The S-phase-induced lncRNA SUNO1 promotes cell proliferation by controlling YAP1/Hippo signaling pathway

Cell cycle is a cellular process that is subject to stringent control. In contrast to the wealth of knowledge of proteins controlling the cell cycle, very little is known about the molecular role of lncRNAs (long noncoding RNAs) in cell-cycle progression. By performing genome-wide transcriptome analyses in cell-cycle-synchronized cells, we observed cell-cycle phase-specific induction of >2000 lncRNAs. Further, we demonstrate that an S-phase-upregulated lncRNA, SUNO1, facilitates cell-cycle progression by promoting YAP1-mediated gene expression. SUNO1 facilitates the cell-cycle-specific transcription of WTIP, a positive regulator of YAP1, by promoting the co-activator, DDX5-mediated stabilization of RNA polymerase II on chromatin. Finally, elevated SUNO1 levels are associated with poor cancer prognosis and tumorigenicity, implying its pro-survival role. Thus, we demonstrate the role of a S-phase up-regulated lncRNA in cell-cycle progression via modulating the expression of genes controlling cell proliferation.

WT1-interacting protein inhibits cell proliferation and tumorigenicity in non-small-cell lung cancer via the AKT/FOXO1 axis

Lung cancer is the most common cancer and the leading cause of cancer‐related death worldwide; hence, it is imperative that the mechanisms underlying the malignant properties of lung cancer be uncovered in order to efficiently treat this disease. Increasing evidence has shown that WT1‐interacting protein (WTIP) plays important roles both physiologically and pathologically in humans; however, the role of WTIP in cancer is unknown. Here, we investigated the role and mechanism of WTIP in cell proliferation and tumorigenesis of non‐small‐cell lung cancer (NSCLC). We report that WTIP is a tumor suppressor in human NSCLC. We found that WTIP expression was significantly reduced in both NSCLC cell lines and clinical specimens compared to that in normal controls; this reduction was largely attributed to promoter hypermethylation. Downregulation of WTIP significantly correlates with poor prognosis and predicts a shorter overall survival and progression‐free survival among NSCLC patients. Moreover, ectopic overexpression of WTIP dramatically inhibits cell proliferation and tumorigenesis in vitro and in vivo; conversely, depletion of WTIP expression shows the opposite effects. Mechanistically, WTIP impairs AKT phosphorylation and activation, leading to enhanced expression and transcriptional activity of FOXO1, which further increases p21Cip1 and p27Kip1, and decreases cyclin D1, which consequently results in cell cycle arrest. Collectively, the results of the current study indicate that WTIP is an important proliferation‐related gene and that WTIP expression may represent a novel prognostic biomarker for NSCLC.

Identification of the UBA2-WTIP fusion gene in acute myeloid leukemia

Identifying and targeting oncogenic fusion genes have revolutionized the treatment of leukemia, such as PML-RARα fusion gene in acute promyelocytic leukemia. Here we identified an intrachromosomal fusion gene located on chromosome 19q.13 between UBA2 and WTIP gene in a case of acute myeloid leukemia. The UBA2-WTIP fusion gene contains the N-terminal E1_enzyme_family, VAE_Ubl domains of UBA2, and the C-terminal LIM domains of WTIP. The UBA2-WTIP fusion was detected by reverse transcriptase polymerase chain reaction and Sanger sequencing in 19 of 56 acute myeloid leukemia samples (33.9%). Ectopic expression of the UBA2-WTIP fusion in human acute myeloid leukemia KG-1a cells showed enhanced cell proliferation both in vitro and in vivo. The UBA2-WTIP fusion induced phosphorylation of STAT3, STAT5 and ERK1/2, and abrogates WTIP-mediated mammalian processing body formation. Finally, triptolide displayed selective cytotoxicity against KG-1a cells harboring the UBA2-WTIP fusion. Collectively, our findings suggest that the UBA2-WTIP fusion is an oncogenic fusion gene, as well as a promising therapeutic target for the treatment of acute myeloid leukemia.

