Identification and sequence analysis of a new member of the mouse HSP70 gene family and characterization of its unique cellular and developmental pattern of expression in the male germ line

[Molecular cell biology of the heat stress response. Part I]

In a physiological range of hyperthermia all living systems respond with a complex reprogramming of cellular activities to provide a basis for survival during the stress period and for a rapid restoration of normal activities in the recovery period. A prominent characteristic of the response is the induced synthesis of heat-stress proteins which is likewise evoked by numerous chemical stressors. The common signal transduction chain leading to the activation of heat-stress genes evidently involves the transient accumulation of abnormal proteins. The dominant HSPs belong to five conserved stress protein families, whose members are essential components of all living cells with general functions by far exceeding the stress response.

Characterization and sequence of a mouse hsp70 gene and its expression in mouse cell lines

A heat-inducible member of the mouse hsp70 gene family has been isolated and characterized. The gene, hsp70.1, has a primary transcript of 2.8 kb before and 3.1-3.5 kb after polyadenylation. It includes a 645-nucleotide (nt) 3'-nontranslated terminus and a 225-nt 5' leader. The leader sequence is unusual in that it contains a 33-nt triple tandem repeat element proximal to the ATG codon. As expected, a single open reading frame encodes a 642-amino acid (aa) 70-kDa protein with 95% aa homology and 91% nt homology to a human hsp70 gene. While there is no homology through the 5'- and 3'-nontranslated regions, the human and mouse hsp70 gene promoters can be aligned to give 65% homology. Of three mouse cell lines studied, two expressed the 3.1- to 3.5-kb mRNA during heat shock. One line also expressed an additional, smaller, 2.6-kb hsp70 mRNA transcribed from a separate gene(s). Mouse erythroleukemia cells were unresponsive to heat shock, with neither hsp70 RNA being induced by heat shock. These results suggest that cell lineage has a major influence on the cellular response to heat shock and that the response is not universal in all cell types.

Isolation and nucleotide sequence analysis of the rat testis-specific major heat-shock protein (HSP70)-related gene

The isolation of a rat hsp 70-related gene which is specifically and highly expressed in testis is described together with the complete nucleotide sequence of the transcription unit (2947 bp), 5' flanking (about 1 kbp) and 3' flanking (about 0.3 kbp) regions. The sequence analysis and nuclease S1 mapping revealed that the isolated gene (referred to as the hst70 gene) represents a novel, distinct member of the hsp70 multigene family. Its transcription unit lacks introns and a single open reading frame encodes a protein of 69.5 kDa. The predicted amino acid sequence of this protein is highly similar (only four out of 633 amino acids are different) to that encoded by the mouse testis-specific hsp70.2 gene (Zakeri, Z.F., Wolgemuth, D.J. and Hunt, C.R. (1988) Mol. Cell. Biol. 8, 2925-2932). The functional significance of multiple potentially regulatory sequences (e.g. TATA-boxes, heat-shock element and estrogen receptor binding site) present in the 5' flanking region of the rat hst70 gene is discussed.

Cloning of a hsp70-related gene expressed in mouse spermatids

A cDNA library of spermatids was screened by a differential hybridization in order to isolate genes expressed in haploid cells of the mouse male germ line. A clone was found that encoded a protein related to the heat shock protein 70. A genomic DNA clone comparable to this cDNA clone was also isolated from a mouse genomic library. This gene had only one continuous open reading frame capable of coding a 630 amino-acid protein. There was an excellent match of the sequence with the heat shock protein 70 family but a difference from any previous 70 kilodalton heat shock protein. A 2.7kb transcript derived from this gene was expressed in spermatids but not in other testicular germ cells and somatic tissues. We have referred to this gene as hsc70t.

cis-acting sequences and trans-acting factors required for constitutive expression of a microinjected HSP70 gene after the midblastula transition of Xenopus laevis embryogenesis

Microinjected human HSP70 promoter-chloramphenical acetyl transferase (CAT) chimeric genes are constitutively expressed immediately after the midblastula transition of Xenopus embryogenesis. Analysis of a series of 5'-deletion mutants in the HSP70 promoter revealed that sequences within 74 bases of the transcriptional start site were sufficient for strong basal activity. We investigated the role of specific sequences in the basal promoter by injecting HSP70-CAT vectors containing linker-scanner mutations in the basal elements (CCAAT, purine-rich element, GC-element, ATF/AP1, and TATA). Our data reveal that deletion of any of these cis-acting elements in the basal promoter prevents expression after the midblastula stage of development. Furthermore, we have identified specific binding activities in embryonic nuclear extracts that complex with basal promoter elements (CCAAT, ATF, and GC) of the heterologous HSP70 promoter. These trans-acting factors are detectable in nuclear extracts of early blastula embryos, and their respective binding activity increases dramatically after the midblastula transition. The expression of the human HSP70 gene after the midblastula transition of Xenopus embryogenesis requires an array of cis-acting elements, which interact with specific Xenopus transcription factors.

