Identification of B-cell translocation gene 1 as a biomarker for monitoring the remission of acute myeloid leukemia

Advances in Microflow Cytometry-Based Molecular Detection Methods for Improved Future MDS Cancer Diagnosis

Myelodysplastic syndromes (MDS) are a rare form of early-stage blood cancer that typically leads to leukemia and other deadly complications. The typical diagnosis for MDS involves a mixture of blood tests, a bone marrow biopsy, and genetic analysis. Flow cytometry has commonly been used to analyze these types of samples, yet there still seems to be room for advancement in several areas, such as the limit of detection, turnaround time, and cost. This paper explores recent advancements in microflow cytometry technology and how it may be used to supplement conventional methods of diagnosing blood cancers, such as MDS and leukemia, through flow cytometry. Microflow cytometry, a more recent adaptation of the well-researched and conventional flow cytometry techniques, integrated with microfluidics, demonstrates significant potential in addressing many of the shortcomings flow cytometry faces when diagnosing a blood-related disease such as MDS. The benefits that this platform brings, such as portability, processing speed, and operating cost, exemplify the importance of exploring microflow cytometry as a point-of-care (POC) diagnostic device for MDS and other forms of blood cancer.

Application of omics in the diagnosis, prognosis, and treatment of acute myeloid leukemia

Acute myeloid leukemia (AML) is the most frequent leukemia in adults with a high mortality rate. Current diagnostic criteria and selections of therapeutic strategies are generally based on gene mutations and cytogenetic abnormalities. Chemotherapy, targeted therapies, and hematopoietic stem cell transplantation (HSCT) are the major therapeutic strategies for AML. Two dilemmas in the clinical management of AML are related to its poor prognosis. One is the inaccurate risk stratification at diagnosis, leading to incorrect treatment selections. The other is the frequent resistance to chemotherapy and/or targeted therapies. Genomic features have been the focus of AML studies. However, the DNA-level aberrations do not always predict the expression levels of genes and proteins and the latter is more closely linked to disease phenotypes. With the development of high-throughput sequencing and mass spectrometry technologies, studying downstream effectors including RNA, proteins, and metabolites becomes possible. Transcriptomics can reveal gene expression and regulatory networks, proteomics can discover protein expression and signaling pathways intimately associated with the disease, and metabolomics can reflect precise changes in metabolites during disease progression. Moreover, omics profiling at the single-cell level enables studying cellular components and hierarchies of the AML microenvironment. The abundance of data from different omics layers enables the better risk stratification of AML by identifying prognosis-related biomarkers, and has the prospective application in identifying drug targets, therefore potentially discovering solutions to the two dilemmas. In this review, we summarize the existing AML studies using omics methods, both separately and combined, covering research fields of disease diagnosis, risk stratification, prognosis prediction, chemotherapy, as well as targeted therapy. Finally, we discuss the directions and challenges in the application of multi-omics in precision medicine of AML. Our review may inspire both omics researchers and clinical physicians to study AML from a different angle.

The predictive value of BTG1 for the response of newly diagnosed acute myeloid leukemia to decitabine

BACKGROUND

Decitabine has been widely used to treat acute myeloid leukemia (AML); however as AML is a heterogeneous disease, not all patients benefit from decitabine. This study aimed to identify markers for predicting the response to decitabine.

METHODS

An intersection of in vitro experiments and bioinformatics was performed using a combination of epigenetic and transcriptomic analysis. A tumor-suppressor gene associated with methylation and the response to decitabine was screened. Then the sensitivity and specificity of this marker in predicting the response to decitabine was confirmed in 54 samples from newly diagnosed AML patients treated with decitabine plus IA regimen in a clinical trial (ChiCTR2000037928).

RESULTS

In vitro experiments showed that decitabine caused hypomethylation and upregulation of BTG1, while downregulation of BTG1 attenuated the inhibitory effect of decitabine. In newly diagnosed AML patients who received decitabine plus IA regimen, the predictive value of BTG1 to predict complete remission (CR) was assigned with a sensitivity of 86.7% and a specificity of 100.0% when BTG1 expression was < 0.292 (determined using real-time quantitative PCR), with area under the curve (AUC) = 0.933, P = 0.021. The predictive value of BTG1 to predict measurable residual disease (MRD) negativity was assigned with a sensitivity of 100.0% and a specificity of 80.0% when BTG1 expression was < 0.292 (AUC = 0.892, P = 0.012). Patients were divided into low and high BTG1 expression groups according to a cutoff of 0.292, and the CR rate of the low-expression group was significantly higher than that of the high-expression group (97.5% vs. 50%, P < 0.001).

