Remarkably, the oxidant treatment alone induced similar sequential molecular events: ROS increase, activation of JNK MAP kinases, activation of the PITSLRE kinase, p110, by both Caspase-1 and Caspase-3-like activities and apoptotic cell death. Pharmacological intervention using the combination of the antioxidant Trolox and a pan-caspase inhibitor Boc-(Asp)-fmk (BAF) exerted significant neuroprotection against ROS-induced dopaminergic cell death. Finally, the high throughput cDNA microarray screening using the current model identified downstream response genes, such as heme oxygenase-1, a constituent of Lewy bodies, that can be the useful biomarkers to monitor the pathological conditions of dopaminergic neurons under neurotoxic insult.

Proteolytic regulation of apoptosis

Much of the proteolysis that occurs during apoptosis is directed by caspases, a family of related cysteinyl proteases. A relatively small number of cellular proteins are targeted by caspases, yet their function is dramatically affected and apoptosis is triggered. Other proteases, such as granzymes and calpain, are also involved in the apoptotic signaling process, but in a much more cell type- and/or stimulus type-specific manner. At least three distinct caspase-signaling pathways exist; one activated through ligand-dependent death receptor oligomerization, the second through mitochondrial disruption, and the third through stress-mediated events involving the endoplasmic reticulum. These pathways also appear to interact to amplify weak apoptotic signals and shorten cellular execution time. Finally, defects in caspases contribute to autoimmune disease, cancer and certain neurological disorders.

Caspase 8 is deleted or silenced preferentially in childhood neuroblastomas with amplification of MYCN

Caspase 8 is a cysteine protease regulated in both a death-receptor-dependent and -independent manner during apoptosis. Here, we report that the gene for caspase 8 is frequently inactivated in neuroblastoma, a childhood tumor of the peripheral nervous system. The gene is silenced through DNA methylation as well as through gene deletion. Complete inactivation of CASP8 occurred almost exclusively in neuroblastomas with amplification of the oncogene MYCN. Caspase 8-null neuroblastoma cells were resistant to death receptor- and doxorubicin-mediated apoptosis, deficits that were corrected by programmed expression of the enzyme. Thus, caspase 8 acts as a tumor suppressor in neuroblastomas with amplification of MYCN.

Caspase-8 activation and bid cleavage contribute to MCF7 cellular execution in a caspase-3-dependent manner during staurosporine-mediated apoptosis

There are at least two distinct classes of caspases, initiators (e.g. caspases-8, -9, and -10) and effectors (e.g. caspase-3). Furthermore, it is believed that there are two distinct primary apoptotic signaling pathways, one of which is mediated by death receptors controlled by caspases-8/10, and the other by the release of cytochrome c and activation of a caspase-9/Apaf1/cytochrome c apoptosome. However, several recent reports have demonstrated that caspase-8, and its substrate Bid, are frequently activated in response to certain apoptotic stimuli in a death receptor-independent manner. These results suggest that significant cross-talk may exist between these two distinct signaling arms, allowing each to take advantage of elements unique to the other. Here we provide evidence that activation of caspase-8, and subsequent Bid cleavage, does indeed participate in cytochrome c-mediated apoptosis, at least in certain circumstances and cell types. Furthermore, the participation of activated caspase-3 is essential for activation of caspase-8 and Bid processing to occur. Although caspase-8 activation is not required for the execution of a cytochrome c-mediated death signal, we found that it greatly shortens the execution time. Thus, caspase-8 involvement in cytochrome c-mediated cell death may help to amplify weaker death signals and ensure that apoptosis occurs within a certain time frame.

Cell cycle regulation and RNA polymerase II

The cell cycle and transcription by RNA polymerase II (RNAP II) are closely related. They utilize shared components. RNAP II transcriptional activity is modulated during the cell cycle. Cell cycle dependent changes in the phosphorylation status of the carboxyl-terminal domain (CTD) of the largest subunit of RNAP II (RNAP II-LS) alter transcription. Several CTD kinases are members of the cyclin-dependent kinase (cdk) superfamily, including p34cdc2 (cdk1), cdk7, cdk8, and cdk9. Each of these cdks, with their respective cyclin partners, have been linked to cell cycle regulatory events. Other CTD kinases such as casein kinase II (CKII) and c-abl have also been implicated in cell cycle dependent modifications of the CTD. In addition, the stalling of RNAP II complexes at DNA lesions helps stimulate p53 accumulation which largely determines the cell's DNA damage response, including cell cycle arrest. Alzheimer's disease pathology results partially from activation of mitotic cdks in postmitotic neurons which can phosphorylate RNAP II-LS and other targets.

Fas-induced apoptosis in human malignant melanoma cell lines is associated with the activation of the p34(cdc2)-related PITSLRE protein kinases

The Cdc2L locus encoding the PITSLRE protein kinases maps to chromosome band 1p36 and consists of two duplicated and tandemly linked genes. The purpose of the present study was to determine whether diminution of PITSLRE kinases leads to deregulation of apoptosis. The human melanoma cell lines A375 (Cdc2L wild-type alleles) and UACC 1227 (mutant Cdc2L alleles) were tested with agonist anti-Fas monoclonal antibody. We found that exposure of these cells to anti-Fas for 24, 48, or 72 h resulted in differential sensitivity to Fas-induced apoptosis. In A375, cell death started at 24-48 h post-treatment, and it was maximal by 72 h. Conversely, UACC 1227 cells were resistant to Fas-mediated apoptosis. Induction of PITSLRE histone H1 kinase activity was observed in A375 anti-Fas treated but not in UACC 1227 cells. Also, the PITSLRE protein kinase activity in A375 anti-Fas-treated cells preceded maximal levels of apoptosis. Finally, fluorescence confocal microscopy revealed a nuclear localization of PITSLRE proteins in normal melanocytes and A375 cells but a cytoplasmic localization in UACC 1227 cells. The differences in PITSLRE protein and cellular localization between A375 and UACC 1227 cells appear to account for the differences in sensitivity of the two cells lines to anti-Fas and staurosporine. These observations suggest that alterations in PITSLRE gene expression and protein localization may result in the loss of apoptotic signaling.

Database search strategies used to isolate cell death proteins

The identification of proteins involved in the early phases of cell death has relied primarily on the modular organization of shared sequences and structural motifs of previously identified proteins in the apoptotic machinery. This property has facilitated the isolation of proteins that interact with each other through structural domains using yeast two-hybrid cloning. Likewise, the conservation in primary sequence of the various shared domains has promoted the use of polymerase chain reaction and database search strategies to isolate additional family members. Here, we discuss the use of database search strategies in the isolation of novel death proteins, as well as how similar strategies may be extended to discover additional, novel cell death proteins.

