Structure and alternate tissue-preferred transcription initiation of the mouse alpha B-crystallin/small heat shock protein gene

Amyloidosis in Retinal Neurodegenerative Diseases

As a part of the central nervous system, the retina may reflect both physiological processes and abnormalities related to pathologies that affect the brain. Amyloidosis due to the accumulation of amyloid-beta (Aβ) was initially regarded as a specific and exclusive characteristic of neurodegenerative alterations seen in the brain of Alzheimer's disease (AD) patients. More recently, it was discovered that amyloidosis-related alterations, similar to those seen in the brain of Alzheimer's patients, also occur in the retina. Remarkably, these alterations were identified not only in primary retinal pathologies, such as age-related macular degeneration (AMD) and glaucoma, but also in the retinas of Alzheimer's patients. In this review, we first briefly discuss the biogenesis of Aβ, a peptide involved in amyloidosis. We then discuss some pathological aspects (synaptic dysfunction, mitochondrial failure, glial activation, and vascular abnormalities) related to the neurotoxic effects of Aβ. We finally highlight common features shared by AD, AMD, and glaucoma in the context of Aβ amyloidosis and further discuss why the retina, due to the transparency of the eye, can be considered as a "window" to the brain.

Is newer safer? Adverse events associated with first-line therapies for ANCA-associated vasculitis and lupus nephritis

Clinical outcomes in ANCA-associated vasculitis (AAV) and lupus nephritis have improved greatly with treatment regimens containing high-dose glucocorticoids and cyclophosphamide. However, with the use of these medications come significant adverse events, most notably infections, cytopenias, malignancies, and reproductive abnormalities. Multiple recent randomized controlled trials in AAV and lupus nephritis have compared cyclophosphamide-based regimens with agents such as rituximab, mycophenolate mofetil, and azathioprine, with the hope of providing better clinical outcomes with improved safety profiles. Although some of these newer regimens are now considered first-line treatments of these diseases, their adverse event profiles have been disappointingly similar to those of cyclophosphamide-based protocols. Physicians and patients should consider the adverse event profiles generated by these trials in the context of their extensive use in other patient populations, as well as available measures to prevent such events, when choosing the ideal regimen for an individual patient.

Differential expression and regulation of Cryab in mouse uterus during preimplantation period

The aim of this study was to examine the expression and regulation of the crystallin, alpha B (Cryab) gene in mouse uterus during the peri-implantation period by in situ hybridization and real-time PCR. There was no detectable Cryab mRNA signal on days 1-4 of pregnancy. On day 5 of pregnancy when embryo implanted, a high level of Cryab mRNA signal was found in the subluminal stroma surrounding the implanting blastocyst. On days 6-8, Cryab mRNA was strongly expressed in the primary decidua. By real-time PCR, a high level of Cryab expression was detected on days 7 and 8 of pregnancy, although Cryab expression was seen from days 1 to 8. Under in vivo and in vitro artificial decidualization, Cryab expression was significantly elevated. Compared with the progesterone-primed delayed implantation uterus, a high level of Cryab mRNA expression was observed in estrogen-activated implantation uterus. In the uterine stromal cells, cAMP, estrogen, and progesterone could induce the expression of Cryab gene. In the ovariectomized mouse uterus, estrogen could also induce the expression of Cryab while progesterone inhibited its expression. Our data suggest that Cryab may play an important role during mouse embryo implantation and decidualization and that estrogen and progesterone can regulate the expression of Cryab gene.

