LPXN, a member of the paxillin superfamily, is fused to RUNX1 in an acute myeloid leukemia patient with a t(11;21)(q12;q22) translocation

The non-coding RNome after splenectomy

Splenectomy is a common surgical procedure performed in millions of people worldwide. Epidemiologic data show that splenectomy is followed by infectious (sepsis) and non-infectious complications, with unknown mechanisms. In order to explore the role of the non-coding transcripts involved in these complications, we analysed a panel of circulating microRNAs (miRNAs), which were previously reported to be deregulated in sepsis, in the plasma of splenectomized patients. MiR-223 was overexpressed immediately and late after splenectomy, while miR-146a was overexpressed immediately after splenectomy, returning latter to basal levels; and miR-16, miR-93, miR-26a and miR-26b were overexpressed only late after splenectomy, suggesting similarities with sepsis. We also explored the non-coding (nc)RNome of circulating peripheral blood leucocytes by performing a ncRNA full genome profiling. We observed a reorganization of the ncRNoma after splenectomy, characterized by up-regulation of miRNAs and down-regulation of transcribed pyknons (T-PYKs). Pathway analysis revealed that deregulated miRNAs control pathways involved in immunity, cancer and endothelial growth. We checked the expression of the ncRNAs in 15 immune cell types from healthy donors and observed that plasma miRNAs, cellular miRNAs and T-PYKs have a cell-specific expression pattern and are abundant in different types of immune cells. These findings suggest that the ncRNAs potentially regulate the immune changes observed after splenectomy.

Downregulation of LPXN expression by siRNA decreases the malignant proliferation and transmembrane invasion of SHI-1 cells

The aim of the present study was to investigate the effects of decreasing leupaxin (LPXN) expression on the proliferation and invasion of human acute monocytic leukemia SHI-1 cells. The transfection efficiency of fluorescein amidite (FAM)-small interfering RNA (siRNA) was determined using flow cytometry, and the protein expression levels of LPXN, phosphorylated (p)-c-Jun N-terminal kinase (JNK), p-p38 mitogen-activated protein kinase (p38 MAPK) and p-extracellular-signal-regulated kinase (ERK) were detected by western blot analysis. Proliferation was determined using the cell counting kit-8 reagent and cellular transmembrane invasion ability was determined using a Transwell chamber system. The gelatinase levels of matrix metalloproteinase (MMP)-2 and MMP-9 in the cell culture supernatant were also analyzed by gelatin zymography. In SHI-1 cells, the optimal transfection conditions of siRNA were a cell density of 4×10⁵ cells/ml and a ratio of siRNA/Lipofectamine^® 2000 of 200 pmol/1 µl. The highest transfection efficiency of FAM-siRNA was 74.5%. In the present study, L2-siRNA was selected to effectively decrease the expression of LPXN. Following downregulation of LPXN expression by L2-siRNA, proliferation inhibition rates increased to 27.043±2.051 and cell transmembrane invasion rates decreased to 25.270±2.145 (P<0.05). The results of the western blot analysis and the gelatin zymography indicated that downregulation of LPXN expression increased the expression of p-p38 MAPK and p-JNK, and attenuated the secretion levels of MMP-2 and MMP-9. However, downregulation of LPXN expression had no effect on p-ERK expression in SHI-1 cells. The results of the present study indicated that downregulation of LPXN expression decreased the malignant proliferation and transmembrane invasion of SHI-1 cells by activating JNK and p38 MAPK, and inhibiting MMP-2 and MMP-9 secretion.

[Small interfering RNA-mediated LPXN silencing suppresses proliferation and enhances drug sensitivity of human acute monocytic leukemia SHI-1 cells in vitro]

OBJECTIVE

To investigate the effect of silencing LPXN expression by RNA interference on the proliferation and drug sensitivity of human acute monocytic leukemia SHI-1 cells in vitro.

METHODS

Small interfering RNA (siRNA) sequences targeting LPXN were designed and transiently transfected in SHI-1 cells via Lipofectamine 2000, and the most efficient siRNA sequence for LPXN silencing was identified using Western blotting. The protein expression levels of LPXN, p-JNK, p-P38 MAPK and p-ERK were in the cells transfected with the selected siRNA were detected using Western blotting, and the cell proliferation changes were assessed using CCK-8 reagent.

RESULTS

LPXN silencing by siRNA transfection resulted in significant proliferation suppression in SHI-1 cells with an inhibition rate of(27.04±2.05) % (P < 0.05). Western blotting showed that treatment of the siRNA-transfected SHI-1 cells with 0-25 μmol/L curcumin or with 0-2.0 μmol/L Ara-C further increased the cell inhibition rate and obviously enhanced the expressions of p-P38 MAPK and p-JNK without significantly affecting p-ERK expression.

