Functional elements DE2A, DE2B, and DE1A and the TATA box are required for activity of the chicken alpha A-crystallin gene in transfected lens epithelial cells

Apoptotic DNase network: Mutual induction and cooperation among apoptotic endonucleases

DNA fragmentation produced by apoptotic DNases (endonucleases) leads to irreversible cell death. Although apoptotic DNases are simultaneously induced following toxic/oxidative cell injury and/or failed DNA repair, the study of DNases in apoptosis has generally been reductionist in approach, focusing on individual DNases rather than their possible cooperativity. Coordinated induction of DNases would require a mechanism of communication; however, mutual DNase induction or activation of DNases by enzymatic or non‐enzymatic mechanisms is not currently recognized. The evidence presented in this review suggests apoptotic DNases operate in a network in which members induce each other through the DNA breaks they produce. With DNA breaks being a common communicator among DNases, it would be logical to propose that DNA breaks from other sources such as oxidative DNA damage or actions of DNA repair endonucleases and DNA topoisomerases may also serve as triggers for a cooperative DNase feedback loop leading to elevated DNA fragmentation and subsequent cell death. Therefore, mutual induction of apoptotic DNases has serious implications for studies focused on activation or inhibition of specific DNases as a strategy for therapeutic intervention aimed at modulation of cell death.

Regulation of human myocilin/TIGR gene transcription in trabecular meshwork cells and astrocytes: role of upstream stimulatory factor

BACKGROUND

Mutations in the myocilin (MYOC)/TIGR gene are responsible for autosomal-dominant juvenile primary open-angle glaucoma (POAG). In patients with non-autosomal-dominant POAG, such mutations are rare, but the expression of MYOC/TIGR in the trabecular meshwork (TM) of the eye is considerably higher than in normals. We performed transfection, DNAse I footprinting, mutagenesis and electrophoretic mobility shift assays (EMSA) to identify elements responsible for the basal transcription of MYOC/TIGR in TM cells and astrocytes.

RESULTS

DNAse I footprinting experiments of the human MYOC/TIGR promoter showed a major protected area between nt -106 to -77, which was not conserved in the homologous region of the mouse myoc/tigr promoter. In addition, the TATA-box was protected, as well as at least three downstream sites, including an AP-1-like sequence. Deletion of the -106 to -77 region caused a substantial loss of functional promotor activity in all cell types. Site-directed mutagenesis and EMSA experiments revealed the presence of two regulatory elements in the -106 to -77 region. Each of these cis-elements is essential for minimal promoter activity. The 5'-half of the region contains a sequence with similarities to NF-kappaB-related sites, however, binding of NF-kappaB could not be confirmed by EMSA. The 3'-half contains a canonical E-box sequence. EMSA experiments showed that the upstream regulatory factor (USF) was binding to the E-box sequence and that the binding can be supershifted by specific antibodies.

CONCLUSIONS

Several DNA-protein binding elements contribute to a transcription of MYOC/TIGR, and USF is critically required for its basal transcription in trabecular meshwork cells and astrocytes.

Transcription factor CP2 is essential for lens-specific expression of the chicken alphaA-crystallin gene

BACKGROUND

Lens-specific transcriptional activation of the chicken alphaA-crystallin gene is controlled by the distal and proximal enhancers, alphaCE1 and alphaCE2, respectively. Analysis using specific monoclonal antibodies against purified alphaCE1-binding factor alphaCEF1 revealed that alphaCEF1 is composed of two distinct subunits.

RESULTS

We have demonstrated that one of the subunits of alphaCEF1 is encoded by chicken ubiquitous transcription factor CP2 (cCP2), which is homologous to mouse CP2, and human CP2/LBP-1/LSF-1. Electrophoretic mobility shift assays and cross-linking experiments showed that alphaCEF1 and bacterially expressed cCP2 form a tetramer. Overexpression of cCP2 activates transcription through alphaCE1, but a mutant cCP2 lacking the DNA-binding domain reduced the transcription to basal levels. Although cCP2 binds to the CP2 template from the mouse alpha-globin promoter, it fails to promote transcription through this template. Element substitution experiments between alphaCE1 and the CP2 template revealed that the lens-specific enhancer activity of alphaCE1 is due to the 6 bp sequence (-139/-134; lens-specific element (LSE)) adjacent to the 3' of the cCP2 binding site within alphaCE1.

