Stat3 modulates heat shock 27kDa protein expression in breast epithelial cells

HSPs/STAT3 Interplay Sustains DDR and Promotes Cytokine Release by Primary Effusion Lymphoma Cells

Primary effusion lymphoma (PEL) is a rare and aggressive B-cell lymphoma, against which current therapies usually fail. In the present study, we show that targeting HSPs, such as HSP27, HSP70 and HSP90, could be an efficient strategy to reduce PEL cell survival, as it induces strong DNA damage, which correlated with an impairment of DDR. Moreover, as HSP27, HSP70 and HSP90 cross talk with STAT3, their inhibition results in STAT3 de-phosphorylation and. On the other hand, the inhibition of STAT3 may downregulate these HSPs. These findings suggest that targeting HSPs has important implications in cancer therapy, as it can reduce the release of cytokines by PEL cells, which, besides affecting their own survival, could negatively influence anti-cancer immune response.

In silico screening and exploration into phenotypic alterations of deleterious oncogenic single nucleotide polymorphisms in HSPB1 gene

A small heat shock protein, HSP27, encoded by HSPB1 gene strongly favors survival, proliferation and metastasis of cancer cells and its expression is dependent on post-translational modifications like phosphorylation. This study performed an extensive in silico screening of 20 deleterious non-synonymous SNPs in the coding region of HSPB1 gene, among which four were identified to be cancer associated. The SNP variant I181S introduced a new phosphorylation site in position 181, which might elevate the protein's activation potential. Emergence of other post-translational modifications was also observed in SNP variants: L144P and E130K.Significant conformational changes were observed in I181S, L144P and E130K SNP variants with respect to wild-type HSP27. These SNPs appear in one among 10⁵ individuals, making them more susceptible towards cancer. This study would therefore, instigate development of novel biomarkers for cancer risk detection and would provide a detailed understanding towards varied cancer susceptibility of human population.

Chaperoning STAT3/5 by Heat Shock Proteins: Interest of Their Targeting in Cancer Therapy

While cells from multicellular organisms are dependent upon exogenous signals for their survival, growth, and proliferation, commitment to a specific cell fate requires the correct folding and maturation of proteins, as well as the degradation of misfolded or aggregated proteins within the cell. This general control of protein quality involves the expression and the activity of molecular chaperones such as heat shock proteins (HSPs). HSPs, through their interaction with the STAT3/STAT5 transcription factor pathway, can be crucial both for the tumorigenic properties of cancer cells (cell proliferation, survival) and for the microenvironmental immune cell compartment (differentiation, activation, cytokine secretion) that contributes to immunosuppression, which, in turn, potentially promotes tumor progression. Understanding the contribution of chaperones such as HSP27, HSP70, HSP90, and HSP110 to the STAT3/5 signaling pathway has raised the possibility of targeting such HSPs to specifically restrain STAT3/5 oncogenic functions. In this review, we present how HSPs control STAT3 and STAT5 activation, and vice versa, how the STAT signaling pathways modulate HSP expression. We also discuss whether targeting HSPs is a valid therapeutic option and which HSP would be the best candidate for such a strategy.

Circulating level of heat shock protein 27 is elevated in dogs with mammary tumors

In the current study, we have synthesized canine recombinant Hsp27 in E. coli and raised hyperimmune serum against the protein in mice. Using the hyperimmune serum, an indirect ELISA was developed to estimate circulating levels of Hsp27 in dogs with various types of mammary neoplasia and to compare their levels with those of tumor-free apparently healthy dogs. The developed assay had a high specificity (83.3%) and sensitivity (96.6%) for a cut-off value of 0.45 with respect to histopathological examination in discriminating healthy dogs from those bearing mammary tumors. Serum Hsp27 levels were found to be significantly elevated in tumor subjects (20.33 ± 1.23 ng/ml) as compared to healthy controls (6.56 ± 0.51 ng/ml) and the increase in the Hsp27 levels was irrespective of mammary tumor histotypes. However, dogs with grade-II tumors had higher Hsp27 levels as compared to grade-I types. Therefore, Hsp27 can be exploited as one of the 'neoplastic signatures' of canine mammary tumors.

Osteogenic Effect and Cell Signaling Activation of Extremely Low-Frequency Pulsed Electromagnetic Fields in Adipose-Derived Mesenchymal Stromal Cells

Extremely low-frequency pulsed electromagnetic field (ELF-PEMF) devices have been used in the clinic for the treatment of bone disorders over the past 30 years. However, the underlying mechanism of which ELF-PEMFs exert an effect on tissues at a cellular level is not well understood. Hence, in this study, we explored the potential of different ELF-PEMF signals in modulating human adipose-derived mesenchymal stromal cells' (hAMSC) osteogenic capability. The cell proliferation rate was assessed using carboxyfluorescein succinimidyl ester (CFSE) method. The osteogenesis potential of cells was determined by alkaline phosphatase (ALP) activity, Alizarin-Red S staining, and RT-qPCR. Finally, the intracellular signaling pathway of a selected ELF-PEMF signal was examined using the PathScan Intracellular Signaling Array. Among the tested ELF-PEMF signals, program 20 (26 Hz) showed activation of the Akt and MAPK/ERK signaling cascade and significant upregulations of collagen I, alkaline phosphatase, and osteocalcin when compared to nonstimulated cells. This study demonstrates the potential of certain ELF-PEMF signal parameters to induce osteogenic differentiation of hAMSC and provides important clues in terms of the molecular mechanisms for the stimulation of osteogenic effects by ELF-PEMF on hAMSC.

Moderate High Temperature Condition Induces the Lactation Capacity of Mammary Epithelial Cells Through Control of STAT3 and STAT5 Signaling

In lactating mammary glands, alveolar mammary epithelial cells (MECs) synthesize and secrete milk components. MECs also form less permeable tight junctions (TJs) to prevent the leakage of milk components. During lactation, MECs are exposed to temperature changes by metabolic heat production and air ambient temperature. In this study, we investigated whether temperature changes influence milk production ability and TJ barriers in MECs by using two lactating culture models. The results showed that 39 °C treatment activated milk production and enhanced the formation of less-permeable TJs. In contrast, 41 °C treatment caused adverse effects on the TJ barrier and cell viability, although the milk production ability of MECs was temporarily up-regulated. MECs cultured at 37 °C showed relatively low milk production ability and high proliferation activity. Furthermore, we investigated three kinds of transcription factors relating to lactogenesis, signal transducer and activator of transcription 5 (STAT5), STAT3 and glucocorticoid receptor (GR). STAT5 signaling was activated at 39 and 41 °C by an increase in total STAT5. However, long-term treatment led to a decrease in total STAT5. STAT3 signaling was inactivated by high temperature treatment through a decrease in total STAT3 and inhibited phosphorylation of STAT3. GR signaling was continuously activated regardless of temperature. These results indicate that a moderate high temperature condition at 39 °C induces a high lactation capacity of MECs through control of STAT5 and STAT3 signaling. In contrast, long-term exposure at 41 °C leads to a decline in milk production capacity by inactivation of STAT5 and a decrease in the total number of MECs.

