Phosphorylation of the small heat-shock protein is regulated by interleukin 1, tumour necrosis factor, growth factors, bradykinin and ATP

Heat therapy: mechanistic underpinnings and applications to cardiovascular health

Cardiovascular diseases (CVD) are the leading cause of death worldwide, and novel therapies are drastically needed to prevent or delay the onset of CVD to reduce the societal and healthcare burdens associated with these chronic diseases. One such therapy is "heat therapy," or chronic, repeated use of hot baths or saunas. Although using heat exposure to improve health is not a new concept, it has received renewed attention in recent years as a growing number of studies have demonstrated robust and widespread beneficial effects of heat therapy on cardiovascular health. Here, we review the existing literature, with particular focus on the molecular mechanisms that underscore the cardiovascular benefits of this practice.

Cancer progression in COVID-19: integrating the roles of renin angiotensin aldosterone system, angiopoietin-2, heat shock protein-27 and epithelial mesenchymal transition

The ongoing coronavirus disease 2019 (COVID-19) pandemic has affected millions worldwide and has been found to cause severe disease in patients with underlying comorbidities. In patients with known malignancies, in addition to constraints in routine healthcare, the risk of being susceptible to developing severe forms of the disease is of grave concern. While follow-up studies on survivors of the severe acute respiratory syndrome (SARS) 2003 outbreak revealed increased susceptibility to infections, tumours and cardiovascular abnormalities, recent studies implicating angiopoietin 2 in induction of inflammatory intussusceptive angiogenesis and diffuse alveolar damage in COVID-19 patients raises the possibility of progression of carcinogenetic processes in patients with known malignancies. Angiotensin converting enzyme-2 (ACE-2) mediated cellular entry of SARS-Cov2 leads to receptor shedding of ACE-2 and disrupts the renin angiotensin aldosterone axis (RAAS). This augments the pro-inflammatory and proliferative effects of RAAS, while attenuating the anti-inflammatory and anti-proliferative angiotensin 1-7 /Mas pathway. Angiopoietin-2, a molecule responsible for angiogenesis and cancer progression which corelates with tumour load in certain cancers, is upregulated by angiotensin 2-AT1 Receptor axis. Tumour microenvironment-comprising of various cells, blood vessels and extra cellular matrix which express the RAAS peptides-plays a key role in cancer initiation, progression and metastasis. Angiotensin 2 induces the formation of a desmoplastic environment, favouring cancer cell growth. ACE-2 downregulation causes bradykinin accumulation which may exert its proliferative action via mitogen activated protein kinase pathways which has established roles in cancers of breast and kidney. In addition to cytokine storm causing organ damage, acute inflammation in COVID-19 may also cause epithelial mesenchymal transition and heat shock protein 27 phosphorylation, both of which are key mediators in cancer signalling pathways. We hypothesise that SARS-Cov2, by impacting the RAAS and immune system, has the potential to cause tumour cell proliferation, apoptosis evasion and metastasis, thereby increasing the possibility of cancer progression in patients with known malignancies.

Distinct IL-1α-responsive enhancers promote acute and coordinated changes in chromatin topology in a hierarchical manner

How cytokine-driven changes in chromatin topology are converted into gene regulatory circuits during inflammation still remains unclear. Here, we show that interleukin (IL)-1α induces acute and widespread changes in chromatin accessibility via the TAK1 kinase and NF-κB at regions that are highly enriched for inflammatory disease-relevant SNPs. Two enhancers in the extended chemokine locus on human chromosome 4 regulate the IL-1α-inducible IL8 and CXCL1-3 genes. Both enhancers engage in dynamic spatial interactions with gene promoters in an IL-1α/TAK1-inducible manner. Microdeletions of p65-binding sites in either of the two enhancers impair NF-κB recruitment, suppress activation and biallelic transcription of the IL8/CXCL2 genes, and reshuffle higher-order chromatin interactions as judged by i4C interactome profiles. Notably, these findings support a dominant role of the IL8 "master" enhancer in the regulation of sustained IL-1α signaling, as well as for IL-8 and IL-6 secretion. CRISPR-guided transactivation of the IL8 locus or cross-TAD regulation by TNFα-responsive enhancers in a different model locus supports the existence of complex enhancer hierarchies in response to cytokine stimulation that prime and orchestrate proinflammatory chromatin responses downstream of NF-κB.

The primary cilium influences interleukin-1β-induced NFκB signalling by regulating IKK activity

The primary cilium is an organelle acting as a master regulator of cellular signalling. We have previously shown that disruption of primary cilia assembly, through targeting intraflagellar transport, is associated with muted nitric oxide and prostaglandin responses to the inflammatory cytokine interleukin-1β (IL-1β). Here, we show that loss of the primary cilium disrupts specific molecular signalling events in cytosolic NFκB signalling. The induction of cyclooxygenase 2 (COX2) and inducible nitrous oxide synthase (iNOS) protein is abolished. Cells unable to assemble cilia exhibit unaffected activation of IκB kinase (IKK), but delayed and reduced degradation of IκB, due to diminished phosphorylation of inhibitor of kappa B (IκB) by IKK. This results in both delayed and reduced NFκB p65 nuclear translocation and nuclear transcript binding. We also demonstrate that heat shock protein 27 (hsp27), an established regulator of IKK, is localized to the ciliary axoneme and cellular levels are dramatically disrupted with loss of the primary cilium. These results suggest that the primary cilia compartment exerts influence over NFκB signalling. We propose that the cilium is a locality for regulation of the molecular events defining NFκB signalling events, tuning signalling as appropriate.

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Hypermorphic mutation of IFT88 results in partial loss of the primary cilium.

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Cilia loss leads to inhibition of COX2 and iNOS induction in response to IL-1.

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In cells without cilia, IKK is activated but does not phosphorylate IκB.

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This leads to sustained IκB expression, and reduced and mistimed NFκB signalling.

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We propose the cilium to be a location for hsp27 regulation of IKK activity.

Small molecule sensitization to TRAIL is mediated via nuclear localization, phosphorylation and inhibition of chaperone activity of Hsp27

The small chaperone protein Hsp27 confers resistance to apoptosis, and therefore is an attractive anticancer drug target. We report here a novel mechanism underlying the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) sensitizing activity of the small molecule LY303511, an inactive analog of the phosphoinositide 3-kinase inhibitor inhibitor LY294002, in HeLa cells that are refractory to TRAIL-induced apoptosis. On the basis of the fact that LY303511 is derived from LY294002, itself derived from quercetin, and earlier findings indicating that quercetin and LY294002 affected Hsp27 expression, we investigated whether LY303511 sensitized cancer cells to TRAIL via a conserved inhibitory effect on Hsp27. We provide evidence that upon treatment with LY303511, Hsp27 is progressively sequestered in the nucleus, thus reducing its protective effect in the cytosol during the apoptotic process. LY303511-induced nuclear translocation of Hsp27 is linked to its sustained phosphorylation via activation of p38 kinase and MAPKAP kinase 2 and the inhibition of PP2A. Furthermore, Hsp27 phosphorylation leads to the subsequent dissociation of its large oligomers and a decrease in its chaperone activity, thereby further compromising the death inhibitory activity of Hsp27. Furthermore, genetic manipulation of Hsp27 expression significantly affected the TRAIL sensitizing activity of LY303511, which corroborated the Hsp27 targeting activity of LY303511. Taken together, these data indicate a novel mechanism of small molecule sensitization to TRAIL through targeting of Hsp27 functions, rather than its overall expression, leading to decreased cellular protection, which could have therapeutic implications for overcoming chemotherapy resistance in tumor cells.

Lithium protects cartilage from cytokine-mediated degradation by reducing collagen-degrading MMP production via inhibition of the P38 mitogen-activated protein kinase pathway

OBJECTIVES

To determine the effects and mechanism of action of lithium chloride (LiCl) on cartilage destruction induced by the pro-inflammatory cytokines IL-1, IL-1 + oncostatin M and TNF-α.

METHODS

The release of collagen was assessed in bovine cartilage explant cultures, whereas collagenolytic activities (active and total) in conditioned culture supernatants were determined by bioassay. The expression and production of MMP from chondrocytes were analysed by real-time RT-PCR and ELISA. Signalling pathway analysis was performed using a phospho-antibody array and standard immunoblotting.

RESULTS

LiCl, but not selective glycogen synthase kinase 3 (GSK-3) inhibitor compounds SB-415286 and TDZD-8, significantly decreased pro-inflammatory cytokine-induced collagen release from bovine cartilage via the down-regulation of collagenolytic activity. Furthermore, MMP-1 and MMP-13 expression was reduced in both bovine and human chondrocytes. Pathway analysis revealed that LiCl selectively inhibited activation of the p38 mitogen-activated protein kinase pathway; effects that were recapitulated by specific p38 pathway inhibition.

