Four-and-a-half LIM domain proteins inhibit transactivation by hypoxia-inducible factor 1

Proximal tubular FHL2, a novel downstream target of hypoxia inducible factor 1, is a protector against ischemic acute kidney injury

Four-and-a-half LIM domains protein 2 (FHL2) is an adaptor protein that may interact with hypoxia inducible factor 1α (HIF-1α) or β-catenin, two pivotal protective signaling in acute kidney injury (AKI). However, little is known about the regulation and function of FHL2 during AKI. We found that FHL2 was induced in renal tubular cells in patients with acute tubular necrosis and mice model of ischemia-reperfusion injury (IRI). In cultured renal proximal tubular cells (PTCs), hypoxia induced FHL2 expression and promoted the binding of HIF-1 to FHL2 promoter. Compared with control littermates, mice with PTC-specific deletion of FHL2 gene displayed worse renal function, more severe morphologic lesion, more tubular cell death and less cell proliferation, accompanying by downregulation of AQP1 and Na, K-ATPase after IRI. Consistently, loss of FHL2 in PTCs restricted activation of HIF-1 and β-catenin signaling simultaneously, leading to attenuation of glycolysis, upregulation of apoptosis-related proteins and downregulation of proliferation-related proteins during IRI. In vitro, knockdown of FHL2 suppressed hypoxia-induced activation of HIF-1α and β-catenin signaling pathways. Overexpression of FHL2 induced physical interactions between FHL2 and HIF-1α, β-catenin, GSK-3β or p300, and the combination of these interactions favored the stabilization and nuclear translocation of HIF-1α and β-catenin, enhancing their mediated gene transcription. Collectively, these findings identify FHL2 as a direct downstream target gene of HIF-1 signaling and demonstrate that FHL2 could play a critical role in protecting against ischemic AKI by promoting the activation of HIF-1 and β-catenin signaling through the interactions with its multiple protein partners.

Upregulation of the Four and a Half LIM Domains 1 linked with familial venous dysplasia in a familial genetic examination

BACKGROUND

This study aimed to analyze the mutation site in a family diagnosed with venous dysplasia to identify possible pathogenic genes.

METHODS

A 15-year-old female presented with lower extremity venous tortuosity aggravated by ulceration. Only the young sister exhibited similar symptoms within the immediate family of the proband. Whole genome sequencing (WGS) was used to evaluate the mutation sites and chromosome copy number variations (CNV) within the family. The possible pathogenic genes located in the region with CNVs were identified, and the expression of the possible pathogenic genes was verified via quantitative polymerase chain reaction (Q-PCR) and western blotting (WB) analysis. In-vitro models were used to verify the role of possible pathogenic genes linked with the development of venous dysplasia.

RESULTS

The high-resolution karyotype analysis of the chromosomes found no abnormalities. The results of the WGS indicated that the proband and her sister shared the CNV events, including a microdeletion on chromosomes X: 13580000-1358555000 and microduplications of chromosome X: 136055000-136290000, chromosome X: 136475000-13671000. The results of the Q-PCR and WB showed that FHL1 was highly expressed in the proband and her sister, indicating that mutations of the FHL1 may have an important role in the development of vein malformations. The results of the in vitro experiments showed that FHL1 overexpression could inhibit venous development.

CONCLUSION

The CNV in the Xq26 region (136054501-136288300) was found to be linked with the development of venous malformations in this family. However, further studies are required to evaluate the genetic mechanisms involved in the development of venous malformations.

Synergistic activation of genes promoting invasiveness by dual deprivation in oxygen and nutrients

By depriving cancer cells of blood supplies of oxygen and nutrients, anti-angiogenic therapy is aimed at simultaneously asphyxiating and starving the cells. But in spite of its apparent logic, this strategy is generally counterproductive over the long term as the treatment seems to elicit malignancy. Since a defect of blood supply is expected to deprive tumours simultaneously of oxygen and nutrients naturally, we examine here these two deprivations, alone or in combination, on the phenotype and signalling pathways of moderately aggressive MCF7 cancer cells. Each deprivation induces some aspects of the aggressive and migratory phenotypes through activating several pathways, including HIF1-alpha as expected, but also SRF/MRTFA and TCF4/beta-catenin. Strikingly, the dual deprivation has strong cooperative effects on the upregulation of genes increasing the metastatic potential, such as four and a half LIM domains 2 (FHL2) and HIF1A-AS2 lncRNA, which have response elements for both pathways. Using anti-angiogenic agents as monotherapy is therefore questionable as it may give falsely promising short-term tumour regression, but could ultimately exacerbate aggressive phenotypes.

Transcriptional Response to Hypoxia: The Role of HIF-1-Associated Co-Regulators

The Hypoxia Inducible Factor 1 (HIF-1) plays a major role in the cellular response to hypoxia by regulating the expression of many genes involved in adaptive processes that allow cell survival under low oxygen conditions. Adaptation to the hypoxic tumor micro-environment is also critical for cancer cell proliferation and therefore HIF-1 is also considered a valid therapeutical target. Despite the huge progress in understanding regulation of HIF-1 expression and activity by oxygen levels or oncogenic pathways, the way HIF-1 interacts with chromatin and the transcriptional machinery in order to activate its target genes is still a matter of intense investigation. Recent studies have identified several different HIF-1- and chromatin-associated co-regulators that play important roles in the general transcriptional activity of HIF-1, independent of its expression levels, as well as in the selection of binding sites, promoters and target genes, which, however, often depends on cellular context. We review here these co-regulators and examine their effect on the expression of a compilation of well-characterized HIF-1 direct target genes in order to assess the range of their involvement in the transcriptional response to hypoxia. Delineating the mode and the significance of the interaction between HIF-1 and its associated co-regulators may offer new attractive and specific targets for anticancer therapy.

Identification of Human Cell Cycle Phase Markers Based on Single-Cell RNA-Seq Data by Using Machine Learning Methods

The cell cycle is composed of a series of ordered, highly regulated processes through which a cell grows and duplicates its genome and eventually divides into two daughter cells. According to the complex changes in cell structure and biosynthesis, the cell cycle is divided into four phases: gap 1 (G1), DNA synthesis (S), gap 2 (G2), and mitosis (M). Determining which cell cycle phases a cell is in is critical to the research of cancer development and pharmacy for targeting cell cycle. However, current detection methods have the following problems: (1) they are complicated and time consuming to perform, and (2) they cannot detect the cell cycle on a large scale. Rapid developments in single-cell technology have made dissecting cells on a large scale possible with unprecedented resolution. In the present research, we construct efficient classifiers and identify essential gene biomarkers based on single-cell RNA sequencing data through Boruta and three feature ranking algorithms (e.g., mRMR, MCFS, and SHAP by LightGBM) by utilizing four advanced classification algorithms. Meanwhile, we mine a series of classification rules that can distinguish different cell cycle phases. Collectively, we have provided a novel method for determining the cell cycle and identified new potential cell cycle-related genes, thereby contributing to the understanding of the processes that regulate the cell cycle.

