A dominant mutation in the Ikaros gene leads to rapid development of leukemia and lymphoma

Over-expression of short isoforms of Helios in patients with adult T-cell leukaemia/lymphoma

In previous studies, we demonstrated an over-expression of the dominant-negative isoform of the transcription factor Ikaros in patients with blast crisis of both chronic myelogenous leukaemia and B-cell acute lymphoblastic leukaemia (ALL). Recently, we reported an over-expression of the short isoforms of Helios, which is one of the members of the Ikaros gene family, in a patient with T-cell ALL. In the present study, we found over-expression of short isoforms of Helios in human T lymphotropic virus-I (HTLV1)-infected patients who had developed chronic and acute forms of adult T-cell leukaemia/lymphoma. In contrast, we could not detect any over-expression of short isoforms of Helios in healthy HTLV1 carriers. By Southern blotting, we detected a small deletion in the Helios gene locus of adult T-cell leukaemia/lymphoma patients. The present results suggest that Helios gene abnormalities might be one of the important mechanisms in the disease progression of HTLV1 infection.

Binding of Ikaros to germline Ig heavy chain gamma1 and epsilon promoters

Immunoglobulin (Ig) class switching occurs in activated B cells and results in production of antigen-specific IgA, IgE or IgG. It involves a DNA recombination event and is partly regulated by germline (GL) immunoglobulin heavy chain promoters. Ikaros is an abundant nuclear protein expressed in hematopoietic cells. Many different functions have been ascribed to Ikaros, such as transcriptional activation or repression, cell cycle control and tumor suppression. A typical feature of Ikaros is its expression in large clusters in the nucleus of activated lymphocytes. We give evidence that Ikaros can bind to several sites in the germline gamma1 and epsilon immunoglobulin heavy chain promoters, in a cooperative manner. Using a promoter reporter assay, we found evidence that Ikaros can suppress germline gamma1 and epsilon promoter activity in a B cell line. When a mutated non-DNA-binding form of Ikaros was introduced into primary activated B cells by retrovirus transduction, the endogenous Ikaros clusters were disrupted. In spite of this, there was no effect on transcription or Ig class switching. The data are discussed in relation to the different hypotheses for the function of Ikaros.

Homozygous deletions and point mutations of the Rit1/Bcl11b gene in gamma-ray induced mouse thymic lymphomas

Allelic loss (LOH) mapping and sequence analysis were conducted for gamma-ray induced mouse thymic lymphomas and a novel tumor suppressor gene, Rit1/Bcl11b, on chromosome 12 was isolated. Bi-allelic changes were found in 17 of the 66 p53-proficient lymphomas with Rit1 LOH but in only 2 of the 54 p53-deficient lymphomas. This suggests an association between the presence of functional p53 and inactivation of the Rit1 gene in the lymphoma development. Introduction of Rit1 into HeLa cells lacking Rit1 expression suppressed cell growth. These results indicate that loss-of-function mutations of Rit1 contribute to mouse lymphomagenesis and possibly to human cancer development.

Regulation of mouse mammary tumor virus env transcriptional activator initiated mammary tumor virus superantigen transcripts in lymphomas of SJL/J mice: role of Ikaros, demethylation, and chromatin structural change in the transcriptional activation of mammary tumor virus superantigen

Mammary tumor virus (Mtv29)-encoded superantigen expressed by SJL/J mouse B cell lymphomas stimulates CD4+V16+ T cells and thereby acquires T cell help necessary for lymphoma growth. Mtv29 mouse mammary tumor virus env transcriptional activator (META) env-controlled Mtv29 superantigen (vSAg29) mRNA transcripts (1.8 kb) are not expressed in normal B or other somatic cells. Real-time PCR-based assays with DNA from normal SJL liver and vSAg29- lymphoma (cNJ101), digested with methylation-sensitive enzymes, showed hypermethylation at AvaI, FspI, HpaII, ThaI, and the distal HgaI sites of the META env, but vSAg29+ lymphoma cells showed significant demethylation at AvaI, HpaII, and the distal HgaI sites. The distal HgaI site that is adjacent to an Ikaros binding site is significantly demethylated in the META env DNA from primary lymphomas. Gel shift assays showed binding of Ikaros to a sequence representing this region in the META env. SJL lymphomas expressed the Ikaros isoform Ik6 that was absent in normal B cells. vSAg29+ cells exhibited increased DNaseI accessibility to chromatin at the vSAg29 initiation site. Treatment of cNJ101 cells with a demethylating agent, 5-azacytidine, and a histone deacetylase inhibitor, trichostatin A, caused hypomethylation at AvaI, HpaII, and distal HgaI sites and led to chromatin structural change at the vSAg29 initiation site, accompanied by the expression of vSAg29 transcripts. This enabled cNJ101 cells to stimulate SJL lymphoma-responsive CD4+V16+ T hybridoma cells. Thus, demethylation at the distal HgaI site of the Mtv29 META env permits vSAg29 expression, which may have an impact on the development of germinal center-derived B cell lymphomas of SJL/J mice.

Signatures of domain shuffling in the human genome

To elucidate the role of exon shuffling in shaping the complexity of the human genome/proteome, we have systematically analyzed intron phase distributions in the coding sequence of human protein domains. We found that introns at the boundaries of domains show high excess of symmetrical phase combinations (i.e., 0-0, 1-1, and 2-2), whereas nonboundary introns show no excess symmetry. This suggests that exon shuffling has primarily involved rearrangement of structural and functional domains as a whole. Furthermore, we found that domains flanked by phase 1 introns have dramatically expanded in the human genome due to domain shuffling and that 1-1 symmetrical domains and domain families are nonrandomly distributed with respect to their age. The predominance and extracellular location of 1-1 symmetrical domains among domains specific to metazoans suggests that they are associated with the rise of multicellularity. On the other hand, 0-0 symmetrical domains tend to be over-represented among ancient protein domains that are shared between the eukaryotic and prokaryotic kingdoms, which is compatible with the suggestion of primordial domain shuffling in the progenote. To see whether the human data reflect general genomic patterns of metazoans, similar analyses were done for the nematode Caenorhabditis elegans. Although the C. elegans data generally concur with the human patterns, we identified fewer intron-bounded domains in this organism, consistent with the lower complexity of C. elegans genes. [The following individuals kindly provided reagents, samples, or unpublished information as indicated in the paper: Z. Gu and R. Stevens.]

An alternative internal splicing site defines new Ikaros isoforms in Pleurodeles waltl

The Ikaros gene encodes a family of transcription factors which plays a crucial role in hematopoiesis. To improve our knowledge about the immune system of Pleurodeles waltl, we sequenced the cDNA coding for the Ik-1 isoform of that salamander and analyzed its tissue expression by semi-quantitative RT-PCR. Ikaros transcripts are abundant in the thymus and the spleen, thereby confirming that these organs are, respectively, the primary and secondary lymphoid tissues of Pleurodeles. Analysis of the isoforms produced by this animal revealed two isoforms characteristic of amphibians in which an alternative internal splicing site deletes the 3' half of exon 3 which interestingly comprises the first Zn finger of Ikaros. Ikaros transcripts were found at the earliest stages of development of Pleurodeles indicating that Ikaros has a function at the very early lymphopoietic stages. Moreover, the presence of Ikaros transcripts in spermatozoa suggests that this protein could have another and yet unknown function.

