SETBP1 Dysregulation in Congenital Disorders and Myeloid Neoplasms

www.impactjournals.com/oncotarget/ Oncotarget, 2017, Vol. 8, (No. 31), pp: 51920-51935 Review SETBP1 dysregulation in congenital disorders and myeloid neoplasms Nicoletta Coccaro1, Giuseppina Tota1, Antonella Zagaria1, Luisa Anelli1, Giorgina Specchia1 and Francesco Albano1 1Department of Emergency and Organ Transplantation (D.E.T.O.), Hematology Section, University of Bari, Bari, Italy Correspondence to: Francesco Albano, email: [email protected] Keywords: SETBP1, mutation, oncogene, Schinzel–Giedion syndrome, myeloid neoplasms Received: February 24, 2017 Accepted: March 30, 2017 Published: April 19, 2017 Copyright: Coccaro et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License 3.0 (CC BY 3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. ABSTRACT Myeloid malignancies are characterized by an extreme molecular heterogeneity, and many efforts have been made in the past decades to clarify the mechanisms underlying their pathogenesis. In this scenario SET binding protein 1 (SETBP1) has attracted a lot of interest as a new oncogene and potential marker, in addition to its involvement in the Schinzel-Giedon syndrome (SGS). Our review starts with the analysis of the structural characteristics of SETBP1, and extends to its corresponding physiological and pathological functions. Next, we describe the prevalence of SETBP1 mutations in congenital diseases and in hematologic malignancies, exploring how its alterations might contribute to tumor development and provoke clinical effects. Finally, we consider to understand how SETBP1 activation could be exploited in molecular medicine to enhance the cure rate. INTRODUCTION highlighted the existence of a biological difference even between entities that in some cases have overlapping In the past decade important progress has been made diagnostic criteria, as aCML and Chronic Myelomonocytic in understanding the extreme molecular heterogeneity Leukemia (CMML). characterizing myeloid neoplasms. Four years ago a Indeed, the described association of SETBP1 new player appeared in this extensive landscape of mutations with a poor clinical outcome is an important molecular alterations. As often happens when a new beginning on which to build future studies to device gene involved in tumorigenesis is discovered, also in the therapeutic targeting. case of SET binding protein 1 (SETBP1) gene, the first In this review we will discuss the domains and studies reported its involvement in the pathogenesis of a functions of SETBP1 in normal biology and in pathologic congenital disorder, called Schinzel-Giedion syndrome contexts. In the last part, we will focus on how SETBP1 (SGS). Depending on the type of mutation, the same alterations can be exploited in molecular medicine to gene may provoke different pathologic consequences; it enhance the cure rate. is even more evident when the mutation hits at germline or somatic level. FROM GENE TO PROTEIN In hematologic neoplasms, the discovery of SETBP1 as a new oncogene has helped to better define the The human SETBP1 gene, originally called SEB, molecular characteristics of pathologies such as atypical is located at the cytogenetic band q12.3 of chromosome Chronic Myeloid Leukemia (aCML), a disease initially 18, a region that contains candidate tumor suppressor defined only by negative characteristics, like the absence genes associated with deletions in cancer and leukemia of BCR-ABL1 fusion. SETBP1 mutations are found with [1]. There are two isoforms of the SETBP1 gene: the first different frequencies in almost all classes of myeloid (isoform a) encompasses a genomic region of 387613 disorders; these differences in the mutation prevalence pb, and the 6 exons encode an 9899 nt transcript, with www.impactjournals.com/oncotarget 51920 Oncotarget a predicted protein of 1596 aa; the second one (isoform proline-rich repeats, four KxKHKxK, eight LSxxL and ten b) encompasses a genomic region of 197242 pb, and 4 PxxPS repeated sentences [1] (Figure 1). exons encode a 1804 nt transcript with a predicted protein The human SET-binding region of SETBP1 has a of 242 aa. Isoform b shares with isoform a the first 3 exons high identity with mouse Setbp1, suggesting that it may (UCSC; http://genome.ucsc.edu; release Dec 2013). Piazza be conserved and that SETBP1 may play an essential role et al. only observed the longest isoform expression by in cells [1]. The binding of SETBP1 to the SET protein RNA sequencing and transcriptome profiling experiments was identified by co-immunoprecipitation and DNA in 13 aCML cases [2]. There is no other information about transfection experiments. It is well known that SET is a the expression, translation, localization and function of the proto-oncogene