CMYA5 is a novel interaction partner of FHL2 in cardiac myocytes

Four-and-a-half LIM domains protein 2 (FHL2) is an anti-hypertrophic adaptor protein that regulates cardiac myocyte signalling and function. Herein, we identified cardiomyopathy-associated 5 (CMYA5) as a novel FHL2 interaction partner in cardiac myocytes. In vitro pull-down assays demonstrated interaction between FHL2 and the N- and C-terminal regions of CMYA5. The interaction was verified in adult cardiac myocytes by proximity ligation assays. Immunofluorescence and confocal microscopy demonstrated co-localisation in the same subcellular compartment. The binding interface between FHL2 and CMYA5 was mapped by peptide arrays. Exposure of neonatal rat ventricular myocytes to a CMYA5 peptide covering one of the FHL2 interaction sites led to an increase in cell area at baseline, but a blunted response to chronic phenylephrine treatment. In contrast to wild-type hearts, loss or reduced FHL2 expression in Fhl2-targeted knockout mouse hearts or in a humanised mouse model of hypertrophic cardiomyopathy led to redistribution of CMYA5 into the perinuclear and intercalated disc region. Taken together, our results indicate a direct interaction of the two adaptor proteins FHL2 and CMYA5 in cardiac myocytes, which might impact subcellular compartmentation of CMYA5.

The Roles of FHL3 in Cancer

The four and a half LIM domain protein 3, also named the LIM-protein FHL3, belongs to the LIM-only family. Based on the special structure of LIM-only proteins, FHL3 can perform significant functions in muscle proliferation and cardiovascular diseases by regulating cell growth and signal transduction. In recent years, there has been increasing evidence of a relation between FHLs and tumor biology, since FHL3 is often overexpressed or downregulated in different cancers. On the one hand, FHL3 can function as a tumor suppressor and influence the expression of downstream genes. On the other hand, FHL3 can also play a role as an oncoprotein in some cancers to promote tumor progression via phosphorylation. Thus, FHL3 is proposed to have a dual effect on cancer progression, reflecting its complex roles in cancer. This review focuses on the roles of FHL3 in cancer progression and discusses the interaction of FHL3 with other proteins and transcription factors. Finally, the clinical significance of FHL3 for the treatment of cancers is discussed.

FHL1 Overexpression as A Inhibitor of Lung Cancer Cell Invasion via Increasing RhoGDIß mRNA Expression

Objective

Four and a half Lin-11, Isl-1, Mac-3 (LIM) protein 1 (FHL1) is one of the FHL protein family, which is regarded as a tumor suppressor in the multiple malignant tumors. In this study, we aimed to explore the regulatory effects and mechanisms of FHL1 on lung cancer cell invasion.

Materials and Methods

In this experimental study, bioinformatics analysis of FHL1 transcripts in human lung adenocarcinomas of TCGA database was performed. Quantitative real-time polymerase chain reaction (PCR) was performed to detect FHL1 mRNA expression in 15 paired human lung cancer tissues and their adjacent normal lung tissues, or lung cancer cell lines (A549 and H1299) in comparison with human bronchial epithelial cell line (Beas- 2B). Moreover, western blot was used to analyze FHL1 and rho GDP-dissociation inhibitor beta (RhoGDIβ) protein expression in the indicated cell lines. Also, transwell assays were employed to measure the migrated, and invaded of indicated cell lines.

Results

FHL1 transcripts were downregulated in the human lung adenocarcinoma. The impaired FHL1 transcripts were positively correlated with advanced tumor node metastasis (TNM) stage. Moreover, as compared to the adjacent normal lung tissues, FHL1 mRNA was low expressed in 15 paired human lung cancer tissues than their adjacent normal lung tissues. Besides, FHL1 mRNA and protein expression were also reduced in H1299 and A549 cell lines in comparison with Beas-2B cell line. Overexpressed FHL1 protein inhibited the invasive ability of H1299 and A549 cell lines. Mechanically, FHL1 protein overexpression increased the RhoGDIβ protein and mRNA abundance, while knockdown of RhoGDIβ protein, completely restored the invasion ability of A549 (Flag-FHL1) cell line.

Conclusion

Our findings indicated that as a key FHL1 downstream regulator, RhoGDIβ is in charge of FHL1 inhibiting lung cancer cell invasion abilities, providing a critical insight into understanding the role of FHL1 for lung cancer development.

The titin N2B and N2A regions: biomechanical and metabolic signaling hubs in cross-striated muscles

Muscle specific signaling has been shown to originate from myofilaments and their associated cellular structures, including the sarcomeres, costameres or the cardiac intercalated disc. Two signaling hubs that play important biomechanical roles for cardiac and/or skeletal muscle physiology are the N2B and N2A regions in the giant protein titin. Prominent proteins associated with these regions in titin are chaperones Hsp90 and αB-crystallin, members of the four-and-a-half LIM (FHL) and muscle ankyrin repeat protein (Ankrd) families, as well as thin filament-associated proteins, such as myopalladin. This review highlights biological roles and properties of the titin N2B and N2A regions in health and disease. Special emphasis is placed on functions of Ankrd and FHL proteins as mechanosensors that modulate muscle-specific signaling and muscle growth. This region of the sarcomere also emerged as a hotspot for the modulation of passive muscle mechanics through altered titin phosphorylation and splicing, as well as tethering mechanisms that link titin to the thin filament system.

The Adhesome Network: Key Components Shaping the Tumour Stroma

Beyond the conventional perception of solid tumours as mere masses of cancer cells, advanced cancer research focuses on the complex contributions of tumour-associated host cells that are known as "tumour microenvironment" (TME). It has been long appreciated that the tumour stroma, composed mainly of blood vessels, cancer-associated fibroblasts and immune cells, together with the extracellular matrix (ECM), define the tumour architecture and influence cancer cell properties. Besides soluble cues, that mediate the crosstalk between tumour and stroma cells, cell adhesion to ECM arises as a crucial determinant in cancer progression. In this review, we discuss how adhesome, the intracellular protein network formed at cell adhesions, regulate the TME and control malignancy. The role of adhesome extends beyond the physical attachment of cells to ECM and the regulation of cytoskeletal remodelling and acts as a signalling and mechanosensing hub, orchestrating cellular responses that shape the tumour milieu.