Clinicopathological significance of HSP27 in gastric cancer: a meta-analysis

Background

Many studies have provided increasing evidence to demonstrate that HSP27 has been involved in the development of gastric cancer; however, they all include few patients and the results remain controversial. Hence, we conducted a meta-analysis to evaluate correlations between HSP27 and the clinicopathological characteristics of gastric cancer.

Methods

An electronic search for relevant articles was conducted in PubMed, Cochrane Library, Web of Science, EMBASE database, Chinese CNKI, and Wan Fang. Data on the relationship between HSP27 expression and lymph node metastasis, serosal invasion, gender, tumor size, differentiation, and TNM stage were extracted. Pooled odds ratios and 95% confidence intervals were estimated by forest plot.

Results

The pooled analyses suggested that HSP27 expression was significantly associated with the incidence of gastric cancer. However, HSP27 expression had no significant relationship with lymph node metastasis, serosal invasion, gender, tumor size, differentiation, and TNM stage.

Conclusion

Our meta-analysis demonstrated that HSP27 may play vital roles in tumorigenesis and deterioration of gastric cancer. However, further high-quality studies are needed to provide more reliable evidence.

Upregulation of MEK5 by Stat3 promotes breast cancer cell invasion and metastasis

Mitogen extracellular-signal-regulated kinase kinase 5 (MEK5) plays an important role in promoting cell proliferation and tumorigenesis. The aberrant expression of MEK5 has been reported in various malignant diseases including cancers of breast, prostate, lung, colorectal and brain. However, the function and regulation of MEK5 signaling pathway are ambiguous and remain elusive with respect to its oncogenic roles in various cancers, especially in the regulation of the initiation and progression of cancer invasion and metastasis. Ectopic expression of MEK5 or knockdown of MEK5 by shRNA with in vitro cell based models demonstrated the role of MEK5 in regulation of epithelial mesenchymal transition (EMT) and breast cancer invasion and metastasis. Here, we show that MEK5 upregulated by Stat3 promotes breast cancer cell invasion through EMT. Further study demonstrated that Stat3 could bind to promoter region of MEK5 and enhanced MEK5 transcription and expression. In addition, the phosphorylation of MEK5 significantly increased in breast cancer cells corresponding to metastatic capability of breast cancer cells. The depletion of MEK5 by shRNA significantly decreased breast cancer invasion. Ectopic expression of MEK5 could confer non-invasive breast cancer cells to become invasion capable cells. Moreover, the phosphorylation of Erk5, a MEK5-regulated downstream kinase, was also upregulated consistent with the increased level of active MEK5. Our studies provide insights into a molecular mechanism by which MEK5 transcriptionally upregulated by Stat3 augments breast cancer cell EMT, which subsequently enhances cancer cell invasion and metastasis. This finding may suggest that Stat3 and MEK5/Erk5 pathways could be an effective therapeutic target for inhibition of breast cancer invasion and metastasis.

Mild systemic thermal therapy ameliorates renal dysfunction in a rodent model of chronic kidney disease

Thermal therapy has become a nonpharmacological therapy in clinical settings, especially for cardiovascular diseases. However, the practical role of thermal therapy on chronic kidney disease remains elusive. We performed the present study to investigate whether a modified thermal protocol, repeated mild thermal stimulation (MTS), could affect renal damages in chronic kidney disease using a mouse renal ablation model. Mice were subjected to MTS or room temperature (RT) treatment once daily for 4 wk after subtotal nephrectomy (Nx) or sham operation (Sh). We revealed that MTS alleviated renal impairment as indicated by serum creatinine and albuminuria in Nx groups. In addition, the Nx + MTS group showed attenuated tubular histological changes and reduced urinary neutrophil gelatinase-associated lipocalin excretion approximately by half compared with the Nx + RT group. Increased apoptotic signaling, such as TUNEL-positive cell count and cleavage of caspase 3, as well as enhanced oxidative stress were significantly reduced in the Nx + MTS group compared with the Nx + RT group. These changes were accompanied with the restoration of kidney Mn-SOD levels by MTS. Heat shock protein 27, a key molecular chaperone, was phosphorylated by MTS only in Nx kidneys rather than in Sh kidneys. MTS also tended to increase the phosphorylation of p38 MAPK and Akt in Nx kidneys, possibly associated with the activation of heat shock protein 27. Taken together, these results suggest that modified MTS can protect against renal injury in a rodent model of chronic kidney disease.

Phosphorylated heat shock protein 27 promotes lipid clearance in hepatic cells through interacting with STAT3 and activating autophagy

Nonalcoholic fatty liver disease (NAFLD) has become the major liver disease worldwide. Recently, several studies have identified that the activation of autophagy attenuates hepatic steatosis. Heat shock protein 27 (Hsp27) is involved in autophagy in response to various stimuli. In this study, we demonstrate that phosphorylated Hsp27 stimulates autophagy and lipid droplet clearance and interacts with STAT3. In vivo study showed that high fat diet (HFD) feeding increased Hsp25 (mouse orthology of Hsp27) phosphorylation and autophagy in mouse livers. Inhibition of Hsp25 phosphorylation exacerbated HFD-induced hepatic steatosis in mice. In vitro study showed that palmitate-induced lipid overload in hepatic cells was enhanced by Hsp27 knockdown, KRIBB3 treatment and Hsp27-3A (non-phosphorylatable) overexpression but was prevented by Hsp27-WT (wild type) and Hsp27-3D (phosphomimetic) overexpression. Mechanism analysis demonstrated that palmitate could induce Hsp27 phosphorylation which promoted palmitate-induced autophagy. Phosphorylated Hsp27 interacted with STAT3 in response to palmitate treatment, and disrupted the STAT3/PKR complexes, facilitated PKR-dependent eIF2α phosphorylation, and thus stimulated autophagy. To conclude, our study provides a novel mechanism by which the phosphorylated Hsp27 promotes hepatic lipid clearance and suggests a new insight for therapy of steatotic diseases such as nonalcoholic fatty liver disease (NAFLD).

