MDM2-mediated degradation of p14ARF: a novel mechanism to control ARF levels in cancer cells

High expression of CDKN2A is associated with poor prognosis in colorectal cancer and may guide PD-1-mediated immunotherapy

BACKGROUND

Colorectal cancer (CRC) is one of the most common malignancies worldwide. Immunotherapy targeting the programmed death protein 1(PD-1) and its ligand (PD-L1), is a promising treatment option for many cancers, but has exhibited poor therapeutic efficacy in CRC. This study aimed to identify and validate the prognostic value of immune-related genes and PD-1-associated genes for immunotherapy treatment of CRC.

METHODS

An extensive analysis of prognostic immune-related DEGs and PD-1-related genes has highlighted CDKN2A as a vital overlapping gene. To further explore its expression in CRC and its prognostic value, we conducted qRT-PCR, Western blot experiments, and consulted various databases. Subsequently, we conducted gene expression analysis, survival and prognostic analysis, enrichment analysis, immune infiltration assessment, and TIDE analysis to assess the significance of CDKN2A.

RESULTS

In CRC, CDKN2A was highly expressed compared to normal tissue. It was found that CDKN2A expression was related to clinicopathological features such as inflammation and tumor stage. Furthermore, a significant correlation was identified between CDKN2A and immune infiltration, specifically involving CD4 T cells, CD8 T cells, and macrophages. The analysis of the GSEA of CRC samples with high CDKN2A expression identified enrichment of genes involved in MYC target-v2 and metabolism pathways. Furthermore, UBE2I, CDK4, CDK6, TP53, and CCND1 were found to be significantly coexpressed with CDKN2A, suggesting a potential role that these gene play in CRC and immunotherapy.

CONCLUSIONS

Our study revealed that high CDKN2A expression in CRC is a potentially valuable prognostic biomarker, which may guide PD-1-mediated immunotherapy.

Light Quality Potentiates the Antioxidant Properties of Brassica rapa Microgreen Extracts against Oxidative Stress and DNA Damage in Human Cells

Plants are an inexhaustible source of bioactive compounds beneficial for contrasting oxidative stress, leading to many degenerative pathologies. Brassica rapa L. subsp. rapa is well known for its nutraceutical properties among edible vegetable species. In our work, we aimed to explore an eco-friendly way to enhance the beneficial dietary phytochemicals in this vast world of crop-growing plants at selected light quality conditions. White broad-spectrum (W) and red-blue (RB) light regimes were used for growing brassica microgreens. The organic extracts were tested on keratinocytes upon oxidative stress to explore their capability to act as natural antioxidant cell protectors. Our results show that both W and RB extracts caused a notable reduction in reactive oxygen species (ROS) levels induced by H2O2. Interestingly, according to its higher contents of polyphenols and flavonoids, the RB was more efficient in reducing ROS amount and DNA damage than the W extract, particularly at the lowest concentration tested. However, at higher concentrations (up to 100 μg/mL), the antioxidant effect reached a plateau, and there was little added benefit. These findings confirm that RB light effectively increases the antioxidant compounds in Brassica rapa L. microgreens, thus contributing to their enhanced activity against oxidative-induced genotoxicity compared to microgreens grown under W light.

Modulation of intestinal epithelial cell proliferation and apoptosis by Lactobacillus gasseri SF1183

The gut microbiota exerts a variety of positive effects on the intestinal homeostasis, including the production of beneficial molecules, control of the epithelial barrier integrity and the regulation of the balance between host's cell death and proliferation. The interactions between commensal bacteria and intestinal cells are still under-investigated and is then of paramount importance to address such interactions at the molecular and cellular levels. We report an in vitro analysis of the effects of molecules secreted by Lactobacillus gasseri SF1183 on HCT116 cells, selected as a model of intestinal epithelial cells. SF1183 is a L. gasseri strain isolated from an ileal biopsy of a human healthy volunteer, able to prevent colitis symptoms in vivo. Expanding previous findings, we show that bioactive molecules secreted by SF1183 reduce the proliferation of HCT116 cells in a reversible manner determining a variation in cell cycle markers (p21WAF, p53, cyclin D1) and resulting in the protection of HCT116 cells from TNF-alfa induced apoptosis, an effect potentially relevant for the protection of the epithelial barrier integrity and reconstitution of tissue homeostasis. Consistently, SF1183 secreted molecules increase the recruitment of occludin, a major component of TJ, at the cell-cell contacts, suggesting a reinforcement of the barrier function.

