Calcyclin Binding Protein/Siah-1 Interacting Protein Is a Hsp90 Binding Chaperone

Effect of PTGES3 on the Prognosis and Immune Regulation in Lung Adenocarcinoma

Background

PTGES3 is upregulated in multiple cancer types and promotes tumorigenesis and progression. However, the clinical outcome and immune regulation of PTGES3 in lung adenocarcinoma (LUAD) are not fully understood. This study aimed to explore the expression level and prognostic value of PTGES3 and its correlation with potential immunotherapy in LUAD.

Methods

All data were obtained from several databases, including the Cancer Genome Atlas database. Firstly, gene and protein expression of PTGES3 were analyzed using Tumor Immune Estimation Resource (TIMER), R software, Clinical Proteomic Tumor Analysis Consortium (CPTAC), and Human Protein Atlas (HPA). Thereafter, survival analysis was conducted using the R software, Gene Expression Profiling Interactive Analysis 2 (GEPIA2), and Kaplan-Meier Plotter. In addition, gene alteration and mutation analyses were conducted using the cBio Cancer Genomics Portal (cBioPortal) and Catalog of Somatic Mutations in Cancer (COSMIC) databases. The molecular mechanisms associated with PTGES3 were assessed via Search Tool for the Retrieval of Interacting Genes/Proteins (STRING), GeneMANIA, GEPIA2, and R software. Lastly, the role of PTGES3 in immune regulation in LUAD was investigated using TIMER, Tumor-Immune System Interaction Database (TISIDB), and SangerBox.

Results

The gene and protein expression of PTGES3 were elevated in LUAD tissues and compared to the normal tissues, and the high expression of PTGES3 was correlated with cancer stage and tumor grade. Survival analysis revealed that overexpression of PTGES3 was associated with poor prognosis of LUAD patients. Moreover, gene alteration and mutation analysis revealed the occurrence of several types of PTGES3 gene alterations in LUAD. Moreover, co-expression analysis and cross-analysis revealed that three genes, including CACYBP, HNRNPC, and TCP1, were correlated and interacted with PTGES3. Functional analysis of these genes revealed that PTGES3 was primarily enriched in oocyte meiosis, progesterone-mediated oocyte maturation, and arachidonic acid metabolism pathways. Furthermore, we found that PTGES3 participated in a complex immune regulation network in LUAD.

Conclusion

The current study indicated the crucial role of PTGES3 in LUAD prognosis and immune regulation. Altogether, our results suggested that PTGES3 could serve as a promising therapeutic and prognosis biomarker for the LUAD.

Involvement of CacyBP/SIP in differentiation and the immune response of HaCaT keratinocytes

CacyBP/SIP is a multifunctional protein present in various cells and tissues. However, its expression and role in the epidermis has not been explored so far. In this work, using RT-qPCR, Western blot analysis and three-dimensional (3D) organotypic cultures of HaCaT keratinocytes we show that CacyBP/SIP is present in the epidermis. To investigate the possible role of CacyBP/SIP in keratinocytes we obtained CacyBP/SIP knockdown cells and studied the effect of CacyBP/SIP deficiency on their differentiation and response to viral infection. We found that CacyBP/SIP knockdown results in reduced expression of epidermal differentiation markers in both undifferentiated and differentiated HaCaT cells. Since epidermis is engaged in immune defense, the impact of CacyBP/SIP knockdown on this process was also analyzed. By applying RT-qPCR and Western blot it was found that poly(I:C), a synthetic analog of double-stranded RNA that mimics viral infection, stimulated the expression of genes involved in antiviral response, such as IFIT1, IFIT2 and OASL. Interestingly, following poly(I:C) stimulation, the level of expression of these genes was significantly lower in cells with CacyBP/SIP knockdown than control ones. Since the signaling pathway mediating cellular responses to viral infection involves, among others, the STAT1 transcription factor, we measured its activity using luciferase assay and found that it was lower in CacyBP/SIP knockdown HaCaT cells. Altogether, the presented results indicate that CacyBP/SIP promotes epidermal differentiation and might be involved in response of the skin cells to viral infection.

