cancers Review FADD in Cancer: Mechanisms of Altered Expression and Function, and Clinical Implications 1 2,3 2,3,4,5, , José L Marín-Rubio , Laura Vela-Martín , José Fernández-Piqueras * y and 2,3,4,5, , María Villa-Morales * y 1 Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4HH, UK; [email protected] 2 Departamento de Biología, Universidad Autónoma de Madrid, 28049 Madrid, Spain; [email protected] 3 Centro de Biología Molecular Severo Ochoa (CBMSO), 28049 Madrid, Spain 4 Centro de Investigaciones Biomédicas en Red de Enfermedades Raras (CIBERER), 28029 Madrid, Spain 5 IIS-Fundación Jiménez Díaz, 28040 Madrid, Spain * Correspondence: [email protected] (J.F.-P.); [email protected] or [email protected] (M.V.-M.); Tel.: +34-911-964627 (J.F.-P.); +34-911-964653 (M.V.-M.); Fax: +34-911-964420 (J.F.-P. & M.V.-M.) These authors contributed equally to this work. y Received: 12 August 2019; Accepted: 27 September 2019; Published: 29 September 2019 Abstract: FADD was initially described as an adaptor molecule for death receptor-mediated apoptosis, but subsequently it has been implicated in nonapoptotic cellular processes such as proliferation and cell cycle control. During the last decade, FADD has been shown to play a pivotal role in most of the signalosome complexes, such as the necroptosome and the inflammasome. Interestingly, various mechanisms involved in regulating FADD functions have been identified, essentially posttranslational modifications and secretion. All these aspects have been thoroughly addressed in previous reviews. However, FADD implication in cancer is complex, due to pleiotropic effects. It has been reported either as anti- or protumorigenic, depending on the cell type. Regulation of FADD expression in cancer is a complex issue since both overexpression and downregulation have been reported, but the mechanisms underlying such alterations have not been fully unveiled. Posttranslational modifications also constitute a relevant mechanism controlling FADD levels and functions in tumor cells. In this review, we aim to provide detailed, updated information on alterations leading to changes in FADD expression and function in cancer. The participation of FADD in various biological processes is recapitulated, with a mention of interesting novel functions recently proposed for FADD, such as regulation of gene expression and control of metabolic pathways. Finally, we gather all the available evidence regarding the clinical implications of FADD alterations in cancer, especially as it has been proposed as a potential biomarker with prognostic value. Keywords: FADD; chromosomal alterations; mutations; polymorphisms; transcription factors; epigenetic regulation; posttranslational modifications; gene expression; metabolism; clinical implications 1. Regulation of FADD Gene Expression 1.1. Genetic and Chromosomal Alterations Affecting FADD The FADD gene is located on chromosome 11q13.3 in humans, and consists of two exons separated by a 2-kb intron and only one isoform. FADD is expressed in every adult and embryonic tissue in mice and humans [1,2] (Figure1). Cancers 2019, 11, 1462; doi:10.3390/cancers11101462 www.mdpi.com/journal/cancers Cancers 2019, 11, 2 of 27 1. Regulation of FADD Gene Expression 1.1. Genetic and Chromosomal Alterations Affecting FADD The FADD gene is located on chromosome 11q13.3 in humans, and consists of two exons separated by a 2-kb intron and only one isoform. FADD is expressed in every adult and embryonic Cancers 2019, 11, 1462 2 of 27 tissue in mice and humans [1,2] (Figure 1). FigureFigure 1. FADDFADD expressionexpression in in healthy human tissues, performed by RNA sequencing.sequencing. ( (AA)) Data Data obtainedobtained from from BioProject BioProject PRJEB4337 PRJEB4337 of of samples samples from from 95 95 individuals individuals representing representing 27 27 different different healthy healthy tissuestissues [3]. [3]. RPKM, RPKM, Reads Reads Per Per Kilobase Kilobase Million. Million. (B (B) )Data Data obtained obtained from from GTEx GTEx Analysis Analysis Release Release V7 V7 (dbGaP(dbGaP Accession Accession phs000424.v7.p2). phs000424.v7.p2). Ex Expressionpression values values are are shown shown in in transcripts transcripts per per million million (TPM), (TPM), calculatedcalculated from from a a gene gene model model with with isoforms isoforms collapsed collapsed to to a a single single gene gene and and no no other normalization stepssteps applied. applied. Box Box plots plots are are shown shown as as median median and and 25th 25th and and 75th 75th percentiles; percentiles; points points are are displayed displayed as as outliersoutliers if if they they are are above above or below 1.5 times the interquartile range. FADDFADD expression