SIPA1L1/SPAR1 Interacts with the Neurabin Family of Proteins and is Involved in GPCR Signaling.

Signal-induced proliferation-associated 1 (SIPA1)-like 1 (SIPA1L1; also known as SPAR1) has been proposed to regulate synaptic functions that are important in maintaining normal neuronal activities, such as regulating spine growth and synaptic scaling, as a component of the PSD-95/NMDA-R-complex. However, its physiological role remains poorly understood. Here, we performed expression analyses using super-resolution microscopy (SRM) in mouse brain and demonstrated that SIPA1L1 is mainly localized to general submembranous regions in neurons, but surprisingly, not to PSD. Our screening for physiological interactors of SIPA1L1 in mouse brain identified spinophilin and neurabin-1, regulators of G-protein-coupled receptor (GPCR) signaling, but rejected PSD-95/NMDA-R-complex components. Furthermore, Sipa1l1-/- mice showed normal spine size distribution and NMDA-R-dependent synaptic plasticity. Nevertheless, Sipa1l1-/- mice showed aberrant responses to α2-adrenergic receptor (a spinophilin target) or adenosine A1 receptor (a neurabin-1 target) agonist stimulation, and striking behavioral anomalies, such as hyperactivity, enhanced anxiety, learning impairments, social interaction deficits, and enhanced epileptic seizure susceptibility. Male mice were used for all experiments. Our findings revealed unexpected properties of SIPA1L1, suggesting a possible association of SIPA1L1 deficiency with neuropsychiatric disorders related to dysregulated GPCR signaling, such as epilepsy, attention deficit hyperactivity disorder (ADHD), autism, or fragile X syndrome (FXS).SIGNIFICANCE STATEMENT Signal-induced proliferation-associated 1 (SIPA1)-like 1 (SIPA1L1) is thought to regulate essential synaptic functions as a component of the PSD-95/NMDA-R-complex. In our screening for physiological SIPA1L1-interactors, we identified G-protein-coupled receptor (GPCR)-signaling regulators. Moreover, SIPA1L1 knock-out (KO) mice showed striking behavioral anomalies, which may be relevant to GPCR signaling. Our findings revealed an unexpected role of SIPA1L1, which may open new avenues for research on neuropsychiatric disorders that involve dysregulated GPCR signaling. Another important aspect of this paper is that we showed effective methods for checking PSD association and identifying native protein interactors that are difficult to solubilize. These results may serve as a caution for future claims about interacting proteins and PSD proteins, which could eventually save time and resources for researchers and avoid confusion in the field.

Induction of Gastric Cancer by Successive Oncogenic Activation in the Corpus.

BACKGROUND & AIMS: Metaplasia and dysplasia in the corpus are reportedly derived from de-differentiation of chief cells. However, the cellular origin of metaplasia and cancer remained uncertain. Therefore, we investigated whether pepsinogen C (PGC) transcript-expressing cells represent the cellular origin of metaplasia and cancer using a novel Pgc-specific CreERT2 recombinase mouse model. METHODS: We generated a Pgc-mCherry-IRES-CreERT2 (Pgc-CreERT2) knock-in mouse model. Pgc-CreERT2/+ and Rosa-EYFP mice were crossed to generate Pgc-CreERT2/Rosa-EYFP (Pgc-CreERT2/YFP) mice. Gastric tissues were collected, followed by lineage-tracing experiments and histologic and immunofluorescence staining. We further established Pgc-CreERT2;KrasG12D/+ mice and investigated whether PGC transcript-expressing cells are responsible for the precancerous state in gastric glands. To investigate cancer development from PGC transcript-expressing cells with activated Kras, inactivated Apc, and Trp53 signaling pathways, we crossed Pgc-CreERT2/+ mice with conditional KrasG12D, Apcflox, Trp53flox mice. RESULTS: Expectedly, mCherry mainly labeled chief cells in the Pgc-CreERT2 mice. However, mCherry was also detected throughout the neck cell and isthmal stem/progenitor regions, albeit at lower levels. In the Pgc-CreERT2;KrasG12D/+ mice, PGC transcript-expressing cells with KrasG12D/+ mutation presented pseudopyloric metaplasia. The early induction of proliferation at the isthmus may reflect the ability of isthmal progenitors to react rapidly to Pgc-driven KrasG12D/+ oncogenic mutation. Furthermore, Pgc-CreERT2;KrasG12D/+;Apcflox/flox mice presented intramucosal dysplasia/carcinoma and Pgc-CreERT2;KrasG12D/+;Apcflox/flox;Trp53flox/flox mice presented invasive and metastatic gastric carcinoma. CONCLUSIONS: The Pgc-CreERT2 knock-in mouse is an invaluable tool to study the effects of successive oncogenic activation in the mouse corpus. Time-course observations can be made regarding the responses of isthmal and chief cells to oncogenic insults. We can observe stomach-specific tumorigenesis from the beginning to metastatic development.

