CLIC5: a novel ETV6 target gene in childhood acute lymphoblastic leukemia.

The most common rearrangement in childhood precursor B-cell acute lymphoblastic leukemia is the t(12;21)(p13;q22) translocation resulting in the ETV6-AML1 fusion gene. A frequent concomitant event is the loss of the residual ETV6 allele suggesting a critical role for the ETV6 transcriptional repressor in the etiology of this cancer. However, the precise mechanism through which loss of functional ETV6 contributes to disease pathogenesis is still unclear. To investigate the impact of ETV6 loss on the transcriptional network and to identify new transcriptional targets of ETV6, we used whole transcriptome analysis of both pre-B leukemic cell lines and patients combined with chromatin immunoprecipitation. Using this integrative approach, we identified 4 novel direct ETV6 target genes: CLIC5, BIRC7, ANGPTL2 and WBP1L To further evaluate the role of chloride intracellular channel protein CLIC5 in leukemogenesis, we generated cell lines overexpressing CLIC5 and demonstrated an increased resistance to hydrogen peroxide-induced apoptosis. We further described the implications of CLIC5's ion channel activity in lysosomal-mediated cell death, possibly by modulating the function of the transferrin receptor with which it colocalizes intracellularly. For the first time, we showed that loss of ETV6 leads to significant overexpression of CLIC5, which in turn leads to decreased lysosome-mediated apoptosis. Our data suggest that heightened CLIC5 activity could promote a permissive environment for oxidative stress-induced DNA damage accumulation, and thereby contribute to leukemogenesis.

Identification of new ETV6 modulators through a high-throughput functional screening.

ETV6 transcriptional activity is critical for proper blood cell development in the bone marrow. Despite the accumulating body of evidence linking ETV6 malfunction to hematological malignancies, its regulatory network remains unclear. To uncover genes that modulate ETV6 repressive transcriptional activity, we performed a specifically designed, unbiased genome-wide shRNA screen in pre-B acute lymphoblastic leukemia cells. Following an extensive validation process, we identified 13 shRNAs inducing overexpression of ETV6 transcriptional target genes. We showed that the silencing of AKIRIN1, COMMD9, DYRK4, JUNB, and SRP72 led to an abrogation of ETV6 repressive activity. We identified critical modulators of the ETV6 function which could participate in cellular transformation through the ETV6 transcriptional network.

An in vitro comparison of four different immunoassays for the monitoring of Infliximab biosimilars drug levels.

BACKGROUND: SB2 (Renflexis®, Merck) and CT-P13 (Inflectra®, Pfizer) are biosimilars of the reference Infliximab (Remicade®, Janssen) and are approved in Canada for use in indications for which Infliximab is approved, including inflammatory bowel disease. These biosimilars are structurally different but exhibit comparable physicochemical characteristics, pharmaceutical effectiveness and immunogenicity compared to Infliximab. Optimal Infliximab therapy currently relies on therapeutic drug monitoring offered by several reference laboratories. OBJECTIVE: Because the appropriate dosing depends on accurate determination of drug levels and anti-drug antibodies, the ability of current Infliximab assays to measure the biosimilars and corresponding antibodies needs to be demonstrated. METHODS: The correlation between Infliximab and the biosimilars measured with four different enzyme-linked immunosorbent assays for Infliximab detection was evaluated. Spiked serum samples were assayed with kits from (A) Immunodiagnostik/ALPCO Diagnostics, (B) R-Biopharm, (C) Theradiag and (D) Progenika Biopharma. The impact of various concentrations of antibodies to Infliximab on the quantification of biosimilars was also tested. RESULTS: A good correlation of SB2, CT-P13 and reference Infliximab spiked serum samples was observed with the four assays. The observed bias between the original drug and biosimilars is clinically insignificant and less than the usual analytical variability observed with these methods. The quantification of the biosimilars and Infliximab was equally impacted in serums containing antibodies to Infliximab. The recovery of the drugs was inversely correlated with the concentration of anti-Infliximab antibodies, suggesting common immunodominant epitopes for SB2, CT-P13 and Infliximab. CONCLUSION: The ability of these assays to properly quantify the biosimilars Renflexis® and Inflectra® has been demonstrated. The therapeutic drug monitoring required for Infliximab therapy can be adequately performed with the biosimilars using the kits currently in use or available in clinical laboratories.

Genome wide mapping of ETV6 binding sites in pre-B leukemic cells.

Genetic alterations in the transcriptional repressor ETV6 are associated with hematological malignancies. Notably, the t(12;21) translocation leading to an ETV6-AML1 fusion gene is the most common genetic alteration found in childhood acute lymphoblastic leukemia. Moreover, most of these patients also lack ETV6 expression, suggesting a tumor suppressor function. To gain insights on ETV6 DNA-binding specificity and genome wide transcriptional regulation capacities, we performed chromatin immunoprecipitation experiments coupled to deep sequencing in a t(12;21)-positive pre-B leukemic cell line. This strategy led to the identification of ETV6-bound regions that were further associated to gene expression. ETV6 binding is mostly cell type-specific as only few regions are shared with other blood cell subtypes. Peaks localization and motif enrichment analyses revealed that this unique binding profile could be associated with the ETV6-AML1 fusion protein specific to the t(12;21) background. This study underscores the complexity of ETV6 binding and uncovers ETV6 transcriptional network in pre-B leukemia cells bearing the recurrent t(12;21) translocation.