CONCLUSIONS

Low expression of BTG1 was associated with CR and MRD negativity in newly diagnosed AML patients treated with a decitabine-containing regimen, suggesting that BTG1 is a potential marker for predicting the response to decitabine in newly diagnosed AML.

CLINICAL TRIAL REGISTRATION

ChiCTR2000037928.

miR-15a-5p and miR-21-5p contribute to chemoresistance in cytogenetically normal acute myeloid leukaemia by targeting PDCD4, ARL2 and BTG2

Cytarabine and daunorubicin are old drugs commonly used in the treatment of acute myeloid leukaemia (AML). Refractory or relapsed disease because of chemotherapy resistance is a major issue. microRNAs (miRNAs) were incriminated in resistance. This study aimed to identify miRNAs involved in chemoresistance in AML patients and to define their target genes. We focused on cytogenetically normal AML patients with wild‐type NPM1 without FLT3‐ITD as the treatment of this subset of patients with intermediate‐risk cytogenetics is not well established. We analysed baseline AML samples by small RNA sequencing and compared the profile of chemoresistant to chemosensitive AML patients. Among the miRNAs significantly overexpressed in chemoresistant patients, we revealed miR‐15a‐5p and miR‐21‐5p as miRNAs with a major role in chemoresistance in AML. We showed that miR‐15a‐5p and miR‐21‐5p overexpression decreased apoptosis induced by cytarabine and/or daunorubicin. PDCD4, ARL2 and BTG2 genes were found to be targeted by miR‐15a‐5p, as well as PDCD4 and BTG2 by miR‐21‐5p. Inhibition experiments of the three target genes reproduced the functional effect of both miRNAs on chemosensitivity. Our study demonstrates that miR‐15a‐5p and miR‐21‐5p are overexpressed in a subgroup of chemoresistant AML patients. Both miRNAs induce chemoresistance by targeting three pro‐apoptotic genes PDCD4, ARL2 and BTG2.

Identification of BTG1 Status in Solid Cancer for Future Researches Using a System Review and Meta-analysis

Abundant studies have been conducted to identify how B-cell translocation gene 1 protein (BTG1) gene affects the differentiation, proliferation, metastasis of cancer cells, and how it further regulates the generation or development of diseases to influence the prognosis of patients. However, the data from single research were not powerful enough. The correlations between BTG1 expression and mechanisms of tumorigenesis or prognosis of patients are still in controversial. Our system review and meta-analysis provided a complete explanation about the association between BTG1 expression and clinicopathological features or prognosis of patients, which further laid a foundation for future research on BTG1. Fifteen eligible studies consisting of 1992 participants were included. We uncovered that BTG1 expression in solid tumors was associated with lymph node status (RR=0.66, 95% CI: 0.58-0.75, P=0.142), TMN stage status (RR=2.13, 95% CI: 1.71-2.65, P=0.001), T category (RR=1.90, 95% CI: 1.20-3.00, P=0.000), histological differentiation (RR=1.91, 95% CI: 1.55-2.37, P=0.012), vascular invasion (RR=0.90, 95% CI: 0.57-1.41, P=0.001). BTG1 low expression was significantly associated with overall survival (OS) (HR=0.47, 95% CI: 0.38-0.67, P=0.000). It concluded that BTG1 possessed the potential value for future research and could be recommended as a significant biomarker in solid tumor.

Tumor suppressors BTG1 and BTG2: Beyond growth control

Since the identification of B‐cell translocation gene 1 (BTG1) and BTG2 as antiproliferation genes more than two decades ago, their protein products have been implicated in a variety of cellular processes including cell division, DNA repair, transcriptional regulation and messenger RNA stability. In addition to affecting differentiation during development and in the adult, BTG proteins play an important role in maintaining homeostasis under conditions of cellular stress. Genomic profiling of B‐cell leukemia and lymphoma has put BTG1 and BTG2 in the spotlight, since both genes are frequently deleted or mutated in these malignancies, pointing towards a role as tumor suppressors. Moreover, in solid tumors, reduced expression of BTG1 or BTG2 is often correlated with malignant cell behavior and poor treatment outcome. Recent studies have uncovered novel roles for BTG1 and BTG2 in genotoxic and integrated stress responses, as well as during hematopoiesis. This review summarizes what is currently known about the roles of BTG1 and BTG2 in these and other cellular processes. In addition, we will highlight the molecular mechanisms and biological consequences of BTG1 and BTG2 deregulation during cancer progression and elaborate on the potential clinical implications of these findings.

