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Biomedical subjects

Jill M Lahti

Publications and source records attributed to Jill M Lahti.

18 recordsLinked to original sources
PubMed2006

The DNA helicase ChlR1 is required for sister chromatid cohesion in mammalian cells.

It has recently been suggested that the Saccharomyces cerevisiae protein Chl1p plays a role in cohesion establishment. Here, we show that the human ATP-dependent DNA helicase ChlR1 is required for sister chromatid cohesion in mammalian cells. Localization studies show that ChlR1 diffusely coats mitotic chromatin in prophase and then translocates from the chromatids to concentrate at the spindle poles during the transition to metaphase. Depletion of ChlR1 protein by RNA interference results in mitotic failure with replicated chromosomes failing to segregate after a pro-metaphase arrest. We show that depletion also results in abnormal sister chromatid cohesion, determined by increased separation of chromatid pairs at the centromere. Furthermore, biochemical studies show that ChlR1 is in complex with cohesin factors Scc1, Smc1 and Smc3. We conclude that human ChlR1 is required for sister chromatid cohesion and, hence, normal mitotic progression. These functions are important to maintain genetic fidelity.

Animals↗
PubMed2006

Evaluation of IFN-gamma effects on apoptosis and gene expression in neuroblastoma--preclinical studies.

Loss of caspase-8 expression and resistance to cytotoxic agents occurs frequently in late stage neuroblastoma (NB). Interferon-gamma (IFN-gamma) induces caspase-8 in NB cells, sensitizing them to death receptor mediated apoptosis. This study characterizes the kinetics of this phenomenon and examines the effects of IFN-gamma on global gene expression to determine whether IFN-gamma responses are achievable at physiologically relevant doses and to define the biological effects of this cytokine. Here we examine the IFN-gamma responses of 16 NB cell lines. A single <5-min exposure to IFN-gamma (0.5 ng/ml) induced caspase-8 expression in all non-expressing cell lines and in 3/6 cell lines which already expressed high caspase-8. This increase in caspase-8 proteins was observed within 16 h and persisted for up to 9 days. Furthermore, IFN-gamma pretreatment of NB cells increased doxorubicin-induced apoptosis nearly 3-fold. Microarray analysis was used to identify additional genes involved in proliferation, signaling and apoptosis whose expression was modulated via IFN-gamma. Altered expression of these genes should further enhance the responsiveness of NB cells to chemotherapeutics. Thus, the use of IFN-gamma to sensitize NB cells to cytotoxic agents represents an attractive therapeutic strategy and warrants further investigation.

Apoptosis↗
PubMed2006

Does integrin-mediated cell death confer tissue tropism in metastasis?

To develop metastatic capability, tumor cells must evolve the capacity to survive in novel microenvironments. Recently, we showed that metastasis of neuroblastoma cells is enhanced by loss of caspase-8, an event that occurs frequently in this malignancy. In poorly metastatic cells, unligated integrins were found to trigger activation of caspase-8, providing a selective pressure to promote its attenuation and thereby increased survival in foreign adhesive environments. Our findings suggest one mechanism by which the organotropism of metastatic cancer cells can arise.

Animals↗
PubMed2006

Caspase-8 promotes cell motility and calpain activity under nonapoptotic conditions.

Significant caspase-8 activity has been found in normal and certain tumor cells, suggesting that caspase-8 possesses an alternative, nonapoptotic function that may contribute to tumor progression. In this article, we report that caspase-8 promotes cell motility. In particular, caspase-8 is required for the optimal activation of calpains, Rac, and lamellipodial assembly. This represents a novel nonapoptotic function of caspase-8 acting at the intersection of the caspase-8 and calpain proteolytic pathways to coordinate cell death versus cell motility signaling.

Animals↗
PubMed2006

Halting neuroblastoma metastasis by controlling integrin-mediated death.

Neuroblastoma, a common tumor of nervous system origin in young children, is usually detected only after the primary tumor has metastasized and the chances of its complete removal are low. Metastatic neuroblastoma cells commonly suppress expression of the gene encoding caspase-8. In a neuroblastoma murine model, expression of caspase-8 and integrin alpha3beta1 was dramatically reduced during tumor development. Analysis of clinical biopsies supported the observation that expression of both genes is low in human patients with metastatic disease. These data suggest that loss of expression of both caspase-8 and unligated integrins contribute to the survival of tumor cells migrating from the primary tumor. Integrin receptors that are unable to find appropriate ligands can form a large molecular complex containing caspase-8, explaining why cells that have diminished expression of either of these two genes have a significant survival advantage in foreign microenvironments. Thus, upregulating expression of caspase-8 and integrins, or alternatively, antagonizing integrins within the primary tumor may be important therapeutically in halting neuroblastoma metastasis.