Proteomic Identification of Altered Proteins in Skeletal Muscle During Chronic Potassium Depletion: Implications for Hypokalemic Myopathy

Prolonged potassium depletion is a well-known cause of myopathy. The pathophysiology of hypokalemic myopathy, however, remains unclear. We performed a gel-based, differential proteomics study to define altered proteins in skeletal muscles during chronic potassium depletion. BALB/c mice were fed with normal chow (0.36% K+) or K+-depleted (KD) diet (<0.001% K+) for 8 weeks (n = 5 in each group). Left gastrocnemius muscles were surgically removed from each animal. Histopathological examination showed mild-degree infiltration of polymornuclear and mononuclear cells at the interstitium of the KD muscles. Extracted proteins were resolved with two-dimensional electrophoresis (2-DE), and visualized with Coomassie Brilliant Blue R-250 stain. Quantitative intensity analysis revealed 16 up-regulated protein spots in the KD muscles, as compared to the controls. These differentially expressed proteins were subsequently identified by peptide mass fingerprinting and by quadrupole time-of-flight tandem mass spectrometry (Q-TOF MS/MS). Most of the altered proteins induced by chronic potassium depletion were muscle enzymes that play significant roles in several various metabolic pathways. Other up-regulated proteins included myosin-binding protein H, alpha-B Crystallin, and translationally controlled tumor protein (TCTP). These findings may lead to a new roadmap for research on hypokalemic myopathy, to better understanding of the pathophysiology of this medical disease, and to biomarker discovery.

Transcriptional regulation of mouse alphaB- and gammaF-crystallin genes in lens: opposite promoter-specific interactions between Pax6 and large Maf transcription factors

Mammalian alphaB-crystallin is highly expressed both in lens epithelium and lens fibers. In contrast, gammaF-crystallin is highly expressed in the lens fiber cells. Crystallin gene expression in lens is regulated at the level of transcription by a sparse number of specific DNA-binding transcription factors. Here, we report studies on transcriptional regulation of mouse alphaB- and gammaF-crystallin promoters by specific combinations of Pax6/Pax6(5a), large Mafs (MafA, MafB, c-Maf, and NRL), Sox1, Sox2, Six3, and RARbeta/RXRbeta. Two sets of these factors, co-expressed both in lens epithelium and in lens fibers, were tested in co-transfection assays using cultured lens and non-lens cells. Regulation of alphaB-crystallin was studied in the presence of lens epithelial-factors Pax6, MafB, and RARbeta/RXRbeta, and lens fiber-factors Pax6, MafA, c-Maf, and NRL. Pax6 proteins activated the alphaB-crystallin promoter (-162 to +45) with any combination of Mafs. Addition of RARbeta/RXRbeta further increased its promoter activity. Gel shift assays using lens nuclear extracts demonstrated interactions of Pax6, Maf, and retinoic acid nuclear receptor proteins with two lens-specific regions, the distal LSR1 (-147/-118) and proximal LSR2 (-78/-40), of the alphaB-crystallin promoter. In contrast, Pax6 proteins acted as repressors of gammaF-crystallin promoter activity elicited by a combination of large Mafs, Sox, and RARbeta/RXRbeta proteins in transiently transfected lens and non-lens cells. The results show that Pax6 conversely regulates these two lens crystallin promoters. We propose that the opposite roles of Pax6 in crystallin gene regulation are results of different promoter architectures of the alphaB- and gammaF-crystallin genes, developmentally regulated association of transcription factors with the corresponding cis-regulatory sites, and specific recruitment of transcriptional co-activators and co-repressors by Pax6.

Canonical heat shock element in the alpha B-crystallin gene shows tissue-specific and developmentally controlled interactions with heat shock factor

Oligomerization of the heat shock factor (HSF) and its interaction with the heat shock element (HSE) are the hallmark of active transcriptional response to tangible physical or chemical stress. It is unknown if these interactions are subject to control and modulation by developmental cues and thus have tissue or stage specificity. By using promoter sequences containing a canonical HSE from the alphaB-crystallin gene, we demonstrate a tissue-specific transition from monomeric (in fetal and early neonatal stages that lack oligomeric HSF.HSE complexes) to oligomeric HSF-HSE interactions by postnatal day 10-21 in the ocular lens. Developmental control of these interactions is further demonstrated by induction of oligomeric HSF.HSE complexes in neonatal extracts by in vitro manipulations, interestingly, only in the lens and not in the brain, heart, or liver extracts. The exclusive presence of oligomeric HSF.HSE complexes in the postnatal/adult lens corresponds to known highly increased number of alphaB-crystallin transcripts in this tissue.

