Phosphorylation of serine 21 modulates the proliferation inhibitory more than the differentiation inducing effects of C/EBPα in K562 cells

Long non-coding RNA mitophagy and ALK-negative anaplastic lymphoma-associated transcript: a novel regulator of mitophagy in T-cell lymphoma

Long non-coding RNA (lncRNA) are emerging as powerful and versatile regulators of transcriptional programs and distinctive biomarkers of progression of T-cell lymphoma. Their role in the aggressive anaplastic lymphoma kinase-negative (ALK-) subtype of anaplastic large cell lymphoma (ALCL) has been elucidated only in part. Starting from our previously identified ALCL-associated lncRNA signature and performing digital gene expression profiling of a retrospective cohort of ALCL, we defined an 11 lncRNA signature able to discriminate among ALCL subtypes. We selected a not previously characterized lncRNA, MTAAT, with preferential expression in ALK- ALCL, for molecular and functional studies. We demonstrated that lncRNA MTAAT contributes to an aberrant mitochondrial turnover restraining mitophagy and promoting cellular proliferation. Functionally, lncRNA MTAAT acts as a repressor of a set of genes related to mitochondrial quality control via chromatin reorganization. Collectively, our work demonstrates the transcriptional role of lncRNA MTAAT in orchestrating a complex transcriptional program sustaining the progression of ALK- ALCL.

The novel lncRNA BlackMamba controls the neoplastic phenotype of ALK- anaplastic large cell lymphoma by regulating the DNA helicase HELLS

The molecular mechanisms leading to the transformation of anaplastic lymphoma kinase negative (ALK^-) anaplastic large cell lymphoma (ALCL) have been only in part elucidated. To identify new culprits which promote and drive ALCL, we performed a total transcriptome sequencing and discovered 1208 previously unknown intergenic long noncoding RNAs (lncRNAs), including 18 lncRNAs preferentially expressed in ALCL. We selected an unknown lncRNA, BlackMamba, with an ALK^- ALCL preferential expression, for molecular and functional studies. BlackMamba is a chromatin-associated lncRNA regulated by STAT3 via a canonical transcriptional signaling pathway. Knockdown experiments demonstrated that BlackMamba contributes to the pathogenesis of ALCL regulating cell growth and cell morphology. Mechanistically, BlackMamba interacts with the DNA helicase HELLS controlling its recruitment to the promoter regions of cell-architecture-related genes, fostering their expression. Collectively, these findings provide evidence of a previously unknown tumorigenic role of STAT3 via a lncRNA-DNA helicase axis and reveal an undiscovered role for lncRNA in the maintenance of the neoplastic phenotype of ALK^-ALCL.

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.

Overexpression of CCAAT Enhancer-Binding Protein α Inhibits the Growth of K562 Cells via the Foxo3a-Bim Pathway

We aimed to investigate the role of CCAAT enhancer-binding protein α (C/EBPα) in the pathogenesis of chronic myeloid leukemia (CML) and the mechanism underlying its effect. Bone marrow specimens from 50 patients with CML and peripheral blood specimens from 20 healthy individuals were collected. K562 cells were treated with imatinib. Subsequently, a stable cell line, K562-C/EBPα, was constructed. Cell proliferation was assayed with cell counting kit-8, and mRNA levels of C/EBPα, forkhead transcription factor FKHRL1 (Foxo3a) and Bim were detected by semiquantitative PCR. The correlation of C/EBPα and BCR-ABL was assessed by Spearman's correlation analysis. The results showed that C/EBPα mRNA levels were significantly reduced in CML patients compared with healthy subjects (p < 0.001) and were negatively correlated with BCR-ABL1 (r = -0.5046, p < 0.01). Additionally, imatinib enhanced the expression of C/EBPα in K562 cells compared with untreated cells (p < 0.05). Overexpression of C/EBPα significantly decreased cell proliferation and upregulated the expressions of the apoptosis-related genes Foxo3a (p < 0.01) and Bim (p < 0.05) in K562 cells. In conclusion, C/EBPα expression was decreased in patients with CML. Imatinib enhances the expression of C/EBPα in K562 cells, and the overexpression of C/EBPα inhibits cell proliferation and increases apoptosis via the Foxo3a-Bim pathway.

[The expression and role of the transcription factor C/EBPα in chronic myeloid leukemia]

OBJECTIVE

To investigate the expression and the possible mechanism of the transcription factor C/EBPα in chronic myeloid leukemia（CML).

METHODS

Bone marrow samples from 50 CML patients（including 33 patients in chronic phase, 7 in accelerated phase and 10 in blast crisis）and peripheral blood specimens of 20 healthy donors were collected. The expression of C/EBPα gene and the effect of Imatinib on its expression was detected by RT- PCR. C/EBPα gene was inserted into lentivirus expression vector pLVX- EGFP- 3FLAG- Puro by recombinant DNA technology to construct C/EBPα stable expression in K562 cells. Cell proliferation was assayed by CCK-8. The expressions of Foxo3a and Bim genes were detected by RT-PCR.

RESULTS

The level of C/EBPα expression was significantly declined in CML patients compared with that of normal control group（P<0.01）and had negative correlation with bcr- abl expression（Spearman r=－ 0.505, P<0.01). The stable K562- C/EBPα cell line was successfully established and confirmed by RT-PCR and Western blot. Cell proliferation ability was lower in the K562- C/EBPα group than that in the non- transfection and mock-vehicle groups. The expressions of Foxo3a and Bim genes were 1.06 ± 0.06 and 0.53 ± 0.07, respectively, which was higher than that of nontransfection and mock-vehicle groups（P<0.01, P<0.05).

CONCLUSION

C/EBPα expression was decreased in CML patients, overexpression of C/EBPα could inhibit K562 cell growth.

Expression of p89(c-Mybex9b), an alternatively spliced form of c-Myb, is required for proliferation and survival of p210BCR/ABL-expressing cells

The c-Myb gene encodes the p75^c-Myb isoform and less-abundant proteins generated by alternatively spliced transcripts. Among these, the best known is p^c-Mybex9b, which contains 121 additional amino acids between exon 9 and 10, in a domain involved in protein–protein interactions and negative regulation. In hematopoietic cells, expression of p^c-Mybex9b accounts for 10–15% of total c-Myb; these levels may be biologically relevant because modest changes in c-Myb expression affects proliferation and survival of leukemic cells and lineage choice and frequency of normal hematopoietic progenitors. In this study, we assessed biochemical activities of p^c-Mybex9b and the consequences of perturbing its expression in K562 and primary chronic myeloid leukemia (CML) progenitor cells. Compared with p75^c-Myb, p^c-Mybex9b is more stable and more effective in transactivating Myb-regulated promoters. Ectopic expression of p^c-Mybex9b enhanced proliferation and colony formation and reduced imatinib (IM) sensitivity of K562 cells; conversely, specific downregulation of p^c-Mybex9b reduced proliferation and colony formation, enhanced IM sensitivity of K562 cells and markedly suppressed colony formation of CML CD34⁺ cells, without affecting the levels of p75^c-Myb. Together, these studies indicate that expression of the low-abundance p^c-Mybex9b isoform has an important role for the overall biological effects of c-Myb in BCR/ABL-transformed cells.