Distinct functions of two isoforms of a homeobox gene, BP1 and DLX7, in the regulation of the beta-globin gene

DNA methylation-mediated differential expression of DLX4 isoforms has opposing roles in leukemogenesis

Background

Previously, we reported the expression of DLX4 isoforms (BP1 and DLX7) in myeloid leukemia, but the functional role of DLX4 isoforms remains poorly understood. In the work described herein, we further determined the underlying role of DLX4 isoforms in chronic myeloid leukemia (CML) leukemogenesis.

Methods

The expression and methylation of DLX4 isoforms were detected by real-time quantitative PCR (RT-qPCR) and real-time quantitative methylation-specific PCR (RT-qMSP) in patients with CML. The functional role of DLX4 isoforms was determined in vitro and in vivo. The molecular mechanism of DLX4 isoforms in leukemogenesis was identified based on chromatin immunoprecipitation with high-throughput sequencing (ChIP-Seq)/assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-Seq) and RNA sequencing (RNA-Seq).

Results

BP1 expression was increased in patients with CML with unmethylated promoter, but DLX7 expression was decreased with hypermethylated promoter. Functionally, overexpression of BP1 increased the proliferation rate of K562 cells with S/G2 promotion, whereas DLX7 overexpression reduced the proliferation rate of K562 cells with G1 arrest. Moreover, K562 cells with BP1 overexpression increased the tumorigenicity in NCG mice, whereas K562 cells with DLX7 overexpression decreased the tumorigenicity. Mechanistically, a total of 91 genes including 79 messenger RNAs (mRNAs) and 12 long noncoding RNAs (lncRNAs) were discovered by ChIP-Seq and RNA-Seq as direct downstream targets of BP1. Among the downstream genes, knockdown of RREB1 and SGMS1-AS1 partially revived the proliferation caused by BP1 overexpression in K562 cells. Similarly, using ATAC-Seq and RNA-Seq, a total of 282 genes including 151 mRNA and 131 lncRNAs were identified as direct downstream targets of DLX7. Knockdown of downstream genes PTPRB and NEAT1 partially revived the proliferation caused by DLX7 overexpression in K562 cells. Finally, we also identified and validated a SGMS1-AS1/miR-181d-5p/SRPK2 competing endogenous RNA (ceRNA) network caused by BP1 overexpression in K562 cells.

Conclusions

The current findings reveal that DNA methylation-mediated differential expression of DLX4 isoforms BP1 and DLX7 plays opposite functions in leukemogenesis. BP1 plays an oncogenic role in leukemia development, whereas DLX7 acts as a tumor suppressor gene. These results suggest DLX4 as a therapeutic target for antileukemia therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s11658-022-00358-0.

A Potent Conformation-Constrained Synthetic Peptide Mimic of a Homeodomain Selectively Regulates Target Genes in Cells

DNA, as a target for therapeutic intervention, remains largely unexplored. DLX-4, a homeodomain containing transcription factor, and its spliced isoforms play crucial roles in many aspects of cellular biochemistry and important roles in many diseases. A smaller peptide mimicking the homeodomain of the transcription factor DLX-4 was designed and synthesized by suitable conjoining of its modified DNA-binding elements. The peptide binds to DLX-4 target sites on the regulatory region of the globin gene cluster with native-like affinity and specificity in vitro. When conjugated to cell penetrating and nuclear localization sequences, it upregulated some of the genes repressed by DLX-4 or its isoforms, such as β- and γ-globin genes in erythropoietin-induced differentiating CD34⁺ human hematopoietic stem/progenitor cells with high specificity by competing with the respective binding sites. Engineered peptides mimicking DNA-binding domains of transcription factors offer the potential for creating synthetic molecules for directly targeting DNA sites with high specificity.

Homeoprotein DLX4 expression is increased in inflammatory breast cancer cases from an urban African-American population