Heat shock proteins in human endometrium throughout the menstrual cycle

Human endometrium, in response to steroid hormones, undergoes characteristic cycles of proliferation, secretory changes, and tissue shedding. Human endometrium expresses a molecular repertoire which includes the heat shock proteins (Hsps) Hsp27, Hsp60, Hsp70, Hsp90, and alpha crystallin B chain. The expression of Hsp27, Hsp60, and the constitutive form of Hsp70 (Hsc70) shows a sharp increase in human endometrium after ovulation. The maximal expression of the molecular chaperone, alpha crystallin B chain, occurs during the secretory phase. In view of known functions of the Hsps, it is likely that these proteins are involved in protection of the endometrial proteins against factors with the potential to lead to protein denaturation. Tumor necrosis factor-alpha (TNF-alpha) is a cytotoxic cytokine that is produced in progressive amounts during the secretory phase. The function of the Hsps may be to protect cells against the cytotoxic damage of TNF-alpha, particularly during the critical period of "implantation window."

Phosphorylations of alpha A- and alpha B-crystallin

In addition to being refractive proteins in the vertebrate lens, the two alpha-crystallin polypeptides (alpha A and alpha B) are also molecular chaperones that can protect proteins from thermal aggregation. The alpha B-crystallin polypeptide, a functional member of the small heat shock family, is expressed in many tissues in a developmentally regulated fashion, is stress-inducible, and is overexpressed in many degenerative diseases and some tumors indicating that it plays multiple roles. One possible clue to alpha-crystallin functions is the fact that both polypeptides are phosphorylated on serine residues by cAMP-dependent and cAMP-independent mechanisms. The cAMP-independent pathway is an autophosphorylation that has been demonstrated in vitro, depends on magnesium and requires cleavage of ATP. Disaggregation of alpha A-, but not alpha B-crystallin into tetramers results in an appreciable increase in autophosphorylation activity, reminiscent of other heat shock proteins, and suggests the possibility that changes in the aggregation state of alpha A-crystallin are involved in yet undiscovered signal transduction pathways. The alpha-crystallin polypeptides differ with respect to their abilities to undergo cAMP-dependent phosphorylation, with preference given to the alpha B-crystallin chain. These differences and complexities in alpha-crystallin phosphorylations, coupled with the differences in expression patterns of the two alpha-crystallin polypeptides, are consistent with the idea that each polypeptide has distinctive structural and metabolic roles.

Multifunctional lens crystallins and corneal enzymes. More than meets the eye

The abundant water-soluble proteins, called crystallins, of the transparent, refractive eye lens have been recruited from metabolic enzymes and stress-protective proteins by a process called "gene sharing." Many crystallins are also present at lower concentration in nonocular tissues where they have nonrefractive roles. The complex expression pattern of the mouse alpha B-crystallin/small heat shock protein gene is developmentally controlled at the transcriptional level by a combinatorial use of shared and lens-specific regulatory elements. A number of crystallin genes, including that for alpha B-crystallin, are activated by Pax-6, a conserved transcription factor for eye evolution. Aldehyde dehydrogenase class 3 and transketolase are metabolic enzymes comprising extremely high proportions of the water-soluble proteins of the cornea and may have structural as well as enzymatic roles, reminiscent of lens enzyme-crystallins. Inductive processes appear to be important for the corneal-preferred expression of these enzymes. The use of the same protein for entirely different functions by a gene-sharing mechanism may be a general strategy based on evolutionary tinkering at the level of gene regulation.