A molecular dissection of the repression circuitry of Ikaros

Ikaros is a key regulator of the hemo-lymphoid system in which it is presumed to function by both potentiating and repressing gene expression. Repression is mediated through two independent domains at the N and C terminus of the protein, both of which can independently recruit the corepressors Mi-2beta, Sin3A, and Sin3B and the Class I histone deacetylases 1 and 2; the N-terminal domain can also associate with the corepressor CtBP. Here we describe a detailed dissection of these two domains and identify the minimal repression modules and the corepressor requirements for their activity. Based on these studies, we describe mutations in a full-length Ikaros protein that abrogate interactions with each of the identified corepressors and abolish the protein's function as a repressor. Finally, we show that, barring CtBP, the Ikaros family members Aiolos, Helios, and Eos can associate with all of the identified corepressors of Ikaros including its newly identified interactors, Class II HDACs.

Minor H antigens: genes and peptides

In this review, we describe the evidence from which the existence of non-MHC histocompatibility (H) antigens was deduced, the clinical setting of bone marrow transplantation in which they are important targets for T cell responses, and the current understanding of their molecular identity. We list the peptide epitopes, their MHC restriction molecules and the genes encoding them, of the human and murine minor H antigens now identified at the molecular level. Identification of the peptide epitopes allows T cell responses to these antigens following transplantation of MHC-matched, minor H-mismatched tissues to be enumerated using tetramers and elispot assays. This will facilitate analysis of correlations with HVG, GVH and GVL reactions in vivo. The potential to use minor H peptides to modulate in vivo responses to minor H antigens is discussed. Factors controlling immunodominance of T cell responses to one or a few of many potential minor H antigens remain to be elucidated but are important for making predictions of in vivo HVG, GVH and GVL responses and tailoring therapy after HLA-matched BMT and DLI.

Non-DNA-binding Ikaros isoform gene expressed in adult B-precursor acute lymphoblastic leukemia

Ikaros, a zinc finger transcription factor, is essential for lymphoid development. Mutant mice expressing dominant-negative Ikaros gene (Ikaros) isoforms develop an aggressive form of lymphoid malignancies. We examined the expression of Ikaros isoforms in 11 leukemic cell lines and adult acute lymphoblastic leukemia cells from 36 patients with B-precursor acute lymphoblastic leukemia (pre-B ALL) and nine with T-precursor acute lymphoblastic leukemia (pre-T ALL), using reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. In one pre-B ALL cell line, INC cells, and primary leukemic cells from 16 patients with pre-B ALL, we found the predominant expression of a non-DNA-binding Ikaros isoform, Ik-6. However, Ik-6 was not detected in pre-T ALL cells. All of pre-B ALL cells expressing Ik-6 were CD10(+), whereas CD10(-) pre-B ALL cells did not express Ik-6. The expression of Ik-6 was not related to karyotype abnormalities such as t(9;22) and t(4;11). Proteins from the cells that expressed Ik-6 alone failed to bind to the Ikaros protein-specific binding sequence in DNA. Ikaros proteins lacking the DNA binding sequences were detected in the cytoplasm but not in the nucleus of the cells. When INC and primary pre-B ALL cells that express Ik-6 alone were irradiated and cultured in the absence of serum, these cells produced functional Ikaros isoforms, Ik-1 and Ik-2. Purified CD19(+) CD10(-) and CD19(+) CD10(+) cells from normal human bone marrow did not express Ik-6. The predominant expression of Ik-6, which is the result of post-transcription dysregulation, is characteristic of adult pre-B ALL, especially CD10(+) pre-B ALL.

Ikaros-CtIP interactions do not require C-terminal binding protein and participate in a deacetylase-independent mode of repression

Ikaros and Aiolos are Kruppel zinc finger proteins that play key roles in hemo-lymphoid development and homeostasis. We have previously shown that they can repress transcription through the recruitment of histone deacetylases (HDACs). Here, we provide the first functional evidence that these proteins can also repress gene function in a manner that does not require deacetylase activity. This functionality can be attributed in part to Ikaros interactions with the HDAC-independent corepressor, C-terminal binding protein (CtBP). However, mutations that block Ikaros-CtBP interactions do not abolish Ikaros's repression activity, implicating the involvement of additional corepressors. Consistent with this expectation, we show that Ikaros can interact with a CtBP-interacting protein (CtIP), which has also been linked to a deacetylase-independent strategy of repression. Despite being a CtBP interactor, CtIP's association with Ikaros does not require CtBP but instead relies upon its Rb interaction domain. Significantly, Ikaros can interact with Rb, which itself can repress gene function in a deacetylase-independent manner. A mutation in Ikaros that abrogates CtIP interactions significantly reduces repression, and a double mutation that prevents interaction with both CtIP and CtBP even further alleviates repression. Finally, we show that CtIP and CtBP can interact with the general transcription factors, TATA binding protein and transcription factor IIB, which suggests a possible mechanism for their deacetylase-independent mode of repression.

Expression of the Ikaros gene family in childhood acute lymphoblastic leukaemia

The Ikaros (Ik) gene family, which includes Ik, Aiolos (Ai), and Helios (He), is a primary regulator of lymphocyte differentiation, and is involved in the development of acute lymphoblastic leukaemia (ALL). We analysed the expression of the Ik gene family isoforms in 97 ALL cases, consisting of 64 childhood and 33 infant ALL cases, using reverse transcription-polymerase chain reaction (RT-PCR). Expression of Ik was detected in all cases, 87 of which expressed either Ik1 or Ik2, or both, five of which expressed Ik1/Ik2 and Ik6, and another five of which expressed only Ik6. Therefore, the dominant negative isoform of Ik6 was expressed in 10 of the 38 cases of childhood precursor B ALL, but was absent in other types of childhood ALL (26.3%, chi2-test, P = 0.0001). In terms of Aiolos and Helios expression, 49 (65.3%) out of the 75 and 40 (50%) out of the 80 ALL cases tested showed non-spliced Ai1 and He1 respectively. Only one case of T lineage ALL expressed a small-sized isoform of Helios (designated as He6). It was also found that the expression of Ai1 and He1 was low in Ik6-positive patients (Fisher's exact test; Ai1 P = 0.005, Hel P = 0.035).

The position of the polycystic kidney disease 1 (PKD1) gene mutation correlates with the severity of renal disease

The severity of renal cystic disease in the major form of autosomal dominant polycystic kidney disease (PKD1) is highly variable. Clinical data was analyzed from 324 mutation-characterized PKD1 patients (80 families) to document factors associated with the renal outcome. The mean age to end-stage renal disease (ESRD) was 54 yr, with no significant difference between men and women and no association with the angiotensin-converting enzyme polymorphism. Considerable intrafamilial variability was observed, reflecting the influences of genetic modifiers and environmental factors. However, significant differences in outcome were also found among families, with rare examples of unusually late-onset PKD1. Possible phenotype/genotype correlations were evaluated by estimating the effects of covariants on the time to ESRD using proportional hazards models. In the total population, the location of the mutation (in relation to the median position; nucleotide 7812), but not the type, was associated with the age at onset of ESRD. Patients with mutations in the 5' region had significantly more severe disease than the 3' group; median time to ESRD was 53 and 56 yr, respectively (P = 0.025), with less than half the chance of adequate renal function at 60 yr (18.9% and 39.7%, respectively). This study has shown that the position of the PKD1 mutation is significantly associated with earlier ESRD and questions whether PKD1 mutations simply inactivate all products of the gene.