Molecular and immunological characterization of the calcyclin binding protein in rodent malaria parasite

Malaria remains as a global life-threatening disorder due to the emergence of resistance against standard antimalarials. Consequently, there is a serious need to better understand the biology of the malaria parasite in order to determine appropriate targets for new interventions. Calcyclin binding protein (CacyBP) is a multi-functional and multi-ligand protein that is not well characterized in malaria disease. In this study, we have cloned CacyBP from rodent species Plasmodium yoelii nigeriensis and purified the recombinant protein to carry out its detailed molecular, biophysical and immunological characterization. Molecular characterization indicates that PyCacyBP is a ∼27 kDa protein in parasite lysate and exists in monomer and dimer forms. Bioinformatic analysis of CacyBP showed significant sequence and structural similarities between rodent and human malaria parasites. CacyBP is expressed in all blood stages of P. yoelii nigeriensis parasite. In silico studies proposed the immunogenic potential of CacyBP. The rPyCacyBP immunized mice exhibited elevated levels of IgG1, IgG2a, IgG2b and IgG3 in their serum. Notably, cellular immune response in splenocytes from immunized mice showed increased expression of pro-inflammatory cytokines such as IL-12, IFN-γ and TNF-α. This CacyBP exhibited pro-inflammatory immune response in rodent host. These finding revealed that CacyBP may have the potential to boost the host immunity for protection against malaria infection. The present study provides basis for further exploration of the biological function of CacyBP in malaria parasite.

Siah-1-interacting protein regulates mutated huntingtin protein aggregation in Huntington’s disease models

Background

Huntington’s disease (HD) is a neurodegenerative disorder whereby mutated huntingtin protein (mHTT) aggregates when polyglutamine repeats in the N-terminal of mHTT exceeds 36 glutamines (Q). However, the mechanism of this pathology is unknown. Siah1-interacting protein (SIP) acts as an adaptor protein in the ubiquitination complex and mediates degradation of other proteins. We hypothesized that mHTT aggregation depends on the dysregulation of SIP activity in this pathway in HD.

Results

A higher SIP dimer/monomer ratio was observed in the striatum in young YAC128 mice, which overexpress mHTT. We found that SIP interacted with HTT. In a cellular HD model, we found that wildtype SIP increased mHTT ubiquitination, attenuated mHTT protein levels, and decreased HTT aggregation. We predicted mutations that should stabilize SIP dimerization and found that SIP mutant-overexpressing cells formed more stable dimers and had lower activity in facilitating mHTT ubiquitination and preventing exon 1 mHTT aggregation compared with wildtype SIP.

Conclusions

Our data suggest that an increase in SIP dimerization in HD medium spiny neurons leads to a decrease in SIP function in the degradation of mHTT through a ubiquitin–proteasome pathway and consequently an increase in mHTT aggregation. Therefore, SIP could be considered a potential target for anti-HD therapy during the early stage of HD pathology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00755-0.

Hsp90 and Associated Co-Chaperones of the Malaria Parasite

Heat shock protein 90 (Hsp90) is one of the major guardians of cellular protein homeostasis, through its specialized molecular chaperone properties. While Hsp90 has been extensively studied in many prokaryotic and higher eukaryotic model organisms, its structural, functional, and biological properties in parasitic protozoans are less well defined. Hsp90 collaborates with a wide range of co-chaperones that fine-tune its protein folding pathway. Co-chaperones play many roles in the regulation of Hsp90, including selective targeting of client proteins, and the modulation of its ATPase activity, conformational changes, and post-translational modifications. Plasmodium falciparum is responsible for the most lethal form of human malaria. The survival of the malaria parasite inside the host and the vector depends on the action of molecular chaperones. The major cytosolic P. falciparum Hsp90 (PfHsp90) is known to play an essential role in the development of the parasite, particularly during the intra-erythrocytic stage in the human host. Although PfHsp90 shares significant sequence and structural similarity with human Hsp90, it has several major structural and functional differences. Furthermore, its co-chaperone network appears to be substantially different to that of the human host, with the potential absence of a key homolog. Indeed, PfHsp90 and its interface with co-chaperones represent potential drug targets for antimalarial drug discovery. In this review, we critically summarize the current understanding of the properties of Hsp90, and the associated co-chaperones of the malaria parasite.

Splicing factor arginine/serine-rich 8 promotes multiple myeloma malignancy and bone lesion through alternative splicing of CACYBP and exosome-based cellular communication

BACKGROUND

Multiple myeloma (MM) is a distinctive malignancy of plasma cell within the bone marrow (BM), of which alternative splicing factors play vital roles in the progression. Splicing factor arginine/serine-rich 8 (SFRS8) is the exclusive factor associated with MM prognosis, however its role in MM remains undefined.

