Molecular cloning of a mouse 47-kDa heat-shock protein (HSP47), a collagen-binding stress protein, and its expression during the differentiation of F9 teratocarcinoma cells

Heat shock genes and the heat shock response in zebrafish embryos

Heat shock genes exhibit complex patterns of spatial and temporal regulation during embryonic development in a wide range of organisms. Our laboratory has initiated an analysis of heat shock protein gene expression in the zebrafish, a model system that is now utilized extensively for the examination of early embryonic development of vertebrates. We have cloned members of the zebrafish hsp47, hsp70,\i and hsp90 gene families and shown them to be closely related to their counterparts in higher vertebrates. Whole mount in situ hybridization and Northern blot analyses have revealed that these genes are regulated in distinct spatial, temporal, and stress-specific manners. Furthermore, the tissue-specific expression patterns of the hsp47 and hsp90 alpha genes correlate closely with the expression of genes encoding known chaperone targets of Hsp47 and Hsp90 in other systems. The data raise a number of interesting questions regarding the function and regulation of these heat shock genes in zebrafish embryos during normal development and following exposure to environmental stress.

Expression of the collagen-related heat shock protein HSP47 in fibroblasts treated with hyperthermia or photodynamic therapy

Heat shock protein (HSP) 47 is associated with collagen type I metabolism, both constitutively and after stress-inflicted injury. It has been claimed that, in contrast to hyperthermia (HT), photodynamic therapy (PDT) does not damage collagen, as measured at the level of tissue. We have studied HSP47 expression in normal murine skin fibroblasts (3T6) treated with hyperthermia or photodynamic therapy (PDT) mediated by three different photosensitizers: (1) haematoporphyrin ester (HpE), (2) meta tetra hydroxyphenyl chlorin (mTHPC) and (3) riboflavin (RB). Riboflavin is not an established photosensitizer for PDT and was chosen here because it is known to provoke collagen damage. The applied doses of the treatments were isoeffective in terms of 3T6 clonogenic cell survival. Analysis, at both transcriptional and translational levels, revealed HSP47 elevation after hyperthermia and after PDT with RB. PDT sensitized by HpE and mTHPC did not significantly alter HSP47 expression. These observations are consistent with our hypothesis that this collagen chaperone is up-regulated by laser-mediated modalities known to damage collagen (i.e. HT and RB PDT) but not by more conventional PDT treatments. Additionally, unexpected significant up-regulation of HSP47 was detected after illumination alone (no photosensitizer) of 3T6 cells at 653 nm laser light, but not at 630 nm.

Expression of genes encoding the collagen-binding heat shock protein (Hsp47) and type II collagen in developing zebrafish embryos

Hsp47 is a heat-shock protein which interacts with newly synthesize procollagen chains in the endoplasmic reticulum (ER) of collagen-secreting cells and is thought to assist in procollagen triple helix assembly and subsequent transport to the cis-Golgi. This is supported by studies which have reported that genes encoding collagen and Hsp47 are subject to co-ordinate increases and decreases in expression in cultured cells. However, limited information is available regarding hsp47 expression in vivo, particularly during early embryonic development when a variety of collagen genes are expressed. Here we show that the zebrafish hsp47 gene is expressed in a dynamic spatiotemporal pattern in developing embryos. Strong expression of hsp47 mRNA is co-incident predominantly with expression of the type II collagen gene (col2a1) in a number of chondrogenic and non-chondrogenic tissues including the notochord, otic vesicle and developing fins. Notochordal expression of both genes is disrupted in floating head (flh) and no tail (ntl) embryos, which lack properly differentiated notochords. Surprisingly, no hsp47 mRNA is detectable in the strongly col2a1-expressing cells of the floor plate and hypochord, indicating that the two genes are not strictly co-regulated. Finally, Northern blot analysis revealed two alternative transcripts of col2a1 which are expressed in distinct temporal patterns. Appearance of the larger transcript occurs following somitogenesis, a time which coincides with the co-activation of hsp47 and col2a1 gene expression in tissues outside of the notochord.

