Molecular findings in childhood leukemia in Brazil: high frequency of MLL-ENL Fusion/t(11;19) in infant leukemia

Cytogenetic abnormalities and TP53 and RAS gene profiles of childhood acute lymphoblastic leukemia in Morocco

BACKGROUND

Recurrent genetic abnormalities affecting pivotal signaling pathways are the hallmark of childhood acute lymphoblastic leukemia (ALL). The identification of these aberrations remains clinically important. Therefore, we sought to determine the cytogenetic profile and the mutational status of TP53 and RAS genes among Moroccan childhood cases of ALL.

METHODS

In total, 35 patients with childhood ALL were enrolled in the study. The diagnosis and treatment were established in the Pediatric Hematology and Oncology Center at the Children's Hospital of Rabat. Chromosome banding analysis and fluorescence in situ hybridization were used to detect genetic aberrations. Blood samples were screened for TP53 and RAS mutations using Sanger sequencing.

RESULTS

Of the 35 cases, 30 were B-lineage ALL (85.7 %). Moreover, a male predominance was observed. Cytogenetic analysis revealed chromosomal anomalies in 27 cases (77.1 %). The most frequent aberrations were high hyperdiploidy and BCR/ABL rearrangement. Interestingly, we found the rare t(15;16) and the t(8;14), which are uncommon translocations in pediatric B-ALL. The mutational analysis revealed Pro72Arg (rs1042522:C > G) and Arg213Arg (rs1800372:A > G) in TP53. In correlation with cytogenetic data, rs1042522:C > G showed a significant association with the occurrence of chromosomal translocations (p = 0.04). However, no variant was detected in NRAS and KRAS genes.

CONCLUSION

Our findings emphasize the significance of detecting chromosomal abnormalities as relevant prognostic markers. We also suggest a low occurrence of genetic variants among Moroccan children with ALL.

The antigen processing-associated transporter gene polymorphism: Role on gene and protein expression in HPV-infected pre-cancerous cervical lesion

Human papillomavirus (HPV) is the major pathogen for cervical lesions. The evasion mechanism of the immune response and persistence of HPV infection can be influenced by polymorphisms (SNPs) in genes associated with transporter associated with antigen processing (TAP), which may change the peptide binding affinity or the TAP expression impacting the efficiency of peptide transport in the secretory pathway, and the presentation of peptides to cytotoxic T lymphocytes. This study aimed to evaluate the role of the TAP1 and TAP2 polymorphisms, TAP1, and TAP2 genes expressions, and protein levels in cervical cells presenting different degrees of pre-cancerous lesions in 296 immunocompetent women infected or not by HPV. TAP SNPs were genotyped by Sanger sequencing, and gene expression by real-time PCR. Aneuploidy was determined by DNA index using flow cytometry. TAP-1 and TAP-2 tissue expressions were evaluated by immunohistochemistry. The Asp697Gly SNP of TAP1 presented a risk for cellular aneuploidy (P=0.0244). HPV+ women had higher TAP-2 mRNA (P=0.0212) and protein (P<0.0001) levels. The TAP2D and TAP2E haplotypes were associated with the risk for aneuploidy and pre-cancerous lesions. In conclusion, nucleotide variability at the peptide binding region of peptide transporter genes, particularly of the TAP2 gene, may influence the HPV-peptide transportation from the cytosol to the endoplasmic reticulum, increasing the susceptibility to the development of high-grade cervical lesions.

Differentially Expressed Bone Marrow microRNAs Are Associated With Soluble HLA-G Bone Marrow Levels in Childhood Leukemia

HLA-G is a nonclassical histocompatibility class I molecule that plays a role in immune vigilance in cancer and infectious diseases. We previously reported that highly soluble HLA-G (sHLA-G) levels in the bone marrow were associated with a high blood cell count in T-acute lymphoblastic leukemia, a marker associated with a poor prognosis. To understand the posttranscriptional HLA-G gene regulation in leukemia, we evaluated the bone marrow microRNA profile associated with the HLA-G bone marrow mRNA expression and sHLA-G bone marrow levels in children exhibiting acute leukemia (B-ALL, T-ALL, and AML) using massively parallel sequencing. Ten differentially expressed miRNAs were associated with high sHLA-G bone marrow levels, and four of them (hsa-miR-4516, hsa-miR-486-5p, hsa-miR-4488, and hsa-miR-5096) targeted HLA-G, acting at distinct HLA-G gene segments. For qPCR validation, these miRNA expression levels (ΔCt) were correlated with HLA-G5 and RREB1 mRNA expressions and sHLA-G bone marrow levels according to the leukemia subtype. The hsa-miR-4488 and hsa-miR-5096 expression levels were lower in B-ALL than in AML, while that of hsa-miR-486-5p was lower in T-ALL than in AML. In T-ALL, hsa-miR-5096 correlated positively with HLA-G5 and negatively with sHLA-G. In addition, hsa-miR-4516 correlated negatively with sHLA-G levels. In AML, hsa-miR-4516 and hsa-miR-4488 correlated positively with HLA-G5 mRNA, but the HLA-G5 negatively correlated with sHLA-G. Our findings highlight the need to validate the findings of massively parallel sequencing since the experiment generally uses few individuals, and the same type of leukemia can be molecularly quite variable. We showed that miRNA's milieu in leukemia's bone marrow environment varies according to the type of leukemia and that the regulation of sHLA-G expression exerted by the same miRNA may act by a distinct mechanism in different types of leukemia.

MicroRNA expression profiles discriminate childhood T- from B-acute lymphoblastic leukemia

MicroRNAs (miRNAs) play a critical role on biological and cellular processes; the search for functional markers may be of importance for differential diagnosis, prognosis, and development of new therapeutic regimens. In this context, we evaluated the bone marrow miRNA profile of Brazilian children exhibiting T- or B-cell acute lymphoblastic leukemia (T-ALL or B-ALL), using massive parallel sequencing, using the HiSeq 2500 platform (Illumina). The differential expression analysis was conducted considering a leave-one-out approach and FDR ≤ 0.05. Machine learning algorithms were applied to search for the disease subset biomarkers. Target prediction, functional enrichment, and classification of biological categories were also performed. Sixteen miRNAs were differentially expressed between T- and B-ALL, of which 10 (miR-708-5p, miR-497-5p, miR-151a-5p, miR-151b, miR-371b-5p, miR-455-5p, miR-195-5p, miR-1266-5p, miR-574-5p, and miR-425-5p) were downregulated and six (miR-450b-5p, miR-450a-5p, miR-542-5p, miR-424-5p, miR-629-5p, and miR-29c-5p) were upregulated in childhood T-ALL. These miRNAs may be used for distinguishing childhood lymphoblastic leukemia subtypes, since it provided the clear separation of patients in these two distinct groups. Six relevant biological pathways were identified according to their role in leukemia, namely, viral carcinogenesis, cell cycle, and B-cell receptor signaling pathways for induced miRNAs and TGF-beta signaling, apoptosis, and NF-kappa B signaling for the repressed miRNAs, of which several miRNA gene targets participate in cell differentiation and hematopoiesis processes. Machine learning analysis pointed out miR-29c-5p expression as the best discriminator between childhood T- and B-ALL, which is involved in calcium signaling, critical for B-cell lymphocyte fate. Further studies are needed to assure the role of the 16 miRNAs and miR-29c-5p on acute lymphoblastic leukemia subtypes and on disease prognosis.