Protein expression of Distal-less homeobox 4 (DLX4) was analyzed in inflammatory breast cancer (IBC) cases from an African-American (AA) population to determine if a) DLX4 gene over expression exists in this cohort and b) if the overexpression is associated with breast cancer clinicopathological characteristics (ER, PR, HER2, triple-negative). Twenty-nine blocks of formalin-fixed paraffin-embedded (FFPE) tissue from well-characterized human IBC cases were used for immunohistochemical staining (IHC). IHC results were assigned an intensity and percentage score. Percentage scores were assigned as 0, 1, 2, 3, or 4 and intensity scores were assigned 0, 1+, 2+ or 3+. For the analysis of the IHC, a percentage score of 3 or 4 and an intensity score of 2+ or 3+ were categorized as high. Chi-square or Fisher's exact tests were used to compare the high and low groups. In this cohort, 89.7% (26 out of 29) of IBC cases showed high percentages of positive cells staining for the DLX4 protein, while 40.0% (12 out of 30) of normal breast tissue from reduction mammoplasty cases demonstrated DLX4 expression (p < 0.01). In IBC patients, 65.5% of cases showed a high level of staining intensity, compared to 20.0% of normal breast tissues (test, p = 0.001). Intensity to DLX4 was higher in the HER2 negative status (78.3%) than the HER2 positive status (16.7%) (test, p = 0.011). DLX4 expression is higher in the IBC cases in this study of an urban AA population than in normal breast tissue cases. HER2 negative status is positively associated with high intensity of DLX4.

BP1, a potential biomarker for breast cancer prognosis

Homeobox genes are critical in tumor development. An isoform protein of DLX4 called BP1 is expressed in 80% of invasive ductal breast carcinomas. BP1 overexpression is implicated in an aggressive phenotype and poor prognosis. BP1 upregulation is associated with estrogen receptor negativity so those tumors do not respond to antiestrogens. Breast cancer is the second leading cause of death in women. BP1 could serve as both a novel prognostic biomarker for breast cancer and a therapeutic target. In this review, we address the role of BP1 protein in tumorigenesis of breast cancer and four other malignancies. A number of functions of BP1 in cancer are also discussed.

Copy Number Analysis of the DLX4 and ERBB2 Genes in South African Breast Cancer Patients

Breast cancer is one of the main causes of cancer death among South African women. Although several risk factors can be attributed to the observed high mortality rate, the biology of the tumors is not extensively investigated. Copy number gain of the DLX4 homeobox gene has been observed in breast cancer in association with poor prognosis and specific racial groups. Therefore, we aimed to assess the copy number and prognostic role of DLX4 in breast cancer from South African patients. Due to the co-location of ERBB2 and DLX4 in the 17q21 region, its copy number was also evaluated. Our results in the analysis of 66 cases demonstrated copy number gains of DLX4 and ERBB2 in 24.1 and 29.7% of the cases, respectively. Linear regression analysis showed no dependency between the copy number alterations in these genes. Although not significant, patients with DLX4 and ERBB2 gains presented a higher frequency of advanced-grade tumors. In addition, copy number alterations of these genes were not significantly differently observed in the 3 main racial groups of the Western Cape population: Colored, White, and Black. These findings indicate that gains of DLX4 and ERBB2 occur in South African breast cancer patients irrespectively of their race and factors known to influence prognosis.

DLX4 is associated with orofacial clefting and abnormal jaw development

Cleft lip and/or palate (CL/P) are common structural birth defects in humans. We used exome sequencing to study a patient with bilateral CL/P and identified a single nucleotide deletion in the patient and her similarly affected son—c.546_546delG, predicting p.Gln183Argfs*57 in the Distal-less 4 (DLX4) gene. The sequence variant was absent from databases, predicted to be deleterious and was verified by Sanger sequencing. In mammals, there are three Dlx homeobox clusters with closely located gene pairs (Dlx1/Dlx2, Dlx3/Dlx4, Dlx5/Dlx6). In situ hybridization showed that Dlx4 was expressed in the mesenchyme of the murine palatal shelves at E12.5, prior to palate closure. Wild-type human DLX4, but not mutant DLX4_c.546delG, could activate two murine Dlx conserved regulatory elements, implying that the mutation caused haploinsufficiency. We showed that reduced DLX4 expression after short interfering RNA treatment in a human cell line resulted in significant up-regulation of DLX3, DLX5 and DLX6, with reduced expression of DLX2 and significant up-regulation of BMP4, although the increased BMP4 expression was demonstrated only in HeLa cells. We used antisense morpholino oligonucleotides to target the orthologous Danio rerio gene, dlx4b, and found reduced cranial size and abnormal cartilaginous elements. We sequenced DLX4 in 155 patients with non-syndromic CL/P and CP, but observed no sequence variants. From the published literature, Dlx1/Dlx2 double homozygous null mice and Dlx5 homozygous null mice both have clefts of the secondary palate. This first finding of a DLX4 mutation in a family with CL/P establishes DLX4 as a potential cause of human clefts.

