Breast cancer preferentially develops osteolytic bone metastasis, which makes patients suffer from pain, fractures and spinal cord compression. Accumulating evidences have shown that exosomes play an ...irreplaceable role in pre-metastatic niche formation as a communication messenger. However, the function of exosomes secreted by breast cancer cells remains incompletely understood in bone metastasis of breast cancer.
Mouse xenograft models and intravenous injection of exosomes were applied for analyzing the role of breast cancer cell-derived exosomes
. Effects of exosomes secreted by the mildly metastatic MDA231 and its subline SCP28 with highly metastatic ability on osteoclasts formation were confirmed by TRAP staining, ELISA, microcomputed tomography, histomorphometric analyses, and pit formation assay. The candidate exosomal miRNAs for promoting osteoclastogenesis were globally screened by RNA-seq. qRT-PCR, western blot, confocal microscopy, and RNA interfering were performed to validate the function of exosomal miRNA.
Implantation of SCP28 tumor cells
leads to increased osteoclast activity and reduced bone density, which contributes to the formation of pre-metastatic niche for tumor cells. We found SCP28 cells-secreted exosomes are critical factors in promoting osteoclast differentiation and activation, which consequently accelerates bone lesion to reconstruct microenvironment for bone metastasis. Mechanistically, exosomal miR-21 derived from SCP28 cells facilitates osteoclastogenesis through regulating PDCD4 protein levels. Moreover, miR-21 level in serum exosomes of breast cancer patients with bone metastasis is significantly higher than that in other subpopulations.
Our results indicate that breast cancer cell-derived exosomes play an important role in promoting breast cancer bone metastasis, which is associated with the formation of pre-metastatic niche via transferring miR-21 to osteoclasts. The data from patient samples further reflect the significance of miR-21 as a potential target for clinical diagnosis and treatment of breast cancer bone metastasis.
The kinase PDK1 is a crucial regulator for immune cell development by connecting PI3K to downstream AKT signaling. However, the roles of PDK1 in CD4
T cell differentiation, especially in T follicular ...helper (Tfh) cell, remain obscure. Here we reported PDK1 intrinsically promotes the Tfh cell differentiation and germinal center responses upon acute infection by using conditional knockout mice. PDK1 deficiency in T cells caused severe defects in both early differentiation and late maintenance of Tfh cells. The expression of key Tfh regulators was remarkably downregulated in PDK1-deficient Tfh cells, including
,
,
, and
. Mechanistically, ablation of PDK1 led to impaired phosphorylation of AKT and defective activation of mTORC1, resulting in substantially reduced expression of Hif1α and p-STAT3. Meanwhile, decreased p-AKT also suppresses mTORC2-associated GSK3β activity in PDK1-deficient Tfh cells. These integrated effects contributed to the dramatical reduced expression of TCF1 and ultimately impaired the Tfh cell differentiation.
Introduction
Intrathymic T-cell development is a coordinated process accompanied by dynamic changes in gene expression. Although the transcriptome characteristics of developing T cells in both human ...fetal and postnatal thymus at single-cell resolution have been revealed recently, the differences between human prenatal and postnatal thymocytes regarding the ontogeny and early events of T-cell development still remain obscure. Moreover, the transcriptional heterogeneity and posttranscriptional gene expression regulation such as alternative polyadenylation at different stages are also unknown.
Method
In this study, we performed integrative single-cell analyses of thymocytes at distinct developmental stages.
Results
The subsets of prenatal CD4
–
CD8
–
double-negative (DN) cells, the most immature thymocytes responsible for T-cell lineage commitment, were characterized. By comprehensively comparing prenatal and postnatal DN cells, we revealed significant differences in some key gene expressions. Specifically, prenatal DN subpopulations exhibited distinct biological processes and markedly activated several metabolic programs that may be coordinated to meet the required bioenergetic demands. Although showing similar gene expression patterns along the developmental path, prenatal and postnatal thymocytes were remarkably varied regarding the expression dynamics of some pivotal genes for cell cycle, metabolism, signaling pathway, thymus homing, and T-cell commitment. Finally, we quantified the transcriptome-wide changes in alternative polyadenylation across T-cell development and found diverse preferences of polyadenylation site usage in divergent populations along the T-cell commitment trajectory.
Discussion
In summary, our results revealed transcriptional heterogeneity and a dynamic landscape of alternative polyadenylation during T-cell development in both human prenatal and postnatal thymus, providing a comprehensive resource for understanding T lymphopoiesis in human thymus.
