Skeletal muscle contractile function and neuromuscular performance in Zmpste24 -/- mice, a murine model of human progeria

Human progeroid syndromes and premature aging mouse models present as segmental, accelerated aging because some tissues and not others are affected. Skeletal muscle is detrimentally changed by normal aging but whether it is an affected tissue in progeria has not been resolved. We hypothesized that mice which mimic Hutchinson-Gilford progeria syndrome would exhibit age-related alterations of skeletal muscle. Zmpste24 (-/-) and Zmpste24 (+/+) littermates were assessed for skeletal muscle functions, histo-morphological characteristics, and ankle joint mechanics. Twenty-four-hour active time, ambulation, grip strength, and whole body tension were evaluated as markers of neuromuscular performance, each of which was at least 33% lower in Zmpste24 (-/-) mice compared with littermates (p < 0.06). Contractile capacity of the posterior leg muscles were not affected in Zmpste24 (-/-) mice, but muscles of the anterior leg were 30-90% weaker than those of Zmpste24 (+/+) mice (p < 0.01). Leg muscles were 32-47% smaller in the Zmpste24 (-/-) mice and contained ~60% greater collagen relative to littermates (p < 0.01). Soleus and extensor digitorum longus muscles of Zmpste24 (-/-) mice had excessive myonuclei and altered fiber size distributions but, otherwise, appeared normal. Ankle range of motion was 70% lower and plantar- and dorsiflexion passive torques were nearly 3-fold greater in Zmpste24 (-/-) than Zmpste24 (+/+) mice (p ≤ 0.01). The combined factors of muscle atrophy, collagen accumulation, and perturbed joint mechanics likely contributed to poor neuromuscular performance and selective muscle weakness displayed by Zmpste24 (-/-)mice. In summary, these characteristics are similar to those of aged mice indicating accelerated aging of skeletal muscle in progeria.

Zebrafish stromal cells have endothelial properties and support hematopoietic cells

The goal of this study was to determine if we could establish a mesenchymal stromal line from zebrafish that would support hematopoietic cells. Such a coculture system would be a great benefit to study of the hematopoietic cell-stromal cell interaction in both in vitro and in vivo environments. Zebrafish stromal cells (ZStrC) were isolated from the "mesenchymal" tissue of the caudal tail and expanded in a specialized growth media. ZStrC were evaluated for phenotype, gene expression, and ability to maintain zebrafish marrow cells in coculture experiments. ZStrC showed mesenchymal and endothelial gene expression. Although ZStrC lacked the ability to differentiate into classic mesenchymal stromal cell lineages (i.e., osteocytes, adipocytes, chondrocytes), they did have the capacity for endotube formation on Matrigel and low-density lipoprotein uptake. ZStrC supported marrow cells for >2 weeks in vitro. Importantly, marrow cells were shown to retain homing ability in adoptive transfer experiments. ZStrC were also shown to improve hematopoietic recovery after sublethal irradiation after adoptive transfer. As the zebrafish model grows in popularity and importance in the study of hematopoiesis, new tools to aid in our understanding of the hematopoietic cell-stromal cell interaction are required. ZStrC represent an additional tool in the study of hematopoiesis and will be useful in understanding the factors that mediate the stromal cell-hematopoietic cell interactions that are important in hematopoietic cell maintenance.

LTQ-iQuant: A freely available software pipeline for automated and accurate protein quantification of isobaric tagged peptide data from LTQ instruments