Transcription Factors Runx1 and Runx3 Suppress Keratin Expression in Undifferentiated Keratinocytes.

The Runt-related transcription factor (Runx) family has been suggested to play roles in stem cell regulation, tissue development, and oncogenesis in various tissues/organs. In this study, we investigated the possible functions of Runx1 and Runx3 in keratinocyte differentiation. Both Runx1 and Runx3 proteins were detected in primary cultures of mouse keratinocytes. Proteins were localized in the nuclei of undifferentiated keratinocytes but translocated to the cytoplasm of differentiated cells. The siRNA-mediated inhibition of Runx1 and Runx3 expression increased expression of keratin 1 and keratin 10, which are early differentiation markers of keratinocytes. In contrast, overexpression of Runx1 and Runx3 suppressed keratin 1 and keratin 10 expression. Endogenous Runx1 and Runx3 proteins were associated with the promoter sequences of keratin 1 and keratin 10 genes in undifferentiated but not differentiated keratinocytes. In mouse skin, the inhibition of Runx1 and Runx3 expression by keratinocyte-specific gene targeting increased the ratios of keratin 1- and keratin 10-positive cells in the basal layer of the epidermis. On the other hand, inhibition of Runx1 and Runx3 expression did not alter the proliferation capacity of cultured or epidermal keratinocytes. These results suggest that Runx1 and Runx3 likely function to directly inhibit differentiation-induced expression of keratin 1 and keratin 10 genes but are not involved in the regulation of keratinocyte proliferation.

Iqgap3-Ras axis drives stem cell proliferation in the stomach corpus during homoeostasis and repair.

OBJECTIVE: Tissue stem cells are central regulators of organ homoeostasis. We looked for a protein that is exclusively expressed and functionally involved in stem cell activity in rapidly proliferating isthmus stem cells in the stomach corpus. DESIGN: We uncovered the specific expression of Iqgap3 in proliferating isthmus stem cells through immunofluorescence and in situ hybridisation. We performed lineage tracing and transcriptomic analysis of Iqgap3 +isthmus stem cells with the Iqgap3-2A-tdTomato mouse model. Depletion of Iqgap3 revealed its functional importance in maintenance and proliferation of stem cells. We further studied Iqgap3 expression and the associated gene expression changes during tissue repair after tamoxifen-induced damage. Immunohistochemistry revealed elevated expression of Iqgap3 in proliferating regions of gastric tumours from patient samples. RESULTS: Iqgap3 is a highly specific marker of proliferating isthmus stem cells during homoeostasis. Iqgap3+isthmus stem cells give rise to major cell types of the corpus unit. Iqgap3 expression is essential for the maintenance of stem potential. The Ras pathway is a critical partner of Iqgap3 in promoting strong proliferation in isthmus stem cells. The robust induction of Iqgap3 expression following tissue damage indicates an active role for Iqgap3 in tissue regeneration. CONCLUSION: IQGAP3 is a major regulator of stomach epithelial tissue homoeostasis and repair. The upregulation of IQGAP3 in gastric cancer suggests that IQGAP3 plays an important role in cancer cell proliferation.

The RNA-binding protein Mex-3B plays critical roles in the development of steroid-resistant neutrophilic airway inflammation.

While most asthma can be treated with steroids, about 10%, called severe asthma, is refractory to steroids. It has recently been shown that in a subgroup of severe asthma cases, neutrophils that infiltrate into the airways play an important role in inflammation. However, the mechanisms underlying this increased neutrophil infiltration are not well understood. Here, using a mouse model of steroid-resistant neutrophilic inflammation, we show that mice deficient for the RNA-binding protein Mex-3B have significantly less neutrophil infiltration in the airways than wild-type mice. We further demonstrate that Mex-3B post-transcriptionally upregulates CXCL2, a chemokine that induces neutrophil chemotaxis and migration. Moreover, we show that treatment with either anti-CXCL2 antibody or anti-Mex-3B antisense oligonucleotide suppresses neutrophilic allergic airway inflammation. These results suggest that Mex-3B-mediated induction of CXCL2 is crucial for steroid-resistant neutrophilic allergic airway inflammation. Our findings suggest new strategies for therapeutic intervention in steroid-resistant severe asthma.

