Cytoprotective effects of acidosis via heat shock protein HSP27 against the anticancer drug doxorubicin

Proteomic Profiling and Pathway Analysis of Acid Stress-Induced Vasorelaxation of Mesenteric Arteries In Vitro

Although metabolic acidosis is associated with numerous pathophysiological conditions and its vasorelaxation effects have been well described in different animal and culture models, the molecular mechanisms of acidosis-induced vasorelaxation are not fully understood. Mesenteric artery models have been used extensively to examine the vascular response to various pathophysiological conditions. Our previous studies and several other reports have suggested the vascular responses of goat mesenteric arteries and human arteries to various stimuli, including acidic stress, are highly similar. In this study, to further identify the signaling molecules responsible for altered vasoreactivity in response to acidic pH, we examined the proteomic profile of acid stress-induced vasorelaxation using a goat mesenteric artery model. The vascular proteomes under acidic pH were compared using 2D-GE with 7 cm IPG strips and mini gels, LC-MS/MS, and MALDI TOF MS. The unique proteins identified by mass spectroscopy were actin, transgelin, WD repeat-containing protein 1, desmin, tropomyosin, ATP synthase β, Hsp27, aldehyde dehydrogenase, pyruvate kinase, and vitamin K epoxide reductase complex subunit 1-like protein. Out of five protein spots identified as actin, three were upregulated > 2-fold. ATP synthase β was also upregulated (2.14-fold) under acid stress. Other actin-associated proteins upregulated were transgelin, desmin, and WD repeat-containing protein 1. Isometric contraction studies revealed that both receptor-mediated (histamine) and non-receptor-mediated (KCl) vasocontraction were attenuated, whereas acetylcholine-induced vasorelaxation was augmented under acidosis. Overall, the altered vasoreactivity under acidosis observed in the functional studies could possibly be attributed to the increase in expression of actin and ATP synthase β.

Effects of extracellular acidity on resistance to chemotherapy treatment: a systematic review

Metabolic alterations in the tumor microenvironment have a complex effect on cancer progression. Extracellular acidity is a consequence of metabolic switch in cancer and results in cell phenotypes with higher resistance to chemotherapeutics. However, mechanisms underlying the relationship between the extracellular acidity and chemoresistance are not clearly understood. This systematic review was carried out by searching the databases PubMed and EMBASE using the keywords "cancer" and "acidosis" or "acidic" and "chemoresistance" or "drug resistance." In vitro and in vivo studies that evaluated the effects of acidification of the tumor microenvironment on chemotherapeutic treatments were included. Literature reviews, letters to the editor, and articles that were not published in English were excluded. The search resulted in a total of 352 articles. After discarding 75 duplicate references, 277 articles were analyzed by sequentially reading through their titles, abstracts, and finally full-text. A total of 14 articles was selected. Acidification of the tumor microenvironment can trigger resistance through different mechanisms, such as increase in drug efflux transporters, inhibition of proton pumps, induction of the unfolded protein response (UPR), and cellular autophagy.

pH-dependent structural modulation is conserved in the human small heat shock protein HSBP1

The holdase activity and oligomeric propensity of human small heat shock proteins (sHSPs) are regulated by environmental factors. However, atomic-level details are lacking for the mechanisms by which stressors alter sHSP responses. We previously demonstrated that regulation of HSPB5 is mediated by a single conserved histidine over a physiologically relevant pH range of 6.5-7.5. Here, we demonstrate that HSPB1 responds to pH via a similar mechanism through pH-dependent structural changes that are induced via protonation of the structurally analogous histidine. Results presented here show that acquisition of a positive charge, either by protonation of His124 or its substitution by lysine, reduces the stability of the dimer interface of the α-crystallin domain, increases oligomeric size, and modestly increases chaperone activity. Our results suggest a conserved mechanism of pH-dependent structural regulation among the human sHSPs that possess the conserved histidine, although the functional consequences of the structural modulations vary for different sHSPs.

Troponins, heat shock proteins and glycogen phosphorylase BB in umbilical cord blood of complicated pregnancies

PURPOSE OF THE STUDY

Heat shock proteins (Hsp) are evolutionary conserved molecules with a chaperone role in cell survival. We hypothesized that cord blood concentrations of molecules reflecting fetal cardiac muscle insult, including Hsp, troponins cTnI and cTnT, and glycol-phosphorylase BB (GP-BB) would be elevated in pregnancies complicated by gestational diabetes (GDM) or preeclampsia (PIH) compared to healthy controls.