Mutation of the Conserved Threonine 8 within the Human ARF Tumour Suppressor Protein Regulates Autophagy

Background: The ARF tumour suppressor plays a well-established role as a tumour suppressor, halting cell growth by both p53-dependent and independent pathways in several cellular stress response circuits. However, data collected in recent years challenged the traditional role of this protein as a tumour suppressor. Cancer cells expressing high ARF levels showed that its expression, far from being dispensable, is required to guarantee tumour cell survival. In particular, ARF can promote autophagy, a self-digestion pathway that helps cells cope with stressful growth conditions arising during both physiological and pathological processes. Methods: We previously showed that ARF is regulated through the activation of the protein kinase C (PKC)-dependent pathway and that an ARF phospho-mimetic mutant on the threonine residue 8, ARF-T8D, sustains cell proliferation in HeLa cells. We now explored the role of ARF phosphorylation in both basal and starvation-induced autophagy by analysing autophagic flux in cells transfected with either WT and ARF phosphorylation mutants by immunoblot and immunofluorescence. Results: Here, we show that endogenous ARF expression in HeLa cells is required for starvation-induced autophagy. Further, we provide evidence that the hyper-expression of ARF-T8D appears to inhibit autophagy in both HeLa and lung cancer cells H1299. This effect is due to the cells’ inability to elicit autophagosomes formation upon T8D expression. Conclusions: Our results lead to the hypothesis that ARF phosphorylation could be a mechanism through which the protein promotes or counteracts autophagy. Several observations underline how autophagy could serve a dual role in cancer progression, either protecting healthy cells from damage or aiding cancerous cells to survive. Our results indicate that ARF phosphorylation controls protein’s ability to promote or counteract autophagy, providing evidence of the dual role played by ARF in cancer progression.

In Vitro and In Vivo Toxicity Evaluation of Natural Products with Potential Applications as Biopesticides

The use of natural products in agriculture as pesticides has been strongly advocated. However, it is necessary to assess their toxicity to ensure their safe use. In the present study, mammalian cell lines and fish models of the zebrafish (Danio rerio) and medaka (Oryzias latipes) have been used to investigate the toxic effects of ten natural products which have potential applications as biopesticides. The fungal metabolites cavoxin, epi-epoformin, papyracillic acid, seiridin and sphaeropsidone, together with the plant compounds inuloxins A and C and ungeremine, showed no toxic effects in mammalian cells and zebrafish embryos. Conversely, cyclopaldic and α-costic acids, produced by Seiridium cupressi and Dittrichia viscosa, respectively, caused significant mortality in zebrafish and medaka embryos as a result of yolk coagulation. However, both compounds showed little effect in zebrafish or mammalian cell lines in culture, thus highlighting the importance of the fish embryotoxicity test in the assessment of environmental impact. Given the embryotoxicity of α-costic acid and cyclopaldic acid, their use as biopesticides is not recommended. Further ecotoxicological studies are needed to evaluate the potential applications of the other compounds.