CONCLUSION

We have shown that the tetrameric transcription factor cCP2 is essential for lens-specific transcription of the chicken alphaA-crystallin gene, although it is ubiquitously expressed. We propose a model where cCP2 cooperates with a putative lens-specific factor which binds to LSE.

Sequence, initial functional analysis and protein-DNA binding sites of the mouse beta B2-crystallin-encoding gene

An 800-bp fragment of genomic DNA upstream from the origin of transcription of the mouse beta B2-crystallin-encoding gene (beta B2-Cry) has been isolated and its nucleotide sequence determined. Promoter fragments 275 to +30 or -110 to +30, fused to cat reporter gene, activated transcription in transiently transfected rabbit lens epithelial cells, but not in various non-lens cells. The beta B2-Cry mouse promoter contains a typical TATA-box located approx. 25 bp upstream from the transcription start point. Binding sites (upstream from the TATA-box) for transcription factors possibly involved in the regulation of gene expression have been identified by DNaseI footprinting analysis and lens cell nuclear extracts. Most notably is the binding of the Pax-6 paired domain (PrD) which correlates with the binding of lens cell nuclear proteins at the -80 to -40 region.

Effects of c-Jun and a negative dominant mutation of c-Jun on differentiation and gene expression in lens epithelial cells

We have used a retroviral vector (RCAS) to overexpress wild-type chicken c-Jun or a deletion mutant of chicken c-Jun (Jun delta 7) lacking the DNA binding region to investigate the possible role of c-Jun in lens epithelial cell proliferation and differentiation. Both constructs were efficiently expressed in primary cultures of embryonic chicken lens epithelial cells. Overexpression of c-Jun increased the rate of cell proliferation and greatly delayed the appearance of "lentoid bodies," structures which contain differentiated cells expressing fiber cell markers. Excess c-Jun expression also significantly decreased the level of beta A3/A1-crystallin mRNA, without affecting alpha A-crystallin mRNA. In contrast, the mutated protein, Jun delta 7, had no effect on proliferation or differentiation but markedly increased the level of alpha A-crystallin mRNA in proliferating cell cultures. These results suggest that c-Jun or Jun-related proteins may be negative regulators of alpha A- and beta A3/A1-crystallin genes in proliferating lens cells.

cDNA encoding a chicken protein (CRP1) with homology to hnRNP type A/B

The sequence of a cDNA encoding a putative chicken RNA-binding protein is reported. The C-terminal portion of the predicted protein is similar to a family of nucleic acid binding proteins that includes murine CArG box-binding factor CBF-A, human hnRNP A/B, hepatitis B enhancer-binding protein E2BP, and AU-rich RNA-binding protein AUF1. These proteins all have two consecutive RNA recognition motifs. However, the N-terminal 72 amino acids of this deduced chicken protein show no relation to the N-terminal sequences of the other proteins. We call this protein chicken ribonucleoprotein, CRP1.

Chicken beta B1 crystallin: gene sequence and evidence for functional conservation of promoter activity between chicken and mouse