METHODS

The analyses of 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di- phenytetrazoliumromide (MTT) assay, immunohistochemistry, flow cytometry and xenograft model were performed to examine cell proliferation, cell cycle and apoptosis in SFRS8 overexpression or knockdown MM cells in vitro and in vivo. The SFRS8-regulated alternative splicing events were identified by RNA immunoprecipitation sequencing (RIP-seq) and validated by RIP-qPCR and Co-IP methods. Exosomes were extracted from the supernatant of myeloma cells by ultracentrifugation. Bone lesion was evaluated by TRAP staining in vitro and SCID/NOD-TIBIA mouse model. A neon electroporation system was utilised to deliver siRNA through exosomes. The effect of siRNA-loaded exosomes in vivo was evaluated by using a patient-derived tumor xenograft (PDX) model and SCID/NOD-TIBIA mouse model.

RESULTS

SFRS8 was significantly upregulated in MM samples and positively associated with poor overall survival (OS) in MM patients. SFRS8 promoted MM cell proliferation in vitro and in vivo. Furthermore, calcyclin binding protein (CACYBP) was identified as the downstream target of SFRS8. Particularly, SFRS8 could reduce CACYBP isoform1 (NM_014412.3) and increase CACYBP isoform2 (NM_001007214.1) by mediating the alternative splicing of CACYBP, thereby altering the ubiquitination degradation of β-catenin to promote MM progression. In addition, SFRS8 promoted osteoclast differentiation through exosomes in vitro and in vivo. More importantly, exosomal siRNA targeting CACYBP isoform2 inhibited tumour growth in PDX and SCID/NOD-TIBIA mouse models.

CONCLUSION

Our findings demonstrate that targeting the SFRS8/CACYBP/β-catenin axis may be a promising strategy for MM diagnosis and treatment.

Phosphorylation in the Charged Linker Modulates Interactions and Secretion of Hsp90β

Hsp90β is a major chaperone involved in numerous cellular processes. Hundreds of client proteins depend on Hsp90β for proper folding and/or activity. Regulation of Hsp90β is critical to coordinate its tasks and is mediated by several post-translational modifications. Here, we focus on two phosphorylation sites located in the charged linker region of human Hsp90β, Ser226 and Ser255, which have been frequently reported but whose function remains unclear. Targeted measurements by mass spectrometry indicated that intracellular Hsp90β is highly phosphorylated on both sites (>90%). The level of phosphorylation was unaffected by various stresses (e.g., heat shock, inhibition with drugs) that impact Hsp90β activity. Mutating the two serines to alanines increased the amount of proteins interacting with Hsp90β globally and increased the sensitivity to tryptic cleavage in the C-terminal domain. Further investigation revealed that phosphorylation on Ser255 and to a lesser extent on Ser226 is decreased in the conditioned medium of cultured K562 cells, and that a non-phosphorylatable double alanine mutant was secreted more efficiently than the wild type. Overall, our results show that phosphorylation events in the charged linker regulate both the interactions of Hsp90β and its secretion, through changes in the conformation of the chaperone.

The role and therapeutic potential of Hsp90, Hsp70, and smaller heat shock proteins in peripheral and central neuropathies

Heat shock proteins (Hsps) are molecular chaperones that also play important roles in the activation of the heat shock response (HSR). The HSR is an evolutionary conserved and protective mechanism that is used to counter abnormal physiological conditions, stressors, and disease states, such as those exemplified in cancer and/or neurodegeneration. In normal cells, heat shock factor-1 (HSF-1), the transcription factor that regulates the HSR, remains in a dormant multiprotein complex that is formed upon association with chaperones (Hsp90, Hsp70, etc.), co-chaperones, and client proteins. However, under cellular stress, HSF-1 dissociates from Hsp90 and induces the transcriptional upregulation of Hsp70 to afford protection against the encountered cellular stress. As a consequence of both peripheral and central neuropathies, cellular stress occurs and results in the accumulation of unfolded and/or misfolded proteins, which can be counterbalanced by activation of the HSR. Since Hsp90 is the primary regulator of the HSR, modulation of Hsp90 by small molecules represents an attractive therapeutic approach against both peripheral and central neuropathies.