MATERIALS AND METHODS

Pregnant women admitted for delivery at >28 weeks were divided into four groups: healthy patients delivered vaginally (VAG), healthy patients delivered by c-section (CS), patients with PIH, and patients with GDM. Demographics, clinical characteristics, and cord blood concentrations of Hsp, troponins cTnI and cTnT, and GP-BB were compared between groups. Statistical analyses included t-test, Chi square, and Wilcoxon rank sum as appropriate.

RESULTS

cTnI concentrations were significantly higher in the PIH group compared to the GDM and VAG groups and they were higher in the CS group compared to the VAG group. Concentrations of Hsp70 were higher in the GDM group compared to the VAG and CS groups. Concentration of GP-BB was higher in the PIH group compared to the VAG group.

CONCLUSIONS

GP-BB and cTNI are the most sensitive markers for PIH-related fetal myocyte injury as is Hsp70 in pregnancies complicated by GDM.

Glucose-regulated protein 78 (Grp78) confers chemoresistance to tumor endothelial cells under acidic stress

OBJECTIVES

This study was designed to investigate the activation of the unfolded protein response (UPR) in tumor associated endothelial cells (TECs) and its association with chemoresistance during acidic pH stress.

MATERIALS AND METHODS

Endothelial cells from human oral squamous cell carcinomas (OSCC) were excised by laser capture microdissection (LCM) followed by analysis of UPR markers (Grp78, ATF4 and CHOP) using quantitative PCR. Grp78 expression was also determined by immunostaining. Acidic stress was induced in primary human dermal microvascular endothelial cells (HDMECs) by treatment with conditioned medium (CM) from tumor cells grown under hypoxic conditions or by adjusting medium pH to 6.4 or 7.0 using lactic acid or hydrochloric acid (HCl). HDMEC resistance to the anti-angiogenic drug Sunitinib was assessed with SRB assay.

RESULTS

UPR markers, Grp78, ATF4 and CHOP were significantly upregulated in TECs from OSCC compared to HDMECs. HDMECs cultured in acidic CM (pH 6.0-6.4) showed increased expression of the UPR markers. However, severe acidosis led to marked cell death in HDMECs. Alternatively, HDMECs were able to adapt when exposed to chronic acidosis at pH 7.0 for 7 days, with concomittant increase in Grp78 expression. Chronic acidosis also confers drug resistance to HDMECs against Sunitinib. Knockdown of Grp78 using shRNA resensitizes HDMECs to drug treatment.

CONCLUSIONS

UPR induction in ECs under acidic pH conditions is related to chemoresistance and may contribute to therapeutic failures in response to chemotherapy. Targeting Grp78, the key component of the UPR pathway, may provide a promising approach to overcome ECs resistance in cancer therapy.

SB202190-induced cell type-specific vacuole formation and defective autophagy do not depend on p38 MAP kinase inhibition

SB202190, a widely used inhibitor of p38 MAPKα and β, was recently described to induce autophagic vacuoles and cell death in colon and ovarian cancer cells lines and, therefore, this effect was supposed to be specific for transformed cells and to open therapeutic options. Here, we demonstrate that SB202190 and the structurally related inhibitor SB203580 induce pro-autophagic gene expression and vacuole formation in various cancer and non-cancer cell lines of human, rat, mouse and hamster origin. This effect seems to induce defective autophagy leading to the accumulation of acidic vacuoles, p62 protein and lipid conjugated LC3. Using further p38 inhibitors we show that p38 MAPK inhibition is not sufficient for the autophagic response. In line with these results, expression of a SB202190-resistant mutant of p38α, which significantly increases activity of the p38 pathway under inhibitory conditions, does not block SB202190-dependent vacuole formation, indicating that lack of p38α activity is not necessary for this effect. Obviously, the induction of autophagic vacuole formation by SB203580 and SB202190 is due to off-target effects of these inhibitors on post-translational protein modifications, such as phosphorylation of the MAPKs ERK1/2 and JNK1/2, ribosomal protein S6, and PKB/Akt. Interestingly, the PI3K-inhibitor wortmannin induces transient vacuole formation indicating that the PI3K-PKB/Akt-mTOR pathway is essential for preventing autophagy and that cross-inhibition of this pathway by SB202190 could be the reason for the early part of the effect observed.