is altered in many cancer types. This This is, is, however, however, a a controversial issue, issue, since since bothboth overexpression [4[4–10]–10] and and downregulation downregulation [11 [11–15]–15] have have been been observed, observed, depending depending on the on cancer the cancertype. Accordingtype. According to The to Human The Human Protein Protein Atlas, FADDAtlas, FADD protein protein levels arelevels low are in mostlow in normal most normal tissues. tissues.In cancer, In FADDcancer,is FADD detected is indetected all tumor in all types tumor analyzed types byanalyzed RNA sequencing by RNA sequencing according toaccording The Cancer to TheGenome Cancer Atlas Genome (TCGA), Atlas and FADD(TCGA), protein and levelsFADD obtained protein bylevels immunohistochemistry obtained by immunohistochemistry with two different withantibodies two different reveal results antibodies that arereveal consistent results with that RNA-seqare consistent and/or with protein RNA-seq/gene characterizationand/or protein/gene data characterization(Figure2). A variety data (Figure of FADD 2). A protein variety levelsof FADD can protein be observed levels can across be observed the di ff acrosserent tumorthe different types; tumorthe mechanisms types; the mechanisms responsible for responsible altered expression for altered are, expression however, are, not however, always elucidated. not always elucidated. Cancers 2019, 11, 1462 3 of 27 Cancers 2019, 11, 3 of 27 FigureFigure 2. FADD 2. FADDexpression expression in cancer.in cancer. ( A(A)) RNA-sequencingRNA-sequencing data data from from The TheCancer Cancer Genome Genome Atlas Atlas (TCGA) project of Genomic Data Commons (GDC). Seventeen cancer types representing 21 cancer (TCGA) project of Genomic Data Commons (GDC). Seventeen cancer types representing 21 cancer subtypes with a corresponding major cancer type in The Human Pathology Atlas were included to subtypesallow with for a correspondingcomparisons with major the protein cancer staining type in data The from Human The PathologyHuman Protein Atlas Atlas. were The included FPKMs to allow for comparisons(number fragments with the per protein kilobase staining of exon per data million from re Theads) Humanwere used Protein for quantification Atlas. The of expression FPKMs (number fragmentswith per a detection kilobase threshold of exon of per1 FPKM. million (B,C) reads) FADD wereprotein used levels for from quantification The Human Protein of expression Atlas. For with a detectioneach threshold cancer, color-coded of 1 FPKM. bars (B indicate,C) FADD the proteinpercentage levels of patients from The (maximum: Human 12) Protein with high Atlas. and For each cancer,medium color-coded protein bars expression indicate level. the Low percentage or not detect of patientsed protein(maximum: expression results 12) within a white high bar. and (B medium) Results obtained using HPA001464 antibody. Cases of colorectal, breast, ovarian, urothelial, gastric, protein expression level. Low or not detected protein expression results in a white bar. (B) Results pancreatic, and liver cancers, and melanomas showed weak to moderate cytoplasmic positivity. The obtainedremaining using HPA001464 cancers were antibody. negative. ( CasesC) Results of colorectal, obtained using breast, CAB ovarian,010209 antibody. urothelial, The gastric,majority pancreatic, of and liver cancers, and melanomas showed weak to moderate cytoplasmic positivity. The remaining cancers were negative. (C) Results obtained using CAB010209 antibody. The majority of cancer cells showed weak to moderate cytoplasmic positivity. Nucleolar staining was observed in several cases. A few breast cancers were strongly stained. (D) Selection of five standard cancer tissue samples representative of the overall staining pattern. Scale bar: 50 µm. Cancers 2019, 11, 1462 4 of 27 A major event leading to overexpression is DNA amplification. Chromosome 11q13.3 is a 1.7 Mb-region that contains 12 other genes apart from FADD [7]. Amplification of this region has been frequently found in human cancers and is associated with poor prognosis. Among the candidate genes within the region, FADD has attracted interest since it was described as the only gene in the minimum region of overlap within the amplification in a series of squamous cell carcinomas of the head and neck (HNSCC) [16]. Furthermore, this group and others have demonstrated the association between FADD amplification and high FADD levels with poor overall survival and disease-free survival, especially if both events occur together [6,17,18]. This supports the notion that FADD is a driver of the tumorigenic effects of the 11q13.3 amplification. Based on the results from the recent TCGA PanCancer Atlas Studies