Regulation of the oncogenic function of distal-less 4 by microRNA-122 in hepatocellular carcinoma

Distal-less 4 (DLX4) is a member of the DLX family of homeobox genes. Recent reports have suggested that abnormal expression of DLX4 is present in several types of human tumors, including breast cancer, leukemia and colon cancer. However, the function and the mechanistic regulation of DLX4 in hepatocellular carcinoma (HCC) are elusive. In the present study, a proportion of hepatocellular carcinomas were identified to exhibit upregulated DLX4 expression. This study proposed that the overexpression of DLX4 is associated with the downregulation of miR-122, an underexpressed miRNA in human HCC. Functional studies have demonstrated that the downregulation of DLX4 in hepatocellular carcinoma cell lines is regulated by miR-122 through binding to its 3'UTR. Furthermore, a DLX4 overexpression vector lacking the 3'UTR was shown to abolish miR-122-induced inhibition of proliferation in the HCC cell line Hep3B. These results gave new insight into the mechanism of the miR-122/DLX4 axis in HCC.

Increased copy number of the DLX4 homeobox gene in breast axillary lymph node metastasis

DLX4 is a homeobox gene strongly implicated in breast tumor progression and invasion. Our main objective was to determine the DLX4 copy number status in sentinel lymph node (SLN) metastasis to assess its involvement in the initial stages of the axillary metastatic process. A total of 37 paired samples of SLN metastasis and primary breast tumors (PBT) were evaluated by fluorescence in situ hybridization, quantitative polymerase chain reaction and array comparative genomic hybridization assays. DLX4 increased copy number was observed in 21.6% of the PBT and 24.3% of the SLN metastasis; regression analysis demonstrated that the DLX4 alterations observed in the SLN metastasis were dependent on the ones in the PBT, indicating that they occur in the primary tumor cell populations and are maintained in the early axillary metastatic site. In addition, regression analysis demonstrated that DLX4 alterations (and other DLX and HOXB family members) occurred independently of the ones in the HER2/NEU gene, the main amplification driver on the 17q region. Additional studies evaluating DLX4 copy number in non-SLN axillary lymph nodes and/or distant breast cancer metastasis are necessary to determine if these alterations are carried on and maintained during more advanced stages of tumor progression and if could be used as a predictive marker for axillary involvement.

BP1, an isoform of DLX4 homeoprotein, negatively regulates BRCA1 in sporadic breast cancer

Introduction: Several lines of evidence point to an important role for BP1, an isoform of DLX4 homeobox gene, in breast carcinogenesis and progression. BRCA1 is a well-known player in the etiology of breast cancer. While familial breast cancer is often marked by BRCA1 mutation and subsequent loss of heterozygosity, sporadic breast cancers exhibit reduced expression of wild type BRCA1, and loss of BRCA1 expression may result in tumor development and progression.

Methods: The Cister algorithm and Genomatix program were used to identify potential BP1 binding sites in BRCA1 gene. Real-time PCR, Western blot and immunohistochemistry analysis were performed to verify the expression of BRCA1 and BP1 in cell lines and breast cancer tissues. Double-stranded siRNA transfection was carried out for silencing BP1 expression. ChIP and EMSA were used to confirm that BP1 specifically binds to BRCA1.

Results: A putative BP1 binding site was identified in the first intron of BRCA1, which was confirmed by chromatin immunoprecipiation and electrophoresis mobility shift assay. BP1 and BRCA1 expression were inversely correlated in breast cancer cell lines and tissues, suggesting that BP1 may suppress BRCA1 transcription through consensus sequence binding.

Conclusions: BP1 homeoprotein represses BRCA1 expression through direct binding to its first intron, which is consistent with a previous study which identified a novel transcriptional repressor element located more than 500 base pairs into the first intron of BRCA1, suggesting that the first intron plays an important role in the negative regulation of BRCA1. Although further functional studies are necessary to confirm its repressor activity towards BRCA1, the elucidation of the role of BP1 in breast tumorigenesis holds great promise in establishing BP1 as a novel target for drug therapy.