Characterization, cloning, and expression of porcine alpha B crystallin

alpha-Crystallin is a major lens protein present in the lenses of all vertebrate species. Recent studies have revealed that bovine alpha-crystallins possess genuine chaperone activity similar to small heat-shock proteins. In order to compare this chaperone-like structural protein from the eye lenses of different mammalian species, we have cloned and expressed one of the main alpha-crystallin subunits, i.e., alpha B crystallin, from the porcine lenses in order to facilitate the structure-function evaluation and comparison of this chaperonin protein. cDNA encoding alpha B subunit chain was obtained using a new "Marathon cDNA amplification" protocol of Polymerase Chain Reaction (PCR). PCR-amplified product corresponding to alpha B subunit was then ligated into pGEM-T plasmid and prepared for nucleotide sequencing by the dideoxy-nucleotide chain-termination method. Sequencing several positive clones containing DNA inserts coding for alpha B-crystallin subunit constructed only one complete full-length reading frame of 525 base pairs similar to human and bovine alpha B subunits, covering a deduced protein sequence of 175 amino acids including the universal translation-initiating methionine. The porcine alpha B crystallin shows only 3 and 7 residues difference to bovine and human alpha B crystallins respectively, revealing the close relatedness among mammalian eye lens proteins. The sequence differences between porcine and sub-mammalian species such as chicken and bullfrog are much greater, especially at the N- and C-terminal regions of these alpha B crystallins. Expression of alpha B subunit chain in E. coli vector generated a polypeptide which can cross-react with the antiserum against the native and purified alpha B subunit from the native porcine lenses albeit with a much lower activity.

The mouse transketolase (TKT) gene: cloning, characterization, and functional promoter analysis

The transketolase (TKT) gene is expressed 30-50 times more highly in the mature mouse cornea than in other tissues. Here, we have cloned and characterized the 30- to 40-kb single-copy mouse TKT gene. Sequence analysis supports the suggestion that present-day TKT and TKT-like genes arose from the duplication of a single common ancestral gene. A 6-bp polymorphism is present between different mouse strains in the noncoding region of exon 2. 5' RACE and primer extension analyses indicated that two regions separated by 630 bp are used as transcription initiation sites; both mRNAs appear to use a common initiator ATG codon. The minor distal transcription initiation site, preceded by a TATA sequence, is utilized in liver and is followed by an untranslated exon (exon 1). The major proximal transcription initiation site lies within intron 1, is used in cornea and liver, lacks a TATA sequence, is GC rich, and initiates at multiple sites within a 10-bp span, resembling the promoters of other housekeeping genes. In transfected cornea and lens cell lines, the -49/+90 fragment fused to the CAT gene acted as a minimal promoter, with higher activity noted for the -510/+91 fragment. TKT mRNA levels increased sixfold in the mouse cornea in vivo within 1-2 days of eye opening and were elevated in a lens cell line exposed to H2O2 or the glutathione-specific oxidizing agent diamide and in whole newborn mouse eyes incubated in the presence of light, consistent with multiple consensus stress-inducible control sequences in the TKT promoter regions. Taken together, these observations suggest that oxidative stress may play a role in the regulation of this gene in the cornea.

Identification and characterization of the gene encoding a new member of the alpha-crystallin/small hsp family, closely linked to the alphaB-crystallin gene in a head-to-head manner

alphaB-Crystallin is a member of the alpha-crystallin/small heat shock protein (hsp) family and under various neuropathologic conditions accumulates in reactive astrocytes and degenerating neurons. In the 5'-flanking region of the alphaB-crystallin gene on human chromosome 11q22-q23, where a constitutive DNase I hypersensitive site is located, we identified a gene transcribed in the opposite direction. Analysis of its mRNA structure by RT-PCR and 5'/3'RACE revealed that this gene is composed of two exons and encodes a new member of the alpha-crystallin/small hsp family. This gene was designated the HSPB2 gene by the HMGW Nomenclature Committee. The complete genomic structure of the rat homologue was also determined. Northern blot analysis revealed that the HSPB2 gene is expressed preferentially in skeletal muscle and heart but not in the lens, while the neighboring alphaB-crystallin gene is highly expressed in all three tissues. The two related genes are arranged in a head-to-head manner with an intergenic sequence of less than 1 kb, raising a possibility of shared regulatory elements for their expression.

