SIAH2 (seven in absentia homolog 2 (Drosophila))

2011-01-01   Jianfei Qi , Zeev Ronai 

Signal Transduction Program, Sanford-Burnham Medical Research Institute, La Jolla, CA, 92037, USA




Atlas Image
Genomic organization of human Siah2. The line indicates intron and boxes indicate coding regions (exon 1-2) of the gene. Exon and intron lengths, the ATG transcription start site and the TGA stop codon are indicated.


The human Siah2 gene is composed of 2 exons spanning a genomic region of about 22.4 Kb.


The transcript length of human Siah2 is 2632 bp. The open reading frame of the coding region is 975 bp.


No pseudogene of Siah2 has been reported.


Atlas Image
Domains of human Siah2 protein.


Human Siah2 protein consists of 324 amino acids, with a molecular weight of 36 KDa. Siah protein consists of an N-terminal ring domain, followed by two zinc finger motifs, and a C-terminal substrate binding domain (SBD). The ring domain is the catalytic domain that recruits E2 ubiquitin-conjugating enzymes, while the SBD mediates the binding of adaptor proteins or some Siah substrate proteins. The structure of murine Siah1a SBD has been solved. The structure reveals that Siah is a dimeric protein, and the SBD adopts an eight-stranded beta-sandwich fold (Polekhina et al., 2001). The substrate binding groove is formed by the beta-sandwich fold and the beta-strand that connects to the second zinc finger domain (House et al., 2005).


Siah2 mRNA is widely expressed in the embryonic and adult mouse tissues. It is expressed at a higher level in the olfactory epithelium, retina, forebrain and proliferating cartilage of developing bone (Della et al., 1993). Siah2 mRNA is also expressed in most human tissues (Hu et al., 1997).


Siah protein can be localized in both cytoplasm and nucleus.


Siah2 is the mammalian homolog of Drosophila SINA (seven in absentia), which interacts with transcriptional repressor Tramtrack via adaptor protein PHYL (Phyllopod) and induces the proteasomal degradation of Tramtrack, thereby determining R7 cell fate (Li et al., 1997; Tang et al., 1997). As a ring-finger E3 ubiquitin ligase, Siah targets the degradation of diverse substrates via ubiquitin-proteasome pathway, and affects multiple signaling pathways such as HIF (Nakayama et al., 2004), Ras (Nadeau et al., 2007; Schmidt et al., 2007), NF-kB (Polekhina et al., 2002; Habelhah et al., 2002), and beta-catenin (Liu et al., 2001; Matsuzawa and Reed, 2001). Siah2 transcription is upregulated by hypoxia (Nakayama et al., 2004); p38-mediated phosphorylation of mouse Siah2 on Thr24 and Ser29 alters its subcellular localization (Khurana et al., 2006); HIPK2-mediated phosphorylation of human Siah2 on Thr 26, Ser 28 and Ser 68 decreases the stability of Siah2 and impairs its interaction with HIPK2 (Calzado et al., 2009).
Over 20 Siah substrates have been reported (Nakayama et al., 2009) and some of them can be degradated by Siah2, Siah1 or both of them. In contrast to Siah1a knockout mice which exibit growth retardation and spermatogenesis defect, Siah2 knockout mice display no apparent phenotype, whereas Siah2 and Siah1a double knockout mice are embryonic or neonatal lethal, suggesting that the two Siah homologs have both overlapping and distinct functions in vivo (Frew et al., 2003). Despite the diverse substrates of Siah identified in vitro, loss of Siah2 (or both Siah2 and Siah1a) in vivo largely has no effect on the levels of many Siah substrates and the physiological processes associated with these substrates (Frew et al., 2002; Frew et al., 2003).
Siah2 is implicated in the regulation of hypoxia response through its effect on HIF prolyl hydroxylases or HIPK2 (Nakayama et al., 2004; Calzado et al., 2009). Siah2 knockout mice subject to hypoxia showed impaired respiratory response and defect to adjust levels of red blood cells (Nakayama et al., 2004). Siah2 has been shown to be required for development and progression of several types of cancers via its regulation of HIF or Ras pathways (House et al., 2009). Siah2-dependent degradation of Pard3A is found to control germinal zone exit of neuronal progenitors or immature neurons in mice (Famulski et al., 2010).