Intracellular interaction of collagen-specific stress protein HSP47 with newly synthesized procollagen

Heat shock protein 47 (HSP47), a collagen-specific stress protein, has been postulated to be a collagen-specific molecular chaperone localized in the ER. We previously demonstrated that HSP47 transiently associated with newly synthesized procollagen in the ER (Nakai, A., M. Satoh, K. Hirayoshi, and K. Nagata. 1992. J. Cell Biol. 117:903-914). In the present work, we examined the location where HSP47 binds to and dissociates from newly synthesized procollagen within the cells, and whether HSP47 associates with nascent single procollagen polypeptide chains and/or with mature triple-helix procollagen. This was accomplished by biochemical coprecipitation with anti-HSP47 and anticollagen antibodies, combined with pulse-label and chase experiments in the presence or absence of various inhibitors for protein secretion, as well as by confocal laser microscopic observation of the cells double stained with both antibodies. We further examined whether the RDEL (Arg-Asp-Glu-Leu) sequence at the COOH terminus of HSP47 can act as an ER-retention signal, as the KDEL sequence does. When the secretion of procollagen was inhibited by the presence of alpha, alpha'-dipyridyl, an iron chelator that inhibits procollagen triple-helix formation, or by the presence of brefeldin A. which inhibits protein transport between the ER and the Golgi apparatus, procollagen was found to be bound to HSP47 during the chase period in the intermediate compartment. In contrast, the dissociation of procollagen chains from HSP47 was not inhibited when procollagen secretion was inhibited by monensin or bafilomycin A1, both of which are known to be inhibitors of post-cis-Golgi transport. These findings suggest that HSP47 and procollagen dissociated between the post-ER and the cis-Golgi compartments. HSP47 was shown to bind to nascent, single-polypeptide chains of newly synthesized procollagen, as well as to the mature triple-helix form of procollagen. HSP47 with the RDEL sequence deleted was secreted out of the cells, which suggests that the RDEL sequence actually acts as an ER-retention signal, as the KDEL sequence does. This secreted HSP47 did not acquire endoglycosidase H resistance. The biological significance of the interaction between HSP47 and procollagen in the central secretory pathway, as well as possible mechanisms for this pathway, will be discussed.

Cloning and characterization of a cDNA encoding the collagen-binding stress protein hsp47 in zebrafish

Hsp47 is a major stress-inducible protein that is localized to the endoplasmic reticulum of avian and mammalian cells and is thought to act as a molecular chaperone specific for the processing of procollagen. Although hsp47 is coordinately expressed together with several collagen types, and vertebrate embryos are known to express collagen genes in complex spatial and temporal patterns, limited information is available regarding the function or regulation of hsp47 during early embryonic development. We have initiated an examination of hsp47 in the zebrafish, Danio rerio, which offers a number of features that make it attractive as a model developmental system with which to examine the expression and function of hsp47. A polymerase chain reaction (PCR)-based cloning strategy was used to isolate a hsp47 cDNA from an embryonic zebrafish cDNA library. The deduced translation product of the cDNA is a 404-amino-acid polypeptide that is 72% identical to chicken, 64% identical to mouse and rat, and 69% identical to human hsp47. The protein contains a typical hydrophobic signal sequence, an RDEL endoplasmic reticulum retention signal, and a serine protease inhibitor signature sequence, all of which are characteristic of hsp47 in higher vertebrates. Thus, it is likely that hsp47 in zebrafish is also localized to the endoplasmic reticulum and may play a similar role to its counterpart in higher vertebrates. Northern blot analysis revealed that the hsp47 gene is expressed at relatively low levels in embryos during normal development but is strongly induced following exposure to heat shock at the gastrula, midsomitogenesis, 2-day, and 3-day larval stages. The level of induction was much higher than has previously been reported in chicken and mouse cells.

Age-related alteration of proline hydroxylase and collagen-binding heat shock protein (HSP47) expression in human fibroblasts

Changes in the expression of alpha and beta subunits of proline 4-hydroxylase (PH alpha and PH beta) and HSP47, implicated as a molecular chaperone specific for procollagen processing, were examined in human embryonal fibroblasts in relation to in vitro aging. For this purpose a model with treatments causing the decreased hydroxylation of proline residues in procollagens was used. In cells at a low population doubling level (PDL) induction of PH alpha, PH beta, and HSP47 by depletion of ascorbate or addition of alpha-alpha' dipyridyl could be clearly demonstrated by immunoprecipitation and Northern blotting. In contrast, the induction of PH alpha and HSP47 expression was markedly attenuated in high PDL cells, indicating an age-related decrease in response to procollagen retention in the ER caused by hypohydroxylation of proline residues of procollagens.