Cycloheximide-induced T-cell death is mediated by a Fas-associated death domain-dependent mechanism

Cycloheximide (CHX) can contribute to apoptotic processes, either in conjunction with another agent (e.g. tumor necrosis factor-alpha) or on its own. However, the basis of this CHX-induced apoptosis has not been clearly established. In this study, the molecular mechanisms of CHX-induced cell death were examined in two different human T-cell lines. In T-cells undergoing CHX-induced apoptosis (Jurkat), but not in T-cells resistant to the effects of CHX (CEM C7), caspase-8 and caspase-3 were activated. However, the Fas ligand was not expressed in Jurkat cells either before or after treatment with CHX, suggesting that the activation of these caspases does not involve the Fas receptor. To determine whether CHX-induced apoptosis was mediated by a Fas-associated death domain (FADD)-dependent mechanism, a FADD-DN protein was expressed in cells prior to CHX treatment. Its expression effectively inhibited CHX-induced cell death, suggesting that CHX-mediated apoptosis primarily involves a FADD-dependent mechanism. Since CHX treatment did not result in the induction of Fas or FasL, and neutralizing anti-Fas and anti-tumor necrosis factor receptor-1 antibodies did not block CHX-mediated apoptosis, these results may also indicate that FADD functions in a receptor-independent manner. Surprisingly, death effector filaments containing FADD and caspase-8 were observed during CHX treatment of Jurkat, Jurkat-FADD-DN, and CEM C7 cells, suggesting that their formation may be necessary, but not sufficient, for cell death.

Structure and chromosome localization of the human CASP8 gene

The human CASP8 gene, whose product is also known as caspase 8 and FLICE, encodes an interleukin-1beta converting enzyme (ICE)-related cysteine protease that is activated by the engagement of several different death receptors. Caspase 8 is immediately recruited to the Fas receptor once it oligomerizes, and its protease activity is crucial for the apoptotic response generated by the resulting death-inducing signaling complex (DISC). We report here that the CASP8 gene contains at least 11 exons spanning approximately 30kb on human chromosome band 2q33-34. This region of human chromosome 2 was previously reported as the location of the CASP10 gene, whose product is closely related to caspase 8. Chromosome 2 band q33-34 is also involved in tumorigenesis, with loss of heterogeneity (LOH) being reported in a number of tumors. We also report EcoRI and HindIII polymorphisms that may prove to be useful in disease analysis. Both caspases 8 and 10 contain long pro-domains with duplicated death effector domains (DEDs), as well as their corresponding cysteine protease catalytic domains. Thus, it appears that CASP8 and CASP10 have evolved by tandem gene duplication, much like the CASP1, CASP4 and CASP5 gene cluster on human chromosome 11q22.2-22.3.

Abnormalities in the p34cdc2-related PITSLRE protein kinase gene complex (CDC2L) on chromosome band 1p36 in melanoma

The two genes encoding the PITSLRE protein kinase isoforms, CDC2L1 and CDC2L2, are localized to human chromosome band 1p36. The PITSLRE protein kinases are a part of the p34cdc2 supergene family. Several protein products of the CDC2L locus may be effector(s) in apoptotic signaling. The larger PITSLRE p110 isoforms appear to regulate some aspect of RNA splicing/transcription during the cell cycle. One or more of these genes may function as tumor suppressor genes in melanoma. Using fluorescence in situ hybridization, one allele of the CDC2L gene complex on chromosome 1 was either deleted or translocated in 8 of 14 different melanoma cell lines. We also observed mutations in the 5' promoter region of the CDC2L1 gene in four different cell lines relative to normal melanocytes using PCR-SSCP analysis and direct DNA sequencing. Western blot analysis revealed decreased level of PITSLRE protein expression in several cell lines, as well as in four surgical malignant melanoma specimens relative to normal melanocytes. Thus, the decreased PITSLRE protein expression appears to result from deletion of the CDC2L alleles and possibly by mutations within the 5' promoter region. We propose that aberrations in the CDC2L genes may contribute to the pathogenesis or progression of melanoma.

Fluorescence in situ hybridization analysis of chromosome 1p36 deletions in human MYCN amplified neuroblastoma

BACKGROUND/PURPOSE

Deletion of the short arm of chromosome 1 (1p) is one of the poor prognostic factors in human neuroblastomas. Recent studies have suggested that one or more of the neuroblastoma tumor suppressor genes reside in this region and have identified the shortest region of overlap (SRO) on 1p36. The purpose of this study was to examine deletions of 1p in human neuroblastomas by fluorescence in situ hybridization (FISH).

METHODS

Two-color FISH analysis was performed to detect chromosome 1p36 abnormalities in 42 MYCN-amplified neuroblastomas. Four different probes from the 1p36 region, the E2F2, NPPA, D1S160, and CDC2L1 loci were used for detection of 1p abnormalities. A repeat sequence probe, which is specific for the heterochromatic region of chromosome 1 (pUC1.77), was used as a control.

RESULTS

Large deletions of 1p36 were observed in 31 (73.8%) of 42 tumors, whereas the remaining 11 (26.2%) showed no deletion. In these 11 tumors, a translocation of 1p was found in one and a duplication of 1p was detected in another.

CONCLUSIONS

A strong correlation between 1p abnormalities and MYCN amplification was found in this study. MYCN-amplified neuroblastomas were found to show large deletions of 1p encompassing the SRO. FISH provided a rapid and reliable method to detect hemizygous deletions of 1p.

Cleavage of DFF-45/ICAD by multiple caspases is essential for its function during apoptosis

Apoptosis involves the proteolysis of specific cellular proteins by a group of cysteine proteases known as caspases. Many of these cellular targets are either functionally inactivated (e.g. poly(ADP-ribose) polymerase) or activated (e.g. other caspases, gelsolin) by such processing, thereby facilitating the cell death process. Caspase 3 is involved in the processing of many of these proteins. Recently, however, it was reported that caspase 3 is dispensable for the cleavage of a large number of cellular caspase substrates during apoptosis. Among these substrates is DFF-45/ICAD, a subunit of the heterodimeric DNA fragmentation factor (DFF), otherwise known as caspase-activated DNase (CAD), that mediates genomic DNA degradation during apoptosis. Conversely, others have reported that caspase 3 is essential for the cleavage and activation of DFF-45/ICAD. To resolve this controversy we examined DFF-45/ICAD processing during apoptosis in MCF-7 breast carcinoma cells that lack functional caspase 3 and in MCF-7 cells expressing caspase 3. We found that DFF-45/ICAD is cleaved by two distinct caspases, one of which is caspase 3. Furthermore, cleavage of the carboxyl-terminal region of DFF-45/ICAD, which is necessary for activation of the enzyme, requires functional caspase 3. In the absence of caspase 3 cleavage of the amino-terminal region of DFF-45/ICAD by another caspase occurs, but the DFF-45 enzyme remains inactive.

