Heat shock protein 40/DjB1 is required for thermotolerance in early phase

Oncogenic Addiction of Fibrolamellar Hepatocellular Carcinoma to the Fusion Kinase DNAJB1-PRKACA

PURPOSE

Gene fusions are drivers of many pediatric tumors. In fibrolamellar hepatocellular carcinoma (FLC), a fusion of DNAJB1 and PRKACA is the dominant recurrent mutation. Expression of the DNAJB1-PRKACA fusion gene in mice results in a tumor that recapitulates FLC. However, it is not known whether transient expression of DNAJB1-PRKACA is sufficient only to trigger tumor formation or whether ongoing expression is necessary for maintenance and progression.

EXPERIMENTAL DESIGN

We screened short hairpin RNAs (shRNA) tiled over the fusion junction and identified several potent and specific candidates in vitro and two independent FLC patient-derived xenografts (PDX).

RESULTS

We show that continued DNAJB1-PRKACA expression is not only required for continued tumor growth, but additionally its inhibition results in cell death. Inhibition of DNAJB1-PRKACA by an inducible shRNA in cells of PDX of FLC resulted in cell death in vitro. Induction of the shRNA inhibits FLC tumors growing in mice with no effect on xenografts from a hepatocellular carcinoma cell line engineered to express DNAJB1-PRKACA.

CONCLUSIONS

Our results validate DNAJB1-PRKACA as the oncogene in FLC and demonstrate both a continued requirement for the oncogene for tumor growth as well as an oncogenic addiction that can be exploited for targeted therapies. We anticipate our approach will be useful for investigations of other fusion genes in pediatric cancers and spur development of precision therapies.

Chaperone-assisted protein aggregate reactivation: Different solutions for the same problem

The oligomeric AAA+ chaperones Hsp104 in yeast and ClpB in bacteria are responsible for the reactivation of aggregated proteins, an activity essential for cell survival during severe stress. The protein disaggregase activity of these members of the Hsp100 family is linked to the activity of chaperones from the Hsp70 and Hsp40 families. The precise mechanism by which these proteins untangle protein aggregates remains unclear. Strikingly, Hsp100 proteins are not present in metazoans. This does not mean that animal cells do not have a disaggregase activity, but that this activity is performed by the Hsp70 system and a representative of the Hsp110 family instead of a Hsp100 protein. This review describes the actual view of Hsp100-mediated aggregate reactivation, including the ATP-induced conformational changes associated with their disaggregase activity, the dynamics of the oligomeric assembly that is regulated by its ATPase cycle and the DnaK system, and the tight allosteric coupling between the ATPase domains within the hexameric ring complexes. The lack of homologs of these disaggregases in metazoans has suggested that they might be used as potential targets to develop antimicrobials. The current knowledge of the human disaggregase machinery and the role of Hsp110 are also discussed.

Tumour suppressor HLJ1: A potential diagnostic, preventive and therapeutic target in non-small cell lung cancer

Lung cancer is the leading cause of cancer-related mortality throughout the world. Non-small cell lung cancer (NSCLC) accounts for 85% of all diagnosed lung cancers. Despite considerable progress in the diagnosis and treatment of the disease, the overall 5-year survival rate of NSCLC patients remains lower than 15%. The most common causes of death in lung cancer patients are treatment failure and metastasis. Therefore, developing novel strategies that target both tumour growth and metastasis is an important and urgent mission for the next generation of anticancer therapy research. Heat shock proteins (HSPs), which are involved in the fundamental defence mechanism for maintaining cellular viability, are markedly activated during environmental or pathogenic stress. HSPs facilitate rapid cell division, metastasis, and the evasion of apoptosis in cancer development. These proteins are essential players in the development of cancer and are prime therapeutic targets. In this review, we focus on the current understanding of the molecular mechanisms responsible for HLJ1’s role in lung cancer carcinogenesis and progression. HLJ1, a member of the human HSP 40 family, has been characterised as a tumour suppressor. Research studies have also reported that HLJ1 shows promising dual anticancer effects, inhibiting both tumour growth and metastasis in NSCLC. The accumulated evidence suggests that HLJ1 is a potential biomarker and treatment target for NSCLC.

