Analysis of protein expression regulated by lumican in PANC-1 cells using shotgun proteomics

The Novel SLRP Family Member Lumican Suppresses Pancreatic Cancer Cell Growth

OBJECTIVES

The past studies clearly indicated that lumican was important in the context of pancreatic cancer (PC) onset and progression, but failed to clarify the underlying mechanistic basis for such activity. As such, we evaluated the functional importance of lumican in the context of pancreatic ductal adenocarcinoma (PDAC) to understand its mechanistic role in PC.

METHODS

Lumican levels were evaluated in PDAC patient tissues via quantitative real-time polymerase chain reaction, Western blotting, and immunohistochemistry approaches. The role of lumican was additionally assessed via transfecting PDAC cell lines (BxPC-3, PANC-1) with lumican knockdown or overexpression constructs and treating PDAC cell lines with exogenous recombinant human lumican.

RESULTS

Lumican expression levels were significantly higher in pancreatic tumor tissues relative to healthy paracancerous tissues. Lumican knockdown in BxPC-3 and PANC-1 enhanced their proliferation and migration, but reduced cellular apoptosis. Alternatively, lumican overexpression and exogenous lumican exposure failed to alter the proliferative activity of these cells. Further, lumican knockdown in BxPC-3 and PANC-1 cells results in marked P53 and P21 dysregulation.

CONCLUSIONS

Lumican may suppress PDAC tumor growth by regulating P53 and P21, and the function of lumican sugar chains in the context of PC is worth studying in future studies.

Retinal proteomic evaluation of rats following streptozotocin‑injection using shotgun proteomics

It is important to elucidate how retinal stimulation leads to retinal protection and dysfunction. The current study aimed to identify factors that are up‑ and downregulated in the retinas of streptozotocin (STZ)‑induced diabetic rats with acute retinal dysfunction. Retinal function was measured and changes in protein expressions were determined using electroretinograms (ERGs) and liquid chromatography/mass spectroscopy‑based shotgun proteomics, respectively. The results revealed that the plasma glucose levels of STZ rats were markedly higher when compared with normal rats. Furthermore, levels of a‑waves, b‑waves and oscillatory potential amplitudes on ERGs in STZ rats were decreased compared with healthy animals. With use of shotgun proteomics, 391 proteins were identified in the retinas of normal rats and 541 proteins were found in the retinas of STZ rats. Of the 560 proteins identified in rat retinas, 372 (66.4%) were present in both normal and STZ rats. Of these, 19 (3.39%) were unique to normal rats and 169 (30.1%) were unique to STZ rats. Gene Ontology analysis was performed on the candidate proteins that were differentially regulated in the retinas of STZ rats and focused on those classified as 'protein binding', which serve important roles in retinal neurodegeneration. The results revealed an excessive expression of retinol‑binding protein 1 (RBP1) and a negative expression of rod outer segment membrane protein 1 (Rom-1) in the retinas of STZ rats. Therefore, retinal function may be decreased with STZ‑induced injury, and expressions of Rom‑1 and RBP1 may be altered in the retinas of STZ rats.

A Proteomic Approach for Understanding the Mechanisms of Delayed Corneal Wound Healing in Diabetic Keratopathy Using Diabetic Model Rat

Diabetes mellitus is a widespread metabolic disorder, and long-term hyperglycemia in diabetics leads to diabetic keratopathy. In the present study, we used a shotgun liquid chromatography/mass spectrometry-based global proteomic approach using the cornea of streptozotocin-induced diabetic (STZ) rats to examine the mechanisms of delayed corneal wound healing in diabetic keratopathy. Applying a label-free quantitation method based on spectral counting, we identified 188 proteins that showed expression changes of >2.0-fold in the cornea of STZ rats. In particular, the level of lumican expression in the cornea of STZ rats was higher than that of the normal rats. In the cornea of the normal rat, the expression level of lumican was elevated during the wound healing process, and it returned to the same expression level as before cornea injury after the wound was healed completely. On the other hand, a high expression level of lumican in the cornea of STZ rats was still maintained even after the wound was healed completely. In addition, adhesion deficiency in corneal basal cells and Bowman’s membrane was observed in the STZ rat. Thus, abnormally overexpressed lumican may lead to adhesion deficiency in the cornea of STZ rats.

Shotgun label-free proteomic analysis for identification of proteins in HaCaT human skin keratinocytes regulated by the administration of collagen from soft-shelled turtle

Soft‐shelled turtles (Pelodiscus sinensis) are widely distributed in some Asian countries, and we previously reported that soft‐shelled turtle tissue could be a useful material for collagen. In the present study, we performed shotgun liquid chromatography (LC)/mass spectrometry (MS)‐based global proteomic analysis of collagen‐administered human keratinocytes to examine the functional effects of collagen from soft‐shelled turtle on human skin. Using a semiquantitative method based on spectral counting, we were able to successfully identify 187 proteins with expression levels that were changed more than twofold by the administration of collagen from soft‐shelled turtle. Based on Gene Ontology analysis, the functions of these proteins closely correlated with cell–cell adhesion. In addition, epithelial–mesenchymal transition was induced by the administration of collagen from soft‐shelled turtle through the down‐regulation of E‐cadherin expression. Moreover, collagen‐administered keratinocytes significantly facilitated wound healing compared with nontreated cells in an in vitro scratch wound healing assay. These findings suggest that collagen from soft‐shelled turtle provides significant benefits for skin wound healing and may be a useful material for pharmaceuticals and medical care products. © 2017 The Authors Journal of Biomedical Materials Research Part B: Applied Biomaterials Published by Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2403–2413, 2018.

