Transient Loss of αB-Crystallin: An Early Cellular Response to Mechanical Stretch

Mitton, Kenneth P.; Tumminia, Santa J.; Arora, J.; Zelenka, Peggy S.; Epstein, D.L.; Russell, Paul

doi:10.1006/bbrc.1997.6737

Cited by 52 publications

(33 citation statements)

References 38 publications

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“…Increased IOP results in distention and stretching of the outflow pathway and its contained cells, while decreased IOP leads to relaxation of the tissue. It has also been demonstrated that mechanical stress can trigger certain responses in TM cells, including cytoskeletal changes, induction of gene expression, and activation of regulatory pathways [13][14][15][16][17][18][19][20][21] One of the reported responses to increased IOP in perfused human anterior segments observed by gene array analysis is an increase in interleukin-6 (IL-6) mRNA [16]. IL-6 is well known to increase the permeability of vascular endothelium through effects on the paracellular pathway, induction of matrix metalloproteinases (MMPs), and vesicular trafficking [22][23][24].…”

Section: Introductionmentioning

confidence: 99%

Induction of IL-6 expression by mechanical stress in the trabecular meshwork

Liton

Luna

Bodman

et al. 2005

Biochemical and Biophysical Research Communications

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The trabecular meshwork (TM)/Schlemm's canal (SC) outflow pathway is the tissue responsible for maintaining normal levels of intraocular pressure. In the present study, we investigate the effects of mechanical stress on the expression of IL-6 in the TM meshwork, as well as the effects of this cytokine on outflow pathway function. Application of cyclic mechanical stress to human TM primary cultures resulted in a statistically significant increase in both secretion and transcription of IL-6, compared to nonstressed controls. Addition of TGF-β1, which has been reported to be upregulated in TM cells under mechanical stress, also induced a significant activation of both the transcription and secretion of IL-6. Moreover, anti-TGF-b1 antibodies partially blocked the stretch-induced IL-6 production. Injection of IL-6 into perfused porcine anterior segments resulted in a 30% increase in outflow facility, as well as increased permeability through SC cell monolayers. These results suggest a role for IL-6 in the homeostatic modulation of aqueous humor outflow resistance. KeywordsTrabecular meshwork; Interleukin-6; Mechanical stress; TGF-β1; glaucomaThe trabecular meshwork (TM)/Schlemm's canal (SC) outflow pathway system constitutes the main route by which the aqueous humor exits the anterior chamber of the eye [1]. Maintenance of appropriate levels of aqueous humor outflow resistance through this pathway is critical in sustaining normal levels of intraocular pressure (IOP) [2,3]. Although it has been hypothesized that the TM/SC outflow pathway may respond to transient changes in IOP by altering its resistance to aqueous humor [4][5][6], thereby maintaining normal IOP levels, there is little experimental evidence explaining such potential homeostatic mechanisms.As a result of cyclic fluctuations of IOP with each heartbeat, the conventional outflow pathway is subjected to continuous cycles of stretch and relaxation that might be involved in tissue homeostasis and, consequently, in IOP regulation [7]. It has been well described that changes in IOP exert dramatic effects on the morphology of the outflow pathway [8][9][10][11][12]. Increased IOP results in distention and stretching of the outflow pathway and its contained cells, while decreased IOP leads to relaxation of the tissue. It has also been demonstrated that mechanical stress can trigger certain responses in TM cells, including cytoskeletal changes, induction of gene expression, and activation of regulatory pathways [13][14][15][16][17][18][19][20][21] One of the reported responses to increased IOP in perfused human anterior segments observed by gene array analysis is an increase in interleukin-6 (IL-6) mRNA [16]. IL-6 is well known to increase the permeability of vascular endothelium through effects on the paracellular pathway, induction of matrix metalloproteinases (MMPs), and vesicular trafficking [22][23][24]. This array of effects mediated by IL-6 suggests that this cytokine could affect aqueous humor outflow resistance in the outflow pathway by increasing ...

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Section: Introductionmentioning

confidence: 99%

Induction of IL-6 expression by mechanical stress in the trabecular meshwork

Liton

Luna

Bodman

et al. 2005

Biochemical and Biophysical Research Communications

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“…Both proteins have been shown to protect from cellular stress by several mechanisms. They facilitate renaturation of denatured proteins (Derham and Harding 1999) and protect cytoskeletal elements from ischemic injury and aggregation (Liang and MacRae 1997;Mitton et al 1997;Kamradt et al 2001;Parcellier et al 2005). AlphaBcrystallin stabilizes actin filaments and decreases actin depolymerization (Wang and Spector 1996).…”

Section: Introductionmentioning

confidence: 99%

Differential expression of alphaB-crystallin and Hsp27-1 in anaplastic thyroid carcinomas because of tumor-specific alphaB-crystallin gene (CRYAB) silencing