Identification of Stem Cells in the Epithelium of the Stomach Corpus and Antrum of Mice.

BACKGROUND & AIMS: Little is known about the mechanisms of gastric carcinogenesis, partly because it has been a challenge to identify characterize gastric stem cells. Runx genes regulate development and their products are transcription factors associated with cancer development. A Runx1 enhancer element, eR1, is a marker of hematopoietic stem cells. We studied expression from eR1 in the stomach and the roles of gastric stem cells in gastric carcinogenesis in transgenic mice. METHODS: We used in situ hybridization and immunofluorescence analyses to study expression of Runx1 in gastric tissues from C57BL/6 (control) mice. We then created mice that expressed enhanced green fluorescent protein (EGFP) or CreERT2 under the control of eR1 (eR1-CreERT2;Rosa-Lox-Stop-Lox [LSL]-tdTomato, eR1-CreERT2;Rosa-LSL-EYFP mice). Gastric tissues were collected and lineage-tracing experiments were performed. Gastric organoids were cultured from eR1-CreERT2(5-2);Rosa-LSL-tdTomato mice and immunofluorescence analyses were performed. We investigated the effects of expressing oncogenic mutations in stem cells under control of eR1 using eR1-CreERT2;LSL-KrasG12D/+ mice; gastric tissues were collected and analyzed by histology and immunofluorescence. RESULTS: Most proliferation occurred in the isthmus; 86% of proliferating cells were RUNX1-positive and 76% were MUC5AC-positive. In eR1-EGFP mice, EGFP signals were detected mainly in the upper part of the gastric unit, and 83% of EGFP-positive cells were located in the isthmus/pit region. We found that eR1 marked undifferentiated stem cells in the isthmus and a smaller number of terminally differentiated chief cells at the base. eR1 also marked cells in the pyloric gland in the antrum. Lineage-tracing experiments demonstrated that stem cells in the isthmus and antrum continuously gave rise to mature cells to maintain the gastric unit. eR1-positive cells in the isthmus and pyloric gland generated organoid cultures in vitro. In eR1-CreERT2;LSL-Kras G12D/+ mice, MUC5AC-positive cells rapidly differentiated from stem cells in the isthmus, resulting in distinct metaplastic lesions similar to that observed in human gastric atrophy. CONCLUSIONS: Using lineage-tracing experiments in mice, we found that a Runx1 enhancer element, eR1, promotes its expression in the isthmus stem cells of stomach corpus as well as pyloric gland in the antrum. We were able to use eR1 to express oncogenic mutations in gastric stem cells, proving a new model for studies of gastric carcinogenesis.

T-cell receptor signaling induces proximal Runx1 transactivation via a calcineurin-NFAT pathway.

Runx1 transcription factor is a key player in the development and function of T cells. Runx1 transcripts consist of two closely related isoforms (proximal and distal Runx1) whose expressions are regulated by different promoters. Which Runx1 isoform is expressed appears to be tightly regulated. The regulatory mechanism for differential transcription is, however, not fully understood. In this study, we investigated the regulation of the proximal Runx1 promoter in T cells. We showed that proximal Runx1 was expressed at a low level in naïve T cells from C57BL/6 mice, but its expression was remarkably induced upon T-cell activation. In the promoter of proximal Runx1, a highly conserved region was identified which spans from -412 to the transcription start site and harbors a NFAT binding site. In a luciferase reporter assay, this region was found to be responsive to T-cell activation through Lck and calcineurin pathways. Mutagenesis studies and chromatin immunoprecipitation assay indicated that the NFAT site was essential for NFAT binding and transactivation of the proximal Runx1 promoter. Furthermore, TCR signaling-induced expression of proximal Runx1 was blocked by treatment of cells with cyclosporin A. Together, these results demonstrate that the calcineurin-NFAT pathway regulates proximal Runx1 transcription upon TCR stimulation.

Reciprocal control of G1-phase progression is required for Th-POK/Runx3-mediated CD4/8 thymocyte cell fate decision.