CLDN6 promotes chemoresistance through GSTP1 in human breast cancer

BACKGROUND

Claudin-6 (CLDN6), a member of CLDN family and a key component of tight junction, has been reported to function as a tumor suppressor in breast cancer. However, whether CLDN6 plays any role in breast cancer chemoresistance remains unclear. In this study, we investigated the role of CLDN6 in the acquisition of chemoresistance in breast cancer cells.

METHODS

We manipulated the expression of CLDN6 in MCF-7 and MCF-7/MDR cells with lv-CLDN6 and CLDN6-shRNA and investigated whether CLDN6 manipulation lead to different susceptibilities to several chemotherapeutic agents in these cells. The cytotoxicity of adriamycin (ADM), 5-fluorouracil (5-FU), and cisplatin (DDP) was tested by cck-8 assay. Cell death was determined by DAPI nuclear staining. The enzyme activity of glutanthione S-transferase-p1 (GSTP1) was detected by a GST activity kit. Then lv-GSTP1 and GSTP1-shRNA plasmids were constructed to investigate the potential of GSTP1 in regulating chemoresistance of breast cancer. The TP53-shRNA was adopted to explore the regulation mechanism of GSTP1. Finally, immunohistochemistry was used to explore the relationship between CLDN6 and GSTP1 expression in breast cancer tissues.

RESULTS

Silencing CLDN6 increased the cytotoxicity of ADM, 5-FU, and DDP in MCF-7/MDR cells. Whereas overexpression of CLDN6 in MCF-7, the parental cell line of MCF-7/MDR expressing low level of CLDN6, increased the resistance to the above drugs. GSTP1 was upregulated in CLDN6-overexpressed MCF-7 cells. RNAi -mediated silencing of CLDN6 downregulated both GSTP1 expression and GST enzyme activity in MCF-7/MDR cells. Overexpresssion of GSTP1 in CLDN6 silenced MCF-7/MDR cells restored chemoresistance, whereas silencing GSTP1 reduced the chemoresistance due to ectopic overexpressed of CLDN6 in MCF-7 cells. These observations were also repeated in TNBC cells Hs578t. We further confirmed that CLDN6 interacted with p53 and promoted translocation of p53 from nucleus to cytoplasm, and both the expression and enzyme activity of GSTP1 were regulated by p53. Clinicopathologic analysis revealed that GSTP1 expression was positively associated with CLDN6 in human breast cancer samples.

CONCLUSION

High expression of CLDN6 confers chemoresistance on breast cancer which is mediated by GSTP1, the activity of which is regulated by p53. Our findings provide a new insight into mechanisms and strategies to overcome chemoresistance in breast cancer.

Recent advances in proteomic profiling of pancreatic ductal adenocarcinoma and the road ahead

INTRODUCTION

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest cancers worldwide. However, there remain many unmet clinical needs, from diagnosis to treatment strategies. The inherent complexity of the molecular characteristics of PDAC has made it difficult to meet these challenges, rendering proteomic profiling of PDAC a critical area of research. Area covered: In this review, we present recent advances in mass spectrometry (MS) and its current application in proteomic studies on PDAC. In addition, we discuss future directions for research that can efficiently incorporate current MS-based technologies that address key issues of PDAC proteomics. Expert commentary: Compared with other cancer studies, little progress has been made in PDAC proteomics, perhaps attributed to the difficulty in performing in-depth and large-scale clinical studies on PDAC. However, recent advances in mass spectrometry can advance PDAC proteomics past the fundamental research stage.

Proteomic profile of the lens in a streptozotocin-induced diabetic rat model using shotgun proteomics

Streptozotocin (STZ)-induced diabetic rats (STZ rats) were used to investigate diabetic cataracts. In the current study, a shotgun liquid chromatography (LC)/mass spectrometry (MS)-based global proteomic analysis method was used to examine the mechanism of lens opacification as a result of hyperglycemia in STZ rats. The 6-week old Wistar rats were injected with STZ for 2 days (100 mg/kg/day, i.p.) and housed for 3 weeks. The plasma glucose levels were identified to be significantly higher when compared with the normal rats and insulin was not detected in the STZ rats. Furthermore, opacification of the cortical epithelium was observed in the lenses of STZ rats. A total of 235 proteins were identified in the lenses of the STZ rats and 229 in the lenses of the normal rats. A label-free semi-quantitative method, based on spectral counting, identified 52 proteins that were differentially expressed in the lenses of STZ rats compared with normal rats. In particular, superoxide dismutase, which is a critical antioxidant enzyme that detoxifies superoxide through redox cycling, was downregulated when analyzed by the semi-quantitative method. In addition, phosphorylated-p38, which is important in the signaling pathway involved in the oxidative stress response, was significantly increased in the lenses of STZ rats when compared with normal rats (P<0.05). Thus, the changes in protein expression were evaluated in the lenses of STZ rats using a shotgun LC/MS-based global proteomic analysis approach, and a decrease in antioxidant enzymes and an increase in oxidative stress were identified in the lenses of STZ rats. Further studies are required to examine the role of these proteins in the onset or progression of diabetic cataracts.