Age-related attenuation of HSP47 heat response in fibroblasts

The collagen-binding heat shock protein of molecular weight 47,000 (HSP47), resident in the endoplasmic reticulum (ER), is assumed to play a specific role as a molecular chaperon in the processing of procollagen molecules. The present investigation of age-related alteration in the HSP47 heat response in cultured murine and human fibroblasts revealed expression in cells with a low population doubling level (PDL) derived from young mice and people more inducible by heat treatment than those from older mice and people. On the other hand, cells with a high PDL showed a very low heat response in terms of HSP47 expression regardless of the donor age. Northern blot analysis of HSP47 m-RNA indicated that the age related attenuation of HSP47 expression was regulated by transcriptional mechanisms. Furthermore, immunofluorescent analysis using a monoclonal antibody against the carboxylterminal propeptide of type I procollagen revealed far greater retention of procollagen molecules in the ER lumen of cells from old persons than in those from young persons. This was particularly prominent in heat-treated cells from old persons, indicating the possibility that the observed decrease in HSP47 heat response might cause blockage of procollagen transport to the Golgi and therefore secretion.

Association of Hsp47, Grp78, and Grp94 with procollagen supports the successive or coupled action of molecular chaperones

Hsp47, Grp78, and Grp94 have been implicated with procollagen maturation events. In particular, Hsp47 has been shown to nascent procollagen alpha 1(I) chains in the course of synthesis and/or translocation into the endoplasmic reticulum (ER). Although, Hsp47 binding to gelatin and collagen has previously been suggested to be independent of ATP. Grp78 and Grp94 are known to dissociate from its substrates by an ATP-dependent release mechanism. The early association of Hsp47 with procollagen and its relatively late release suggested that other chaperones, Grp78 and Grp94, interact successively or concurrently with Hsp47. Herein, we examined how these events occur in cells metabolically stressed by depletion of ATP. In cells depleted of ATP, the release of Hsp47, Grp78, and Grp94 from maturing procollagen is delayed. Thus, in cells experiencing metabolic stress, newly synthesized procollagen unable to properly fold became stably bound to a complex of molecular chaperones. In that Hsp47, Grp78, and Grp94 could be recovered with nascent procollagen and as oligomers in ATP depleted cells suggests that these chaperones function in a series of coupled or successive reactions.

Coexpression of the collagen-binding stress protein HSP47 gene and the alpha 1(I) and alpha 1(III) collagen genes in carbon tetrachloride-induced rat liver fibrosis

HSP47 is a collagen-binding stress protein and is assumed to act as a collagen-specific molecular chaperone during the biosynthesis and secretion of procollagen in the living cell. The synthesis of HSP47 has been reported to correlate with that of collagen in several cell lines. We examined the expression of HSP47 mRNA during the progression of carbon tetrachloride (CCl4)-induced liver fibrosis in rats. Northern blot analysis revealed that the expression of HSP47 mRNA was markedly induced during the progression of fibrosis in parallel with alpha 1(I) and alpha 1(III) collagen mRNAs. By in situ hybridization, the distribution of HSP47 transcripts was similar to that of alpha 1(I) collagen and was observed only in cells lining collagen fibrils. These collagen-positive cells were confirmed to be Ito cells by immunohistochemistry for desmin. The absence of high levels of HSP47 mRNA in the liver of rats treated with only a single administration of CCl4 indicated that the induction of HSP47 mRNA was not due to the direct effect of CCl4 as a stressor, but was due to the progression of liver fibrosis. The function of HSP47 in liver fibrosis will also be discussed.