Cisplatin suppresses proliferation, migration and invasion of nasopharyngeal carcinoma cells in vitro by repressing the Wnt/β-catenin/Endothelin-1 axis via activating B cell translocation gene 1

PURPOSE

Nasopharyngeal carcinoma (NPC) is one of the most commonly diagnosed cancers worldwide with significantly high prevalence in Southern China. Chemoprevention of cancer with alkylating agent compounds could potentially reverse, suppress, or prevent cancer progression. Cisplatin (CIS) is an antineoplastic or cytotoxic platinum-based drug used for chemotherapy of different types of human cancers such as NPC. Nevertheless, the effects of CIS on the migration and invasion of human NPC cells and the underlying molecular mechanisms have not yet been fully scrutinized.

METHODS

In this work, we tested the effect of CIS on the proliferation, migration and invasion of NPC cells. The results exhibited that this drug exerts remarkable inhibitory effects on the proliferation, migration and invasion of NPC cells in a dose-dependent manner. Western blotting and real time RT-PCR were used for expression analyses.

RESULTS

We found that CIS treatment led to a dose-dependent inhibition of Endothelin-1 (ET1) expression, at protein as well as mRNA levels in NPC cells. CIS was also found to activate the expression of BTG1 in NPC cells. Moreover, mechanistic analyses revealed that CIS increased the expression of B cell translocation gene 1 (BTG1) to suppress the expression of ET1. Furthermore, we show that ET1 could not be induced in CIS-resistant cells with suppressed BTG1 expression, and subsequently demote the proliferation, migration and invasion of NPC cells.

CONCLUSIONS

These findings provided compelling evidence of the role of CIS in suppressing NPC metastasis and its underlying molecular mechanisms.

BTG1 might be employed as a biomarker for carcinogenesis and a target for gene therapy in colorectal cancers

Here, BTG1 overexpression inhibited proliferation, induced differentiation, autophagy, and apoptosis in colorectal cancer cells (p₂ arrest might be related to Cyclin B1 and Cdc25B hypoexpression in HCT-15 transfectants, while G₁ arrest in HCT-116 transfectants overexpressing p21 and p27. BTG1 overexpression decreased the expression of Bcl-2, Bcl-xL, XIAP, Akt1 or survivin and increased the expression of Bax or p53 in colorectal cancer cells. BTG1-induced autophagy was dependent on Beclin-1 expression. BTG1 overexpression might weaken β-catenin pathway in colorectal cancer cells. The chemosensitivity of BTG1 transfectants to paclitaxel, cisplatin, MG132 or SAHA was positively correlated with its apoptotic induction. There was a lower expression level of BTG1 in cancer than matched non-neoplastic mucosa by RT-PCR (p

miR-511 promotes the proliferation of human hepatoma cells by targeting the 3'UTR of B cell translocation gene 1 (BTG1) mRNA

Aberrant expression of miR-511 is involved in the development of cancer, but the role of miR-511 in hepatocellular carcinoma (HCC) is not well documented. In this study, we explored the molecular mechanisms of miR-511 in hepatocarcinogenesis. Our results of bioinformatics analysis suggested that B cell translocation gene 1 (BTG1), a member of anti-proliferative gene family, was one of the putative targets of miR-511. The expression levels of miR-511 were significantly higher in 30 clinical HCC tissues than in corresponding peritumor tissues, and were negatively correlated with those of BTG1 in the HCC tissues (r=-0.6105, P<0.01). In human hepatoma cell lines HepG2 and H7402, overexpression of miR-511 dose-dependently inhibited the expression of BTG1, whereas knockdown of miR-511 dose-dependently increased the expression of BTG1. Luciferase reporter gene assays verified that miR-511 targeted the 3'UTR of BTG1 mRNA. In the hepatoma cells, overexpression of miR-511 significantly decreased BTG1-induced G₁ phase arrest, which was rescued by overexpression of BTG1. Furthermore, overexpression of miR-511 promoted the proliferation of the hepatoma cells, which was rescued by overexpression of BTG1. Conversely, knockdown of miR-511 inhibited cell proliferation, which was reversed by knockdown of BTG1. In conclusion, miR-511 promotes the proliferation of human hepatoma cells in vitro by targeting the 3'UTR of BTG1 mRNA.