Examination of the molecular basis for the lack of alphaB-crystallin expression in L929 cells

We have previously shown that murine L929 cells do not express the small heat shock protein alphaB-crystallin upon exposure to thermal stress (Mol Cell Biochem 155: 51-60, 1996). In these studies, we demonstrate that L929 cells also fail to express alphaB-crystallin upon exposure dexamethasone, whereas NIH 3T3 and Swiss 3T3 murine cells exhibit alphaB-crystallin expression under identical conditions. Mobility shift assays demonstrated heat-inducible binding, presumably by heat shock factor(s), to an alphaB-crystallin heat shock element (HSE) oligomeric sequence in total cellular extracts from L929 cells. Transient transfection of a plasmid containing the alphaB-crystallin promoter linked to a CAT reporter gene exhibited heat-inducible expression in L929 cells. In addition, L929 cells stably transfected with a plasmid containing the complete alphaB-crystallin gene showed expression of this gene following heat shock. The presence of the endogenous alphaB-crystallin gene was detected by Southern blot hybridization of genomic L929 DNA, and sequence analysis revealed identical nucleotide structure to published murine sequences throughout the entire promoter. Treatment of L929 cells with 5-azacytidine enabled heat-inducible expression of alphaB-crystallin from the endogenous gene, however, methylation of the putative heat shock element (HSE) and flanking promoter sequences of L929 cell genomic DNA was not detected. In vivo genomic footprinting demonstrated constitutive binding to the endogenous HSE of the alphaB-crystallin promoter in L929, L929/alphaB-crystallin transfectant cells, and Swiss 3T3 cells during unstressed and heat stressed conditions. Therefore, the genomic alphaB-crystallin HSE region in L929 cells appears to be available for binding of putative transcription factors, but methylation in other regions of the gene or genome repress the expression of alphaB-crystallin in L929 cells. In vitro culture of L929 cells appears to have rendered the alphaB-crystallin gene loci inactive through methylation, thus providing a unique system by which to study the function of transfected small heat shock proteins.

Alternative transcriptional initiation and alternative use of polyadenylation signals in the alphaB-crystallin gene expressed in different chicken tissues

Overexpression of alphaB-crystallin is associated with numerous neurodegenerative diseases and abnormal cell growth patterns. To study the mechanisms involved in the control of the transcriptional activity of the gene we have characterized its expression in different chicken tissues. The sequence of the alphaB-crystallin cDNA isolated from chicken testis and 6-day-old chick embryo is highly homologous to the duck alphaB-crystallin cDNA and differs from the previously reported chicken lens alphaB-crystallin cDNA in the 5' untranslated region (5'-UTR) and in one amino acid of the coding sequence. Four forms of the alphaB-crystallin cDNA detected in chicken testes arise from the use of alternative transcription initiation sites and alternative polyadenylation signals. The two principal hybridizing bands found in lens and embryonic tissues possess a short 5'-UTR and differ in the length of the 3'-UTR. Forms with longer 5'-UTR are present in testis, muscle, and heart. The use of different start sites and polyadenylation signals could modulate transcriptional activity and the stability of the messages. The expression of the alphaB-crystallin gene decreases from day 6 to day 8 of chick embryogenesis, in parallel with the expression of the polyubiquitin gene UbII.