Duplication of a genomic region containing the Cdc2L1-2 and MMP21-22 genes on human chromosome 1p36.3 and their linkage to D1Z2

Cdc2L1 and Cdc2L2 span approximately 140 kb on human chromosome 1p36.3. The products of the Cdc2L genes encode almost identical protein kinases, the PITSLRE kinases, which have functions that may be relevant to the regulation of transcription/splicing and apoptotic signaling. These genes are deleted/translocated in neuroblastomas with MYCN gene amplification, a subset of malignant melanomas, and in a newly delineated deletion syndrome. Here we report that the p36.3 region of human chromosome 1 consists of two identical genomic regions, each of which contain a Cdc2L gene linked to a metalloprotease (MMP) gene in a tail-to-tail configuration. This duplicated genomic region is also linked tightly to D1Z2, a genetic marker containing a highly polymorphic VNTR (variable number tandem repeat) consisting of an unusual 40-bp reiterated sequence. Thus, these genes and the polymorphic marker D1Z2 are organized as follows: telomere-D1Z2-5'-MMP22-3'-3'-Cdc2L2-5'-5'-Cdc2L1 -3'- 3'-MMP21-5'-centromere. Remarkably, the introns and exons of Cdc2L1 and Cdc2L2, as well as their flanking regions, are essentially identical. A total of 15 amino acid differences, 12 nonconservative and 3 conservative, can be found in the 773-786 amino acids specified by the various products of the Cdc2L genes. Two separate promoter/5' untranslated (UT) regions, CpG1 and CpG2, are identical to a reported previously methylated genomic CpG sequence and are used to express >20 different Cdc2L transcripts from the two genes. The expression of CpG2 transcripts from Cdc2L1 and Cdc2L2 is tissue/cell-line specific. CpG1 transcripts are expressed ubiquitously from both genes, with perhaps some bias towards the expression of CpG1 Cdc2L1 mRNAs in certain hematopoietic cells.

Isolation and characterization of two novel metalloproteinase genes linked to the Cdc2L locus on human chromosome 1p36.3

The terminal end of the short arm of human chromosome 1, 1p36.3, is frequently deleted in a number of tumors and is believed to be the location of multiple tumor suppressor genes. Thus far, a bona fide tumor suppressor gene from this region has not been identified. The isolation and characterization of new 1p36 genes is, therefore, of some interest. Two novel matrix metalloproteinase genes, MMP21 and MMP22, have been identified in the Cdc2L1-2 locus, which spans approximately 120 kb on 1p36.3. These genes encode novel metalloproteinases that contain prepro, catalytic, cysteine-rich, interleukin-1 receptor-related, and proline-rich domains. Their catalytic domains are most closely related to stromelysin-3 and contain the consensus HEXXH zinc-binding region required for enzyme activation, while their cysteine-rich domains appear to be related to a number of human, mouse, and Caenorhabditis elegans metalloproteinase sequences. Of some possible interest is the absence of a highly conserved cysteine residue in the proenzyme domain, the so-called "cysteine switch," which has been shown to be involved in the autocatalytic activation of many metalloproteinases. The MMP genes are located less than 1 kb from the 3' regions of Cdc2L1 and Cdc2L2, suggesting that the MMP and Cdc2L genes are part of a larger region that has been duplicated. Finally, the MMP21/22 genes express multiple mRNAs, some of which are derived by alternative splicing, in a tissue-specific manner.

Phosphorylation of PITSLRE p110 isoforms accompanies their processing by caspases during Fas-mediated cell death

A number of cellular proteins have been identified as caspase targets during cell death, including the PITSLRE protein kinases. These targets generally fall into one of three possible categories: 1) other caspases, 2) proteins that are inactivated during apoptosis, and 3) proteins that are required for execution of the cell death program. However, not all proteins are cleaved by caspases during apoptosis. Why only specific proteins are destined to be processed by caspases during cell death is currently not clear. Here we show that multiple caspase-like activities are involved in the processing of the PITSLRE p110 isoforms during Fas-induced apoptosis in Jurkat T-cells. Three p110 caspase cleavage sites have been mapped to the amino-terminal domain of p110 and verified by site-directed mutagenesis. Curiously, the mutagenesis studies revealed that cleavage of two juxtaposed caspase sites is necessary for the complete processing of this protein during cell death in vivo. Finally, we demonstrate that the PITSLRE p110 protein is rapidly phosphorylated during Fas-induced apoptosis in Jurkat cells and that phosphorylation of an amino-terminal portion of the protein may enhance caspase cleavage in this region.

Disruption of the cyclin D/cyclin-dependent kinase/INK4/retinoblastoma protein regulatory pathway in human neuroblastoma

The p16INK4a (MTS1) and pl8INK4c gene products are normal, and highly expressed, in human neuroblastoma cell lines. The retinoblastoma protein (pRb) was, nonetheless, phosphorylated and functional in these cells. Such high levels of p16INK4a/p18INK4c should normally inhibit cyclin-dependent kinase (CDK) 4 and 6 activities in cells containing functional pRb, delaying cell cycle progression and growth. These neuroblastoma cell lines express both CDK4 and CDK6 mRNA and protein, but only significant CDK6 protein kinase activity was detected in this study. In addition, CDK6 was not present in p16INK4a immune complexes in cells with significant kinase activity, although p16INK4a levels were high. Others have shown that a specific mutation in the NH2-terminal region of the CDK4 gene product can disrupt p16INK4a binding, thereby bypassing its inhibitory activity. To determine whether mutation of the CDK6 gene, or some other mechanism, is responsible for the CDK6 kinase activity in these cell lines, several complementary analyses were performed. The CDK6 gene from each cell line was examined for mutations that might affect p16INK4a binding, whereas p16INKa add-back experiments were performed with CDK6 immune complexes to assess p16INK4a function. A bona fide CDK6 mutation that disrupts p16INK4a binding and prevents inhibition of CDK6 protein kinase activity was identified in 1 of 17 neuroblastoma cell lines. The mechanism(s) responsible for disruption of p16INK4a inhibitory activity in the remaining cell lines is unknown, but these results suggest that neuroblastoma cells may bypass the cell cycle block imposed by constitutive expression of wild-type p16INK4a in novel ways.