Hsp27 Inhibition with OGX-427 Sensitizes Non-Small Cell Lung Cancer Cells to Erlotinib and Chemotherapy

Non-small cell lung cancer (NSCLC) is the most frequent cause of death from cancer worldwide. Despite the availability of active chemotherapy regimens and EGFR tyrosine kinase inhibitors, all advanced patients develop recurrent disease after first-line therapy. Although Hsp27 is a stress-induced chaperone that promotes acquired resistance in several cancers, its relationship to treatment resistance in NSCLC has not been defined. Understanding adaptive responses of acquired resistance will help guide new strategies to control NSCLC. Hsp27 levels were evaluated in an HCC827 erlotinib-resistant-derived cell line (HCC-827Resistant), and sensitivity to erlotinib was examined in Hsp27-overexpressing A549 cells. The role of Hsp27 in both erlotinib and cytotoxic treatment resistance was evaluated in HCC-827 and A549 NSCLC cells using the Hsp27 antisense drug OGX-427. The effect of OGX-427 in combination with erlotinib was also assessed in mice bearing A549 xenografts. Hsp27 is induced by erlotinib and protects NSCLC cells from treatment-induced apoptosis, whereas OGX-427 sensitizes NSCLC cells to erlotinib. Interestingly, increased resistance to erlotinib was observed when Hsp27 was increased either in HCC827 erlotinib-resistant or overexpressing A549 cells. Combining OGX-427 with erlotinib significantly enhanced antitumor effects in vitro and delayed A549 xenograft growth in vivo. OGX-427 also significantly enhanced the activity of cytotoxic drugs used for NSCLC. These data indicate that treatment-induced Hsp27 contributes to the development of resistance, and provides preclinical proof-of-principle that inhibition of stress adaptive pathways mediated by Hsp27 enhances the activity of erlotinib and chemotherapeutics.

Contribution of chaperones to STAT pathway signaling

Aberrant STAT signaling is associated with the development and progression of many cancers and immune related diseases. Recent findings demonstrate that proteostasis modulators under clinical investigation for cancer therapy have a significant impact on STAT signaling, which may be critical for mediating their anti-cancer effects. Chaperones are critical for protein folding, stability and function and, thus, play an essential role in the maintenance of proteostasis. In this review we discuss the role of chaperones in STAT and tyrosine kinase (TK) protein folding, modulation of STAT and TK activity, and degradation of TKs. We highlight the important role of chaperones in STAT signaling, and how this knowledge has provided a framework for the development of new therapeutic avenues of targeting STAT signaling related pathologies.

Hepatocyte growth factor promotes long-term survival and axonal regeneration of retinal ganglion cells after optic nerve injury: comparison with CNTF and BDNF

AIMS

Different trophic factors are known to promote retinal ganglion cell survival and regeneration, but each had their own limitations. We report that hepatocyte growth factor (HGF) confers distinct advantages in supporting ganglion cell survival and axonal regeneration, when compared to two well-established trophic factors ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF).

METHODS

Ganglion cells in adult hamster were injured by cutting the optic nerve. HGF, CNTF, or BDNF was injected at different dosages intravitreally after injury. Ganglion cell survival was quantified at 7, 14, or 28 days postinjury. Peripheral nerve (PN) grafting to the cut optic nerve of the growth factor-injected eye was performed either immediately after injury or delayed until 7 days post-injury. Expression of heat-shock protein 27 and changes in microglia numbers were quantified in different growth factor groups. The cellular distribution of c-Met in the retina was examined by anti-c-Met immunostaining.

RESULTS

Hepatocyte Growth Factor (HGF) was equally potent as BDNF in promoting short-term survival (up to 14 days post-injury) and also supported survival at 28 days post-injury when ganglion cells treated by CNTF or BDNF failed to be sustained. When grafting was performed without delay, HGF stimulated twice the number of axons to regenerate compared with control but was less potent than CNTF. However, in PN grafting delayed for 7 days after optic nerve injury, HGF maintained a better propensity of ganglion cells to regenerate than CNTF. Unlike CNTF, HGF application did not increase HSP27 expression in ganglion cells. Microglia proliferation was prolonged in HGF-treated retinas compared with CNTF or BDNF. C-Met was localized to both ganglion cells and Muller cells, suggesting HGF could be neuroprotective via interacting with both neurons and glia.

CONCLUSION

Compared with CNTF or BDNF, HGF is advantageous in sustaining long-term ganglion cell survival and their propensity to respond to favorable stimuli.

HspB1, HspB5 and HspB4 in Human Cancers: Potent Oncogenic Role of Some of Their Client Proteins

Human small heat shock proteins are molecular chaperones that regulate fundamental cellular processes in normal unstressed cells as well as in many cancer cells where they are over-expressed. These proteins are characterized by cell physiology dependent changes in their oligomerization and phosphorylation status. These structural changes allow them to interact with many different client proteins that subsequently display modified activity and/or half-life. Nowdays, the protein interactomes of small Hsps are under intense investigations and will represent, when completed, key parameters to elaborate therapeutic strategies aimed at modulating the functions of these chaperones. Here, we have analyzed the potential pro-cancerous roles of several client proteins that have been described so far to interact with HspB1 (Hsp27) and its close members HspB5 (αB-crystallin) and HspB4 (αA-crystallin).

Regulation of embryonic stem cell pluripotency by heat shock protein 90

Deciphering the molecular basis of stem cell pluripotency is fundamental to the understanding of stem cell biology, early embryonic development, and to the clinical application of regenerative medicine. We report here that the molecular chaperone heat shock protein 90 (Hsp90) is essential for mouse embryonic stem cell (ESC) pluripotency through regulating multiple pluripotency factors, including Oct4, Nanog, and signal transducer and activator of transcription 3. Inhibition of Hsp90 by either 17-N-Allylamino-17-demethoxygeldanamycin or miRNA led to ESC differentiation. Overexpression of Hsp90β partially rescued the phenotype; in particular, the levels of Oct4 and Nanog were restored. Notably, Hsp90 associated with Oct4 and Nanog in the same cellular complex and protected them from degradation by the ubiquitin proteasome pathway, suggesting that Oct4 and Nanog are potential novel Hsp90 client proteins. In addition, Hsp90 inhibition reduced the mRNA level of Oct4, but not that of Nanog, indicating that Hsp90 participates in Oct4 mRNA processing or maturation. Hsp90 inhibition also increased expression of some protein markers for mesodermal lineages, implying that Hsp90 suppresses mesodermal differentiation from ESCs. These findings support a new role for Hsp90 in maintaining ESC pluripotency by sustaining the level of multiple pluripotency factors, particularly Oct4 and Nanog.