Four and a half LIM domains protein 1 can be as a double-edged sword in cancer progression

Four and a half LIM domains protein 1 (FHL1), as the name suggests, contains four and a half LIM domains capable of interacting with various molecules, including structural proteins, kinases, and transcriptional machinery. FHL1 contains a zinc-finger domain and performs diverse roles in regulation of gene transcription, cytoarchitecture, cell proliferation, and signal transduction. Several studies have validated the importance of FHL1 in muscle development, myopathy, and cardiovascular diseases. Mutations in the FHL1 gene are associated with various myopathies. Recently, FHL1 was identified as a major host factor for chikungunya virus (CHIKV) infection in both humans and mice. Based on more recent findings over the last decade, FHL1 is proposed to play a dual role in cancer progression. On the one hand, FHL1 expression is suppressed in several cancer types, which correlates with increased metastatic disease and decreased survival. Moreover, FHL1 is reported to inhibit tumor cell growth and migration by associating with diverse signals, such as TGF-β and ER, and therefore considered a tumor suppressor. On the other hand, FHL1 can function as an oncogenic protein that promotes tumor progression upon phosphorylation, reflecting complex roles in cancer. This review primarily focuses on the dual role and underlying mechanisms of action of FHL1 in human cancer progression and its clinical relevance.

Mechanistic Justifications of Systemic Therapeutic Oxygenation of Tumors to Weaken the Hypoxia Inducible Factor 1α-Mediated Immunosuppression

Long-term studies of anti-pathogen and anti-tumor immunity have provided complementary genetic and pharmacological evidence for the immunosuppressive and immunomodulatory effects of Hypoxia-HIF-1α and adenosine-mediated suppression via the A2A adenosine receptor signaling pathway (Hypoxia-A2A-adenosinergic). This pathway is life saving when it protects inflamed tissues of vital organs from collateral damage by overactive anti-pathogen immune cells or enables the differentiation of cells of adaptive immunity. However, the Hypoxia-A2A-adenosinergic immunosuppression can also prevent tumor rejection by inhibiting the anti-tumor effects of T and NK cells. In addition, this suppressive pathway has been shown to mask tumors due to the hypoxia-HIF-α-mediated loss of MHC Class I molecules on tumor cells. It is suggested that it will be impossible to realize the full anti-tumor capacities of current cancer immunotherapies without simultaneous administration of anti-Hypoxia-A2A-Adenosinergic drugs that inactivate this tumor-protecting mechanism in hypoxic and adenosine-rich tumors.Here, we overview the supporting evidence for the conceptually novel immunotherapeutic motivation to breathe supplemental oxygen (40-60%) or to repurpose already available oxygenation agents in combination with current immunotherapies. Preclinical studies provide strong support for oxygen immunotherapy to enable much stronger tumor regression by weakening immunosuppression by A2A adenosine receptors and by the Hypoxia➔HIF-1α axis. The results of these studies emphasize the value of systemic oxygenation as clinically feasible, promising, and as a valuable tool for mechanistic investigations of tumor biology and cancer immunology. Perhaps the most effective and feasible among individual members of this novel class of anti-tumor drugs are oxygenation agents.

FHL3 links cell growth and self-renewal by modulating SOX4 in glioma

Differentiation status significantly affects the properties of malignant glioma cells, with non-stem cells inducing tumor enlargement and stem-like cells driving tumor initiation and treatment resistance. It is not completely understood how the same protein can have a distinct role in these cell populations. Here, we report that four and a half LIM domain protein 3 (FHL3) has an inhibitory effect on proliferation in non-stem glioma cells and a non-proliferative effect in glioma stem cells (GSCs). In GSCs, we show that FHL3 interacts with the Smad2/3 protein complex at the SOX4 promoter region, inhibits SOX4 transcriptional activity by recruiting PPM1A phosphatase to Smad2/3, and then suppresses GSC tumor sphere formation and self-renewal in vitro and in vivo via downregulation of SOX2 expression. Altogether, these findings highlight the role of FHL3 as a stemness-suppressor in regulation of the Smad2/3-SOX4-SOX2 axis in glioma.

Epigenetic regulators: multifunctional proteins modulating hypoxia-inducible factor-α protein stability and activity

The hypoxia-inducible factor (HIF) is a heterodimeric transcription factor governing a transcriptional program in response to reduced O2 availability in metazoans. It contributes to physiology and pathogenesis of many human diseases through its downstream target genes. Emerging studies have shown that the transcriptional activity of HIF is highly regulated at multiple levels and the epigenetic regulators are essential for HIF-mediated transactivation. In this review, we will discuss the comprehensive regulation of HIF transcriptional activity by different types of epigenetic regulators.

A compendium of proteins that interact with HIF-1α

Hypoxia-inducible factor 1 (HIF-1) is the founding member of a family of transcription factors that function as master regulators of oxygen homeostasis. HIF-1 is composed of an O₂-regulated HIF-1α subunit and a constitutively expressed HIF-1β subunit. This review provides a compendium of proteins that interact with the HIF-1α subunit, many of which regulate HIF-1 activity in either an O₂-dependent or O₂-independent manner.

MicroRNA-338-5p modulates pulmonary hypertension-like injuries caused by SO2, NO2 and PM2.5 co-exposure through targeting the HIF-1α/Fhl-1 pathway

The role of ambient air pollution is considered to be important in the development of chronic obstructive pulmonary disease (COPD), and pulmonary hypertension (PH) is a common clinical manifestation of COPD. However, many studies have mainly focused on the adverse health effects of a single air pollutant, ignoring the combined toxicity of multiple pollutants. In the present study, we co-exposed mice to coal-burning air pollutants (SO₂, NO₂ and PM_2.5), and confirmed PH-like injury occurrence by airflow limitation, marked abnormal endothelin-1 (ET-1) and endothelial nitric oxide synthase (eNOS) expression, and histopathological and ultrastructural alteration. Global microRNA (miRNA) arrays identified three significantly changed miRNAs homologous with humans (miR-338-5p, miR-450b-3p and miR-142-5p), and we targeted miR-338-5p based on real-time reverse transcription-PCR (RT-PCR) validation. Furthermore, bioinformatic and dual-luciferase reporter gene analyses indicated that miR-338-5p bound to 3'-UTR of hypoxia-inducible factor 1α (HIF-1α) mRNA and down-regulation of miR-338-5p led to the increased expression of HIF-1α and its related gene four-and-a-half LIM (Lin-11, Isl-1 and Mec-3) domain 1 (Fhl-1) and contributed to PH. This study provides evidence for the role of miRNAs in PH through targeting HIF-1α/Fhl-1 pathway after air pollutants co-exposure and implies new insights into the molecular markers for COPD caused by air pollution.