that has a histone acetylation inhibitory shorter isoform. activity and acts by inhibiting tumor suppressors as The SETBP1 protein, with an estimated molecular NM23-H1 and PP2A [3]. The cleavage of SET by mass of 170 kDa [1], is composed of a SET-binding Granzyme A during cytotoxic T lymphocyte-induced region, an oncoprotein SKI homologous region, three apoptosis removes the inhibition of NM23-H1, which bipartite NLS (nuclear localization signal) motifs, three translocates into the nucleus and cuts DNA [4, 5]. PP2A, AT hook domains, six PEST sequences, three sequential a major protein phosphatase, can be bound and inhibited Figure 1: SETBP1 protein structure and mutations distribution. From left to right: position map of the SETBP1 locus on chromosome 18, SETBP1 gene organization (isoform a), SETBP1 protein domains, and distribution of mutations reported on the COSMIC database (release Nov 2016). The image shows three AT hook domains (amino acids 584–596, 1016–1028, 1451–1463) [2], a SKI homologous region (amino acids 706–917) [2], a SET-binding domain (amino acids 1292–1488) [2], four repeat domains (amino acids 1466-1473, 1474-1481, 1482-1489, 1520–1543) [1, 2], three bipartite NLS motifs (amino acids 462-477, 1370-1384, 1383-1399) [1], and six PEST sequences (amino acids 1-13, 269-280, 548-561, 678-689, 806-830, 1502-1526) [1]. www.impactjournals.com/oncotarget 51921 Oncotarget by SET and likely by a homeobox protein, HOX11, acting mechanism in leukemic cells [21]. In 2012 we reported on several cell processes [6–10], such as cell proliferation, SETBP1 overexpression in a Primary Myelofibrosis differentiation, and transformation [11, 12]. The effect of (PMF) case with t(12;18)(p13;q12) evolving to AML. PP2A inhibition, observed in a human T-cell line, is the The observation of the concomitant downregulation of disruption of a G2/M cell-cycle checkpoint. SETBP1 the intronic regulatory MIR_4319 suggested a possible regulates the SET inhibitory activity of PP2A and SET/ mechanism for SETBP1 altered expression [23]. PP2A interaction by its specific SET-binding [1]. Indeed, In 2010, Hoischen et al. described for the first time SETBP1 is a major counterpart of SET, and SET/SETBP1 germline mutations in SETBP1 in a congenital disorder interaction is stronger than that of SET/PP2A, in fact called SGS [22, 24]. Then in 2013, Piazza et al. performed SETBP1 replaces PP2A in the SET/PP2A complex [1]. exome sequencing of eight aCML cases, identifying The SKI-homologous region of SETBP1 is so somatic SETBP1 mutations in two cases. Subsequent named because of the homology to the proto-oncogene analysis of the SETBP1 mutation status of a further 70 SKI. SKI intervenes as a transcriptional co-repressor, aCMLs, 574 diverse hematological malignancies and inhibiting the transcription of target genes downstream of 344 cancer cell lines revealed mutations in 24% cases. the Transforming Growth Factor-β (TGF-β) superfamily These analyses found a hotspot mutation region between [13]. This region in SETBP1 could be involved in the codons 858–871; most SETBP1 mutations (92%) were regulation of the SKI/SKI homodimer and the SKI/SNON the same as those seen in SGS, and were associated with heterodimer, causing cellular transformation [14]. higher white blood cell counts and a worse prognosis [2]. Three putative bipartite NLS motifs might be The SETBP1 region where mutations cluster is highly involved in signal-dependent nuclear transport of this conserved among vertebrates, and this suggests that it protein across the nuclear pore [1]. might have an important but still unknown biological role. The AT-hook motifs probably confer a DNA- According to the Eukaryotic Linear Motif (ELM) server, binding capability to SETBP1; especially when present in this region is a virtually perfect degron, i.e. an amino multiple copies, AT-hook motifs can cause a DNA bending acids specific sequence that channels a protein to the which could be crucial for transcriptional regulation [15]. initial degradation step. This degron in SETBP1 contains Several proteins containing these motifs are components a consensus-binding region (DpSGXXpS/pT, where pS of chromatin remodeling complexes in yeast, Drosophila, and pT are phosphorylated residues) for β-TrCP1, the and mammalian cells [16–18]. Through its AT-hook substrate recognition subunit of the E3 ubiquitin ligase, motifs, SETBP1 may control gene transcription as and might be critical for protein degradation through part of a chromatin-remodeling complex; this is also ubiquitin binding [2]. When mutated, the SETBP1 protein consistent with its predominantly nuclear localization [19]. is incapable of binding this E3 ligase subunit; this triggers Furthermore,

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