BP1 Homeoprotein Enhances Metastatic Potential in ER-negative Breast Cancer

Tumor invasion and metastasis remain a major cause of mortality in breast cancer patients. It was reported that BP1, a homeobox isoform of DLX4, is overexpressed in 80% of breast cancer patients and in 100% of estrogen receptor negative (ER-) tumors. The prevalence of BP1 positive cells and the intensity of BP1 immunoreactivity increased with the extent of ductal proliferation and tumorigenesis. These findings imply that BP1 may play an important role in ER- breast cancer. We sought to determine the effects and mechanisms of BP1 on cell proliferation and metastasis using ER- Hs578T cells as a model. Cells were transfected with either pcDNA3.2 plasmid containing BP1 gene, or pcDNA3.2 vector, then selected and cloned. Overexpression of BP1 increased cell proliferation rate by 2-5 fold (p<0.005), and enhanced the in vitro invasive activity by 25-65 fold (p<0.001). Microarray experiments were performed to identify differentially expressed genes when BP1 is overexpressed. The gene expression profile of the transfected cell lines were compared, resulting in 71 differentially expressed genes with a fold-change of >=2.0. Of those genes, 49 were up-regulated and 22 were down-regulated. Significant pathways were identified involving cell proliferation and metastasis. These data demonstrated that overexpression of BP1 significantly enhanced cell proliferation and metastatic potential in ER- Hs578T cells. Further analysis with more ER- cell lines and patient samples is warranted to establish BP1 as a therapeutic target for ER- breast cancer.

Characteristics and treatment modalities for African American women diagnosed with stage III breast cancer

BACKGROUND

Stage III breast cancers account for about 6% to 7% of all invasive breast cancers diagnosed annually in the United States. In African American (AA) women, the incidence of stage III breast cancers is almost double that in Caucasian women. The aim of this study was to correlate age, receptor status, nuclear grade, and differences in treatment modalities for stage III breast cancer in an inner-city hospital serving a large AA population.

METHODS

A retrospective review was performed for all stage III primary breast cancers diagnosed and or treated from 2000 to 2006.

RESULTS

: Of 840 primary invasive breast cancers, the authors identified 107 as stage III, 40.2% IIIA, 32.7% IIIB, 16.8% T4D, and 10.3% IIIC. The majority of the patients were AA (n = 93, 86.9%). Stage IIIC patients were younger (P < .05). Triple negative tumors (TNT) accounted for 29.0%. TNT were more likely among the inflammatory breast cancers (50.0%) compared with the other 3 groups (P < .05). Twenty-two patients (20.5%) refused chemotherapy, and 24 of the 91 patients (26.3%) who should have received chest wall radiation refused. There was no difference in race, marital status, religion, or age in the patients that refused chemotherapy or radiation therapy versus the majority of patients in this series who received standard care.

CONCLUSIONS

Stage III breast cancers in AA women have distinct clinical characteristics. A high number of these patients refused chemotherapy and radiation therapy. Reasons for refusal need to be better defined so strategies can be implemented to improve compliance for these advanced stage patients.

Amplification of the BP1 homeobox gene in breast cancer

The homeobox gene BP1 is expressed in over 80% of breast cancers and is associated with tumor progression and invasion. However, the mechanism of BP1 activation in these tumors remains unknown. Therefore our aim in this study is to assess the amplification status of the BP1 gene in breast cancer and to determine whether BP1 protein expression is caused by gene amplification in these tumors. BP1 amplification and expression were assessed in 36 samples. Twenty primary breast tumors (PBT) and 14 sentinel lymph node (SLN) metastases were analyzed using fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC), respectively. Because of the close proximity of BP1 and HER2/NEU genes on 17q, correlation between their amplification/expression was also investigated. Increased BP1 copy number was observed in 33% of the cases, with a frequency of 36% and 29% in the PBT and SLN metastasis, respectively. BP1 protein was expressed in 91% of the samples: in all of the PBT with increased BP1 copy number and 65% of PBT with normal copy number. HER2/NEU amplification was detected in 22% of the cases. Concordance between BP1 and HER2/NEU copy numbers was found in 68% of the PBT and 90% of the SLN metastasis. In conclusion, we demonstrated that the BP1 homeobox gene is amplified in breast cancer, both in PBT and SLN metastasis, with a significant correlation with HER2/NEU amplification. Considering that BP1 expression was observed in cases with both increased and normal BP1 copy number, we conclude that other mechanisms in addition to gene amplification play a role in BP1 protein expression.