Spatial and temporal activity of the alpha B-crystallin/small heat shock protein gene promoter in transgenic mice

In order to study the spatial and temporal activity of the mouse alpha B-crystallin/small heat shock gene promoter during embryogenesis, we generated mice harboring a transgene consisting of approximately 4 kbp of alpha B-crystallin promoter sequence fused to the Escherichia coli lacZ reporter gene. beta-galactosidase activity was first observed in the heart rudiment of 8.5 days post coitum (d.p.c.) embryos. An identical expression pattern was obtained for the endogenous alpha B-crystallin gene by whole mount in situ hybridization. At 9.5 d.p.c., beta-galactosidase activity was detected in the lens placode, in the myotome of the somites, in Rathke's pouch (future anterior pituitary), and in some regions of oral ectoderm. We also examined the stress inducibility of the alpha B-crystallin promoter in vivo. Injection of sodium arsenite into mice resulted in increased endogenous alpha B-crystallin expression in the adrenal gland and possibly the liver. Our results indicate that visualization of beta-galactosidase activity provides an accurate reflection of endogenous alpha B-crystallin expression and demonstrate that the complex developmental pattern of mouse alpha B-crystallin gene expression is regulated at the transcriptional level. This expression pattern, coupled with the present literature which addresses functions of the protein, suggests a role for the alpha B-crystallin/small heat shock protein in intermediate filament turnover and cellular remodeling which occur during normal development and differentiation.

Transcription regulation of alpha B-crystallin in astrocytes: analysis of HSF and AP1 activation by different types of physiological stress

The coordinated cellular responses to physiological stress are known to be effected in part by the activation of heat-shock factor 1, a transcriptional activator protein capable of binding to, and inducing transcription from genes containing heat shock elements. Other stress responsive signal transduction pathways also exist including the stress activated protein kinase cascade that regulates the activity of the transcription factor AP1. We have examined the expression of the low molecular stress proteins, heat shock protein 27 and alpha B-crystallin in astrocytes in response to physiological stress of different types and asked what component of this induction is effected at the transcriptional level and whether activation of heat shock factor 1 and AP1 might account for these events. We have found that stress regulated induction of alpha B-crystallin has a strong transcriptional component and that it may be effected by at least two different transcriptional mechanisms. In one set of phenomena, represented here by cadmium exposure, alpha B-crystallin and heat shock protein 27 are coordinately regulated and this occurs in the presence of activated heat shock factor 1. In the second series of phenomena, represented here by hypertonic stress, alpha B-crystallin is induced in the absence of heat shock factor activation and in the absence of any corresponding change in heat shock protein 27 expression. Although hypertonic stress does activate an AP1-like binding activity, the AP1 consensus binding site in the alpha B-crystallin promoter does not appear to be a target for this hypertonic stress inducible activity. These data suggest that the hypertonic stress response is effected through a heat shock factor independent mechanism and that hypertonic stress regulated induction of alpha B-crystallin does not directly depend on the SAPK pathway and AP1 activity.

The duck gene for alpha B-crystallin shows evolutionary conservation of discrete promoter elements but lacks heat and osmotic shock response

The gene for alpha Beta-crystallin from a bird (the domestic duck, Anas platyrhynchos) has been cloned and sequenced to allow comparison with its mammalian homologues. The duck gene has the same general structure as those of humans and rodents although, unlike those of mammals, the duck gene has two polyadenylation signals at the 3' end. The most interesting comparisons are in the 5'flanking promoter regions. In contrast to the broad conservation of promoter sequence among mammals, only two significant blocks and a few smaller elements have been conserved during evolution in the more distantly related avian gene. Block 1 (-350/-308) corresponds to alpha BE-2, a functional element defined in the mouse gene. Further downstream, block 2 (-98/-65) shows 27/33 identity among all three species but does not correspond to any previously defined element. Other regions are less well-conserved. In particular, putative heat-shock response elements of the mammalian alpha B-crystallin genes are absent from the duck gene. In contrast to the heat and osmotic stress-inducibility of mouse alpha B-crystallin in NIH 3T3 cells, duck alpha B-crystallin showed no inducibility in duck cells in culture. Thus, although high expression in lens is common to alpha B-crystallin genes in birds and mammals, other modes of expression appear to be taxon-specific.