The role of glutathione S-transferase P1-1 in colorectal cancer: friend or foe?

Mass Spectrometry: A Powerful Method for Monitoring Various Type of Leukemia, Especially MALDI-TOF in Leukemia's Proteomics Studies Review

Recent success in studying the proteome, as a source of biomarkers, has completely changed our understanding of leukemia (blood cancer). The identification of differentially expressed proteins, such as relapse and drug resistance proteins involved in leukemia by using various ionization sources and mass analyzers of mass spectrometry techniques, has helped scientists find better diagnosis, prognosis, and treatment strategies. With the aid of this powerful analytical technique, we can investigate the qualification/quantification of proteins, protein-protein interactions, post-translational modifications, and find the correlation between proteins and their genes with the hope of finding the missing parts of the successful therapy puzzle. In this review, we followed different MS sources and analyzers which used for monitoring various type of leukemia, then focused on MALDI-TOF MS as a quick and reliable method for studying proteins. Due to several review published for other techniques, the present review is the first work in this field. Also, by classifying more than 400 proteins, we have found 42 proteins are involved in two or three different stages of leukemia. Finally, we have suggested six specific biomarkers for AML, one for ALL, three biomarkers with a role in the etiology of leukemia and 13 markers with the potential for further studies.

Modulation of cell death in human colorectal and breast cancer cells through a manganese chelate by involving GSH with intracellular p53 status

Chemotherapy is central to current treatment modality especially for advanced and metastatic colorectal and breast cancers. Targeting the key molecular events of the neoplastic cells may open a possibility to treat cancer. Although some improvements in understanding of colorectal and breast cancer treatment have been recorded, the involvement of glutathione (GSH) and dependency of p53 status on the modulation of GSH-mediated treatment efficacy have been largely overlooked. Herein, we tried to decipher the underlying mechanism of the action of Mn-N-(2-hydroxyacetophenone) glycinate (MnNG) against differential p53 status bearing Hct116, MCF-7, and MDA-MB-468 cells on the backdrop of intracellular GSH level and reveal the role of p53 status in modulating GSH-dependant abrogation of MnNG-induced apoptosis in these cancer cells. Present study discloses that MnNG targets specifically wild-type-p53 expressing Hct116 and MCF-7 cells by significantly depleting both cytosolic, mitochondrial GSH, and modulating nuclear GSH through Glutathione reductase and Glutamate-cysteine ligase depletion that may in turn induce p53-mediated intrinsic apoptosis in them. Thus GSH addition abrogates p53-mediated apoptosis in wild-type-p53 expressing cells. GSH addition also overrides MnNG-induced modulation of phase II detoxifying parameters in them. However, GSH addition partially replenishes the down-regulated or modulated GSH pool in cytosol, mitochondria, and nucleus, and relatively abrogates MnNG-induced intrinsic apoptosis in p53-mutated MDA-MB-468 cells. On the contrary, although MnNG induces significant cell death in p53-null Hct116 cells, GSH addition fails to negate MnNG-induced cell death. Thus p53 status with intracellular GSH is critical for the modulation of MnNG-induced apoptosis.

Response of glutathione S-transferase Pi (GSTP1) to neoadjuvant therapy in rectal adenocarcinoma

AIM

The response of rectal adenocarcinoma to neoadjuvant therapy is variable. Accurate prediction of response would enable selective administration of therapy. The enzyme glutathione S-transferase Pi (GSTP1) has been shown to influence response to therapy in some solid tumours. Few data are available for rectal cancer.

METHOD

The GSTP1 levels in rectal adenocarcinoma and adjacent normal mucosa were quantified before and after exposure to neoadjuvant therapy. Venous blood samples and biopsies of normal rectal mucosa and tumour were prospectively obtained from patients with primary rectal cancer. Patients were stratified by exposure to neoadjuvant therapy or surgery alone. GSTP1 was quantitatively measured using an enzyme-linked immunosorbent assay.

RESULTS

Ninety-two patients (54 men; median age 68 years) were recruited. The median GSTP1 level was significantly higher in rectal adenocarcinoma than in matched normal mucosa [6.59 μg/mg vs 4.57 μg/mg; P < 0.001]. The median tumour GSTP1 level was significantly lower in the therapy group compared with unmatched samples from the no-therapy group [4.47 μg/mg vs 7.76 μg/mg; P < 0.001].