Human Hsp90 cochaperones: perspectives on tissue-specific expression and identification of cochaperones with similar in vivo functions

The Hsp90 molecular chaperone is required for the function of hundreds of different cellular proteins. Hsp90 and a cohort of interacting proteins called cochaperones interact with clients in an ATP-dependent cycle. Cochaperone functions include targeting clients to Hsp90, regulating Hsp90 ATPase activity, and/or promoting Hsp90 conformational changes as it progresses through the cycle. Over the last 20 years, the list of cochaperones identified in human cells has grown from the initial six identified in complex with steroid hormone receptors and protein kinases to about fifty different cochaperones found in Hsp90-client complexes. These cochaperones may be placed into three groups based on shared Hsp90 interaction domains. Available evidence indicates that cochaperones vary in client specificity, abundance, and tissue distribution. Many of the cochaperones have critical roles in regulation of cancer and neurodegeneration. A more limited set of cochaperones have cellular functions that may be limited to tissues such as muscle and testis. It is likely that a small set of cochaperones are part of the core Hsp90 machinery required for the folding of a wide range of clients. The presence of more selective cochaperones may allow greater control of Hsp90 activities across different tissues or during development.

HSP90 Co-Chaperone, CacyBP/SIP, Protects α-Synuclein from Aggregation

Recently, it has been found that the CacyBP/SIP protein acts as HSP90 co-chaperone and exhibits chaperone properties itself. Namely, CacyBP/SIP has been shown to protect citrate synthase from aggregation and to recover the activity of thermally denatured luciferase in vitro. In the present work, we have analyzed the influence of CacyBP/SIP on aggregation of α-synuclein, a protein present in Lewy bodies of Parkinson’s disease brain. By applying a thioflavin T (ThT) fluorescence assay, we have found that CacyBP/SIP protects α-synuclein from aggregation and that the fragment overlapping the N-terminal part and the CS domain of CacyBP/SIP is crucial for this activity. This protective effect of CacyBP/SIP has been confirmed by results obtained using high-speed ultracentrifugation followed by dot-blot and by transmission electron microscopy (TEM). Interestingly, CacyBP/SIP exhibits the protective effect only at the initial phase of α-synuclein aggregation. In addition, we have found that, in HEK293 cells overexpressing CacyBP/SIP, there are less α-synuclein inclusions than in control ones. Moreover, these cells are more viable when treated with rotenone, an agent that mimics PD pathology. By applying proximity ligation assay (PLA) on HEK293 cells and in vitro assays with the use of purified recombinant proteins, we have found that CacyBP/SIP directly interacts with α-synuclein. Altogether, in this work, we show for the first time that CacyBP/SIP is able to protect α-synuclein from aggregation in in vitro assays. Thus, our results point to an important role of CacyBP/SIP in the pathology of Parkinson’s disease and other synucleinopathies.

Identification of a Novel Gene, Osbht, in Response to High Temperature Tolerance at Booting Stage in Rice

Rice is one of the world’s leading food crops, and over 90% of the world’s rice production stems from Asia. In particular, an increase of 1 °C in the minimum temperature reduces the quantity of rice by 10%. Therefore, the development of rice varieties that can stably maintain the yield and quality of the rice even under these rapid climate changes is indispensable. In this study, we performed quantitative trait loci (QTL) mapping after treatment with heat stress during the booting stage in rice. We performed a QTL analysis using the Cheongcheong/Nagdong double haploid (CNDH) line and identified 19 QTLs during the 2 year analysis. Of these QTL regions, the 2.2 cM region of RM3709–RM11694 on chromosome 1 was shared among the six traits (heading date; culm length; panicle length; number of tiller; 1000 grain weight; and content of chlorophyll) examined. Rice Microsatellite (RM) 3709–RM11694 contained 27 high-temperature-tolerance candidate genes. Among the candidate genes, OsBHT showed a different gene expression level between CNDH75, which is a high-temperature tolerant line, and CNDH11 which is a susceptible line. Although some existing high-temperature-tolerant genes have been reported, OsBHT can be used more effectively for the development of heat tolerance in rice.

S100A6 and Its Brain Ligands in Neurodegenerative Disorders

The S100A6 protein is present in different mammalian cells and tissues including the brain. It binds Ca²⁺ and Zn²⁺ and interacts with many target proteins/ligands. The best characterized ligands of S100A6, expressed at high level in the brain, include CacyBP/SIP and Sgt1. Research concerning the functional role of S100A6 and these two ligands indicates that they are involved in various signaling pathways that regulate cell proliferation, differentiation, cytoskeletal organization, and others. In this review, we focused on the expression/localization of these proteins in the brain and on their possible role in neurodegenerative diseases. Published results demonstrate that S100A6, CacyBP/SIP, and Sgt1 are expressed in various brain structures and in the spinal cord and can be found in different cell types including neurons and astrocytes. When it comes to their possible involvement in nervous system pathology, it is evident that their expression/level and/or subcellular localization is changed when compared to normal conditions. Among diseases in which such changes have been observed are Alzheimer’s disease (AD), amyotrophic lateral sclerosis (ALS), epileptogenesis, Parkinson’s disease (PD), Huntington’s disease (HD), and others.

