FIH-1 engages novel binding partners to positively influence epithelial proliferation via p63

Factor-inhibiting HIF (FIH) promotes lung cancer progression

Factor-inhibiting HIF (FIH) is an asparagine hydroxylase that acts on hypoxia-inducible factors (HIFs) to control cellular adaptation to hypoxia. FIH is expressed in several tumor types, but its impact in tumor progression remains largely unexplored. We observed that FIH was expressed on human lung cancer tissue. Deletion of FIH in mouse and human lung cancer cells resulted in an increased glycolytic metabolism, consistent with increased HIF activity. FIH-deficient lung cancer cells exhibited decreased proliferation. Analysis of RNA-Seq data confirmed changes in the cell cycle and survival and revealed molecular pathways that were dysregulated in the absence of FIH, including the upregulation of angiomotin (Amot), a key component of the Hippo tumor suppressor pathway. We show that FIH-deficient tumors were characterized by higher immune infiltration of NK and T cells compared with FIH competent tumor cells. In vivo studies demonstrate that FIH deletion resulted in reduced tumor growth and metastatic capacity. Moreover, high FIH expression correlated with poor overall survival in non-small cell lung cancer (NSCLC). Our data unravel FIH as a therapeutic target for the treatment of lung cancer.

FAM193A is a positive regulator of p53 activity

Inactivation of the p53 tumor suppressor, either by mutations or through hyperactivation of repressors such as MDM2 and MDM4, is a hallmark of cancer. Although many inhibitors of the p53-MDM2/4 interaction have been developed, such as Nutlin, their therapeutic value is limited by highly heterogeneous cellular responses. We report here a multi-omics investigation of the cellular response to MDM2/4 inhibitors, leading to identification of FAM193A as a widespread regulator of p53 function. CRISPR screening identified FAM193A as necessary for the response to Nutlin. FAM193A expression correlates with Nutlin sensitivity across hundreds of cell lines. Furthermore, genetic codependency data highlight FAM193A as a component of the p53 pathway across diverse tumor types. Mechanistically, FAM193A interacts with MDM4, and FAM193A depletion stabilizes MDM4 and inhibits the p53 transcriptional program. Last, FAM193A expression is associated with better prognosis in multiple malignancies. Altogether, these results identify FAM193A as a positive regulator of p53.

Targeting Type I IFN/STAT1 signaling inhibited and reversed corneal squamous metaplasia in Aire-deficient mouse

Corneal transparency and integrity are essential for obtaining good vision; nevertheless, squamous metaplasia (SQM) of ocular epithelium is a kind of serious blinding corneal diseases, without therapeutic medication in clinic. Here, we found that deficiency of the autoimmune regulator (AIRE) in corneas spontaneously developed corneal plaques. Using corneal abrasion model, we revealed that deletion of Aire not only resulted in delayed corneal re-epithelialization, but also promoted a cell-fate transition from transparent corneal epithelium to keratinized epithelium, histopathologically characterized with SQM based on the transcriptomic analysis. Mechanistically, Aire-deficient corneas led to the heightened Type I interferon (IFN-I)/STAT1 signaling after abrasion. Pharmacological blockade of IFN-I/JAK/STAT1 signaling in Aire-knockout (KO) corneas not only accelerated epithelial wound healing, but also alleviated corneal plaques and SQM. Collectively, our findings revealed critical roles of AIRE in governing corneal epithelial homeostasis and pathologic keratinization, and further identified IFN-I/STAT1 signaling as a potential target for treating ocular surface diseases with SQM, and even for treating pathological scenarios related to SQM in other tissues.

The Asparagine Hydroxylase FIH: A Unique Oxygen Sensor

Significance: Limited oxygen availability (hypoxia) commonly occurs in a range of physiological and pathophysiological conditions, including embryonic development, physical exercise, inflammation, and ischemia. It is thus vital for cells and tissues to monitor their local oxygen availability to be able to adjust in case the oxygen supply is decreased. The cellular oxygen sensor factor inhibiting hypoxia-inducible factor (FIH) is the only known asparagine hydroxylase with hypoxia sensitivity. FIH uniquely combines oxygen and peroxide sensitivity, serving as an oxygen and oxidant sensor. Recent Advances: FIH was first discovered in the hypoxia-inducible factor (HIF) pathway as a modulator of HIF transactivation activity. Several other FIH substrates have now been identified outside the HIF pathway. Moreover, FIH enzymatic activity is highly promiscuous and not limited to asparagine hydroxylation. This includes the FIH-mediated catalysis of an oxygen-dependent stable (likely covalent) bond formation between FIH and selected substrate proteins (called oxomers [oxygen-dependent stable protein oligomers]). Critical Issues: The (patho-)physiological function of FIH is only beginning to be understood and appears to be complex. Selective pharmacologic inhibition of FIH over other oxygen sensors is possible, opening new avenues for therapeutic targeting of hypoxia-associated diseases, increasing the interest in its (patho-)physiological relevance. Future Directions: The contribution of FIH enzymatic activity to disease development and progression should be analyzed in more detail, including the assessment of underlying molecular mechanisms and relevant FIH substrate proteins. Also, the molecular mechanism(s) involved in the physiological functions of FIH remain(s) to be determined. Furthermore, the therapeutic potential of recently developed FIH-selective pharmacologic inhibitors will need detailed assessment. Antioxid. Redox Signal. 37, 913-935.