Genome-wide analysis of BP1 transcriptional targets in breast cancer cell line Hs578T

Homeobox genes are known to be critically important in tumor development and progression. The BP1 (Beta Protein 1) gene, an isoform of DLX4, belongs to the Distal-less (DLX) subfamily of homeobox genes and encodes a homeodomain-containing transcription factor. Our studies have shown that the BP1 gene was overexpressed in 81% of primary breast cancer and its expression was closely correlated with the progression of breast cancer. However, the exact role of BP1 in breast has yet to be elucidated. Therefore, it is important to explore the potential transcriptional targets of BP1 via whole genome-scale screening. In this study, we used the chromatin immunoprecipitation on chip (ChIP-on-chip) and gene expression microarray assays to identify candidate target genes and gene networks, which are directly regulated by BP1 in ER negative (ER-) breast cancer cells. After rigorous bioinformatic and statistical analysis for both ChIP-on-chip and expression microarray gene lists, 18 overlapping genes were noted and verified. Those potential target genes are involved in a variety of tumorigenic pathways, which sheds light on the functional mechanisms of BP1 in breast cancer development and progression.

Distal-less homeobox transcription factors regulate development and maturation of natural killer cells

Natural killer (NK) cells constitute a subpopulation of lymphocytes that develop from precursors in the bone marrow (BM), but the transcriptional regulation of their development and maturation is only beginning to be understood, in part due to their relatively rare abundance, especially of developmental subsets. Using a mouse model in which NK cells are arrested at an immature stage of development, and a gene expression profiling approach, we uncovered transient normal NK cell expression of a homeobox transcription factor (TF) family, called Distal-less (Dlx), which had been primarily implicated in murine CNS, craniofacial, limb, and skin development. Our studies demonstrate that Dlx1, Dlx2, and Dlx3 are transiently expressed in immature Mac-1(lo) NK cells within the BM, with Dlx3 being the predominantly expressed member. These genes are expressed in a temporally regulated pattern with overlapping waves of expression, and they display functional redundancy. Expression is extinguished in fully mature splenic NK cells, and persistent expression of Dlx genes leads to functionally immature NK cells arrested at the Mac-1(lo) stage. Whereas conventional splenic NK cells develop but are arrested at an immature stage, there appears to be a complete failure to develop CD127(+) thymic NK cells when Dlx genes are persistently expressed. We also observed that T and B cells fail to develop in the context of persistent Dlx1 expression. Thus, these studies indicate that Dlx TFs play a functional role in lymphocyte development.

Prognostic significance of BP1 mRNA expression level in patients with non-small cell lung cancer

OBJECTIVES

To examine the association of BP1 mRNA level with tumor characteristics and clinical prognosis in non-small cell lung cancer (NSCLC) patients.

DESIGN AND METHODS

Tumor specimens from 98 NSCLC patients who underwent surgical resection were quantitatively determined for BP1 mRNA expression by real-time RT-PCR.

RESULTS

BP1 mRNA was expressed at significantly higher levels in tumors than in adjacent nontumorous tissues and normal lung samples. The level of BP1 transcript was significantly associated with tumor histological type and cell differentiation grade, but not related with other clinicopathological factors and p53 mutations. Patients with high BP1 mRNA expression had a poorer prognosis in terms of both disease-free survival (DFS) and overall survival (OS) rates. Additionally, BP1 mRNA expression level was an independent prognostic factor for DFS.

CONCLUSIONS

BP1 may be part of a pathway contributing to NSCLC development and/or progression. BP1 mRNA level could be a novel prognostic marker for NSCLC.

BP1 transcriptionally activates bcl-2 and inhibits TNFalpha-induced cell death in MCF7 breast cancer cells

INTRODUCTION

We have previously shown that the Beta Protein 1 (BP1) homeodomain protein is expressed in 81% of invasive ductal breast carcinomas, and that increased BP1 expression correlates with tumor progression. The purpose of our current investigation was to determine whether elevated levels of BP1 in breast cancer cells are associated with increased cell survival.

METHODS

Effects on cell viability and apoptosis of MCF7 cells stably overexpressing BP1 were determined using MTT and Annexin V assays, and through examination of caspase activation. TNFalpha was used to induce apoptosis. The potential regulation of apoptosis-associated genes by BP1 was studied using real-time PCR and western blot analyses. Electrophoretic mobility shift assays, site-directed mutagenesis, and transient assays were performed to specifically characterize the interaction of BP1 with the promoter of the bcl-2 gene.

RESULTS

Stable overexpression of BP1 led to inhibition of apoptosis in MCF7 breast cancer cells challenged with TNFalpha. Increased BP1 resulted in reduced processing and activation of caspase-7, caspase-8, and caspase-9, and inactivation of the caspase substrate Poly(ADP-Ribose) Polymerase (PARP). Increased levels of full-length PARP and a decrease in procaspase-8 were also associated with BP1 overexpression. The bcl-2 gene is a direct target of BP1 since: (i) BP1 protein bound to a consensus binding sequence upstream of the bcl-2 P1 promoter in vitro. (ii) MCF7 cells overexpressing BP1 showed increased levels of bcl-2 mRNA and protein. (iii) Transient assays indicated that increased bcl-2 promoter activity is due to direct binding and modulation by BP1 protein. BP1 expression also prevented TNFalpha-mediated downregulation of bcl-2 mRNA and protein.

