SKI Domain Analysis

The SKI-homologous domain / beta-TrCP degron motif 1

[1] R 2013

Recurrent SETBP1 mutations in atypical chronic myeloid leukemia. Nat Genet (2013)

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spans positions 858-871 in SETBP1. Somatic SETBP1 mutations in myeloid malignancies 2

[2] H 2013

Somatic SETBP1 mutations in myeloid malignancies. Nat Genet (2013)

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cluster at key residues: D868, S869, G870, I871. Mutations at these positions disrupt degron recognition by the SCF(beta-TrCP) E3 ubiquitin ligase complex, preventing ubiquitination and proteasomal degradation. The result is nuclear SETBP1 accumulation, which inhibits PP2A tumor suppressor activity 1

[1] R 2013

Recurrent SETBP1 mutations in atypical chronic myeloid leukemia. Nat Genet (2013)

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and upregulates HOXA9/HOXA10 transcription factors — a key oncogenic axis in myeloid neoplasms.

STRING v12.0 protein-protein interaction analysis reveals DNMT3A-EZH2 as the strongest interaction in the entire network (confidence 0.999). Both are epigenetic regulators — DNMT3A controls DNA methylation, EZH2 controls histone methylation (H3K27me3) 9

[9] T 2010

Inactivating mutations of the histone methyltransferase gene EZH2 in myeloid disorders. Nat Genet (2010)

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10

[10] A 2020

Mutational mechanisms of EZH2 inactivation in myeloid neoplasms. Leukemia (2020)

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. Their co-mutation creates a bidirectional epigenetic collapse: loss of DNA methylation fidelity (DNMT3A R882H) combined with loss of Polycomb-mediated gene silencing (EZH2 V662A LoF).

SETBP1 connects to this axis as an epigenetic hub 3

[3] R 2018

SETBP1 induces transcription of a network of development genes by acting as an epigenetic hub. Nat Commun (2018)

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through HCF1/KMT2A interaction and PP2A inhibition 1

[1] R 2013

Recurrent SETBP1 mutations in atypical chronic myeloid leukemia. Nat Genet (2013)

PubMedDOI

leading to HOXA9/HOXA10 upregulation. Runx1 repression 5

[5] BA 2016

Runx1 repression by histone deacetylation is critical for Setbp1-induced mouse myeloid leukemia development. Leukemia (2016)

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further compounds the transcriptional deregulation. With both DNMT3A (which also upregulates HOXA via hypomethylation) and SETBP1 converging on HOXA, the oncogenic signaling is amplified.

The Jaccard pathway similarity between SETBP1-IDH2 (0.588) and DNMT3A-IDH2 (0.590) is remarkably similar despite opposite co-occurrence patterns, suggesting the mutual exclusivity mechanism operates at a finer level than broad pathway redundancy.

The degron motif (codons 858-871) characterized by Piazza et al. (2013) contains 92% of all somatic SETBP1 mutations in the GENIE myeloid cohort. G870S is the second most common hotspot (136 patients), trailing only D868N (93 patients). SKI-domain mutations show consistently amplified co-occurrence ratios compared to non-SKI mutations: CSF3R O/E rises from 9.93 overall to 10.83 within the SKI subset, and CBL from 5.08 to 5.73. The SKI domain hotspot defined by Makishima et al. (2013) concentrates mutations at positions associated with monosomy 7 and poor prognosis. The SKI-domain enrichment pattern (206 of 271 SETBP1-mutated patients) validates the biological significance of this region.