CONCLUSIONS

This study demonstrates for the first time that LiCl can protect against cartilage damage induced by pro-inflammatory cytokines, and indicates that LiCl-mediated cartilage protection is not via a GSK-3-dependent mechanism, but potentially via inhibition of the p38 pathway. These data indicate that lithium administration may represent a potential therapy for arthritis.

Transcription factor network reconstruction using the living cell array

The objective of identifying transcriptional regulatory networks is to provide insights as to what governs an organism's long term response to external stimuli. We explore the coupling of the living cell array (LCA), a novel microfluidics device which utilizes fluorescence levels as a surrogate for transcription factor activity with reverse Euler deconvolution (RED) a computational technique proposed in this work to decipher the dynamics of the interactions. It is hypothesized that these two methods will allow us to first assess the underlying network architecture associated with the transcription factor network as well as specific mechanistic consequences of transcription factor activation such as receptor dimerization or tolerance. The overall approach identifies evidence of time-lagged response which may be indicative of mechanisms such as receptor dimerization, tolerance mechanisms which are evidence of various receptor mediated dynamics, and feedback loops which regulate the response of an organism to changing environmental conditions. Furthermore, through the exploration of multiple network architectures, we were able to obtain insights as to the role each transcription factor plays in the overall response and their overall redundancy in the organism's response to external perturbations. Thus, the LCA along with the proposed analysis technique is a valuable tool for identifying the possible architectures and mechanisms underlying the transcriptional response.

Changes in the phosphorylation status of the 27 kDa heat shock protein (HSP27) associated with the modulation of growth and/or differentiation in MCF-7 cells

We have used human mammary cells of the MCF-7 strain, which constitutively express high levels of the small heat shock protein HSP27 and we have compared the changes in the phosphorylation status of this protein together with changes in cell growth and/or morphology induced by the action of one of the following agents: (1) TPA (12-O-tetradecanoylphorbol-13-acetate), known as a differentiation inducer in MCF-7 cells; (2) OH-TAM (hydroxytamoxifen), which exerts a cytostatic and cytotoxic action; or (3) TNF alpha (tumour necrosis factor), which induces apoptotic cell death in this cell line. Our data show that TPA and TNF stimulate an immediate and massive phosphorylation of HSP27, whereas OH-TAM affect the phosphorylation status of the protein only after a 3 day delay. In the case of TPA, high levels of HSP27 phosphorylation were maintained for at least 4 days, along with growth inhibition and acquisition by the cells of a secretory phenotype. TPA and OH-TAM exerted similar immediated effects on cell growth, despite the different time course of their action on HSP27 phosphorylation. This excludes the possibility that the latter is a necessary consequence of, or an absolute requisite to, growth inhibition. With OH-TAM and TNF the increase in HSP27 phosphorylation was concomitant with the appearance of apoptosis, not observed with TPA. This indicates that increased phosphorylation of HSP27 is not specifically associated with the triggering or the execution of apoptosis in these cells. Altogether, our data support the concept that phosphorylated HSP27 is involved (and might then be rate limiting in some instances) in the execution of vital cell programmes (including resistance to stress, proliferation and differentiation), as well as in that of cell death. This is consistent with its role in actin polymerization and its position downstream of the p38/RK-type MAPkinase, itself a point of convergence for diverse signal transduction pathways.

Heat shock protein 27 functions in inflammatory gene expression and transforming growth factor-beta-activated kinase-1 (TAK1)-mediated signaling

Heat shock protein (HSP) 27 has long been known to be a component of the p38 mitogen-activated protein kinase (MAPK) signaling pathway. p38 MAPK has important functions in the inflammatory response, but the role of HSP27 in inflammation has remained unknown. We have used small interfering RNAs to suppress HSP27 expression in HeLa cells and fibroblasts and found that it is required for pro-inflammatory cell signaling and the expression of pro-inflammatory genes. HSP27 is needed for the activation by interleukin (IL)-1 of TAK1 and downstream signaling by p38 MAPK, JNK, and their activators (MKK-3, -4, -6, -7) and IKKbeta. IL-1-induced ERK activation appears to be independent of HSP27. HSP27 is required for both IL-1 and TNF-induced signaling pathways for which the most upstream common signaling protein is TAK1. HSP27 is also required for IL-1-induced expression of the pro-inflammatory mediators, cyclooxygenase-2, IL-6, and IL-8. HSP27 functions to drive cyclooxygenase-2 and IL-6 expression by augmenting the activation of the kinase downstream of p38 MAPK, MK2, resulting in stabilization of cyclooxygenase-2 and IL-6 mRNAs. The mechanism may not occur in cells of myeloid lineage because HSP27 protein was undetectable in human monocytes and murine macrophages.

Retinal glial cell responses and Fas/FasL activation in rats with chronic ocular hypertension

Responses in the retina post injury provoke glial reactions that are not completely understood. This study investigated the reaction of retinal glial cells and the expression and localization of the Fas and Fas-ligand (FasL) in rats with chronic ocular hypertension. Experimental glaucoma was induced in one eye of 60 Sprague-Dawley rats by cauterizing three episcleral vessels. It caused a moderate intraocular pressure (IOP) elevation and significant retinal ganglion cell (RGC) loss for at least 6 weeks in all animals. Immunohistochemical analysis revealed that the expression of GFAP and OX-42 increased in the injured retinae. Fas/FasL immunoreactivity was elevated in the microglia, and we also observed an incremental increase in Fas associated death domain (FADD) immunoreactivity in Müller glial cells and RGCs in the IOP-elevated retinae. The activation of glial cells and upregulation of Fas and FasL suggest that glial cells may contribute to Fas-mediated cell death in the neurodegeneration process of chronic ocular hypertensive retinal insult.

Overexpression of wild-type heat shock protein 27 and a nonphosphorylatable heat shock protein 27 mutant protects against ischemia/reperfusion injury in a transgenic mouse model

BACKGROUND

The small heat shock protein 27 (hsp27) increases in expression with ischemia/reperfusion (I/R) insult in the heart. One feature of the small hsps is their ability to oligomerize and form intracellular aggregates. Oligomerization pattern is governed by the phosphorylation state of the protein that may influence their ability to protect against cellular stresses.

METHODS AND RESULTS

We generated transgenic (tg) mice that overexpress a wild-type human hsp27 (hsp27tg) protein or a mutant hsp27 protein (mut-hsp27tg), in which serine residues (aa15, aa78, and aa82) were replaced by alanine residues, rendering them incapable of phosphorylation. Using a Langendorff perfusion model and an intraventricular balloon, we subjected hearts to 20 minutes of ischemia followed by 1 hour of reperfusion. During reperfusion, negative and positive pressure derivatives as well as developed pressures were significantly higher in both hsp27tg and mut-hsp27tg compared with control (P<0.01) mice, with no significant difference between hsp27tg and mut-hsp27tg. Creatine kinase release during reperfusion was higher in control compared with both hsp27tg and mut-hsp27tg (P<0.05). Malondialdehyde content as well as protein oxidation products were lower in mut-hsp27tg compared with control (P<0.05). hsp27tg hearts possessed oligomers that ranged in size from small to large, whereas mut-hsp27tg hearts contained no small oligomers.

CONCLUSIONS

These results indicate that in a tg mouse model, overexpression of either wild-type hsp27 or a nonphosphorylatable hsp27 mutant was equally capable of protecting the heart from I/R injury. Furthermore, the phosphorylation status of hsp27 may influence its ability to decrease oxidative stress.

Retaining of the assembly capability of vimentin phosphorylated by mitogen-activated protein kinase-activated protein kinase-2

Intermediate filament (IF) networks can be regulated by phosphorylation of unit proteins, such as vimentin, by specific kinases leading to reorganization of the IF filamentous structure. Recently, we identified mitogen-activated protein kinase-activated protein kinase-2 (MAPKAP kinase-2) as a vimentin kinase (Cheng and Lai [1998] J. Cell. Biochem. 71:169-181). Herein we describe the results of further in vitro studies investigating the effects of MAPKAP kinase-2 phosphorylation on vimentin and the effects of the phosphorylation on the filamentous structure. We show that MAPKAP kinase-2 mainly phosphorylates vimentin at Ser-38, Ser-50, Ser-55, and Ser-82, residues all located in the head domain of the protein. Surprisingly, and in stark contrast to phosphorylation by most other kinases, phosphorylation of vimentin by MAPKAP kinase-2 has no discernable effect on its assembly. It suggested that structure disassembly is not the only obligated consequence of phosphorylated vimentin as regulated by other kinases. Finally, a mutational analysis of each of the phosphorylated serine residues in vimentin suggested that no single serine site was primarily responsible for structure maintenance, implying that the retention of filamentous structure may be the result of the coordinated action of several phosphorylated serine sites. This also shed new lights on the functional task(s) of vimentin that is intermediate filament proteins might provide a phosphate reservoir to accommodate the phosphate surge without any structural changes.