Homologs: Human has two Siah genes (Siah1 and Siah2) (Hu et al., 1997), while mouse has three Siah genes (Siah2, Siah1a, Siah1b) (Della et al., 1993). Human Siah2 shares 77% identity with human Siah1 (Hu et al., 1997).
Orthologs: Highly conserved Siah2 orthologs have been identified in all multicellular organisms examined (Nakayama et al., 2009).



No SIAH2 mutations have been reported.

Implicated in

Entity name
Lung cancer
Ahmed et al. showed that Siah2 knockdown in human lung cancer cell lines (BZR, A549, H727, and UMC11) inhibited MAPK-ERK signaling, reduced cell proliferation and increased apoptosis; Siah2 knockdown also reduced anchorage-independent growth of A549 cells in soft agar, and blocked the growth of A549 xenograft tumors in nude mice (Ahmed et al., 2007).
Entity name
Qi et al. showed that inhibition of Siah2 activity using different inhibitory proteins blocked tumor formation or metastasis of SW1 melanoma cells in a syngeneic mouse model due to the inhibition of Ras and HIF pathways, respectively (Qi et al., 2008). Similary, Shah et al. showed that a putative chemical inhibitor of Siah2, menadione, decreased the levels of HIF-1alpha and phospho-ERK in human melanoma cell line UACC903 and abolished the growth of xenograft tumor in nude mice (Shah et al., 2009).
Entity name
Breast cancer
Möller et al. showed that inhibition of Siah in a mouse breast cancer cell line reduced the xenograft tumor growth and prolonged the survival of mice due to inhibition of HIF pathway (Möller et al., 2009). Behling et al. examined the SIAH staining in 65 patients of ductal carcinoma in situ (DCIS). Higher level of Siah staining was observed in tumors compared with the normal adjacent tissues, and in tumors with more aggressive features. There was also higher Siah staining in specimens from patients with recurrence as compared to patients without recurrence. This study stuggests that Siah may serve as a prognostic biomarker that predicts DCIS progression to invasive breast cancer (Behling et al., 2010).
Entity name
Pancreatic cancer
Schmidt et al. showed that inhibition of Siah activity attenuated MAPK-ERK signaling, blocked RAS-induced focus formation in fibroblasts, abolished anchorage-independent growth of human pancreatic cancer cells in soft agar and xenograft tumor growth in nude mice (Schmidt et al., 2008).
Entity name
Prostate cancer
Qi et al. showed that knockout of Siah2 in the TRAMP model abolished the formation of prostate neuroendocrine tumor, inhibition of Siah2 activity blocked hypoxia-induced neuroendocrine differentiation (NED) in prostate cancer cells or in the xenogaft tumors, and Siah2 protein levels were higher in high-grade PCa that expresss NE markers. This study suggests that Siah2 plays a key role in development of prostate NE tumor and NED of human PCa by controling a cooperation between HIF and NE-specific transcription factor FoxA2 (Qi et al., 2010).


