The E3 ubiquitin ligase Itch and Yap1 have antagonistic roles in the regulation of ASPP2 protein stability

Exploring the Roles of HERC2 and the NEDD4L HECT E3 Ubiquitin Ligase Subfamily in p53 Signaling and the DNA Damage Response

Cellular homeostasis is governed by the precise expression of genes that control the translation, localization, and termination of proteins. Oftentimes, environmental and biological factors can introduce mutations into the genetic framework of cells during their growth and division, and these genetic abnormalities can result in malignant transformations caused by protein malfunction. For example, p53 is a prominent tumor suppressor protein that is capable of undergoing more than 300 posttranslational modifications (PTMs) and is involved with controlling apoptotic signaling, transcription, and the DNA damage response (DDR). In this review, we focus on the molecular mechanisms and interactions that occur between p53, the HECT E3 ubiquitin ligases WWP1, SMURF1, HECW1 and HERC2, and other oncogenic proteins in the cell to explore how irregular HECT-p53 interactions can induce tumorigenesis.

YAP/TAZ Are Required to Suppress Osteogenic Differentiation of Vascular Smooth Muscle Cells

Vascular smooth muscle cells (VSMCs) represent the prevailing cell type of arterial vessels and are essential for blood vessel structure and homeostasis. They have substantial potential for phenotypic plasticity when exposed to various stimuli in their local microenvironment. How VSMCs maintain their differentiated contractile phenotype is still poorly understood. Here we demonstrate that the Hippo pathway effectors YAP and TAZ play a critical role in maintaining the differentiated contractile phenotype of VSMCs. In the absence of YAP/TAZ, VSMCs lose their differentiated phenotype and undergo osteogenic differentiation, which results in vascular calcification. Osteogenic transdifferentiation was accompanied by the upregulation of Wnt target genes. The absence of YAP/TAZ in VSMCs led to Disheveled 3 (DVL3) nuclear translocation and upregulation of osteogenesis-associated genes independent of canonical Wnt/β-catenin signaling activation. Our data indicate that cytoplasmic YAP/TAZ interact with DVL3 to avoid its nuclear translocation and osteogenic differentiation, thereby maintaining the differentiated phenotype of VSMCs.

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YAP/TAZ play an important role in maintaining vascular SMCs contractile phenotype

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Loss of YAP/TAZ in vSMCs leads to reduced expression of smooth muscle marker genes

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Loss of YAP/TAZ in vSMCs results in reduced artery contractility

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Deficiency of YAP/TAZ in vSMCs leads to osteogenic transdifferentiation

Silencing of ASPP2 promotes the proliferation, migration and invasion of triple-negative breast cancer cells via the PI3K/AKT pathway

Apoptosis-stimulating p53 protein 2 (ASPP2) is an apoptosis inducer that acts via binding with p53 and then enhancing the transcriptional activities toward pro‑apoptosis genes. ASPP2 has recently been reported to serve a major role in p53‑independent pathways. Triple‑negative breast cancer (TNBC) is a type of breast cancer that is more aggressive and highly lethal when p53 is mutated. In the present study, the mRNA level of ASPP2 was found to be suppressed in breast tumors compared with that in adjacent normal breast tissues, and the expression of ASPP2 was also decreased in a series of breast cancer cell lines compared with that in MCF‑10A normal breast cells. Downregulation of ASPP2 by specific small interfering RNA (siRNA) transfection was able to promote cell growth, reduce cell apoptosis, and contribute to cell migration and invasion. Furthermore, downregulation of ASPP2 promoted cell epithelial‑mesenchymal transition (EMT) in MDA‑MB‑231 and HCC‑1937 TNBC cells. Furthermore, it was found that when ASPP2 siRNA was transfected into MDA‑MB‑231 and HCC‑1937 cells, the expression of phosphoinositide‑3‑kinase regulatory subunit 1 (p85α) decreased and phosphorylation of protein kinase B (AKT) increased, which are key molecular regulators in the phosphatidylinositol 3-kinase (PI3K)/AKT pathway. In conclusion, the present data indicated that ASPP2 had a crucial influence on the proliferation and metastasis in TNBC, and that the functional mechanism may be p53‑independent to a great extent. ASPP2 and its link with the PI3K/AKT pathway deserve further investigation and may provide novel insights into therapeutic targets for TNBC.

p53 shades of Hippo

The three p53 family members, p53, p63 and p73, are structurally similar and share many biochemical activities. Yet, along with their common fundamental role in protecting genomic fidelity, each has acquired distinct functions related to diverse cell autonomous and non-autonomous processes. Similar to the p53 family, the Hippo signaling pathway impacts a multitude of cellular processes, spanning from cell cycle and metabolism to development and tumor suppression. The core Hippo module consists of the tumor-suppressive MST-LATS kinases and oncogenic transcriptional co-effectors YAP and TAZ. A wealth of accumulated data suggests a complex and delicate regulatory network connecting the p53 and Hippo pathways, in a highly context-specific manner. This generates multiple layers of interaction, ranging from interdependent and collaborative signaling to apparent antagonistic activity. Furthermore, genetic and epigenetic alterations can disrupt this homeostatic network, paving the way to genomic instability and cancer. This strengthens the need to better understand the nuances that control the molecular function of each component and the cross-talk between the different components. Here, we review interactions between the p53 and Hippo pathways within a subset of physiological contexts, focusing on normal stem cells and development, as well as regulation of apoptosis, senescence and metabolism in transformed cells.

ASPP2 suppresses invasion and TGF-β1-induced epithelial-mesenchymal transition by inhibiting Smad7 degradation mediated by E3 ubiquitin ligase ITCH in gastric cancer

ASPP2 regulates cell polarity and cell-cell adhesion by binding to, and co-localizing with PAR3 at tight junctions. Here we show a novel role of ASPP2 in suppressing gastric cancer (GC) invasiveness. Immunoprecipitation and immunofluorescence analyses showed that ASPP2 promoted the recruitment of PAR3 to cell-cell junctions in GC cells. Diminished expression of ASPP2 and loss of junctional PAR3 localization were significantly associated with diffuse-type histology, deeper invasion depth, positive peritoneal dissemination and worse prognosis in primary GC. ASPP2 suppressed migration and invasion of GC cells in vitro and peritoneal dissemination of GC cells in vivo in a mouse model. ASPP2 suppressed epithelial-mesenchymal transition (EMT) induced by TGF-β1-Smad2/3 signaling in GC cells through suppression of the degradation of Smad7, a negative regulator of TGF-β1-Smad2/3 signaling, by interacting with the E3 ubiquitin ligase ITCH. In conclusion, ASPP2 suppresses invasion, peritoneal dissemination and TGF-β1-induced EMT by inhibiting Smad7 degradation mediated by ITCH.