CONCLUSION

These findings suggest mechanisms by which increased BP1 may impart a survival advantage to breast cancer cells, which could lead to increased resistance to therapeutic agents in patients.

Expression level of beta protein 1 mRNA in Chinese breast cancer patients: a potential molecular marker for poor prognosis

Recent studies revealed high ectopic beta protein 1 (BP1) expression in breast cancer. Remarkably, up to 100% (18/18) of estrogen receptor (ER)-negative tumors and 89% (25/28) of tumors from African American women were BP1-positive. However, the role of BP1 in breast cancer development and its clinical significance still has not been well defined. In the present study, we analyzed the quantitative level of BP1 mRNA in breast carcinomas using real-time polymerase chain reaction and aimed to elucidate its association with tumor characteristics and patient prognosis. Our data showed that BP1 mRNA was expressed at significantly higher levels in tumors with lymph node metastasis, with a high histological grade, and in those that were of ER-negative status. Furthermore, overexpression of BP1 was significantly associated with poor outcome of patients harboring tumors with a high histological grade and negative ER. Using both in vitro and in vivo systems, we also showed that the transcript level of BP1 was positively correlated to the growth rate of breast tumor cells. Taken together, our results support the notion that BP1 might contribute to breast neoplastic transformation or tumor progression and suggest for the first time that BP1 mRNA level has potential as a prognostic predictor for breast cancer.

Overexpression of BP1, a homeobox gene, is associated with resistance to all-trans retinoic acid in acute promyelocytic leukemia cells

BP1, a homeobox gene, is overexpressed in the bone marrow of 63% of acute myeloid leukemia patients. In this study, we compared the growth-inhibitory and cyto-differentiating activities of all-trans retinoic acid (ATRA) in NB4 (ATRA-responsive) and R4 (ATRA-resistant) acute promyelocytic leukemia (APL) cells relative to BP1 levels. Expression of two oncogenes, bcl-2 and c-myc, was also assessed. NB4 and R4 cells express BP1, bcl-2, and c-myc; the expression of all three genes was repressed after ATRA treatment of NB4 cells but not R4 cells. To determine whether BP1 overexpression affects sensitivity to ATRA, NB4 cells were transfected with a BP1-expressing plasmid and treated with ATRA. In cells overexpressing BP1: (1) proliferation was no longer inhibited; (2) differentiation was reduced two- to threefold; (3) c-myc was no longer repressed. These and other data suggest that BP1 may regulate bcl-2 and c-myc expression. Clinically, BP1 levels were elevated in all pretreatment APL patients tested, while BP1 expression was decreased in 91% of patients after combined ATRA and chemotherapy treatment. Two patients underwent disease relapse during follow-up; one patient exhibited a 42-fold increase in BP1 expression, while the other showed no change. This suggests that BP1 may be part of a pathway involved in resistance to therapy. Taken together, our data suggest that BP1 is a potential therapeutic target in APL.

The study of sequence configuration and functional impact of the (AC)n(AT)xTy motif in human beta-globin gene promoter

In this report we examine the (AC)n(AT)xTy motif residing -530 bp 5' upstream of the beta-globin gene in Chinese thalassaemic patients. This motif is a putative binding site for a repressor protein, termed beta protein 1 (BP1) (Berg et al., Nucleic Acids Res 1989;17:8833-8852). Variations in the (AC)n(AT)xTy repeats affect the binding affinity of BP1, thereby altering the expression of the beta-globin gene. Eight different configurations of this repeat motif are identified in our population of Chinese beta-thalassaemia patients. A (AC)3(AT)7T5 motif was identified among these thalassaemia patients and its influence in beta-globin gene expression was studied using stable transfection assay in murine erythroleukemia (MEL) cells. Our data demonstrated that the (AC)3(AT)7T5 motif has a moderately strong repressor effect on the expression of the cis-linked beta-globin gene. The high affinity of BP1 for this motif may result in the suppression of the transcription of the beta-globin gene (Berg et al., Am J Hematol 1991;36:42-47). We postulate that silencer elements in the beta-globin promoter play an important role in modifying the clinical presentation of the disease.