Unconventional potentiation of gene expression by Ikaros

Ikaros is essential for the normal development and regulated proliferation of lymphoid cells. In lymphocytes, Ikaros exists as an integral component of chromatin-remodeling complexes, including the Mi-2beta/nucleosome remodeling and deacetylation complex (NuRD) complex. It is expected that Ikaros, together with these associated activities effects repression, but here we show that they may also potentiate gene expression in cycling cells. Ikaros cannot activate transcription by itself; instead, it enhances the activity of both weak and strong activators. For this role in potentiation, Ikaros requires its DNA binding and dimerization domains. The DNA binding and dimerization properties of Ikaros are also responsible for its targeting to pericentromeric heterochromatin (PC-HC). Significantly, Ikaros mutants with altered specificity for DNA binding that are unable to localize to PC-HC are incapable of stimulating transcription from reporters bearing their cognate sites. Thus, potentiation of gene expression by Ikaros correlates strongly with its ability to localize to PC-HC in combination with the chromatin remodeler Mi-2beta.

Overexpression of novel short isoforms of Helios in a patient with T-cell acute lymphoblastic leukemia

OBJECTIVE

In previous studies, we demonstrated overexpression of the dominant-negative isoform of the transcription factor Ikaros, Ik-6, in patients with blast crisis of chronic myelogenous leukemia and B-cell acute lymphoblastic leukemia. In the present study, we analyzed expression of the Ikaros family genes Ikaros, Aiolos, and Helios in a panel of human T-cell leukemia/lymphoma cell lines and bone marrow samples of patients with T-cell acute lymphoblastic leukemia.

MATERIALS AND METHODS

We performed reverse transcriptase polymerase chain reaction, sequencing analysis, immunoblotting, and Southern blotting.

RESULTS

We found overexpression of novel short isoforms of Helios (Hel-5 and Hel-6) in the HD-Mar cell line. Southern blot analysis suggested that there might be a small deletion in the Helios locus of HD-Mar. In addition, we observed decreased expression of more than one Ikaros family gene in 3 of 9 patients with T-cell acute lymphoblastic leukemia. Moreover, one of the patients overexpressed novel short isoforms of Helios (Hel-7 and Hel-8).

CONCLUSION

This study provides the first evidence of an Ikaros family member (other than Ikaros) of which novel short isoforms become overexpressed in human leukemia.

Expression of a unique helios isoform in human leukemia cells

The purpose of the present study was to characterize the human Helios gene products expressed in leukemia cells. A 3.5 kb human Helios cDNA clone was isolated from a human T-cell cDNA library derived from the human T-acute lymphoblastic leukemia (ALL) cell line JURKAT. This cDNA clone had a unique open reading frame (ORF) encoding a novel 304 amino acid (AA) peptide, which was designated as Helios 3. The sequence of the 289 AA C-terminal portion of Helios 3 downstream of V-16 is identical to the corresponding sequence found in Helios 1 and 2 and contains two zinc fingers. By contrast, the 15 AA N-terminal portion of Helios 3 is unique and does not contain the N-terminal zinc finger motifs that are conserved in Helios 1 and 2 as well as other previously identified members of the Ikaros family. Southern blot analysis of genomic DNA fragments of the human Helios gene locus showed that Helios 3 is encoded by the same genomic locus as Helios 1 and 2. The expression of Helios 3 mRNA was not restricted to T-lineage ALL cells or another immunophenotypically distinct subset of leukemias. Helios 3 mRNA was expressed in freshly obtained primary leukemic cells from six of 15 children with newly diagnosed ALL. Helios 3 exhibited a unique protein interaction profile via its N-terminal portion, which may have biological significance in pathogenesis of human leukemias.

Spectrum of Znfn1a1 (Ikaros) inactivation and its association with loss of heterozygosity in radiogenic T-cell lymphomas in susceptible B6C3F1 mice

Ikaros (now known as Znfn1a1), a Krüppel-type zinc-finger transcription factor that plays a critical role in both lineage commitment and differentiation of lymphoid cells, has recently been shown to function as a tumor suppressor gene. We have previously reported a high frequency of LOH (approximately 50%) at the Znfn1a1 locus in radiation-induced T-cell lymphoma in susceptible B6C3F1 mice. The aim of the present study was to delineate the types of Znfn1a1 inactivation, with special reference to the LOH status, and to determine the relative contribution of each type of Znfn1a1 inactivation in radiation-induced T-cell lymphomas in B6C3F1 mice. We demonstrated that Znfn1a1 was frequently altered (in approximately 50% of T-cell lymphomas), and that its inactivation was caused by a variety of mechanisms, which came under one of the following four categories: (1) null expression (14%); (2) expression of unusual dominant-negative isoforms (11%); (3) amino acid substitutions in the N-terminal zinc-finger domain for DNA binding caused by point mutations (22%); (4) lack of the Znfn1a1 isoform 1 due to the creation of a stop codon by insertion of a dinucleotide in exon 3 (3%). The null expression, amino acid substitutions, and dinucleotide insertion inactivation types were well correlated with LOH at the Znfn1a1 allele (86%) and were consistent with Knudson's two-hit theory. On the other hand, T-cell lymphomas expressing dominant-negative Znfn1a1 isoforms retained both alleles. These results indicate that Znfn1a1 inactivation takes place by a variety of mechanisms in radiation-induced murine T-cell lymphomas and is frequently associated with LOH, this association depending on the type of inactivation.

High frequency of Ikaros isoform 6 expression in acute myelomonocytic and monocytic leukemias: implications for up-regulation of the antiapoptotic protein Bcl-XL in leukemogenesis

While studying Ikaros proteins in childhood acute myeloid leukemia (AML), Ikaros isoform 6 (Ik6) expression was detected in 7 of 10 cases of M4 and M5 leukemia, but in none of the remaining French-American-British subtypes (M2, 8 cases; M7, 6 cases). The spliced Ikaros isoforms 4 to 8 (Ik4-8) suppress the function of full-length Ik1 or Ik2 in a dominant-negative manner, owing to their reduced numbers of DNA binding sites. Thus, dominant-negative Ikaros isoforms may inhibit the normal transcriptional regulation of hematopoietic cell development. To clarify the function of Ik6 in developing blood cells, this isoform was transiently transfected into an Ik2(+), interleukin-3 (IL-3)-dependent 32D murine myeloid precursor cell line and studied the expression of Bcl-2 family proteins in relation to in vitro cell growth, using a tetracycline-inducible TREx system. The possibility of aberrant cell regulation due to Ikaros functional changes was examined by cotransfecting both Ik2 and Ik6 into Ikaros/Aiolos/Helios triple-negative Cos-7 cells. The results demonstrated IL-3-independent growth by Ik6-transfected 32D clones coincident with up-regulation of the antiapoptotic protein Bcl-XL. Up-regulation of Bcl-XL, but not of other Bcl-2 family proteins, was associated with the suppression of functional Ik2 by Ik6 in a dominant-negative fashion. Thus, the pathogenesis of myelomonocytic/monocytic AML may involve aberrant regulation of apoptosis due to unscheduled expression of the Ik6 isoform.