Molecular biomarkers in acute myeloid leukemia

Acute myeloid leukemia (AML) is the most common acute leukemia in adults. The pathophysiology of this disease is just beginning to be understood at the cellular and molecular level, and currently cytogenetic markers are the most important for risk stratification and treatment of AML patients. However, with the advent of new technologies, the detection of other molecular markers such as point mutations and characterization of epigenetic and proteomic profiles, have begun to play an important role in how the disease is approached. Recent evidence shows that the identification of new AML biomarkers contributes to a better understanding of the molecular basis of the disease, is significantly useful in screening, diagnosis, prognosis and monitoring of AML, as well as the possibility of predicting each individual's response to treatment. This review summarizes the most relevant molecular (genetic, epigenetic, and protein) biomarkers associated with acute myeloid leukemia and discusses their clinical importance in terms of risk prediction, diagnosis and prognosis.

Diversity of clinical implication of B-cell translocation gene 1 expression by histopathologic and anatomic subtypes of gastric cancer

BACKGROUND

Genetic signatures may differ by histopathologic and anatomic subtypes of gastric cancer (GC). B-cell translocation gene 1 (BTG1) was identified as one of genes downregulated in GC tissues from our microarray data.

AIMS

To evaluate the clinical implications of BTG1 expression in GC and the genetic diversity among GC subtypes.

METHODS

BTG1 mRNA expression was analyzed in GC cell lines and 233 pairs of surgical specimens. The mutational and methylation status of BTG1 in GC cell lines was analyzed, and immunohistochemistry was conducted to determine the distribution of BTG1. The pattern and prognostic significance of BTG1 expression were correlated with the three proposed GC subtypes.

RESULTS

BTG1 mRNA was downregulated in 82 % of GC cell lines and in 88 % of clinical GC tissues. Promoter hypermethylation events or sequence mutations were not detected in GC cell lines. The pattern of BTG1 expression as observed by immunohistochemistry was consistent with that of its mRNA. Downregulation of BTG1 mRNA in GCs was significantly associated with shorter disease-specific and recurrence-free survival. Multivariate analysis of disease-specific survival identified downregulation of BTG1 transcription as an independent prognostic factor. BTG1 mRNA expression was more strongly suppressed in proximal nondiffuse and diffuse GC compared with distal nondiffuse GC, and subgroup analysis revealed that BTG1 downregulation led to adverse prognosis, specifically in patients with proximal nondiffuse and diffuse GC.

CONCLUSIONS

Altered expression of BTG1 is a potential biomarker for carcinogenesis and progression of GC, particularly for proximal nondiffuse and diffuse GC.

B‑cell translocation gene 1 serves as a novel prognostic indicator of hepatocellular carcinoma

Although the B‑cell translocation gene 1 (BTG1) plays an important role in apoptosis and negatively regulates cell proliferation, BTG1 expression in hepatocellular carcinoma (HCC) has not been evaluated. In this study expression analysis of BTG1 was conducted to clarify the role of BTG1 in the initiation of HCC carcinogenesis and progression. BTG1 mRNA expression levels were determined for HCC cell lines and 151 surgical specimen pairs using quantitative real‑time reverse transcription polymerase chain reaction (RT‑qPCR) assay. The mutational and methylation status of HCC cell lines were analyzed via high resolution melting (HRM) analysis and direct sequencing analysis to elucidate the regulatory mechanisms of BTG1 expression. The expression and distribution of the BTG1 protein in liver tissues were evaluated using immunohistochemistry (IHC). Decreased expression of BTG1 mRNA was confirmed in the majority of HCC cell lines (89%) and clinical HCC tissues (85%) compared with non‑cancerous liver tissues. Mutations or promoter hypermethylation were not identified in HCC cell lines. BTG1 mRNA expression levels were not influenced by background liver status. The pattern of BTG1 protein expression was consistent with that of BTG1 mRNA. Downregulation of BTG1 mRNA in HCC was significantly associated with shorter disease‑specific and recurrence‑free survival rates. Multivariate analysis of disease‑specific survival rates identified BTG1 mRNA downregulation as an independent prognostic factor for HCC (hazard ratio 2.12, 95% confidence interval 1.12‑4.04, P=0.022). Our results indicate that altered BTG1 expression might affect hepatocarcinogenesis and may represent a novel biomarker for HCC carcinogenesis and progression.