Argonaute Utilization for miRNA Silencing Is Determined by Phosphorylation-Dependent Recruitment of LIM-Domain-Containing Proteins

As core components of the microRNA-induced silencing complex (miRISC), Argonaute (AGO) proteins interact with TNRC6 proteins, recruiting other effectors of translational repression/mRNA destabilization. Here, we show that LIMD1 coordinates the assembly of an AGO-TNRC6 containing miRISC complex by binding both proteins simultaneously at distinct interfaces. Phosphorylation of AGO2 at Ser 387 by Akt3 induces LIMD1 binding, which in turn enables AGO2 to interact with TNRC6A and downstream effector DDX6. Conservation of this serine in AGO1 and 4 indicates this mechanism may be a fundamental requirement for AGO function and miRISC assembly. Upon CRISPR-Cas9-mediated knockout of LIMD1, AGO2 miRNA-silencing function is lost and miRNA silencing becomes dependent on a complex formed by AGO3 and the LIMD1 family member WTIP. The switch to AGO3 utilization occurs due to the presence of a glutamic acid residue (E390) on the interaction interface, which allows AGO3 to bind to LIMD1, AJUBA, and WTIP irrespective of Akt signaling.

Nephrin Suppresses Hippo Signaling through the Adaptor Proteins Nck and WTIP

Podocytes are key components of the kidney blood filtration barrier, and their ability to withstand hemodynamic strain is proposed to be closely tied to their unique and flexible cytoarchitecture. However, the mechanisms that control such mechanotransduction are poorly understood. We have previously established that tyrosine phosphorylation of the transmembrane protein nephrin promotes recruitment of the Nck1/2 cytoskeletal adaptor proteins and downstream actin remodeling. We now reveal that Nck integrates nephrin with the Hippo kinase cascade through association with the adaptor protein WTIP. Using mutational analysis, we show that Nck sequesters WTIP and its binding partner Lats1 to phosphorylated nephrin, resulting in decreased phospho-activation of Lats1. We further demonstrate that, coincident with nephrin dephosphorylation in a transient model of podocyte injury in mice, Lats1 is rapidly activated, and this precedes significant down-regulation of the transcription regulator Yap. Moreover, we show reduced levels of Yap protein in mice with chronic disruption of nephrin phospho-signaling. Together, these findings support the existence of a dynamic molecular link between nephrin signaling and the canonical Hippo pathway in podocytes, which may facilitate the conversion of mechanical cues to biochemical signals promoting podocyte viability.

Role of Asxl1 in kidney podocyte development via its interaction with Wtip

Additional sex comb-like (ASXL) family proteins are chromatin factors that function in transcriptional activation and repression. However, the underlying mechanisms and biological implications have not been well established. Here, we identified a LIM domain-containing protein, Wilms tumor 1-interacting protein (WTIP), as an ASXL1-binding partner. Biochemical assays confirmed an interaction between the murine homologs Asxl1 and Wtip. The suppressive role of Wtip in WT1 function and the expression of Wtip in kidney podocytes prompted us to investigate the role of Asxl1 in the kidney using Asxl1-null mice. In homozygous Asxl1(-/-) embryos, defects in kidney size and glomerular podocyte morphology were observed. Furthermore, up-regulation of Wt1/Wtip target genes was observed in the kidneys of Asxl1-null embryos. Overall, these findings implicate Asxl1 in the maintenance of podocyte structure via its association with Wtip and in the regulation of WT1 signaling during early kidney development.

WTIP interacts with ASXL2 and blocks ASXL2-mediated activation of retinoic acid signaling

The Asx-like (ASXL) family proteins are chromatin factors that play dual roles in transcriptional activation and repression. ASXL2 is highly expressed in the heart and is required for proper heart development and function. Here, we identify a novel ASXL2-binding partner, the LIM domain-containing protein WTIP. Genetic and biochemical assays show a direct interaction between ASXL2 and WTIP. In HeLa cells, ASXL2 enhances retinoic acid-dependent luciferase activity, while WTIP represses it. Furthermore, WTIP blocks ASXL2's stimulatory effect on transcription. In addition, we found that ASXL2 and WTIP are expressed in mouse embryonic epicardial cells, a tissue that is regulated by retinoic acid signaling. Together, these results implicate ASXL2 and WTIP in regulation of retinoic acid signaling during heart development.