Tissue and cellular localization of a novel polycystic kidney disease-like gene product, polycystin-L

Polycystin-L (PCL), the third member of the polycystin family of proteins, functions as a Ca2+-modulated nonselective cation channel when expressed in Xenopus oocytes. Polycystin-1 and -2 are mutated in autosomal-dominant polycystic kidney disease (ADPKD), but the role of PCL in disease has not been determined. In this study, an anti-peptide polyclonal antiserum was generated against the carboxyl terminal domain of human PCL and used to determine the patterns of expression and distribution of PCL by indirect immunofluorescence in both developing and adult mice. The results show that PCL is predominantly expressed in adult mouse tissues and has a more restricted pattern of expression than either polycystin-1 or -2. In the kidney, PCL expression was first detected at E16, and levels increased into adulthood. Localization of PCL was predominantly found in the apical region of the principal cells of inner medullary collecting ducts. PCL was also found in discrete cell types of the retina, testis, liver, pancreas, heart, and spleen, but it was not detected in the lung. These data in combination with evidence of PCL channel activity are crucial for elucidating the physiologic role of this novel cation channel and may shed light on the function of inner medullary collecting ducts and polycystins. The expression pattern of PCL suggests that it is unlikely to be a candidate gene for ADPKD, but it remains a potential candidate for other as yet unmapped human cystic disorders.

Enforced expression of the Ikaros isoform IK5 decreases the numbers of extrathymic intraepithelial lymphocytes and natural killer 1.1+ T cells

The zinc-finger protein Ikaros plays an important role in lymphoid homeostasis, and loss of Ikaros expression through germline disruption impairs lymphoid development. However, the role played by Ikaros after commitment to the T-cell lineage is unclear. To address this question, this study used the lck proximal promoter to drive the expression in T-cell progenitors of a naturally occurring short Ikaros isoform (IK5), which lacks the DNA-binding domain, reasoning that IK5 will form heterodimers with long isoforms and perturb their function. The IK5 transgene led to a selective and dramatic decrease in extrathymic intestinal intraepithelial lymphocytes (IELs) and natural killer 1.1+ T (NK T) cells with little effect on conventional alphabeta T cells, which resembles the T-cell phenotype of interleukin-15 receptor alpha chain (IL-15Ralpha) and IL-2/IL-15 receptor beta chain (IL-2Rbeta) knockout mice. The expression of IL-2Rbeta on double-negative T-cell progenitors of bi-5 was reduced, but enforced expression of IL-2Rbeta did not rescue IELs or NK T cells in bi-5 transgenic mice, suggesting that Ikaros or Ikaros family members regulate the expression of additional genes that are essential for the development of IELs and NK T cells. The study concludes that modest changes in the ratio of short to long Ikaros isoforms can substantially perturb T-cell development, and the development of IELs and NK T cells is particularly sensitive to such changes.

The Polycomb-group gene eed regulates thymocyte differentiation and suppresses the development of carcinogen-induced T-cell lymphomas

The mouse Polycomb-group gene, embryonic ectoderm development (eed), appears to regulate cellular growth and differentiation in a developmental and tissue specific manner. During embryogenesis, eed regulates axial patterning, whereas in the adult eed represses proliferation of myeloid and B cell precursors. The present report demonstrates two novel functional activities of eed: alteration of thymocyte maturation and suppression of thymic lymphoma development. Mice that inherit the viable hypomorphic 17Rn5(1989SB) eed allele sustain a partial developmental block at or before the CD4(-)CD8(-)CD44(-)CD25(+) stage of thymocyte differentiation. Furthermore, mice that are homozygous or heterozygous for the hypomorphic eed allele have an increased incidence and decreased latency of N-methyl-N-nitrosourea-induced thymic lymphoma compared to wild-type littermates. These findings support the notion that Polycomb-group genes exert pleiotropic effects dictated by developmental stage and cellular context.

Ikaros gene expression and leukemia

The Ikaros (Ik) protein, or LyF1, was initially described as a protein binding to regulatory sequences of a number of genes expressed in murine lymphoid cells. Ikaros is a critical regulator of normal hematopoietic stem cell differentiation, as evidenced by dramatic defects in the lymphoid compartments, in homozygous animals with gene inactivation. Because differential splicing produces multiple isoforms with potentially different functions, Ikaros provides a unique model to study how post-transcriptional mechanisms may be involved in neoplastic processes. Indeed, several groups including ours have underlined evidences that expression of different Ikaros isoforms vary among different types of leukemias. The predominance of short isoforms in certain subsets is intriguing. Here, additional observations reinforced the hypothesis that Ikaros expression may be deregulated in human leukemias. Whether this is a cause or a consequence of the leukemic process remains speculative. Other human diseases however, provide examples of abnormal post-transcriptional regulations that have been further characterized.

Interaction of the leucine-rich repeats of polycystin-1 with extracellular matrix proteins: possible role in cell proliferation

Polycystin-1, the product of the PKD1 gene, is a membrane-bound multidomain protein with a unique structure and a molecular weight of approximately 460 kD. The purpose of this study is to investigate the binding of the cystein-flanked leucine-rich repeats (LRR) of polycystin-1 to extracellular matrix (ECM) components. These interactions may play a role in normal renal development as well as the pathogenesis of autosomal-dominant polycystic kidney disease (ADPKD). In vitro assays were used to assess the binding of a fusion protein containing the LRR of polycystin-1 and that of affinity purified polycystin-1 to a number of ECM components. The results showed that the LRR modulate the binding of polycystin-1 to collagen I, fibronectin, laminin, and cyst fluid-derived laminin fragments. The addition of the LRR fusion protein to cells in culture resulted in a significant dose-dependent reduction in the rate of proliferation. Cyst fluid-derived laminin fragments had a stimulatory effect on cell proliferation, which was reversed by the LRR fusion protein. These results suggest that the LRR of polycystin-1 act as mediators of the polycystin-1 interaction with the ECM. The observed suppression effect of the LRR on cell proliferation suggests a functional role of the LRR-mediated polycystin-1 involvement in cell-matrix and cell-cell interactions. These interactions may result in the enhanced cell proliferation that is a characteristic feature of ADPKD.

Both normal and leukemic B lymphocytes express multiple isoforms of the human Aiolos gene

Aiolos is a chromatin remodeling transcription regulator that plays an antiproliferative role in B lymphocyte function. In contrast to the related Ikaros factors, mammalian Aiolos has not been reported to generate splice variants. In addition, although human leukemic lymphoblasts express non-DNA-binding Ikaros isoforms with potential dominant negative effect on other interacting factors,the role of Aiolos in human lymphoid disorders has remained obscure. To address the question, why Aiolos should delineate from Ikaros in such a marked way, we have here analyzed whether also human Aiolos could generate alternate isoforms. According to the results obtained, both normal and neoplastic B lineage cells were found to express at least five novel Aiolos variants. Also structurally dominant negative variants with less than three DNA-binding domains were identified. In conclusion, given the multiplicity of also human Aiolos isoforms and thereby the evidently more intricate contribution of Aiolos to the chromatin remodeling machinery, it is suggested, that not only Ikaros, but also Aiolos could participate in a more versatile manner in the regulation of B lymphocyte function.

