Biology subjects

Xu, L. S.

Publications and source records attributed to Xu, L. S..

4 recordsLinked to original sources

bioRxiv2023

N-Acetylcysteine alters disease progression and increases Janus Kinase mutation frequency in a mouse model of precursor B cell acute lymphoblastic leukemia

B cell acute lymphoblastic leukemia (B-ALL) is the most prevalent type of cancer in young children and is associated with high levels of reactive oxygen species (ROS). The antioxidant N-acetylcysteine (NAC) was tested for its ability to alter disease progression in a mouse model of B-ALL. Mb1-Cre{Delta}PB mice have deletions in genes encoding PU.1 and Spi-B in B cells and develop B-ALL at 100% incidence. Treatment of Mb1-Cre{Delta}PB mice with NAC in drinking water significantly reduced the frequency of CD19+ pre-B ALL cells infiltrating the thymus at 11 weeks of age. However, treatment with NAC did not reduce leukemia progression or increase survival by median 16 weeks of age. NAC significantly altered gene expression in leukemias in treated mice. Mice treated with NAC had increased frequencies of activating mutations in genes encoding Janus Kinases 1 and 3. In particular, frequencies of Jak3 R653H mutations were increased in mice treated with NAC compared to control drinking water. NAC opposed oxidization of PTEN protein ROS in cultured leukemia cells. These results show that NAC alters leukemia progression in this mouse model, ultimately selecting for leukemias with high Jak3 R653H mutation frequencies.

cancer biology↗

bioRxiv2022

Spi-C and PU.1 counterregulate Rag1 and Igκ transcription to effect immunoglobulin kappa recombination in small pre-B cells

B cell development requires the ordered rearrangement of Ig genes encoding H and L chain proteins that assemble into BCRs or Abs capable of recognizing specific Ags. Ig{kappa} rearrangement is promoted by chromatin accessibility and by relative abundance of RAG1/2 proteins. Expression of the E26-transformation-specific (ETS) transcription factor Spi-C is activated in response to double-stranded DNA breaks (DSBs) in small pre-B cells to negatively regulate pre-BCR signaling and Ig{kappa} rearrangement. However, it is not clear if Spi-C regulates Ig{kappa} rearrangement through transcription or by controlling RAG expression. In this study, we investigated the mechanism of Spi-C negative regulation of Ig{kappa} light chain rearrangement. Using an inducible expression system in a pre-B cell line, we found that Spi-C negatively regulated Ig{kappa} rearrangement, Ig{kappa} transcript levels, and Rag1 transcript levels. We found that Ig{kappa} and Rag1 transcript levels were increased in small pre-B cells from Spic-/- mice. In contrast, Ig{kappa} and Rag1 transcript levels were activated by PU.1 and were decreased in small pre-B cells from PU.1-deficient mice. Using chromatin immunoprecipitation analysis, we identified an interaction site for PU.1 and Spi-C located in the Rag1 promoter region. These results suggest that Spi-C and PU.1 counterregulate Ig{kappa} transcription and Rag1 transcription to effect Ig{kappa} recombination in small pre-B cells.

immunology↗

bioRxiv2021

The E26 Transformation-Specific-family transcription factor Spi-C is dynamically regulated by external signals in B cells

Spi-C is an E26 transformation-specific transcription factor closely related to PU.1 and Spi-B. Spi-C has lineage-instructive functions important in antibody-generating responses, B cell development, and red pulp macrophage generation. Spi-C is inducible by heme- and NF-{kappa}B-dependent pathways in macrophages. The present research aimed to examine the regulation of Spi-C expression in B cells. RT-qPCR analysis revealed that Spic expression was reduced in B cells following addition of lipopolysaccharide, anti-IgM antibodies, CD40L, or cytokines BAFF + IL-4 + IL-5. Cytochalasin treatment partially prevented downregulation of Spic. Unstimulated B cells upregulated Spic over time in culture. To determine the mechanism of Spic regulation, we examined the Spic promoter and upstream regulatory elements. The Spic promoter had unidirectional activity, which was reduced by mutation of an NF-{kappa}B binding site. Spic was repressed by an upstream regulatory region interacting with the heme-binding regulator Bach2. Taken together, these data indicate that Spi-C is dynamically regulated by external signals in B cells and provide insight into the mechanism of regulation.

immunology↗

bioRxiv2018

Deletion of genes encoding PU.1 and Spi-B leads to B cell acute lymphoblastic leukemia associated with driver mutations in Janus Kinases

Precursor B-cell acute lymphoblastic leukemia (B-ALL) is associated with recurrent mutations that occur in cancer-initiating cells. There is a need to understand how spontaneous driver mutations influence clonal evolution in leukemia. The ETS-transcription factors PU.1 and Spi-B (encoded by Spi1 and Spib) execute a critical role in B cell development and serve as complementary tumour suppressors by opposing the proliferative events mediated by IL-7R signaling. Here, we used a mouse model to conditionally delete Spi1 and Spib genes in developing B cells. These mice developed B-ALL with a median time to euthanasia of 18 weeks. We performed RNA and whole-exome sequencing (WES) on leukemias isolated from Mb1-Cre{Delta}PB mice and identified single-nucleotide variants (SNVs) in Jak1, Jak3 and Ikzf3 genes, resulting in amino acid changes and in the gain of early stop-codons. JAK3 mutations resulted in amino acid substitutions located in the pseudo-kinase (R653H, V670A) and in the kinase (T844M) domains. Introduction of these mutations into wild-type pro-B cells conferred survival and proliferation advantages. We conclude that mutations in Janus kinases represent secondary drivers of leukemogenesis in the absence of Spi-B and PU.1 transcription factors. This mouse model represents an useful tool to study clonal evolution and tumour heterogeneity in B-ALL.

cancer biology↗