Dual transcripts of BCR-ABL & different polymorphisms in chronic myeloid leukaemia patients

Background & objectives:

Chronic myeloid leukaemia is (CML) characterized by the presence of a hallmark chromosomal translocation, the Philadelphia chromosome. Although there are many reports available regarding the different variants of BCR-ABL in CML, we studied the co-expression of e13a2 and e14a2 transcripts and a few polymorphisms in CML patients.

Methods:

Molecular genetics approach was adapted to screen for polymorphisms, mutation and translocation in BCR, ABL kinase domain and BCR-ABL breakpoint region in 73 CML patients.

Results:

All eight patients with dual transcripts were found to harbour an exonic polymorphism (c.2700 T>C) and an intronic polymorphism (g.109366A>G) that were earlier reported to be associated with co-expression of both the transcripts. We also observed c.763G>A mutation in ABL kinase domain and two polymorphisms, c.2387 A>G and c.2736A>G in the BCR gene.

Interpretation & conclusions:

Though our data support the previous findings that co-expression of BCR-ABL transcripts is due to the occurrence of exonic and intronic polymorphisms in the BCR gene, it also shows that the intronic polymorphism can arise without the linked exonic polymorphism. The occurrence of ABL kinase domain mutation is less frequent in Indian population.

Ecotropic viral integration site I regulates alpha1, 6-fucosyl transferase expression and blocks erythropoiesis in chronic myeloid leukemia

Although BCR-ABL is the hallmark genetic abnormality of chronic myeloid leukemia (CML), secondary molecular events responsible for the evolution of the disease to blast crisis are yet to be deciphered. Taking into account the significant association of ecotropic viral integration site I (EVI1) in CML drug resistance, it is necessary to decipher the other roles played by EVI1 in CML disease progression. In this regard, we cross-hybridized three microarray datasets and deduced a set of 11 genes that seems to be regulated by EVI1 in CML. We observed a strong correlation between EVI1 and alpha1, 6-fucosyltransferase (FUT8) in the chronic phase of the disease and both of them were found to be up-regulated with the progression of the disease. Knockdown of EVI1 in a CML cell line not only down-regulated FUT8, but also rendered the cells towards erythroid differentiation. Our study shows the involvement of EVI1 and FUT8 axis in blocking erythropoiesis in CML.

EVI1 targets ΔNp63 and upregulates the cyclin dependent kinase inhibitor p21 independent of p53 to delay cell cycle progression and cell proliferation in colon cancer cells

Several lines of evidence suggest that specific transcriptional events are involved in cell cycle, proliferation and differentiation processes; however, their deregulation by proto-oncogenes are involved in the development of leukemia and tumors. One such proto-oncogene is ecotropic viral integration site I which can differentially effect cell cycle progression and proliferation, in cell types of different origin. Our data for the first time shows that ecotropic viral integration site I binds to ΔNp63 promoter element directly and down regulates its expression. Down regulation of ΔNp63 induces the expression of p21 in HT-29 cells and also in colon carcinoma cells that do not express p53 including patient samples expressing low level of p53, that eventually delay cell cycle progression at G0/G1 phase. Concomitant silencing of ecotropic viral integration site I from the cells or introduction of ΔNp63 to the cells significantly rescued this phenotype, indicating the growth defect induced by ΔNp63 deficiency to be, at least in part, attributable to ecotropic viral integration site I function. The mutual regulation between ecotropic viral integration site I and ΔNp63 may constitute a novel axis which might affect the downstream pathways in cells that do not express functional p53.

EVI1 up-regulates the stress responsive gene SIRT1 which triggers deacetylation and degradation of EVI1

EVI1 (Ecotropic Viral Integration site I), which was originally identified as a site of viral integration in murine myeloid tumors, encodes a complex protein required for embryogenesis. The gene is known to express inappropriately in many types of human myeloid leukemias and solid tumors. Forced expression of EVI1 in murine hematopoietic precursor cells lead to abnormal differentiation and increased proliferation. EVI1 encodes two sets of zinc finger domains due to which it behaves as a transcriptional factor. However, except a few, the targets of EVI1 are not well understood and hence also the mechanism by which it initiates oncogenesis is not very clear. In this report, we show that SIRT1, a histone deacetylase is a direct target of EVI1. In vivo chromatin immunoprecipitation assay revealed that EVI1 binds to the promoter region of SIRT1 approximately 1kb upstream of the transcription start site. The functionality of the site was deduced by luciferase assay which showed that EVI1 significantly increases the SIRT1 promoter activity. SIRT1 was also found to be up regulated in cell lines and in chronic myeloid leukemia patient samples where EVI1 was detected. Over expression of SIRT1 in cells shows that it interacts with EVI1 and this interaction lead to the deacetylation of the protein. Upon deacetylation the stability of EVI1 was found to be affected which was negatively regulated by nicotinamide (NAM). Our results thus identify an EVI1-SIRT1 axis in the regulation of EVI1 activity suggesting a possible role of SIRT1 in EVI1 positive neoplasms.