Protein kinase A-dependent phosphorylation stimulates the transcriptional activity of hypoxia-inducible factor 1

Hypoxia-inducible factor 1 (HIF-1) activates the transcription of genes encoding proteins that enable cells to adapt to reduced O2 availability. Proteins encoded by HIF-1 target genes play a central role in mediating physiological processes that are dysregulated in cancer and heart disease. These diseases are also characterized by increased production of cyclic adenosine monophosphate (cAMP), the allosteric activator of cAMP-dependent protein kinase A (PKA). Using glutathione S-transferase pull-down, coimmunoprecipitation, and mass spectrometry analyses, we demonstrated that PKA interacts with HIF-1α in HeLa cervical carcinoma cells and rat cardiomyocytes. PKA phosphorylated Thr(63) and Ser(692) on HIF-1α in vitro and enhanced HIF transcriptional activity and target gene expression in HeLa cells and rat cardiomyocytes. PKA inhibited the proteasomal degradation of HIF-1α in an O2-independent manner that required the phosphorylation of Thr(63) and Ser(692) and was not affected by prolyl hydroxylation. PKA also stimulated the binding of the coactivator p300 to HIF-1α to enhance its transcriptional activity and counteracted the inhibitory effect of asparaginyl hydroxylation on the association of p300 with HIF-1α. Furthermore, increased cAMP concentrations enhanced the expression of HIF target genes encoding CD39 and CD73, which are enzymes that convert extracellular adenosine 5'-triphosphate to adenosine, a molecule that enhances tumor immunosuppression and reduces heart rate and contractility. These data link stimuli that promote cAMP signaling, HIF-1α-dependent changes in gene expression, and increased adenosine, all of which contribute to the pathophysiology of cancer and heart disease.

X-linked FHL1 as a novel therapeutic target for head and neck squamous cell carcinoma

To identify X-linked novel tumor suppressors could provide novel insights to improve prognostic prediction and therapeutic strategy for some cancers. Using bioinformatics and Venn analysis of gene transcriptional profiling, we identified downregulation of X-linked four-and-a-half LIM domains protein 1 (FHL1) gene in head and neck squamous cell carcinoma (HNSCC). FHL1 functions were investigated and confirmed in vitro and in vivo. FHL1 downregulated mechanisms were analyzed in HNSCCs by using methylation specific PCR, bisulfate-based sequencing, 5-Aza-dC treatment and chromatin immunoprecipitation assays. Two independent HNSCC cohorts (the training cohort n = 105 and the validation cohort n = 101) were enrolled to evaluate clinical implications of FHL1 expression by using real-time PCR or immunohistochemistry. FHL1 mRNA and protein expressions were frequently decreased in HNSCCs. FHL1 overexpression or depletion gave rise to suppress or promote cell growth through Cyclin D1, Cyclin E and p27 dysregulations. Abundant occupy of EZH2 or H3K27Me3 was observed in FHL1 promoter except for DNA hypermethylation. Reduced FHL1 mRNA expression was notably associated with poor differentiation (p = 0.020). Multivariate analysis demonstrated FHL1 mRNA expression was identified as independent prognostic predictors of overall survival (OS) (p = 0.036; HR 0.520; Cl, 0.283-0.958) and disease-free survival (DFS) (p = 0.041; HR 0.527; Cl, 0.284-0.975), which was validated by another independent cohort (p = 0.021; HR 0.404; Cl, 0.187-0.871 for OS; p = 0.011; HR 0.407; Cl, 0.203-0.815 for DFS). These results suggest epigenetic silencing of X-linked FHL1 may have an important role in adjuvant therapeutic intervention of HNSCCs and is an independent prognostic factor in patients with HNSCCs.

PRDX2 and PRDX4 are negative regulators of hypoxia-inducible factors under conditions of prolonged hypoxia

Hypoxia-inducible factors (HIFs) control the transcription of genes that are crucial for the pathogenesis of cancer and other human diseases. The transcriptional activity of HIFs is rapidly increased upon exposure to hypoxia, but expression of some HIF target genes decreases during prolonged hypoxia. However, the underlying mechanism for feedback inhibition is not completely understood. Here, we report that peroxiredoxin 2 (PRDX2) and PRDX4 interact with HIF-1α and HIF-2α in vitro and in hypoxic HeLa cells. Prolonged hypoxia increases the nuclear translocation of PRDX2 and PRDX4. As a result, PRDX2 and PRDX4 impair HIF-1 and HIF-2 binding to the hypoxia response elements of a subset of HIF target genes, thereby inhibiting gene transcription in cells exposed to prolonged hypoxia. PRDX2 and PRDX4 have no effect on the recruitment of p300 and RNA polymerase II to HIF target genes and the enzymatic activity of PRDX2 and PRDX4 is not required for inhibition of HIF-1 and HIF-2. We also demonstrate that PRDX2 is a direct HIF target gene and that PRDX2 expression is induced by prolonged hypoxia. These findings uncover a novel feedback mechanism for inhibition of HIF transcriptional activity under conditions of prolonged hypoxia.

Protein-protein interactions of the LIM-only protein FHL2 and functional implication of the interactions relevant in cardiovascular disease

FHL2 belongs to the LIM-domain only proteins and contains four and a half LIM domains, each of which are composed of two zinc finger structures. FHL2 exhibits specific interaction with proteins exhibiting diverse functions, including transmembrane receptors, transcription factors and transcription co-regulators, enzymes, and structural proteins. The function of these proteins is regulated by FHL2, which modulates intracellular signal transduction pathways involved in a plethora of cellular tasks. The present review summarizes the current knowledge on the protein interactome of FHL2 and provides an overview of the functional implication of these interactions in apoptosis, migration, and regulation of nuclear receptor function. FHL2 was originally identified in the heart and there is extensive literature available on the role of FHL2 in the cardiovascular system, which is also summarized in this review.

