A novel interaction between ATOH8 and PPP3CB

Significant role of PPP3CB in malignant gliomas development, prognosis and potential therapeutic application-a study based on comprehensive bioinformatics, cell experiments and immunohistochemistry analyses

Introduction

Malignant gliomas are the most prevalent and fatal types of primary malignant brain tumors with poor prognosis. Protein phosphatase 3 catalytic subunit beta (PPP3CB) is a pivotal constituent of the Ca2+/calmodulin-dependent serine/threonine protein phosphatases and widely expressed in brain. We aimed at identifying whether PPP3CB has potential in being a novel biomarker of malignant gliomas, bringing new insights to clinical management and therapy.

Methods

Transcriptomes and clinical data of Glioblastoma (GBM) and low-grade glioma (LGG) samples were downloaded from TCGA and CGGA. We first explored the expressional and survival features of tumor tissues. Then, PPP3CB-associated genes were identified and their functional pathways were explored through GSEA analyses. Western blotting was conducted to modify PPP3CB expression. Samples of glioma patients and healthy controls were collected and immunohistochemistry (IHC) staining was performed to detect protein level. Further, we carried out an immune infiltration analysis, explored the correlation between PPP3CB and immune checkpoint genes, as well as to assessed the tumor mutation burden (TMB) and tumor microenvironment score (TMEscore) of PPP3CB.

Results

PPP3CB expression in malignant glioma tissues was significantly downregulated and was considered an independent prognostic factor. Several functional pathways were observed through functional pathway analyses. PPP3CB's expression was strongly related to the infiltration of various immune cells and expression of key immune checkpoint genes. PPP3CB expression in high-grade gliomas was significantly lower, affecting glioma cells' proliferation and apoptosis in vitro.

Conclusion

PPP3CB was a potential biomarker for the diagnosis and prognosis of malignant gliomas.

Calcineurin in development and disease

Calcineurin (CaN) is a unique calcium (Ca²⁺) and calmodulin (CaM)-dependent serine/threonine phosphatase that becomes activated in the presence of increased intracellular Ca²⁺ level. CaN then functions to dephosphorylate target substrates including various transcription factors, receptors, and channels. Once activated, the CaN signaling pathway participates in the development of multiple organs as well as the onset and progression of various diseases via regulation of different cellular processes. Here, we review current literature regarding the structural and functional properties of CaN, highlighting its crucial role in the development and pathogenesis of immune system disorders, neurodegenerative diseases, kidney disease, cardiomyopathy and cancer.

Atoh8 in Development and Disease

Atoh8 belongs to a large superfamily of transcriptional regulators called basic helix-loop-helix (bHLH) proteins. bHLH proteins have been identified in a wide range of organisms from yeast to humans. The members of this special group of transcription factors were found to be involved not only in embryonic development but also in disease initiation and its progression. Given their importance in several fundamental processes, the translation, subcellular location and turnover of bHLH proteins is tightly regulated. Alterations in the expression of bHLH proteins have been associated with multiple diseases also in context with Atoh8 which seems to unfold its functions as both transcriptional activator and repressor. Like many other bHLH transcription factors, so far, Atoh8 has also been observed to be involved in both embryonic development and carcinogenesis where it mainly acts as tumor suppressor. This review summarizes our current understanding of Atoh8 structure, function and regulation and its complex and partially controversial involvement in development and disease.

Calcineurin in the heart: New horizons for an old friend

Calcineurin, also known as PP2B or PPP3, is a member of the PPP family of protein phosphatases that also includes PP1 and PP2A. Together these three phosphatases carryout the majority of dephosphorylation events in the heart. Calcineurin is distinct in that it is activated by the binding of calcium/calmodulin (Ca2+/CaM) and therefore acts as a node for integrating Ca2+ signals with changes in phosphorylation, two fundamental intracellular signaling cascades. In the heart, calcineurin is primarily thought of in the context of pathological cardiac remodeling, acting through the Nuclear Factor of Activated T-cell (NFAT) family of transcription factors. However, calcineurin activity is also essential for normal heart development and homeostasis in the adult heart. Furthermore, it is clear that NFAT-driven changes in transcription are not the only relevant processes initiated by calcineurin in the setting of pathological remodeling. There is a growing appreciation for the diversity of calcineurin substrates that can impact cardiac function as well as the diversity of mechanisms for targeting calcineurin to specific sub-cellular domains in cardiomyocytes and other cardiac cell types. Here, we will review the basics of calcineurin structure, regulation, and function in the context of cardiac biology. Particular attention will be given to: the development of improved tools to identify and validate new calcineurin substrates; recent studies identifying new calcineurin isoforms with unique properties and targeting mechanisms; and the role of calcineurin in cardiac development and regeneration.

Targeted deletion of Atoh8 results in severe hearing loss in mice

Atoh8, also named Math6, is a bHLH gene reported to have important functions in the developing nervous system, pancreas and kidney. However, the expression pattern and function of Atoh8 in the inner ear are still unclear. To study the function of Atoh8 in the developing mouse inner ear, we performed targeted deletion of Atoh8 by intercrossing Atoh8^lacZ/+ mice. We studied the expression pattern of Atoh8 in the inner ear and found interesting results that Atoh8‐null (Atoh8^lacZ/lacZ) mice were viable but smaller than their littermates and they were severely hearing impaired, which was confirmed by hearing tests (ABR, DPOAE). We collected 129 viable newborns from 18 litters by crossing Atoh8^lacZ/+ mice and found that the distributions of Atoh8^lacZ/+, Atoh8^lacZ/lacZ and wild type were very close to their expected Mendelian ratio by χ² testing. However, no remarkable morphological changes in cochleae in mutant mice were detected under plastic sectioning and electron microscopy. No remarkable differences in the expression of Myosin6, Prestin, TrkC, GAD65, Tuj1, or Calretinin were detected between the mutant mice and the control mice. These findings indicate that Atoh8 plays an important role in the development of normal hearing, while further studies are required to elucidate its exact function in hearing.