Forced expression of the Ikaros 6 isoform in human placental blood CD34(+) cells impairs their ability to differentiate toward the B-lymphoid lineage

Studies in mice suggest that the Ikaros (Ik) gene encodes several isoforms and is a critical regulator of hematolymphoid differentiation. Little is known on the role of Ikaros in human stem cell differentiation. Herein, the biological consequences of the forced expression of Ikaros 6 (Ik6) in human placental blood CD34(+) progenitors are evaluated. Ik6 is one of the isoforms produced from the Ikaros premessenger RNA by alternative splicing and is thought to behave as a dominant negative isoform of the gene product because it lacks the DNA binding domain present in transcriptionally active isoforms. The results demonstrate that human cord blood CD34(+) cells that express high levels of Ik6 as a result of retrovirally mediated gene transfer have a reduced capacity to produce lymphoid B cells in 2 independent assays: (1) in vitro reinitiation of human hematopoiesis during coculture with the MS-5 murine stromal cell line and (2) xenotransplantation in nonobese diabetic-severe combined immunodeficient mice. These results suggest that Ikaros plays an important role in stem cell commitment in humans and that the balance between the different isoforms is a key element of this regulatory system; they support the hypothesis that posttranscriptional events can participate in the control of human hematopoietic differentiation.

Minor H antigens: genes and peptides

In this review, we describe the evidence from which the existence of non-MHC histocompatibility (H) antigens was deduced, the clinical setting of bone marrow transplantation in which they are important targets for T-cell responses, and the current understanding of their molecular identity. We list the peptide epitopes of the human and murine minor H antigens now identified at the molecular level, their MHC restriction molecules and the genes encoding them. Identification of the peptide epitopes allows T-cell responses to these antigens following transplantation of MHC-matched, minor H-mismatched tissues to be enumerated using tetramers and elispot assays. This will facilitate analysis of correlations with host-versus-graft (HVG), graft-versus-host (GVH) and graft-versus-leukaemia (GVL) reactions in vivo. The potential to use minor H peptides to modulate in vivo responses to minor H antigens is discussed. Factors controlling immunodominance of T-cell responses to one or a few of many potential minor H antigens remain to be elucidated but are important for making predictions of in vivo HVG, GVH and GVL responses and tailoring therapy after HLA-matched bone marrow transplantation and donor lymphocyte infusion.

Physiology, phylogeny, and functions of the TRP superfamily of cation channels

The transient receptor potential (TRP) protein superfamily consists of a diverse group of Ca(2+) permeable nonselective cation channels that bear structural similarities to Drosophila TRP. TRP-related proteins play important roles in nonexcitable cells, as demonstrated by the recent finding that a mammalian TRPC protein is expressed in endothelial cells and functions in vasorelaxation. However, an emerging theme is that many TRP-related proteins are expressed predominantly in the nervous system and function in sensory physiology. The TRP superfamily can be divided into six subfamilies, the first of which is composed of the "classical TRPs" (TRPC subfamily). These proteins all share the common features of three to four ankryin repeats, >/=30% amino acid homology over >/=750 amino acids, and a gating mechanism that operates through phospholipase C. Some classical TRPs may be store-operated channels (SOCs), which are activated by release of Ca(2+) from internal stores. The mammalian TRPC proteins are also expressed in the central nervous system, and several are highly enriched in the brain. One TRPC protein has been implicated in the pheromone response. The archetypal TRP, Drosophila TRP, is predominantly expressed in the visual system and is required for phototransduction. Many members of a second subfamily (TRPV) function in sensory physiology. These include VR1 and OSM-9, which respond to heat, osmolarity, odorants, and mechanical stimuli. A third subfamily, TRPN, includes proteins with many ankyrin repeats, one of which, NOMPC, participates in mechanotransduction. Among the members of a fourth subfamily, TRPM, is a putative tumor suppressor termed melastatin, and a bifunctional protein, TRP-PLIK, consisting of a TRPM channel fused to a protein kinase. PKD2 and mucolipidin are the founding members of the TRPP and TRPML subfamilies, respectively. Mutations in PKD2 are responsible for polycystic kidney disease, and mutations in mucolipidin result in a severe neurodegenerative disorder. Recent studies suggest that alterations in the activities of SOC and TRP channels may be at the heart of several additional neurodegenerative diseases. Thus, TRP channels may prove to be important new targets for drug discovery.

Detection of reciprocal fusion 5'-BCL6/partner-3' transcripts in lymphomas exhibiting reciprocal BCL6 translocations

It has been believed that replacement of the endogenous promoter and the non-coding first exon of the BCL6 gene by a sequence derived from the translocational partner gene is a main mechanism of the BCL6 dysregulation resulting from translocation. In this study, we found that reciprocal BCL6 translocation led to the expression of not only the 5'-partner/BCL6-3' fusion transcripts but also the 5'-BCL6/partner-3' fusion transcripts, suggesting that reciprocal 5'-BCL6/partner-3' fusion genes are transcriptionally active. These findings raise the possibility that reciprocal BCL-6 translocation may lead to dysregulation of the partner gene as well as the BCL6 gene.

Polycystin: new aspects of structure, function, and regulation

Polycystin-1 is a modular membrane protein with a long extracellular N-terminal portion that bears several ligand-binding domains, 11 transmembrane domains, and a > or =200 amino acid intracellular C-terminal portion with several phosphorylation signaling sites. Polycystin-1 is highly expressed in the basal membranes of ureteric bud epithelia during early development of the metanephric kidney, and disruption of the PKD1 gene in mice leads to cystic kidneys and embryonic or perinatal death. It is proposed that polycystin-1 functions as a matrix receptor to link the extracellular matrix to the actin cytoskeleton via focal adhesion proteins. Co-localization, co-sedimentation, and co-immunoprecipitation studies show that polycystin-1 forms multiprotein complexes with alpha2beta1-integrin, talin, vinculin, paxillin, p130cas, focal adhesion kinase, and c-src in normal human fetal collecting tubules and sub-confluent epithelial cultures. In normal adult kidneys and confluent epithelial cultures, polycystin-1 is downregulated and forms complexes with the cell-cell adherens junction proteins E-cadherin and beta-, gamma-, and alpha-catenin. Polycystin-1 activation at the cell membrane leads to intracellular signaling via phosphorylation through the c-Jun terminal kinase and wnt pathways leading to activation of AP-1 and TCF/LEF-dependent genes, respectively. The C-terminal of polcystin-1 has been shown to be phosphorylated by c-src at Y4237, by protein kinase A at S4252, and by focal adhesion kinase and protein kinase X at yet-to-be identified residues. Inhibition of tyrosine phosphorylation or increased cellular calcium increases polycystin-1 focal adhesion complexes versus polycystin-1 adherens junction complexes, whereas disruption of the actin cytoskeleton dissociates all polycystin-1 complexes. Genetic evidence suggests that PKD1, PKD2, NPHP1, and tensin are in the same pathway.