FHL3 differentially regulates the expression of MyHC isoforms through interactions with MyoD and pCREB

In skeletal muscle, muscle fiber types are defined by four adult myosin heavy chain (MyHC) isoforms. Four and a half LIM domain protein 3 (FHL3) regulates myoblasts differentiation and gene expression by acting as a transcriptional co-activator or co-repressor. However, how FHL3 regulates MyHC expression is currently not clear. In this study, we found that FHL3 down-regulated the expression of MyHC 1/slow and up-regulated the expression of MyHC 2a and MyHC 2b, whereas no significant effect was found on MyHC 2x expression. MyoD and phosphorylated cAMP response element binding protein (pCREB) played important roles in the regulation of MyHC 1/slow and MyHC 2a expression by FHL3, respectively. FHL3 could interact with MyoD, CREB and pCREB in vivo. pCREB had stronger interaction with the cyclic AMP-responsive elements (CRE) of the MyHC 2a promoter compared with CREB, and FHL3 significantly affected the binding capacity of pCREB to CRE. We established a model in which FHL3 promotes the expression of MyHC 2a through CREB-mediated transcription and inhibits the expression of MyHC 1/slow by inhibiting MyoD transcription activity during myogenesis. Our data support the notion that FHL3 plays important roles in the regulation of muscle fiber type composition.

Ribotrap analysis of proteins associated with FHL3 3'untranslated region in glioma cells

OBJECTIVE

To screen the proteins associated with four-and-a-half LIM domains 3 (FHL3) 3' untranslated region (3'UTR) in glioma cells.

METHODS

Western blot was adopted to detect the regulatory effect of poly(C)-binding protein 2 (PCBP2) on FHL3. Biotin pull-down and sliver staining were employed to screen and verify the candidate binding proteins of FHL3 3'UTR. Then liquid chromatography-tandem mass spectrometry (LC-MS/MS) and molecule annotation system were used to identify and analyze the candidate binding proteins. Immuno- precipitation was conducted to study the interaction between PCBP2 and polypyrimidine tract-binding protein 1 (PTBP1), a binding protein identified by LC-MS/MS.

RESULTS

PCBP2 could bind to FHL3 mRNA 3'UTR-A and inhibited the expression of FHL3 in T98G glioms cells. 22 candidate binding proteins were identified. Among them, there were 11 RNA binding proteins, including PCBP2. PTBP1 associated with FHL3 mRNA 3'UTR and interacted with PCBP2 protein.

CONCLUSIONS

PCBP2 and PTBP1 can both associate with FHL3 mRNA 3'UTR through forming a protein complex.

Systemic oxygenation weakens the hypoxia and hypoxia inducible factor 1α-dependent and extracellular adenosine-mediated tumor protection

Intratumoral hypoxia and hypoxia inducible factor-1α (HIF-1-α)-dependent CD39/CD73 ectoenzymes may govern the accumulation of tumor-protecting extracellular adenosine and signaling through A2A adenosine receptors (A2AR) in tumor microenvironments (TME). Here, we explored the conceptually novel motivation to use supplemental oxygen as a treatment to inhibit the hypoxia/HIF-1α-CD39/CD73-driven accumulation of extracellular adenosine in the TME in order to weaken the tumor protection. We report that hyperoxic breathing (60 % O2) decreased the TME hypoxia, as well as levels of HIF-1α and downstream target proteins of HIF-1α in the TME according to proteomic studies in mice. Importantly, oxygenation also downregulated the expression of adenosine-generating ectoenzymes and significantly lowered levels of tumor-protecting extracellular adenosine in the TME. Using supplemental oxygen as a tool in studies of the TME, we also identified FHL-1 as a potentially useful marker for the conversion of hypoxic into normoxic TME. Hyperoxic breathing resulted in the upregulation of antigen-presenting MHC class I molecules on tumor cells and in the better recognition and increased susceptibility to killing by tumor-reactive cytotoxic T cells. Therapeutic breathing of 60 % oxygen resulted in the significant inhibition of growth of established B16.F10 melanoma tumors and prolonged survival of mice. Taken together, the data presented here provide proof-of principle for the therapeutic potential of systemic oxygenation to convert the hypoxic, adenosine-rich and tumor-protecting TME into a normoxic and extracellular adenosine-poor TME that, in turn, may facilitate tumor regression. We propose to explore the combination of supplemental oxygen with existing immunotherapies of cancer.

KEY MESSAGES

Oxygenation decreases levels of tumor protecting hypoxia. Oxygenation decreases levels of tumor protecting extracellular adenosine. Oxygenation decreases expression of HIF-1alpha dependent tumor-protecting proteins. Oxygenation increases MHC class I expression and enables tumor regression.

Cyclin-dependent kinases regulate lysosomal degradation of hypoxia-inducible factor 1α to promote cell-cycle progression

Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that mediates adaptive responses to oxygen deprivation. In addition, the HIF-1α subunit has a nontranscriptional role as a negative regulator of DNA replication through effects on minichromosome maintenance helicase loading and activation. However, some cell types continue to replicate under hypoxic conditions. The mechanism by which these cells maintain proliferation in the presence of elevated HIF-1α levels is unclear. Here we report that HIF-1α physically and functionally interacts with cyclin-dependent kinase 1 (Cdk1) and Cdk2. Cdk1 activity blocks lysosomal degradation of HIF-1α and increases HIF-1α protein stability and transcriptional activity. By contrast, Cdk2 activity promotes lysosomal degradation of HIF-1α at the G1/S phase transition. Blocking lysosomal degradation by genetic or pharmacological means leads to HIF-1α-dependent cell-cycle arrest, demonstrating that lysosomal degradation of HIF-1α is an essential step for the maintenance of cell-cycle progression under hypoxic conditions.

Analysis of the transcriptome in hyperoxic lung injury and sex-specific alterations in gene expression

Exposure to high concentration of oxygen (hyperoxia) leads to lung injury in experimental animal models and plays a role in the pathogenesis of diseases such as Acute Respiratory Distress Syndrome (ARDS) and Bronchopulmonary dysplasia (BPD) in humans. The mechanisms responsible for sex differences in the susceptibility towards hyperoxic lung injury remain largely unknown. The major goal of this study was to characterize the changes in the pulmonary transcriptome following hyperoxia exposure and further elucidate the sex-specific changes. Male and female (8-10 wk) wild type (WT) (C57BL/6J) mice were exposed to hyperoxia (FiO2>0.95) and gene expression in lung tissues was studied at 48 h. A combination of fold change ≥1.4 and false discovery rate (FDR)<5% was used to define differentially expressed genes (DEGs). Overrepresentation of gene ontology terms representing biological processes and signaling pathway impact analysis (SPIA) was performed. Comparison of DEG profiles identified 327 genes unique to females, 585 unique to males and 1882 common genes. The major new findings of this study are the identification of new candidate genes of interest and the sex-specific transcriptomic changes in hyperoxic lung injury. We also identified DEGs involved in signaling pathways like MAP kinase and NF-kappa B which may explain the differences in sex-specific susceptibility to hyperoxic lung injury. These findings highlight changes in the pulmonary transcriptome and sex-specific differences in hyperoxic lung injury, and suggest new pathways, whose components could serve as sex-specific biomarkers and possible therapeutic targets for acute lung injury (ALI)/acute respiratory distress (ARDS) in humans.