Animals↗
PubMed2006

Potentiation of neuroblastoma metastasis by loss of caspase-8.

Neuroblastoma, the most common paediatric solid tumour, arises from defective neural crest cells. Genetic alterations occur frequently in the most aggressive neuroblastomas. In particular, deletion or suppression of the proapoptotic enzyme caspase-8 is common in malignant, disseminated disease, although the effect of this loss on disease progression is unclear. Here we show that suppression of caspase-8 expression occurs during the establishment of neuroblastoma metastases in vivo, and that reconstitution of caspase-8 expression in deficient neuroblastoma cells suppressed their metastases. Caspase-8 status was not a predictor of primary tumour growth; rather, caspase-8 selectively potentiated apoptosis in neuroblastoma cells invading the collagenous stroma at the tumour margin. Apoptosis was initiated by unligated integrins by means of a process known as integrin-mediated death. Loss of caspase-8 or integrin rendered these cells refractory to integrin-mediated death, allowed cellular survival in the stromal microenvironment, and promoted metastases. These findings define caspase-8 as a metastasis suppressor gene that, together with integrins, regulates the survival and invasive capacity of neuroblastoma cells.

Animals↗
PubMed2005

Role of CDK/cyclin complexes in transcription and RNA splicing.

The production of mRNAs in all living organisms is an extremely complex process that includes multiple catalytic activities such as transcription, capping, splicing, polyadenylation, cleavage and export. All of these processes are controlled by a large group of proteins which form very dynamic complexes interacting with DNA and pre-mRNAs to coordinate these activities. Phosphorylations play a central role in regulating formation, activation and inactivation of these complexes. A growing number of protein kinases have been identified that are capable of phosphorylating proteins involved in mRNA production. Among them, Cyclin-dependent Kinases (CDKs) represent a family of serine/threonine protein kinases that become active upon binding to a cyclin regulatory partner. CDK/cyclin complexes were first identified as crucial regulators of cell cycle progression. More recently, CDK/cyclin complexes have also been implicated in transcription and mRNA processing leading to the concept of an intricate network of CDK/cyclin complexes regulating cell cycle, transcription and mRNA processing via cross-talk between multiple CDKs. In this review, we discuss the role of CDK/cyclin-dependent phosphorylation in the regulation of transcription and RNA splicing and highlight recent findings that indicate the involvement of CDK/cyclin complexes in connecting transcription and RNA splicing.

Amino Acid Sequence↗
PubMed2004

The carboxyl-terminus directs TAF(I)48 to the nucleus and nucleolus and associates with multiple nuclear import receptors.

The protein complex Selectivity Factor 1, composed of TBP, TAF(I)48, TAF(I)63 and TAF(I)110, is required for rRNA transcription by RNA polymerase I in the nucleolus. The steps involved in targeting Selectivity Factor 1 will be dependent on the transport pathways that are used and the localization signals that direct this trafficking. In order to investigate these issues, we characterized human TAF(I)48, a subunit of Selectivity Factor 1. By domain analysis of TAF(I)48, the carboxyl-terminal 51 residues were found to be required for the localization of TAF(I)48, as well as sufficient to direct Green Fluorescent Protein to the nucleus and nucleolus. The carboxyl-terminus of TAF(I)48 also has the ability to associate with multiple members of the beta-karyopherin family of nuclear import receptors, including importin beta (karyopherin beta1), transportin (karyopherin beta2) and RanBP5 (karyopherin beta3), in a Ran-dependent manner. This property of interacting with multiple beta-karyopherins has been previously reported for the nuclear localization signals of some ribosomal proteins that are likewise directed to the nucleolus. This study identifies the first nuclear import sequence identified within the TBP-Associated Factor subunits of Selectivity Factor 1.

Active Transport, Cell Nucleus↗
PubMed2004

Failure to proliferate and mitotic arrest of CDK11(p110/p58)-null mutant mice at the blastocyst stage of embryonic cell development.