Allelic loss mapping and physical delineation of a region harboring a thymic lymphoma suppressor gene on mouse chromosome 16

Our previous mapping of allelic loss in gamma-ray induced thymic lymphomas in F(1) hybrid and backcross mice between BALB/c and MSM strains identified three regions with high frequencies of allelic loss which probably harbor a tumor suppressor gene. One region, Tlsr7, exists near the D16 Mit122 locus on chromosome 16. This study has further localized Tlsr7 by constructing a physical map and scanning a total of 587 thymic lymphomas. The map consists of 13 overlapping BAC clones and isolation of BAC-derived polymorphic probes leads to fine mapping of allelic losses. Eleven lymphomas show informative breakpoints of allelic loss regions relative to the flanking markers on the map. Pulsed-field gel electrophoresis of NotI digests of the clones shows that the commonly lost region is localized within an approximately 300 kb interval near D16Mit192. This map is invaluable to facilitate the identification of genes in the Tlsr7 region.

Vascular expression of polycystin-2

The expression of polycystin-1 in the vascular smooth muscle cells (VSMC) of elastic and large distributive arteries suggests that some vascular manifestations of autosomal-dominant polycystic kidney disease (ADPKD) result directly from the genetic defect. Intracranial aneurysms have been reported in PKD2, as well as in PKD1 families. To determine whether the vascular expression of polycystin-2 is similar to that of polycystin-1, the expression of PKD2 mRNA and protein in cultured pig aortic VSMC was studied and immunofluorescence and immunohistochemistry were used to study the localization of polycystin-2 in cultured pig aortic VSMC, pig ascending thoracic aorta, and normal elastic and intracranial arteries and intracranial aneurysms obtained at autopsy from patients without or with ADPKD. Tissues derived from Pkd2 wild-type and Pkd2 null mice were used to confirm the specificity of the immunostaining for polycystin-2. Northern blots of VSMC revealed the expected 5.3-kb band. Western blotting detected a 110-kb band in a 100,000 x g fraction of VSMC homogenates. Cultured VSMC as well as VSMC between the elastic lamellae of pig thoracic aorta were positive for polycystin-2 by immunofluorescence. The staining pattern was cytoplasmic. Treatment of the cells before fixation with Taxol, colchicine, or cytochalasin-D altered the pattern of staining in a way suggesting alignment with the cytoskeleton. The immunohistochemical staining for polycystin-2 was abolished by extraction with 0.5% Triton X-100, indicating that polycystin-2 is not associated with the cytoskeleton. Weak immunoreactivity for polycystin-2, which was markedly enhanced by protease digestion, was detected in formaldehyde-fixed normal human elastic and intracranial arteries. Immunostaining of variable intensity for polycystin-2, which was not consistently enhanced by protease digestion, was seen in the spindle-shaped cells of the wall of the intracranial aneurysms. The similar expression of polycystin-1 and polycystin-2 in the vascular smooth muscle is consistent with the proposed interaction of these proteins in a single pathway. These observations suggest a direct pathogenic role for PKD1 and PKD2 mutations in the vascular complications of ADPKD.

Genetic mapping and allelic loss analysis in mouse thymic lymphomas of Helios and Aiolos belonging to the Ikaros gene family

The Ikaros gene undergoes bi-allelic changes at a high frequency in gamma-ray-induced mouse thymic lymphomas, suggesting the relevance of Ikaros to the lymphoma development. Here we test whether Helios and Aiolos, two other members of the Ikaros gene family, are also involved in lymphomagenesis. Genetic mapping showed that Helios is located between D1Mit531 and D1Mit19 on chromosome 1 and Aiolos is between D11Mit222 and D11Mit332 on chromosome 11. Analysis using polymorphic markers around the two regions revealed that neither locus exhibited allelic loss in the 78 lymphomas that were induced in p53 wild-type mice, whereas in 102 p53(KO / + ) mouse-derived lymphomas Helios and Aiolos loci showed allelic loss in 8% (8 / 102) and 33% (34 / 102), respectively. However, 33 of the 34 lymphomas showing allelic loss at Aiolos were p53(KO / - ) and were accompanied by loss of the p53 wild-type allele on the same chromosome. Homozygous deletion and mutation analyses failed to detect bi-allelic alterations. These results do not suggest any obvious contribution of Helios or Aiolos to oncogenesis of the mouse thymic lymphomas.

Eos and pegasus, two members of the Ikaros family of proteins with distinct DNA binding activities

Members of the Ikaros family of transcription factors, Ikaros, Aiolos, and Helios, are expressed in lymphocytes and have been implicated in controlling lymphoid development. These proteins contain two characteristic clusters of zinc fingers, an N-terminal domain important for DNA recognition, and a C-terminal domain that mediates homo- and heterotypic associations between family members. The conservation of these domains is such that all three proteins recognize related DNA sequences, and all are capable of dimerizing with other family members. Here we describe two additional Ikaros family proteins, Eos and Pegasus. Eos is most highly related to Helios and shares its DNA binding and protein association properties. Pegasus is related to other Ikaros proteins in its C-terminal dimerization domain but contains a divergent N-terminal zinc finger domain. Pegasus self-associates and binds to other family members but recognizes distinct DNA-binding sites. Eos and Pegasus repress the expression of reporter genes containing their recognition elements. Our results suggest that these proteins may associate with previously described Ikaros family proteins in lymphoid cells and play additional roles in other tissues.

Ikaros expression in human hematopoietic lineages

The Ikaros gene has been implicated in lymphoid development and proliferation from the results of gene targeting studies in mice. Recently we reported that the Ikaros gene may be involved in the disease progression of chronic myelogenous leukemia (CML). In this report, we investigated Ikaros isoforms in human non-lymphoid leukemia cell lines and normal granulocyte/macrophage (CFU-GM) and erythroid (BFU-E)-derived colonies. We evaluated Ikaros gene expression by RT-PCR, Southern blotting, sequencing analysis, Northern blotting, and immunoblotting.Ikaros isoforms Ik-1 and Ik-2, 3 were predominantly expressed in human non-lymphoid leukemia cell lines. Ik-4 and Ik-8 were also detectable as a minor population. In contrast to the previous report in mice, multiple Ikaros isoforms were expressed in human CFU-GM and BFU-E-derived colonies, and the dominant-negative isoform Ik-6 was not detectable. We also showed that human Ikaros isoforms contained an additional coding sequence in the N-terminal region, which was highly homologous to the sequence reported in mice. These observations suggest that the Ikaros gene may play some role in the development of human non-lymphoid lineage hematopoiesis. Moreover, the finding that the dominant-negative isoform Ik-6, which was overexpressed in patients with blast crisis of CML, was rarely detectable in non-lymphoid lineages supports its pathogenetic role in human hematologic malignancies.

Detection of different Ikaros isoforms in human leukaemias using real-time quantitative polymerase chain reaction

The Ikaros gene is an essential regulator in development and haematopoiesis. Dysregulated Ikaros gene expression participates in leukaemic processes, as evidenced in animal models, and by analyses of blast-cell populations from leukaemic patients. We used real-time quantitative polymerase chain reaction (PCR) to evaluate the relative abundance of several Ikaros transcript isoforms in a variety of leukaemic-cell samples. Total RNA was isolated from bone-marrow or blood-cell samples collected at diagnosis in children or adult patients, 18 of whom had acute myeloblastic leukaemia (AML), 61 of whom had acute lymphoblastic leukaemia (ALL) and 11 of whom had chronic myeloid leukaemia (CML). The ratio (Ik1 + Ik2)/(Ik1 + Ik2 + Ik4 + Ik7 + Ik8) ranged from 13.5% to 85% and was lower (P < 0. 05) in samples from patients with m-bcr-abl ALL. An alternative splicing resulting in the deletion of 30 nucleotides at the end of exon 6 was observed in leukaemic samples, and in normal thymus and bone marrow. Our results are consistent with previous reports and suggest that the pattern of expression of the different human Ikaros isoforms are not homogeneous among different subsets of leukaemias.