Pulsed Q dissociation enables combining LTQ ion trap instruments with isobaric peptide tagging. Unfortunately, this combination lacks a technique which accurately reports protein abundance ratios and is implemented in a freely available, flexible software pipeline. We developed and implemented a technique assigning collective reporter ion intensity-based weights to each peptide abundance ratio and calculating a protein's weighted average abundance ratio and p-value. Using an iTRAQ-labeled standard mixture, we compared our technique's performance to the commercial software MASCOT, finding that it performed better than MASCOT's nonweighted averaging and median peptide ratio techniques, and equal to its weighted averaging technique. We also compared performance of the LTQ-Orbitrap plus our technique to 4800 MALDI TOF/TOF plus Protein Pilot, by analyzing an iTRAQ-labeled stem cell lysate. We found highly correlated protein abundance ratios, indicating that the LTQ-Orbitrap plus our technique yields results comparable to the current standard. We implemented our technique in a freely available, automated software pipeline, called LTQ-iQuant, which is mzXML-compatible; supports iTRAQ 4-plex and 8-plex LTQ data; and can be modified for and have weights trained to a user's LTQ and other isobaric peptide tagging methods. LTQ-iQuant should make LTQ instruments and isobaric peptide tagging accessible to more proteomic researchers.

Induced pluripotent stem cells from individuals with recessive dystrophic epidermolysis bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is an inherited blistering skin disorder caused by mutations in the COL7A1 gene-encoding type VII collagen (Col7), the major component of anchoring fibrils at the dermal-epidermal junction. Individuals with RDEB develop painful blisters and mucosal erosions, and currently, there are no effective forms of therapy. Nevertheless, some advances in patient therapy are being made, and cell-based therapies with mesenchymal and hematopoietic cells have shown promise in early clinical trials. To establish a foundation for personalized, gene-corrected, patient-specific cell transfer, we generated induced pluripotent stem (iPS) cells from three subjects with RDEB (RDEB iPS cells). We found that Col7 was not required for stem cell renewal and that RDEB iPS cells could be differentiated into both hematopoietic and nonhematopoietic lineages. The specific epigenetic profile associated with de-differentiation of RDEB fibroblasts and keratinocytes into RDEB iPS cells was similar to that observed in wild-type (WT) iPS cells. Importantly, human WT and RDEB iPS cells differentiated in vivo into structures resembling the skin. Gene-corrected RDEB iPS cells expressed Col7. These data identify the potential of RDEB iPS cells to generate autologous hematopoietic grafts and skin cells with the inherent capacity to treat skin and mucosal erosions that typify this genodermatosis.

Mesenchymal stromal cells from donors varying widely in age are of equal cellular fitness after in vitro expansion under hypoxic conditions

BACKGROUND AIMS

Mesenchymal stromal cells (MSC) are gaining in popularity as an experimental therapy for a number of conditions that often require expansion ex vivo prior to use. Data comparing clinical-grade MSC from various ages of donors are scant. We hypothesized that MSC from older donors may display differences in cellular fitness when expanded for clinical use.

METHODS

We evaluated the expression of several markers of aging, oxidative stress and growth kinetics, and telomere length, in MSC obtained from a wide age range (8 months to 58 years).

RESULTS

To evaluate cellular fitness we compared MSC expanded from younger (8 months-6 years) versus older (38-58 years) donors in terms of selected cell-surface markers, lipofuscin, migration ability, telomere length and expression of iNOS, PGE₂, p16INK and SOD. Results did not differ between these groups. Neither SOD activity (0.025 versus 0.028 U/mL) nor death after oxidative challenge was significantly different (1% versus 1.5%, P = 0.14). We did find that, although MSC from older individuals produced slightly fewer cells over a 28-day culture period and had a slightly longer doubling time (54 h versus 42 hr, a satisfactory clinical product could still be obtained regardless of age cohort.

CONCLUSIONS

Collectively, these data show that MSC can be expanded without significant alterations in expansile properties or obvious changes in parameters associated with senescence. Because cellular fitness was equivalent in these cohorts, MSC from donors up to age 58 years can be used as a source of cells for cellular therapy.

Expression of telomerase and telomere length are unaffected by either age or limb regeneration in Danio rerio

Background

The zebrafish is an increasingly popular model for studying many aspects of biology. Recently, ztert, the zebrafish homolog of the mammalian telomerase gene has been cloned and sequenced. In contrast to humans, it has been shown that the zebrafish maintains telomerase activity for much of its adult life and has remarkable regenerative capacity. To date, there has been no longitudinal study to assess whether this retention of telomerase activity equates to the retention of chromosome telomere length through adulthood.