An exploration of heat tolerance in mice utilizing mRNA and microRNA expression analysis

BACKGROUND

Individuals who rapidly develop hyperthermia during heat exposure (heat-intolerant) are vulnerable to heat associated illness and injury. We recently reported that heat intolerant mice exhibit complex alterations in stress proteins in response to heat exposure. In the present study, we further explored the role of genes and molecular networks associated with heat tolerance in mice.

METHODOLOGY

Heat-induced physiological and biochemical changes were assessed to determine heat tolerance levels in mice. We performed RNA and microRNA expression profiling on mouse gastrocnemius muscle tissue samples to determine novel biological pathways associated with heat tolerance.

PRINCIPAL FINDINGS

Mice (n = 18) were assigned to heat-tolerant (TOL) and heat-intolerant (INT) groups based on peak core temperatures during heat exposures. This was followed by biochemical assessments (Hsp40, Hsp72, Hsp90 and Hsf1 protein levels). Microarray analysis identified a total of 3,081 mRNA transcripts that were significantly misregulated in INT compared to TOL mice (p<0.05). Among them, Hspa1a, Dnajb1 and Hspb7 were differentially expressed by more than two-fold under these conditions. Furthermore, we identified 61 distinct microRNA (miRNA) sequences significantly associated with TOL compared to INT mice; eight miRNAs corresponded to target sites in seven genes identified as being associated with heat tolerance pathways (Hspa1a, Dnajb1, Dnajb4, Dnajb6, Hspa2, Hspb3 and Hspb7).

CONCLUSIONS

The combination of mRNA and miRNA data from the skeletal muscle of adult mice following heat stress provides new insights into the pathophysiology of thermoregulatory disturbances of heat intolerance.

Metazoan Hsp70 machines use Hsp110 to power protein disaggregation

Accumulation of aggregation-prone misfolded proteins disrupts normal cellular function and promotes ageing and disease. Bacteria, fungi and plants counteract this by solubilizing and refolding aggregated proteins via a powerful cytosolic ATP-dependent bichaperone system, comprising the AAA+ disaggregase Hsp100 and the Hsp70-Hsp40 system. Metazoa, however, lack Hsp100 disaggregases. We show that instead the Hsp110 member of the Hsp70 superfamily remodels the human Hsp70-Hsp40 system to efficiently disaggregate and refold aggregates of heat and chemically denatured proteins in vitro and in cell extracts. This Hsp110 effect relies on nucleotide exchange, not on ATPase activity, implying ATP-driven chaperoning is not required. Knock-down of nematode Caenorhabditis elegans Hsp110, but not an unrelated nucleotide exchange factor, compromises dissolution of heat-induced protein aggregates and severely shortens lifespan after heat shock. We conclude that in metazoa, Hsp70-Hsp40 powered by Hsp110 nucleotide exchange represents the crucial disaggregation machinery that reestablishes protein homeostasis to counteract protein unfolding stress.

Optimal functional levels of activation-induced deaminase specifically require the Hsp40 DnaJa1

The enzyme activation-induced deaminase (AID) deaminates deoxycytidine at the immunoglobulin genes, thereby initiating antibody affinity maturation and isotype class switching during immune responses. In contrast, off-target DNA damage caused by AID is oncogenic. Central to balancing immunity and cancer is AID regulation, including the mechanisms determining AID protein levels. We describe a specific functional interaction between AID and the Hsp40 DnaJa1, which provides insight into the function of both proteins. Although both major cytoplasmic type I Hsp40s, DnaJa1 and DnaJa2, are induced upon B-cell activation and interact with AID in vitro, only DnaJa1 overexpression increases AID levels and biological activity in cell lines. Conversely, DnaJa1, but not DnaJa2, depletion reduces AID levels, stability and isotype switching. In vivo, DnaJa1-deficient mice display compromised response to immunization, AID protein and isotype switching levels being reduced by half. Moreover, DnaJa1 farnesylation is required to maintain, and farnesyltransferase inhibition reduces, AID protein levels in B cells. Thus, DnaJa1 is a limiting factor that plays a non-redundant role in the functional stabilization of AID.