PTEN suppresses SPARC-induced pMAPKAPK2 and inhibits SPARC-induced Ser78 HSP27 phosphorylation in glioma

BACKGROUND

Secreted protein acidic and rich in cysteine (SPARC) is overexpressed in astrocytomas (World Health Organization grades II-IV). We previously demonstrated that SPARC promotes glioma migration and invasion-in part, by activating the P38 mitogen-activated protein kinase (MAPK)-heat shock protein (HSP)27 signaling pathway. The commonly lost tumor suppressor phosphatase and tensin homolog (PTEN) suppresses SPARC-induced migration, which is accompanied by suppression of Shc-Ras-Raf-MEK-ERK1/2 and Akt signaling. As PTEN completely suppresses SPARC-induced migration, we proposed that PTEN must also interfere with SPARC-induced HSP27 signaling. Therefore, this study determined the effects of PTEN expression on SPARC-induced expression and phosphorylation of HSP27.

METHODS

Control and SPARC-expressing clones transfected with control- or PTEN-expression plasmids were plated on fibronectin-coated tissue culture plates for 3, 6, 24, and 48 h and then lysed. Equal amounts of protein were subjected to Western blot and densitometric analyses.

RESULTS

The results show that SPARC enhances phosphorylated (p)P38 MAPK, phosphorylated MAPK-activated protein kinase 2 (pMAPKAPK2), and serine (Ser)78 HSP27 phosphorylation relative to total HSP27. PTEN suppresses pAkt and pMAPKAPK2, suggesting that PTEN effects are downstream of pP38 MAPK. PTEN suppressed SPARC-induced sustained phosphorylation at Ser78 HSP27. As the level of total HSP27 differed based on the presence of SPARC or PTEN, the ratios of phosphorylation-specific to total HSP27 were examined. The data demonstrate that SPARC-induced phosphorylation at Ser78 remains elevated despite increasing levels of total HSP27. In contrast, PTEN inhibits SPARC-induced increases in Ser78 HSP27 phosphorylation relative to total HSP27.

CONCLUSION

These data describe a novel mechanism whereby PTEN inhibits SPARC-induced migration through suppression and differential regulation of pAkt and the P38 MAPK-MAPKAPK2-HSP27 signaling pathway.

LEDGF gene silencing impairs the tumorigenicity of prostate cancer DU145 cells by abating the expression of Hsp27 and activation of the Akt/ERK signaling pathway

Lens epithelium-derived growth factor (LEDGF) maintains survival pathways by augmenting the transcription of stress-response genes such as small heat-shock protein 27. Recently, aberrant expression of LEDGF was found in prostate cancer (PC). Herein, we showed that LEDGF overexpression upregulated Hsp27 in PC cells, DU145, PC-3 and LNCaP and promoted antiapoptotic pathways in PCs. We found that these cells had higher abundance of Hsp27, which was correlated with the levels of LEDGF expression. Transactivation assay in DU145 cells revealed that transactivation of Hsp27 was related to the magnitude of LEDGF expression. Silencing of LEDGF in DU145 cells abrogated Hsp27 expression and inhibited stimulated cell proliferation, invasiveness and migration. These cells were arrested in S and G2 phase, and failed to accumulate cyclin B1, and showed increased apoptosis. Furthermore, LEDGF-depleted DU145 cells displayed elevated Bax and cleaved caspase 9 expression and reduced levels of Bcl2, Bcl-_XL. The activated survival pathway(s), ERK1/2 and Akt, were selectively decreased in these cells, which characteristically have lower tumorigenicity. Conversely, the depleted cells, when re-overexpressed with LEDGF or Hsp27, regained tumorigenic properties. Collectively, results reveal the involvement of LEDGF-mediated elevated expression of Hsp27-dependent survival pathway(s) in PC. Our findings suggest new lines of investigation aimed at developing therapies by targeting LEDGF or its aberrant expression-associated stimulated antiapoptotic pathway(s).

Suppression of heat shock protein 27 induces long-term dormancy in human breast cancer

The mechanisms underlying tumor dormancy have been elusive and not well characterized. We recently published an experimental model for the study of human tumor dormancy and the role of angiogenesis, and reported that the angiogenic switch was preceded by a local increase in VEGF-A and basic fibroblast growth factor. In this breast cancer xenograft model (MDA-MB-436 cells), analysis of differentially expressed genes revealed that heat shock protein 27 (HSP27) was significantly up-regulated in angiogenic cells compared with nonangiogenic cells. The effect of HSP27 down-regulation was further evaluated in cell lines, mouse models, and clinical datasets of human patients with breast cancer and melanoma. Stable down-regulation of HSP27 in angiogenic tumor cells was followed by long-term tumor dormancy in vivo. Strikingly, only 4 of 30 HSP27 knockdown xenograft tumors initiated rapid growth after day 70, in correlation with a regain of HSP27 protein expression. Significantly, no tumors escaped from dormancy without HSP27 expression. Down-regulation of HSP27 was associated with reduced endothelial cell proliferation and decreased secretion of VEGF-A, VEGF-C, and basic fibroblast growth factor. Conversely, overexpression of HSP27 in nonangiogenic cells resulted in expansive tumor growth in vivo. By clinical validation, strong HSP27 protein expression was associated with markers of aggressive tumors and decreased survival in patients with breast cancer and melanoma. An HSP27-associated gene expression signature was related to molecular subgroups and survival in breast cancer. Our findings suggest a role for HSP27 in the balance between tumor dormancy and tumor progression, mediated by tumor-vascular interactions. Targeting HSP27 might offer a useful strategy in cancer treatment.

HSP27 modulates survival signaling networks in cells treated with curcumin and TRAIL

The combination of curcumin and TRAIL and their role in enhancing apoptotic cell death has been reported by many studies. However, the exact molecular mechanism of apoptosis mediated by curcumin and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is not yet completely understood. In this study, we observed a close connection between dephosphorylated Akt and an increase in phosphorylated heat shock protein 27 (HSP27) during combined treatment with curcumin and TRAIL. Akt dephosphorylation was cumulatively regulated by protein phosphatase 1 (PP1), phosphoinositide-dependent kinase-1 (PDK1), and src. PP1 and PDK1 directly interacted with HSP27, whereas src indirectly interacted with HSP27 via the tumor necrosis factor receptor-associated factor 6 complex. In conclusion, HSP27 modulated cell survival by its interactions with various binding partners, depending on the level of phosphorylated HSP27.