Methodology/Principal Findings

We have systematically analyzed individual organs of zebrafish with regard to both telomere length and telomerase activity at various time points in its adult life. Heart, gills, kidney, spleen, liver, and intestine were evaluated at 3 months, 6 months, 9 months, and 2 years of age by Southern blot analysis. We found that telomeres do not appreciably shorten throughout the lifespan of the zebrafish in any organ. In addition, there was little difference in telomere lengths between organs. Even when cells were under the highest pressure to divide after fin-clipping experiments, telomere length was unaffected. All aged (2 year old) tissues examined also expressed active amounts of telomerase activity as assessed by TRAP assay.

Conclusions/Significance

In contrast to several other species including humans, the retention of lifelong telomerase and telomeres, as we have reported here, would be necessary in the zebrafish to maintain its tremendous regenerative capacity. The ongoing study of the zebrafish's ability to maintain telomerase activity may be helpful in unraveling the complexity involved in the maintenance (or lack thereof) of telomeres in other species such the mouse or human.

Identification of mitochondrial genome concatemers in AIDS-associated lymphomas and lymphoid cell lines

Since most oncogenic viruses persist as extrachromosomal covalently closed circular DNA (cccDNA) in tumor cells, we developed an assay to visualize and identify cccDNA in primary lymphomas. We identified concatemers of the mitochondrial genome in all samples analyzed, but not in normal lymphocytes. One AIDS-associated lymphoma (EL) was further studied in detail as its mitochondrial genome consisted of tandem head-to-tail duplications. Insertion of C-residues was noted near the origin of replication of EL mtDNA. EL cells responded weakly to Fas-apoptotic stimulus, displayed reduced mitochondrial activity and mass, and produced higher levels of reactive oxygen intermediates. Screening of several AIDS-associated lymphomas and established lymphoid cell lines also revealed the presence of mitochondrial genome concatemers consisting of interlinked monomer molecules. Taken together, our results suggest that formation of mtDNA concatemers is associated with oncogenic transformation in lymphoid cells.

O-glycoside biomarker of apolipoprotein C3: responsiveness to obesity, bariatric surgery, and therapy with metformin, to chronic or severe liver disease and to mortality in severe sepsis and graft vs host disease

The glyco-isoforms of intact apolipoprotein C3 (ApoC3) were used to probe glycomic changes associated with obesity and recovery following bariatric surgery, liver diseases such as chronic hepatitis C (CHC) and alcoholic liver cirrhosis, as well as severe, multiorgan diseases such as sepsis and graft vs host disease (GVHD). ApoC3 glyco-isoform ratios responded to unique stimuli that did not correlate with serum lipids or with other blood components measured in either a control population or a group of extremely obese individuals. However, glyco-isoform ratios correlated with obesity with a 1.8-fold change among subjects eligible for bariatric surgery relative to a nonobese control population. Bariatric surgery resulted in rapid change of isoform distribution to that of nonobese individuals, after which the distribution was stable in each individual. Although multiple simultaneous factors complicated effector attribution, the isoform ratios of very obese individuals were nearly normal for diabetic individuals on metformin therapy. Glyco-isoform ratios were sensitive to liver diseases such as chronic hepatitis C and alcoholic liver cirrhosis. The correlation coefficient with fibrosis was superior to that of current assays of serum enzyme levels. Diseases of pregnancy that can result in liver damage, HELLP syndrome and pre-eclampsia, did not alter ApoC3 glyco-isoform ratios. Early after umbilical cord blood transplantation the isoform ratios changed and returned to normal in long-term survivors. Larger changes were observed in persons who died. GVHD had little effect. Persons with severe sepsis showed altered ratios. Similar cut-points for mortality (3.5-fold difference from controls) were found for UCBT and sepsis. Similar values characterized liver cirrhosis. Overall, while changes of glyco-isoform ratios occurred in many situations, individual stability of isoform distribution was evident and large changes were limited to high-level disease. If ratio changes associated with obesity are found to document a risk factor for long-term outcomes, the information provided by glyco-isoform ratio changes may provide important, novel information for diagnostic, prognostic and therapy response to metabolic conditions.