The RNP protein, RNPS1, associates with specific isoforms of the p34cdc2-related PITSLRE protein kinase in vivo

The PITSLRE protein kinases are members of the p34cdc2 superfamily, with >20 different isoforms expressed from two linked genes in humans. PITSLRE homologues have been identified in mouse, chicken, Drosophila, Xenopus, and possibly Plasmodium falciparum, suggesting that their function may be well conserved. A possible role for a caspase processed PITSLRE isoform has been suggested by studies of Fas- and TNF-induced cell death. However, the function of these kinases in proliferating cells is still unknown. Here we demonstrate that the 110 kDa PITSLRE isoforms (p110) are localized to both the nucleoplasm and nuclear speckles, and that these isoforms specifically interact in vitro and in vivo with the RNA-binding protein RNPS1. RNPS1 is also localized to nuclear speckles, and its over expression disrupts normal nuclear speckle organization by causing the aggregation of many nuclear speckles into approximately 6 ‘mega’ speckles. This type of nuclear speckle aggregation closely resembles what occurs when cells are treated with several transcriptional inhibitors. These data indicate that the PITSLRE p110 isoforms interact with RNPS1 in vivo, and that these proteins may in turn influence some aspect of transcriptional and/or splicing regulation.

Duplication of the DR3 gene on human chromosome 1p36 and its deletion in human neuroblastoma

The human DR3 gene, whose product is also known as Wsl-1/APO-3/TRAMP/LARD, encodes a tumor necrosis factor-related receptor that is expressed primarily on the surface of thymocytes and lymphocytes. DR3 is capable of inducing both NF-kappa B activation and apoptosis when overexpressed in mammalian cells, although its ligand has not yet been identified. We report here that the DR3 gene locus is tandemly duplicated on human chromosome band 1p36.2-p36.3 and that these genes are hemizygously deleted and/or translocated to another chromosome in neuroblastoma (NB) cell lines with amplified MYCN. Duplication of at least a portion of the DR3 gene, including the extracellular and transmembrane regions but not the cytoplasmic domain, was demonstrated by both fluorescence in situ hybridization and genomic Southern blotting. In most NB cell lines, both the DR3 and the DR3L sequences are simultaneously deleted and/or translocated to another chromosome. Finally, DR3/ Wsl-1 protein expression is quite variable among these NB cell lines, with very low or undetectable levels in 7 of 17 NB cell lines.

Proteolytic activities that mediate apoptosis

Since the discovery that cells can activate their own suicide program, investigators have attempted to determine whether the events that are associated with this form of cell death are genetically determined. The discovery that the ced-3 gene of Caenorhabditis elegans encodes a cysteine protease essential for developmentally regulated apoptosis ignited interest in this area of research. As a result, we now know that cell death is specified by a number of genes and that this biologic process contributes significantly to development, tumorigenesis, and autoimmune disease. In this review I summarize what is currently known about signaling pathways involved in apoptosis, with particular emphasis on the function of the cysteine proteases known as caspases. However, there is also evidence that protease-independent cell death pathways exist. Is there a relationship between these two distinct mechanisms? If so, how do they communicate? Finally, even though the involvement of tumor necrosis factor/nerve growth factor family of receptors and cysteine proteases has been elegantly established as a component of many apoptotic signaling pathways, what happens downstream of these initial events? Why are only a selected group of cellular proteins--many nuclear--the targets of these proteases? Are nuclear events essential for apoptosis in vivo? Are the cellular genes that encode products involved in apoptotic signaling frequent targets of mutation/alteration during tumorigenesis? These are only a few questions that may be answered in the next ten years.

The PITSLRE protein kinase family

A family of p34Cdc2 related protein kinases, the PITSLRE kinases, is generated by alternative splicing and promoter utilization from three duplicated and tandemly linked genes on human chromosome 1p36.3, which is frequently deleted during the late stages of tumorigenesis. PITSLRE mRNA, protein, and enzyme activity are induced during Fas receptor- and glucocorticoid-mediated apoptosis of human T cells. Several PITSLRE isoforms are specific targets of proteolysis during apoptosis, generating an enzymatically active 50 kDa isoform. Inhibition of this protease activity blocks PITSLRE processing and enzyme activation, as well as apoptosis. Thus, PITSLRE kinases may be integral downstream components of apoptotic signal transduction pathway(s). Furthermore, PITSLRE genes, and their products, are physically altered in human neuroblastoma tumors, suggesting that they may be tumor suppressors.

Fas activates NF-κB and induces apoptosis in T-cell lines by signaling pathways distinct from those induced by TNF-α

The p55 tumor necrosis factor (TNF) receptor and the Fas (CD95/APO-1) receptor share an intracellular domain necessary to induce apoptosis, suggesting they utilize common signaling pathways. To define pathways triggered by Fas and TNF-alpha we utilized human CEM-C7 T-cells. As expected, stimulation of either receptor induced apoptosis and TNF-alpha-induced signaling included the activation of NF-kappaB. Surprisingly, Fas-induced signaling also triggered the activation of NF-kappaB in T cells, yet the kinetics of NF-kappaB induction by Fas was markedly delayed. NF-kappaB activation by both pathways was persistent and due to the sequential degradation of IkappaB-alpha and IkappaB-beta. However, the kinetics of IkappaB degradation were different and there were differential effects of protease inhibitors and antioxidants on NF-kappaB activation. Signaling pathways leading to activation of apoptosis were similarly separable and were also independent of NF-kappaB activation. Thus, the Fas and TNF receptors utilize distinct signal transduction pathways in T-cells to induce NF-kappaB and apoptosis.

Cleavage of PITSLRE kinases by ICE/CASP-1 and CPP32/CASP-3 during apoptosis induced by tumor necrosis factor

Emerging evidence suggests that multiple aspartate-specific cysteine proteases (caspases (CASPs)) play a crucial role in programmed cell death. Many cellular proteins have been identified as their substrates and serve as markers to assay the activation of CASPs during the death process. However, no substrate has yet been unambiguously identified as an effector molecule in apoptosis. PITSLRE kinases are a superfamily of Cdc2-like kinases that have been implicated in apoptotic signaling and tumorigenesis. In this paper we report that tumor necrosis factor (TNF)-mediated apoptosis is associated with a CrmA- and Bcl-2-inhibitable cleavage of PITSLRE kinases, indicating a role for CASPs. Testing of seven murine CASPs for their ability to cleave p110 PITSLRE kinase alpha2-1 in vitro revealed that only CASP-1 (ICE (interleukin-1beta-converting enzyme)) and CASP-3 (CPP32) were able to produce the same 43-kDa cleavage product as observed in cells undergoing TNF-induced apoptosis. Mutational analysis revealed that cleavage of p110 PITSLRE kinase alpha2-1 occurred at Asp393 within the sequence YVPDS, which is similar to that involved in the CASP-1-mediated cleavage of prointerleukin-1beta. TNF-induced proteolysis of PITSLRE kinases was still observed in fibroblasts from CASP-1(0/0) mice. These data implicate CASP-3 as a potentially important CASP family protease responsible for the cleavage of PITSLRE kinases during TNF-induced apoptosis.

