Overexpression of heparan sulfate 6-O-sulfotransferase-2 in colorectal cancer.

The heparan sulfate sulfotransferase gene family catalyzes the transfer of sulfate groups to heparan sulfate and regulates various growth factor-receptor signaling pathways. However, the involvement of this gene family in cancer biology has not been elucidated. It was demonstrated that the heparan sulfate D-glucosaminyl 6-O-sulfotransferase-2 (HS6ST2) gene is overexpressed in colorectal cancer (CRC) and its clinical significance in patients with CRC was investigated. The mRNA levels of HS6ST2 in clinical CRC samples and various cancer cell lines were assessed using a microarray analysis and quantitative RT-PCR, respectively. An immunohistochemical (IHC) analysis of the HS6ST2 protein was performed using 102 surgical specimens of CRC. The correlations between the HS6ST2 expression status and clinicopathological characteristics were then evaluated. HS6ST2 mRNA was significantly overexpressed by 37-fold in CRC samples compared to paired colonic mucosa. High levels of HS6ST2 mRNA expression were also observed in colorectal, esophageal and lung cancer cell lines. The IHC analysis demonstrated that HS6ST2 was expressed in the cytoplasmic region of CRC cells, but not in normal colonic mucosal cells. Positive staining for HS6ST2 was detected in 40 patients (39.2%). There was no significant association between the clinicopathological characteristics and HS6ST2 expression. However, positive staining for HS6ST2 was associated with a poor survival (P=0.074, log-rank test). In conclusion, HS6ST2 was found to be overexpressed in CRC and its expression tended to be a poor prognostic factor, although the correlation was not significant. These findings indicate that HS6ST2 may be a novel cancer-related marker that may provide insight into the glycobiology of CRC.

Protein kinase substrate profiling with a high-density peptide microarray.

We describe a powerful peptide microarray for profiling protein kinase substrates that combines the merits of chemoselective immobilization of peptides to achieve high density spots with the advantages of fluorescence-based analysis of phosphorylation for nonhazardous detection. For detection of on-chip phosphorylation, we used a fluorescence-labeled antiphosphotyrosine antibody to detect phosphotyrosine and a biotinylated Phostag, which was subsequently bound with a fluorescence-labeled streptavidin for phosphoserine/threonine. More than 290 kinds of Tyr peptides and over 1,100 kinds of Ser/Thr peptides were chemoselectively immobilized onto a glass surface in a high-density format to profile a panel of protein kinases, including c-Src, c-Abl, EGFR, JNK1, ERK2, p38α, and PKA. Many novel, highly reactive and specific peptides were identified as substrates for each protein kinase. Most substrates had the consensus motifs that have been reported previously but some new motifs were also found. The identification of two designed peptides that have higher reactivity than the famous PKA substrate (Kemptide) indicates that analysis of the amino acid biases of substrates is very helpful to the design of new substrates with high reactivity. Thus, the high-density peptide microarray is expected to be a powerful approach for high-throughput discovery of potential substrates for protein kinases.

Monitoring protein kinase activity in cell lysates using a high-density peptide microarray.

Monitoring and targeting protein kinases is widely accepted as a promising approach for disease diagnosis and drug discovery. For this purpose, the authors have developed an original type of peptide array as a high-throughput screening assay for quantitatively evaluating kinase activity. A volume of 2 nL of peptide solution was spotted onto a formyl group-modified glass slide by using an arrayer, which was designed for use with protein chip technology. The phosphorylation was recognized by fluorescence-label antibody and detected with an automatic microarray scanner widely used in DNA chip technology. The system needs low sample volume, provides a high-density peptide array, and supplies high reproducibility. It provided enough sensitivity for inhibitor screening, even though a relatively low concentration of purified kinase was employed. The assay also proved useful for the detection of intracellular kinase activity as well as for the measurement of the fluctuations of intracellular protein kinase activity with drug stimulation. Thus, this peptide array would be applicable for kinase-targeted diagnosis, cell-based drug screening, and signal pathway investigation.

Surface plasmon resonance imaging measurements of caspase reactions on peptide microarrays.

Enzymatic activity monitoring of caspases, which are a class of cysteine protease, was performed by using peptide arrays based on surface plasmon resonance (SPR) imaging. The strategy of the detection is straightforward, using streptavidin to amplify the SPR signals of the surface-immobilized substrate peptides labeled with biotin at the C termini. Thus, the cleavage of the substrate peptides by caspases was detected as a signal decrease. Using this method, we succeeded in monitoring the activities of purified caspases and caspases in cell lysates. The SPR imaging-based peptide array would be applicable to cell-based drug screening and biochemical studies to reveal signal transduction processes.

Evaluation of protein kinase activities of cell lysates using peptide microarrays based on surface plasmon resonance imaging.

We developed a peptide microarray based on surface plasmon resonance (SPR) imaging for monitoring protein kinase activities in cell lysates. The substrate peptides of kinases were tethered to the microarray surface modified with a self-assembled monolayer of an alkanethiol with triethylene glycol terminus to create a low nonspecific binding surface. The phosphorylation of the substrate peptides immobilized on the surface was detected with the following phosphate specific binders by amplifying SPR signals: anti-phosphotyrosine antibody for tyrosine kinases and Phos-tag biotin (a phosphate-specific ligand with biotin tag) for serine/threonine kinases. Using the microarray, 9 kinds of protein kinases were evaluated as a pattern of phosphorylation of 26 kinds of substrate peptides. The pattern was unique for each protein kinase. The microarray could be used to evaluate the inhibitory activities of kinase inhibitors. The microarray was applied successfully for kinase activity monitoring of cell lysates. The chemical stimuli responsive activity changes of protein kinases in cell lysates could also be monitored by the peptide microarray. Thus, the peptide microarray based on SPR imaging would be applicable to cell-based drug discovery, diagnosis using tissue lysates, and biochemical studies to reveal signal transduction pathways.

A peptide microarray for the detection of protein kinase activity in cell lysate.

DNA microarray enables the analysis of DNA or mRNA expression levels, but it has not been possible to completely understand life using obtained information. Consequently, protein or peptide arrays have attracted much interest. Since the development of a practical protein microarray is still far away in light of handling difficulties, the peptide microarray is a promising tool for analyzing protein functions. We have developed a peptide microarray to detect protein kinase activity in cell lysate. All substrate peptides for kinases were immobilized chemoselectively on amino-coated glass slides. After phosphorylation of the immobilized peptides, phosphorylation was detected by fluorescence imaging. We detected the protein kinase activities, including that in cell lysate, in response to drug stimulation. Therefore, this peptide microarray would be useful for a high-throughput kinase assay of intracellular signals and would be applicable to drug screening.