Comparative proteomic profiles of the normal and aganglionic hindgut in human Hirschsprung disease

BACKGROUND

Hirschsprung disease (HSCR) is the third most common congenital disorder of the gastrointestinal tract. This study aims to elucidate changes in protein expression between the normal and aganglionic hindgut in human HSCR.

METHODS

The biopsies were obtained from the normal and aganglionic hindgut in human HSCR, and the comparative proteomics were analyzed by mass spectrometry (MS)-based two-dimensional gel electrophoresis (2DE).

RESULTS

A total of 932-986 protein spots were identified in each of the gut segments, among which 30 spots had at least an eightfold difference in volume (%). Of the 30 differentially expressed spots, 15 proteins were identified via sequence analysis. Among these 15 proteins, eight were upregulated and seven were downregulated in the aganglionic group. The well-represented classes included biomarkers of enteric ganglions, extracellular matrix proteins, LIM domain proteins, serum proteins, and other pleiotropic proteins. Five proteins were selected and verified by western blotting and real-time PCR, and the results were consistent with the results of 2DE.

CONCLUSION

MS-based 2DE can help to identify pathological relevant proteins in HSCR; it defines an extensive protein catalog of the normal and aganglionic hindgut and may constitute the basis to understand pathophysiological mechanisms related to the HSCR.

Biophysical properties of intrinsically disordered p130Cas substrate domain--implication in mechanosensing

Mechanical stretch-induced tyrosine phosphorylation in the proline-rich 306-residue substrate domain (CasSD) of p130Cas (or BCAR1) has eluded an experimentally validated structural understanding. Cellular p130Cas tyrosine phosphorylation is shown to function in areas without internal actomyosin contractility, sensing force at the leading edge of cell migration. Circular dichroism shows CasSD is intrinsically disordered with dominant polyproline type II conformations. Strongly conserved in placental mammals, the proline-rich sequence exhibits a pseudo-repeat unit with variation hotspots 2–9 residues before substrate tyrosine residues. Atomic-force microscopy pulling experiments show CasSD requires minimal extension force and exhibits infrequent, random regions of weak stability. Proteolysis, light scattering and ultracentrifugation results show that a monomeric intrinsically disordered form persists for CasSD in solution with an expanded hydrodynamic radius. All-atom 3D conformer sampling with the TraDES package yields ensembles in agreement with experiment when coil-biased sampling is used, matching the experimental radius of gyration. Increasing β-sampling propensities increases the number of prolate conformers. Combining the results, we conclude that CasSD has no stable compact structure and is unlikely to efficiently autoinhibit phosphorylation. Taking into consideration the structural propensity of CasSD and the fact that it is known to bind to LIM domains, we propose a model of how CasSD and LIM domain family of transcription factor proteins may function together to regulate phosphorylation of CasSD and effect machanosensing.

Mechanical stretching of cells causes the substrate domain of p130Cas (CasSD) to be phosphorylated on 15 tyrosine residues embedded along its length. CasSD is rich in proline and surprisingly well conserved in placental mammals. Stretching of CasSD by atomic force microscopy has identified that it requires far less force than normal folded proteins. Classical biophysical analyses have determined that CasSD is a typical intrinsically disordered protein, a difficult-to-study group of molecules covering about 30% of human proteins. The average size of CasSD is larger and elongated than folded globular proteins but smaller than chemically denatured proteins. We have simulated a large number of all-atom protein structures using a fast all-atom sampling method. The result is in good agreement with the experimental observation. As it is already known that stretching somehow exposes the tyrosine residues to phosphorylation, a mechanism is proposed where straightening of the p130Cas substrate domain backbone conformation through mechanical stretching can lead to dissociation of p130Cas-binding LIM domain proteins and exposure of CasSD tyrosine residues for phosphorylation. This study has led to a new model of a protein-based mechanism of force sensing at the leading edge of cells that allows the cells to feel their way as they move.

Identification and characterization of MT-1X as a novel FHL3-binding partner

Four and a half LIM domain protein 3 (FHL3) is a member of the FHL protein family that plays roles in the regulation of cell survival, cell adhesion and signal transduction. However, the mechanism of action for FHL3 is not yet clear. The aim of present study was to identify novel binding partner of FHL3 and to explore the underlying mechanism. With the use of yeast two-hybrid screening system, FHL3 was used as the bait to screen human fetal hepatic cDNA library for interacting proteins. Methionine-1X was identified as a novel FHL3 binding partner. The interaction between FHL3 and the full length MT-1X was further confirmed by yeast two-hybrid assay, co-immunoprecipitation and GST pull-down assays. Furthermore,the result demonstrated that MT-1X knockdown promoted the FHL3-induced inhibitory effect on HepG2 cells by regulating FHL3-mediated Smad signaling and involving in the modulation the expression of G2/M phase-related proteins through interaction with FHL3. These findings suggest that functional interactions between FHL3 and MT-1X may provide some clues to the mechanisms of FHL3-regulated cell proliferation.

Four-and-a-half LIM domains proteins are novel regulators of the protein kinase D pathway in cardiac myocytes

PKD (protein kinase D) is a serine/threonine kinase implicated in multiple cardiac roles, including the phosphorylation of the class II HDAC5 (histone deacetylase isoform 5) and thereby de-repression of MEF2 (myocyte enhancer factor 2) transcription factor activity. In the present study we identify FHL1 (four-and-a-half LIM domains protein 1) and FHL2 as novel binding partners for PKD in cardiac myocytes. This was confirmed by pull-down assays using recombinant GST-fused proteins and heterologously or endogenously expressed PKD in adult rat ventricular myocytes or NRVMs (neonatal rat ventricular myocytes) respectively, and by co-immunoprecipitation of FHL1 and FHL2 with GFP–PKD1 fusion protein expressed in NRVMs. In vitro kinase assays showed that neither FHL1 nor FHL2 is a PKD1 substrate. Selective knockdown of FHL1 expression in NRVMs significantly inhibited PKD activation and HDAC5 phosphorylation in response to endothelin 1, but not to the α₁-adrenoceptor agonist phenylephrine. In contrast, selective knockdown of FHL2 expression caused a significant reduction in PKD activation and HDAC5 phosphorylation in response to both stimuli. Interestingly, neither intervention affected MEF2 activation by endothelin 1 or phenylephrine. We conclude that FHL1 and FHL2 are novel cardiac PKD partners, which differentially facilitate PKD activation and HDAC5 phosphorylation by distinct neurohormonal stimuli, but are unlikely to regulate MEF2-driven transcriptional reprogramming.