Neurobiology of glaucomatous optic neuropathy: diverse cellular events in neurodegeneration and neuroprotection

Although glaucomatous optic nerve degeneration is a leading cause of worldwide blindness, neither the precise cellular mechanisms underlying neurodegeneration in glaucoma, nor effective strategies for neuroprotection are yet clear. This review focuses on diverse cellular events associated with glaucomatous neurodegeneration whose balance is critical for determination of ultimate cell fate. An improved understanding of the site of primary injury to optic nerve, the mediator pathways of apoptotic cell death and intrinsic protection mechanisms in retinal ganglion cells, the role of glial activation on the survival and death of retinal ganglion cell bodies and their axons, and the protective and destructive consequences of immune system involvement can facilitate development of effective neuroprotective strategies in glaucoma.

Identification of a phosphoprotein that is downregulated in immortalized human fibroblasts

Many lines of evidence indicate that the immortalization step is critical for the neoplastic transformation of normal human cells. Once normal human cells have been immortalized, they are relatively easily transformed into neoplastic cells. In order to understand these phenomena, patterns of protein phosphorylation in proliferating normal human fibroblast cell strains and their immortalized cell lines were compared by using two-dimensional polyacrylamide gel electrophoresis. It was found that the expression and phosphorylation levels of the human heat shock protein 27 (HSP27) were predominantly downregulated in the immortalized cells compared with those in their normal counterparts. In the normal cells, HSP27 expression and phosphorylation were markedly increased by physiological and nonphysiological stresses, such as serum addition, treatment with a carcinogenic agent like 4-nitroquinoline-1-oxide, and a high osmotic pressure. This may be a normal defense against acute changes of cellular environment and cytotoxic effects. However, these stresses had no effects on the expression and phosphorylation of HSP27 in the immortalized cells. These results suggest that an abnormal regulation of HSP27 expression and phosphorylation may be one of the reasons for easy neoplastic transformation of the immortalized cells by the treatment with carcinogenic agents.

Two distinct forms of MAPKAP kinase-2 in adult cardiac ventricular myocytes

Hsp27 kinase activities were studied in adult rat ventricular myocytes following sequential chromatography on Mono Q and Mono S. A basal level of activity was present following cell isolation. FPLC on Mono Q revealed three peaks of activity, peaks 'a', 'b', and 'c'. A fourth peak, 'd', was detected upon subsequent chromatography of the Mono Q flow-through on Mono S. Immunoblotting revealed that peaks 'a', 'b', and 'c' contained predominantly a 49 kDa form of MAPKAP kinase-2. Peak 'd' contained a 43 kDa form. 'In-gel' kinase assays using hsp27 indicated both forms of MAPKAP kinase-2 were active. No other bands of hsp27 kinase activity were detected. Both forms of hsp27 kinase immunoprecipitated with a MAPKAP kinase-2 antibody and have therefore been named MAPKAP kinase-2alpha (p49) and MAPKAP kinase-2beta (p43). MAPKAP kinase-2beta chromatographed on Superose 12 as a 60.7 kDa monomer whereas the behavior of MAPKAP kinase-2alpha suggested both a 65.7 kDa monomer and higher molecular mass complexes. Both activities phosphorylated hsp27 on serine residues, and two-dimensional phosphopeptide mapping indicated the same sites were phosphorylated. A tumor-promoting phorbol ester, phorbol 12-myristate 13-acetate (PMA), stimulated both MAPKAP kinase-2alpha and MAPKAP kinase-2beta activity. Inhibition of MEK activation with PD 98059 or p38alpha/beta MAP kinase activity with SB203580 blocked activation by PMA. However, whereas PD 98059 inhibited only the PMA-stimulated activation, SB203580 inhibited both PMA-stimulated and basal hsp27 phosphorylation. These data demonstrate the presence of two forms of MAPKAP kinase-2 in adult ventricular myocytes. Both forms are activated indirectly by the ERK MAP kinase pathway and directly by p38 MAP kinase but independently regulated.

Differential expression of small heat shock proteins in reactive astrocytes after focal ischemia: possible role of beta-adrenergic receptor

Small heat shock proteins (sHSPs), a family of HSPs, are known to accumulate in the CNS, mainly in astrocytes, in several pathological conditions such as Alexander's disease, Alzheimer's disease, and Creutzfeldt-Jakob disease. sHSPs may act not only as molecular chaperones, protecting against various stress stimuli, but may also play a physiological role in regulating cell differentiation and proliferation. In the present study, we have demonstrated that transient focal ischemia in rats dramatically induced HSP27 but not alpha B-crystallin (alphaBC), both of which are members of sHSPs, in reactive astrocytes. In contrast, in vitro chemical ischemic stress induced both HSP27 and alphaBC in cultured glial cells to the same extent. Dibutyryl cAMP (dBcAMP) and isoproterenol, a beta-adrenergic receptor (betaAR) agonist, enhanced HSP27 expression but suppressed alphaBC, and changed the shape of the cells to a stellate form. dBcAMP and isoproterenol inhibited cell proliferation under normal conditions. An increase in betaAR-like immunoreactivity was also observed in reactive astrocytes in vivo. These results, together with recent findings that betaAR plays an important role in glial scar formation in vivo, raise the possibility that betaAR activation modulates sHSP expression after focal ischemia and is involved in the transformation of astrocytes to their reactive form.

Differential expression of small heat shock proteins in reactive astrocytes after focal ischemia: possible role of beta-adrenergic receptor

Small heat shock proteins (sHSPs), a family of HSPs, are known to accumulate in the CNS, mainly in astrocytes, in several pathological conditions such as Alexander's disease, Alzheimer's disease, and Creutzfeldt-Jakob disease. sHSPs may act not only as molecular chaperones, protecting against various stress stimuli, but may also play a physiological role in regulating cell differentiation and proliferation. In the present study, we have demonstrated that transient focal ischemia in rats dramatically induced HSP27 but not alpha B-crystallin (alphaBC), both of which are members of sHSPs, in reactive astrocytes. In contrast, in vitro chemical ischemic stress induced both HSP27 and alphaBC in cultured glial cells to the same extent. Dibutyryl cAMP (dBcAMP) and isoproterenol, a beta-adrenergic receptor (betaAR) agonist, enhanced HSP27 expression but suppressed alphaBC, and changed the shape of the cells to a stellate form. dBcAMP and isoproterenol inhibited cell proliferation under normal conditions. An increase in betaAR-like immunoreactivity was also observed in reactive astrocytes in vivo. These results, together with recent findings that betaAR plays an important role in glial scar formation in vivo, raise the possibility that betaAR activation modulates sHSP expression after focal ischemia and is involved in the transformation of astrocytes to their reactive form.

Induction of stress proteins by electromagnetic fields in cultured HL-60 cells

HL-60 cells in culture were exposed for 2 h to a sinusoidal 0.1 or 1 mT (1 or 10 Gauss) magnetic field at 60 Hz and pulse labeled after exposure with radioactive isotopes by incubation by using either [(35)S]methionine, [(3)H]leucine, or [(33)P]phosphate. The radioactive labels were incorporated into cellular proteins through synthesis or phosphorylation. Proteins were extracted from electrostatically sorted nuclei, and the heat shock/stress proteins (sp) were analyzed for synthesis and phosphorylation by two-dimensional polyacrylamide gel electrophoresis. In the control cultures (no exposure to the magnetic field), sp 72c (cognate form) was faintly observed. A 0.1 mT exposure did not show sp metabolism to be different from that of the controls; however, after a 1 mT exposure of the HL-60 cells, sp 70i (inducible form) was synthesized ([(35)S]methionine incorporation). Sp 90 was not synthesized at either field level, but was phosphorylated ([(33)P]phosphate incorporation) in the 1 mT exposure. Sp 27 (isoforms a and b) was induced after a 1 mT exposure as reflected by labeling with [(3)H]leucine. These sps were not detected after a 0.1 mT exposure. After a 1 mT exposure and labeling with [(33)P], sp 27 isoforms b and c were phosphorylated whereas isoform 'a' was not observed. Sps 70i, 72c, and 90 were identified by commercial sp antibodies. Likewise, polypeptides a, b, and c were verified as sp 27 isoforms by Western blotting. Statistical evaluation of sp areas and densities, determined from fluorographs by Western-blot analysis, revealed a significant increase in sps 90 and 27a after a 1 mT magnetic field exposure. The 1 mT magnetic field interacts at the cellular level to induce a variety of sp species. Bioelectromagnetics 20:347-357, 1999. Published 1999 Wiley-Liss, Inc.