Granulocyte colony-stimulating factor mobilized CFU-F can be found in the peripheral blood but have limited expansion potential

Bone marrow mesenchymal stem cells are multipotent cells found lining the bone marrow cavity supporting the growth and differentiation of hematologic progenitors. There is growing evidence that these cells can, under the right circumstances, enter the peripheral circulation. We show that granulocyte colony-stimulating factor mobilized peripheral blood contains cells which form colonies and have a similar fibroblastic morphology (termed CFU-F) to bone marrow mesenchymal stem cells. These cells were found at a very low incidence (0.0002%). Mobilized peripheral blood CFU-F were successfully differentiated into osteogenic and adipogenic lineages. FACS analysis showed that the cells had a similar profile to bone marrow mesenchymal stem cells. Importantly, mobilized peripheral blood CFU-F had limited expansion potential and became senescent 20-25 days after isolation. Mobilized peripheral blood CFU-F also did not have any telomerase activity and displayed significant telomere shortening. The rarity of CFU-F in mobilized peripheral blood and the subsequent pressure to divide in cell culture probably contribute to early cellular senescence. Their potential for use in transplant or gene therapy is, therefore, limited.

Telomere shortening in diaphragm and tibialis anterior muscles of aged mdx mice

The progression of Duchenne muscular dystrophy (DMD) is, in part, due to satellite cell senescence driven by high replicative pressure as these muscle stem cells repeatedly divide and fuse to damaged muscle fibers. We hypothesize that telomere shortening in satellite cells underlies their senescence. To test this hypothesis, we evaluated the diaphragm and a leg muscle from dystrophic mice of various ages for telomere dynamics. We found 30% telomere shortening in tibialis anterior muscles from 600-day-old mdx mice relative to age-matched wildtype mice. We also found a more severe shortening of telomere length in diaphragm muscles of old mdx mice. In those muscles, telomeres were shortened by approximately 15% and 40% in 100- and 600-day-old mdx mice, respectively. These findings indicate that satellite cells undergo telomere erosion, which may contribute to the inability of these cells to perpetually repair DMD muscle.

iTRAQ is a useful method to screen for membrane-bound proteins differentially expressed in human natural killer cell types

We are interested in the biological as well as the molecular processes involved in natural killer (NK) cell development and function. Determining the proteomic complement could be a useful tool in predicting cellular function and fate. For the first time shown here, we have utilized iTRAQ, a new method that allows identification and quantification of proteins between multiple samples, to determine the expression of membrane-bound proteins in two previously characterized human NK cell populations. One population was derived from umbilical cord blood (UCB) stem cells (CD34+38-Lin-) and the other from expanded CD3-depleted adult peripheral blood. iTRAQ was employed for multiplex peptide labeling of proteins from fractionated membranes followed by two-dimensional high-performance liquid chromatography (2D-HPLC), and tandem mass spectrometry was used to identify protein signatures. We were able to identify and quantify differences in expression levels of 400-800 proteins in a typical experiment. Ontology analysis showed the majority of the proteins to be involved in cell signaling, nucleic acid binding, or mitochondrial function. Nearly all proteins were associated with the plasma membrane, membrane-bound organelle (lysosome or mitochondria), or nucleus. We found several novel proteins highly expressed in UCB stem cell derived NK cells compared to adult NK cells including CD9, alpha-2 macroglobulin, brain abundant signaling protein (BASP1), and allograft inflammatory factor-1 (AIF-1). In addition, we were able to confirm several of our iTRAQ results by RT-PCR, Western blot, and fluorescence-activated cell-sorting (FACS) analysis. This is the first demonstration and verification using iTRAQ to screen for membrane-bound protein differences in human NK cells and represents a powerful new tool in the field of proteomics.

