Universität zu Köln

Li, Ping (2015). Novel functions of SUN1. PhD thesis, Universität zu Köln.

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Abstract

Mutations in several genes encoding nuclear envelope associated proteins cause Emery-Dreifuss muscular dystrophy (EDMD). We analyzed fibroblasts from a patient who had a mutation in the EMD gene (p.L84Pfs*6) leading to loss of Emerin and a heterozygous mutation in SUN1 (p.A203V). The second patient harbored a heterozygous mutation in LAP2alpha (p.P426L) and a further mutation in SUN1 (p.A614V). p.A203V is located in the N-terminal domain of SUN1 facing the nucleoplasm and situated in the vicinity of the Nesprin-2 and Emerin binding site. p.A614V precedes the SUN domain which interacts with the KASH domain of Nesprins in the periplasmic space and forms the center of the LINC complex. At the cellular level we observed alterations in the amounts for several components of the nuclear envelope (NE) in patient fibroblasts and further phenotypic characteristics generally attributed to laminopathies such as increased sensitivity to heat stress. The defects were more severe than observed in EDMD cells with mutations in a single gene. In particular, in patient fibroblasts carrying the p.A203V mutation in SUN1 the alterations were aggravated. Moreover, both patient fibroblasts exhibited reduced interaction of SUN1 with Lamin A/C and when expressed ectopically in wild-type fibroblasts the SUN1 mutant proteins exhibited reduced interactions with Emerin as well. Nuclear export of mRNPs through the NPC can be roughly classified into two forms: bulk and specific export, involving an NXF1-dependent pathway and CRM1-dependent pathway, respectively. Here, we show that mammalian cells require SUN1 for efficient nuclear mRNP export. The results show that both SUN1 and SUN2 interact with hnRNP F/H and hnRNP K/J. SUN1 depletion inhibits the mRNP export, with accumulations of both hnRNPs and poly(A)+RNA in the nucleus. LMB treatment indicates that SUN1 functions in mRNA export independent of the CRM1-dependent pathway. SUN1 mediates mRNA export through its association with mRNP complex by a direct interaction with NXF1. Overexpression of GFP fused SUN1 N-terminus leads to the formation of GFP-SUN1-NT positive aggregates which contain NXF1. Additionally, SUN1 associates with the NPC through a direct interaction with Nup153, a nuclear pore component involved in mRNA export. Taken together, our results reveal that the INM protein SUN1 has additional functions aside from being a central component of the LINC complex and that it is an integral component of the mammalian mRNA export pathway suggesting a model whereby SUN1 recruits NXF1-containing mRNP onto the nuclear envelope, and hands it over to Nup153.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Li, Ping pli6@uni-koeln.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-63715
Date:	27 April 2015
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Medicine > Biochemie > Institut I für Biochemie
Subjects:	Life sciences
Uncontrolled Keywords:	Keywords Language SUN1 English EDMD English mRNA export English
Date of oral exam:	29 June 2015
Referee:	Name Academic Title Noegel, Angelika Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/6371