Anti-sense inhibition of small-heat-shock-protein (HSP27) expression in MCF-7 mammary-carcinoma cells induces their spontaneous acquisition of a secretory phenotype

This work was aimed at testing the hypothesis (hitherto supported only by indirect evidence) that, besides contributing to resistance to stress, the small heat-shock-protein HSP27 might be involved in the control of growth and differentiation in mammary-tumour cells, where it is known to be oestrogen-regulated. Therefore, MCF-7 cells were transfected with a modulatable human hsp27 anti-sense cDNA. Clones of transfectants (designated alphahsp27) were selected which, upon expression of the anti-sense, exhibited a decline in HSP27 accumulation, associated with a decrease in resistance to heat shock and in proliferation rate, the degree of the latter reflecting their respective reduction in HSP27 content. The effects of anti-sense inhibition of HSP27 production were similar to those exerted on parental cells by phorbol myristate (TPA). Both resulted in growth inhibition, accumulation of lipid droplets in the cytoplasm, formation of secretory microvesicles with internal microvilli and increased release of several proteins, including the isoforms of a 52-kDa protein, which we identified as the oestrogen-regulated protein cathepsin D, all this without noticeable change in actin organization. These data constitute the first direct support for the hypothesis that, at least in some cell types, HSP27 might play a modulatory role in cell differentiation and (perhaps by this) in proliferation. While allowing dissociation of this role from the known action of HSP27 on actin polymerization, they suggest similar modulation of the function of some protein(s) implicated in the acquisition of the secretory phenotype by MCF-7 cells, with HSP27 also exerting an inhibitory action that can be alleviated either by its phosphorylation (as occurs with TPA) or by inhibition of its production.

Heat shock protein 27: developmental regulation and expression after peripheral nerve injury

The heat shock protein (HSP) 27 is constitutively expressed at low levels in medium-sized lumbar dorsal root ganglion (DRG) cells in adult rats. Transection of the sciatic nerve results in a ninefold upregulation of HSP27 mRNA and protein in axotomized neurons in the ipsilateral DRG at 48 hr, without equivalent changes in the mRNAs encoding HSP56, HSP60, HSP70, and HSP90. Dorsal rhizotomy, injuring the central axon of the DRG neuron, does not upregulate HSP27 mRNA levels. After peripheral axotomy, HSP27 mRNA and protein are present in small, medium, and large DRG neurons, and HSP27 protein is transported anterogradely, accumulating in the dorsal horn and dorsal columns of the spinal cord, where it persists for several months. Axotomized motor neurons also upregulate HSP27. Only a minority of cultured adult DRG neurons are HSP27-immunoreactive soon after dissociation, but all express HSP27 after 24 hr in culture with prominent label throughout the neuron, including the growth cone. HSP27 differs from most axonal injury-regulated and growth-associated genes, which are typically present at high levels in early development and downregulated on innervation of their targets, in that its mRNA is first detectable in the DRG late in development and only approaches adult levels by postnatal day 21. In non-neuronal cells, HSP27 has been shown to be involved both in actin filament dynamics and in protection against necrotic and apoptotic cell death. Therefore, its upregulation after adult peripheral nerve injury may both promote survival of the injured neurons and contribute to alterations in the cytoskeleton associated with axonal growth.

Heat shock protein 27: developmental regulation and expression after peripheral nerve injury

The heat shock protein (HSP) 27 is constitutively expressed at low levels in medium-sized lumbar dorsal root ganglion (DRG) cells in adult rats. Transection of the sciatic nerve results in a ninefold upregulation of HSP27 mRNA and protein in axotomized neurons in the ipsilateral DRG at 48 hr, without equivalent changes in the mRNAs encoding HSP56, HSP60, HSP70, and HSP90. Dorsal rhizotomy, injuring the central axon of the DRG neuron, does not upregulate HSP27 mRNA levels. After peripheral axotomy, HSP27 mRNA and protein are present in small, medium, and large DRG neurons, and HSP27 protein is transported anterogradely, accumulating in the dorsal horn and dorsal columns of the spinal cord, where it persists for several months. Axotomized motor neurons also upregulate HSP27. Only a minority of cultured adult DRG neurons are HSP27-immunoreactive soon after dissociation, but all express HSP27 after 24 hr in culture with prominent label throughout the neuron, including the growth cone. HSP27 differs from most axonal injury-regulated and growth-associated genes, which are typically present at high levels in early development and downregulated on innervation of their targets, in that its mRNA is first detectable in the DRG late in development and only approaches adult levels by postnatal day 21. In non-neuronal cells, HSP27 has been shown to be involved both in actin filament dynamics and in protection against necrotic and apoptotic cell death. Therefore, its upregulation after adult peripheral nerve injury may both promote survival of the injured neurons and contribute to alterations in the cytoskeleton associated with axonal growth.

Phosphorylation of alphaB-crystallin and HSP27 is induced by similar stressors in HeLa cells

Three members of the small heat shock protein family, alphaA-, alphaB-crystallin, and HSP27, confer thermoresistance upon their overexpression in mammalian cells. Phosphorylation, in conjunction with the molecular chaperone-like activity of these small HSPs, is believed to be important for this in situ functional property. We here report the influence of heat shock and other kinds of stress on the phosphorylation of alphaA-, alphaB-crystallin, and HSP27 in stably transfected HeLa cells. It is observed that alphaB-crystallin becomes phosphorylated upon exposure to the same inducers as is HSP27, although to a lesser extent. In contrast, phosphorylation of alphaA-crystallin is very low upon heat stress and even absent when other stressors are used. This indicates that phosphorylation is not in all instances essential for the stress protective functioning of the various small HSPs.

Heat-shock protein-25/27 phosphorylation by the delta isoform of protein kinase C

Small heat-shock proteins (sHSPs) are widely expressed 25-28 kDa proteins whose functions are dynamically regulated by phosphorylation. While recent efforts have clearly delineated a stress-responsive p38 mitogen-activated protein-kinase (MAPK)-dependent kinase pathway culminating in activation of the heat-shock (HSP)-kinases, mitogen-activated protein-kinase-activated protein kinase-2 and -3, not all sHSP phosphorylation events can be explained by the p38 MAPK-dependent pathway. The contribution of protein kinase C (PKC) to sHSP phosphorylation was suggested by early studies but later questioned on the basis of the reported poor ability of purified PKC to phosphorylate sHSP in vitro. The current study re-evaluates the role of PKC in sHSP phosphorylation in the light of the isoform complexity of the PKC family. We evaluated the sHSP phosphorylation status in rat corpora lutea obtained from two stages of pregnancy, mid-pregnancy and late-pregnancy, which express different levels of the novel PKC isoform, PKC-delta. Two-dimensional Western blot analysis showed that HSP-27 was more highly phosphorylated in vivo in corpora lutea of late pregnancy, corresponding to the developmental stage in which PKC-delta is abundant and active. Late-pregnant luteal extracts contained a lipid-sensitive HSP-kinase activity which exactly co-purified with PKC-delta using hydroxyapatite and S-Sepharose column chromatography. To determine whether there might be preferential phosphorylation of sHSP by a particular PKC isoform, purified recombinant PKC isoforms corresponding to those PKC isoforms detected in rat corpora lutea were evaluated for HSP-kinase activity in vitro. Recombinant PKC-delta effectively catalysed the phosphorylation of sHSP in vitro, and PKC-alpha was 30-50% as effective as an HSP-kinase; other PKCs tested (beta1, beta2, epsilon and zeta) were poor HSP-kinases. These results show that select PKC family members can function as direct HSP-kinases in vitro. Moreover, the observation of enhanced luteal HSP-27 phosphorylation in vivo, in late pregnancy, when PKC-delta is abundant and active, suggests that select PKC family members contribute to sHSP phosphorylation events in vivo.

