SP3 and AP-1 mediate transcriptional activation of the lamin A proximal promoter

Veratramine modulates AP-1-dependent gene transcription by directly binding to programmable DNA

Because the transcription factor activator protein-1 (AP-1) regulates a variety of protein-encoding genes, it is a participant in many cellular functions, including proliferation, transformation, epithelial mesenchymal transition (EMT), and apoptosis. Inhibitors targeting AP-1 have potential use in the treatment of cancer and other inflammatory diseases. Here, we identify veratramine as a potent natural modulator of AP-1, which selectively binds to a specific site (TRE 5'-TGACTCA-3') of the AP-1 target DNA sequence and regulates AP-1-dependent gene transcription without interfering with cystosolic signaling cascades that might lead to AP-1 activation. Moreover, RNA-seq experiments demonstrate that veratramine does not act on the Hedgehog signaling pathway in contrast to its analogue, cyclopamine, and likely does not harbor the same teratogenicity and toxicity. Additionally, veratramine effectively suppresses EGF-induced AP-1 transactivation and transformation of JB6 P+ cells. Finally, we demonstrate that veratramine inhibits solar-ultraviolet-induced AP-1 activation in mice. The identification of veratramine and new findings in its specific regulation of AP-1 down stream genes pave ways to discovering and designing regulators to regulate transcription factor.

Identification of tissue-specific regulatory region in the zebrafish lamin A promoter

Lamins are major structural proteins present in the nuclei of metazoan cells and contribute significantly to nuclear organization and function. The expression of different types of lamins is developmentally regulated and lamin A is detectable in most differentiated tissues. Although the proximal promoter of the mammalian lamin A gene has been characterized, the tissue-specific regulatory elements of the gene have not been identified. In this study, we have cloned and functionally characterized a 2.99 kb segment upstream of exon 1 in the zebrafish lamin A gene. This fragment was able to drive GFP expression in several tissues of the developing embryo at 14-72 h post fertilization in stable transgenic lines. Deletion fragments of the 2.99 kb promoter were analyzed by microinjection into zebrafish embryos in transient assays as well as by luciferase reporter assays in cultured cells. A minimal promoter segment of 1.24 kb conferred tissue-specific expression of GFP in the zebrafish embryo as well as in a myoblast cell line. An 86 bp fragment of this 1.24 kb segment was able to activate a heterologous promoter in myoblasts. Mutational analysis revealed the importance of muscle-specific regulatory motifs in the promoter. Our results have important implications for understanding the tissue-specific regulation and functions of the lamin A gene.

The protein kinase Akt/PKB regulates both prelamin A degradation and Lmna gene expression

The serine/threonine kinase Akt/PKB is a major signaling hub integrating metabolic, survival, growth, and cell cycle regulatory signals. The definition of the phospho-motif cipher driving phosphorylation by Akt led to the identification of hundreds of putative substrates, and it is therefore pivotal to identify those whose phosphorylation by Akt is of consequence to biological processes. The Lmna gene products lamin A/C and the lamin A precursor prelamin A are type V intermediate filament proteins forming a filamentous meshwork, the lamina, underneath the inner nuclear membrane, for nuclear envelope structures organization and interphase chromatin anchoring. In our previous work, we reported that A-type lamins are phosphorylated by Akt at S301 and S404 in physiological conditions and are therefore bona fide substrates of Akt. We report here that Akt phosphorylation at S404 targets the precursor prelamin A for degradation. We further demonstrate that Akt also regulates Lmna transcription. Our study unveils a previously unknown function of Akt in the control of prelamin A stability and expression. Moreover, given the large number of diseases related to prelamin A, our findings represent a further important step bridging basic A-type lamin physiology to therapeutic approaches for lamin A-linked disorders.

Adult stem cell maintenance and tissue regeneration in the ageing context: the role for A-type lamins as intrinsic modulators of ageing in adult stem cells and their niches

Adult stem cells have been identified in most mammalian tissues of the adult body and are known to support the continuous repair and regeneration of tissues. A generalized decline in tissue regenerative responses associated with age is believed to result from a depletion and/or a loss of function of adult stem cells, which itself may be a driving cause of many age-related disease pathologies. Here we review the striking similarities between tissue phenotypes seen in many degenerative conditions associated with old age and those reported in age-related nuclear envelope disorders caused by mutations in the LMNA gene. The concept is beginning to emerge that nuclear filament proteins, A-type lamins, may act as signalling receptors in the nucleus required for receiving and/or transducing upstream cytosolic signals in a number of pathways central to adult stem cell maintenance as well as adaptive responses to stress. We propose that during ageing and in diseases caused by lamin A mutations, dysfunction of the A-type lamin stress-resistant signalling network in adult stem cells, their progenitors and/or stem cell niches leads to a loss of protection against growth-related stress. This in turn triggers an inappropriate activation or a complete failure of self-renewal pathways with the consequent initiation of stress-induced senescence. As such, A-type lamins should be regarded as intrinsic modulators of ageing within adult stem cells and their niches that are essential for survival to old age.

