Progress on the role of LIN28A/B in tumor development and progression.

LIN28A and its homolog LIN28B are highly conserved RNA-binding proteins that play important roles in early embryonic development, somatic cell reprogramming, metabolism and tumorigenesis. LIN28A/B are highly expressed in a variety of malignant tumors such as breast cancer. They play important roles in the initiation, maintenance, and metastasis of tumors and are associated with poor prognosis. Previous studies have shown that the main regulatory mechanisms of LIN28A/B include let-7s dependent ways and let-7s independent ways, such as directly targeting mRNA. In this review, we summarize the function and molecular regulatory mechanisms of LIN28A/B in malignant tumors such as liver cancer, breast cancer and colorectal cancer, in order to provide references for further exploring the function and mechanism of LIN28A/B and their possible roles in clinical applications.

Liver cancer initiation requires translational activation by an oncofetal regulon involving LIN28 proteins.

It is unknown which posttranscriptional regulatory mechanisms are required for oncogenic competence. Here, we show that the LIN28 family of RNA-binding proteins (RBPs), which facilitate posttranscriptional RNA metabolism within ribonucleoprotein networks, is essential for the initiation of diverse oncotypes of hepatocellular carcinoma (HCC). In HCC models driven by NRASG12V/Tp53, CTNNB1/YAP/Tp53, or AKT/Tp53, mice without Lin28a and Lin28b were markedly impaired in cancer initiation. We biochemically defined an oncofetal regulon of 15 factors connected to LIN28 through direct mRNA and protein interactions. Interestingly, all were RBPs and only 1 of 15 was a Let-7 target. Polysome profiling and reporter assays showed that LIN28B directly increased the translation of 8 of these 15 RBPs. As expected, overexpression of LIN28B and IGFBP1-3 was able to genetically rescue cancer initiation. Using this platform to probe components downstream of LIN28, we found that 8 target RBPs were able to restore NRASG12V/Tp53 cancer formation in Lin28a/Lin28b-deficient mice. Furthermore, these LIN28B targets promote cancer initiation through an increase in protein synthesis. LIN28B, central to an RNP regulon that increases translation of RBPs, is important for tumor initiation in the liver.

Image-based quantification of histological features as a function of spatial location using the Tissue Positioning System.

BACKGROUND: Tissues such as the liver lobule, kidney nephron, and intestinal gland exhibit intricate patterns of zonated gene expression corresponding to distinct cell types and functions. To quantitatively understand zonation, it is important to measure cellular or genetic features as a function of position along a zonal axis. While it is possible to manually count, characterize, and locate features in relation to the zonal axis, it is labor-intensive and difficult to do manually while maintaining precision and accuracy. METHODS: We addressed this challenge by developing a deep-learning-based quantification method called the "Tissue Positioning System" (TPS), which can automatically analyze zonation in the liver lobule as a model system. FINDINGS: By using algorithms that identified vessels, classified vessels, and segmented zones based on the relative position along the portal vein to central vein axis, TPS was able to spatially quantify gene expression in mice with zone specific reporters. INTERPRETATION: TPS could discern expression differences between zonal reporter strains, ages, and disease states. TPS could also reveal the zonal distribution of cells previously thought to be positioned randomly. The design principles of TPS could be generalized to other tissues to explore the biology of zonation. FUNDING: CPRIT (RP190208, RP220614, RP230330) and NIH (P30CA142543, R01AA028791, R01CA251928, R01DK1253961, R01GM140012, 1R01GM141519, 1R01DE030656, 1U01CA249245). The Pollack Foundation, Simmons Comprehensive Cancer Center Cancer & Obesity Translational Pilot Award, and the Emerging Leader Award from the Mark Foundation For Cancer Research (#21-003-ELA).

IGFBP2 expressing midlobular hepatocytes preferentially contribute to liver homeostasis and regeneration.

Although midlobular hepatocytes in zone 2 are a recently identified cellular source for liver homeostasis and regeneration, these cells have not been exclusively fate mapped. We generated an Igfbp2-CreER knockin strain that specifically labels midlobular hepatocytes. During homeostasis over 1 year, zone 2 hepatocytes increased in abundance from occupying 21%-41% of the lobular area. After either pericentral injury with carbon tetrachloride or periportal injury with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC), IGFBP2+ cells replenished lost hepatocytes in zones 3 and 1, respectively. IGFBP2+ cells also preferentially contributed to regeneration after 70% partial hepatectomy, as well as liver growth during pregnancy. Because IGFBP2 labeling increased substantially with fasting, we used single nuclear transcriptomics to explore zonation as a function of nutrition, revealing that the zonal division of labor shifts dramatically with fasting. These studies demonstrate the contribution of IGFBP2-labeled zone 2 hepatocytes to liver homeostasis and regeneration.

cGAS restricts colon cancer development by protecting intestinal barrier integrity.