Phosphorylation of alphaB-crystallin in response to various types of stress

Phosphorylation of alphaB-crystallin, a member of the hsp27 family, in human glioma (U373 MG) cells was stimulated by exposure of the cells to various stimuli, which included heat, arsenite, phorbol 12-myristate 13-acetate (PMA), okadaic acid, H2O2, anisomycin, and high concentrations of NaCl or sorbitol, but not in response to agents that elevated intracellular levels of cyclic AMP. Cells exposed to PMA together with okadaic acid yielded three bands of 32P-labeled alphaB-crystallin when immunoprecipitated samples were subjected to electrophoresis on an isoelectric focusing gel. All of the phosphorylated residues were identified as serine, an indication that three different serine residues can act as sites of phosphorylation in alphaB-crystallin. Structural analysis by mass spectrometry revealed that phosphorylation of alphaB-crystallin occurred at serines 19, 45, and 59. Dithiothreitol and staurosporine selectively inhibited the phosphorylation induced by arsenite and the phorbol ester, respectively. SB202190, an inhibitor of p38 mitogen-activated protein (MAP) kinase, suppressed the phosphorylation induced by arsenite, anisomycin, H2O2, sorbitol, NaCl, and heat shock, but not that induced by PMA and okadaic acid. The PMA-induced phosphorylation was selectively suppressed by an inhibitor of p44 MAP kinase kinase, PD98059. Although PMA and arsenite preferentially stimulated the phosphorylation of Ser-45 and Ser-59, respectively, as determined with antibodies that recognized the respective phosphorylated forms of alphaB-crystallin, all three sites were phosphorylated in response to each stimulus. These results suggest that p38 MAP kinase or p44 MAP kinase might be involved in the signal transduction cascade that leads to the phosphorylation of alphaB-crystallin. The phosphorylation of alphaB-crystallin was also enhanced in the heart and diaphragm when rats were exposed to heat stress (42 degrees C for 20 min).

Heat shock proteins and heat adaptation of the whole organism

Adaptation to heat may occur through acclimatization or thermotolerance; however, the linkage of these phenomena is poorly understood. The importance of heat shock proteins (HSPs) in thermotolerance and differences in their accumulation in organisms adapted to the heat suggest a role for HSPs in acclimatization as well. The role of HSPs in heat adaptation of the whole organism and the interrelationships among heat adaptation, endotoxin tolerance, and cytokine resistance through HSPs are reviewed.

Phosphorylation of HSP25 during lens cell differentiation

Small heat shock proteins and alpha-crystallins are related proteins with several common structural and functional properties including homologous amino acid sequences and similar chaperone-like activity. Furthermore, small heat shock proteins and alpha-crystallins are phosphorylated in vivo at serine residues within homologous amino acid sequences. During the differentiation of lens epithelial cells to fiber cells, significant changes in the patterns of expression and phosphorylation of alpha-crystallins take place, leading to the accumulation of phosphorylated forms of these proteins in lens fiber cells. To determine whether the small heat shock protein HSP25 undergoes phosphorylation in lens cells and to ascertain whether its phosphorylation state changes during lens cell differentiation, a comparative analysis of the HSP25 phosphorylation pattern in epithelial and fiber cells was undertaken. Analysis of phosphorylated and non-phosphorylated forms of HSP25 was carried out in cell extracts from rat lens epithelium and cortex by isoelectric focusing and Western blot using an antibody specific for the recombinant murine protein. The phosphorylated forms were identified by their isoelectric points and the characteristic shift upon in vitro dephosphorylation with phosphoprotein phosphatase 2B. HSP25 accounted for up to 2.4% of the protein content of rat lens extracts where it was present predominantly in mono- and bi-phosphorylated forms. Compared to epithelial cells extracts, the fiber cells extracts contained 67% more total HSP25 and a significantly higher proportion of bi-phosphorylated form. Phosphorylated HSP25 was sensitive to dephosphorylation by phosphoprotein phosphatase 2B in both cell extracts but the apparent dephosphorylation rate was significantly slower in the fiber cell extracts. The results demonstrate that HSP25 is phosphorylated in the lens in vivo. Furthermore, synthesis and phosphorylation of HSP25 change with lens cell differentiation resulting in a significant accumulation of bi-phosphorylated form in the fiber cells. These findings indicate that HSP25 and its phosphorylation may have important roles in lens cell differentiation.

Inhibition of protein tyrosine phosphatases causes phosphorylation of tyrosine-331 in the p60 TNF receptor and inactivates the receptor-associated kinase

Inhibition of protein tyrosine phosphatases blocks tumor necrosis factor (TNF)-induced growth modulation and NF-kappaB activation, both mediated primarily through the p60 TNF receptor. How inhibition of the phosphatases affects the p60 TNF receptor or the recently described receptor-associated serine/threonine kinase (p60TRAK) is not known. In this report, we show that this inhibition, when induced by pervanadate, caused the tyrosine phosphorylation of the cytoplasmic domain (CD) of the p60 receptor, as revealed by phosphoamino acid analysis. Furthermore, site-directed mutagenesis indicated that pervanadate specifically induced the phosphorylation of tyrosine-331, which is located in the death domain of the TNF receptor, a domain to which p60TRAK binds. This tyrosine residue was also phosphorylated by purified, recombinant pp60Src in vitro. Inhibition of protein tyrosine phosphatases by pervanadate also led to the inactivation of p60TRAK. In contrast, okadaic acid, a specific inhibitor of protein serine/threonine phosphatase, increased p60TRAK activity. Taken together, these results suggest that protein tyrosine phosphatases play an essential role in phosphorylation of the cytoplasmic domain of the TNF receptor and in regulation of the receptor-associated kinase, and this in turn may play a role in TNF-mediated growth modulation and NF-kappaB activation.

UVB irradiation induces changes in cellular localization and phosphorylation of mouse HSP27

We investigated the induction, cellular localization and phosphorylation of a low-molecular weight stress protein (heat shock protein 27, HSP27) by UVB (290-320 nm, max. 312 nm) irradiation stress using immunoblot and indirect immunofluorescence analysis in in vivo and in vitro experiments. The HSP27 was constitutively expressed and distributed in the cytoplasmic fraction of Pam 212 cells (mouse keratinocyte line) or dorsal skin. The increase in the cytoplasm HSP27 level induced by UVB irradiation was less than two-fold that in nonirradiated controls. On the other hand, the translocation of HSP27 from cytoplasm to the nucleus or perinuclear area was time- and dose-dependently induced by UVB irradiation. After UVB irradiation, three isoforms having different isoelectric points were detected in nucleic HSP27 by two-dimensional immunoblotting. The most basic isoform was the unphosphorylated type and the two acidic isoforms were phosphorylated, suggesting that HSP27 is phosphorylated in response to UVB irradiation and accumulates in or around the nucleus as a phosphorylated isoform. These results suggest that the translocation and phosphorylation of HSP27 are induced in response to UVB-irradiation stress.

Hemopoietic growth factors with the exception of interleukin-4 activate the p38 mitogen-activated protein kinase pathway

The mammalian mitogen-activated protein (MAP) kinase homologue p38 has been shown to be activated by pro-inflammatory cytokines as well as physical and chemical stresses. We now show that a variety of hemopoietic growth factors, including Steel locus factor, colony stimulating factor-1, granulocyte/macrophage-colony stimulating factor, and interleukin-3, activate p38 MAP kinase and the downstream kinase MAPKAP kinase-2. Furthermore, although these growth factors activate both p38 MAP kinase and Erk MAP kinases, we demonstrate using a specific inhibitor of p38 MAP kinase, SB 203580, that p38 MAP kinase activity was required for MAP kinase-activated protein kinase-2 activation. Conversely p38 MAP kinase was shown not to be required for in vivo activation of p90(rsk), known to be downstream of the Erk MAP kinases. Interleukin-4 was unique among the hemopoietic growth factors we examined in failing to induce activation of either p38 MAP kinase or MAP kinase-activated protein kinase-2. These findings demonstrate that the activation of p38 MAP kinase is involved not only in responses to stresses but also in signaling by growth factors that regulate the normal development and function of cells of the immune system.