CONCLUSIONS

Down-regulation of LPXN expression by siRNA transfection can suppress the proliferation and increase the drug sensitivity of SHI-1 cells probably by activating JNK and P38 MAPK.

RUNX1 truncation resulting from a cryptic and novel t(6;21)(q25;q22) chromosome translocation in acute myeloid leukemia: A case report

Fluorescence in situ hybridization examination of a pediatric AML patient whose bone marrow cells carried trisomy 4 and FLT3-ITD mutation, demonstrated that part of the RUNX1 probe had unexpectedly moved to chromosome band 6q25 indicating a cryptic t(6;21)(q25;q22) translocation. RNA sequencing showed fusion of exon 7 of RUNX1 with an intergenic sequence of 6q25 close to the MIR1202 locus, something that was verified by RT-PCR together with Sanger sequencing. The RUNX1 fusion transcript encodes a truncated protein containing the Runt homology domain responsible for both heterodimerization with CBFB and DNA binding, but lacking the proline-, serine-, and threonine-rich (PST) region which is the transcription activation domain at the C terminal end. Which genetic event (+4, FLT3-ITD, t(6;21)-RUNX1 truncation or other, undetected acquired changes) was more pathogenetically important in the present case of AML, remains unknown. The case illustrates that submicroscopic chromosomal rearrangements may accompany visible numerical changes and perhaps should be actively looked for whenever a single trisomy is found. An active search for them may provide both pathogenetic and prognostic novel information.

ETV6-LPXN fusion transcript generated by t(11;12)(q12.1;p13) in a patient with relapsing acute myeloid leukemia with NUP98-HOXA9

ETV6, which encodes an ETS family transcription factor, is frequently rearranged in human leukemias. We show here that a patient with acute myeloid leukemia with t(7;11)(p15;p15) gained, at the time of relapse, t(11;12)(q12.1;p13) with a split ETV6 FISH signal. Using 3'-RACE PCR analysis, we found that ETV6 was fused to LPXN at 11q12.1, which encodes leupaxin. ETV6-LPXN, an in-frame fusion between exon 4 of ETV6 and exon 2 of LPXN, did not transform the interleukin-3-dependent 32D myeloid cell line to cytokine independence; however, an enhanced proliferative response was observed when these cells were treated with G-CSF without inhibition of granulocytic differentiation. The 32D and human leukemia cell lines each transduced with ETV6-LPXN showed enhanced migration towards the chemokine CXCL12. We show here for the first time that LPXN is a fusion partner of ETV6 and present evidence indicating that ETV6-LPXN plays a crucial role in leukemia progression through enhancing the response to G-CSF and CXCL12.

Susceptibility loci associated with specific and shared subtypes of lymphoid malignancies

The genetics of lymphoma susceptibility reflect the marked heterogeneity of diseases that comprise this broad phenotype. However, multiple subtypes of lymphoma are observed in some families, suggesting shared pathways of genetic predisposition to these pathologically distinct entities. Using a two-stage GWAS, we tested 530,583 SNPs in 944 cases of lymphoma, including 282 familial cases, and 4,044 public shared controls, followed by genotyping of 50 SNPs in 1,245 cases and 2,596 controls. A novel region on 11q12.1 showed association with combined lymphoma (LYM) subtypes. SNPs in this region included rs12289961 near LPXN, (P(LYM) = 3.89×10(-8), OR = 1.29) and rs948562 (P(LYM) = 5.85×10(-7), OR = 1.29). A SNP in a novel non-HLA region on 6p23 (rs707824, P(NHL) = 5.72×10(-7)) was suggestive of an association conferring susceptibility to lymphoma. Four SNPs, all in a previously reported HLA region, 6p21.32, showed genome-wide significant associations with follicular lymphoma. The most significant association with follicular lymphoma was for rs4530903 (P(FL) = 2.69×10(-12), OR = 1.93). Three novel SNPs near the HLA locus, rs9268853, rs2647046, and rs2621416, demonstrated additional variation contributing toward genetic susceptibility to FL associated with this region. Genes implicated by GWAS were also found to be cis-eQTLs in lymphoblastoid cell lines; candidate genes in these regions have been implicated in hematopoiesis and immune function. These results, showing novel susceptibility regions and allelic heterogeneity, point to the existence of pathways of susceptibility to both shared as well as specific subtypes of lymphoid malignancy.