The DNA-sensing enzyme cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) regulates inflammation and immune defense against pathogens and malignant cells. Although cGAS has been shown to exert antitumor effects in several mouse models harboring transplanted tumor cell lines, its role in tumors arising from endogenous tissues remains unknown. Here, we show that deletion of cGAS in mice exacerbated chemical-induced colitis and colitis-associated colon cancer (CAC). Interestingly, mice lacking cGAS were more susceptible to CAC than those lacking stimulator of interferon genes (STING) or type I interferon receptor under the same conditions. cGAS but not STING is highly expressed in intestinal stem cells. cGAS deficiency led to intestinal stem cell loss and compromised intestinal barrier integrity upon dextran sodium sulfate-induced acute injury. Loss of cGAS exacerbated inflammation, led to activation of STAT3, and accelerated proliferation of intestinal epithelial cells during CAC development. Mice lacking cGAS also accumulated myeloid-derived suppressive cells within the tumor, displayed enhanced Th17 differentiation, but reduced interleukin (IL)-10 production. These results indicate that cGAS plays an important role in controlling CAC development by defending the integrity of the intestinal mucosa.

Liver homeostasis is maintained by midlobular zone 2 hepatocytes.

The liver is organized into zones in which hepatocytes express different metabolic enzymes. The cells most responsible for liver repopulation and regeneration remain undefined, because fate mapping has only been performed on a few hepatocyte subsets. Here, 14 murine fate-mapping strains were used to systematically compare distinct subsets of hepatocytes. During homeostasis, cells from both periportal zone 1 and pericentral zone 3 contracted in number, whereas cells from midlobular zone 2 expanded in number. Cells within zone 2, which are sheltered from common injuries, also contributed to regeneration after pericentral and periportal injuries. Repopulation from zone 2 was driven by the insulin-like growth factor binding protein 2-mechanistic target of rapamycin-cyclin D1 (IGFBP2-mTOR-CCND1) axis. Therefore, different regions of the lobule exhibit differences in their contribution to hepatocyte turnover, and zone 2 is an important source of new hepatocytes during homeostasis and regeneration.

Dendrimer-Based Lipid Nanoparticles Deliver Therapeutic FAH mRNA to Normalize Liver Function and Extend Survival in a Mouse Model of Hepatorenal Tyrosinemia Type I.

mRNA-mediated protein replacement represents a promising concept for the treatment of liver disorders. Children born with fumarylacetoacetate hydrolase (FAH) mutations suffer from Hepatorenal Tyrosinemia Type 1 (HT-1) resulting in renal dysfunction, liver failure, neurological impairments, and cancer. Protein replacement therapy using FAH mRNA offers tremendous potential to cure HT-1, but is currently hindered by the development of effective mRNA carriers that can function in diseased livers. Structure-guided, rational optimization of 5A2-SC8 mRNA-loaded dendrimer lipid nanoparticles (mDLNPs) increases delivery potency of FAH mRNA, resulting in functional FAH protein and sustained normalization of body weight and liver function in FAH-/- knockout mice. Optimization using luciferase mRNA produces DLNP carriers that are efficacious at mRNA doses as low as 0.05 mg kg-1 in vivo. mDLNPs transfect > 44% of all hepatocytes in the liver, yield high FAH protein levels (0.5 mg kg-1 mRNA), and are well tolerated in a knockout mouse model with compromised liver function. Genetically engineered FAH-/- mice treated with FAH mRNA mDLNPs have statistically equivalent levels of TBIL, ALT, and AST compared to wild type C57BL/6 mice and maintain normal weight throughout the month-long course of treatment. This study provides a framework for the rational optimization of LNPs to improve delivery of mRNA broadly and introduces a specific and viable DLNP carrier with translational potential to treat genetic diseases of the liver.

Arid1a Has Context-Dependent Oncogenic and Tumor Suppressor Functions in Liver Cancer.