Phosphorylation of A 27-kDa protein correlates with survival of protein-synthesis-inhibited MCF-7 cells

Previously, we have shown that IGF-1, the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) and aurintricarboxylic acid (ATA) protected MCF-7 cells against death induced by the protein synthesis inhibitor cycloheximide (CHX). We proposed that phosphorylation of a putative cellular proteins(s) may be involved in this survival mechanism. In the present study we investigated the ability of several agents to induce phosphorylation of cellular proteins and correlated this ability to their survival effect. We found that TPA, ATA, and IGF-1 increased the degree of phosphorylation of a 27-kDa protein in a dose- and time-dependent manner in CHX-treated MCF-7 cells. The ED50 values observed were 25 ng/ml, 40 micrograms/ml and 15 ng/ml for TPA, ATA, and IGF-1, respectively. The effect was measured upon 10 min of cell treatment with each agent; it reached maximum at 60 min and thereafter decreased continuously to control levels. The 27-kDa protein was found in the cytosolic fraction as a phosphorylated serine residue. Further characterization with two-dimensional electrophoresis indicated that the 27-kDa phosphorylated serine residue. Further characterization with two-dimensional electrophoresis indicated that the 27-kDa phosphoprotein was resolved into two isoforms with pI 5.7 and 5.9. Such characteristics were observed for the small molecular weight heat shock protein HSP27. Indeed, a single band of 27 kDa was detected immunologically with rabbit polyclonal anti-human HSP27. The inactive phorbol ester alpha TPA, epidermal growth factor (EGF), and 8-bromoadenosine 3'5'-cyclic monophosphate (Br-cAMP) did not increase phosphorylation of the 27-kDa protein. Cell survival was measured by exposure of the CHX-pretreated cells to increasing concentrations of the various agents for 60 min, followed by a further incubation for 48 h in the presence of CHX only. TPA, ATA, and IGF-1 were found to enhance cell survival, whereas alpha-TPA, EGF and Br-cAMP did not. Our results indicate a correlation between phosphorylation of a 27-kDa protein, probably HSP27, and enhanced cell survival, suggesting a role for this phosphoprotein in the survival mechanism.

Inhibition of colony formation of NIH 3T3 cells by the expression of the small molecular weight heat shock protein HSP27: involvement of its phosphorylation and aggregation at the C-terminal region

The ectopic expression of the small molecular weight heat shock protein HSP27 reportedly confers resistance to heat and other types of stress, but our recent findings indicated that it rendered human immortalized fibroblast cells (KMST-6) more sensitive to oxidative stress and caused irreversible growth arrest (Arata et al., 1995, J. Cell. Physiol., 163:458-465). To clarify the relationship between HSP27 and growth regulation, we investigated the effect of overexpression of HSP27 and its mutants on the growth potential of several cell lines. Mammalian expression vectors of the wild-type, hypophosphorylatable, or C-terminal deletion mutants of human HSP27 were constructed from the pRc/CMV plasmid that contained the neomycin-resistant gene. The plasmid was introduced into mouse fibroblasts (NIH 3T3), normal human fibroblasts (TIG-3), Chinese hamster ovary (CHO-K1), or mammary tumor cells (MCF-7), which were then selected in medium containing G418. The number of drug-resistant colonies was significantly decreased by transfection with the expression vector for wild-type HSP27 compared with vector alone, whereas the overexpression of HSP27 in CHO-K1 cells had essentially no effect. The expression vectors of an hypophosphorylatable mutant (pKSm, human HSP27 gene in which codons for Ser-15, -78, and -82 were converted to code for Gly by site-directed mutagenesis) as well as C-terminal deletion mutants in which 12-36 amino acid residues from the C-terminus were deleted had no significant effect on the colony-forming efficiency of NIH 3T3 cells. Cells isolated from G418-resistant colonies formed by transfection of NIH 3T3 cells with the HSP27 expression vector expressed no detectable levels of wild-type HSP27 and did not form stable clonal transformants expressing high levels of HSP27 from NIH 3T3 cells. In contrast, several clones expressing high levels of HSP27 were obtained from CHO-K1 cells transfected with the HSP27 expression vector. In KMST-6 clones expressing high levels of HSP27, the wild-type HSP27 formed aggregates with a mean molecular mass of about 200 kDa as determined by gel filtration, and the size of the oligomers changed with oxidative stress. On the other hand, the size of aggregates of HSP27 encoded by pKSm or C-terminal deletion mutants did not change. These observations indicated that the forced expression of wild-type HSP27 participates in inhibiting the growth of some cell types and that the inhibition may be associated with its phosphorylation and aggregation.

Tumor necrosis factor receptors (Tnfr) in mouse fibroblasts deficient in Tnfr1 or Tnfr2 are signaling competent and activate the mitogen-activated protein kinase pathway with differential kinetics

To dissect tumor necrosis factor receptor (Tnfr)-1 (CD120a) and Tnfr2 (CD120b)-dependent signal transduction pathways, primary fibroblasts isolated from inguinal adipose tissue of wild type (wt), tnfr1(o), tnfr2(o), and tnfr1(o)/tnfr2(o) mice were studied. The mitogen-activated protein kinases Erk1 and Erk2 were found to be tyrosine-phosphorylated and activated by Tnf treatment in all wt, tnfr1(o), and tnfr2(o) fibroblasts; the activation was down-regulated 60 min after the start of steady state Tnf treatment. Distinct kinetics of Erk1 and Erk2 activation were detected; the Tnfr1-mediated activation of Erk1 and Erk2 started more slowly and persisted for more prolonged times as compared with Tnfr2 activation. Raf-1, Raf-B, Mek-1, Mek kinase, and p90(rsk) kinases were also shown to be activated independently in a distinct time-dependent pattern through the two Tnf receptors. In addition, both Tnfr1 and Tnfr2 mediated independently the activation of the transcription factor Ap-1 albeit with parallel activation kinetics. In contrast, Tnfr1 exclusively mediated activation of NF-kappaB and fibroblast proliferation; however, Tnfr2 enhanced proliferation triggered through Tnfr1. These findings indicate distinct but also overlapping roles of Tnfr1 and Tnfr2 in primary mouse fibroblasts and suggest different regulation mechanisms of signal transduction pathways under the control of both Tnf receptors.

Role of protein kinase activity in apoptosis

The transmission of signals from the plasma membrane to the nucleus involves a number of different pathways all of which have in common protein modification. The modification is primarily in the form of phosphorylation which leads to the activation of a series of protein kinases. It is now evident that these pathways are common to stimuli that lead to mitogenic and apoptotic responses. Even the same stimuli under different physiological conditions can cause either cell proliferation or apoptosis. Activation of specific protein kinases can in some circumstances protect against cell death, while in others it protects the cell against apoptosis. Some of the pathways involved lead to activation of transcription factors and the subsequent induction of genes involved in the process of cell death or proliferation. In other cases, such as for the tumour suppressor gene product p53, activation may be initiated both at the level of gene expression or through pre-existing proteins. Yet in others, while the initial steps in the pathway are ill-defined, it is clear that downstream activation of a series of cystein proteases is instrumental in pushing the cell towards apoptosis. In this report we review the involvement of protein kinases at several different levels in the control of cell behaviour.

Distinct effects of heat shock and ATP depletion on distribution and isoform patterns of human Hsp27 in endothelial cells

To study the cytoprotective capacity of Hsp27 under various cellular stresses, we compared the effects of heating and energy deprivation on its distribution and isoform composition. Cultured endothelial cells from human aorta or umbilical vein were subjected to heat shock (45 degrees C) and ATP-depleting metabolic stress (CCCP or rotenone in a glucose-free medium). Both exposures led to the translocation of Hsp27 into the Triton X-100-insoluble cellular fraction, whereas the immunofluorescent Hsp27 pattern was characteristic for each stress employed. Heating (5-30 min) caused unexpected association of Hsp27 with thick bundles of actin microfilaments (stress fibers). ATP depletion within 30-120 min resulted in the appearance of Hsp27-containing compact granules in the nucleus. The insolubilization and relocalization of Hsp27 were reversible in both cases. The stress-induced shifts in the Hsp27 isoform spectrum indicate an increase in phosphorylation of Hsp27 in heat-shocked cells and its dephosphorylation in ATP-depleted cells. We suggest that these stresses diversely affect the phosphorylation status of endothelial Hsp27, thus altering its localization, supramolecular organization and functional activity toward actin.

HSP25 in isolated perfused rat hearts: localization and response to hyperthermia

Recent investigations concentrate on the correlation between the myocardial expression of the inducible 70-kDa heat shock protein (HSP70i) by different stress conditions and its possible protective effects. Only few studies have focused on the involvement of small heat shock proteins in this process. We analyzed the location of the small heat shock protein HSP25 in isolated cardiomyocytes as well as its location and induction in isolated perfused hearts of rats. By immunofluorescence microscopy HSP25 was found to colocalize with actin in the I-band of myofibrils in cardiomyocytes of isolated perfused hearts as well as in isolated neonatal and adult cardiomyocytes. Hyperthermic perfusion of isolated hearts for 45 min resulted in modulation of different parameters of heart function and in induction of HSP25 is constitutively expressed even in normothermic perfused (44-46 degrees C) were lethal with respect to the contractile function of the hearts. Compared to control hearts perfused at 37 degrees C, significant increases during hyperthermic perfusion at 42 degrees C and 43 degrees C were obtained for heart rate, contraction velocity and relaxation velocity. In response to hyperthermia at 43 degrees C and after subsequent normothermic perfusion for 135 min at 37 degrees C, left to control values immediately after the period of heat treatment. HSP25 is constitutively expressed even in normothermic perfused hearts as shown by Western blotting. Hyperthermia increased the content of HSP25 only in the left ventricular tissue. In contrast, HSP70i was strongly induced in all analyzed parts of the myocardium (left ventricle, right ventricle, septum). Our findings suggest a differential regulation of HSP25 and HSP70i expression in response to hyperthermia in isolated perfused hearts. The constitutively expressed HSP25 seems to be located adjacent to the myofibrils which implies a specific role of this protein even under unstressed conditions for the contractile function of the myocardium.