Members of the Ikaros gene family are present in early representative vertebrates

Members of the Ikaros multigene family of zinc finger proteins are expressed in a tissue-specific manner and most are critical determinants in the development of both the B and T lymphocytes as well as NK and dendritic APC lineages. A PCR amplification strategy that is based on regions of shared sequence identity in Ikaros multigene family members found in mammals and several other vertebrates has led to the recovery of cDNAs that represent the orthologues of Ikaros, Aiolos, Helios, and Eos in Raja eglanteria (clearnose skate), a cartilaginous fish that is representative of an early divergence event in the phylogenetic diversification of the vertebrates. The tissue-specific patterns of expression for at least two of the four Ikaros family members in skate resemble the patterns observed in mammals, i.e., in hematopoietic tissues. Prominent expression of Ikaros in skate also is found in the lymphoid Leydig organ and epigonal tissues, which are unique to cartilaginous fish. An Ikaros-related gene has been identified in Petromyzon marinus (sea lamprey), a jawless vertebrate species, in which neither Ig nor TCRs have been identified. In addition to establishing a high degree of evolutionary conservation of the Ikaros multigene family from cartilaginous fish through mammals, these studies define a possible link between factors that regulate the differentiation of immune-type cells in the jawed vertebrates and related factors of unknown function in jawless vertebrates.

cAMP regulates cell proliferation and cyst formation in autosomal polycystic kidney disease cells

Both epithelial cell proliferation and fluid accumulation are responsible for cyst growth in autosomal dominant polycystic kidney disease (ADPKD). It was previously reported that the cystic fibrosis transmembrane conductance regulator (CFTR) is expressed in cysts from ADPKD patients and suggested that cAMP-stimulated Cl(-) and fluid secretion occurs through CFTR. The purpose of this study was to investigate the role of cell proliferation in cyst formation in ADPKD and to explore further the role of fluid secretion in cyst growth. Primary cultures both of ADPKD epithelial cells and a mixed population of normal renal epithelial cells isolated from the cortex (HRCE cells) were used. This study tested whether cAMP was involved both in stimulating cell proliferation and formation of cysts in vitro. (3)H-Thymidine incorporation assays showed that epidermal growth factor stimulated proliferation both in ADPKD cells and HRCE cells. In addition, cAMP stimulated DNA synthesis and cell proliferation in ADPKD, but not HRCE, cells. The effects of cAMP and epidermal growth factor on cell growth in ADPKD cells were additive. cAMP also stimulated cyst enlargement and fluid secretion in ADPKD cells. By contrast, cyst formation and enlargement from HRCE cells occurred without cAMP. Fluid secretion into the cyst lumen was blocked by diphenylamine carboxylic acid (DPC) and glibenclamide in ADPKD cells but blocked only by DPC in HRCE cells. This study showed that ADPKD cells have unique characteristics; cAMP stimulates fluid secretion and cell proliferation, indicating cAMP plays a very important role in cyst growth during the course of ADPKD.

Ikaros interactions with CtBP reveal a repression mechanism that is independent of histone deacetylase activity

We have previously shown that Ikaros can repress transcription through the recruitment of histone deacetylase complexes. Here we provide evidence that Ikaros can also repress transcription through its interactions with the co-repressor, C-terminal binding protein (CtBP). CtBP interacts with Ikaros isoforms through a PEDLS motif present at the N terminus of these proteins but not with homologues like Aiolos which lack this motif. Mutations in Ikaros that prevent CtBP interactions reduce its ability to repress transcription. CtBP interacts with Sin3A but not with the Mi-2 co-repressor and it represses transcription in a manner that is independent of histone deacetylase activity. These data strongly suggest that CtBP contributes to a histone deacetylase activity independent mechanism of repression by Ikaros. Finally, we show that the viral oncoprotein E1A, which binds to CtBP, also shows a strong association with Ikaros. This Ikaros-E1A interaction may underlie Ikaros's decreased ability to repress transcription in E1A transformed cells.

Expression of aberrantly spliced oncogenic ikaros isoforms in childhood acute lymphoblastic leukemia

PURPOSE

We sought to determine if molecular abnormalities involving the Ikaros gene could contribute to the development of acute lymphoblastic leukemia (ALL) in children.

PATIENTS AND METHODS

We studied Ikaros gene expression in normal human bone marrow, normal thymocytes, normal fetal liver-derived immature lymphocyte precursor cell lines, eight different ALL cell lines, and leukemic cells from 69 children with ALL (T-lineage ALL, n = 18; B-lineage ALL, n = 51). Expression of Ikaros protein and its subcellular localization were examined by immunoblotting and confocal laser-scanning microscopy, respectively. Polymerase chain reaction (PCR) and nucleotide sequencing were used to identify the specific Ikaros isoforms expressed in these cells. Genomic sequencing of splice junction regions of the Ikaros gene was performed in search for mutations.

RESULTS

In each of the ALL cases, we found high-level expression of a non-DNA-binding or aberrant DNA-binding isoform of Ikaros with abnormal subcellular compartmentalization patterns. In contrast, only wild-type Ik-1 and Ik-2 isoforms with normal subcellular localization were found in normal bone marrow cells and thymus-derived or fetal liver-derived normal lymphocyte precursors. In leukemic cells expressing the aberrant Ikaros coding sequences with the 30-base-pair deletion, genomic sequence analysis of the intron-exon junctions between exons 6 and 7 yielded the wild-type sequence. We identified a single nucleotide polymorphism (SNP) affecting the third base of the triplet codon for a proline (CCC or CCA) in the highly conserved bipartite activation region (viz, A or C at position 1002 numbering from the translation start site of Ik-1) within our Ikaros clones. Bi-allelic expression of truncated and/or non-DNA-binding isoforms along with wild-type isoforms was observed in leukemic cells, which implicates trans-acting factor(s) affecting splice site recognition.

CONCLUSION

Our findings link specific molecular defects involving the Ikaros gene to childhood ALL. Posttranscriptional regulation of alternative splicing of Ikaros RNA seems to be defective in leukemic lymphocyte precursors from most children with ALL. Consequently, leukemic cells from ALL patients, in contrast to normal lymphocyte precursors, express high levels of non-DNA-binding Ikaros isoforms that are reminiscent of the non-DNA-binding Ikaros isoforms that lead to lymphoblastic leukemia in mice.

Homozygous deletions and point mutations of the Ikaros gene in gamma-ray-induced mouse thymic lymphomas

Our previous genome-wide analysis of allelic loss for thymic lymphomas that were induced by gamma-irradiation in F1 hybrid mice between BALB/c and MSM strains suggested the centromeric region on chromosome 11 as a site harboring a tumor suppressor gene. Interestingly, to this region the mouse Ikaros gene was mapped which was postulated to participate in oncogenic process from the study of Ikaros knockout mice. Here we show fine allelic loss mapping in the vicinity of Ikaros in 191 lymphomas, indicating that the critical region of allelic loss was centered at the Ikaros locus. PCR analysis revealed that nine lymphomas failed to give PCR-amplification for either of two exon primer pairs, indicative of homozygous deletion. Six and five mutations were detected in the N-terminal zinc finger domain and the activation domain of Ikaros, respectively, and six of the eleven were frameshift or nonsense mutations that resulted in truncation of Ikaros protein. The results strongly suggest a direct role for Ikaros in development of mouse thymic lymphomas. This provides the experimental basis for further analysis of Ikaros mutations in human cancer.

