High frequency of BTG1 deletions in patients with BCR-ABL1-positive acute leukemia

Expression of B Cell Translocation Gene 1 Protein in Colon Carcinoma and its Clinical Significance

BACKGROUND

Colon cancer is one of the most common malignant tumors, and B cell Translocation Gene (BTG)1 is involved in the occurrence and development of colon cancer, however, the underlying molecular mechanism remains unclear.

OBJECTIVE

In this study, we investigated the expression of BTG1 protein in colon cancer, and its association with clinicopathology and prognosis.

METHODS

The tumor specimens from 59 patients with colon cancer who had undergone radical colectomy were selected as the observation group. Para-carcinoma tissues from the same patients were selected as the control group. The expressions of BTG1 mRNA and protein in the specimen of two groups were analyzed by quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) and Western blot. According to the immunohistochemical results, the patients were divided into BTG1-negative and BTG1-positive groups. The postoperative cumulative survival rate in the two groups was analyzed. The association of the expression of BTG1 protein with the clinicopathological features and postoperative survival was investigated.

RESULTS

Compared with the control group, the expression levels of BTG1 mRNA and BTG1 protein were significantly decreased in the observation group (P < 0.05). Immunohistochemical analysis revealed that there were 12 positive tumor samples and 47 negative samples. The expression of BTG1 was negatively associated with the degree of differentiation and lymphatic metastasis. The cumulative survival rate of BTG1-positive patients was significantly increased compared with that of BTG1- negative patients (P < 0.05). Stepwise Cox regression analysis showed that lymphatic metastasis, tumor size and BTG1 expression level were independent prognostic factors for overall survival in patients with colon cancer.

CONCLUSION

BTG1 protein in colon cancer tissues were expressed at low levels, which was associated with the clinicopathological features, postoperative recurrence and survival of patients.

Molecular profiling of gene copy number abnormalities in key regulatory genes in high-risk B-lineage acute lymphoblastic leukemia: frequency and their association with clinicopathological findings in Indian patients

Genes related to key cellular pathways are frequently altered in B cell ALL and are associated with poor survival especially in high-risk (HR) subgroups. We examined gene copy number abnormalities (CNA) in 101 Indian HR B cell ALL patients and their correlation with clinicopathological features by multiplex ligation-dependent probe amplification. Overall, CNA were detected in 59 (59%) cases, with 26, 10 and 23% of cases harboring 1, 2 or +3 CNA. CNA were more prevalent in BCR-ABL1 (60%), pediatric (64%) and high WCC (WBC count) (63%) patients. Frequent genes deletions included CDNK2A/B (26%), IKZF1 (25%), PAX5 (14%), JAK2 (7%), BTG1 (6%), RB1 (5%), EBF1 (4%), ETV6 (4%), while PAR1 region genes were predominantly duplicated (20%). EBF1 deletions selectively associated with adults, IKZF1 deletions occurred frequently in high WCC and BCR-ABL1 cases, while PAR1 region gains significantly associated with MLL-AF4 cases. IKZF1 haploinsufficiency group was predominant, especially in adults (65%), high WCC (60%) patients and BCR-ABL1-negative (78%) patients. Most cases harbored multiple concurrent CNA, with IKZF1 concomitantly occurring with CDNK2A/B, PAX5 and BTG1, while JAK2 occurred with CDNK2A/B and PAX5. Mutually exclusive CNA included ETV6 and IKZF1/RB1, and EBF1 and JAK2. Our results corroborate with global reports, aggregating molecular markers in Indian HR B-ALL cases. Integration of CNA data from rapid methods like MLPA, onto background of existing gold-standard methods detecting significant chromosomal abnormalities, provides a comprehensive genetic profile in B-ALL.

Tumor suppressors BTG1 and IKZF1 cooperate during mouse leukemia development and increase relapse risk in B-cell precursor acute lymphoblastic leukemia patients

Deletions and mutations affecting lymphoid transcription factor IKZF1 (IKAROS) are associated with an increased relapse risk and poor outcome in B-cell precursor acute lymphoblastic leukemia. However, additional genetic events may either enhance or negate the effects of IKZF1 deletions on prognosis. In a large discovery cohort of 533 childhood B-cell precursor acute lymphoblastic leukemia patients, we observed that single-copy losses of BTG1 were significantly enriched in IKZF1-deleted B-cell precursor acute lymphoblastic leukemia (P=0.007). While BTG1 deletions alone had no impact on prognosis, the combined presence of BTG1 and IKZF1 deletions was associated with a significantly lower 5-year event-free survival (P=0.0003) and a higher 5-year cumulative incidence of relapse (P=0.005), when compared with IKZF1-deleted cases without BTG1 aberrations. In contrast, other copy number losses commonly observed in B-cell precursor acute lymphoblastic leukemia, such as CDKN2A/B, PAX5, EBF1 or RB1, did not affect the outcome of IKZF1-deleted acute lymphoblastic leukemia patients. To establish whether the combined loss of IKZF1 and BTG1 function cooperate in leukemogenesis, Btg1-deficient mice were crossed onto an Ikzf1 heterozygous background. We observed that loss of Btg1 increased the tumor incidence of Ikzf1^+/− mice in a dose-dependent manner. Moreover, murine B cells deficient for Btg1 and Ikzf1^+/− displayed increased resistance to glucocorticoids, but not to other chemotherapeutic drugs. Together, our results identify BTG1 as a tumor suppressor in leukemia that, when deleted, strongly enhances the risk of relapse in IKZF1-deleted B-cell precursor acute lymphoblastic leukemia, and augments the glucocorticoid resistance phenotype mediated by the loss of IKZF1 function.

The Philadelphia chromosome in leukemogenesis

The truncated chromosome 22 that results from the reciprocal translocation t(9;22)(q34;q11) is known as the Philadelphia chromosome (Ph) and is a hallmark of chronic myeloid leukemia (CML). In leukemia cells, Ph not only impairs the physiological signaling pathways but also disrupts genomic stability. This aberrant fusion gene encodes the breakpoint cluster region-proto-oncogene tyrosine-protein kinase (BCR-ABL1) oncogenic protein with persistently enhanced tyrosine kinase activity. The kinase activity is responsible for maintaining proliferation, inhibiting differentiation, and conferring resistance to cell death. During the progression of CML from the chronic phase to the accelerated phase and then to the blast phase, the expression patterns of different BCR-ABL1 transcripts vary. Each BCR-ABL1 transcript is present in a distinct leukemia phenotype, which predicts both response to therapy and clinical outcome. Besides CML, the Ph is found in acute lymphoblastic leukemia, acute myeloid leukemia, and mixed-phenotype acute leukemia. Here, we provide an overview of the clinical presentation and cellular biology of different phenotypes of Ph-positive leukemia and highlight key findings regarding leukemogenesis.