After receiving a TCR-mediated differentiation signal, CD4 and CD8 double-positive thymocytes diverge into CD4 or CD8 single-positive T cells, for which Th-POK and Runx3 have been identified as pivotal transcription factors, respectively. The cross-antagonistic regulation of Th-POK and Runx3 seems to be essential for CD4/8 thymocyte lineage commitment. However, the process for determining which pivotal factor acts dominantly has not been established. To explore the determining process, we used an in vitro culture system in which CD4 or CD8 single-positive cells are selectively induced from CD4/8 double-positive cells. Surprisingly, we found that control of G(1) cell cycle phase progression is critical for the determination. In the CD4 pathway, sustained TCR signal, as well as Th-POK, induces G(1)-phase extension and represses CD8 expression in a G(1) extension-dependent manner. In the CD8 pathway, after receiving a transient TCR signal, the IL-7R signal, as well as Runx3, antagonizes TCR signal-mediated G(1) extension and CD8 repression. Importantly, forced G(1) extension cancels the functions of Runx3 to repress Th-POK and CD4 and to reactivate CD8. In contrast, it is suggested that forced G(1) progression inhibits Th-POK function to repress CD8. Collectively, Th-POK and Runx3 are reciprocally involved in the control of G(1)-phase progression, on which they exert their functions dependently. These findings may provide novel insight into how CD4/CD8 cell lineages are determined by Th-POK and Runx3.

Runx1 deficiency in CD4+ T cells causes fatal autoimmune inflammatory lung disease due to spontaneous hyperactivation of cells.

The Runx1 transcription factor is abundantly expressed in naive T cells but rapidly downregulated in activated T cells, suggesting that it plays an important role in a naive stage. In the current study, Runx1(-/-)Bcl2(tg) mice harboring Runx1-deleted CD4(+) T cells developed a fatal autoimmune lung disease. CD4(+) T cells from these mice were spontaneously activated, preferentially homed to the lung, and expressed various cytokines, including IL-17 and IL-21. Among these, the deregulation of IL-21 transcription was likely to be associated with Runx binding sites located in an IL-21 intron. IL-17 produced in Runx1-deleted cells mobilized innate immune responses, such as those promoted by neutrophils and monocytes, whereas IL-21 triggered humoral responses, such as plasma cells. Thus, at an initial stage, peribronchovascular regions in the lung were infiltrated by CD4(+) lymphocytes, whereas at a terminal stage, interstitial regions were massively occupied by immune cells, and alveolar spaces were filled with granular exudates that resembled pulmonary alveolar proteinosis in humans. Mice suffered from respiratory failure, as well as systemic inflammatory responses. Our data indicate that Runx1 plays an essential role in repressing the transcription of cytokine genes in naive CD4(+) T cells and, thereby, maintains cell quiescence.

Transcriptional activation of the Pirb gene in B cells by PU.1 and Runx3.

Cells in the immune system are regulated positively or negatively by sets of receptor pairs that conduct balanced, activating, or inhibitory intracellular signaling. One such receptor pair termed paired Ig-like receptor (PIR) is composed of the inhibitory PIR-B and its activating isoform, PIR-A. Upon binding to their shared ligand, MHC class I molecules, these receptors control the threshold for immune cell activation. Gene-targeting studies on PIR-B in mice revealed the importance of the inhibition mediated by the PIR-B-MHC interaction in the immune system. Recent studies also revealed the significance of the interaction of PIR-B with neurite outgrowth inhibitors, including Nogo in the CNS. The coordinated regulation by PIR-B and PIR-A is considered to be primarily dependent on their expression balance in cells. However, the mechanism underlying transcriptional control of the genes for PIR-B and PIR-A (Pirb and Pira, respectively) remains to be clarified. In this study, we identified the major cis-acting promoter segment for Pirb and Pira in B cells as the -212 to -117 region upstream from the translation initiation codon. PU.1 and Runx3 were found to bind to this Pirb promoter. Truncation of the PU.1-binding motif significantly reduced the promoter activity, whereas the influence of elimination of the Runx3 site was marginal in B lymphoma BCL1-B20 cells. Unexpectedly, PU.1, but not Runx3, knockdown reduced the levels of both the Pirb and Pira transcripts. We conclude that the major promoter of Pirb, and probably Pira as well, is activated dominantly by PU.1 and marginally by Runx3 in B cells.