Pubmed IDLast YearTitleAuthors
190016092008Effect of disrupting seven-in-absentia homolog 2 function on lung cancer cell growth.Ahmed AU et al
210888882011Increased SIAH expression predicts ductal carcinoma in situ (DCIS) progression to invasive carcinoma.Behling KC et al
190434062009An inducible autoregulatory loop between HIPK2 and Siah2 at the apex of the hypoxic response.Calzado MA et al
84045351993Isolation and characterisation of murine homologues of the Drosophila seven in absentia gene (sina).Della NG et al
211096322010Siah regulation of Pard3A controls neuronal cell adhesion during germinal zone exit.Famulski JK et al
124177192002Normal p53 function in primary cells deficient for Siah genes.Frew IJ et al
146455262003Generation and analysis of Siah2 mutant mice.Frew IJ et al
124114932002Stress-induced decrease in TRAF2 stability is mediated by Siah2.Habelhah H et al
166159112006Elucidation of the substrate binding site of Siah ubiquitin ligase.House CM et al
199201902009Siah proteins: novel drug targets in the Ras and hypoxia pathways.House CM et al
94030641997Characterization of human homologs of the Drosophila seven in absentia (sina) gene.Hu G et al
170030452006Regulation of the ring finger E3 ligase Siah2 by p38 MAPK.Khurana A et al
92670271997Photoreceptor cell differentiation requires regulated proteolysis of the transcriptional repressor Tramtrack.Li S et al
113898402001Siah-1 mediates a novel beta-catenin degradation pathway linking p53 to the adenomatous polyposis coli protein.Liu J et al
113898392001Siah-1, SIP, and Ebi collaborate in a novel pathway for beta-catenin degradation linked to p53 responses.Matsuzawa SI et al
188500112009Inhibition of Siah ubiquitin ligase function.Möller A et al
168888012007Regulation of Sprouty2 stability by mammalian Seven-in-Absentia homolog 2.Nadeau RJ et al
193725752009The ubiquitin ligase Siah2 and the hypoxia response.Nakayama K et al
117423462002Siah ubiquitin ligase is structurally related to TRAF and modulates TNF-alpha signaling.Polekhina G et al
206093502010Siah2-dependent concerted activity of HIF and FoxA2 regulates formation of neuroendocrine phenotype and neuroendocrine prostate tumors.Qi J et al
180898102007Inhibition of RAS-mediated transformation and tumorigenesis by targeting the downstream E3 ubiquitin ligase seven in absentia homologue.Schmidt RL et al
197122062009Inhibition of Siah2 ubiquitin ligase by vitamin K3 (menadione) attenuates hypoxia and MAPK signaling and blocks melanoma tumorigenesis.Shah M et al
92670261997PHYL acts to down-regulate TTK88, a transcriptional repressor of neuronal cell fates, by a SINA-dependent mechanism.Tang AH et al

Other Information

Locus ID:

NCBI: 6478
MIM: 602213
HGNC: 10858
Ensembl: ENSG00000181788


dbSNP: 6478
ClinVar: 6478
TCGA: ENSG00000181788


Gene IDTranscript IDUniprot

Expression (GTEx)



PathwaySourceExternal ID
Metabolism of proteinsREACTOMER-HSA-392499
Post-translational protein modificationREACTOMER-HSA-597592
Amyloid fiber formationREACTOMER-HSA-977225
Immune SystemREACTOMER-HSA-168256
Adaptive Immune SystemREACTOMER-HSA-1280218
Class I MHC mediated antigen processing & presentationREACTOMER-HSA-983169
Antigen processing: Ubiquitination & Proteasome degradationREACTOMER-HSA-983168
Developmental BiologyREACTOMER-HSA-1266738
Axon guidanceREACTOMER-HSA-422475
Netrin-1 signalingREACTOMER-HSA-373752
Ub-specific processing proteasesREACTOMER-HSA-5689880

Protein levels (Protein atlas)

Not detected


Pubmed IDYearTitleCitations
152101142004Siah2 regulates stability of prolyl-hydroxylases, controls HIF1alpha abundance, and modulates physiological responses to hypoxia.148
254380542015Hypoxia regulates Hippo signalling through the SIAH2 ubiquitin E3 ligase.71
235183482013The E3 ubiquitin ligase Siah2 contributes to castration-resistant prostate cancer by regulation of androgen receptor transcriptional activity.63
180708882008Monoubiquitylation of alpha-synuclein by seven in absentia homolog (SIAH) promotes its aggregation in dopaminergic cells.62
197306832009The variant rs1867277 in FOXE1 gene confers thyroid cancer susceptibility through the recruitment of USF1/USF2 transcription factors.59
190434062009An inducible autoregulatory loop between HIPK2 and Siah2 at the apex of the hypoxic response.44
161413432005Estrogen down-regulation of the corepressor N-CoR: mechanism and implications for estrogen derepression of N-CoR-regulated genes.36
190016092008Effect of disrupting seven-in-absentia homolog 2 function on lung cancer cell growth.33
170030452006Regulation of the ring finger E3 ligase Siah2 by p38 MAPK.30
188500112009Inhibition of Siah ubiquitin ligase function.29


Jianfei Qi ; Zeev Ronai

SIAH2 (seven in absentia homolog 2 (Drosophila))

Atlas Genet Cytogenet Oncol Haematol. 2011-01-01

Online version: