Lens-specific activity of the mouse alpha A-crystallin promoter in the absence of a TATA box: functional and protein binding analysis of the mouse alpha A-crystallin PE1 region

Transcriptional regulation of small HSP-HSF1 and beyond

The members of the small heat shock protein (sHSP) family are molecular chaperones that play major roles in development, stress responses, and diseases, and have been envisioned as targets for therapy, particularly in cancer. The molecular mechanisms that regulate their transcription, in normal, stress, or pathological conditions, are characterized by extreme complexity and subtlety. Although historically linked to the heat shock transcription factors (HSFs), the stress-induced or developmental expression of the diverse members, including HSPB1/Hsp27/Hsp25, αA-crystallin/HSPB4, and αB-crystallin/HSPB5, relies on the combinatory effects of many transcription factors. Coupled with remarkably different cis-element architectures in the sHsp regulatory regions, they confer to each member its developmental expression or stress-inducibility. For example, multiple regulatory pathways coordinate the spatio-temporal expression of mouse αA-, αB-crystallin, and Hsp25 genes during lens development, through the action of master genes, like the large Maf family proteins and Pax6, but also HSF4. The inducibility of Hsp27 and αB-crystallin transcription by various stresses is exerted by HSF-dependent mechanisms, by which concomitant induction of Hsp27 and αB-crystallin expression is observed. In contrast, HSF-independent pathways can lead to αB-crystallin expression, but not to Hsp27 induction. Not surprisingly, deregulation of the expression of sHSP is associated with various pathologies, including cancer, neurodegenerative, or cardiac diseases. However, many questions remain to be addressed, and further elucidation of the developmental mechanisms of sHsp gene transcription might help to unravel the tissue- and stage-specific functions of this fascinating class of proteins, which might prove to be crucial for future therapeutic strategies. This article is part of a Directed Issue entitled: Small HSPs in physiology and pathology.

Prediction of Gene Expression Levels and the Role of Cis-Acting Elements in Age-Related Cataract by Applying a Promoter-Based Modeling Approach

Cataract is a dynamical process of lens opacity formation involving many inter- and intracellular regulations, as well as metabolic genes and transcription factors. Using a series of microarray-derived mRNA profiles for human cataractogenesis (Hawse et al. Mol. Vision 2003, 9, 515-537), we develop a promoter-based system-theoretic modeling to demonstrate model-driven prediction of gene expression levels and to identify the role of critical cis-acting elements. In this study, 14 key mRNA expression data from the structural and pathological molecules of age-related cataract samples are used. The first seven genes consist of structural molecules, and the second half of genes are composed of heat shock proteins, filensin, and glutathione peroxidase 3. The presented result demonstrates that mRNA expression levels of structural proteins such as crystallins can be successfully predicted from 5' flanking regulatory DNA sequences. In addition, predicted gene expression levels of heat shock protein, beta-tubulin, and alphaA-crystallin accurately estimate the stimulatory or inhibitory role of distributed cis-acting elements, i.e., c-Myc, GATA-1, GR, NE-E, and Pit-1. Although it is difficult to predict the overall gene expression levels in cataract samples, the present study shows the potential use of promoter-based modeling and prediction of the gene expression levels for age-related cataract.

Recapitulation of human betaB1-crystallin promoter activity in transgenic zebrafish

Development of the eye is morphologically similar among vertebrates, indicating that the underlying mechanism regulating the process may have been highly conserved during evolution. Herein we analyzed the promoter of the human betaB1-crytallin gene in zebrafish by transgenic experiments. To delineate the evolutionarily conserved regulatory elements, we performed serial deletion assays in the promoter region. The results demonstrated that the -90/+61-bp upstream proximal promoter region is sufficient to confer lens-tissue specificity to the human betaB1-crystallin gene in transgenic zebrafish. Through phylogenetic sequence comparisons and an electrophoretic mobility shift assay (EMSA), a highly conserved cis-element of a six-base pair sequence TG(A/C)TGA, the consensus sequence for the Maf protein binding site, within the proximal promoter region was revealed. Further, a site-mutational assay showed that this element is crucial for promoter activity. These data suggest that the fundamental transcriptional regulatory mechanism of the betaB1-crystallin gene has been well conserved between humans and zebrafish, and plausibly among all vertebrates, during evolution.