Quantification of Calcyclin and Heat Shock Protein 90 in Sera from Women with and without Preeclampsia by Mass Spectrometry

PURPOSE

The objective of present study is to determine serum levels and placental distribution of two interacting proteins calcyclin and heat shock protein 90 in preeclampsia.

EXPERIMENTAL DESIGN

Maternal serum levels of calcyclin and heat shock protein 90 are compared throughout pregnancy from the first trimester till term among women with preeclampsia (n = 43) and age-matched normotensive pregnant controls (n = 46). A serum-based 2D LC-MS assay using Parallel Reaction Monitoring is applied to quantify both calcyclin and heat shock protein 90.

RESULTS

Serum levels of calcyclin are significantly lower in patients with preeclampsia in the second trimester of pregnancy as compared to controls (p < 0.05). Serum levels of heat shock protein 90 are significantly higher in patients with preeclampsia in the third trimester as compared to controls (p < 0.001).

CONCLUSION AND CLINICAL RELEVANCE

Both interacting proteins calcyclin and heat shock protein 90 are notably changed in preeclamptic patients compared to controls. Calcyclin is already decreased before the onset of preeclampsia in the second trimester and HSP90 is strongly increased in the third trimester. This suggests that these proteins may play a role in the pathogenesis of preeclampsia and ought to be investigated in large cohort studies as molecular biomarkers.

Interaction of CacyBP/SIP with NPM1 and its influence on NPM1 localization and function in oxidative stress

Calcyclin (S100A6) binding protein/Siah-1 interacting protein (CacyBP/SIP) is mainly a cytoplasmic protein; however, some literature data suggested its presence in the nucleus. In this work we examined more precisely the nuclear localization and function of CacyBP/SIP. By applying mass spectrometry, we have identified several nuclear proteins, among them is nucleophosmin (NPM1), that may interact with CacyBP/SIP. Subsequent assays revealed that CacyBP/SIP forms complexes with NPM1 in the cell and that the interaction between these two proteins is direct. Interestingly, although CacyBP/SIP exhibits phosphatase activity, we have found that its overexpression favors phosphorylation of NPM1 on S125. In turn, the RNA immunoprecipitation assay indicated that the altered CacyBP/SIP level has an impact on the amount of 28S and 18S rRNA bound to NPM1. The overexpression of CacyBP/SIP resulted in a significant increase in the binding of 28S and 18S rRNA to NPM1, whereas silencing of CacyBP/SIP expression decreased 28S rRNA binding and had no effect on the binding of 18S rRNA. Further studies have shown that under oxidative stress, CacyBP/SIP overexpression alters NPM1 distribution in cell nuclei. In addition, staining for a nucleolar marker, fibrillarin, revealed that CacyBP/SIP is indispensable for maintaining the nucleolar structure. These results are in agreement with data obtained by western blot analysis, which show that upon oxidative stress the NPM1 level decreases but that CacyBP/SIP overexpression counteracts the effect of stress. Altogether, our results show for the first time that CacyBP/SIP binds to and affects the properties of a nuclear protein, NPM1, and that it is indispensable for preserving the structure of nucleoli under oxidative stress.

CacyBP/SIP, a Hsp90 binding chaperone, in cellular stress response

CacyBP/SIP interacts with Hsp90 and is able to protect proteins from denaturation and/or aggregation induced by elevated temperature. In this work we studied the influence of different stress factors on CacyBP/SIP level in HEp-2 cells. We have found that H₂O₂ and radicicol treatment resulted in a significant increase (up to 40%) in the CacyBP/SIP level. We have also found that HEp-2 cells overexpressing CacyBP/SIP were more resistant to stress-induced death. Further studies have revealed that the Hsf1 transcription factor binds to the CacyBP/SIP gene promoter and up-regulates CacyBP/SIP expression under stress conditions. To check whether the CacyBP/SIP protein might play a role in stress responses in vivo, we analyzed its level in selected brain structures of control and stressed mice. We have found that the level of the CacyBP/SIP protein was higher in the thalamus/hypothalamus, hippocampus and brainstem of stressed mice. Thus, the presented results clearly indicate that CacyBP/SIP is involved in cellular stress response.