CONCLUSION

The GSTP1 level is increased in rectal adenocarcinoma compared with adjacent normal mucosa. It decreases following neoadjuvant therapy. Future studies correlating pre-therapy GSTP1 levels with pathological response would be of interest.

Serum glutathione transferase does not respond to indole-3-carbinol: A pilot study

Background:

Despite the well recognized protective effect of cruciferous vegetables against various cancers, including human colorectal cancers, little is known about how this effect is conferred. It is thought that some phytochemicals found only in these vegetables confer the protection. These compounds include the glucosinolates, of which indole-3-carbinol is one. They are known to induce carcinogen-metabolizing (phase II) enzymes, including the glutathione S-transferase (GST) family. Other effects in humans are not well documented. We wished to assess the effect of indole-3-carbinol on GST enzymes.

Methods:

We carried out a placebo-controlled human volunteer study. All patients were given 400 mg daily of indole-3-carbinol for three months, followed by placebo. Serum samples were tested for the GSTM1 genotype by polymerase chain reaction. Serum GST levels were assessed using enzyme-linked immunosorbent assay and Western Blot methodologies.

Results:

Forty-nine volunteers completed the study. GSTM1 genotypes were obtained for all but two volunteers. A slightly greater proportion of volunteers were GSTM1-positive, in keeping with the general population. GST was detected in all patients. Total GST level was not affected by indole-3-carbinol dosing compared with placebo. Although not statistically significant, the GSTM1 genotype affected the serum GST level response to indole-3-carbinol.

Conclusion:

Indole-3-carbinol does not alter total serum GST levels during prolonged dosing.

Protein phosphorylation analysis by site-specific arginine-mimic labeling in gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Although recent advances in gel electrophoresis and mass spectrometry have greatly facilitated separation, purification, and identification of proteins, significant challenges remain in relation to phosphoprotein analysis. Here we introduce a powerful method for analysis of protein phosphorylation in which phosphorylation sites are labeled with guanidinoethanethiol (GET) by beta-elimination/Michael addition prior to proteolysis and mass spectrometry (MS) analysis. This technique is especially useful in conjunction with gel-based technology in that all of the processes involved, including GET labeling, washing, and phosphospecific enzymatic hydrolysis, can be carried out in excised gel slices, thereby minimizing sample loss and contamination. The novel GET tag, which has a highly basic guanidine group, increases the peak intensities for the GET-labeled tryptic peptides by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS. In addition, phosphospecific proteolytic cleavage occurs at guanidinoethylcysteine (Gec) residue, which is arginine-mimic formed by GET tagging of phosphorylated serine residues. Thus, GET tagging is especially useful in analysis of long tryptic phosphopeptides. To illustrate the utility of the in-gel GET tagging and digestion approach, we used it to precisely analyze the phosphorylation sites of human glutathione S-transferase P1 (GSTP1), an enzyme involved in phase II metabolism of many carcinogens and anticancer drugs. The in-gel GET tagging/digestion technique significantly enhances the analytical potential of gel electrophoresis/MS in studies of proteome phosphorylation.

Glutathione S-transferase pi1 promotes tumorigenicity in HCT116 human colon cancer cells

GSTP1 is a member of the glutathione S-transferase enzyme superfamily, which catalyzes the conjugation of electrophiles with glutathione in the process of detoxification. GSTP1 is widely overexpressed in colorectal cancer, from aberrant crypt foci to advanced carcinomas. Increased expression of GSTP1 is associated with multidrug resistance and a worse clinical prognosis. However, GSTP1-null mice have an increased risk of tumor formation. Thus, the biological function of GSTP1 in colorectal cancer biology remains speculative. In an effort to gain further insights into the role of GSTP1 in tumorigenesis, we disrupted the GSTP1 gene in HCT116 human colorectal cancer cells using targeted homologous recombination. We find that loss of GSTP1 resulted in impaired clonogenic survival and proliferation. Specifically, under growth-limiting conditions, (a) GSTP1 protected HCT116 cells from oxidative stress and associated apoptosis and (b) promoted mitogen-activated protein kinase-extracellular signal-regulated kinase kinase/extracellular signal-regulated kinase-mediated G1-S cell cycle progression. In vivo, GSTP1 was critical for engraftment and growth of HCT116 tumor xenografts. These studies directly show that GSTP1 promotes clonogenic survival and proliferation in HCT116 human colon cancer cells.