The complete sequence was determined for the chicken beta B1-crystallin gene and 2.2 kbp of its 5' flanking region; the chicken gene was then compared to its rat ortholog. Although both have a 5' non-coding exon followed by 5 protein coding exons, the chicken gene is only 2.2 kbp while the rat gene is 13.6 kpb due to longer introns. The coding exons of the chicken beta B1-crystallin gene, like those of the rat and other beta-crystallin genes, each correspond to one of the four 'Greek key' motifs of the encoded protein. The only obvious similarity between the 5' flanking sequences of the chicken and rat beta B1-crystallin gene is associated with the TATA box. A CR1 repetitive element is present at positions -559 to -730 of the chicken beta B1-crystallin gene. In vivo footprinting using dimethyl sulfate/ligation mediated PCR showed that the PL-1 (-116/-102), PL-2 (-90/-76), OL-2 (-75/-68) and OL-1 (-125/-118) control elements identified previously (Roth et al. (1991) Mol. Cell. Biol. 11, 1488-1499) bind proteins within the chromatin of cultured embryonic chicken lens cells. Both -2448/+30 and -434/+30 promoter fragments from the chicken beta B1-crystallin gene directed lens-specific CAT gene expression in a copy number and position independent manner in transgenic mice. These data indicate that the structure and lens-specific expression of this gene are highly conserved although, like other crystallin genes, the 5' flanking sequences have diverged appreciably during evolution.

Convergent evolution of crystallin gene regulation in squid and chicken: the AP-1/ARE connection

Previous experiments have shown that the minimal promoters required for function of the squid SL20-1 and SL11 crystallin genes in transfected rabbit lens epithelial cells contain an overlapping AP-1/antioxidant responsive element (ARE) upstream of the TATA box. This region resembles the PL-1 and PL-2 elements of the chicken beta B1-crystallin promoter which are essential for promoter function in transfected primary chicken lens epithelial cells. Here we demonstrate by site-directed mutagenesis that the AP-1/ARE sequence is essential for activity of the squid SL20-1 and SL11 promoters in transfected embryonic chicken lens cells and fibroblasts. Promoter activity was higher in transfected lens cells than in fibroblasts. Electrophoretic mobility shift and DNase protection experiments demonstrated the formation of numerous complexes between nuclear proteins of the embryonic chicken lens and the AP-1/ARE sequences of the squid SL20-1 and SL11 crystallin promoters. One of these complexes comigrated and cross-competed with that formed with the PL-1 element of the chicken beta B1-crystallin promoter. This complex formed with nuclear extracts from the lens, heart, brain, and skeletal muscle of embryonic chickens and was eliminated by competition with a consensus AP-1 sequence. The nonfunctional mutant AP-1/ARE sequences did not compete for complex formation. These data raise the intriguing possibility that entirely different, nonhomologous crystallin genes of the chicken and squid have convergently evolved a similar cis-acting regulatory element (AP-1/ARE) for high expression in the lens.

Identification of negative-acting and protein-binding elements in the mouse alpha A-crystallin -1556/-1165 region

The mouse alpha A-crystallin-encoding gene (alpha A-cry) is expressed in a highly lens-preferred manner. To date, it has been shown that this lens-preferred expression is controlled by four proximal positive-acting transcriptional regulatory elements: DE1 (-111/-97), alpha A-CRYBP1 (-66/-57), PE1/TATA (-35/-19) and PE2 (+24/+43). The present study extends our knowledge of mouse alpha A-cry transcriptional regulatory elements to the far upstream region of that gene by demonstrating that the -1556 to -1165 region contains negative-acting sequence elements which function in transfected lens cells derived from mouse, rabbit and chicken. This is the first negative-acting regulatory region identified in mouse alpha A-cry. The -1556 to -1165 region contains sequences similar to repressor/silencer elements identified in other genes, including those highly expressed in the lens, such as the delta 1-crystallin (delta 1-cry) and vimentin (vim) genes. The -1480 to -1401 region specifically interacts with nuclear proteins isolated from the alpha TN4-1 mouse lens cell line. Contained within this protein-binding region and positioned at -1453 to -1444 is a sequence (RS1) similar to the chicken delta 1-cry intron 3 repressor, and which competes for the formation of -1480 to -1401 DNA-protein complexes. Our findings suggest that lens nuclear proteins bind to the mouse alpha A-cry RS1 region. We demonstrate that the chicken delta 1-cry intron repressor binds similar nuclear proteins in chicken embryonic lens cells and mouse alpha TN4-1 lens cells.(ABSTRACT TRUNCATED AT 250 WORDS)