An expression microarray approach for the identification of metastable epialleles in the mouse genome

Genetic loci displaying environmentally responsive epigenetic marks, termed metastable epialleles, offer a solution to the paradox presented by genetically identical yet phenotypically distinct individuals. The murine viable yellow agouti (A (vy) ) metastable epiallele exhibits stochastic DNA methylation and histone modifications associated with coat color variation in isogenic individuals. The distribution of A (vy)  variable expressivity shifts following maternal nutritional and environmental exposures. To characterize additional murine metastable epialleles, we utilized genome-wide expression arrays (N = 10 male individuals, 3 tissues per individual) and identified candidates displaying large variability in gene expression among individuals (Vi = inter-individual variance), concomitant with a low variability in gene expression across tissues from the three germ layers (Vt = inter-tissue variance), two features characteristic of the A (vy)  metastable epiallele. The CpG island in the promoter of Dnajb1 and two contraoriented ERV class II repeats in Glcci1 were validated to display underlying stochasticity in methylation patterns common to metastable epialleles. Furthermore, liver DNA methylation in mice exposed in utero to 50 mg bisphenol A (BPA)/kg diet (N = 91) or a control diet (N = 79) confirmed environmental lability at validated candidate genes. Significant effects of exposure on mean CpG methylation were observed at the Glcci1 Repeat 1 locus (p < 0.0001). Significant effects of BPA also were observed at the first and fifth CpG sites studied in Glcci1 Repeat 2 (p < 0.0001 and p = 0.004, respectively). BPA did not affect methylation in the promoter of Dnajb1 (p = 0.59). The characterization of metastable epialleles in humans is crucial for the development of novel screening and therapeutic targets for human disease prevention.

Microarray analysis of cellular thermotolerance

BACKGROUND AND OBJECTIVES

Previously, we have shown that a 43°C pretreatment can provide thermotolerance to a following, more severe, thermal stress at 45°C. Using cells that lack the Hsp70 gene, we have also shown that there is still some thermotolerance in the absence of HSP70 protein. The purpose of this study was to determine which genes play a role in thermotolerance by measuring viability and proliferation of the cells at 2 days after heating. Specifically, we wanted to understand which pathways may be responsible for protecting cells in the absence of HSP70.

STUDY DESIGN/MATERIALS AND METHODS

Murine embryonic fibroblast cells with and without Hsp70 (MEF(+/+) and MEF(-/-), respectively) were exposed to a mild heat shock of 43°C for 30 minutes in a constant temperature water bath. After 3 hours of recovery, RNA was harvested from three heated samples alongside three untreated controls using a MicroRNeasy kit with DNAse treatment. RNA quality was verified by an Agilent Bioanalyzer. The RNA was then converted to cDNA and hybridized to Affymetrix gene expression DNA microarrays. The genes that showed a twofold change (up or down) relative to unheated controls were filtered by t-test for significance at a threshold of P < 0.05 using Genespring software. Data were verified by qRT-PCR. Genes were then categorized based upon their ontology.

RESULTS

While many genes were similarly upregulated, the main difference between cell types was an increase in transcription factors and nucleic acid binding proteins. Several genes known to be involved in the heat response were upregulated more than twofold (Hsp70, Hsp40, Hsp110, Hsp25, Atf3), however, another well studied heat responsive gene Hsp90 only increased by 1.5-fold under these conditions despite its role in thermotolerance.

CONCLUSIONS

The data herein presents genetic pathways which are candidates for further study of pretreatment protocols in laser irradiation.

Co-chaperones are limiting in a depleted chaperone network

To probe the limiting nodes in the chaperoning network which maintains cellular proteostasis, we expressed a dominant negative mutant of heat shock factor 1 (dnHSF1), the regulator of the cytoplasmic proteotoxic stress response. Microarray analysis of non-stressed dnHSF1 cells showed a two- or more fold decrease in the transcript level of 10 genes, amongst which are the (co-)chaperone genes HSP90AA1, HSPA6, DNAJB1 and HSPB1. Glucocorticoid signaling, which requires the Hsp70 and the Hsp90 folding machines, was severely impaired by dnHSF1, but fully rescued by expression of DNAJA1 or DNAJB1, and partially by ST13. Expression of DNAJB6, DNAJB8, HSPA1A, HSPB1, HSPB8, or STIP1 had no effect while HSP90AA1 even inhibited. PTGES3 (p23) inhibited only in control cells. Our results suggest that the DNAJ co-chaperones in particular become limiting in a depleted chaperoning network. Our results also suggest a difference between the transcriptomes of cells lacking HSF1 and cells expressing dnHSF1.

