Miz-1 regulates translation of Trp53 via ribosomal protein L22 in cells undergoing V(D)J recombination

Abstract

To be effective, the adaptive immune response requires a large repertoire of antigen receptors, which are generated through V(D)J recombination in lymphoid precursors. These precursors must be protected from DNA damage-induced cell death, however, because V(D)J recombination generates double-strand breaks and may activate p53. Here we show that the BTB/POZ domain protein Miz-1 restricts p53-dependent induction of apoptosis in both pro-B and DN3a pre-T cells that actively rearrange antigen receptor genes. Miz-1 exerts this function by directly activating the gene for ribosomal protein L22 (Rpl22), which binds to p53 mRNA and negatively regulates its translation. This mechanism limits p53 expression levels and thus contains its apoptosis-inducing functions in lymphocytes, precisely at differentiation stages in which V(D)J recombination occurs.T he development of T lymphocytes starts with early thymic progenitors (ETPs) that first enter the thymus after transiting through the bloodstream from the bone marrow. These progenitor cells differentiate through four CD4 − CD8 − double-negative stages of development (DN1-4) before becoming first CD4 + CD8 + double-positive (DP) cells and then either CD4 + or CD8 + single positive T cells. The four DN subsets are differentiated based on their expression of the cell surface markers CD44 and CD25. Cells at the DN3 stage (CD44 − CD25 + ) are fully committed to the T cell lineage and require signaling through cytokine receptors and Notch1 to survive (1). This DN3 population can be further subdivided into DN3a and DN3b based on their size and CD27 surface expression.Importantly, DN3a cells (FSC lo CD27 lo ) actively rearrange the genes encoding the T cell receptor β (TCRβ) chain through V(D)J recombination (1-3). Those DN3a cells that do not productively rearrange the TCRβ locus on both alleles are eliminated by apoptosis. In contrast, cells that productively rearrange their TCRβ chain genes are selected and become DN3b cells (FSC hi CD27 hi ), which express a pre-T cell receptor (pre-TCR), a heterodimer between the TCRβ chain and a pTα chain. DN3b cells grow in size, owing in part to increased metabolic activity (4), and give rise to the (CD44 − CD25 − ) DN4 subset, which in turn rapidly expands to produce CD4 + CD8 + DP cells.

Rpl22 Loss Selectively Impairs αβ T Cell Development by Dysregulating Endoplasmic Reticulum Stress Signaling

“…We next asked how Rpl22 loss was influencing p53 synthesis. Rpl22 is an RNA binding protein that has been reported to directly regulate p53 synthesis through direct binding to p53 mRNA (33). Rpl22 binds RNA targets through recognition of a stem loop structure with a G-C-U at the neck of the stem (34).…”

Transcription factors and target genes of pre-TCR signaling

“…Although it is known that the guanine nucleotide binding protein/GTPase Rho suppresses p53-mediated apoptosis downstream of the pre-TCR [ 127 ], the signaling steps that link the pre-TCR to inhibition of p53 are not fully elucidated. Recent evidence shows that the transcription factor Miz-1 induces the expression of the gene encoding ribosomal protein L22 (RPL22), a negative regulator of p53 translation [ 208 ], which is consistent with the role of Miz-1 and RPL22 as prosurvival molecules that antagonize p53 during the β-selection checkpoint of thymocytes [ 209 -211 ].…”

“…Although it is known that the guanine nucleotide binding protein/GTPase Rho suppresses p53-mediated apoptosis downstream of the pre-TCR [ 127 ], the signaling steps that link the pre-TCR to inhibition of p53 are not fully elucidated. Recent evidence shows that the transcription factor Miz-1 induces the expression of the gene encoding ribosomal protein L22 (RPL22), a negative regulator of p53 translation [ 208 ], which is consistent with the role of Miz-1 and RPL22 as prosurvival molecules that antagonize p53 during the β-selection checkpoint of thymocytes [ 209 -211 ].Besides the regulators discussed in previous sections, there are some pre-TCR induced proteins that regulate thymocyte function, but whose connection with signaling components of the pre-TCR complex is poorly characterized. For instance, cyclin D3 is upregulated after β-selection to promote cell-cycle entry, and thymocytes lacking it show defective expansion and are more susceptible to oncogenic transformation [ 212 ].…”

Structural Insights into c-Myc-interacting Zinc Finger Protein-1 (Miz-1) Delineate Domains Required for DNA Scanning and Sequence-specific Binding

“…Delays of 0, 10, 30, 90, 120, 150, 250, 350, 450, 550, 650, 800, and 1000 ms and of 0, 10,30,50,70,90,110,130,150,170,190,210, and 250 ms were used to obtain T 1 and T 2 , respectively.…”