Defects in hemopoietic stem cell activity in Ikaros mutant mice

Here we provide evidence that the Ikaros family of DNA binding factors is critical for the activity of hemopoietic stem cells (HSCs) in the mouse. Mice homozygous for an Ikaros null mutation display a >30-fold reduction in long-term repopulation units, whereas mice homozygous for an Ikaros dominant negative mutation have no measurable activity. The defect in HSC activity is also illustrated by the ability of wild-type marrow to repopulate unconditioned Ikaros mutants. A progressive reduction in multipotent CFU-S(14) (colony-forming unit-spleen) progenitors and the earliest erythroid-restricted precursors (BFU-E [burst-forming unit-erythroid]) is also detected in the Ikaros mutant strains consistent with the reduction in HSCs. Nonetheless, the more mature clonogenic erythroid and myeloid precursors are less affected, indicating either the action of a compensatory mechanism to provide more progeny or a negative role of Ikaros at later stages of erythromyeloid differentiation. In Ikaros mutant mice, a decrease in expression of the tyrosine kinase receptors flk-2 and c-kit is observed in the lineage-depleted c-kit(+)Sca-1(+) population that is normally enriched for HSCs and may in part contribute to the early hemopoietic phenotypes manifested in the absence of Ikaros.

Human aiolos, an ikaros-related zinc finger DNA binding protein: cDNA cloning, tissue expression pattern, and chromosomal mapping

The Ikaros gene (symbol ZNFN1A1) encodes the hematopoietic zinc finger DNA binding protein, which is now recognized as a central regulator of lymphoid differentiation and has been implicated in leukemogenesis. Recently, an Ikaros-related zinc finger protein, called Aiolos (ZNFN1A3), has been identified and characterized, thus establishing the presence of a gene family whose members may be hematopoietic transcription factors. Among Aiolos-mutant mice, development of B-cell lymphoma was frequently seen. As an initial approach to examining the possible involvement of Aiolos in the pathogenesis of human lymphoid proliferative disease, we isolated cDNA clones for human Aiolos from a B-cell cDNA library. The human Aiolos protein predicted from the cDNA sequence consists of 509 amino acid residues and shares 86% sequence identity with its mouse counterpart. As in the case with mouse Aiolos, no isoform for human Aiolos has been found. Northern blot analysis of various human tissues revealed that the Aiolos transcripts are expressed most strongly in peripheral blood leukocytes, the spleen, and the thymus, supporting the notion that Aiolos plays an important role in lymphoid lineages. Fluorescence in situ hybridization using a BAC clone established that the Aiolos gene is mapped to human chromosome band 17q11.2.

Pre-T cell receptor (TCR) and TCR-controlled checkpoints in T cell differentiation are set by Ikaros

T cell differentiation relies on pre-T cell receptor (TCR) and TCR signaling events that take place at successive steps of the pathway. Here, we show that two of these T cell differentiation checkpoints are regulated by Ikaros. In the absence of Ikaros, double negative thymocytes can differentiate to the double positive stage without expression of a pre-TCR complex. Subsequent events in T cell development mediated by TCR involving transition from the double positive to the single positive stage are also regulated by Ikaros. Nonetheless, in Ikaros-deficient thymocytes, the requirement of pre-TCR expression for expansion of immature thymocytes as they progress to the double positive stage is still maintained, and the T cell malignancies that invariably arise in the thymus of Ikaros-deficient mice are dependent on either pre-TCR or TCR signaling. We conclude that Ikaros regulates T cell differentiation, selection, and homeostasis by providing signaling thresholds for pre-TCR and TCR.

Prf, a novel Ets family protein that binds to the PU.1 binding motif, is specifically expressed in restricted stages of B cell development

During the development of lymphocytes, expression of the Ig genes is strictly regulated in a tissue-specific manner and in a time-ordered fashion. We have previously shown that the PU.1 binding motif in the Igkappa 3' enhancer (kappaE3') and a novel Ets family protein other than PU.1 may be possibly involved in the control of V(kappa)-J(kappa) joining. In the attempt to isolate the novel Ets family protein, we have screened cDNA libraries with the yeast one-hybrid method and identified a new PU.1-related factor, Prf. This novel Ets family protein is shown to interact with the PU.1 binding sequences in various promoters and enhancers, including kappaE3'. It was found that expression of the prf gene is predominant in the B-lineage cells, with the exception of immature B cells. Since Prf does not exhibit functions of transcriptional activity, this novel protein may act as an antagonist against other Ets family proteins, e.g. PU.1 and Spi-B. Possible roles of Prf with respect to the B cell differentiation are discussed.

Transduction of renal cells in vitro and in vivo by adeno-associated virus gene therapy vectors

There has been an increasing interest recently in the possibility of treating renal diseases using gene therapy. The ability to pursue gene therapy for renal diseases has been limited by the availability of an adequate system for gene delivery to the kidney. Adeno-associated virus (AAV) is a defective virus of the parvovirus family that has a number of properties attractive for renal gene delivery: recombinant AAV contains no viral genes; expression of genes delivered by these vectors does not activate cell-mediated immunity; the virus is able to transduce nondividing as well as dividing cells; and both wild-type and recombinant AAV integrate into the host chromosome resulting in long-term gene expression. Studies were performed to determine whether AAV can deliver reporter genes to kidney cells in vitro and in vivo. These studies show that AAV can deliver reporter genes with approximately equal efficiency to human mesangial, proximal tubule, thick ascending limb, collecting tubule, and renal cell carcinoma cells in primary culture. Immortalized mouse mesangial cells are transduced at a much greater efficiency. Transduction can be enhanced by pharmaceutical agents up to sevenfold in primary cells (transducing up to 20% of primary cells per well) and as much as 400-fold in immortalized mesangial cells. AAV delivered in vivo by intraparenchymal injection results in at least 3 mo of reporter gene expression in tubular epithelial, but not glomerular or vascular, cells at the injection site. These data indicate that AAV can deliver genes to renal cells both in vitro and in vivo resulting in prolonged gene expression, and thus AAV can be a useful tool for renal gene delivery.

Transcriptional regulation of lymphocyte lineage commitment

The development of T cells and B cells from pluripotent hematopoietic precursors occurs through a stepwise narrowing of developmental potential that ends in lineage commitment. During this process, lineage-specific genes are activated asynchronously, and lineage-inappropriate genes, although initially expressed, are asynchronously turned off. These complex gene expression events are the outcome of the changes in expression of multiple transcription factors with partially overlapping roles in early lymphocyte and myeloid cell development. Key transcription factors promoting B-cell development and candidates for this role in T-cell development are discussed in terms of their possible modes of action in fate determination. We discuss how a robust, stable, cell-type-specific gene expression pattern may be established in part by the interplay between endogenous transcription factors and signals transduced by cytokine receptors, and in part by the network of effects of particular transcription factors on each other.