Post-Translational Regulation of ARF: Perspective in Cancer

Tumorigenesis can be induced by various stresses that cause aberrant DNA mutations and unhindered cell proliferation. Under such conditions, normal cells autonomously induce defense mechanisms, thereby stimulating tumor suppressor activation. ARF, encoded by the CDKN2a locus, is one of the most frequently mutated or deleted tumor suppressors in human cancer. The safeguard roles of ARF in tumorigenesis are mainly mediated via the MDM2-p53 axis, which plays a prominent role in tumor suppression. Under normal conditions, low p53 expression is stringently regulated by its target gene, MDM2 E3 ligase, which induces p53 degradation in a ubiquitin-proteasome-dependent manner. Oncogenic signals induced by MYC, RAS, and E2Fs trap MDM2 in the inhibited state by inducing ARF expression as a safeguard measure, thereby activating the tumor-suppressive function of p53. In addition to the MDM2-p53 axis, ARF can also interact with diverse proteins and regulate various cellular functions, such as cellular senescence, apoptosis, and anoikis, in a p53-independent manner. As the evidence indicating ARF as a key tumor suppressor has been accumulated, there is growing evidence that ARF is sophisticatedly fine-tuned by the diverse factors through transcriptional and post-translational regulatory mechanisms. In this review, we mainly focused on how cancer cells employ transcriptional and post-translational regulatory mechanisms to manipulate ARF activities to circumvent the tumor-suppressive function of ARF. We further discussed the clinical implications of ARF in human cancer.

Colloidal Silver Induces Cytoskeleton Reorganization and E-Cadherin Recruitment at Cell-Cell Contacts in HaCaT Cells

Up until the first half of the 20th century, silver found significant employment in medical applications, particularly in the healing of open wounds, thanks to its antibacterial and antifungal properties. Wound repair is a complex and dynamic biological process regulated by several pathways that cooperate to restore tissue integrity and homeostasis. To facilitate healing, injuries need to be promptly treated. Recently, the interest in alternatives to antibiotics has been raised given the widespread phenomenon of antibiotic resistance. Among these alternatives, the use of silver appears to be a valid option, so a resurgence in its use has been recently observed. In particular, in contrast to ionic silver, colloidal silver, a suspension of metallic silver particles, shows antibacterial activity displaying less or no toxicity. However, the human health risks associated with exposure to silver nanoparticles (NP) appear to be conflicted, and some studies have suggested that it could be toxic in different cellular contexts. These potentially harmful effects of silver NP depend on various parameters including NP size, which commonly range from 1 to 100 nm. In this study, we analyzed the effect of a colloidal silver preparation composed of very small and homogeneous nanoparticles of 0.62 nm size, smaller than those previously tested. We found no adverse effect on the cell proliferation of HaCaT cells, even at high NP concentration. Time-lapse microscopy and indirect immunofluorescence experiments demonstrated that this preparation of colloidal silver strongly increased cell migration, re-modeled the cytoskeleton, and caused recruitment of E-cadherin at cell-cell junctions of human cultured keratinocytes.

Dual Role of the Alternative Reading Frame ARF Protein in Cancer

The CDKN2a/ARF locus expresses two partially overlapping transcripts that encode two distinct proteins, namely p14ARF (p19Arf in mouse) and p16INK4a, which present no sequence identity. Initial data obtained in mice showed that both proteins are potent tumor suppressors. In line with a tumor-suppressive role, ARF-deficient mice develop lymphomas, sarcomas, and adenocarcinomas, with a median survival rate of one year of age. In humans, the importance of ARF inactivation in cancer is less clear whereas a more obvious role has been documented for p16INK4a. Indeed, many alterations in human tumors result in the elimination of the entire locus, while the majority of point mutations affect p16INK4a. Nevertheless, specific mutations of p14ARF have been described in different types of human cancers such as colorectal and gastric carcinomas, melanoma and glioblastoma. The activity of the tumor suppressor ARF has been shown to rely on both p53-dependent and independent functions. However, novel data collected in the last years has challenged the traditional and established role of this protein as a tumor suppressor. In particular, tumors retaining ARF expression evolve to metastatic and invasive phenotypes and in humans are associated with a poor prognosis. In this review, the recent evidence and the molecular mechanisms of a novel role played by ARF will be presented and discussed, both in pathological and physiological contexts.