ARID1A, an SWI/SNF chromatin-remodeling gene, is commonly mutated in cancer and hypothesized to be tumor suppressive. In some hepatocellular carcinoma patients, ARID1A was highly expressed in primary tumors but not in metastatic lesions, suggesting that ARID1A can be lost after initiation. Mice with liver-specific homozygous or heterozygous Arid1a loss were resistant to tumor initiation while ARID1A overexpression accelerated initiation. In contrast, homozygous or heterozygous Arid1a loss in established tumors accelerated progression and metastasis. Mechanistically, gain of Arid1a function promoted initiation by increasing CYP450-mediated oxidative stress, while loss of Arid1a within tumors decreased chromatin accessibility and reduced transcription of genes associated with migration, invasion, and metastasis. In summary, ARID1A has context-dependent tumor-suppressive and oncogenic roles in cancer.

RNA polymerase III component Rpc9 regulates hematopoietic stem and progenitor cell maintenance in zebrafish.

Hematopoietic stem and progenitor cells (HSPCs) are capable of self-renewal and replenishing all lineages of blood cells throughout life and are thus crucial for tissue homeostasis. However, the mechanism regulating HSPC development is still incompletely understood. Here, we isolate a zebrafish mutant with defective T lymphopoiesis and positional cloning identifies that Rpc9, a component of DNA-directed RNA polymerase III (Pol III) complex, is responsible for the mutant phenotype. Further analysis shows that rpc9 deficiency leads to the impairment of HSPCs and their derivatives in zebrafish embryos. Excessive apoptosis is observed in the caudal hematopoietic tissue (CHT; the equivalent of fetal liver in mammals) of rpc9(-/-) embryos and the hematopoietic defects in these embryos can be fully rescued by suppression of p53 Thus, our work illustrates that Rpc9, a component of Pol III, plays an important tissue-specific role in HSPC maintenance during zebrafish embryogenesis and might be conserved across vertebrates, including mammals.

A Highly Efficient and Simple Construction Strategy for Producing Recombinant Baculovirus Bombyx mori Nucleopolyhedrovirus.

The silkworm baculovirus expression system is widely used to produce recombinant proteins. Several strategies for constructing recombinant viruses that contain foreign genes have been reported. Here, we developed a novel defective-rescue BmNPV Bacmid (reBmBac) expression system. A CopyControl origin of replication was introduced into the viral genome to facilitate its genetic manipulation in Escherichia coli and to ensure the preparation of large amounts of high quality reBmBac DNA as well as high quality recombinant baculoviruses. The ORF1629, cathepsin and chitinase genes were partially deleted or rendered defective to improve the efficiency of recombinant baculovirus generation and the expression of foreign genes. The system was validated by the successful expression of luciferase reporter gene and porcine interferon γ. This system can be used to produce batches of recombinant baculoviruses and target proteins rapidly and efficiently in silkworms.

Direct regulation of p53 by miR-142a-3p mediates the survival of hematopoietic stem and progenitor cells in zebrafish.

Hematopoietic stem and progenitor cells have the capacity to self-renew and differentiate into all blood cell lineages, and thus sustain life-long homeostasis of the hematopoietic system. Although intensive studies have focused on the orchestrated genetic network of hematopoietic stem and progenitor cell specification and expansion, relatively little is known on the regulation of hematopoietic stem and progenitor cell survival during embryogenesis. Here, we generated two types of miR-142a-3p genetic mutants in zebrafish and showed that the loss-of-function mutants displayed severe reduction of hematopoietic stem and progenitor cells. Further analysis showed that the diminished proliferation and excessive apoptosis in miR-142a-3p mutants were attributed to the increased p53 signaling. Mechanistically, we demonstrated that miR-142a-3p directly targets p53 during hematopoietic stem and progenitor cell development, and the hematopoietic stem and progenitor cell survival defect in miR-142a-3p mutants could be rescued by loss of p53. Therefore, our work reveals the significance of the miR-142a-3p-p53 pathway in controlling hematopoietic stem and progenitor cell survival, and thus advances our understanding of the role of p53 in vertebrate hematopoiesis.

Ncor2 is required for hematopoietic stem cell emergence by inhibiting Fos signaling in zebrafish.

Nuclear receptor corepressors (Ncors) are important for developmental and homeostatic processes in vertebrates, which exert transcriptional repression by coordinating with histone deacetylases. However, little is known about their roles in definitive hematopoiesis. In this study, we show that in zebrafish, ncor2 is required for hematopoietic stem cell (HSC) development by repressing fos-vegfd signaling. ncor2 is specifically expressed in the aorta-gonad-mesonephros (AGM) region in zebrafish embryos. ncor2 deficiency reduced the population of HSCs in both the AGM region and T cells in the thymus. Mechanistically, ncor2 knockdown upregulated fos transcription by modulating the acetylation level in the fos promoter region, which then enhanced Vegfd signaling. Consequently, the augmented Vegfd signaling induced Notch signaling to promote the arterial endothelial fate, therefore, possibly repressing the hemogenic endothelial specification, which is a prerequisite for HSC emergence. Thus, our findings identify a novel regulatory mechanism for Ncor2 through Fos-Vegfd-Notch signaling cascade during HSC development in zebrafish embryos.

