Alternative titles; symbols
HGNC Approved Gene Symbol: SMURF2
Cytogenetic location: 17q23.3-q24.1 Genomic coordinates (GRCh38) : 17:64,542,282-64,662,307 (from NCBI)
Ubiquitination controls various cellular functions by tagging proteins for proteasomal degradation or incorporation into other regulatory complexes. Central to this system are E3 ubiquitin ligases, which function in the chain of reactions resulting in attachment of ubiquitin moieties to substrate proteins. SMURF2 is a HECT domain E3 ubiquitin ligase involved in degradation of SMADs (see 601595), TGF-beta receptor (TGFBR; see 190181), and other substrates. SMURF2 also functions in regulation of neuronal and planar cell polarity, induction of senescence, and tumor suppression (summary by Blank et al., 2012).
By searching sequence databases for proteins related to the E3 ubiquitin ligase SMURF1 (605568), Kavsak et al. (2000) identified SMURF2, which encodes a C2-WW-HECT domain ubiquitin ligase.
Using a similar strategy, Lin et al. (2000) independently cloned a cDNA encoding SMURF2, a 748-amino acid ubiquitin E3 ligase that is 83% identical to SMURF1.
Scott (2001) mapped the SMURF2 gene to chromosome 17q22-q23 based on sequence similarity between the SMURF2 sequence (GenBank AF310676) and a genomic contig (GenBank NT_010748).
Kavsak et al. (2000) found that SMURF2 associated constitutively with SMAD7 (602932). SMURF2 was nuclear, but binding to SMAD7 induced export and recruitment to activated TGFBR, where it caused degradation of receptors and of SMAD7 via proteasomal and lysosomal pathways. Gamma-interferon (IFNG; 147570), which stimulates expression of SMAD7, induced SMAD7-SMURF2 complex formation and increased TGFBR turnover, which was stabilized by blocking SMAD7 or SMURF2 expression. Furthermore, SMAD7 mutants that interfered with recruitment of SMURF2 to the receptors were compromised in their inhibitory activity. These studies defined SMAD7 as an adaptor in an E3 ubiquitin ligase complex that targets TGFBR for degradation.
Using yeast 2-hybrid assays and GST fusion-binding analysis, Lin et al. (2000) found a strong interaction of the second and third SMURF2 WW domains with the receptor-activated SMAD1 (601595), SMAD2 (601366), and SMAD3 (603109), but not the common SMAD4 (600993). Western blot analysis showed that SMURF2 selectively regulated the expression of SMAD2 and, to some extent, SMAD1, but not SMAD3, through a ubiquitination- and proteasome-dependent degradation process catalyzed by the HECT ligase. Immunoprecipitation and immunoblot analysis determined that the SMURF2/phosphorylated SMAD2 interaction was dependent on the presence of TGFB1 (190180) and occurred in the nucleus. Reporter assay analysis indicated that SMURF2 decreased SMAD2-dependent transcription.
Using protein pull-down and immunoprecipitation assays, Subramaniam et al. (2003) found that RNF11 (612598) interacted with SMURF2, leading to ubiquitination of both proteins. The interaction required the PY motif of RNF11 and WW domains 2 and 3 of SMURF2. RNF11 also interacted with the ubiquitin-conjugating protein UBCH5 (UBE2D1; 602961), but not with UBC3 (CDC34; 116948), and ubiquitination of RNF11 by SMURF2 required the PY motif. SMURF2 represses TGF-beta signaling, and Subramaniam et al. (2003) showed that RNF11 relieved SMURF2-mediated transcriptional inhibition of a TGF-beta-responsive promoter in reporter gene assays.
Using RNF11 as bait in a yeast 2-hybrid screen of a human ovary cDNA library, Li and Seth (2004) showed that human RNF11 interacted with several proteins, including AMSH (STAMBP; 606247). AMSH was ubiquitinated by SMURF2 in the presence of RNF11, and reduction in the steady-state level of AMSH required both RNF11 and SMURF2. Li and Seth (2004) concluded that RNF11 recruits AMSH to SMURF2 for ubiquitination, leading to its degradation by the 26S proteasome.