Theileria highjacks JNK2 into a complex with the macroschizont GPI (GlycosylPhosphatidylInositol)-anchored surface protein p104

Constitutive c-Jun N-terminal kinase (JNK) activity characterizes bovine T and B cells infected with Theileria parva, and B cells and macrophages infected with Theileria annulata. Here, we show that T. annulata infection of macrophages manipulates JNK activation by recruiting JNK2 and not JNK1 to the parasite surface, whereas JNK1 is found predominantly in the host cell nucleus. At the parasite's surface, JNK2 forms a complex with p104, a GPI-(GlycosylPhosphatidylInositol)-anchor T. annulata plasma membrane protein. Sequestration of JNK2 depended on Protein Kinase-A (PKA)-mediated phosphorylation of a JNK-binding motif common to T. parva and a cell penetrating peptide harbouring the conserved p104 JNK-binding motif competitively ablated binding, whereupon liberated JNK2 became ubiquitinated and degraded. Cytosolic sequestration of JNK2 suppressed small mitochondrial ARF-mediated autophagy, whereas it sustained nuclear JNK1 levels, c-Jun phosphorylation, and matrigel traversal. Therefore, T. annulata sequestration of JNK2 contributes to both survival and dissemination of Theileria-transformed macrophages.

Oxidative Stress Causes Enhanced Secretion of YB-1 Protein that Restrains Proliferation of Receiving Cells

The prototype cold-shock Y-box binding protein 1 (YB-1) is a multifunctional protein that regulates a variety of fundamental biological processes including cell proliferation and migration, DNA damage, matrix protein synthesis and chemotaxis. The plethora of functions assigned to YB-1 is strictly dependent on its subcellular localization. In resting cells, YB-1 localizes to cytoplasm where it is a component of messenger ribonucleoprotein particles. Under stress conditions, YB-1 contributes to the formation of stress granules (SGs), cytoplasmic foci where untranslated messenger RNAs (mRNAs) are sorted or processed for reinitiation, degradation, or packaging into ribonucleoprotein particles (mRNPs). Following DNA damage, YB-1 translocates to the nucleus and participates in DNA repair thereby enhancing cell survival. Recent data show that YB-1 can also be secreted and YB-1-derived polypeptides are found in plasma of patients with sepsis and malignancies. Here we show that in response to oxidative insults, YB-1 assembly in SGs is associated with an enhancement of YB-1 protein secretion. An enriched fraction of extracellular YB-1 (exYB-1) significantly inhibited proliferation of receiving cells and such inhibition was associated to a G2/M cell cycle arrest, induction of p21WAF and reduction of ΔNp63α protein level. All together, these data show that acute oxidative stress causes sustained release of YB-1 as a paracrine/autocrine signal that stimulate cell cycle arrest.

Dynamics of p14ARF and Focal Adhesion Kinase-Mediated Autophagy in Cancer

It has been widely shown that the focal adhesion kinase (FAK) is involved in nearly every aspect of cancer, from invasion to metastasis to epithelial–mesenchymal transition and maintenance of cancer stem cells. FAK has been shown to interact with p14ARF (alternative reading frame)—a well-established tumor suppressor—and functions in the negative regulation of cancer through both p53-dependent and -independent pathways. Interestingly, both FAK and ARF (human and mouse counterpart) proteins, as well as p53, are involved in autophagy—a process of “self-digestion”—whose main function is the recycling of cellular components and quality control of proteins and organelles. In the last years, an unexpected role of p14ARF in the survival of cancer cells has been underlined in different cellular contexts, suggesting a novel pro-oncogenic function of this protein. In this review, the mechanisms whereby ARF and FAK control autophagy are presented, as well as the role of autophagy in cell migration and spreading. Integrated investigation of these cell functions is extremely important to understand the mechanism of the basis of cell transformation and migration and thus cancer development.