BP1 is a negative modulator of definitive erythropoiesis

Beta protein 1 (BP1), a human homeotic transcription factor, is expressed during hematopoeisis in the erythroid lineage. To determine the in vivo role of BP1 in erythropoiesis, we have undertaken two complementary approaches using enforced BP1 expression in both transgenic mice and embryonic stem (ES) cells. Despite repeated attempts, only one adult transgenic BP1 founder mouse among 121 mice was obtained. This mouse presumably survived due to transgene mosaicism because the transgene could not be transmitted. This mouse expressed BP1 and displayed splenomegaly, extramedullary erythropoiesis and severe amyloidosis A in the kidney, a phenotype compatible with thalassemia. Consistently, the presence of BP1 transgene in fetuses was associated with paleness and lethality. In ES cells, BP1 expression in primary differentiation appeared to antagonize adult β-globin expression. In secondary differentiation, BP1 expression reduced significantly β-globin gene expression in both primitive and definitive erythroid cells, whereas it impaired only the definitive erythroid cell differentiation. These studies showed that BP1 can negatively modulate adult β-globin gene expression and definitive erythroid cell differentiation, and suggest that BP1 could play a role in thalassemia.

Expression of BP1, a novel homeobox gene, correlates with breast cancer progression and invasion

BACKGROUND

Our previous studies revealed that the mRNA encoded by BP1, a member of the homeobox gene superfamily of transcription factors, was expressed in leukemia and infiltrating breast ductal carcinoma (IDC). This study investigated the immunohistochemical profile of BP1, to determine whether the expression of BP1 protein correlated with breast tumor progression and invasion and whether BP1 was co-localized with erbB2.

DESIGN

Paraffin sections from normal reduction mammoplasties (n = 34) and a variety of in situ and invasive breast cancers (n = 270) were either singly immunostained for BP1, or doubly immunostained for BP1 plus either erbB2 or Ki-67.

RESULTS

The prevalence of BP1 positive cells and the intensity of BP1 immunoreactivity increased with the extent of ductal proliferation and carcinogenesis. BP1 expression was barely detectable in normal reduction mammoplasties compared to distinct staining in 21, 46, and 81% of hyperplastic, in situ, and infiltrating lesions, respectively. In cases with co-existing normal, hyperplastic, in situ, and invasive lesions, the tumor cells of the invasive lesions consistently showed the highest frequency and the highest intensity of BP1 immunostaining, followed by in situ tumor cells. Double immunostaining revealed that BP1 co-localized with a subset of erbB2 positive cells in all 15 in situ and IDC tumors examined, and that BP1 positive cells had a substantially higher proliferation rate than morphologically similar cells without BP1 expression.

CONCLUSION

These findings suggest that BP1 is an important upstream factor in an oncogenic pathway, and that expression of BP1 may reliably reflect or directly contribute to tumor progression and/or invasion.

Inhibition of β protein 1 expression enhances β-globin promoter activity and β-globin mRNA levels in the human erythroleukemia (K562) cell line

OBJECTIVE

In this paper, we report new observations related to the mechanism of the negative regulation of the important adult beta-globin gene in the erythroid cells at the embryonic-fetal stage of their development. We focused on the role of the silencer II region located upstream of the beta-globin gene, which along with its cognate binding protein BP1, negatively regulates beta-globin transcription.

MATERIALS AND METHODS

We prepared plasmid constructs containing the wild-type silencer II sequence, a mutated silencer II sequence, or a mutated control sequence in the beta-globin promoter 690-bp insert, which in turn was linked to an enhanced green fluorescent protein (EGFP) reporter gene. A human erythroleukemia cell line (K562) with embryonic-fetal phenotype was transfected with these EGFP constructs.

RESULTS

Flow cytometry and fluorescence digital imaging showed about threefold increase in the beta-globin promoter activity of the mutated silencer II construct. Introduction of a small interfering RNA (siRNA) complementary to BP1 into the cells caused a 75% decrease in BP1 expression and a simultaneous approximately 40% elevation of beta-globin promoter activity as well as an increase in beta-globin mRNA levels, as compared with controls. We detected no changes in the mRNA levels of positive regulators of hemoglobin transcription such as EKLF and GATA-1.

CONCLUSION

Our results support the involvement of BP1 in the mechanism of the negative regulation of beta-globin transcription. A better understanding of this mechanism may lay the groundwork for novel gene therapy approaches to inhibit the expression of abnormal structural variants of adult beta globin, such as sickle hemoglobin.