The CDK11(p110) protein kinases are part of large-molecular-weight complexes that also contain RNA polymerase II, transcriptional elongation factors, and general pre-mRNA splicing factors. CDK11(p110) isoforms may therefore couple transcription and pre-mRNA splicing by their effect(s) on certain proteins required for these processes. The CDK11(p58) kinase isoform is generated from the CDK11(p110) mRNA through the use of an internal ribosome entry site in a mitosis-specific manner, suggesting that this kinase may regulate the cell cycle during mitosis. The in vivo role and necessity of CDK11(p110/p58) kinase function during mammalian development were examined by generating CDK11(p110/p58)-null mice through targeted disruption of the corresponding gene using homologous recombination. While heterozygous mice develop normally, disruption of both CDK11(p110/p58) alleles results in early embryonic lethality due to apoptosis of the blastocyst cells between 3.5 and 4 days postcoitus. Cells within these embryos exhibit both proliferative defect(s) and a mitotic arrest. These results are consistent with the proposed cellular functions of the CDK11(p110/p58) kinases and confirm that the CDK11(p110/p58) kinases are essential for cellular viability as well as normal early embryonic development.

Animals↗
PubMed2003

Prevalence of necrosis in C2-ceramide-induced cytotoxicity in NB16 neuroblastoma cells.

The mechanism of cell death triggered by C2-ceramide was investigated using the NB16 neuroblastoma cell line. Treatment of NB16 cells with 20 microM C2-ceramide for 20 h resulted in approximately 75% loss of cell viability, but only 25% of cells were scored as apoptotic based on terminal deoxynucleotidyl transferase nick-end labeling. Ultrastructural analysis revealed early development of necrotic cytoplasmic vacuolization. After 20 h of treatment with C2-ceramide, the majority of cells possessed necrotic morphology with pronounced cytoplasmic vacuolization and without any nuclear changes, although a quarter of the cell population also exhibited clear perinuclear chromatin condensation characteristic of apoptosis. Flow cytometric analysis of cells labeled with both annexin V and propidium iodide showed the rapid accumulation of C2-ceramide-treated cells in the necrotic/late apoptotic fraction. In contrast, cells treated with tumor necrosis factor alpha plus cycloheximide (TNFalpha + CHX) first appeared in the early apoptotic fraction and then accumulated in the necrotic/late apoptotic fraction. Both C2-ceramide and TNFalpha + CHX increased caspase 8- and 3-like activities in cytosolic extracts; however, treatment of cells with the broad-spectrum caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone protected NB16 cells from TNFalpha + CHX-induced cell death but did not prevent C2-ceramide cytotoxicity. Although C2-ceramide triggered apoptosis in a fraction of the cells, cell death in the population was primarily caused by necrosis. Thus, C2-ceramide does not faithfully mimic the effects of apoptotic ligands such as TNFalpha, which are thought to be mediated by an accumulation of endogenous ceramide. The inhibition of phosphatidylcholine synthesis is a target for C2-ceramide-mediated cytotoxicity, and this work suggests that other agents that kill cells by inhibiting this pathway may also use a mixture of mechanisms, including necrosis as well as apoptosis.

Antineoplastic Agents↗
PubMed2003

The murine G+C-rich promoter binding protein mGPBP is required for promoter-specific transcription.

The archetypal TATA-box deficient G+C-rich promoter of the murine adenosine deaminase gene (Ada) requires a 48-bp minimal self-sufficient promoter element (MSPE) for function. This MSPE was used to isolate a novel full-length cDNA clone that encodes a 66-kDa murine G+C-rich promoter binding protein (mGPBP). The mGPBP mRNAs are ubiquitously expressed as either 3.0- or 3.5-kb forms differing in 3' polyadenylation site usage. Purified recombinant mGPBP, in the absence of any other mammalian cofactors, binds specifically to both the murine Ada gene promoter's MSPE and the nonhomologous human Topo IIalpha gene's G+C-rich promoter. In situ binding assays, immunoprecipitation, and Western blot analyses demonstrated that mGPBP is a nuclear factor that can form complexes with TATA-binding protein, TFIIB, TFIIF, RNA polymerase II, and P300/CBP both in vitro and in intact cells. In cotransfection assays, increased mGPBP expression transactivated the murine Ada gene's promoter. Sequestering of GPBP present in HeLa cell nuclear extract by immunoabsorption completely and reversibly suppressed extract-dependent in vitro transcription from the murine Ada gene's G+C-rich promoter. However, transcription from the human Topo IIalpha gene's TATA box-containing G+C-rich promoter was only partially suppressed and the adenovirus major late gene's classical TATA box-dependent promoter is totally unaffected under identical assay conditions. These results implicate GPBP as a requisite G+C-rich promoter-specific transcription factor and provide a mechanistic basis for distinguishing transcription initiated at a TATA box-deficient G+C-rich promoter from that initiated at a TATA box-dependent promoter.