Protein kinase D has multiple roles in cardiac myocytes, where its regulatory mechanisms remain incompletely defined. In the present study we identify four-and-a-half LIM domains proteins 1 and 2 as novel binding partners and regulators of protein kinase D in this cell type.

EAF2 suppresses hypoxia-induced factor 1α transcriptional activity by disrupting its interaction with coactivator CBP/p300

Previous studies revealed that the potential tumor suppressor EAF2 binds to and stabilizes pVHL, suggesting that EAF2 may function by disturbing the hypoxia signaling pathway. However, the extent to which EAF2 affects hypoxia and the mechanisms underlying this activity remain largely unknown. In this study, we found that EAF2 is a hypoxia response gene harboring the hypoxia response element (HRE) in its promoter. By taking advantage of the pVHL-null cell lines RCC4 and 786-O, we demonstrated that hypoxia-induced factor 1α (HIF-1α), but not HIF-2α, induced EAF2 under hypoxia. Subsequent experiments showed that EAF2 bound to and suppressed HIF-1α but not HIF-2α transactivity. In addition, we observed that EAF2 inhibition of HIF-1α activity resulted from the disruption of p300 recruitment and that this occurred independently of FIH-1 (factor inhibiting HIF-1) and Sirt1. Furthermore, we found that EAF2 protected cells against hypoxia-induced cell death and inhibited cellular uptake of glucose under hypoxic conditions, suggesting that EAF2 indeed may act by modulating the hypoxia-signaling pathway. Our findings not only uncover a unique feedback regulation loop between EAF2 and HIF-1α but also provide a novel insight into the mechanism of EAF2 tumor suppression.

Sirtuin-7 inhibits the activity of hypoxia-inducible factors

Hypoxia-inducible factor (HIF) 1 and HIF-2 are heterodimeric proteins composed of an oxygen-regulated HIF-1α or HIF-2α subunit, respectively, and a constitutively expressed HIF-1β subunit, which mediate adaptive transcriptional responses to hypoxia. Here, we report that Sirt7 (sirtuin-7) negatively regulates HIF-1α and HIF-2α protein levels by a mechanism that is independent of prolyl hydroxylation and that does not involve proteasomal or lysosomal degradation. The effect of Sirt7 was maintained in the presence of the sirtuin inhibitor nicotinamide and upon deletion or mutation of its deacetylase domain, indicating a non-catalytic function. Knockdown of Sirt7 led to an increase in HIF-1α and HIF-2α protein levels and an increase in HIF-1 and HIF-2 transcriptional activity. Thus, we identify a novel molecular function of Sirt7 as a negative regulator of HIF signaling.

Epigenetic regulation of hypoxia-responsive gene expression: focusing on chromatin and DNA modifications

Mammalian cells constantly encounter hypoxia, which is a stress condition occurring during development and physiological processes. To adapt to this inevitable condition, cells develop various mechanisms to cope with this stress and survive. In addition to the activation/stabilization of transcriptional regulators (hypoxia-inducible factors), other epigenetic mechanisms of gene regulation are used. These mechanisms are mediated by various players including transcriptional coregulators, chromatin-modifying complexes, histone modification enzymes and changes in DNA methylation status. Recent progress in all the fields mentioned above has greatly improved the knowledge of how gene regulation contributes to the hypoxic response. This review should shed light on the molecular epigenetic mechanisms of hypoxia-induced gene regulation and help understand the processes adapted by cells to cope with hypoxia.

MicroRNA-206 is involved in hypoxia-induced pulmonary hypertension through targeting of the HIF-1α/Fhl-1 pathway

Hypoxia-induced pulmonary hypertension (PH), which is characterized by vasoconstriction and subsequent structural remodeling of blood vessels, is an important event in chronic obstructive pulmonary disease patients and in people living at high altitudes. Hypoxia-inducible factor-1α (HIF-1α) and its regulator four-and-a-half LIM (Lin-11, Isl-1 and Mec-3) domain 1 (Fhl-1) have important roles in hypoxia-induced PH. MicroRNA-206 (miR-206) is critical for myogenesis and related diseases; however, the role of miR-206 in hypoxia-induced PH is unknown. miR-206 expression was evaluated in a hypoxic rat model and in cultured hypoxic pulmonary artery smooth muscle cells (PASMCs) using real-time quantitative PCR (RT-qPCR). HIF-1α and Fhl-1 expression were evaluated using RT-qPCR, western blotting, immunohistochemistry and immunofluorescence. The function of miR-206 was assessed by transfecting miR-206 mimics and inhibitors. Dual-luciferase reporter gene assays and western blotting were performed to validate the target genes of miR-206. siRNA targeted against Fhl-1 was used to investigate the effect of Fhl-1 on miR-206. Flow cytometry was used to detect the cell cycle phase distribution in each group of PASMCs. Significant downregulation of miR-206 in hypoxic lung tissue and PASMCs was identified, whereas HIF-1α and Fhl-1 were upregulated in these samples. The expression of miR-206 in the serum was different from that in the lung tissue. Transfection of pre-miR miR-206 in hypoxic conditions led to increased expression of HIF-1α and Fhl-1 rather than abolishing hypoxia-induced HIF-1α and Fhl-1, as was expected, and promoted the entry of cells into the S phase and enhanced PASMC proliferation. Fhl-1-targeted siRNA in PASMC prevented cell proliferation and led to an increased proportion of cells in the G1 phase without altering miR-206 expression. Bioinformatic analysis and dual-luciferase reporter gene assays revealed direct evidence for miR-206 targeting of HIF-1α. In conclusion, hypoxia-induced downregulation of miR-206 promotes PH by targeting the HIF-1α/Fhl-1 pathway in PASMCs. miR-206 could be a triggering factor of early stage of hypoxia-induced PH.