Activation-induced cytidine deaminase (AID) mediates class switching by binding to a small fraction of single-stranded DNA (ssDNA) to diversify the antibody repertoire. The precise mechanism for ...highly selective AID targeting in the genome has remained elusive. Here, we report an RNA-binding protein, ROD1 (also known as PTBP3), that is both required and sufficient to define AID-binding sites genome-wide in activated B cells. ROD1 interacts with AID via an ultraconserved loop, which proves to be critical for the recruitment of AID to ssDNA using bi-directionally transcribed nascent RNAs as stepping stones. Strikingly, AID-specific mutations identified in human patients with hyper-IgM syndrome type 2 (HIGM2) completely disrupt the AID interacting surface with ROD1, thereby abolishing the recruitment of AID to immunoglobulin (Ig) loci. Together, our results suggest that bi-directionally transcribed RNA traps the RNA-binding protein ROD1, which serves as a guiding system for AID to load onto specific genomic loci to induce DNA rearrangement during immune responses.
N6-methyladenosine (m6A) methyltransferase Mettl3 is involved in conventional T cell immunity; however, its role in innate immune cells remains largely unknown. Here, we show that Mettl3 ...intrinsically regulates invariant natural killer T (iNKT) cell development and function in an m6A-dependent manner. Conditional ablation of Mettl3 in CD4+CD8+ double-positive (DP) thymocytes impairs iNKT cell proliferation, differentiation, and cytokine secretion, which synergistically causes defects in B16F10 melanoma resistance. Transcriptomic and epi-transcriptomic analyses reveal that Mettl3 deficiency disturbs the expression of iNKT cell-related genes with altered m6A modification. Strikingly, Mettl3 modulates the stability of the Creb1 transcript, which in turn controls the protein and phosphorylation levels of Creb1. Furthermore, conditional targeting of Creb1 in DP thymocytes results in similar phenotypes of iNKT cells lacking Mettl3. Importantly, ectopic expression of Creb1 largely rectifies such developmental defects in Mettl3-deficient iNKT cells. These findings reveal that the Mettl3-m6A-Creb1 axis plays critical roles in regulating iNKT cells at the post-transcriptional layer.
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•Mettl3-dependent m6A methylation plays a key role in iNKT cell development•A comprehensive m6A landscape of low-input iNKT cells is established by m6A-LACE-seq•Mettl3 deficiency disrupts iNKT cell-related gene network in an m6A-dependent manner•The Mettl3-m6A-Creb1 axis is critical for sustaining iNKT cell differentiation and function
You et al. demonstrate that Mettl3 is essential for regulating iNKT cell proliferation, differentiation, and melanoma resistance. The study highlights the critical role of Mettl3-dependent m6A modification in controlling iNKT cell-related gene expression, particularly in maintaining the stability of Creb1 and c-Myc transcripts.
Tcf-1 (encoded by Tcf7) not only plays critical roles in promoting T cell development and differentiation but also has been identified as a tumor suppressor involved in preventing T cell malignancy. ...However, the comprehensive mechanisms of Tcf-1 involved in T cell transformation remain poorly understood. In this study, Tcf7
mice were crossed with Vav-cre, Lck-cre, or Cd4-cre mice to delete Tcf-1 conditionally at the beginning of the HSC, DN2-DN3, or DP stage, respectively. The defective T cell development phenotypes became gradually less severe as the deletion stage became more advanced in distinct mouse models. Interestingly, consistent with Tcf7
mice, Tcf7
Vav-cre mice developed aggressive T cell lymphoma within 45 weeks, but no tumors were generated in Tcf7
Lck-cre or Tcf7
Cd4-cre mice. Single-cell RNA-seq (ScRNA-seq) indicated that ablation of Tcf-1 at distinct phases can subdivide DN1 cells into three clusters (C1, C2, and C3) and DN2-DN3 cells into three clusters (C4, C5, and C6). Moreover, Tcf-1 deficiency redirects bifurcation among divergent cell fates, and clusters C1 and C4 exhibit high potential for leukemic transformation. Mechanistically, we found that Tcf-1 directly binds and mediates chromatin accessibility for both typical T cell regulators and proto-oncogenes, including Myb, Mycn, Runx1, and Lyl1 in the DN1 phase and Lef1, Id2, Dtx1, Fyn, Bcl11b, and Zfp36l2 in the DN2-DN3 phase. The aberrant expression of these genes due to Tcf-1 deficiency in very early T cells contributes to subsequent tumorigenesis. Thus, we demonstrated that Tcf-1 plays stage-specific roles in regulating early thymocyte development and transformation, providing new insights and evidence for clinical trials on T-ALL leukemia.