Knock down of heat shock protein 27 (HspB1) induces degradation of several putative client proteins

Hsp27 belongs to the heat shock protein family and displays chaperone properties in stress conditions by holding unfolded polypeptides, hence avoiding their inclination to aggregate. Hsp27 is often referenced as an anti-cancer therapeutic target, but apart from its well-described ability to interfere with different stresses and apoptotic processes, its role in non-stressed conditions is still not well defined. In the present study we report that three polypeptides (histone deacetylase HDAC6, transcription factor STAT2 and procaspase-3) were degraded in human cancerous cells displaying genetically decreased levels of Hsp27. In addition, these proteins interacted with Hsp27 complexes of different native size. Altogether, these findings suggest that HDAC6, STAT2 and procaspase-3 are client proteins of Hsp27. Hence, in non stressed cancerous cells, the structural organization of Hsp27 appears to be a key parameter in the regulation by this chaperone of the level of specific polypeptides through client-chaperone type of interactions.

RP101 (brivudine) binds to heat shock protein HSP27 (HSPB1) and enhances survival in animals and pancreatic cancer patients

BACKGROUND

Several reports describe the importance of the chaperone HSP27 (HSPB1) in cancer progression, and the demand for drugs that modulate HSPB1-activity is increasing rapidly. We reported earlier that RP101 (Bromovinyldeoxyuridine, BVDU, Brivudine) improves the efficacy of chemotherapy in pancreatic cancer.

METHODS

Chemistry: Binding of RP101 and HSPB1 was discovered by affinity chromatography. Molecular and cell biology: HSPB1 in vitro transcription/translation (TNT), Pull down using RP101-coupled magnetic beads, Immuno Co-precipitations, Structural modeling of HSP27 (HSPB1), Introduction of point mutations into linear expression templates by PCR, Heat shock, Tumor Invasion. Animal experiments: Treatment of AH13r Sarcomas in SD-rats. Clinical Studies with late-stage pancreatic cancer patients: Pilot study, Dose finding study, Phase II study (NCT00550004).

RESULTS

Here, we report that RP101 binds in vitro to the heat shock protein HSPB1 and inhibits interaction with its binding partners. As a result, more activated CASP9 was detected in RP101-treated cancer cells. We modeled HSPB1-structure and identified the RP101 binding site. When we tested RP101 as an anti-cancer drug in a rat model, we found that it improved chemotherapy. In clinical studies with late-stage pancreatic cancer patients, the dose of 500 mg/day was safe and efficient, but 760 mg/day turned out to be too high for lightweight patients.

CONCLUSIONS

The development of RP101 as a cancer drug represents a truly novel approach for prevention of chemoresistance and enhancement of chemosensitivity.

Heat shock protein 27 phosphorylation: kinases, phosphatases, functions and pathology

The small heat shock protein Hsp27 or its murine homologue Hsp25 acts as an ATP-independent chaperone in protein folding, but is also implicated in architecture of the cytoskeleton, cell migration, metabolism, cell survival, growth/differentiation, mRNA stabilization, and tumor progression. A variety of stimuli induce phosphorylation of serine residues 15, 78, and 82 in Hsp27 and serines 15 and 86 in Hsp25. This post-translational modification affects some of the cellular functions of Hsp25/27. As a consequence of the functional importance of Hsp25/27 phosphorylation, aberrant Hsp27 phosphorylation has been linked to several clinical conditions. This review focuses on the different Hsp25/27 kinases and phosphatases that regulate the phosphorylation pattern of Hsp25/27, and discusses the recent findings of the biological implications of these phosphorylation events in physiological and pathological processes. Novel therapeutic strategies aimed at restoring anomalous Hsp27 phosphorylation in human diseases will be presented.

Hsp-27 expression at diagnosis predicts poor clinical outcome in prostate cancer independent of ETS-gene rearrangement

BACKGROUND

This study was performed to test the hypothesis that expression of small heat shock protein Hsp-27 is, at diagnosis, a reliable predictive biomarker of clinically aggressive prostate cancer.

METHODS

A panel of tissue microarrays constructed from a well-characterised cohort of 553 men with conservatively managed prostate cancer was stained immunohistochemically to detect Hsp-27 protein. Hsp-27 expression was compared with a series of pathological and clinical parameters, including outcome.

RESULTS

Hsp-27 staining was indicative of higher Gleason score (P<0.001). In tissue cores having a Gleason score >7, the presence of Hsp-27 retained its power to independently predict poor clinical outcome (P<0.002). Higher levels of Hsp-27 staining were almost entirely restricted to cancers lacking ERG rearrangements (chi2 trend=31.4, P<0.001), although this distribution did not have prognostic significance.

INTERPRETATION

This study has confirmed that, in prostate cancers managed conservatively over a period of more than 15 years, expression of Hsp-27 is an accurate and independent predictive biomarker of aggressive disease with poor clinical outcome (P<0.001). These findings suggest that apoptotic and cell-migration pathways modulated by Hsp-27 may contain targets susceptible to the development of biologically appropriate chemotherapeutic agents that are likely to prove effective in treating aggressive prostate cancers.

Knockdown of the co-chaperone Hop promotes extranuclear accumulation of Stat3 in mouse embryonic stem cells

A key event in the mechanism of mouse embryonic stem cell (mESC) pluripotency is phosphorylation, dimerisation and translocation to the nucleus of the signal transducer and activator of transcription3, Stat3. We used RNAi to suppress the levels of the co-chaperone Hsp70/Hsp90 organising protein (Hop) in an mESC line. Hop knockdown caused 68% depletion in Stat3 mRNA levels, decreased soluble pYStat3 levels, and led to an extranuclear accumulation of Stat3. The major binding partner of Hop, Hsp90, co-localised with a small non-nuclear fraction of Stat3 in mESCs, and both Stat3 and Hop co-precipitated with Hsp90. Hop knockdown did not affect Nanog and Oct4 protein levels; however, Nanog mRNA levels were decreased. We found that in the absence of Hop, mESCs lost their pluripotent ability to form embryoid bodies with a basement membrane. These data suggest that Hop facilitates the phosphorylation and nuclear translocation of Stat3, implying a role for the Hsp70/Hsp90 chaperone heterocomplex machinery in pluripotency signalling.