BTG1 expression correlates with the pathogenesis and progression of ovarian carcinomas

BTG (B-cell translocation gene) can inhibit cell proliferation, metastasis, and angiogenesis and regulate cell cycle progression and differentiation in a variety of cell types. We aimed to clarify the role of BTG1 in ovarian carcinogenesis and progression. A BTG1-expressing plasmid was transfected into ovarian carcinoma cells and their phenotypes and related proteins were examined. BTG1 mRNA expression was detected in ovarian normal tissue (n = 17), ovarian benign tumors (n = 12), and ovarian carcinoma (n = 64) using real-time RT-PCR. Ectopic BTG1 expression resulted in lower growth rate, high cisplatin sensitivity, G₁ arrest, apoptosis, and decreased migration and invasion. Phosphoinositide 3-kinase, protein kinase B, Bcl-xL, survivin, vascular endothelial growth factor, and matrix metalloproteinase-2 mRNA and protein expression was reduced in transfectants as compared to control cells. There was higher expression of BTG1 mRNA in normal tissue than in carcinoma tissue (p = 0.001) and in benign tumors than in carcinoma tissue (p = 0.027). BTG1 mRNA expression in International Federation of Gynecology and Obstetrics (FIGO) stage I/II ovarian carcinomas was higher than that in FIGO stage III/IV ovarian carcinomas (p = 0.038). Altered BTG1 expression might play a role in the pathogenesis and progression of ovarian carcinoma by modulating proliferation, migration, invasion, the cell cycle, and apoptosis.

BTG1 inhibits breast cancer cell growth through induction of cell cycle arrest and apoptosis

BTG1, which belongs to the BTG/Tob family, regulates cell cycle progression in a variety of cell types and appears to play roles in inhibiting proliferation, promoting apoptosis and stimulating cellular differentiation in multiple cell types. However, it remains unclear whether BTG1 is a breast cancer suppressor gene, and the role of BTG1 in breast cancer cell growth has not yet been determined. In the present study, we observed that BTG1 was weakly expressed in human breast tumors and in breast cancer cells (MCF-7 and MDA-MB-231). In addition, we investigated the potential effects of BTG1 on breast cancer cell proliferation, cell cycle distribution and apoptosis after stable transfection with the BTG1 expression vector. We found that overexpression of BTG1 inhibited cell proliferation, induced G0/G1 cell cycle arrest and promoted apoptosis. Further investigation indicated that overexpression of BTG1 was involved in the inhibition of the expression of cell cycle-related proteins, cyclin B1 and cyclin D1, and pro-apoptotic factors, Bax and caspase-3, and was also involved in the promotion of anti-apoptotic factor Bcl-2. In vivo, animal experiments showed that tumors overexpressing BTG1 displayed a slower growth rate than the control xenografts. TUNEL end staining assay revealed that BTG1 induced tumor necrosis and apoptosis. Taken together, our data revealed that, in breast cancer cells, BTG1 inhibits cell growth through induction of cell cycle arrest and apoptosis. These results indicate that BTG1 may be used as a novel therapeutic target for human breast cancer treatment.

Comparative proteome analysis of acute myeloid leukemia with and without maturation

Acute myeloid leukemia (AML) is a severe, rapidly progressing disease triggered by blocking granulocyte or monocyte differentiation and maturation. Because of its heterogeneity, AML is divided into a number of subtypes. Unfortunately, so far very few correlations have been found between AML classification and its clinical course or patient response to treatment. In addition, as yet only a few subtype-specific AML biomarkers have been discovered. To solve these problems here, we focused on two AML subtypes M1 and M2 that are especially difficult to differentiate. Using 2D electrophoresis and mass spectrometry, we analyzed the protein profiles of peripheral blood (PB) and/or bone marrow (BM) samples collected from 38 AML-M1/M2 patients and 17 healthy volunteers. Comparative analysis of AML-M1/M2 and control PB/BM cells revealed 25 proteins that accumulated differentially. Hierarchical clustering of proteomic results clearly divided the AML samples into 2 groups (M1 and M2). Annexin III, L-plastin and 6-phosphogluconate dehydrogenase were found only in the M2 group. We also observed that the levels of annexin I and actin gamma 1 were correlated with resistance to treatment and the time of relapse. It appears that these five proteins can serve as potential AML biomarkers.