Invariant natural killer T (iNKT) cells are highly conserved innate-like T lymphocytes that originate from CD4
CD8
double-positive (DP) thymocytes. Here, we report that serine/arginine splicing ...factor 1 (SRSF1) intrinsically regulates iNKT cell development by directly targeting Myb and balancing the abundance of short and long isoforms. Conditional ablation of SRSF1 in DP cells led to a substantially diminished iNKT cell pool due to defects in proliferation, survival, and TCRα rearrangement. The transition from stage 0 to stage 1 of iNKT cells was substantially blocked, and the iNKT2 subset was notably diminished in SRSF1-deficient mice. SRSF1 deficiency resulted in aberrant expression of a series of regulators that are tightly correlated with iNKT cell development and iNKT2 differentiation, including Myb, PLZF, Gata3, ICOS, and CD5. In particular, we found that SRSF1 directly binds and regulates pre-mRNA alternative splicing of Myb and that the expression of the short isoform of Myb is substantially reduced in SRSF1-deficient DP and iNKT cells. Strikingly, ectopic expression of the Myb short isoform partially rectified the defects caused by ablation of SRSF1. Furthermore, we confirmed that the SRSF1-deficient mice exhibited resistance to acute liver injury upon α-GalCer and Con A induction. Our findings thus uncovered a previously unknown role of SRSF1 as an essential post-transcriptional regulator in iNKT cell development and functional differentiation, providing new clinical insights into iNKT-correlated disease.
T cell factor 1 (Tcf1) is known as a critical mediator for natural killer (NK) cell development and terminal maturation. However, its essential targets and precise mechanisms involved in early NK ...progenitors (NKP) are not well clarified. To investigate the role of Tcf1 in NK cells at distinct developmental phases, we employed three kinds of genetic mouse models, namely,
,
and
mice, respectively. Similar to Tcf1 germline knockout mice, we found notably diminished cell number and defective development in BM NK cells from all strains. In contrast,
mice exhibited modest defects in splenic NK cells compared with those in the other two strains. By analyzing the published ATAC-seq and ChIP-seq data, we found that Tcf1 directly targeted 110 NK cell-related genes which displayed differential accessibility in the absence of Tcf1. Along with this clue, we further confirmed that a series of essential regulators were expressed aberrantly in distinct BM NK subsets with conditional ablating Tcf1 at NKP stage.
,
,
,
,
,
,
,
,
,
,
, and
were downregulated, whereas
and
were upregulated in distinct NK subsets due to Tcf1 deficiency. The dysregulation of these genes jointly caused severe defects in NK cells lacking Tcf1. Thus, our study identified essential targets of Tcf1 in NK cells, providing new insights into Tcf1-dependent regulatory programs in step-wise governing NK cell development.
Abstract
T follicular helper (T
FH
) cells are specialized effector CD4
+
T cells critical to humoral immunity. Whether post-transcriptional regulation has a function in T
FH
cells is unknown. Here, ...we show conditional deletion of METTL3 (a methyltransferase catalyzing mRNA
N
6
-methyladenosine (m
6
A) modification) in CD4
+
T cells impairs T
FH
differentiation and germinal center responses in a cell-intrinsic manner in mice. METTL3 is necessary for expression of important T
FH
signature genes, including
Tcf7
,
Bcl6
,
Icos
and
Cxcr5
and these effects depend on intact methyltransferase activity. m
6
A-miCLIP-seq shows the 3′ UTR of
Tcf7
mRNA is subjected to METTL3-dependent m
6
A modification. Loss of METTL3 or mutation of the
Tcf7
3′ UTR m
6
A site results in accelerated decay of
Tcf7
transcripts. Importantly, ectopic expression of TCF-1 (encoded by
Tcf7
) rectifies T
FH
defects owing to METTL3 deficiency. Our findings indicate that METTL3 stabilizes
Tcf7
transcripts via m
6
A modification to ensure activation of a T
FH
transcriptional program, indicating a pivotal function of post-transcriptional regulation in promoting T
FH
cell differentiation.
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