Mammalian plasma membrane proteomics

Plasma membrane proteins serve essential functions for cells, interacting with both cellular and extracellular components, structures and signaling molecules. Additionally, plasma membrane proteins comprise more than two-thirds of the known protein targets for existing drugs. Consequently, defining membrane proteomes is crucial to understanding the role of plasma membranes in fundamental biological processes and for finding new targets for action in drug development. MS-based identification methods combined with chromatographic and traditional cell-biology techniques are powerful tools for proteomic mapping of proteins from organelles. However, the separation and identification of plasma membrane proteins remains a challenge for proteomic technology because of their hydrophobicity and microheterogeneity. Creative approaches to solve these problems and potential pitfalls will be discussed. Finally, a representative overview of the impressive achievements in this field will also be given.

Phosphorylation of Ser78 of Hsp27 correlated with HER-2/neu status and lymph node positivity in breast cancer

Background

Abnormal amplification/expression of HER-2/neu oncogene has been causally linked with tumorigenesis and metastasis in breast cancer and associated with shortened overall survival of patients. Recently, heat shock protein 27 (Hsp27) was reported to be highly expressed in HER-2/neu positive tumors and cell lines. However, putative functional links between phosphorylation of Hsp27 with HER-2/neu status and other clinicopathological features remain to be elucidated.

Results

Comparative phosphoproteomic studies of HER-2/neu positive and -negative breast tumors revealed that Hsp27, one of the identified phosphoproteins, was highly phosphorylated in HER-2/neu positive tumors. The extent of Hsp27 phosphorylation at its Ser¹⁵, Ser⁷⁸ and Ser⁸² residues were further evaluated with site-specific antibodies in tumor samples by tissue lysate array- and tissue microarray-based analyses, and in the BT474 breast cancer cell line treated with heregulin α1 (HRG α1) or the p38 MAPK inhibitor, SB203580. The tissue lysate array study indicated that only the level of pSer⁷⁸ in HER-2/neu positive tumors was more than 2-fold that in HER-2/neu negative tumors. Treatment of BT474 cells with HRG α1 and SB203580 indicated that Ser⁷⁸ phosphorylation was mainly regulated by the HER-2/neu-p38 MAPK pathway. Immunohistochemical staining of sections from a tissue microarray with 97 breast tumors showed that positive staining of pSer⁷⁸ significantly correlated with HER-2/neu (p = 0.004) and lymph node positivity (p = 0.026).

Conclusion

This investigation demonstrated the significant correlation of enhanced phosphorylation of the Ser⁷⁸ residue of Hsp27 with HER-2/neu and lymph node positivity in breast cancer.

Proteomic analysis of liver cancer cells treated with suberonylanilide hydroxamic acid

PURPOSE

Suberonylanilide hydroxamic acid (SAHA) is an orally administered histone deacetylase inhibitor (HDACI) that has shown significant antitumor activity in a variety of tumor cells. To evaluate if SAHA has an activity against liver cancer, and with an aim to identify the altered cellular factors upon SAHA treatment, human HepG2 cancer cell line was used as a model, and proteomic approach was utilized to elucidate the molecular mechanisms underlying SAHA's antitumor activity.

METHODS

Cell growth inhibition was measured by MTT method, and apoptosis was detected by means of flow cytometry analysis and TUNEL assay. Protein expression profiles were analyzed by 2-DE coupled with MALDI-Q-TOF MS/MS analysis.

RESULTS

A total of 55 differentially expressed proteins were visualized by 2-DE and Coomassie Brilliant Blue (CBB) staining. Of these, 34 proteins were identified via MS/MS analysis. Among the identified proteins, six proteins also displayed significant expression changes at earlier time points upon SAHA treatment, and such alterations were further confirmed by semi-quantitative RT-PCR. Together, at both the mRNA and protein levels, SAHA suppressed the expression of reticulocalbin 1 precursor (RCN1), annexin A3 (ANXA3) and heat shock 27 kDa protein 1 (HSP27), while increasing the expression of aldose reductase (AR), triosephosphate isomerase 1 (TPI) and manganese superoxide dismutase (SOD2).

CONCLUSION

SAHA remarkably inhibited proliferation of HepG2 cancer cells, and induced apoptosis in vitro. Using proteomics approaches, a variety of differentially expressed proteins were identified in HepG2 cancer cells before and after treatment with SAHA. This study will enable a better understanding of the molecular mechanisms underlying SAHA-mediated antitumor effects at the protein level.

Hsp27 (HspB1) and alphaB-crystallin (HspB5) as therapeutic targets

Hsp27 and alphaB-crystallin are molecular chaperones that are constitutively expressed in several mammalian cells, particularly in pathological conditions. These proteins share functions as diverse as protection against toxicity mediated by aberrantly folded proteins or oxidative-inflammation conditions. In addition, these proteins share anti-apoptotic properties and are tumorigenic when expressed in cancer cells. This review summarizes the current knowledge about Hsp27 and alphaB-crystallin and the implications, either positive or deleterious, of these proteins in pathologies such as neurodegenerative diseases, myopathies, asthma, cataracts and cancers. Approaches towards therapeutic strategies aimed at modulating the expression and/or the activities of Hsp27 and alphaB-crystallin are presented.

Evaluation of anin vitro model of androgen ablation and identification of the androgen responsive proteome in LNCaP cells

Proteins responsive to androgen and anti-androgen may be involved in the development and progression of prostate cancer and the ultimate failure of androgen-ablation therapy. These proteins represent potential diagnostic and therapeutic targets for improved management of prostate cancer. We have investigated the effect of androgen (R1881) and anti-androgen (bicalutamide) on the androgen-responsive prostate cancer LNCaP cell line using a quantitative gel-based proteomic approach. Prior to analysis, the in vitro system was evaluated for reproducibility and validated by appropriate molecular responses to treatment. Six replicate samples were independently generated and analysed by 2-D DIGE. According to strict statistical criteria, 197 spots were differentially expressed, of which we have successfully identified 165 spots corresponding to 125 distinct proteins. Following androgen supplementation, 108 spots (68 proteins) were increased and 57 spots (39 proteins) were decreased. Essentially no difference was observed between control and anti-androgen-treated samples, confirming the absence of "off-target" effects of bicalutamide. Identified proteins were involved in diverse processes including the stress response and intracellular signalling. The potential contribution to disease of these processes and identified constituent proteins are discussed. This rigorous, statistically supported study of androgen responses has provided a number of potential candidates for development as diagnostic/prognostic markers and drug targets.