Human nerve growth factor receptor and cytosine deaminase fusion genes

Cytosine deaminase (CD) converts 5-fluorocytosine (5-FC) to the toxic metabolite 5-fluorouracil (5-FU), and has been investigated extensively as a potential tool for selective cellular eradication. In this paper, genetic constructs were designed to express the CD enzyme fused to the transmembrane and extracellular domains of the human nerve growth factor receptor (NGFR), thus allowing for positive identification of transduced cells by flow cytometry and positive selection by magnetic bead technology. Constructs were designed to encode a [Gly(4)Ser](2) flexible linker between the nucleic acid coding sequences for the NGFR and CD genes. Retroviral vectors constructed with wild-type CD and NG/CD fusion genes were used to transduce 3T3 fibroblasts and the human T cell line CEM. The function of CD fusion genes was comparable to that of wild-type genes as determined in cytotoxicity assays. By flow cytometry, the NGFR antigen was detectable after expression of the fusion gene derived from either Escherichia coli (NG/CDe) or Saccharomyces cerevisiae (NG/CDs), but the greatest antigen density was observed in cells transduced with the NG/CDs vector. Similarly, superior 5-FC sensitivity was observed with NG/CDs fusion gene in both murine fibroblasts and human T cells. In addition, CEM cells expressing NG/CDs were more efficiently eliminated in vivo. Engineering of cells utilizing the chimeric NG/CD genes provides a new modality in gene therapy allowing positive and negative selection using a single protein-coding sequence.

Spontaneous circulation of myeloid-lymphoid-initiating cells and SCID-repopulating cells in sickle cell crisis

The only curative therapy for sickle cell disease (SCD) is allogeneic hematopoietic stem cell (HSC) transplantation. Gene therapy approaches for autologous HSC transplantation are being developed. Although earlier engraftment is seen when cells from GCSF-mobilized blood are transplanted than when bone marrow is transplanted, administration of GCSF to patients with SCD can cause significant morbidity. We tested whether primitive hematopoietic progenitors are spontaneously mobilized in the blood of patients with SCD during acute crisis (AC-SCD patients). The frequency of myeloid-lymphoid-initiating cells (ML-ICs) and SCID-repopulating cells (SRCs) was significantly higher in blood from AC-SCD patients than in blood from patients with steady-state SCD or from normal donors. The presence of SRCs in peripheral blood was not associated with detection of long-term culture-initiating cells, consistent with the notion that SRCs are more primitive than long-term culture-initiating cells. As ML-ICs and SRCs were both detected in blood of AC-SCD patients only, these assays may both measure primitive progenitors. The frequency of ML-ICs also correlated with increases in stem cell factor, GCSF, and IL-8 levels in AC-SCD compared with steady-state SCD and normal-donor sera. Because significant numbers of ML-ICs and SRCs are mobilized in the blood without exogenous cytokine treatment during acute crisis of SCD, collection of peripheral blood progenitors during crisis may yield a source of autologous HSCs suitable for ex-vivo correction by gene therapy approaches and subsequent transplantation.

Blockerette-ligated capture T7-amplified RT-PCR, a new method for determining flanking sequences

