Hypomorphism in human NSMCE2 linked to primordial dwarfism and insulin resistance
Felicity Payne, … , Mark O’Driscoll, Robert Semple
Felicity Payne, … , Mark O’Driscoll, Robert Semple
Published August 8, 2014
Citation Information: J Clin Invest. 2014;124(9):4028-4038. https://doi.org/10.1172/JCI73264.
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Research Article Endocrinology

Hypomorphism in human NSMCE2 linked to primordial dwarfism and insulin resistance

Abstract

Structural maintenance of chromosomes (SMC) complexes are essential for maintaining chromatin structure and regulating gene expression. Two the three known SMC complexes, cohesin and condensin, are important for sister chromatid cohesion and condensation, respectively; however, the function of the third complex, SMC5–6, which includes the E3 SUMO-ligase NSMCE2 (also widely known as MMS21) is less clear. Here, we characterized 2 patients with primordial dwarfism, extreme insulin resistance, and gonadal failure and identified compound heterozygous frameshift mutations in NSMCE2. Both mutations reduced NSMCE2 expression in patient cells. Primary cells from one patient showed increased micronucleus and nucleoplasmic bridge formation, delayed recovery of DNA synthesis, and reduced formation of foci containing Bloom syndrome helicase (BLM) after hydroxyurea-induced replication fork stalling. These nuclear abnormalities in patient dermal fibroblast were restored by expression of WT NSMCE2, but not a mutant form lacking SUMO-ligase activity. Furthermore, in zebrafish, knockdown of the NSMCE2 ortholog produced dwarfism, which was ameliorated by reexpression of WT, but not SUMO-ligase–deficient NSMCE. Collectively, these findings support a role for NSMCE2 in recovery from DNA damage and raise the possibility that loss of its function produces dwarfism through reduced tolerance of replicative stress.

Authors

Felicity Payne, Rita Colnaghi, Nuno Rocha, Asha Seth, Julie Harris, Gillian Carpenter, William E. Bottomley, Eleanor Wheeler, Stephen Wong, Vladimir Saudek, David Savage, Stephen O’Rahilly, Jean-Claude Carel, Inês Barroso, Mark O’Driscoll, Robert Semple

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Figure 4

Increased micronucleus formation, impaired S phase progression, and increased SCE in LCLs with NSMCE2/MMS21 mutations.

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Increased micronucleus formation, impaired S phase progression, and incr...
(A) Binucleates in LCLs from WT, P1, and from a Bloom syndrome patient, either untreated (Unt) or following repeated exposure to HU (50 μM/d for 4 days). (B) HU-induced MN formation in Cyt-B–induced binucleate LCLs. (C) BrdU flow cytometry profiles from WT and P1 LCLs either untreated or following treatment with low-dose HU (250 μM). S phase content (boxed area) following a BrdU pulse 30 minutes prior to each time point is shown. (D) Normalized total S phase content compared with that of untreated cells at each time point. Means ± SD are shown (n = 3). (E) BLM foci formation in P1 LCLs relative to WT following treatment with HU (1 mM for 16 hours) or IR (10 Gy for 16 hours). (F) BLM foci formation in primary dermal fibroblasts from P1 compared with WT following HU exposure (1 mM for 24 hours). (G) UV radiation–induced SCEs in WT and P1 LCLs compared with untreated cells. These effects, although significant, were not as profound as those observed in BLM patient LCLs, which exhibited 23 ± 6 SCEs/metaphase in untreated cells and 38 ± 4 SCEs/metaphase following UV irradiation. *P < 0.05 (unpaired t test).