Zhang and Cohen (2004) found that telomere attrition in human fibroblasts induced SMURF2 upregulation, and this upregulation was sufficient to produce the senescence phenotype. Infection of early passage fibroblasts with retrovirus carrying SMURF2 led to morphologic and biochemical alterations characteristic of senescence, including altered gene expression and reversal of cellular immortalization by TERT (187270). Senescence induction occurred in the absence of detectable DNA damage or stress response and was independent of the E3 ligase activity of SMURF2. Zhang and Cohen (2004) showed that SMURF2 activated senescence through the RB1 (614041) and p53 (TP53; 191170) pathways.
Blank et al. (2012) found that knockdown of SMURF2 in human tumor cell lines resulted in increased levels of RNF20 protein (607699) and ubiquitination of the RNF20 substrate histone H2B (see 609904), similar to findings in Smurf2 -/- mouse embryonic fibroblasts (MEFs) (see ANIMAL MODEL). Knockdown of RNF20 increased chromatin compaction. Immunohistochemical analysis of 40 breast cancer tissues and 55 lymphomas and matched adjacent normal tissue showed that tumor formation was associated with low SMURF2 expression and high RNF20 expression. Blank et al. (2012) concluded that SMURF2 is directly involved in regulation of the DNA damage response by directing polyubiquitination and proteasomal degradation of RNF20.
Blank et al. (2012) found that Smurf2 -/- mice appeared normal at birth and early in adulthood; however, a large number of them developed tumors of all types with age. Smurf2 -/- MEFs proliferated more rapidly than wildtype at all stages. In later passages, Smurf2 -/- MEFs lost contact inhibition, showed evidence of DNA damage, and readily induced tumors following injection into nude mice. Smurf2 -/- MEFs also showed elevated protein level, but not mRNA level, of Rnf20, which was associated with relaxed chromatin compaction and elevated ubiquitination of H2B. In wildtype cells, but not Smurf2 -/- cells, proteasome inhibition elevated Rnf20 protein content. Knockdown of Rnf20 in Smurf2 -/- cells retarded cell growth and oncogenic transformation and reduced the amount of ubiquitinated H2B.
Blank, M., Tang, Y., Yamashita, M., Burkett, S. S., Cheng, S. Y., Zhang, Y. E. A tumor suppressor function of Smurf2 associated with controlling chromatin landscape and genome stability through RNF20. Nature Med. 18: 227-234, 2012. [PubMed: 22231558] [Full Text: https://doi.org/10.1038/nm.2596]
Kavsak, P., Rasmussen, R. K., Causing, C. G., Bonni, S., Zhu, H., Thomsen, G. H., Wrana, J. L. Smad7 binds to Smurf2 to form an E3 ubiquitin ligase that targets the TGF-beta receptor for degradation. Molec. Cell 6: 1365-1375, 2000. [PubMed: 11163210] [Full Text: https://doi.org/10.1016/s1097-2765(00)00134-9]
Li, H., Seth, A. An RNF11: Smurf2 complex mediates ubiquitination of the AMSH protein. Oncogene 23: 1801-1808, 2004. [PubMed: 14755250] [Full Text: https://doi.org/10.1038/sj.onc.1207319]
Lin, X., Liang, M., Feng, X.-H. Smurf2 is a ubiquitin E3 ligase mediating proteasome-dependent degradation of Smad2 in transforming growth factor-beta signaling. J. Biol. Chem. 275: 36818-36822, 2000. [PubMed: 11016919] [Full Text: https://doi.org/10.1074/jbc.C000580200]
Scott, A. F. Personal Communication. Baltimore, Md. 1/12/2001.
Subramaniam, V., Li, H., Wong, M., Kitching, R., Attisano, L., Wrana, J., Zubovits, J., Burger, A. M., Seth, A. The RING-H2 protein RNF11 is overexpressed in breast cancer and is a target of Smurf2 E3 ligase. Brit. J. Cancer 89: 1538-1544, 2003. [PubMed: 14562029] [Full Text: https://doi.org/10.1038/sj.bjc.6601301]
Zhang, H., Cohen, S. N. Smurf2 up-regulation activates telomere-dependent senescence. Genes Dev. 18: 3028-3040, 2004. [PubMed: 15574587] [Full Text: https://doi.org/10.1101/gad.1253004]