A novel RUNX1-C11orf41 fusion gene in a case of acute myeloid leukemia with a t(11;21)(p14;q22)

The RUNX1 locus, which encodes a transcription factor that is essential for normal hematopoiesis, is a frequent location of chromosomal rearrangements in human hematological malignancies. We report the case of a 78-year-old man with acute myeloid leukemia (AML), M1 subtype (French-American-British classification), with a t(11;21)(p14;q22). Fluorescence in situ hybridization showed a split signal for RUNX1, which indicated that RUNX1 was involved in this translocation. Using 3'-rapid amplification of cDNA ends and reverse transcription-polymerase chain reaction analyses, we found that RUNX1 was fused to C11orf41 on 11p14 and detected two in-frame C11orf41-RUNX1 fusion transcripts. One was a fusion between exon 5 of RUNX1 and exon 13 of C11orf41, and the other was between exon 6 of RUNX1 and exon 13 of C11orf41. This suggested that the RUNX1 breakpoint was in intron 6 and had generated alternative fusion splice variants. A reciprocal C11orf41-RUNX1 fusion was not detected. Thus, we identified C11orf41 as a novel fusion partner of RUNX1 in AML.

RUNX1 translocations and fusion genes in malignant hemopathies

The RUNX1 gene, located in chromosome 21q22, is crucial for the establishment of definitive hematopoiesis and the generation of hematopoietic stem cells in the embryo. It contains a 'Runt homology domain' as well as transcription activation and inhibition domains. RUNX1 can act as activator or repressor of target gene expression depending upon the large number of transcription factors, coactivators and corepressors that interact with it. Translocations involving chromosomal band 21q22 are regularly identified in leukemia patients. Most of them are associated with a rearrangement of RUNX1. Indeed, at present, 55 partner chromosomal bands have been described but the partner gene has solely been identified in 21 translocations at the molecular level. All the translocations that retain Runt homology domains but remove the transcription activation domain have a leukemogenic effect by acting as dominant negative inhibitors of wild-type RUNX1 in transcription activation.

Deregulated transcription factors in leukemia

Specific chromosomal translocations and other mutations associated with acute myeloblastic leukemia (AML) often involve transcription factors and transcriptional coactivators. Such target genes include AML1, C/EBPα, RARα, MOZ, p300/CBP, and MLL, all of which are important in the regulation of hematopoiesis. The resultant fusion or mutant proteins deregulate the transcription of the affected genes and disrupt their essential role in hematopoiesis, causing differentiation block and abnormal proliferation and/or survival. This review focuses on such transcription factors and coactivators, and describes their roles in leukemogenesis and hematopoiesis.

CLCA2, a novel RUNX1 partner gene in a therapy-related leukemia with t(1;21)(p22;q22)

The RUNX1 gene is frequently rearranged in de novo and therapy-related leukemia. In the present study, we identified the CLCA2 gene as a novel fusion partner of RUNX1 in a case of therapy-related acute myeloid leukemia associated with t(1;21)(p22;q22). Reverse transcriptase-polymerase chain reaction analysis and sequencing revealed that the t(1;21) results in out-of-frame RUNX1-CLCA2 fusions. Alternative splicing generates at least six fusion transcripts, including a major transcript fusing RUNX1 exon 6 with CLCA2 exon 2. These out-of-frame fusions produce putative truncated RUNX1 isoforms retaining the DNA binding Runt domain but not the transcriptional regulatory domain of RUNX1. No mutations were found in the exons encoding the Runt and C-terminal domains of the nonrearranged RUNX1 gene. Similar to truncated RUNX1 isoforms previously described, these shortened products could act as dominant negative inhibitors of RUNX1-dependent transactivation. CLCA2 is a breast tumor suppressor gene that encodes a member of the calcium-activated chloride channel family and is involved for the first time in a chromosomal translocation. The RUNX1-CLCA2 fusion is another example of out-of-frame fusion generating truncated RUNX1 isoforms that represent a recurrent molecular mechanism in RUNX1-related leukemias.

A retroviral vector common integration site between leupaxin and zinc finger protein 91 (ZFP91) observed in baboon hematopoietic repopulating cells

OBJECTIVE

Retroviral vector proviruses can lead to aberrant expression of nearby genes in hematopoietic repopulating cells, leading to an over-representation of clones with dysregulated genes that affect hematopoiesis. Common integration sites (CISs) identified using the vector provirus as a molecular tag can be used to identify these genes. Here we characterized a retroviral CIS observed at high frequency in baboon hematopoietic repopulating cells that has not been described previously.

MATERIALS AND METHODS

Gammaretroviral vector integration sites in baboon repopulating cells identified by polymerase chain reaction amplification were localized to the human genome to identify a CIS. The presence of each clone was tracked over time using allele-specific polymerase chain reaction.

RESULTS

In three different animals that received gammaretrovirally transduced CD34-enriched bone marrow cells, vector proviruses were identified at three distinct sites within a window of 664 base pairs between leupaxin and zinc finger protein 91 (ZFP91). All three integrants of the CIS occurred within a CpG island between leupaxin and zinc finger protein 91 (ZFP91).

CONCLUSIONS

We describe a novel CIS between leupaxin and ZFP91 in hematopoietic repopulating cells. Our data suggest that leupaxin and/or ZFP91 may play a role in hematopoietic repopulating cells.