Eph signaling is regulated by miRNA-210: Implications for corneal epithelial repair

A distinct boundary exists between the progenitor cells in the basal limbal epithelium and the more differentiated corneal epithelial basal cells. We have shown that reciprocal expression patterns of EphA2 and Ephrin-A1 are likely to contribute to normal limbal-corneal epithelial compartmentalization as well as play a role in response to injury. How this signaling axis is regulated remains unclear. We have demonstrated that microRNAs (miRNAs) play critical roles in corneal epithelial wound healing and several miRNAs (e.g. miR-210) have been predicted to target ephrins. Previous expression profiling experiments demonstrated that miR-210 is prominently expressed in corneal epithelial cells. RNA-seq data acquired from miR-210-depleted HCECs showed up-regulation of genes involved in cellular migration. In addition, miR-210 is decreased after corneal injury while EphA2 is increased. Moreover, antago-210-treated HCECs markedly enhanced wound closure in a scratch wound assay. Antago-210 treatment resulted in increased EphA2 protein levels as well as pS897-EphA2, the pro-migratory form of EphA2. As expected, Ephrin-A1 levels were reduced, while levels of a well-known target of miR-210, Ephrin-A3, were increased by antago-210 treatment. The increase in migration with antago-210 could be inhibited by Ephrin-A1 overexpression, Ephrin-A1-Fc treatment or siRNA depletion of EphA2. However, depletion of Ephrin-A3 did not have effects on the antago-210-induced increase in migration. In addition, Ephrin-A1 overexpression and siEphA2 dampened EGFR signaling, which is increased by antago-210. Our data clearly demonstrate a link between miR-210 and EphA2/Ephrin-A1 signaling that regulates, in part, corneal epithelial migration. This interaction might potentially control the limbal-corneal epithelial boundary.

Ciliogenesis and autophagy are coordinately regulated by EphA2 in the cornea to maintain proper epithelial architecture

PURPOSE

To understand the relationship between ciliogenesis and autophagy in the corneal epithelium.

METHODS

siRNAs for EphA2 or PLD1 were used to inhibit protein expression in vitro. Morpholino-anti-EphA2 was used to knockdown EphA2 in Xenopus skin. An EphA2 knockout mouse was used to conduct loss of function studies. Autophagic vacuoles were visualized by contrast light microscopy. Autophagy flux, was measured by LC3 turnover and p62 protein levels. Immunostaining and confocal microscopy were conducted to visualize cilia in cultured cells and in vivo.

RESULTS

Loss of EphA2 (i) increased corneal epithelial thickness by elevating proliferative potential in wing cells, (ii) reduced the number of ciliated cells, (iii) increased large hollow vacuoles, that could be rescued by BafA1; (iv) inhibited autophagy flux and (v) increased GFP-LC3 puncta in the mouse corneal epithelium. This indicated a role for EphA2 in stratified epithelial assembly via regulation of proliferation as well as a positive role in both ciliogenesis and end-stage autophagy. Inhibition of PLD1, an EphA2 interacting protein that is a critical regulator of end-stage autophagy, reversed the accumulation of vacuoles, and the reduction in the number of ciliated cells due to EphA2 depletion, suggesting EphA2 regulation of both end-stage autophagy and ciliogenesis via PLD1. PLD1 mediated rescue of ciliogenesis by EphA2 depletion was blocked by BafA1, placing autophagy between EphA2 signaling and regulation of ciliogenesis.

CONCLUSION

Our findings demonstrate a novel role for EphA2 in regulating both autophagy and ciliogenesis, processes that are essential for proper corneal epithelial homeostasis.