Elimination of cyclin D1 in vertebrate cells leads to an altered cell cycle phenotype, which is rescued by overexpression of murine cyclins D1, D2, or D3 but not by a mutant cyclin D1

DT40 lymphoma B-cells normally express cyclins D1 and D2 but not D3. When cyclin D1 expression was extinguished in these cells by gene knockout, specific alterations in their ability to transit the cell cycle were observed. These changes are exemplified by a delay of approximately 2 h in their progression through a normal 14-h cell cycle. This delay results in an increase in the number of cells in the G2/M phase population, most likely due to triggering of checkpoints in G2/M, inability to enter G1 normally, and/or alterations of crucial event(s) in early G1. The defect(s) in the cell cycle of these D1 "knockout" cells can be rescued by overexpression of any normal mouse D-type cyclin but not by a mutant mouse cyclin D1 protein that lacks the LXCXE motif at its amino terminus. These data suggest that the cell cycle alterations observed in the D1-/- cells are a direct effect of the absence of the cyclin D1 protein and support the hypothesis that the D-type cyclins have separate, but overlapping, functions. Elimination of cyclin D1 also resulted in enhanced sensitivity to radiation, resulting in a significant increase in apoptotic cells. Expression of any normal murine D-type cyclin in the D1-/- cells reversed this phenotype. Intriguingly, expression of the mutant cyclin D1 in the D1 -/- cells partially restored resistance to radiation-induced apoptosis. Thus, there may be distinct differences in cyclin D1 complexes and/or its target(s) in proliferating and apoptotic DT40 lymphoma B-cells.

Characterization of putative human homologues of the yeast chromosome transmission fidelity gene, CHL1

Helicases are components of numerous protein complexes, including those regulating transcription, translation, DNA replication and repair, splicing, and mitotic chromosome transmission. Helicases unwind double-stranded DNA and RNA homo- and hetero-duplexes. The yeast CHL1 helicase has been linked to maintenance of the high fidelity of chromosome transmission during mitosis. Mutations in this gene result in a 200-fold increase in the rate of aberrant chromosome segregation with a concomitant delay in the cell cycle at G2-M, suggesting that CHL1 is required for the maintenance of proper chromosome transmission. Two highly related human cDNA clones encoding proteins which are homologous to the yeast CHL1 gene product have been isolated. Here we show that these two distinct human CHL1-related mRNAs and proteins (hCHLR1 and hCHLR2) are expressed only in proliferating human cell lines. Quiescent normal human fibroblasts stimulated to re-enter the cell cycle by addition of serum begin to express the CHL1-related proteins as the cells enter S phase, concomitant with the expression of proliferating cell nuclear antigen. Furthermore, expression of the CHL1-related mRNAs is lost when human K562 cells cease to proliferate and terminally differentiate in response to phorbol ester treatments. Human hCHLR expression is not extinguished during hemin-induced differentiation of the same cell line, which produces erythrocyte-like cells that continue to proliferate. These experiments are consistent with the requirement of this putative helicase during either S or G2-M phase but not G1. In vitro transcribed and translated hCHLR1 protein binds to both single- and double-stranded DNA, supporting the possibility that these proteins are DNA helicases. Finally, affinity-purified hCHLR1 antisera was used to demonstrate the localization of the hCHLR proteins to the nucleolus by indirect immunofluorescence as well as by cell fractionation.

Alternatively spliced cyclin C mRNA is widely expressed, cell cycle regulated, and encodes a truncated cyclin box

The cyclin C protein has recently been shown to associate with a unique cyclin dependent protein kinase (cdk8) and it has been proposed that this complex may regulate RNA transcription during the cell cycle. In addition, the human cyclin C gene has been localized to human chromosome 6q21 and it was found to be frequently deleted in a subset of acute lymphoblastic leukemias (ALL's). Screening of an avian T-cell cDNA library resulted in the isolation of a cyclin C homologue as well as an abundant, yet distinct, cyclin C-related cDNA. The predicted open reading frame (ORF) of the cyclin C cDNA predicted a 283 amino acid protein that was > 99% identical to the human protein and 72% identical to the Drosophila melanogaster protein. However, the predicted ORF of the cyclin C-related cDNA predicted a much smaller 105 amino acid protein that was identical to cyclin C well into the cyclin-box region (amino acid residue 98), where it abruptly diverges and then terminates. Using PCR analysis of cDNA derived from a range of cell lines and tissues, alternative splicing of the avian cyclin C gene has been demonstrated. Furthermore, a smaller approximately 19 kDa protein that co-migrates with the in vitro transcribed and translated truncated cyclin C protein was detected in normal and virally-transformed avian cells with a cyclin C-specific antibody. Expression of alternatively spliced cyclin C mRNA and protein is regulated in a cell cycle-dependent manner reminiscent of cyclin B2. The function of this truncated cyclin C protein is not known, but its expression in avian cells suggest that this truncated cyclin C protein may participate as an early endogenously encoded cyclin C inhibitor.

Molecular cloning and chromosomal localization of the human cyclin C (CCNC) and cyclin E (CCNE) genes: deletion of the CCNC gene in human tumors

The human Gi-phase cyclins are important regulators of cell cycle progression that interact with various cyclin-dependent kinases and facilitate entry into S-phase. We have confirmed the localization of the human cyclin C (CCNC) gene to chromosome 6q21 and of human cyclin E (CCNE) to 19q12. The CCNC gene structure was also determined, and we have shown that it is deleted in a subset of acute lymphoblastic leukemias, including a patient sample containing a t(2;6)(p21;q15), with no apparent cytogenetic deletion. Single-strand conformational polymorphism analysis of the remaining CCNC allele from patients with a deletion of one allele established that there were no further mutations within the exons or the flanking intronic sequences. These results suggest either that haploinsufficiency of the cyclin C protein is sufficient to promote tumorigenesis or that the important tumor suppressor gene is linked to the CCNC locus.

