PTBP2 exon 10 inclusion is associated with the progression of CML and it is BCR-ABL1 dependent

Altered or aberrant expression of several splicing factors leads to the progression of different cancers. Though there are several ongoing studies underscoring the role of the splicing regulator polypyrimidine tract binding protein 2 (PTBP2) in neuronal cells, we unveil the role of PTBP2 in chronic myeloid leukemia (CML). Different RNA binding proteins (RBP's) earlier reported in chronic myeloid leukemia blast crisis (CML-BC) cases (n = 28) from Radich Oncomine leukemia dataset, were compared. We observed increased expression of MSI2 followed by PTBP2 in BC cases and increased PTBP2 expression in relapsed cases (n = 10) from the same dataset compared to other RBPs. We also observed increased PTBP2 exon 10 inclusion in KCL22, a granulocytic lineage CML cell line when compared to other CML cell lines of different lineages. As PTBP2 protein expression is associated with PTBP2 exon 10 inclusion, we observed in cell lines and in a set of progressed cases (n = 4) that increased BCR-ABL1 expression potentiates PTBP2 exon 10 inclusion and thus confers the existence of a functional protein. Inhibition of BCR-ABL1 with imatinib not only blocks the inclusion of exon 10 but also deregulates PTBP2 expression in CML cells. Knockdown of PTBP2 in KCL22 cells leads to reduced cell proliferation, increased G2/M cell cycle arrest and increased apoptosis. Taken together our study portrays PTBP2 as a new possible target for CML and progressive inclusion/exclusion of PTBP2 exon 10 might play an important role in CML progression.

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.