Nuclear lamins: major factors in the structural organization and function of the nucleus and chromatin

Over the past few years it has become evident that the intermediate filament proteins, the types A and B nuclear lamins, not only provide a structural framework for the nucleus, but are also essential for many aspects of normal nuclear function. Insights into lamin-related functions have been derived from studies of the remarkably large number of disease-causing mutations in the human lamin A gene. This review provides an up-to-date overview of the functions of nuclear lamins, emphasizing their roles in epigenetics, chromatin organization, DNA replication, transcription, and DNA repair. In addition, we discuss recent evidence supporting the importance of lamins in viral infections.

An essential GT motif in the lamin A promoter mediates activation by CREB-binding protein

Lamin A is an important component of nuclear architecture in mammalian cells. Mutations in the human lamin A gene lead to highly degenerative disorders that affect specific tissues. In studies directed towards understanding the mode of regulation of the lamin A promoter, we have identified an essential GT motif at -55 position by reporter gene assays and mutational analysis. Binding of this sequence to Sp transcription factors has been observed in electrophoretic mobility shift assays and by chromatin immunoprecipitation studies. Further functional analysis by co-expression of recombinant proteins and ChIP assays has shown an important regulatory role for CREB-binding protein in promoter activation, which is mediated by the GT motif.

c-Jun and Sp1 family are critical for retinoic acid induction of the lamin A/C retinoic acid-responsive element

The expression of A-type lamins, subdivided into lamin A and C, is developmentally regulated. Retinoic acid (RA)-induced differentiation of P19 embryonic carcinoma cells, in which A-type lamins are absent, increases the expression of lamin A/C. We previously showed, using P19 cells as a model system, that the lamin A/C promoter has a retinoic acid-responsive element (L-RARE), and that Sp1 and Sp3 bind the CACCC box of the L-RARE. In this study, we report that Sp1, Sp3, and c-Jun increase transactivation of the L-RARE during RA treatment. Sp1 and Sp3 regulate the lamin A/C promoter in Sp1-deficient SL2 cells and contribute to RA-dependent activation in GAL4-based transcriptional assays. Overexpression of c-Jun causes transactivation of a chimeric promoter consisting of four tandem L-RARE repeats fused with the luciferase gene in P19 cells. c-Jun also transactivates a reporter construct with five tandem GAL4-binding sites, only when co-expressed with either GAL4-Sp1 or Sp3 fusion proteins. Furthermore, we detect a physiological interaction between c-Jun with Sp1/Sp3 in RA-treated cells. Our data suggest that Sp1, Sp3, and c-Jun play an important role in gene expression through the L-RARE during RA treatment.

Cell-type-specific interactions at regulatory motifs in the first intron of the lamin A gene

Lamins A, C and C2 are alternatively spliced products of the LMNA gene; lamins A and C are expressed in differentiated somatic cells, whereas lamin C2 is expressed in germ cells. We have analyzed a segment of the first intron of the LMNA gene for cell-type-specific regulatory elements. We identified a 420-bp fragment that increased promoter activity in lamin A-expressing cells but repressed activity in undifferentiated cells. DNase I footprinting and electrophoretic mobility shift assays revealed two binding motifs, footprinted region A (FPRA) and FPRB. The hepatocyte nuclear factor-3beta was bound to FPRA only in somatic cell extracts and this motif had an inhibitory effect on promoter activity. The retinoic X receptor beta, RXRbeta, bound near FPRB with extracts from lamin A- or C2-expressing cells, and this site enhanced promoter activity. We have, thus, identified two novel binding sites for transcription factors in a region likely to function as an important regulatory element for the cell-type-specific transcription of A-type lamins.

Characterization and promoter analysis of the mouse nestin gene

The intermediate filament protein nestin is expressed in the neural stem cells of the developing central nervous system (CNS). Promoter analysis revealed that the minimal promoter of the mouse nestin gene resides in the region -11 to +183 of the 5'-non-coding and upstream flanking region, and that two adjacent Sp1-binding sites are necessary for promoter activity. Electrophoretic mobility-shift assays (EMSA) and supershift assays showed that Sp1 and Sp3 proteins selectively bind to the upstream Sp1 site. These results demonstrate an important functionality of Sp1 and Sp3 in regulating the expression of the mouse nestin gene.

GC box-binding transcription factors control the neuronal specific transcription of the cyclin-dependent kinase 5 regulator p35

Cyclin-dependent kinase 5 (cdk5)/p35 kinase activity is highest in post-mitotic neurons of the central nervous system and is critical for development and function of the brain. The neuronal specific activity of the cdk5/p35 kinase is achieved through the regulated expression of p35 mRNA. We have identified a small 200-bp fragment of the p35 promoter that is sufficient for high levels of neuronal specific expression. Mutational analysis of this TATA-less promoter has identified a 17-bp GC-rich element, present twice, that is both required for promoter activity and sufficient for neuronal specific transcription. A GC box within the 17-bp element is critical for both promoter activity and protein-DNA complex formation. The related transcription factors Sp1, Sp3, and Sp4 constitute most of the GC box DNA binding activity in neurons. We have found that both the relative contribution of the Sp family proteins to GC box binding and the transcriptional activity of these proteins is regulated during neuronal differentiation. Thus, our data show that the GC box-binding Sp proteins contribute to the regulation of p35 expression in neurons, suggesting changes in the Sp transcription factors level and activity may contribute to cell type-specific expression of many genes in the central nervous system.