Localization of chi1-related helicase genes to human chromosome regions 12p11 and 12p13: similarity between parts of these genes and conserved human telomeric-associated DNA

The helicase enzymes are essential components of a number of multi-protein complexes, including those that regulate transcription, splicing, translation, and DNA repair. These enzymes assist in the unwinding of double-stranded DNA and RNA as an essential part of their function. The yeast Chl1 gene encodes a putative helicase that appears to be essential for normal chromosome transmission. Human cDNAs related to this yeast gene, hCHLR1 and hCHLR2, were recently isolated and shown to encode products that localize to the nucleus. Two corresponding genes have now been partially characterized and localized to human chromosome regions 12p11 and 12p13, indicating that this gene is contained within a duplicated region localized to 12p. In addition, a comparison of the hCHLR gene sequences with available databases indicates that a large portion of these genes, including exons encoding two functional domains of the carboxyl-terminal region of these proteins, has been duplicated as part of a larger human telomeric repeat sequence found on many human chromosomes. Our results suggest that duplication of a relatively large region of chromosome 12p containing this putative helicase gene has resulted in the creation of numerous pseudogenes as part of a subtelomeric repeat. The presence of these helicase pseudogenes, as well as pseudogenes for other genes such as the interleukin-9 receptor, within many subtelomeric regions support the possibility that the spread of this region is subject to exchange between different chromosomes and may have implications for elucidation of the mechanism of intra- and interchromosomal duplication events.

Structure and gene expression of avian cyclin D2

Avian cyclin D2 (Cyl D2)-encoding cDNA clones were isolated from a chicken UG9 T-cell lambda gt10 library. Sequence analysis revealed a high degree of sequence conservation with both the mouse and human Cyl D2, and somewhat lower similarity with the mouse and human Cyl D1 and D3. The homology is highest between species in the Cyl-box domain which is well conserved among human, mouse and chicken. A single 6.0-kb CYL2 mRNA is produced in both avian B- and T-cells, as expected.

Molecular cloning, expression pattern, and chromosomal localization of human CDKN2D/INK4d, an inhibitor of cyclin D-dependent kinases

Progression through the G1 phase of the cell cycle is dependent on the activity of holoenzymes formed between D-type cyclins and their catalytic partners, the cyclin-dependent kinases cdk4 and cdk6. p16INK4a, p15INK4b, and p18INK4c, a group of structurally related proteins, function as specific inhibitors of the cyclin D-dependent kinases and are likely to play physiologic roles as specific regulators of these kinases in vivo. A new member of the INK4 gene family, murine INK4d, has recently been identified. Here we report the isolation of human INK4d (gene symbol CDKN2D), which is 86% identical at the amino acid level to the murine clone and approximately 44% identical to each of the other human INK4 family members. The INK4d gene is ubiquitously expressed as a single 1.4-kb mRNA with the highest levels detected in thymus, spleen, peripheral blood leukocytes, fetal liver, brain, and testes. The abundance of INK4d mRNA oscillates in a cell-cycle-dependent manner with expression lowest at mid G1 and maximal during S phase. Using a P1-phage genomic clone of INK4d for fluorescence in situ hybridization analysis, the location of this gene was mapped to chromosome 19p13. No rearrangements or deletions of the INK4d gene were observed in Southern blot analysis of selected cases of pediatric acute lymphoblastic leukemia (ALL) containing a variant (1;19)(q23;p13) translocation that lacks rearrangement of either E2A or PBX1, or in ALL cases containing homozygous or hemizygous deletions of the related genes, INK4a and INK4b.

Structure and expression of chicken protein kinase PITSLRE-encoding genes

The human PITSLRE protein kinases (PK), members of the p34cdc2 kinase family named according to the single amino acid (aa) code of an important (PSTAIRE) regulatory region [Meyerson et al., EMBO J. 11 (1992) 2909-2917], are candidate tumor suppressor gene(s) localized to human chromosome 1p36.2 and a syntenic region of mouse chromosome 4 [Lahti et al., Nature Genet. 7 (1994) 370-375; Mock et al., Mammal. Genome 5 (1994) 191-192]. At least ten isoforms of this PK family are expressed from three duplicated and tandemly linked genes in humans [Xiang et al., J. Biol. Chem. 269 (1994) 15786-15794]. We have now isolated two different species of PITSLRE PK cDNAs from chicken that encode identical polypeptides, but are clearly expressed from different genes, based on nucleotide (nt) differences. Isolation of one of the corresponding chicken PITSLRE PK genes confirms that only one of the two species of PITSLRE mRNA is expressed from this gene. Comparison of the predicted avian PITSLRE PK aa sequence to human and mouse sequences shows a high degree of sequence identity (> 91%). Like humans, the PITSLRE PK genes in chickens must be closely linked, based on fluorescent in situ hybridization (FISH) localization of these genes to a single chicken microchromosome. PITSLRE PK mRNAs are expressed in two avian B- and T-cell lines. These results suggest that the PITSLRE PK gene family has been well conserved evolutionarily, that the gene duplication observed in humans is not a recent event, and that expression of redundant PITSLRE mRNAs is observed in different vertebrate species.

PITSLRE protein kinase activity is associated with apoptosis

Minimal ectopic expression of a 58-kDa protein kinase (PITSLRE beta 1), distantly related to members of the cdc2 gene family, induces telophase delay, abnormal chromosome segregation, and decreased growth rates in Chinese hamster ovary cells. Here we show that this decrease in cell growth rate is due to apoptosis. Apoptosis is also induced by ectopic expression of an amino-terminal deletion mutant containing the catalytic and C-terminal domains of PITSLRE beta 1 but not by other mutants lacking histone H1 kinase activity or by other members of the cdc2 gene family. However, unlike the wild-type PITSLRE beta 1 over-expressors, ectopic expression of the N-terminal PITSLRE beta 1 mutant does not result in telophase delay or abnormal chromosome segregation. These results suggested that the function of this protein kinase could be linked to apoptotic signaling. To test this hypothesis, we examined levels of PITSLRE mRNA, steady-state protein, and enzyme activity in human T cells undergoing apoptosis after activation with the anti-Fas monoclonal antibody (MAb). All were substantially elevated shortly after Fas MAb treatment. In addition to new transcription and translation, proteolysis contributed to the increased steady-state levels of a novel 50-kDa PITSLRE protein, as suggested by the diminution of larger PITSLRE isoforms observed in the same cells. Indeed, treatment of the Fas-activated T cells with a serine protease inhibitor prevented apoptotic death and led to the accumulation of larger, less active PITSLRE kinase isoforms but not the enzymatically active 50-kDa PITSLRE isoform. Finally, induction of apoptosis by glucocorticoids in the same cell line, as well as by Fas MAb treatment of another T-cell line, led to a similar induction of 50-kDa PITSLRE protein levels over time. These findings suggest that (i) PITSLRE kinase(s) may lie within apoptotic signaling pathway(s), (ii) serine protease activation may be an early event in Fas-activated apoptosis of human T cells, and (iii) some PITSLRE kinase isoforms may be targets of apoptotic proteases.