PKC Dependent p14ARF Phosphorylation on Threonine 8 Drives Cell Proliferation

ARF role as tumor suppressor has been challenged in the last years by several findings of different groups ultimately showing that its functions can be strictly context dependent. We previously showed that ARF loss in HeLa cells induces spreading defects, evident as rounded morphology of depleted cells, accompanied by a decrease of phosphorylated Focal Adhesion Kinase (FAK) protein levels and anoikis. These data, together with previous finding that a PKC dependent signalling pathway can lead to ARF stabilization, led us to the hypothesis that ARF functions in cell proliferation might be regulated by phosphorylation. In line with this, we show here that upon spreading ARF is induced through PKC activation. A constitutive-phosphorylated ARF mutant on the conserved threonine 8 (T8D) is able to mediate both cell spreading and FAK activation. Finally, ARF-T8D expression confers growth advantage to cells thus leading to the intriguing hypothesis that ARF phosphorylation could be a mechanism through which pro-proliferative or anti proliferative signals could be transduced inside the cells in both physiological and pathological conditions.

The 9p21 locus as a potential therapeutic target and prognostic marker in colorectal cancer

Colorectal cancer (CRC) is a major cause of cancer-related-death worldwide. Despite extensive efforts to identify valid biomarkers for the risk stratification of CRC patients, there are few of proven clinical utility. It is recognized that genetic factors play a major role in determining susceptibility to CRC. Recent genome-wide association studies have demonstrated common genetic variants in a region on chromosome 9p21 associated with an increased risk of CRC. Several genetic polymorphisms have been identified in this region that are associated with CRC. Three genes are located at this locus; CDKN2B(encoding-p15ink4b), CDKN2A (encoding-p16ink4a/p14ARF) and 3′ end of CDKN2BAS (termed-antisense-noncoding-RNA in the INK4-locus [ANRIL]). ANRIL has a post-transcriptional modulatory activity, which has been shown to perturb the expression of nearby genes. It also plays an important role in coordinating tissue remodeling through regulation of cell proliferation, apoptosis, aging, extra-cellular matrix remodeling and inflammatory response. However, the role of ANRIL is not well understood in CRC. Hypermethylation of the p14ARF and p16INK4a genes is often found in some tumors, including CRC. However, further studies are necessary to explore the clinical utility of these putative markers in risk stratification, and in the assessment of prognosis. In this review, we have summarized the prognostic and therapeutic potential of the p14ARF and p16INK4a genes in patients with colorectal cancer.

Sumoylation and ubiquitylation crosstalk in the control of ΔNp63α protein stability

ΔNp63α is finely and strictly regulated during embryogenesis and differentiation. ΔNp63α is the only p63 isoform degraded by the proteasome after Ubiquitin and SUMO (Small Ubiquitin-like MOdifier) conjugation. Here, we show that p63 ubiquitylation per se is not the signal triggering p63 proteasomal degradation. Taking advantage of natural ΔNp63α mutants isolated by patients with Split Hand and Foot Malformation IV syndrome, we found that SUMO and Ub modifications are not redundant and both are required to guarantee efficient ΔNp63α degradation. Here, we present evidence that sumoylation and ubiquitylation of ΔNp63α are strongly intertwined, and none of the two can efficiently occur if the other is impaired.

Hibiscus syriacus Extract from an Established Cell Culture Stimulates Skin Wound Healing