Comparative proteomics in acute myeloid leukemia

The term proteomics was used for the first time in 1995 to describe large-scale protein analyses. At the same time proteomics was distinguished as a new domain of the life sciences. The major object of proteomic studies is the proteome, i.e. the set of all proteins accumulating in a given cell, tissue or organ. During the last years several new methods and techniques have been developed to increase the fidelity and efficacy of proteomic analyses. The most widely used are two-dimensional electrophoresis (2DE) and mass spectrometry (MS). In the past decade proteomic analyses have also been successfully applied in biomedical research. They allow one to determine how various diseases affect the pattern of protein accumulation. In this paper, we attempt to summarize the results of the proteomic analyses of acute myeloid leukemia (AML) cells. They have increased our knowledge on the mechanisms underlying AML development and contributed to progress in AML diagnostics and treatment.

Change in serum proteome during allogeneic hematopoietic stem cell transplantation and clinical significance of serum C-reactive protein and haptoglobin

Successful hematopoietic stem cell transplantation (HSCT) involves the restoration of hematopoietic function after engraftment, arising from the differentiation and proliferation of hematopoietic stem cells. Several factors could influence the course of allogeneic-HSCT (allo-HSCT). Therefore, knowledge of serum proteome changes during the allo-HSCT period might increase the efficacy of diagnosis and disease prevention efforts. This study conducted proteomic analyses to find proteins that were significantly altered in response to allo-HSCT. Sera from five representative patients who underwent allo-HSCT were analyzed by 2-dimensional gel electrophoresis and liquid chromatography tandem mass spectrometry, and were measured on a weekly basis before and after allo-HSCT in additional 78 patients. Fourteen protein spots showing changes in expression were further examined, and most proteins were identified as acute phase proteins (APPs). Studies of 78 additional patients confirmed that C-reactive protein (CRP) and haptoglobin undergo expression changes during allo-HSCT and thus may have the potential to serve as representative markers of clinical events after allo-HSCT. Maximal CRP level affected the development of major transplant-related complications (MTCs) and other problems such as fever of unknown origin. Particularly, an increase in CRP level 21 days after allo-HSCT was found to be an independent risk factor for MTC. Maximal haptoglobin and haptoglobin level 14 days after allo-HSCT were predictive of relapses in underlying hematologic disease. Our results indicated that CRP and haptoglobin were significantly expressed during allo-HSCT, and suggest that their level can be monitored after allo-HSCT to assess the risks of early transplant-related complications and relapse.

Proteomic analysis of secreted exosomes

This chapter focuses on the contribution of proteomic analysis to the understanding of the process of exosome secretion and the mechanism and function of exosomes. It also describes the potential of exosome proteomic analysis to aid in the development of exosomes for therapeutic use.

How will haematologists use proteomics?

Proteomics technologies are emerging as a useful tool in the identification of disease biomarkers, and in defining and characterising both normal physiological and disease processes. Many cellular changes in protein expression in response to an external stimulus or mutation can only be characterised at the proteome level. In these cases protein expression is often controlled by altered rates of translation and/or degradation, making proteomics an important tool in the analysis of biological systems. In the leukaemias, post-translational modification of proteins (e.g. phosphorylation, acetylation) plays a key role in the molecular pathology of the disease: such modifications can now be detected with novel proteomic methods. In a clinical setting, serum remains a relatively un-mined source of information for prognosis and response to therapy. This protein rich fluid represents an opportunity for proteomics research to benefit hematologists and others. In this review, we discuss the technologies available for the study of the proteome that offer realistic opportunities in haematology.

B cell translocation gene 1 contributes to antisense Bcl-2-mediated apoptosis in breast cancer cells

The antiapoptotic protein Bcl-2 is overexpressed in a majority of breast cancers, and is associated with a diminished apoptotic response and resistance to various antitumor agents. Bcl-2 inhibition is currently being explored as a possible strategy for sensitizing breast cancer cells to standard chemotherapeutic agents. Antisense Bcl-2 oligonucleotides represent one method for blocking the antiapoptotic effects of Bcl-2. In this study, we show that antisense Bcl-2 efficiently blocks Bcl-2 expression, resulting in the apoptosis of breast cancer cells. Antisense Bcl-2-mediated cytotoxicity was associated with the induction of the B cell translocation gene 1 (BTG1). Importantly, knockdown of BTG1 reduced antisense Bcl-2-mediated cytotoxicity in breast cancer cells. Furthermore, BTG1 expression seems to be negatively regulated by Bcl-2, and exogenous expression of BTG1 induced apoptosis. These results suggest that BTG1 is a Bcl-2-regulated mediator of apoptosis in breast cancer cells, and that its induction contributes to antisense Bcl-2-mediated cytotoxic effects.