Activation of the glucose-regulated gene (grp78) in regenerating rat liver is nonspecific and is related to acute phase response

The expression pattern of the hsp70 gene family during regeneration or rat liver has been investigated. Northern blots were prepared from total RNA isolated from livers at 0 h (control), 12 h (end of prereplication phase), 24 h (maximum of DNA synthesis) and 36 h (postmitotic phase) after partial hepatectomy. Blots were hybridized with probes specific for the hsp70 (heat-inducible), hsc70 (constitutively expressed), hst70 (testis-specific) and grp78 (glucose-regulated) gene. No hsp70 and hst70 gene transcripts have been detected at any time point investigated, and only a low increase of the hsc70 mRNA level has been observed 24 h after surgery. In contrast, a significant accumulation of the transcript coded by the grp78 gene has been detected in liver remnant 12 and 24 h after partial hepatectomy. However, we observed a comparable activation of this gene in livers of sham-operated rats or in rats injected with turpentine to cause sterile inflammation. Our results indicate that the activation of the grp78 gene in liver of wounded rats (partial hepatectomy or sham operation) is presumably a part of acute-phase response.

Stage-specific localization of cytoskeletal actin mRNA in murine seminiferous tubules and intestinal epithelia as demonstrated by in-situ hybridization

In-situ hybridization experiments have been performed using isoactin (beta and gamma)-specific riboprobes in various tissues of the rat and mouse. Distribution of the grains of actin mRNAs for both beta and gamma types was similar throughout sections of the rat testis. Although both mRNAs were evenly distributed in the seminiferous tubule, extremely heavy labeling was observed in about 10% of the seminiferous tubules that could be identified as stage XII of spermatogenesis. At high magnification, grains of the mRNA were found in the cytoplasm of elongating spermatids and in the Sertoli cell cytoplasm at the adluminal side. Much higher density of the grains of mRNA was observed in the neck region of the spermatids at stage XII. Thus, the dense distribution of cytoskeletal actin mRNAs is stage-specific in the tubule during spermatogenesis in the rat. The high expression of both beta and gamma actin mRNAs was also observed in the epithelial cells of the intestinal crypts.

Characterization of the hsp70 multigene family of Caenorhabditis elegans

Our laboratory has been characterizing the hsp70 multigene family from the nematode Caenorhabditis elegans as the first step to the genetic characterization of the heat shock response in a relatively simple multicellular eukaryote. Two gene members, hsp-1 and hsp-2ps have already been characterized (Snutch et al., 1988; Heschl and Baillie, 1989). The third gene member, hsp-3, is expressed constitutively and is non-heat inducible; its mRNA is most abundant at the L1 larval stage. The hsp-3 protein (hsp70C) shares a high degree of identity with the rat grp78 protein and has a long, hydrophobic leader sequence. The carboxyl terminus of hsp70C has the putative ER-retention signal, KDEL. The fourth gene member, hsp-6 is expressed constitutively and moderately heat inducible. A partial hsp-6 protein (hsp70F) sequence shares a higher degree of identity with the Escherichia coli dnaK protein than with eukaryotic hsp70 proteins. The predicted amino-terminal half of the hsp70F polypeptide also contains a long, amphiphilic leader sequence similar to mitochondrial import leader sequences. These two genes encode proteins that potentially cross intracellular membranes. We compared the 5'-flanking DNA from the C. elegans hsp-3 gene to fragment containing enhancer activity from the rat grp78 gene regulatory region (Lin et al., 1986). A 23-nucleotide sequence was conserved between the two promoter regions. This sequence shares approximately 80% identity between these two evolutionary distant organisms. A comparison to other hsp70 genes did not reveal any conservation of this 23-nucleotide sequence. We propose that this sequence may be involved in a unique aspect of the regulation of the C. elegans' grp78-like gene and the rat grp78 gene.

Regulation of the heat-shock response by interferon in mouse L cells

Interferon (IFN) is not able to induce heat-shock protein (HSP) synthesis. However IFN pretreatment of mouse L cells has been shown to enhance the decrease of overall protein synthesis which follows a heat shock, and to stimulate the accumulation of HSPs. We show here that the synthesis of a protein (the hepatitis B virus surface antigen) under the control of a Drosophila HSP 70 promoter is also stimulated in IFN-pretreated cells. The regulation by IFN takes place at two levels: first, the rate of HSP gene transcription is increased in nuclei isolated from IFN-treated cells; second, the synthesis of HSPs is prolonged after pretreatment with IFN. Experiments performed in the presence of actinomycin D show that this effect is due to a stabilization by IFN of mRNAs coding for HSPs.