We have developed a highly sensitive PCR-based technique termed blockerette-ligated capture T7-amplified reverse-transcription PCR (BCT-RT-PCR), which can be used to characterize unknown proviral flanking sequences from a broad range of samples and depends only on knowing the retroviral sequence. This method incorporates several essential elements to make it both sensitive and specific, including a "blockerette" linker, magnetic capture of target sequences, and exponential replication of potentially rare sequences using a nested promoter for T7 RNA polymerase, followed by nested RT-PCR. This linkage of methods was designed to increase sensitivity by decreasing DNA complexity in favor of specific amplification. The resulting PCR products can be directly sequenced to determine integration sequences. We have successfully determined the integration sequences from as little as 30 pg of provirus-containing DNA in the background of 30 ng of untransduced DNA, representing a 0.1% transduction rate. We also show this technique to have single-cell resolution even in the background of 5000 cells. We describe here for the first time the combined use of BCT-RT-PCR and laser-capture microscopy (LCM) for precise isolation of retrovirally transduced cells followed by determination of the 3' retroviral flanking sequence at the single-cell level. This method will aid significantly in determining clonality both in transplant experiments and in the generation of clonal cell populations.

The herpesvirus saimiri tip484 and tip488 proteins both stimulate lck tyrosine protein kinase activity in vivo and in vitro

Herpesvirus saimiri (HVS) of subgroup C efficiently induces leukemia in New World primates and transforms human lymphocytes. The viral tyrosine kinase interacting protein (Tip) binds to the tyrosine protein kinase Lck and is essential for transformation. Understanding how Tip modulates Lck activity is important for elucidating the mechanism of herpesvirus saimiri leukemogenesis. However, there are reports suggesting that whereas the Tip protein of HVS strain 484 stimulates the activity of Lck, the Tip protein of HVS strain 488 inhibits Lck. To determine whether these two divergent Tip proteins have opposite effects on Lck activity, we compared them in parallel. We found that both Tip proteins stimulated Lck kinase activity in vivo and in vitro and that both stimulated NF-AT- and STAT3-dependent transcription in T cells. Our data support the model that HVS infection increases the activity of Lck through the action of Tip.

The BCR/ABL transgene causes abnormal NK cell differentiation and can be found in circulating NK cells of advanced phase chronic myelogenous leukemia patients

NK cells from the blood of chronic myelogenous leukemia (CML) patients are progressively decreased in number as the disease progresses from chronic phase to blast crisis. We hypothesize that BCR/ABL may be directly responsible by interfering with NK cell differentiation. CD34(+)HLA-DR(+) cells from CML patients were studied for their capacity to differentiate into NK cells. The NK cell cloning frequency was significantly decreased from CML CD34(+)HLA-DR(+) cells compared with cells from normal donors, yet CD34(+)HLA-DR(+) cells gave rise to BCR/ABL(+) NK cells in some patients. This finding prompted us to further investigate circulating NK cells from the blood of CML patients. CD56(+)CD3(-) NK cells were sorted from CML patients and examined by fluorescence in situ hybridization (FISH). In contrast to chronic phase CML, significant numbers of NK cells from advanced phase CML patients were BCR/ABL(+), whereas T cells were always BCR/ABL(-) regardless of the disease stage. To test the effects of BCR/ABL as the sole genetic abnormality, BCR/ABL was transduced into umbilical cord blood CD34(+) cells, and NK development was studied. p210-enhanced green fluorescence protein-transduced cells gave rise to significantly decreased numbers of NK cells compared with enhanced green fluorescence protein transduction alone. In addition, the extrinsic addition of BCR/ABL-transduced autologous CD34(+) cells suppressed the NK cell differentiation of normal umbilical cord blood CD34(+)CD38(-) cells. This study provides the first evidence that BCR/ABL is responsible for the altered differentiation of NK cells and that the NK cell lineage can be involved with the malignant clone in advanced stage CML.