Use of magnetic beads with immobilized monoclonal antibodies for isolation of highly pure plasma membranes

In plasma membrane proteome research, contamination of the isolated plasma membrane fraction with proteins from other organelles is still a problem. Even if highly specific isolation methods are used, such as density gradient centrifugation combined with selective extraction, contaminating proteins cannot be completely removed. To solve this problem, a protocol for the isolation of highly pure plasma membrane fractions from rat liver and two different hepatocellular carcinoma cell lines was developed. Magnetic beads with immobilized mAb's against highly expressed membrane proteins were used for specific binding of membrane vesicles and their separation from other organelles. Isolated plasma membranes were further selectively solubilized with different reagents and analyzed by use of different methods, such as Western blotting, 1- and 2-DE, and MS. Purification and further selective solubilization was validated by use of mAb's against the marker integral plasma membrane protein carcinoembryonic antigen cell adhesion molecule 1, and identification of isolated proteins by MS. The method presented here minimizes contamination with other organelles and enables further identification of membrane proteins.

Heat shock proteins: endogenous modulators of apoptotic cell death

The highly conserved heat shock proteins (Hsps) accumulate in cells exposed to heat and a variety of other stressful stimuli. Hsps, that function mainly as molecular chaperones, allow cells to adapt to gradual changes in their environment and to survive in otherwise lethal conditions. The events of cell stress and cell death are linked and Hsps induced in response to stress appear to function at key regulatory points in the control of apoptosis. Hsps include anti-apoptotic and pro-apoptotic proteins that interact with a variety of cellular proteins involved in apoptosis. Their expression level can determine the fate of the cell in response to a death stimulus, and apoptosis-inhibitory Hsps, in particular Hsp27 and Hsp70, may participate in carcinogenesis. This review summarizes the apoptosis-regulatory function of Hsps.

Proteomic analysis in human breast cancer: Identification of a characteristic protein expression profile of malignant breast epithelium

Gene expression analysis has become a promising tool in predicting the clinical course of malignant disease and the response to antineoplastic therapy. Surprisingly, only little is known about the protein expression pattern of human tumors. Recent advances in proteomic analysis allow proteins of interest to be identified by their expression and/or modification pattern in 2-DE rather than using the traditional approach of translating gene expression data. To identify a proteomic pattern that is characteristic for malignant breast epithelium, we performed differential 2-DE analysis in sets of microdissected malignant breast epithelia and corresponding adjacent normal breast epithelia from five patients with invasive breast carcinoma. Thirty-two protein spots were found to be selectively regulated in malignant epithelium, and were subjected to MALDI-TOF and/or immunoblotting for protein identification. Thirteen of the identified proteins had previously not been associated with breast cancer. The validity of these findings was confirmed by literature review and immunohistochemistry for identified proteins in an independent cohort of 50 breast cancer specimens. We here describe, for the first time, a proteomic analysis of matched normal and malignant epithelia from invasive breast carcinomas. This strategy leads to a better understanding of oncogenesis at an operational level and helps to characterize the malignant phenotype of individual tumors, and thereby to identify novel targets for antineoplastic therapy.

Effects of sequential exposure to lipopolysaccharide and heat stress on dental pulp cells

In the present study, we examined the effects of sequential exposure to bacterial lipopolysaccharide (LPS) and heat stress on dental pulp cells. LPS induced the proliferation of pulp cells through the activation of p38 MAPK. HSP27 was expressed in cells with or without LPS during the entire period of heat stress, while transiently phosphorylated by short-term heat stress. In LPS-treated cells, short-term heat stress also induced the phosphorylation of HSF1. The immediate phosphorylation of HSF1 and HSP27 in LPS-treated cells by short-term heat stress occurred dependent on the activation of p38 MAPK. However, with long-term heat stress, the activation of HSF1 and induction of HSP27 occurred independent of p38 MAPK. Further, full activation of Akt in LPS-treated cells was immediately induced by short-term heat stress and lasted during the entire period of heat stress. IkappaB alpha was induced and phosphorylated throughout sequential exposure to LPS and heat stress. These results suggest that LPS has the unique effects on the cytoprotection and the cell death of pulp cells during heat stress through the modification and the activation of heat stress responsive molecules, HSF1 and HSP27, and cell survival molecules, Akt and NF-kappaB/IkappaB alpha.

Increased Hsp27 after androgen ablation facilitates androgen-independent progression in prostate cancer via signal transducers and activators of transcription 3-mediated suppression of apoptosis

One strategy to improve therapies in prostate cancer involves targeting cytoprotective genes activated by androgen withdrawal to delay the emergence of the androgen-independent (AI) phenotype. The objectives of this study were to define changes in Hsp27 levels after androgen ablation and to evaluate the functional relevance of these changes in AI progression. Using a tissue microarray of 232 specimens of hormone-naïve and post-hormone ablation-treated prostate cancer, we found that Hsp27 levels increase after androgen ablation to become highly expressed (>4-fold, P < or = 0.01) in AI tumors. Hsp27 overexpression rendered LNCaP cells highly resistant to androgen withdrawal both in vitro and in vivo. Tumor volume and serum prostate-specific antigen levels increased 4.3- and 10-fold faster after castration when Hsp27 was overexpressed. Treatment of LNCaP tumor cells in vitro with Hsp27 antisense oligonucleotides (ASO) or short-interfering RNA suppressed Hsp27 levels in a dose-dependent and sequence-specific manner increased the apoptotic sub-G0-G1 fraction and caspase-3 cleavage >2-fold, as well as decreased signal transducers and activators of transcription 3 (Stat3) levels and its downstream genes, c-fos and sPLA-2. The cytoprotection afforded by Hsp27 overexpression was attenuated by Stat3 knockdown using specific Stat3 ASO. Coimmunoprecipitation and immunofluorescence confirmed that Hsp27 interacts with Stat3 and that Stat3 levels correlated directly with Hsp27 levels. Hsp27 ASO treatment in athymic mice bearing LNCaP tumors significantly delayed LNCaP tumor growth after castration, decreasing mean tumor volume and serum prostate-specific antigen levels by 57% and 69%, respectively. These findings identify Hsp27 as a modulator of Stat3-regulated apoptosis after androgen ablation and as a potential therapeutic target in advanced prostate cancer.