Regulation of alphaA-crystallin gene expression. Lens specificity achieved through the differential placement of similar transcriptional control elements in mouse and chicken

The lens-preferred mouse alphaA-crystallin gene contains a conserved stretch (proximal element 2, +24/+43) in its 5'-noncoding region that we have previously shown binds nuclear proteins of lens and non-lens cells. The 5'-half of this sequence (PE2A, +25/+32) has consensus binding sites for AP-1 and other transcription factors. We show here by deletion experiments that PE2A is important for activity of the mouse alphaA-crystallin promoter and mediates phorbol ester and c-Jun responsiveness of this promoter in transfected lens cells. In vitro protein binding studies suggest that AP-1 complexes are capable of binding to PE2A. Our findings suggest that PE2A plays a role in mouse alphaA-crystallin gene expression through AP-1-mediated regulatory mechanisms. We propose that the mouse and chicken alphaA-crystallin genes are expressed with lens specificity using a similar assortment of transcription factors but with a different physical arrangement of their respective cis-elements within the promoter region. A fundamental role for AP-1 in lens-preferred expression of crystallin genes is consistent with the idea that a redox-sensitive mechanism is a selective force for recruiting lens crystallins.

Transcriptional regulation of the mouse alpha A-crystallin gene: binding of USF to the -7/+5 region

Lens preferred-expression of the mouse alpha A-crystallin gene (alpha A-cry) is regulated at the transcriptional level by multiple elements located in the 5' flanking region of the gene. Here we present the first analysis of the functional role of the mouse alpha A-cry +1 region and the protein(s) which bind to it. The -7/+5 region of this promoter exhibits sequence similarity with the consensus upstream stimulating factor (USF) transcription factor binding site. A wild type oligodeoxyribonucleotide (oligo) spanning the mouse alpha A-cry -15/+15 region specifically inhibited the activity of a mouse alpha A-cry promoter-cat gene fusion (p alpha A 111aCAT) in competitive co-transfection studies in the mouse alpha TN4-1 lens cell line, as did an oligo containing the adenovirus 2 major late promoter strong USF binding site. In contrast, an alpha A-cry oligo mutated (-3/+3) within the USF-like binding site did not inhibit p alpha A111aCAT activity. Western blot analysis indicated that alpha TN4-1 cells express USF1. Co-transfection of p alpha A111aCAT and a USF1 cDNA expression vector into alpha TN4-1 cells resulted in a repression of mouse alpha A-cry promoter activity. Electrophoretic mobility shift analyses (EMSA) demonstrated that proteins in an alpha TN4-1 nuclear extract form a single major complex on synthetic oligos spanning the mouse alpha A-cry -15/+15 region. The formation of this complex was inhibited by the presence of unlabeled -15/+15 oligos or an anti-USF1 antibody. In addition, purified USF1 bound to this region, producing a complex similar in size to that observed with alpha TN4-1 nuclear extracts. Taken together, our findings show that USF can bind to the mouse alpha A-cry +1 site, and support the possibility that USF plays a role in promoter activity of this gene. Sequence similarities surrounding the +1 region of the alpha A-cry gene of the mouse, mole rat, hamster, and human, as well as the previously observed utilization of USF by different cry promoters suggest that USF contributes to the high expression of many crys in the ocular lens of diverse species.

Cellular and molecular features of lens differentiation: a review of recent advances

In this paper, the more recent literature pertaining to differentiation in the developing vertebrate lens is reviewed in relation to previous work. The literature reviewed reveals that the developing lens has been, and will continue to be, a useful model system for the examination of many fundamental processes occurring during embryonic development. Areas of lens development reviewed here include: the induction and early embryology of the lens; lens cell culture techniques; the role of growth factors and cytokines; the involvement of gap junctions in lens cell-cell communication; the role of cell adhesion molecules, integrins, and the extracellular matrix; the role of the cytoskeleton; the processes of programmed cell death (apoptosis) and lens fibre cell denucleation; the involvement of Pax and Homeobox genes; and crystallin gene regulation. Finally, some speculation is provided as to possible directions for further research in lens development.

Lens development and crystallin gene expression: many roles for Pax-6

The vertebrate eye lens has been used extensively as a model for developmental processes such as determination, embryonic induction, cellular differentiation, transdifferentiation and regeneration, with the crystallin genes being a prime example of developmentally controlled, tissue-preferred gene expression. Recent studies have shown that Pax-6, a transcription factor containing both a paired domain and homeodomain, is a key protein regulating lens determination and crystallin gene expression in the lens. The use of Pax-6 for expression of different crystallin genes provides a new link at the developmental and transcriptional level among the diverse crystallins and may lead to new insights into their evolutionary recruitment as refractive proteins.

Lens-preferred activity of the -1809/+46 mouse alpha A-crystallin promoter in stably integrated chromatin

The alpha A-crystallin gene is expressed in a highly lens preferred manner. Here we show that the mouse alpha A-crystallin -1809/+46 promoter fragment displays lens-preferred activity in transgenic mice and in stably transfected lens cells. These findings are in contrast to the lack of activity of this promoter previously reported in transiently transfected lens cells. Our current findings suggest that the -1809/+46 mouse alpha A-crystallin promoter functions in a lens preferred manner when stably integrated into chromatin.