Reduced galactosyltransferase mRNA levels are associated with the agalactosyl IgG found in arthritis-prone MRL-lpr/lpr strain mice

MRL-lpr/lpr strain mice have defectively glycosylated IgG. This may be related to the rheumatoid arthritis (RA)-like disease that occurs in these mice, because a similar glycosylation defect is seen in human subjects with RA. Whilst it is known that this defect is associated with reduced activity of the beta-1,4-galactosyltransferase (beta-1,4-GalTase) enzyme, the cause of this reduced activity is at present unknown. We have therefore examined the molecular genetics of beta-1,4-GalTase in MRL-lpr/lpr mice. Using 10 different restriction endonucleases we found no evidence for a polymorphic variant of the gene in glycosylation-defective mice. However, the level of mRNA for beta-1,4-GalTase was lowest in the MRL-lpr/lpr mice, the strain with the most poorly galactosylated IgG of the four strains examined. Thus, the reduced level of IgG oligosaccharide galactosylation found in MRL-lpr/lpr strain mice appears to be related to either an altered transcriptional level of, or altered mRNA stability for, beta-1,4-GalTase in lymphocytes from these mice.

Analysis of the 5' flanking sequences from the human protein kinase p58 (PITSLRE beta 1)-encoding gene

The p58 (PITSLRE beta 1) protein kinase (PK) is a member of a large supergene family related to the master mitotic protein kinase, p34cdc2. This PK is also a member of a sub-family itself, with at least six additional related PITSLRE PK isoforms expressed by alternative splicing and promoter utilization from three duplicated genes. Minimal overproduction of the PITSLRE beta 1 PK in Chinese hamster ovary cells results in a late mitotic delay, suggesting that this PK's function may be related to the cell cycle [Bunnell et al., Proc. Natl. Acad. Sci. USA 87 (1990) 7467-7471]. Further studies using structural and functional mutants have shown that PITSLRE PKs are involved in signaling apoptosis. The gene encoding the PITSLRE beta 1 PK has previously been isolated and structurally characterized [Eipers et al., Genomics 13 (1992) 613-621]. Here we characterize the minimal essential promoter for this gene. Analysis of a 1.18-kb stretch of DNA located upstream from the PITSLRE beta 1 start codon demonstrates that significant cat gene expression can be driven by a construct containing this sequence. Deletion studies of this DNA fragment have defined a minimal promoter that extends 144 bp 5' of the previously mapped transcription start point (tsp), and 521 bp 5' of the start codon. This region of PITSLRE beta 1 DNA does not contain canonical TATA-box sequences or G + C-rich sequences associated with many promoters, yet it has approximately 20% of the promoting activity when compared to the SV40 early promoter. This suggests that this DNA sequence is a relatively strong basal promoter of a previously uncharacterized type.

Alterations in the PITSLRE protein kinase gene complex on chromosome 1p36 in childhood neuroblastoma

p58cdc2L1, a protein kinase implicated in apoptotic signaling, is one of eight separate kinases encoded by three tandemly duplicated and linked genes, which we have termed PITSLRE A, B and C. One allele of this complex on chromosome 1 was either deleted or translocated in each of 18 neuroblastoma cell lines with cytogenetically apparent 1p alterations. A protein encoded by this locus, PITSLRE gamma 1, was absent in three of the lines and a smaller, apparently truncated, PITSLRE polypeptide was found in another line. These findings identify a novel gene complex on chromosome 1 that encodes a protein kinase subfamily. We suggest that the PITSLRE locus may harbour one or more tumour suppressor genes affected by chromosome 1p36 modifications in neuroblastoma.

Molecular cloning and expression of alternatively spliced PITSLRE protein kinase isoforms

Minimal ectopic expression of the p58GTA protein kinase results in a provocative phenotype involving cell cycle delay, mitotic catastrophe, and decreased cell viability. In addition, this kinase is well conserved evolutionarily, ubiquitously expressed, and its genes map to a position on human chromosome 1 frequently deleted in the late stages of tumorigenesis. Here we report that the p58GTA protein kinase is a member of a larger subfamily of proteins. The mRNAs encoding these proteins are generated by alternative splicing from multiple duplicated genes. These isoforms range in size from 50 to 110 kDa. Divergence between the alternatively spliced isoforms is localized to the amino-terminal region of the molecule. The entire p58GTA open reading frame is conserved in most of these p58GTA isoforms. The predicted sequences of the larger isoforms encode bipartite nuclear localization signal sequences and extensive polyglutamic acid domains. Antibodies to the p58GTA isoform were used to confirm the presence of the alternatively spliced isoforms in different cell types as well as identify two additional isoforms that appear to arise from a separate gene(s). Cellular fractionation studies indicate that one of the isoforms is found only in the nucleus, and the remainder are found in both the cytoplasm and the nucleus. Expression and localization of some p58GTA isoforms suggest that they may have specialized cellular functions. Because of the large number of isoforms generated from multiple genes we propose naming these kinases PITSLRE alpha 1, alpha 2-1, alpha 2-2, alpha 2-3 alpha 2-4, beta 1, beta 2-1, and beta 2-2 based on the conserved sequence of the PSTAIRE box unique to p34cdc2 kinases and the gene from which they are transcribed.

2-Aminopurine overrides a late telophase delay created by ectopic expression of the PITSLRE beta 1 protein kinase

Minimal overexpression of the PITSLRE beta 1 protein kinase in CHO cells leads to a marked delay in late mitosis. We have previously shown that this delay is characterized by the presence of substantially increased numbers of tubulin midbodies, inhibition of cytokinesis, and numerous multinucleated and micronucleated cells. Others have shown that the protein kinase inhibitor 2-aminopurine (2-AP) is capable of overriding drug induced cell cycle blocks. In this study we demonstrate that the late mitotic delay and altered cellular morphology caused by ectopic expression of the PITSLRE beta 1 protein kinase can be overcome by 2-aminopurine treatment. Furthermore, 2-aminopurine inhibits PITSLRE beta 1 protein kinase activity in vivo, but does not effect p34cdc2 protein kinase activity in a similar manner.

Chromosomal localization of the IL-6 receptor signal transducing subunit, gp130 (IL6ST)

Signal transduction in eukaryotic cells is a complex process mediated, normally, by the interaction of soluble extrinsic protein factors and their cognate receptors. One example of this phenomena is the inflammatory cytokine interleukin-6 and the IL-6 receptor. However, the IL-6 receptor, once its ligand is bound, associates with another membrane glycoprotein, gp130, to potentiate the cytokine response. To further understand the basis of this interaction, and its possible implications in cellular transforming events, the corresponding gene(s) must be studied. Here we find that the human gp130 gene product is homologous to two distinct chromosomal loci on chromosomes 5 and 17. Furthermore, the presence of two distinct gp130 gene sequences is restricted to primates and is not found in other vertebrates.