Down-regulation of Runx1 expression by TCR signal involves an autoregulatory mechanism and contributes to IL-2 production.

Runx1 transcription factor plays multiple roles in T cell development, differentiation, and function. However, the regulatory mechanisms and functional significance of high Runx1 protein expression in resting peripheral CD4+ T cells is not well understood. Here, we demonstrate that T-cell receptor (TCR) activation down-regulates distal Runx1 transcription, resulting in a significant reduction of Runx1 protein. Interestingly, this down-regulation of distal Runx1 transcription appears to be mediated through a negative auto-regulatory mechanism, whereby Runx1 protein binds to a Runx consensus site in the distal promoter. Through the use of Runx1-overexpressing cells from transgenic mice, we demonstrate that interference with TCR-mediated Runx1 down-regulation inhibits IL-2 production and proliferation in activated CD4+ T cells. In contrast, using Runx1-deficient cells prepared from targeted mice, we show that the absence of Runx1 in unstimulated CD4+ T cells results in IL-2 derepression. In summary, we propose that high levels of Runx1 in resting CD4+ T cells functions negatively in the regulation of IL-2 transcription, and that TCR activation-mediated down-regulation of Runx1 involves negative auto-regulation of the distal Runx1 promoter and contributes to IL-2 production.

A Point Mutation R122C in RUNX3 Promotes the Expansion of Isthmus Stem Cells and Inhibits Their Differentiation in the Stomach.

BACKGROUND & AIMS: RUNX transcription factors play pivotal roles in embryonic development and neoplasia. We previously identified the single missense mutation R122C in RUNX3 from human gastric cancer. However, how RUNX3R122C mutation disrupts stem cell homeostasis and promotes gastric carcinogenesis remained unclear. METHODS: To understand the oncogenic nature of this mutation in vivo, we generated the RUNX3R122C knock-in mice. Stomach tissues were harvested, followed by histologic and immunofluorescence staining, organoid culture, flow cytometry to isolate gastric corpus isthmus and nonisthmus epithelial cells, and RNA extraction for transcriptomic analysis. RESULTS: The corpus tissue of RUNX3R122C/R122C homozygous mice showed a precancerous phenotype such as spasmolytic polypeptide-expressing metaplasia. We observed mucous neck cell hyperplasia; massive reduction of pit, parietal, and chief cell populations; as well as a dramatic increase in the number of rapidly proliferating isthmus stem/progenitor cells in the corpus of RUNX3R122C/R122C mice. Transcriptomic analyses of the isolated epithelial cells showed that the cell-cycle-related MYC target gene signature was enriched in the corpus epithelial cells of RUNX3R122C/R122C mice compared with the wild-type corpus. Mechanistically, RUNX3R122C mutant protein disrupted the regulation of the restriction point where cells decide to enter either a proliferative or quiescent state, thereby driving stem cell expansion and limiting the ability of cells to terminally differentiate. CONCLUSIONS: RUNX3R122C missense mutation is associated with the continuous cycling of isthmus stem/progenitor cells, maturation arrest, and development of a precancerous state. This work highlights the importance of RUNX3 in the prevention of metaplasia and gastric cancer.

Interplay of transcription factors in T-cell differentiation and function: the role of Runx.

Over the past years, increasing numbers of distinct subsets have been discovered and identified for a T lymphocytes' entity. Differentiation and function of each T cell subset are controlled by a specific master transcription factor. Importantly, Runt-related transcription factors, particularly Runx1 and Runx3, interplay with these master regulators in various aspects of T cells' immunity. In this review article, we first explain roles of Th-Pok and Runx3 in differentiation of CD4 versus CD8 single positive cells, and later focus on cross-regulation of Th-Pok and Runx3 and their relationship with other factors such as TCR strength. Next, we provide evidences for the direct interplay of Runx1/3 with T-bet and GATA3 during Th1 versus Th2 commitment to activate or silence transcription of signature cytokine genes, IFNγ and IL4. Lastly, we explain feed-forward relationship between Runx1 and Foxp3 and discuss roles of Runx1 in regulatory T cells' suppressive activity. This review highlights an essential importance of Runx molecules in controlling various T cell subsets' differentiation and functions through molecular interplay with the master transcription factors in terms of protein-protein interaction as well as regulation of gene expression.

The Runx3 transcription factor augments Th1 and down-modulates Th2 phenotypes by interacting with and attenuating GATA3.