Mineva¹,

Gärtner²,

Hauser³

et al. 2005

Cell Stress Chaper

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Expression of the small heat shock protein alphaB-crystallin in differentiated thyroid tumors has been described recently. In this study, we investigated the molecular mechanisms that affect the expression of alphaB-crystallin in benign goiters (n ϭ 7) and highly malignant anaplastic thyroid carcinomas (ATCs) (n ϭ 3). AlphaB-crystallin expression was compared with that of Hsp27-1. Immunoblot and quantitative real-time (RT) polymerase chain reaction revealed marked downregulation of alphaB-crystallin in all the tested ATCs and the ATC-derived cell line C-643 . In contrast, considerable expression of Hsp27-1 in benign and malignant thyroid tissue was demonstrated. Immunofluorescence analysis revealed no relevant topological differences between benign and malignant thyrocytes in the cytoplasmic staining of both proteins. Consistent and marked downregulation of TFCP2L1 was identified as one of the main mechanisms contributing to CRYAB gene silencing in ATCs. In addition, CRYAB gene promoter methylation seems to occur in distinct ATCs. In silico analysis revealed that the differential expression of alphaB-crystallin and Hsp27-1 results from differences between the alphaB-crystallin and Hsp27-1 promoter fragments (712 bp upstream from the transcriptional start site). Biological activity of the analyzed promoter element is confirmed by its heat shock inducibility.In conclusion, we demonstrate downregulation of alphaB-crystallin expression in highly dedifferentiated ATCs because of a tumor-specific transcription factor pattern. The differential expression of alphaB-crystallin and Hsp27-1 indicates functional differences between both proteins.

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“…Small heat shock proteins such as Hsp25, Hsp27, as well as ␣-crystallin have been shown to have a similar function in refolding citrate synthase and ␤-glucosidase in vitro (24). The expression of ␣B-crystallin can be induced by heat shock (7), osmotic stress (25), or mechanical stress (26). We set out to investigate the physiochemical properties of the individual subunits to understand their structural and functional contributions in ␣-crystallin.…”

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confidence: 99%

Differential Temperature-dependent Chaperone-like Activity of αA- and αB-crystallin Homoaggregates

Datta

Rao

1999

Journal of Biological Chemistry

103

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␣-Crystallin, a heteromultimeric protein made up of ␣A-and ␣B-crystallins, functions as a molecular chaperone in preventing the aggregation of proteins. We have shown earlier that structural perturbation of ␣-crystallin can enhance its chaperone-like activity severalfold. The two subunits of ␣-crystallin have extensive sequence homology and individually display chaperonelike activity. We have investigated the chaperone-like activity of ␣A-and ␣B-crystallin homoaggregates against thermal and nonthermal modes of aggregation. We find that, against a nonthermal mode of aggregation, ␣B-crystallin shows significant protective ability even at subphysiological temperatures, at which ␣A-crystallin or heteromultimeric ␣-crystallin exhibit very little chaperone-like activity. Interestingly, differences in the protective ability of these homoaggregates against the thermal aggregation of ␤ L -crystallin is negligible. To investigate this differential behavior, we have monitored the temperature-dependent structural changes in both the proteins using fluorescence and circular dichroism spectroscopy. Intrinsic tryptophan fluorescence quenching by acrylamide shows that the tryptophans in ␣B-crystallin are more accessible than the lone tryptophan in ␣A-crystallin even at 25°C. Protein-bound 8-anilinonaphthalene-1-sulfonate fluorescence demonstrates the higher solvent accessibility of hydrophobic surfaces on ␣B-crystallin. Circular dichroism studies show some tertiary structural changes in ␣A-crystallin above 50°C. ␣B-crystallin, on the other hand, shows significant alteration of tertiary structure by 45°C. Our study demonstrates that despite a high degree of sequence homology and their generally accepted structural similarity, ␣B-crystallin is much more sensitive to temperaturedependent structural perturbation than ␣A-or ␣-crystallin and shows differences in its chaperone-like properties. These differences appear to be relevant to temperature-dependent enhancement of chaperone-like activity of ␣-crystallin and indicate different roles for the two proteins both in ␣-crystallin heteroaggregate and as separate proteins under stress conditions. ␣-Crystallin is a major protein of the mammalian lens and constitutes as much as 50% of its dry weight. Studies over the past few years have shown that ␣-crystallin is expressed in several nonlenticular tissues such as heart, brain, and kidney, and its expression is enhanced severalfold during stress and disease conditions (1-6). ␣-Crystallin is shown to have homology with small heat shock proteins (7-10). Horwitz (11) shows that ␣-crystallin can prevent the thermal aggregation of ␤-and ␥-crystallins and a few other proteins like a molecular chaperone. Demonstration of chaperone-like activity of ␣-crystallin has provided an excellent opportunity to investigate the mechanistic aspects of chaperone function in general and the role of ␣-crystallin under stress conditions in particular. It is possible that, in the lens, ␣-crystallin may chaperone the formation of the transparent and appropriately ...

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Transient Loss of αB-Crystallin: An Early Cellular Response to Mechanical Stretch

Cited by 52 publications

References 38 publications

Induction of IL-6 expression by mechanical stress in the trabecular meshwork

Induction of IL-6 expression by mechanical stress in the trabecular meshwork

Differential expression of alphaB-crystallin and Hsp27-1 in anaplastic thyroid carcinomas because of tumor-specific alphaB-crystallin gene (CRYAB) silencing

Differential Temperature-dependent Chaperone-like Activity of αA- and αB-crystallin Homoaggregates

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