Inhibition of interleukin-1 responsiveness by type II receptor gene transfer: a surface "receptor" with anti-interleukin-1 function

The hypothesis that the type II receptor (RII) acts as a decoy for interleukin-1 (IL-1) was tested by gene transfer in cells expressing only the type I receptor (8387 fibroblasts). RII-transfected cells showed defective responsiveness to IL-1 in terms of NFkappaB activation, cytokine gene expression and production. Blocking monoclonal antibodies against RII restored the capacity of RII-transfected cells to respond to IL-1 beta. Hence defective IL-1 responsiveness of RII-transfected cells requires surface expression of the molecule. RII-transfected cells showed normal responsiveness to TNF, which shares functional properties and elements in the signal transduction pathway with IL-1. Cells transfected with a deletion mutant of RII missing 26 of 29 amino acids of the cytoplasmic portion of the molecule showed impaired responsiveness to IL-2. Cells transfected with full-length or the cytoplasmic deletion mutant of RII released copious amounts of RII in the supernatant. However, transfected cells showed defective responsiveness to brief exposure to IL-1, in the absence of measurable released RII. These results indicate that impairment of the responsiveness to IL-1 following RII gene transfer was dependent upon surface expression of the molecule, specific for IL-1 and unaffected by truncation of the cytoplasmic portion. Thus, the type II "receptor" is a decoy surface molecule, regulated by antiinflammatory signals, whose only known function is to capture and block IL-1.

Intracellular reactive oxygen species as apparent modulators of heat-shock protein 27 (hsp27) structural organization and phosphorylation in basal and tumour necrosis factor alpha-treated T47D human carcinoma cells

The small stress protein heat-shock protein 27 (hsp27) is an oligomeric phosphoprotein, constitutively expressed in most human cells, which enhances cellular resistance to tumour necrosis factor alpha (TNF alpha). This phenomenon correlates with dramatic changes in hsp27 cellular location, structural organization and phosphorylation. To gain a better understanding of the molecular mechanisms regulating these properties of hsp27, we investigated whether they were a consequence of the intracellular production of reactive oxygen species (ROS) generated by TNF alpha. Here, we report that, in T47D carcinoma cell lines, the rapid burst of intracellular ROS production and changes in hsp27 locale, structural organization and phosphoisoform composition induced by TNF alpha were abolished by the overexpression of the antioxidant enzyme seleno-glutathione peroxidase (GSHPx). These effects were greatly diminished when GSHPx-expressing cells were grown in the absence of selenium, a cofactor that is essential for seleno-GSHPx activity, indicating that they are directly linked to the increased GSHPx activity. Moreover, in growing T47D cells, GSHPx expression induced intracellular redistribution of hsp27 and decreased the phosphorylation of this protein without altering its pattern of oligomerization. In contrast, the heat-mediated phosphorylation of hsp27 was not altered by decreased intracellular ROS levels. Hence, in growing and TNF-treated cells, several hsp27 properties appear to be modulated by fluctuations in intracellular ROS levels.

Detection of interleukin-1 signal transduction inhibitors: action of protein kinase inhibitors

The dysregulated production of IL-1 has been shown to play an important role in many pathological processes. Despite the apparent value of compounds able to inhibit either the secretion of IL-1 or its signal transduction pathway in a specific manner, there are no such compounds suitable for clinical use. A major problem in identifying novel and specific inhibitors of signal transduction is the lack of knowledge of the intracellular events which mediate the cellular actions of IL-1. In this study a simple cellular assay has been established to screen natural product and synthetic compound libraries for low molecular weight inhibitors of the cytokine signalling pathways of potential therapeutic value. In addition, we have studied the action of several known modulators of signal transduction on the actions of IL-1.

Casein kinase-1 phosphorylates the p75 tumor necrosis factor receptor and negatively regulates tumor necrosis factor signaling for apoptosis

Cellular responses initiated by tumor necrosis factor (TNF) are mediated by two different cell surface receptors with respective molecular masses of 55 kDa (p55) and 75 kDa (p75). p55 is functional in almost every cell type and can independently transmit most biological activities of TNF. In contrast, TNF signaling via p75 seems so far largely restricted to cells of lymphoid origin, where it can induce proliferation, cytokine production, and/or apoptosis. The mechanisms that regulate TNF receptor activity are largely unknown. Here we report that the p75 of unstimulated p75-responsive PC60 T cells is phosphorylated on serine by a kinase activity present in p75 immune complexes. Several lines of evidence indicate that the latter kinase is casein kinase-1 (CK-1). Previous results have shown that the p75 TNF receptor is constitutively phosphorylated in vivo. Our data show that the latter in vivo phosphorylation is also at least partially due to CK-1. Pretreatment of cells with TNF had no detectable effect on p75 phosphorylation in vitro or in vivo. However, a specific CK-1 inhibitor potentiated TNF-induced apoptosis mediated by p75, suggesting an inhibitory role for phosphorylation by CK-1. Although in vivo p75 phosphorylation could be seen in both p75-unresponsive and p75-responsive cell lines, in vitro p75 phosphorylation in p75 coimmunoprecipitates could not be observed in cell lines that were biologically unresponsive to p75 stimulation. The latter observation further indicates a regulatory role for p75 phosphorylation in p75-mediated signaling. Taken together, our data demonstrate that the p75 TNF receptor is phosphorylated and associated with CK-1, which negatively regulates p75-mediated TNF signaling.

Differential expression of heat shock protein HSP27 in human neurons and glial cells in culture

HSP27 expression was investigated in cultured neurons and glial cells isolated from fetal human brains using immunoblotting and immunocytochemistry. Under unstressed conditions, HSP27 was identified at a high level in astrocytes (> 99%), at a low level in neurons (7%), and at a minimally detectable level in microglia (< 1%), whereas it was undetectable in oligodendrocytes. Under these conditions, HSP27 was located in the cytoplasm, fractionated into the Triton X-100-soluble phase, and composed chiefly of the basic isoform (HSP27a). After exposure to heat stress (43 degrees C/90 min), the level of HSP27 expression was not altered in astrocytes but was elevated significantly in neurons (11-21%) and microglia (4-7%) during 8-48 hr postrecovery periods, while it remained undetectable in oligodendrocytes. In addition, various human neural cell lines exhibited differential patterns of HSP27 expression under unstressed and heat-stressed conditions. Following heat shock treatment (45 degrees C/30 min), granular aggregates of HSP27 were identified in the cytoplasm of astrocytes. Under heat-stressed conditions, HSP27 was distributed within the Triton X-100-insoluble fraction associated with an increase in two more acidic isoforms (HSP27b and HSP27c). HSP27 and alpha B-crystallin were coexpressed in astrocytes under unstressed and heat-stressed conditions. When astrocytes were exposed to known HSP27 inducers, hydrogen peroxide and cysteamine reduced the synthesis of HSP27, while estradiol showed no effects. The differential patterns of constitutive and heat-induced expression of HSP27 in cultured human neurons and glial cells suggest that the cellular mechanisms by which HSP27 expression is regulated are different among various cell types in the human central nervous system.

Effects of the overexpression of the small heat shock protein, HSP27, on the sensitivity of human fibroblast cells exposed to oxidative stress

The role of the human small heat shock protein (HSP27) in oxidative stress was examined using stable transformants of an immortalized human fibroblast cell line (KMST-6) isolated by transfection of HSP27 expression vectors. Several stable transformants that expressed high or low levels of HSP27 protein were obtained. Clones expressing high levels of HSP27 were more sensitive to growth inhibition by a low dose of hydrogen peroxide (0.1 mM) than those expressing low levels. Clones expressing high levels of HSP27 did not acquire obvious resistance to hyperthermy and cytotoxic agents, except for one (#13), in which resistance to cytotoxic agents was increased. The level of phosphorylated HSP27 in clones expressing high levels of this protein increased at 30 min and was sustained even 4 hours after exposing the cells to 0.1 mM of hydrogen peroxide. On the other hand, the levels in clones expressing low levels of HSP27 were reduced within 4 hours after exposure to hydrogen peroxide. Furthermore, overexpression of nonphosphorylatable mutant HSP27 did not affect sensitivity to oxidative stress. These results suggested that constitutively high expression of HSP27 in KMST-6 cells make them susceptible to oxidative stress resulting in growth arrest, and this mechanism could involve the phosphorylation of HSP27.