Fev regulates hematopoietic stem cell development via ERK signaling.

Reprogramming of somatic cells to desired cell types holds great promise in regenerative medicine. However, production of transplantable hematopoietic stem cells (HSCs) in vitro by defined factors has not yet been achieved. Therefore, it is critical to fully understand the molecular mechanisms of HSC development in vivo. Here, we show that Fev, an ETS transcription factor, is a pivotal regulator of HSC development in vertebrates. In fev-deficient zebrafish embryos, the first definitive HSC population was compromised and fewer T cells were found in the thymus. Genetic and chemical analyses support a mechanism whereby Fev regulates HSC through direct regulation of ERK signaling. Blastula transplant assay demonstrates that Fev regulation of HSC development is cell autonomous. Experiments performed with purified cord blood show that fev is expressed and functions in primitive HSCs in humans, indicating its conserved role in higher vertebrates. Our data indicate that Fev-ERK signaling is essential for hemogenic endothelium-based HSC development.

Regulatory mechanisms of thymus and T cell development.

The thymus is a central hematopoietic organ which produces mature T lymphocytes with diverse antigen specificity. During development, the thymus primordium is derived from the third pharyngeal endodermal pouch, and then differentiates into cortical and medullary thymic epithelial cells (TECs). TECs represent the primary functional cell type that forms the unique thymic epithelial microenvironment which is essential for intrathymic T-cell development, including positive selection, negative selection and emigration out of the thymus. Our understanding of thymopoiesis has been greatly advanced by using several important animal models. This review will describe progress on the molecular mechanisms involved in thymus and T cell development with particular focus on the signaling and transcription factors involved in this process in mouse and zebrafish.

Foxn1 maintains thymic epithelial cells to support T-cell development via mcm2 in zebrafish.

The thymus is mainly comprised of thymic epithelial cells (TECs), which form the unique thymic epithelial microenvironment essential for intrathymic T-cell development. Foxn1, a member of the forkhead transcription factor family, is required for establishing a functional thymic rudiment. However, the molecular mechanisms underlying the function of Foxn1 are still largely unclear. Here, we show that Foxn1 functions in thymus development through Mcm2 in the zebrafish. We demonstrate that, in foxn1 knockdown embryos, the thymic rudiment is reduced and T-cell development is impaired. Genome-wide expression profiling shows that a number of genes, including some known thymopoiesis genes, are dysregulated during the initiation of the thymus primordium and immigration of T-cell progenitors to the thymus. Functional and epistatic studies show that mcm2 and cdca7 are downstream of Foxn1, and mcm2 is a direct target gene of Foxn1 in TECs. Finally, we find that the thymus defects in foxn1 and mcm2 morphants might be attributed to reduced cell proliferation rather than apoptosis. Our results reveal that the foxn1-mcm2 axis plays a central role in the genetic regulatory network controlling thymus development in zebrafish.

A blood flow-dependent klf2a-NO signaling cascade is required for stabilization of hematopoietic stem cell programming in zebrafish embryos.

Blood flow has long been thought to be important for vessel development and function, but its role in HSC development is not yet fully understood. Here, we take advantage of zebrafish embryos with circulation defects that retain relatively normal early development to illustrate the combinatorial roles of genetic and hemodynamic forces in HSC development. We show that blood flow is not required for initiation of HSC gene expression, but instead is indispensable for its maintenance. Knockdown of klf2a mimics the silent heart (sih/tnnt2a) phenotype while overexpression of klf2a in tnnt2a morphant embryos can rescue HSC defects, suggesting that klf2a is a downstream mediator of blood flow. Furthermore, the expression of NO synthase (nos) was reduced in klf2a knockdown embryos, and ChIP analysis showed that endogenous Klf2a is bound to the promoters of nos genes in vivo, indicating direct gene regulation. Finally, administration of the NO agonist S-nitroso N-acetylpenicillamine (SNAP) can restore HSC development in tnnt2a and klf2a morphants, suggesting that NO signaling is downstream of Klf2a which is induced by hemodynamic forces. Taken together, we have demonstrated that blood flow is essential for HSC development and is mediated by a klf2a-NO signaling cascade in zebrafish.