Evaluation of potential Stat3-regulated genes in human breast cancer

The constitutive activation of signal transducer and activator of transcription 3 (Stat3) is frequently detected in breast cancer tissues and cell lines. Stat3 has been classified as a proto-oncogene, because an activated form of Stat3 can mediate oncogenic transformation in cultured cells and tumor formation in nude mice. Since Stat3 may play an important role in breast cancer, it is of interest to investigate the expression of phosphorylated Stat3, an activated form of Stat3, and its downstream mediators specifically in breast cancer, and to explore the possible mechanisms of Stat3 signaling pathway in oncogenesis of breast cancer. We analyzed Stat3 phosphorylation and expression of Stat3-regulated genes in breast cancer cell lines as well as invasive breast cancer tissues using tissue microarray slides. Our results showed that elevated levels of phosphorylation of Stat3 protein (Tyr705) were detected in 48 out of total 136 invasive breast tumors (35%) whereas normal breast tissues express much lower levels of Stat3 phosphorylation. The increased levels of Stat3 phosphorylation were associated with the metastasis in regional lymph nodes (P=0.042) and the expression of progesterone receptor (P=0.028) but not with distant metastasis, nor the expression of estrogen receptor. Our results also indicate that elevated levels of Stat3 phosphorylation were significantly associated with increased expression of potential downstream targets of Stat3 which include apoptosis inhibitors (Survivin, Mcl-1, HSP27, Adrenomedullin, and Bcl-xL), cell-cycle regulators (c-Fos, MEK5, and c-Myc), and inducer of tumor angiogenesis (VEGF, COX-2, MMP-2, MMP-10, and MMP-1) in invasive breast cancer tissues. Therefore, our findings suggest that constitutive Stat3 signaling may be one of the key upstream regulators to induce these downstream proteins, which may play important roles in Stat3-mediated oncogenesis in breast cancer.

A low-molecular-weight compound discovered through virtual database screening inhibits Stat3 function in breast cancer cells

This study focused on the screening of small-molecule inhibitors that target signal transducers and activators of transcription 3 (Stat3) in human breast carcinoma. The constitutive activation of Stat3 is frequently detected in human breast cancer cell lines as well as clinical breast cancer specimens and may play an important role in the oncogenesis of breast carcinoma. Activated Stat3 may participate in oncogenesis by stimulating cell proliferation, promoting tumor angiogenesis, and resisting apoptosis. Because a variety of human cancers are associated with constitutively active Stat3, Stat3 represents an attractive target for cancer therapy. In this study, of the nearly 429,000 compounds screened by virtual database screening, chemical samples of top 100 compounds identified as candidate small-molecule inhibitors of Stat3 were evaluated by using Stat3-dependent luciferase reporter as well as other cell-based assays. Through serial functional evaluation based on our established cell-based assays, one compound, termed STA-21, was identified as the best match for our selection criteria. Further investigation demonstrated that STA-21 inhibits Stat3 DNA binding activity, Stat3 dimerization, and Stat3-dependent luciferase activity. Moreover, STA-21 reduces the survival of breast carcinoma cells with constitutive Stat3 signaling but has minimal effect on the cells in which constitutive Stat3 signaling is absent. Together, these results demonstrate that STA-21 inhibits breast cancer cells that express constitutively active Stat3.

Characterization of heat shock protein 27 phosphorylation sites in renal cell carcinoma

The phosphorylation of heat shock protein 27 (HSP27) occurs differently in human renal cell carcinoma (RCC) compared to homologous normal kidney tissue. Two-dimensional electrophoresis was used to separate and visualize HSP27, via immunostaining with anti-HSP27 antibody, in tumor and normal renal samples, obtained after surgery resection from patients with RCC. The mean number of protein species was 21 in RCC and 15 in normal tissues. Selected spots were in-gel digested with trypsin, extracted and analyzed by microcapillary liquid chromatography (LC) electrospray ionization tandem mass spectrometry to confirm HSP27 protein identity and reveal phosphorylation sites. Loss of phosphopeptides due to extensive plumbing and/or metal components in automated LC-systems was limited by manual loading of samples directly onto the LC system using a homemade pressure vessel. Mass spectrometry (MS) analysis revealed that in three of the HSP27 protein species phosphorylation occurred at Serine 15 and in five at Serine 82 in a different pattern. The phosphorylation of Serine 15 and 82 was also investigated by immunohistochemistry on tissue sections. The data obtained using anti-HSP27Serine82phos-antibody are consistent with MS results, while the variance between results achieved by anti-HSP27Serine15phos-antibody and by MS is probably due to the low specificity of the antibody. Knowledge of the diversity and modulation of HSP27 phosphorylation protein species might represent useful markers involved in the differentiation of RCC.

Stat3 upregulates MEK5 expression in human breast cancer cells

The constitutive activation of signal transducer and activator of transcription 3 (Stat3) is frequently detected in breast cancer cell lines but not in normal breast epithelial cells. Stat3 has been classified as an oncogene, because constitutively active Stat3 can mediate oncogenic transformation in cultured cells and tumor formation in nude mice. Since Stat3 appears to play an important role in breast cancer, it is of interest to investigate Stat3-regulated genes and elucidate Stat3-mediated oncogenesis. In this study, we investigated the Stat3-regulated genes in human breast epithelial cells. Upon overexpression of Stat3-C, a constitutively active Stat3 form, in nonmalignant telomerase immortalized breast (TERT) cells, the total mRNA was extracted and subjected to Affymetrix microarray analysis. Our results showed that mitogen-activated protein kinase kinase 5 (MEK5) was markedly induced (more than 22-fold increase, P<0.001) by Stat3-C expression. RT-PCR result also demonstrated that MEK5 mRNA was significantly induced by Stat3-C in TERT cells. The upregulation of MEK5 by Stat3-C was further confirmed by Western blot in MCF10A breast epithelial cells. Furthermore, in MDA-MB-435s breast carcinoma cells, which express high levels of activated Stat3 and MEK5, MEK5 protein was significantly reduced by using Stat3 short interfering RNA. The reduction of MEK5 was consistent with Stat3 knockdown in this breast carcinoma cell line. We also investigated MEK5 expression in different breast carcinoma cell lines and breast cancer tissues using tissue array analysis. Compared with nonmalignant breast epithelial cells or normal tissues without constitutively active Stat3 signaling, MEK5 protein levels are remarkably higher in breast carcinoma cell lines and cancer tissues with constitutively activated Stat3. Taken together, our findings suggest that constitutively active Stat3 upregulates MEK5 in the breast epithelial cells. MEK5 may be one of the Stat3-regulated genes and plays its essential roles in oncogenesis mediated by aberrantly activated Stat3 signaling in breast carcinomatosis and malignancies.