T-cell factor-1 expression during human natural killer cell development and in circulating CD56(+) bright natural killer cells

Transcription factors are essential to govern differentiation along the lymphoid lineage from uncommitted hematopoietic stem cells. Although many of these transcription factors have putative roles based on murine knockout experiments, their function in human lymphoid development is less known and was studied further. Transcription factor expression in fresh and cultured adult human bone marrow and umbilical cord blood progenitors was evaluated. We found that fresh CD34(+)Lin(-) cells that are human leukocyte antigen (HLA)-DR(-) or CD38(-) constitutively express GATA-3 but not T-cell factor-1 (TCF-1) or Id-3. Culture with the murine fetal liver cell line AFT024 and defined cytokines was capable of inducing TCF-1 mRNA. However, no T-cell receptor gene rearrangement was identified in cultured progeny. Id-3, a basic helix loop helix factor with dominant negative function for T-cell differentiation transcription factors, also was upregulated and may explain unsuccessful T-cell maturation. To better understand the developmental link between natural killer (NK) cells derived from progenitors, we studied NK cell subsets circulating in blood. CD56(+bright), but not CD56(+dim), NK cells constitutively express TCF-1 by reverse transcriptase polymerase chain reaction and Western blot analysis. The TCF-1 isoform found in CD56(+bright) cells, which express lectin but not immunoglobulin class I recognizing inhibitory receptors, was identical to that induced in NK cell differentiation culture and was distinctly different from isoforms in T cells. These results suggest that TCF-1 does not target human killer immunoglobulin receptor genes, TCF-1 is uniquely expressed in circulating CD56(+bright) NK cells, and specific TCF-1 isoforms may play an important role in regulating NK differentiation from a common NK/T-cell progenitor.

Activation of the Lck tyrosine protein kinase by the Herpesvirus saimiri tip protein involves two binding interactions

The Tip protein of Herpesvirus saimiri strain 484C binds to and activates the Lck tyrosine protein kinase. Two sequences in the Tip protein were previously shown to be involved in binding to Lck. A proline-rich region, residues 132-141, binds to the SH3 domain of the Lck protein. We show here that the other Lck-binding domain, residues 104-113, binds to the carboxyl-terminal half of Lck and that this binding does not require the Lck SH3 domain. Mutated Tip containing only one functional Lck-binding domain can bind stably to Lck, although not as strongly as wild-type Tip. Interaction of Tip with Lck through either Lck-binding domain increases the activity of Lck in vivo. Simultaneous binding of both domains is required for maximal activation of Lck. The transient expression of Tip in T cells was found to stimulate both Stat3-dependent and NF-AT-dependent transcription. Mutant forms of Tip lacking one or the other of the two Lck-binding domains retained the ability to stimulate Stat3-dependent transcription. Tip lacking the proline-rich Lck-binding domain exhibited almost wild-type activity in this assay. In contrast, ablation of either Lck-binding domain abolished the ability of Tip to stimulate NF-AT-dependent transcription. Full biological activity of Tip, therefore, appears to require both Lck-binding domains.

The Src-family kinase Lck can induce STAT3 phosphorylation and DNA binding activity

Constitutive activation of the Src-family kinase Lck has been shown to lead to transformation. Constitutive activation of the STAT pathway of transcription factors has also been shown to be involved in transformation. An oncogenic form of the prototypical member of the Src-family, v-Src, has been shown to activate STAT3, and this activation is required for v-Src's transforming ability. To investigate whether Lck could directly activate STAT3, a baculovirus expression system was utilised. When Lck and STAT3 were coexpressed, STAT3 was found to have enhanced tyrosine phosphorylation and DNA binding activity. This finding was confirmed with experiments where exogenous Lck was added to baculovirus produced STAT3. Moreover, the activation of STAT3 by exogenous Lck could be attenuated by the Lck-specific inhibitor PP1. In addition, mammalian cells stably expressing a constitutively activated form of Lck were shown to have activated STAT3. These data provide strong evidence that, like v-Src, Lck can also directly activate STAT3, which contributes to the transformation process.