Adenosine Deaminase↗
PubMed2003

ASAP, a novel protein complex involved in RNA processing and apoptosis.

Different isoforms of a protein complex termed the apoptosis- and splicing-associated protein (ASAP) were isolated from HeLa cell extract. ASAP complexes are composed of the polypeptides SAP18 and RNPS1 and different isoforms of the Acinus protein. While Acinus had previously been implicated in apoptosis and was recently identified as a component of the spliceosome, RNPS1 has been described as a general activator of RNA processing. Addition of ASAP isoforms to in vitro splicing reactions inhibits RNA processing mediated by ASF/SF2, by SC35, or by RNPS1. Additionally, microinjection of ASAP complexes into mammalian cells resulted in acceleration of cell death. Importantly, after induction of apoptosis the ASAP complex disassembles. Taken together, our results suggest an important role for the ASAP complexes in linking RNA processing and apoptosis.

Apoptosis↗
PubMed2002

CDK11 complexes promote pre-mRNA splicing.

The PITSLRE protein kinases, hereafter referred to as CDK11 because of their association with the cyclin L regulatory partner, belong to large molecular weight protein complexes that contain RNA polymerase II. These CDK11(p110) complexes have been reported to influence transcription as well as interact with the general pre-mRNA-splicing factor RNPS1. Some of these complexes may also play a role in pre-mRNA splicing. Using a two-hybrid interactive screen, the splicing protein 9G8 was identified as an in vivo partner for CDK11(p110). The identification of several splicing-related factors as CDK11(p110) interactors along with the close relationship between transcription and splicing indicated that CDK11(p110) might influence splicing activity directly. Immunodepletion of CDK11(p110) from splicing extracts greatly reduced the appearance of spliced products using an in vitro assay system. Moreover, the re-addition of these CDK11(p110) immune complexes to the CDK11(p110)-immunodepleted splicing reactions completely restored splicing activity. Similarly, the addition of purified CDK11(p110) amino-terminal domain protein was sufficient to inhibit the splicing reaction. Finally, 9G8 is a phosphoprotein in vivo and is a substrate for CDK11(p110) phosphorylation in vitro. These data are among the first demonstrations showing that a CDK activity is functionally coupled to the regulation of pre-mRNA-splicing events and further support the hypothesis that CDK11(p110) is in a signaling pathway that may help to coordinate transcription and RNA-processing events.

Base Sequence↗
PubMed2002

Casein kinase 2 interacts with cyclin-dependent kinase 11 (CDK11) in vivo and phosphorylates both the RNA polymerase II carboxyl-terminal domain and CDK11 in vitro.

The PITSLRE protein kinases, hereafter referred to as cyclin-dependent kinase 11 (CDK11) due to their association with cyclin L, are part of large molecular weight protein complexes that contain RNA polymerase II (RNAP II) as well as numerous transcription and RNA processing factors. Data presented here demonstrate that the influence of CDK11(p110) on transcription and splicing does not involve phosphorylation of the RNAP II carboxyl-terminal domain by CDK11(p110). We have isolated a DRB- and heparin-sensitive protein kinase activity that co-purifies with CDK11(p110) after ion exchange and affinity purification chromatography. This protein kinase was identified as casein kinase 2 (CK2) by immunoblot and mass spectrometry analyses. In addition to the RNAP II carboxyl-terminal domain, CK2 phosphorylates the CDK11(p110) amino-terminal domain. These data suggest that CDK11(p110) isoforms participate in signaling pathways that include CK2 and that its function may help to coordinate the regulation of RNA transcription and processing events. Future experiments will determine how phosphorylation of CDK11(p110) by CK2 specifically affects RNA transcription and/or processing events.

Casein Kinase II↗
PubMed2002

Caspase-9 and Apaf-1 are expressed and functionally active in human neuroblastoma tumor cell lines with 1p36 LOH and amplified MYCN.

