Nuclear alpha spectrin: Critical roles in DNA interstrand cross-link repair and genomic stability

Abstract

Non-erythroid alpha spectrin (αIISp) is a structural protein which we have shown is present in the nucleus of human cells. It interacts with a number of nuclear proteins such as actin, lamin, emerin, chromatin remodeling factors, and DNA repair proteins. αIISp's interaction with DNA repair proteins has been extensively studied. We have demonstrated that nuclear αIISp is critical in DNA interstrand cross-link (ICL) repair in S phase, in both genomic (non-telomeric) and telomeric DNA, and in maintenance of genomic stability following ICL damage to DNA. We have proposed that αIISp acts as a scaffold aiding to recruit repair proteins to sites of damage. This involvement of αIISp in ICL repair and telomere maintenance after ICL damage represents new and critical functions for αIISp. These studies have led to development of a model for the role of αIISp in DNA ICL repair. They have been aided by examination of cells from patients with Fanconi anemia (FA), a repair-deficient genetic disorder in which a deficiency in αIISp leads to defective ICL repair in genomic and telomeric DNA, telomere dysfunction, and chromosome instability following DNA ICL damage. We have shown that loss of αIISp in FA cells is due to increased breakdown by the protease, µ-calpain. Importantly, we have demonstrated that this deficiency can be corrected by knockdown of µ-calpain and restoring αIISp levels to normal. This corrects a number of the phenotypic deficiencies in FA after ICL damage. These studies suggest a new and unexplored direction for therapeutically restoring genomic stability in FA cells and for correcting numerous phenotypic deficiencies occurring after ICL damage. Developing a more in-depth understanding of the importance of the interaction of αIISp with other nuclear proteins could significantly enhance our knowledge of the consequences of loss of αIISp on critical nuclear processes.

TheDrosophilaEGFR ligand mSpitz is delivered to cytoplasmic capes at sites of non-canonical RNA export on the nuclear envelopeviathe endosomal system

“…bIVS5-spectrin is a predominantly nuclear isoform that associates with PML bodies 36 and the nuclear matrix 37 . aIIS*-spectrin is also found in association with the nuclear matrix (ibid) and has well-documented roles in DNA inter-strand crosslink repair mediated by the FANCA/C proteins in association with the XPF/XPG/XP complex 38,39 . bH has not yet been localized to the nuclear envelope or nucleoplasm by immunofluorescence; however, bH along with the other spectrins were identified as a component of the nuclear matrix 40 suggesting that the role of bH in cape formation and nuclear envelope biology could even be direct.…”

Rare Genetic Diseases with Defects in DNA Repair: Opportunities and Challenges in Orphan Drug Development for Targeted Cancer Therapy

“…Ubiquination of the FANCD2–I complex is essential for the recruitment of nucleases to the ICL for promoting nucleolytic incision flanking the crosslink, a phenomenon referred to as ‘unhooking’ of the ICL ( Figure 2 B) [ 157 ]. FANCD2-Ub first recruits the nuclease scaffolding protein SLX4 (FANCP) to the ICL, which then promotes the recruitment of other structure-specific endonucleases like XPF-ERCC1, MUS81-EME1, FAN1, and SLX1 to the site of the ICL ( Figure 2 B) [ 158 , 159 , 160 , 161 , 162 ]. Following the unhooking step, translesion DNA polymerases such as REV7 (FANCV), and polymerase η inserts a base opposite the unhooked lesion and polymerase ζ extends DNA synthesis from the misincorporated base to fill the ssDNA gaps resulting from ICL unhooking in order to complete replication ( Figure 2 B) [ 163 , 164 ].…”

Spectrin-based pathways underlying electrical and mechanical dysfunction in cardiac disease

“…In neurons, super resolution microscopy has revealed a distinct periodic pattern of ring-like actin structures interconnected by spectrin tetramers aligned along the axon shaft [16]. Spectrin isoforms are found not only at the submembrane but also in the nucleus where they contribute to nucleoskeleton flexibility and chromosome stability [17, 18]. Interestingly, in this regard, studies point to an important role for nuclear α II -spectrin as a scaffold for repair of DNA interstrand cross-links [18].…”

“…Spectrin isoforms are found not only at the submembrane but also in the nucleus where they contribute to nucleoskeleton flexibility and chromosome stability [17, 18]. Interestingly, in this regard, studies point to an important role for nuclear α II -spectrin as a scaffold for repair of DNA interstrand cross-links [18]. Given its central role in formation of the erythrocyte membrane cytoskeleton, it is not surprising that defects in spectrin lead to erythrocyte membrane fragility, which ultimately may manifest as elliptocytosis and anemia [19].…”