FMISO accumulation in tumor is dependent on glutathione conjugation capacity in addition to hypoxic state

OBJECTIVE

¹⁸F-fluoromisonidazole (FMISO), a well-known PET imaging probe for diagnosis of hypoxia, is believed to accumulate in hypoxic cells via covalent binding with macromolecules after reduction of the nitro group. Previously, we showed the majority of ¹⁸F-FMISO was incorporated into low-molecular-weight metabolites in hypoxic tumors, and the glutathione conjugate of reduced FMISO (amino-FMISO-GS) distributed in the tumor hypoxic regions as revealed by imaging mass spectrometry (IMS). The present study was conducted to clarify whether FMISO is metabolized to amino-FMISO-GS within tumor cells and how amino-FMISO-GS contributes to FMISO accumulation in hypoxic cells. We also evaluated the relationship between FMISO accumulation and the glutathione conjugation-related factors in the cells.

METHODS

Tumor cells (FaDu, LOVO, and T24) were treated with ¹⁸F-FMISO and incubated under normoxic or hypoxic conditions for 4 h. The FMISO metabolites were analyzed with LC-ESI-MS. Several glutathione conjugation-related factors of tumor cells were evaluated in vitro. FaDu tumor-bearing mice were intravenously injected with ¹⁸F-FMISO and the tumors were excised at 4 h post-injection. Autoradiography, IMS and histologic studies were performed.

RESULTS

Amino-FMISO-GS was the main contributor to FMISO incorporated in hypoxic FaDu cells in vitro and in vivo. Total FMISO uptake levels and amino-FMISO-GS levels were highest in FaDu, followed by LOVO, and then T24 (total uptake: 0.851 ± 0.009 (FaDu), 0.617 ± 0.021 (LOVO) and 0.167 ± 0.006 (T24) % dose/mg protein; amino-FMISO-GS: 0.502 ± 0.035 (FaDu), 0.158 ± 0.013 (LOVO), and 0.007 ± 0.001 (T24) % dose/mg protein). The glutathione level of FaDu was significantly higher than those of LOVO and T24. The enzyme activity of glutathione-S-transferase catalyzing the glutathione conjugation reaction in FaDu was similar levels to that in LOVO, and was higher than that in T24. Quantitative RT-PCR analysis revealed that the expression levels of efflux transporters of the glutathione conjugate (multidrug resistance-associated protein 1) were lowest in FaDu, followed by LOVO, and then T24.

CONCLUSIONS

FMISO accumulates in hypoxic cells through reductive metabolism followed by glutathione conjugation. We illustrated the possibility that increased production and decreased excretion of amino-FMISO-GS contribute to FMISO accumulation in tumor cells under hypoxic conditions.

Cystatin B as a potential diagnostic biomarker in ovarian clear cell carcinoma

Epithelial ovarian cancer (EOC) consists of four major subtypes: clear cell carcinoma (CCC), endometrioid adenocarcinoma (EA), mucinous adenocarcinoma (MA) and serous adenocarcinoma (SA). Relative to the other subtypes, the prognosis of CCC is poor due to a high recurrence rate and chemotherapy resistance, but CCC-specific biomarkers have yet to be identified. With the aim of identifying diagnostic and treatment biomarkers for CCC, we analyzed 96 cases of EOC (32 CCC, 13 EA, 19 MA, 32 SA) using liquid chromatography/mass spectrometry (LC/MS) followed by immunohistochemistry (IHC) and quantitative reverse transcription PCR (RT-qPCR). Semi-quantification of protein differences between subtypes showed upregulation of 150 proteins and downregulation of 30 proteins in CCC relative to the other subtypes. Based on hierarchical clustering that revealed a marked distinction in the expression levels of cystatin B (CYTB) and Annexin A4 (ANXA4) in CCC relative to the other subtypes, we focused the study on CYTB and ANXA4 expression in EOCs by IHC, RT-qPCR and western blot analyses using tissue specimens and cultured cells. As a result, compared to the other subtypes, CCC showed significantly high expression levels of CYTB and ANXA4 in the analyses. To examine the possibility of CYTB and ANXA4 as serum diagnostic biomarkers of CCC, we checked the protein levels in conditioned media and cell lysates using culture cells. Compared with the other subtypes, CCC cell lines showed a significantly higher level of expression of CYTB in both conditioned media and cell lysates, while ANXA4 showed a higher level of expression in cell lysates only. Our results demonstrate that CYTB and ANXA4 overexpression may be related to carcinogenesis and histopathological differentiation of CCC. CYTB may be a secreted protein, and may serve as a potential serum diagnostic biomarker of CCC, while ANXA4 may be useful as an intracellular marker.