Important roles have been suggested for caspase-8, caspase-9 and Apaf-1 in controlling tumor development and their sensitivity to chemotherapeutic agents. Methylation and deletion of Apaf-1 and CASP8 results in the loss of their expression in melanoma and neuroblastoma, respectively, while CASP9 localization to 1p36.1 suggests it is a good candidate tumor suppressor. The status of CASP9 and Apaf-1 expression in numerous neuroblastoma cell lines with/without amplified MYCN and chromosome 1p36 loss-of-heterozygosity (LOH) was therefore examined to test the hypothesis that one or both of these genes are tumor suppressors in neuroblastoma. Although CASP9 is included in the region encompassing 1p36 LOH in all neuroblastoma cell lines examined, the remaining CASP9 allele(s) express a functional caspase-9 enzyme. Apaf-1 is also expressed in all neuroblastoma tumor cell lines examined. Thus, the CASP9 or Apaf-1 genes do not appear to function as tumor suppressors in MYCN amplified neuroblastomas. However, approximately 20% of the neuroblastoma cell lines with methylated CASP8 alleles are also highly resistant to staurosporine (STS)- and radiation-induced cell death, presumably because cytochrome c is not released from mitochondria. This suggests that a second, smaller sub-group of MYCN amplified neuroblastoma tumors exists with defect(s) in apoptotic signaling components upstream of caspase-9 and Apaf-1. Since no consistent differences in Bcl-2, Bcl-x(L) or Bax expression were seen in the STS- and radiation-resistant neuroblastomas, it suggests that a unique mitochondrial signaling factor(s) is responsible for the defect in cytochrome c release in this sub-group of tumors.

Apoptosis↗
PubMed2002

ERK activation mediates cell cycle arrest and apoptosis after DNA damage independently of p53.

In response to DNA damage, ataxia-telangiectasia mutant and ataxia-telangiectasia and Rad-3 activate p53, resulting in either cell cycle arrest or apoptosis. We report here that DNA damage stimuli, including etoposide (ETOP), adriamycin (ADR), ionizing irradiation (IR), and ultraviolet irradiation (UV) activate ERK1/2 (ERK) mitogen-activated protein kinase in primary (MEF and IMR90), immortalized (NIH3T3) and transformed (MCF-7) cells. ERK activation in response to ETOP was abolished in ATM-/- fibroblasts (GM05823) and was independent of p53. The MEK1 inhibitor PD98059 prevented ERK activation but not p53 stabilization. Maximal ERK activation in response to DNA damage was not attenuated in MEF(p53-/-). However, ERK activation contributes to either cell cycle arrest or apoptosis in response to low or high intensity DNA insults, respectively. Inhibition of ERK activation by PD98059 or U0126 attenuated p21(CIP1) induction, resulting in partial release of the G(2)/M cell cycle arrest induced by ETOP. Furthermore, PD98059 or U0126 also strongly attenuated apoptosis induced by high dose ETOP, ADR, or UV. Conversely, enforced activation of ERK by overexpression of MEK-1/Q56P sensitized cells to DNA damage-induced apoptosis. Taken together, these results indicate that DNA damage activates parallel ERK and p53 pathways in an ATM-dependent manner. These pathways might function cooperatively in cell cycle arrest and apoptosis.

3T3 Cells↗
PubMed2001

PITSLRE p110 protein kinases associate with transcription complexes and affect their activity.

Although the PITSLRE protein kinases are members of the cyclin-dependent kinase superfamily, their cellular function is unclear. Previously we demonstrated that the general RNA splicing factor RNPS1 is a specific PITSLRE p110 kinase interactor in vivo. This suggests that the PITSLRE family of protein kinases is involved in some aspect of RNA processing or transcription. Here we identify multiple transcriptional elongation factors, including ELL2, TFIIF(1), TFIIS, and FACT, as PITSLRE kinase-associated proteins. We demonstrate that PITSLRE p110 protein kinases co-immunoprecipitate and/or co-purify with these elongation factors as well as with RNA polymerase II. Antibody-mediated inhibition of PITSLRE kinase specifically suppressed RNA polymerase II-dependent in vitro transcription initiated at a GC-rich (adenosine deaminase) or TATA box-dependent (Ad2ML) promoter, and this suppression was rescued by readdition of purified PITSLRE p110 kinase. Together, these data strongly suggest that PITSLRE protein kinases participate in a signaling pathway that potentially regulates or links transcription and RNA processing events.

Animals↗