Inhibition of the Oxygen-Sensing Asparaginyl Hydroxylase Factor Inhibiting Hypoxia-Inducible Factor: A Potential Hypoxia Response Modulating Strategy

Factor inhibiting hypoxia-inducible factor (FIH) is a JmjC domain 2-oxogluarate and Fe(II)-dependent oxygenase that catalyzes hydroxylation of specific asparagines in the C-terminal transcriptional activation domain of hypoxia-inducible factor alpha (HIF-α) isoforms. This modification suppresses the transcriptional activity of HIF by reducing its interaction with the transcriptional coactivators p300/CBP. By contrast with inhibition of the HIF prolyl hydroxylases (PHDs), inhibitors of FIH, which accepts multiple non-HIF substrates, are less studied; they are of interest due to their potential ability to alter metabolism (either in a HIF-dependent and/or -independent manner) and, provided HIF is upregulated, to modulate the course of the HIF-mediated hypoxic response. Here we review studies on the mechanism and inhibition of FIH. We discuss proposed biological roles of FIH including its regulation of HIF activity and potential roles of FIH-catalyzed oxidation of non-HIF substrates. We highlight potential therapeutic applications of FIH inhibitors.

Corneal epithelial biology: Lessons stemming from old to new

The anterior surface of the eye functions as a barrier to the external environment and protects the delicate underlying tissues from injury. Central to this protection are the corneal, limbal and conjunctival epithelia. The corneal epithelium is a self-renewing stratified squamous epithelium that protects the underlying delicate structures of the eye, supports a tear film and maintains transparency so that light can be transmitted to the interior of the eye (Basu et al., 2014; Cotsarelis et al., 1989; Funderburgh et al., 2016; Lehrer et al., 1998; Pajoohesh-Ganji and Stepp, 2005; Parfitt et al., 2015; Peng et al., 2012b; Stepp and Zieske, 2005). In this review, dedicated to James Funderburgh and his contributions to visual science, in particular the limbal niche, corneal stroma and corneal stromal stem cells, we will focus on recent data on the identification of novel regulators in corneal epithelial cell biology, their roles in stem cell homeostasis, wound healing, limbal/corneal boundary maintenance and the utility of single cell RNA sequencing (scRNA-seq) in vision biology studies.

Autophagy plays a positive role in induction of epidermal proliferation

Autophagy is a multistage catabolic process that mediates stress responses. However, the role of autophagy in epidermal proliferation, particularly under conditions when the epidermis becomes "activated" (hyperproliferative), remains unclear. We have shown that inhibition of Beclin 1, a key activator in the initiation phase of autophagy, attenuates imiquimod (IMQ)-induced epidermal hyperplasia in adult mice as well as naturally occurring hyperproliferation in neonatal mouse epidermis. Inhibition of Beclin 1 did not change the levels of several key inflammatory molecules or the numbers of immune cells in lesional skins. This indicates that autophagy does not affect inflammatory regulators in IMQ-treated mouse skin. Bioinformatic analysis combined with gene expression quantitative assays, revealed that a deficiency in autophagy decreases the expression of PDZ Binding Kinase (PBK), a regulator of the cell cycle, in mouse epidermis and human epidermal keratinocytes (HEKs). Interestingly, the decrease in PBK results in inhibition of proliferation in HEKs and such reduced proliferation can be rescued by activation of p38, the downstream signaling of PBK. Collectively, autophagy plays a positive role in epidermal proliferation, which is in part via regulating PBK expression.

The ACE2-deficient mouse: A model for a cytokine storm-driven inflammation

Angiotensin converting enzyme 2 (ACE2) plays an important role in inflammation, which is attributable at least, in part, to the conversion of the pro‐inflammatory angiotensin (Ang) II peptide into angiotensin 1‐7 (Ang 1‐7), a peptide which opposes the actions of AngII. ACE2 and AngII are present in many tissues but information on the cornea is lacking. We observed that mice deficient in the Ace2 gene (Ace2^−/−), developed a cloudy cornea phenotype as they aged. Haze occupied the central cornea, accompanied by corneal edema and neovascularization. In severe cases with marked chronic inflammation, a cell‐fate switch from a transparent corneal epithelium to a keratinized, stratified squamous, psoriasiform‐like epidermis was observed. The stroma contained a large number of CD11c, CD68, and CD3 positive cells. Corneal epithelial debridement experiments in young ACE2‐deficient mice showed normal appearing corneas, devoid of haze. We hypothesized, however, that these mice are “primed” for a corneal inflammatory response, which once initiated, would persist. In vitro studies reveal that interleukins (IL‐1a, IL‐1b), chemokines (CCL2, CXCL8), and TNF‐α, are all significantly elevated, resulting in a cytokine storm‐like phenotype. This phenotype could be partially rescued by treatment with the AngII type 1 receptor (AT1R) antagonist, losartan, suggesting that the observed effect was mediated by AngII acting on its main receptor. Since the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) utilizes human ACE2 as the receptor for entry with subsequent downregulation of ACE2, corneal inflammation in Ace2^−/− mice may have a similar mechanism with that in COVID‐19 patients. Thus the Ace2^−/− cornea, because of easy accessibility, may provide an attractive model to explore the molecular mechanisms, immunological changes, and treatment modalities in patients with COVID‐19.