Multiple molecules of Hsc70 and a dimer of DjA1 independently bind to an unfolded protein

Protein folding is a prominent chaperone function of the Hsp70 system. Refolding of an unfolded protein is efficiently mediated by the Hsc70 system with either type 1 DnaJ protein, DjA1 or DjA2, and a nucleotide exchange factor. A surface plasmon resonance technique was applied to investigate substrate recognition by the Hsc70 system and demonstrated that multiple Hsc70 proteins and a dimer of DjA1 initially bind independently to an unfolded protein. The association rate of the Hsc70 was faster than that of DjA1 under folding-compatible conditions. The Hsc70 binding involved a conformational change, whereas the DjA1 binding was bivalent and substoichiometric. Consistently, we found that the bound (14)C-labeled Hsc70 to the unfolded protein became more resistant to tryptic digestion. The gel filtration and cross-linking experiments revealed the predominant presence of the DjA1 dimer. Furthermore, the Hsc70 and DjA1 bound to distinct sets of peptide array sequences. All of these findings argue against the generality of the widely proposed hypothesis that the DnaJ-bound substrate is targeted and transferred to Hsp70. Instead, these results suggest the importance of the bivalent binding of DjA1 dimer that limits unfavorable transitions of substrate conformations in protein folding.

Mesothelioma cells escape heat stress by upregulating Hsp40/Hsp70 expression via mitogen-activated protein kinases

Therapy with hyperthermal chemotherapy in pleural diffuse malignant mesothelioma had limited benefits for patients. Here we investigated the effect of heat stress on heat shock proteins (HSP), which rescue tumour cells from apoptosis. In human mesothelioma and mesothelial cells heat stress (39-42 degrees C) induced the phosphorylation of two mitogen activated kinases (MAPK) Erk1/2 and p38, and increased Hsp40, and Hsp70 expression. Mesothelioma cells expressed more Hsp40 and were less sensitive to heat stress compared to mesothelial cells. Inhibition of Erk1/2 MAPK by PD98059 or by Erk1 siRNA down-regulated heat stress-induced Hsp40 and Hsp70 expression and reduced mesothelioma cell survival. Inhibition of p38MAPK by SB203580 or siRNA reduced Hsp40, but not Hsp70, expression and also increased mesothelioma cell death. Thus hyperthermia combined with suppression of p38 MAPK or Hsp40 may represent a novel approach to improve mesothelioma therapy.

Role of HSP70 in cellular thermotolerance

BACKGROUND AND OBJECTIVE

Thermal pretreatment has been shown to condition tissue to a more severe secondary heat stress. In this research we examined the particular contribution of heat shock protein 70 (HSP70) in thermal preconditioning.

STUDY DESIGN/MATERIALS AND METHODS

For optimization of preshock exposures, a bioluminescent Hsp70-luciferase reporter system in NIH3T3 cells tracked the activation of the Hsp70 gene. Cells in 96-well plates were pretreated in a 43 degrees C water bath for 30 minutes, followed 4 hours later with a severe heat shock at 45 degrees C for 50 minutes. Bioluminescence was measured at 2, 4, 6, 8, and 10 hours after preshock only (PS) and at 4 hours after preshock with heatshock (PS+HS). Viability was assessed 48 hours later with a fluorescent viability dye. Preshock induced thermotolerance was then evaluated in hsp70-containing Murine Embryo Fibroblast (+/+) cells and Hsp70-deficient MEF cells (-/-) through an Arrhenius damage model across varying temperatures (44.5-46 degrees C).

RESULTS

A time gap of 4 hours between preconditioning and the thermal insult was shown to be the most effective for thermotolerance with statistical confidence of P<0.05. The benefit of preshocking was largely abrogated in Hsp70-deficient cells. The Arrhenius data showed that preshocking leads to increases in the activation energies, E(a), and increases in frequency factors, A. The frequency factor increase was significantly greater in Hsp70-deficient cells.

CONCLUSION

The data shows that HSP70 contributes significantly to cellular thermotolerance but there are other pathways that provide residual thermotolerance in cells deficient in Hsp70.