Recently, it was reported that the expression of Runt-related transcription factor 3 (Runx3) is up-regulated in CD4(+) helper T cells during Th1 cell differentiation, and that Runx3 functions in a positive feed-forward manner with the T-box family transcription factor, T-bet, which is a master regulator of Th1 cell differentiation. The relative expression levels of IFN-gamma and IL-4 are also regulated by the Th2-associated transcription factor, GATA3. Here, we demonstrate that Runx3 was induced in Th2 as well as Th1 cells and that Runx3 interacted with GATA3 and attenuated GATA3 transcriptional activity. Ectopic expression of Runx3 in vitro in cultured cells or transgenic expression of Runx3 in mice accelerated CD4(+) cells to a Th1-biased population or down-modulated Th2 responses, in part by neutralizing GATA3. Our results suggest that the balance of Runx3 and GATA3 is one factor that influences the manifestation of CD4(+) cells as the Th1 or Th2 phenotypes.

Serial OX40 engagement on CD4+ T cells and natural killer T cells causes allergic airway inflammation.

RATIONALE: OX40-OX40 ligand (OX40L) interactions have been proposed to support induction of allergic airway inflammation, which may be attributable to OX40 signaling in CD4(+) helper T cells for adaptive immune responses. However, a possible involvement of natural killer T (NKT) cells in the pathogenesis suggests that the underlying mechanisms are not yet fully elucidated. OBJECTIVES: We aimed to characterize the OX40-modulated cellular contribution to allergic airway inflammation in a mouse model of house dust mite (HDM) allergen exposure. METHODS: Mice were sensitized to HDM and, 3 weeks later, challenged with HDM on three consecutive days through the airways. Two days after the last exposure, bronchoalveolar lavage fluids and blood samples and lung tissues were evaluated for the airway inflammation. MEASUREMENTS AND MAIN RESULTS: The development of HDM-induced eosinophilic airway inflammation was dependent on OX40 of both CD4(+) T cells and NKT cells; OX40 engagement on CD4(+) T cells in the sensitization led to pulmonary OX40L augmentation after the allergen challenge, which stimulated pulmonary NKT cells through OX40 to provide the pathogenic cytokine milieu. This was ablated by OX40L blockade by inhalation of the neutralizing antibody during the challenge, suggesting the therapeutic potential of targeting pulmonary OX40-OX40L interactions. Moreover, OX40 expression in CD4(+) T cells, but not in NKT cells, was reciprocally regulated by the helper T cell type 1-skewing transcription factor Runx3. CONCLUSIONS: OX40 on not only CD4(+) T cells but also NKT cells is involved in allergic airway inflammation. Notably, pulmonary blockade of OX40 ligation on NKT cells has therapeutic implications.

Over-expression of Runx1 transcription factor impairs the development of thymocytes from the double-negative to double-positive stages.

Runx1 transcription factor is highly expressed at a CD4/CD8-double-negative (DN) stage of thymocyte development but is down-regulated when cells proceed to the double-positive (DP) stage. In the present study, we examined whether the down-regulation of Runx1 is necessary for thymocyte differentiation from the DN to DP stage. When Runx1 was artificially over-expressed in thymocytes by Lck-driven Cre, the DN3 population was unaffected, as exemplified by proper pre-T-cell receptor expression, whereas the DN4 population was perturbed as shown by the decrease in the CD27(hi) sub-fraction. In parallel, the growth rate of DN4 cells was reduced by half, as measured by bromodeoxyuridine incorporation. These events impaired the transition of DN4 cells to the DP stage, resulting in the drastic reduction of the number of DP thymocytes. The Runx1 gene has two promoters, a proximal and a distal promoter; and, in thymocytes, endogenous Runx1 was mainly transcribed from the distal promoter. Interestingly, only distal, but not proximal, Runx1 over-expression exhibited an inhibitory effect on thymocyte differentiation, suggesting that the distal Runx1 protein may fulfil a unique function. Our collective results indicate that production of the distal Runx1 protein must be adequately down-regulated for thymocytes to transit from the DN to the DP stage, a critical step in the massive expansion of the T-cell lineage.

MicroRNA-27 enhances differentiation of myeloblasts into granulocytes by post-transcriptionally downregulating Runx1.