Differential induction of mRNA species encoding several classes of stress proteins following focal cerebral ischemia in rats

We report here the time-dependent expression of several classes of HSP mRNAs following focal cerebral ischemia in rats. HSP70, GRP78, HSP27, HSP90 and HSP47 have been reported to possess distinct functions under normal and/or stress conditions. These different classes of HSP mRNAs were differentially induced by ischemia, as determined by Northern blot analysis. Messenger RNAs of the HSP70 family proteins were induced within 4 h after ischemia and then rapidly decreased, whereas HSP27 and HSP47 mRNAs reached a maximum level of expression at 24 h and 48 h after ischemic treatment, respectively. In situ hybridization showed that the expression of inducible HSP70 mRNA was observed predominantly in regions adjacent to the ischemic core except during the early periods of ischemia. HSP27 mRNA was expressed over a broad area of the ipsilateral cerebral neocortex except for the ischemic center 24 h after ischemia. The unique induction kinetics for each HSP mRNA species may reflect their distinct roles in the brain during various physiological stresses. We will also discuss that stress proteins may be involved in the central nervous system after ischemia in two important aspects: early protection against stress and restoration of damaged lesions in the brain at later stages after ischemia.

Herpes simplex virus-induced expression of 70 kDa heat shock protein (HSP70) requires early protein synthesis but not viral DNA replication

The major 70 kDa heat shock protein (HSP70), which is scarcely expressed in unstressed rodent cells, was apparently induced by infection with herpes simplex virus (HSV). Infection with HSV types 1 and 2 elevated HSP70 mRNA levels within 4 hr post-infection. HSP70 synthesis and accumulation increased in HSV-infected cells. Irradiation of HSV with UV-light abolished the ability to induce HSP70 mRNA. Inhibitors of viral DNA synthesis did not affect the induction of HSP70 in infected cells. Protein synthesis within 2 hr after infection was necessary for HSP70 induction.

Alternative 5' splice site selection induced by heat shock

The mouse HSP47 gene consists of six exons separated by five introns. Three HSP47 cDNAs differing only in their 5' noncoding regions have been reported. One of these alternatively spliced mRNAs was detected only after heat shock, which caused an alternative 5' splice donor site selection. Other stress inducers, including an amino acid analog and sodium arsenite, had no effect on the alternative splicing. The alternatively spliced mRNA, which was 169 nucleotides longer in the 5' noncoding region compared to mRNA transcribed in non-heat shock conditions, was efficiently translated under heat shock conditions. This novel finding that alternative splicing is caused by artificial treatment like heat shock will provide a useful in vivo model for understanding the exon-intron recognition mechanism as well as heat shock-induced alterations in gene expression.

Alternative 5' splice site selection induced by heat shock

The mouse HSP47 gene consists of six exons separated by five introns. Three HSP47 cDNAs differing only in their 5' noncoding regions have been reported. One of these alternatively spliced mRNAs was detected only after heat shock, which caused an alternative 5' splice donor site selection. Other stress inducers, including an amino acid analog and sodium arsenite, had no effect on the alternative splicing. The alternatively spliced mRNA, which was 169 nucleotides longer in the 5' noncoding region compared to mRNA transcribed in non-heat shock conditions, was efficiently translated under heat shock conditions. This novel finding that alternative splicing is caused by artificial treatment like heat shock will provide a useful in vivo model for understanding the exon-intron recognition mechanism as well as heat shock-induced alterations in gene expression.

Structure of the gene encoding the mouse 47-kDa heat-shock protein (HSP47)

HSP47, a 47-kDa heat-shock protein (HSP), is a member of a group of HSPs with the unique characteristics of collagen binding as well as transformation sensitivity. The protein belongs to the serpin (serine protease inhibitor) superfamily as determined from its amino acid sequence homology. We have isolated and characterized the mouse HSP47 including about 1 kb of the 5'-flanking region. This gene spans about 7.8 kb, consisting of six exons separated by five introns. This exon-intron structure is different from other serpin family proteins. Southern blot analysis revealed the existence of a single copy of HSP47. The promoter region contains a TATA box, four Sp1-binding sites and one AP-1-binding site. A complete heat-shock element (HSE) was found between nucleotides (nt) -61 and -79. Furthermore, the heat inducibility was reproduced by transfecting mouse BALB/3T3 cells with a plasmid carrying cat under the control of the HSE-containing fragment (nt -197 and +38) of HSP47. Computer analysis of the promoter region did not show marked homology to other vertebrate promoters.