Atoh8 acts as a regulator of chondrocyte proliferation and differentiation in endochondral bones

Atonal homolog 8 (Atoh8) is a transcription factor of the basic helix-loop-helix (bHLH) protein family, which is expressed in the cartilaginous elements of endochondral bones. To analyze its function during chondrogenesis we deleted Atoh8 in mice using a chondrocyte- (Atoh8flox/flox;Col2a1-Cre) and a germline- (Atoh8flox/flox;Prx1-Crefemale) specific Cre allele. In both strains, Atoh8 deletion leads to a reduced skeletal size of the axial and appendicular bones, but the stages of phenotypic manifestations differ. While we observed obviously shortened bones in Atoh8flox/flox;Col2a1-Cre mice only postnatally, the bones of Atoh8flox/flox;Prx1-Crefemale mice are characterized by a reduced bone length already at prenatal stages. Detailed histological and molecular investigations revealed reduced zones of proliferating and hypertrophic chondrocytes. In addition, Atoh8 deletion identified Atoh8 as a positive regulator of chondrocyte proliferation. As increased Atoh8 expression is found in the region of prehypertrophic chondrocytes where the expression of Ihh, a main regulator of chondrocyte proliferation and differentiation, is induced, we investigated a potential interaction of Atoh8 function and Ihh signaling. By activating Ihh signaling with Purmorphamine we demonstrate that Atoh8 regulates chondrocyte proliferation in parallel or downstream of Ihh signaling while it acts on the onset of hypertrophy upstream of Ihh likely by modulating Ihh expression levels.

PPP3CB Inhibits Migration of G401 Cells via Regulating Epithelial-to-Mesenchymal Transition and Promotes G401 Cells Growth

PPP3CB belongs to the phosphoprotein phosphatases (PPPs) group. Although the majority of the PPP family play important roles in the epithelial-to-mesenchymal transition (EMT) of tumor cells, little is known about the function of PPP3CB in the EMT process. Here, we found PPP3CB had high expression in kidney mesenchymal-like cells compared with kidney epithelial-like cells. Knock-down of PPP3CB downregulated epithelial marker E-cadherin and upregulated mesenchymal marker Vimentin, promoting the transition of cell states from epithelial to mesenchymal and reorganizing the actin cytoskeleton which contributed to cell migration. Conversely, overexpression of PPP3CB reversed EMT and inhibited migration of tumor cells. Besides, in vitro and in vivo experiments indicated that the loss of PPP3CB suppressed the tumor growth. However, the deletion of the phosphatase domain of PPP3CB showed no effect on the expression of E-cadherin, migration, and G401 cell proliferation. Together, we demonstrate that PPP3CB inhibits G401 cell migration through regulating EMT and promotes cell proliferation, which are both associated with the phosphatase activity of PPP3CB.

Calcineurin-AKAP interactions: therapeutic targeting of a pleiotropic enzyme with a little help from its friends

The ubiquitous Ca²⁺ /calmodulin-dependent phosphatase calcineurin is a key regulator of pathological cardiac hypertrophy whose therapeutic targeting in heart disease has been elusive due to its role in other essential biological processes. Calcineurin is targeted to diverse intracellular compartments by association with scaffold proteins, including by multivalent A-kinase anchoring proteins (AKAPs) that bind protein kinase A and other important signalling enzymes determining cardiac myocyte function and phenotype. Calcineurin anchoring by AKAPs confers specificity to calcineurin function in the cardiac myocyte. Targeting of calcineurin 'signalosomes' may provide a rationale for inhibiting the phosphatase in disease.

Calcineurin signaling in the heart: The importance of time and place

The calcium-activated protein phosphatase, calcineurin, lies at the intersection of protein phosphorylation and calcium signaling cascades, where it provides an essential nodal point for coordination between these two fundamental modes of intracellular communication. In excitatory cells, such as neurons and cardiomyocytes, that experience rapid and frequent changes in cytoplasmic calcium, calcineurin protein levels are exceptionally high, suggesting that these cells require high levels of calcineurin activity. Yet, it is widely recognized that excessive activation of calcineurin in the heart contributes to pathological hypertrophic remodeling and the progression to failure. How does a calcium activated enzyme function in the calcium-rich environment of the continuously contracting heart without pathological consequences? This review will discuss the wide range of calcineurin substrates relevant to cardiovascular health and the mechanisms calcineurin uses to find and act on appropriate substrates in the appropriate location while potentially avoiding others. Fundamental differences in calcineurin signaling in neonatal verses adult cardiomyocytes will be addressed as well as the importance of maintaining heterogeneity in calcineurin activity across the myocardium. Finally, we will discuss how circadian oscillations in calcineurin activity may facilitate integration with other essential but conflicting processes, allowing a healthy heart to reap the benefits of calcineurin signaling while avoiding the detrimental consequences of sustained calcineurin activity that can culminate in heart failure.