LIM-only protein FHL2 activates NF-κB signaling in the control of liver regeneration and hepatocarcinogenesis

Four-and-a-half LIM-only protein 2 (FHL2) is an important mediator in many signaling pathways. In this study, we analyzed the functions of FHL2 in nuclear factor κB (NF-κB) signaling in the liver. We show that FHL2 enhanced tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6) activity in transcriptional activation of NF-κB targets by stabilizing the protein. TRAF6 is a binding partner of FHL2 and an important component of the Toll-like receptor-NF-κB pathway. Knockdown of FHL2 in 293-hTLR4/MD2-CD14 cells impaired lipopolysaccharide (LPS)-induced NF-κB activity, which regulates expression of inflammatory cytokines. Indeed, FHL2(-/-) macrophages showed significantly reduced production of TNF and interleukin 6 (IL-6) following LPS stimulation. TNF and IL-6 are the key cytokines that prime liver regeneration after hepatic injury. Following partial hepatectomy, FHL2(-/-) mice exhibited diminished induction of TNF and IL-6 and delayed hepatocyte regeneration. In the liver, NF-κB signaling orchestrates inflammatory cross talk between hepatocytes and hepatic immune cells that promote chemical hepatocarcinogenesis. We found that deficiency of FHL2 reduced susceptibility to diethylnitrosamine-induced hepatocarcinogenesis, correlating with the activator function of FHL2 in NF-κB signaling. Our findings demonstrate FHL2 as a positive regulator of NF-κB activity in liver regeneration and carcinogenesis and highlight the importance of FHL2 in both hepatocytes and hepatic immune cells.

Epithelial expression of FHL2 is negatively associated with metastasis-free and overall survival in colorectal cancer

Background:

Four-and-a-half LIM domains protein 2 (FHL2) is a component of the focal adhesion structures and has been suggested to have a role in cancer progression. It has been shown to be overexpressed in the colorectal cancer (CRC).

Methods:

Here, we examined a possible prognostic value of FHL2 in CRC. Immunohistochemistry for FHL2 was performed on 296 CRCs without distant metastases at the time of surgery. Staining in the epithelial compartment was quantitatively evaluated using image analysis, and results were related to clinical variables. Antibody specificity was tested using small-interfering RNA transfection in hTERT-immortalised myofibroblasts.

Results:

Varying degrees of cytoplasmic FHL2 expression by neoplastic epithelial cells were detectable in all cases. Higher FHL2 expression in the epithelial compartment was an independent adverse prognostic factor. Multivariate Cox analysis shows that expression in the tumour invasion front (P<0.001) as well as in the centre of the tumour (P<0.001) was associated with metachronous metastases independently of the clinicopathological variables; expression in the tumour invasion front was also associated with overall survival independently of the clinicopathological variables (P<0.01).

Conclusion:

Higher FHL2 expression is involved in CRC progression and correlates with the development of metachronous metastases and overall survival, suggesting that FHL2 is an independent adverse prognostic indicator for CRC.

Chronic carvedilol treatment partially reverses the right ventricular failure transcriptional profile in experimental pulmonary hypertension

Right ventricular failure (RVF) is the most frequent cause of death in patients with pulmonary arterial hypertension (PAH); however, specific therapies targeted to treat RVF have not been developed. Chronic treatment with carvedilol has been shown to reduce established maladaptive right ventricle (RV) hypertrophy and to improve RV function in experimental PAH. However, the mechanisms by which carvedilol improves RVF are unknown. We have previously demonstrated by microarray analysis that RVF is characterized by a distinct gene expression profile when compared with functional, compensatory hypertrophy. We next sought to identify the effects of carvedilol on gene expression on a genome-wide basis. PAH and RVF were induced in male Sprague-Dawley rats by the combination of VEGF-receptor blockade and chronic hypoxia. After RVF was established, rats were treated with carvedilol or vehicle for 4 wk. RNA was isolated from RV tissue and hybridized for microarray analysis. An initial prediction analysis of carvedilol-treated RVs showed that the gene expression profile resembled the RVF prediction set. However, a more extensive analysis revealed a small group of genes differentially expressed after carvedilol treatment. Further analysis categorized these genes in pathways involved in cardiac hypertrophy, mitochondrial dysfunction, and protein ubiquitination. Genes encoding proteins in the cardiac hypertrophy and protein ubiquitination pathways were downregulated in the RV by carvedilol, while genes encoding proteins in the mitochondrial dysfunction pathway were upregulated by carvedilol. These gene expression changes may explain some of the mechanisms that underlie the functional improvement of the RV after carvedilol treatment.

RNA-binding protein PCBP2 modulates glioma growth by regulating FHL3

PCBP2 is a member of the poly(C)-binding protein (PCBP) family, which plays an important role in posttranscriptional and translational regulation by interacting with single-stranded poly(C) motifs in target mRNAs. Several PCBP family members have been reported to be involved in human malignancies. Here, we show that PCBP2 is upregulated in human glioma tissues and cell lines. Knockdown of PCBP2 inhibited glioma growth in vitro and in vivo through inhibition of cell-cycle progression and induction of caspase-3-mediated apoptosis. Thirty-five mRNAs were identified as putative PCBP2 targets/interactors using RIP-ChIP protein-RNA interaction arrays in a human glioma cell line, T98G. Four-and-a-half LIM domain 3 (FHL3) mRNA was downregulated in human gliomas and was identified as a PCBP2 target. Knockdown of PCBP2 enhanced the expression of FHL3 by stabilizing its mRNA. Overexpression of FHL3 attenuated cell growth and induced apoptosis. This study establishes a link between PCBP2 and FHL3 proteins and identifies a new pathway for regulating glioma progression.

Chaperone-mediated autophagy targets hypoxia-inducible factor-1α (HIF-1α) for lysosomal degradation

Hypoxia-inducible factor-1 (HIF-1) is a heterodimeric transcription factor that mediates adaptive responses to hypoxia. We demonstrate that lysosomal degradation of the HIF-1α subunit by chaperone-mediated autophagy (CMA) is a major regulator of HIF-1 activity. Pharmacological inhibitors of lysosomal degradation, such as bafilomycin and chloroquine, increased HIF-1α levels and HIF-1 activity, whereas activators of chaperone-mediated autophagy, including 6-aminonicotinamide and nutrient starvation, decreased HIF-1α levels and HIF-1 activity. In contrast, macroautophagy inhibitors did not increase HIF-1 activity. Transcription factor EB, a master regulator of lysosomal biogenesis, also negatively regulated HIF-1 activity. HIF-1α interacts with HSC70 and LAMP2A, which are core components of the CMA machinery. Overexpression of HSC70 or LAMP2A decreased HIF-1α protein levels, whereas knockdown had the opposite effect. Finally, hypoxia increased the transcription of genes involved in CMA and lysosomal biogenesis in cancer cells. Thus, pharmacological and genetic approaches identify CMA as a major regulator of HIF-1 activity and identify interplay between autophagy and the response to hypoxia.