IL-1 beta regulates rat mesangial cyclooxygenase II gene expression by tyrosine phosphorylation

The pro-inflammatory cytokine, interleukin-1 beta, induces the mRNA for prostaglandin endoperoxide synthase II gene in renal mesangial cells. This inductive effect is selective for prostaglandin endoperoxide synthase II and not prostaglandin endoperoxide synthase I. In the present experiments IL-1 beta increased COX II mRNA, and this was inhibited by genistein and herbimycin A, both inhibitors of protein tyrosine kinases. The dose dependent effect of genistein on inhibition of mRNA for COX II correlated with the inhibition of the release of PGE2 into the media. Induction of COX II by interleukin-1 beta was mimicked by incubating the cells in the presence of a protein tyrosine phosphatase inhibitor, vanadate. These experiments also illustrate selective induction of COX II mRNA without induction of COX I mRNA. Western analysis utilizing antiphosphotyrosine antibodies demonstrated in whole lysates of mesangial cells treated with interleukin-1 beta that the transient phosphorylation of several proteins occurred. Interleukin-1 beta induced the transient phosphorylation of a protein of about 39/40 kD. Similarly, vanadate also produced a rapid and transient phosphorylation of a protein of about 39/40 kD in addition to other proteins. Immunoprecipitation of mesangial cell lysates with agarose conjugated antiphosphotyrosine antibody and Western analysis of precipitated proteins with anti-ERK2 antibody demonstrate that the 39/40 kD protein phosphorylated on tyrosine is ERK2 and suggests participation of one of the MAP kinase family of extracellular receptor kinases in IL-1 beta stimulated induction of the COX II gene.

Interleukin 1-induced phosphorylation of MAD3, the major inhibitor of nuclear factor kappa B of HeLa cells. Interference in signalling by the proteinase inhibitors 3,4-dichloroisocoumarin and tosylphenylalanyl chloromethylketone

The regulation of the inhibitor of nuclear factor kappa B (I kappa B) by interleukin 1 (IL1) was investigated in HeLa cells. Two forms of I kappa B were resolved by ion-exchange chromatography. The major form (75%) was identified as MAD3 by specific antisera. IL1 generated rapidly (6 min) an electrophoretically retarded form of MAD3 that was stable in acid and was converted into the unmodified form by phosphatase 2A. It thus corresponded to a phosphorylation of the protein on serine or threonine. IL1 also caused the disappearance of MAD3 from the cells, which was complete 15 min after stimulation and coincided with a 46% reduction of cellular I kappa B activity. Newly-synthesized MAD3 accumulated to pre-stimulation levels between 60 and 90 min after stimulation and this coincided with the down-regulation of the phosphorylating activity. The serine proteinase inhibitors 3,4-dichloroisocoumarin (DCI) and tosylphenylalanyl chloromethylketone (TPCK) prevented phosphorylation and disappearance of MAD3. At the same concentrations (10-100 microM), they also increased basal phosphorylation of the small heat shock protein (hsp27) and prevented the IL1- and phorbol 12-myristate 13-acetate-induced increases of its phosphorylation. The inhibitors were thus interfering with protein kinases when blocking degradation of MAD3. Recombinant MAD3 phosphorylated in vitro by protein kinase C was not electrophoretically retarded, suggesting that MAD3 was phosphorylated by another kinase in IL1-stimulated cells. Our results suggest that the IL1-induced phosphorylation of MAD3 on serine or threonine leads to its degradation. DCI and TPCK blocked phosphorylation mechanisms and it could not be concluded that serine proteinases were involved in the breakdown of MAD3.

MAPKAP kinase 2 is activated by heat shock and TNF-alpha: in vivo phosphorylation of small heat shock protein results from stimulation of the MAP kinase cascade

The activation of MAPKAP kinase 2 was investigated under heat-shock conditions in mouse Ehrlich ascites tumor cells and after treatment of human MO7 cells with tumor necrosis factor-alpha (TNF-alpha). MAPKAP kinase 2 activity was determined using the small heat-shock proteins (sHsps) Hsp25 and Hsp27 as substrates. In both cell types, about a threefold increase in MAPKAP kinase 2 activity could be detected in a time interval of about 10-15 min after stimulation either by heat shock or TNF-alpha. Phosphorylation of MAPKAP kinase 2, but not the level of MAPKAP kinase 2 mRNA, was increased after heat shock in EAT cells. It is further shown that activation of MAPKAP kinase 2 in MO7 cells is accompanied by increased MAP kinase activity. These data strongly suggest that increased phosphorylation of the sHsps after heat shock or TNF-alpha treatment results from phosphorylation by MAPKAP kinase 2, which itself is activated by phosphorylation through MAP kinases. Hence, we demonstrate that MAPKAP kinase 2 is responsible not only for phosphorylation of sHsps in vitro but also in vivo. The findings link sHsp phosphorylation to the MAP kinase cascade, explaining the early phosphorylation of sHsp that is stimulated by a variety of inducers such as mitogens, phorbol esters, thrombin, calcium ionophores, and heat shock.

Specific activation of beta-casein kinase by the inflammatory cytokines interleukin 1 and tumour necrosis factor

Increases (5-fold) in the rate of phosphorylation of beta-casein were observed in extracts of human gingival fibroblasts that had been stimulated by interleukin 1 (IL-1) or tumour necrosis factor (TNF). The induced kinase was cytosolic and had little activity on alpha-casein. Its chromatographic behaviour on anion-exchange and gel-filtration columns was similar to that of beta-casein kinase, an enzyme detected originally in MRC-5 cells stimulated by IL-1 and TNF. Phosphopeptide maps of beta-casein confirmed that the kinase activated in gingival fibroblasts had the same substrate specificity as beta-casein kinase. In gingival fibroblasts, beta-casein kinase activity was maximum after 15 min of stimulation by IL-1 or TNF, and remained activated for several hours. Activations of small heat-shock protein (hsp27) kinase and mitogen-activated protein (MAP) kinase were also maximum 15 min after stimulation, but decreased to background levels within the next 30 min. Study of the effects of 21 agents other than IL-1 or TNF showed that none activated beta-casein kinase, whereas several activated MAP kinase or hsp27 kinase. beta-Casein kinase was also detected in extracts of bovine articular chondrocytes and human endothelial cells stimulated by IL-1 or TNF. Semi-purified preparations of fibroblast beta-casein kinase were not inactivated by phosphatases in vitro. Our results suggest that it may be involved in responses specific to IL-1 and TNF in a wide range of cell types and that its activation probably involves mechanisms other than its phosphorylation.

Structure and modifications of the junior chaperone alpha-crystallin. From lens transparency to molecular pathology

alpha-Crystallin is a high-molecular-mass protein that for many decades was thought to be one of the rare real organ-specific proteins. This protein exists as an aggregate of about 800 kDa, but its composition is simple. Only two closely related subunits termed alpha A- and alpha B-crystallin, with molecular masses of approximately 20 kDa, form the building blocks of the aggregate. The idea of organ-specificity had to be abandoned when it was discovered that alpha-crystallin occurs in a great variety of nonlenticular tissues, notably heart, kidney, striated muscle and several tumors. Moreover alpha B-crystallin is a major component of ubiquinated inclusion bodies in human degenerative diseases. An earlier excitement arose when it was found that alpha B-crystallin, due to its very similar structural and functional properties, belongs to the heat-shock protein family. Eventually the chaperone nature of alpha-crystallin could be demonstrated unequivocally. All these unexpected findings make alpha-crystallin a subject of great interest far beyond the lens research field. A survey of structural data about alpha-crystallin is presented here. Since alpha-crystallin has resisted crystallization, only theoretical models of its three-dimensional structure are available. Due to its long life in the eye lens, alpha-crystallin is one of the best studied proteins with respect to post-translational modifications, including age-induced alterations. Because of its similarities with the small heat-shock proteins, the findings about alpha-crystallin are illuminative for the latter proteins as well. This review deals with: structural aspects, post-translational modifications (including deamidation, racemization, phosphorylation, acetylation, glycation, age-dependent truncation), the occurrence outside of the eye lens, the heat-shock relation and the chaperone activity of alpha-crystallin.