Evidence for Hsp90 Co-chaperones in Regulating Hsp90 Function and Promoting Client Protein Folding

Molecular chaperones are a diverse group of highly conserved proteins that transiently interact with partially folded polypeptide chains during normal cellular processes such as protein translation, translocation, and disassembly of protein complexes. Prior to folding or after denaturation, hydrophobic residues that are normally sequestered within a folded protein are exposed to the aqueous environment and are prone to aggregation or misfolding. Multiple classes of molecular chaperones, such as Hsp70s and Hsp40s, recognize and transiently bind polypeptides with exposed hydrophobic stretches in order to prevent misfolding. Other types of chaperones, such as Hsp90, have more specialized functions in that they appear to interact with only a subset of cellular proteins. This chapter focuses on the role of Hsp90 and partner co-chaperones in promoting the folding and activation of a diverse group of proteins with critical roles in cellular signaling and function.

Transcriptional regulation of CacyBP/SIP gene and the influence of increased CacyBP/SIP level on gene expression pattern in colorectal cancer HCT116 cells

The CacyBP/SIP protein is expressed at a particularly high level in brain, spleen, and various tumors. In this work, we have studied transcriptional regulation of the CacyBP/SIP gene and the influence of increased CacyBP/SIP level on gene expression in colorectal cancer HCT116 cells. We have shown that E2F1, EGR1, and CREB transcription factors bind to the CacyBP/SIP gene promoter and stimulate transcription of CacyBP/SIP gene. The role of CREB was further confirmed by the observation that forskolin, a strong activator of CREB phosphorylation/activity, increased CacyBP/SIP gene promoter activity. Moreover, we have shown that CREB dominant negative mutants, CREB133 and KCREB, inhibits CacyBP/SIP promoter activity. To check the biological significance of increased CacyBP/SIP expression/level we have applied RNA microarray analysis and have found that upregulation of CacyBP/SIP entails changes in mRNA level of many genes involved, among others, in immune processes. © 2017 IUBMB Life, 70(1):50-59, 2018.

S100A6 - focus on recent developments

The Ca2+-binding protein, S100A6, belongs to the S100 family. Binding of Ca2+ induces a conformational change, which causes an increase in the overall S100A6 hydrophobicity and allows it to interact with many targets. S100A6 is expressed in different normal tissues and in many tumors. Up to now it has been shown that S100A6 is involved in cell proliferation, cytoskeletal dynamics and tumorigenesis, and that it might have some extracellular functions. In this review, we summarize novel discoveries concerning S100A6 targets, its involvement in cellular signaling pathways, and presence in stem/progenitor cells, extracellular matrix and body fluids of diseased patients.

Interaction of a Novel Chaperone PhLP2A With the Heat Shock Protein Hsp90

PhLP2 is a small cytosolic protein that belongs to the highly conserved phosducin-like family of proteins. In amniote genomes there are two PhLP2 homologs, PhLP2A and PhLP2B. It has been shown that mammalian PhLP2A modulates the CCT/TRiC chaperonin activity during folding of cytoskeletal proteins. In order to better understand the function of PhLP2A in cellular protein quality control system, in the present study we have searched for its protein targets. Applying immunoprecipitation followed by mass spectrometry analysis we have identified Hsp90 as a partner of PhLP2A. With pull down experiments, we have confirmed this interaction in protein lysate and using purified proteins we have shown that PhLP2A interacts directly with Hsp90. Furthermore, the proximity ligation assay (PLA) performed on mIMCD-3 cells has shown that PhLP2A forms complexes with Hsp90 which are mainly localized in the cytoplasm of these cells. Further analysis has indicated that the level of PhLP2A increases after heat shock or radicicol treatment, similarly as the level of Hsp90, and that expression of PhLP2A after heat shock is regulated at the transcriptional level. Moreover, using recombinant luciferase we have shown that PhLP2A stabilizes this enzyme in a folding competent state and prevents its denaturation and aggregation. In addition, overexpression of PhLP2A in HEK-293 cells leads to increased heat stress resistance. Altogether, our results have shown that PhLP2A interacts with Hsp90 and exhibits molecular chaperone activity toward denatured proteins. J. Cell. Biochem. 118: 420-429, 2017. © 2016 Wiley Periodicals, Inc.