Lamina-associated polypeptide 2α forms complexes with heat shock proteins Hsp70 and Hsc70 in vivo

Lamin A/C modulates spatial organization and function of the Hsp70 gene locus via nuclear myosin I

The structure-function relationship of the nucleus is tightly regulated, especially during heat shock. Typically, heat shock activates molecular chaperones that prevent protein misfolding and preserve genome integrity. However, the molecular mechanisms that regulate nuclear structure-function relationships during heat shock remain unclear. Here, we show that lamin A and C (hereafter lamin A/C; both lamin A and C are encoded by LMNA) are required for heat-shock-mediated transcriptional induction of the Hsp70 gene locus (HSPA genes). Interestingly, lamin A/C regulates redistribution of nuclear myosin I (NM1) into the nucleus upon heat shock, and depletion of either lamin A/C or NM1 abrogates heat-shock-induced repositioning of Hsp70 gene locus away from the nuclear envelope. Lamins and NM1 also regulate spatial positioning of the SC35 (also known as SRSF2) speckles - important nuclear landmarks that modulates Hsp70 gene locus expression upon heat shock. This suggests an intricate crosstalk between nuclear lamins, NM1 and SC35 organization in modulating transcriptional responses of the Hsp70 gene locus during heat shock. Taken together, this study unravels a novel role for lamin A/C in the regulation of the spatial dynamics and function of the Hsp70 gene locus upon heat shock, via the nuclear motor protein NM1.This article has an associated First Person interview with the first author of the paper.

LEM4/ANKLE-2 deficiency impairs post-mitotic re-localization of BAF, LAP2α and LaminA to the nucleus, causes nuclear envelope instability in telophase and leads to hyperploidy in HeLa cells

The human LEM-domain protein family is involved in fundamental aspects of nuclear biology. The LEM-domain interacts with the barrier-to-autointegration factor (BAF), which itself binds DNA. LEM-domain proteins LAP2, emerin and MAN1 are proteins of the inner nuclear membrane; they have important functions: maintaining the integrity of the nuclear lamina and regulating gene expression at the nuclear periphery. LEM4/ANKLE-2 has been proposed to participate in nuclear envelope reassembly after mitosis and to mediate dephosphorylation of BAF through binding to phosphatase PP2A. Here, we used CRISPR/Cas9 to create several cell lines deficient in LEM4/ANKLE-2. By using time-lapse video microscopy, we show that absence of this protein severely compromises the post mitotic re-association of the nuclear proteins BAF, LAP2α and LaminA to chromosomes. These defects give rise to a strong mechanical instability of the nuclear envelope in telophase and to a chromosomal instability leading to increased number of hyperploid cells. Reintroducing LEM4/ANKLE-2 in the cells by transfection could efficiently restore the telophase association of BAF and LAP2α to the chromosomes. This rescue phenotype was abolished for N- or C-terminally truncated mutants that had lost the capacity to bind PP2A. We demonstrate also that, in addition to binding to PP2A, LEM4/ANKLE-2 binds BAF through its LEM-domain, providing further evidence for a generic function of this domain as a principal interactor of BAF.

Deregulated LAP2α expression in cervical cancer associates with aberrant E2F and p53 activities

Lamina-associated polypeptide 2 alpha (LAP2α) plays a role in maintaining nuclear structure, in nuclear assembly/disassembly, and in transcriptional regulation. Elevated LAP2α mRNA expression has been previously reported to associate with certain cancer types. The aim of this study was to investigate LAP2α expression in cervical cancer and transformed cells and to identify factors that associate with its differential expression. LAP2α expression was found to be elevated in cervical cancer tissue by microarray, qRT-PCR, and immunofluorescence analyses. LAP2α also showed elevated expression in cervical cancer cell lines and in transformed fibroblasts compared with normal cells. To determine factors associated with elevated LAP2α in cervical cancer, the effect of inhibiting HPV E7 and E6 oncoproteins was investigated. E7 inhibition resulted in a decrease in phosphorylated Rb and an associated decrease in LAP2α, suggesting a role for E2F in regulating LAP2α expression. This finding was confirmed by inhibiting DP1, a co-activator of E2F, which resulted in decreased LAP2α levels. Inhibition of E6 resulted in elevated p53 and an associated decrease in LAP2α, suggesting that p53 associates with the negative regulation of LAP2α expression. This hypothesis was tested by inhibiting p53 in normal cells, and a resultant increase in LAP2α expression was observed. In conclusion, this study provides evidence for elevated LAP2α expression in cervical cancer and suggests that E2F and p53 activities associate with the positive and negative regulation of LAP2α expression, respectively.