We investigated the regulation of the transcription factor Runx1 by microRNA (miR)-27 and the resulting effects upon the differentiation of myeloblasts into granulocytes. When 32D.cl3 cell differentiation was induced using granulocyte colony-stimulating factor (CSF3), Runx1 transcription was moderately downregulated, while Runx1 protein levels were completely inhibited, suggesting an involvement of post-transcriptional regulation. Simultaneously, levels of miR-27 and its precursor increased substantially. Reporter assays revealed that miR-27 targets the 3'UTR of the Runx1 transcript. Furthermore, introduction of pre-miR-27 alone into 32D.cl3 cells resulted in downregulation of Runx1 protein, thereby allowing the cell differentiation even in the absence of CSF3. Conversely, transduction of anti-miR-27 caused upregulation of Runx1 protein, thereby antagonizing the CSF3-mediated granulocyte differentiation. Finally, the CSF3-induced transcription factor C/EBPalpha enhanced transcription of a host gene of miR-27, C9orf3, via activation of its promoter. Thus, miR-27 enhances differentiation of myeloblasts into granulocytes via post-transcriptional downregulation of Runx1.

Runx proteins are involved in regulation of CD122, Ly49 family and IFN-gamma expression during NK cell differentiation.

Runx family proteins play indispensable roles in the development of various hematopoietic lineage cells. However, their function in NK cells is still uncertain. We found that NK cells and CD8 T cells dominantly express Runx3 protein, whereas NKT cells and CD4 T cells express Runx1. Reverse transcription-PCR analysis revealed that Runx3 expression is initiated at the NK precursor stage and is maintained along the course of NK cell differentiation. In order to examine their role in the earlier stage of NK cell development, we introduced Runx dominant-negative (Runx dn) form into Lin(-)c-kit(+)Sca-1(+) hematopoietic stem cells, which were applied to NK cell-inducing culture. Post-cultured cells showed a decreased expression of IL-2/IL-15 common receptor beta subunit (CD122), consistent with another finding that Runx binds to promoter region of CD122 gene. To examine the Runx function in the later developmental stage, we used transgenic mouse, in which Runx dn form is expressed in immature and mature NK cells. This mouse showed decreased expressions of NK maturation markers, such as Ly49 family, Mac-1 and CD43, whereas IFN-gamma production was greatly enhanced. These findings suggest that Runx proteins, especially Runx3, play multiple roles in NK cell differentiation.

Filamin A-bound PEBP2beta/CBFbeta is retained in the cytoplasm and prevented from functioning as a partner of the Runx1 transcription factor.

The heterodimeric transcription factor PEBP2/CBF is composed of a DNA-binding subunit, called Runx1, and a non-DNA-binding subunit, called PEBP2beta/CBFbeta. The Runx1 protein is detected exclusively in the nuclei of most cells and tissues, whereas PEBP2beta is located in the cytoplasm. We addressed the mechanism by which PEBP2beta localizes to the cytoplasm and found that it is associated with filamin A, an actin-binding protein. Filamin A retains PEBP2beta in the cytoplasm, thereby hindering its engagement as a Runx1 partner. The interaction with filamin A is mediated by a region within PEBP2beta that includes amino acid residues 68 to 93. The deletion of this region or the repression of filamin A enables PEBP2beta to translocate to the nucleus. Based on these observations, we propose that PEBP2beta has two distinct domains, a newly defined regulatory domain that interacts with filamin A and the previously identified Runx1-binding domain.

Comparison of 30 immunity-related genes from the common marmoset with orthologues from human and mouse.

In the evolution of primates, the common marmoset belongs to the new world monkey family and is distinct from the great ape family (which includes humans). In this study, we predicted the amino acid sequences of 30 immunity-related genes from the common marmoset and compared them with those from human and mouse. The domain composition of each orthologous protein was analyzed by the SMART tool and was found to be the same among the three species. A BLAST search revealed that the common marmoset and human proteins were 86% identical on average, whereas the conservation between the common marmoset and mouse or between the human and mouse was only 60%. This indicates that the common marmoset and human proteins are closely related and are similarly divergent from the mouse. We divided the 30 proteins into two categories based on the degree of conservation between the common marmoset and mouse amino acid sequences. One group included 19 proteins and had a relatively high level of conservation (68% identical), whereas the other 11 proteins were less conserved (45% identical). This suggests that these immunity-related genes do not evolve at a uniform rate. Interestingly, however, ligand/receptor pairs such as interleukin-6 and interleukin-6 receptor appear to have evolved simultaneously.