Structure and expression of the human p58clk-1 protein kinase chromosomal gene

A cDNA corresponding to a 58-kDa cell division control-related protein kinase, p58clk-1, has previously been isolated, sequenced, and assigned to human chromosome 1p36. Aberrant expression of this protein kinase negatively regulates normal cellular growth. The p58clk-1 protein contains a central domain of 299 amino acids that is 46% identical to human p34cdc2, the master mitotic protein kinase. Deletion of 1p36 has been correlated to numerous tumors, and this chromosome region has been suggested to harbor a putative tumor suppressor gene on the basis of the growth characteristics of these tumors. In this report we detail the complete structure of the p58clk-1 chromosomal gene, including its putative promoter region, transcriptional start sites, exonic sequences, and intron/exon boundary sequences. The gene is 10 kb in size and contains 12 exons and 11 introns. Interestingly, the rather large 2.0-kb 3' untranslated region is interrupted by an intron that separates a region containing numerous AUUUA destabilization motifs from the coding region. Furthermore, we detail the expression of this gene in normal human tissues as well as several human tumor cell samples and lines. The origin of multiple human transcripts from the same chromosomal gene, and the possible differential stability of these various transcripts, is discussed with regard to the transcriptional and post-transcriptional regulation of this gene. This is the first report of the chromosomal gene structure of a member of the p34cdc2 supergene family.

Properties of IgA-binding receptors on murine T cells: relative importance of Fc alpha R, beta-galactosyltransferase and anti-secretory component reactive proteins (ASCP)

Murine T cells and T-cell lines express receptors for the Fc of IgA (Fc alpha R); however, their molecular properties remain to be elucidated. In the present study, we examined three candidate molecules for IgA-binding receptors including Fc alpha R, beta-galactosyltransferase (beta-GT) and anti-secretory component (SC) reactive proteins (ASCP) expressed on T cells which might participate in the binding of different molecular forms of IgA. T-cell lines derived from CD4+ T cells of mouse Peyer's patches (PP) (designated PPT 4-6 and PPT 4-16) and from cloned PP T helper (Th) cell lines (ThHA1 #9 and #10) bound both monomeric and dimeric IgA (mIgA and dIgA), while the fusion partners (BW 5147 and R1.1) did not. In contrast, both Fc alpha R+ and Fc alpha R- cell lines bound to high molecular weight polymeric or aggregated IgA (pIgA). All cell lines reacted with a monoclonal anti-beta-GT (MoAb) and beta-GT enzyme activity was associated with the cell lysates and membrane fractions of all cells tested. The anti-beta-GT MoAb stained a 47-kDa band on immunoblots which was identical to that seen with native enzyme. mRNA analysis with beta-GT cDNA showed that all cell lines constitutively produced enzyme-specific mRNA. Both Fc alpha R+ T cells and Fc alpha R- control cell lines showed cell surface specific beta-GT activity. This is the first study which shows that mouse T cells produce beta-GT. However, Fc alpha R and beta-GT appear to be separate receptors, because Fc alpha R+ T cells bound mIgA and dIgA, and this treatment did not affect staining with biotinylated anti-beta-GT MoAb. Further, preincubation of the Fc alpha R+ cells with anti-beta-GT MoAb did not block mIgA binding. However, the anti-beta-GT MoAb partially blocked binding of pIgA to both Fc alpha R+ and Fc alpha R- T cells, suggesting that beta-GT may be a receptor for pIgA. Others have shown that T cells may bind IgA through a receptor serologically related to SC. We found that antibodies both to human SC and to rat SC specifically bound to both Fc alpha R+ and Fc alpha R- T cells. Further, a 72-kDa band was detected when cell membrane fractions were analysed with these antisera (ASCP) by solid phase immunoisolation technique and immunoblot analysis. The ASCP is not an IgA-binding receptor, since anti-SC did not block either mIgA or pIgA binding.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of the p58GTA cell division control-related protein kinase during phorbol 12-myristate 13-acetate-induced terminal differentiation of U937 cells

We describe the regulation of expression, activity and subcellular localization of a cell cycle control-related kinase, p58GTA, during the withdrawal from the cell cycle of U937 human leukemic cells induced by phorbol esters. Our studies indicate that steady-state mRNA, protein levels, transcription and subcellular localization of this kinase are affected in distinctly different manners by phorbol esters (phorbol 12-myristate 13-acetate, PMA). Steady-state mRNA levels increase dramatically within 1 h of PMA treatment, while steady-state protein levels increase only slightly. However, within 24 h of PMA treatment both steady-state p58GTA mRNA and protein levels decrease markedly. Assays of p58GTA protein kinase activity show that, even though steady-state protein levels are relatively constant, protein kinase activity increases within 30 min of PMA treatment, and then peaks at 2 h and 12 h after PMA treatment. Once again, p58GTA protein kinase activity decreases by 48 h to levels similar to unstimulated cells. These results suggest that the expression of the p58GTA protein kinase gene and, quite possibly, its post-translational modification are affected by phorbol esters in a complex manner.

Chromosomal localization of a human cDNA containing a DIDS binding domain and demonstrating high homology to yeast omnipotent suppressor 45

We recently have identified a full-length cDNA (TB3-1) from a human adenocarcinoma cell line T84 cDNA library that encodes a 47.8-kDa protein. TB3-1 shares identity with the putative yeast translation termination factor omnipotent suppressor 45. Using human-mouse somatic cell panel analysis, a family of sequences with high homology to the TB3-1 cDNA clone were localized to human chromosomes 5, 6, 7, and X. Southern analysis of a panel of mammalian and chicken genomic DNA demonstrates that TB3-1 is well conserved in higher vertebrates.

Localization of the expressed human p58 protein kinase chromosomal gene to chromosome 1p36 and a highly related sequence to chromosome 15

The gene for the human p58 protein kinase, a cell division control-related gene, has been mapped by somatic cell hybrid analyses, in situ localization with the chromosomal gene, and nested polymerase chain reaction amplification of microdissected chromosomes. These studies indicate that the expressed p58 chromosomal gene maps to 1p36, while a highly related p58 sequence of unknown nature maps to chromosome 15. Assignment of a p34cdc2-related gene to 1p36 may have implications for numerous tumors that involve deletion of this region, including neuroblastoma, ductal carcinoma of the breast, malignant melanoma, Merkel cell carcinoma, and endocrine neoplasia.