Higher plants are the source of a wide array of bioactive compounds that support skin integrity and health. Hibiscus syriacus, family Malvaceae, is a plant of Chinese origin known for its antipyretic, anthelmintic, and antifungal properties. The aim of this study was to assess the healing and hydration properties of H. syriacus ethanolic extract (HSEE). We established a cell culture from Hibiscus syriacus leaves and obtained an ethanol soluble extract from cultured cells. The properties of the extract were tested by gene expression and functional analyses on human fibroblast, keratinocytes, and skin explants. HSEE treatment increased the healing potential of fibroblasts and keratinocytes. Specifically, HSEE significantly stimulated fibronectin and collagen synthesis by 16 and 60%, respectively, while fibroblasts contractility was enhanced by 30%. These results were confirmed on skin explants, where HSEE accelerated the wound healing activity in terms of epithelium formation and fibronectin production. Moreover, HSEE increased the expression of genes involved in skin hydration and homeostasis. Specifically, aquaporin 3 and filaggrin genes were enhanced by 20 and 58%, respectively. Our data show that HSEE contains compounds capable of stimulating expression of biomarkers relevant to skin regeneration and hydration thereby counteracting molecular pathways leading to skin damage and aging.

p14ARF interacts with the focal adhesion kinase and protects cells from anoikis

The ARF protein functions as an important sensor of hyper-proliferative stimuli restricting cell proliferation through both p53-dependent and -independent pathways. Although to date the majority of studies on ARF have focused on its anti-proliferative role, few studies have addressed whether ARF may also have pro-survival functions. Here we show for the first time that during the process of adhesion and spreading ARF re-localizes to sites of active actin polymerization and to focal adhesion points where it interacts with the phosphorylated focal adhesion kinase. In line with its recruitment to focal adhesions, we observe that hampering ARF function in cancer cells leads to gross defects in cytoskeleton organization resulting in apoptosis through a mechanism dependent on the Death-Associated Protein Kinase. Our data uncover a novel function for p14ARF in protecting cells from anoikis that may reflect its role in anchorage independence, a hallmark of malignant tumor cells.

P53-MDM2 Pathway: Evidences for A New Targeted Therapeutic Approach in B-Acute Lymphoblastic Leukemia

The tumor suppressor p53 is a canonical regulator of different biological functions, like apoptosis, cell cycle arrest, DNA repair, and genomic stability. This gene is frequently altered in human tumors generally by point mutations or deletions. Conversely, in acute lymphoblastic leukemia (ALL) genomic alterations of TP53 are rather uncommon, and prevalently occur in patients at relapse or with poor prognosis. On the other hand, p53 pathway is often compromised by the inactivation of its regulatory proteins, as MDM2 and ARF. MDM2 inhibitor molecules are able to antagonize p53-MDM2 interaction allowing p53 to exert tumor suppressor transcriptional regulation and to induce apoptotic pathways. Recent preclinical and clinical studies propose that MDM2 targeted therapy represents a promising anticancer strategy restoring p53 dependent mechanisms in ALL disease. Here, we discussed the use of new small molecule targeting p53 pathways as a promising drug target therapy in ALL.

Nucleolus-derived mediators in oncogenic stress response and activation of p53-dependent pathways

Rapid growth and division of cells, including tumor ones, is correlated with intensive protein biosynthesis. The output of nucleoli, organelles where translational machineries are formed, depends on a rate of particular stages of ribosome production and on accessibility of elements crucial for their effective functioning, including substrates, enzymes as well as energy resources. Different factors that induce cellular stress also often lead to nucleolar dysfunction which results in ribosome biogenesis impairment. Such nucleolar disorders, called nucleolar or ribosomal stress, usually affect cellular functioning which in fact is a result of p53-dependent pathway activation, elicited as a response to stress. These pathways direct cells to new destinations such as cell cycle arrest, damage repair, differentiation, autophagy, programmed cell death or aging. In the case of impaired nucleolar functioning, nucleolar and ribosomal proteins mediate activation of the p53 pathways. They are also triggered as a response to oncogenic factor overexpression to protect tissues and organs against extensive proliferation of abnormal cells. Intentional impairment of any step of ribosome biosynthesis which would direct the cells to these destinations could be a strategy used in anticancer therapy. This review presents current knowledge on a nucleolus, mainly in relation to cancer biology, which is an important and extremely sensitive element of the mechanism participating in cellular stress reaction mediating activation of the p53 pathways in order to counteract stress effects, especially cancer development.