DLX genes as targets of ALL-1: DLX 2,3,4 down-regulation in t(4;11) acute lymphoblastic leukemias

Dlx genes constitute a gene family thought to be essential in morphogenesis and development. We show here that in vertebrate cells, Dlx genes appear to be part of a regulatory cascade initiated by acute lymphoblastic leukemia (ALL)-1, a master regulator gene whose disruption is implicated in several human acute leukemias. The expression of Dlx2, Dlx3, Dlx5, Dlx6, and Dlx7 was absent in All-1 -/- mouse embryonic stem cells and reduced in All-1 +/- cells. In leukemic patients affected by the t(4;11)(q21;q23) chromosomal abnormality, the expression of DLX2, DLX3, and DLX4 was virtually abrogated. Our data indicate that Dlx genes are downstream targets of ALL-1 and could be considered as important tools for the study of the early leukemic cell phenotype.

HOX and non-HOX homeobox genes in leukemic hematopoiesis

Dysregulation of homeobox (HB)-containing genes is becoming increasingly recognized as the underlying basis of many hematologic malignancies. Expression of clustered HB (HOX) genes within the hematopoietic system, and enforced overexpression and knockout studies have provided support for the concept that these homeodomain-containing transcription factors play a significant role in the developmental biology of hematopoietic cells. Diverged HB (non-HOX) genes have recently been identified as either cofactors and/or accelerators of leukemic disease mediated by HOX genes or as bona fide oncogenes. In this review, we examine the evidence that supports a central role for HB genes in normal and malignant hematopoiesis, paying particular attention to the non-HOX class and the possible mechanisms through which they contribute to leukemic transformation.

Correlation of expression of BP1, a homeobox gene, with estrogen receptor status in breast cancer

BACKGROUND

BP1 is a novel homeobox gene cloned in our laboratory. Our previous studies in leukemia demonstrated that BP1 has oncogenic properties, including as a modulator of cell survival. Here BP1 expression was examined in breast cancer, and the relationship between BP1 expression and clinicopathological data was determined.

METHODS

Total RNA was isolated from cell lines, tumors, and matched normal adjacent tissue or tissue from autopsy. Reverse transcription polymerase chain reaction was performed to evaluate BP1 expression. Statistical analysis was accomplished with SAS.

RESULTS

Analysis of 46 invasive ductal breast tumors demonstrated BP1 expression in 80% of them, compared with a lack of expression in six normal breast tissues and low-level expression in one normal breast tissue. Remarkably, 100% of tumors that were negative for the estrogen receptor (ER) were BP1-positive, whereas 73% of ER-positive tumors expressed BP1 (P = 0.03). BP1 expression was also associated with race: 89% of the tumors of African American women were BP1-positive, whereas 57% of those from Caucasian women expressed BP1 (P = 0.04). However, there was no significant difference in BP1 expression between grades I, II, and III tumors. Interestingly, BP1 mRNA expression was correlated with the ability of malignant cell lines to cause breast cancer in mice.

CONCLUSION

Because BP1 is expressed abnormally in breast tumors, it could provide a useful target for therapy, particularly in patients with ER-negative tumors. The frequent expression of BP1 in all tumor grades suggests that activation of BP1 is an early event.

BP1, a homeodomain-containing isoform of DLX4, represses the beta-globin gene

In earlier studies we identified a putative repressor of the human beta-globin gene, termed beta protein 1 (BP1), which binds to two silencer DNA sequences upstream of the adult human beta-globin gene and to a negative control region upstream of the adult delta-globin gene. Further studies demonstrated an inverse correlation between the binding affinity of the BP1 protein for the distal beta-globin silencer sequence and the severity of sickle cell anemia, suggesting a possible role for BP1 in determining the production of hemoglobin S. We have now cloned a cDNA expressing the BP1 protein. Sequencing revealed that BP1 is a member of the homeobox gene family and belongs to the subfamily called Distal-less (DLX), genes important in early development. Further analysis showed that BP1 is an isoform of DLX4. BP1 protein has repressor function towards the beta-globin promoter, acting through the two beta-globin DNA silencers, demonstrated in transient transfection assays. Strong BP1 expression is restricted to placenta and kidney tissue, with no expression in 48 other human tissues. BP1 exhibits regulated expression in the human erythroid cell line MB-02, where its expression decreases upon induction of the beta-globin gene. BP1 is thus the first member of the DLX family with known DNA binding sites and a function in globin gene regulation.