Activation of the lck tyrosine-protein kinase by the binding of the tip protein of herpesvirus saimiri in the absence of regulatory tyrosine phosphorylation

The Tip protein of herpesvirus saimiri 484 binds to the Lck tyrosine-protein kinase at two sites and activates it dramatically. Lck has been shown previously to be activated by either phosphorylation of Tyr394 or dephosphorylation of Tyr505. We examined here whether a change in the phosphorylation of either site was required for the activation of Lck by Tip. Remarkably, mutation of both regulatory sites of tyrosine phosphorylation did not prevent activation of Lck by Tip either in vivo or in a cell free in vitro system. Tip therefore appears to be able to activate Lck through an induced conformational change that does not necessarily involve altered phosphorylation of the kinase. Tip may represent the prototype of a novel type of regulator of tyrosine-protein kinases.

Interferon-alpha induction of STATs1, -3 DNA binding and growth arrest is independent of Lck and active mitogen-activated kinase in T cells

Type I interferons (IFNs) are a family of cytokines that have antiviral and antiproliferative effects. Data regarding the processes by which these cytokines transduce signals from the cell membrane to the nucleus are becoming increasingly complex. The most characterized pathway is via JAK-STAT signaling. Previous studies established a potential role for the Src-family kinase Lck in JAK-STAT signaling. Therefore, this study was designed to analyze the role of Lck in IFN-alpha signaling by using the Jurkat, JCam (an Lck-defective cell line derived from Jurkat), and JCam/Lck (JCam cells with Lck restored). The results show that IFN-alpha can induce MAPK activity, but only in cells containing Lck. Furthermore, STATs1 and -3 are effectively phosphorylated and activated to bind DNA in the absence of Lck expression in IFN-alpha-treated cells. Finally, the results demonstrate that IFN-alpha exerts an antiproliferative effect in all three cell lines. These data indicate that Lck and active MAPK do not affect IFN-alpha-induced growth arrest or induction of STAT1s1 and -3 DNA binding ability.

The Lck binding domain of herpesvirus saimiri tip-484 constitutively activates Lck and STAT3 in T cells

Constitutive activation of signal transducers and activators of transcription (STATs) has been associated with oncogenesis. Previously, a protein required for T-cell transformation by the DNA tumor virus herpesvirus saimiri (HVS) strain 484, designated tyrosine kinase-interacting protein (Tip-484), was shown to interact with and dramatically upregulate the activity of the STATs in an Lck-dependent manner. The minimal region of Tip-484 responsible for binding Lck was defined as a 10-residue C-terminal Src-related kinase homology domain, an 18-amino-acid spacer, and a 10-residue potential SH3 binding domain. This region is termed the LBD (for Lck binding domain). The present data show that only the LBD of Tip-484 is needed to activate Lck in vitro and in vivo. Finally, the LBD was shown to form a complex with STAT3 in vitro, and expression of the LBD in T cells led to STAT3 activation equal to that of full-length Tip-484. These studies demonstrate that the 48-amino-acid LBD of Tip-484 can perform as effectively as the full-length protein in vitro and in vivo.

Activation of STAT transcription factors by herpesvirus Saimiri Tip-484 requires p56lck

Signal transducers and activators of transcription (STATs) relay signals from activated cell surface receptors directly to the nucleus. Previously, a protein required for T-cell transformation by the DNA tumor virus herpesvirus saimiri (HVS) and designated tyrosine kinase interacting protein (Tip-484) was shown to interact with and dramatically upregulate the activity of p56lck. p56lck is a nonreceptor tyrosine kinase that is essential for signaling by the T-cell receptor and also interacts with the CD4, CD8, and interleukin-2 receptors. The present data show activation of STAT1 and -3 by Tip-484. STAT1 and -3 were also found to complex with glutathione S-transferase-Tip-484 only in the presence of p56lck, and STAT3 was shown to be phosphorylated by the Tip-484-p56lck multiprotein complex in vitro. Infection of T cells with HVS or expression of recombinant Tip-484 significantly increased the DNA-binding activity of the STAT1 and STAT3 transcription factors in nuclear extracts and also increased the phosphorylation of STAT3 in vivo. This is the first report of STAT activation by a DNA tumor virus protein. Moreover, these studies demonstrate that p56lck is required for STAT activation by Tip-484.