Design and Biological Evaluation of Linear and Cyclic Phosphopeptide Ligands of the N-Terminal SH2 Domain of Protein Tyrosine Phosphatase SHP-1

ROS receptor tyrosine kinase: a new potential target for anticancer drugs

ROS kinase is one of the last two remaining orphan receptor tyrosine kinases with an as yet unidentified ligand. The normal functions of human ROS kinase in different body tissues have not been fully identified so far. However, the ectopic expression, as well as the production of variable mutant forms of ROS kinase has been reported in a number of cancers, such as glioblastoma multiforme, and non-small cell lung cancer, suggesting a role for ROS kinase in deriving such tumors. It is thought also that c-ROS gene may have a role in some cardiovascular diseases, and the fact that homozygous male mice targeted against c-ROS gene are healthy but infertile, has inspired researchers to think about ROS inhibition as a method for development of new male contraceptives. The recent discovery of new selective and potent inhibitors for ROS kinase, along with the development of new specific diagnostic methods for the detection of ROS fusion proteins, raises the importance of using these selective inhibitors for targeting ROS mutations as a new method for treatment of cancers harboring such genes. This review focuses on the ectopic expression of ROS and its fusion proteins in different cancer types and highlights the importance of targeting these proteins for treatment of substantial cancers. It describes also the recent advances in the field of ROS kinase inhibition, and the potential clinical applications of ROS kinase inhibitors.

Phosphopeptide ligands of the SHP-1 N-SH2 domain: effects on binding and stimulation of phosphatase activity

Src homology 2 (SH2)-domain-mediated interactions with phosphotyrosine (pY)-containing ligands are critical for the regulation of SHP-1 phosphatase activity. Peptides based on a binding site from receptor tyrosine kinase Ros (EGLN-pY2267-MVL, 1) have recently been shown to bind to the SHP-1 N-terminal SH2 domain (N-SH2) with considerably high affinity. In addition, two peptides cyclized between positions -1 and +2 relative to pY (EGLc[K(COCH(2)NH)pYMX]L-NH(2), 2: X=D, 3: X=E) bound to the N-SH2 domain, but did not activate the enzyme and even partially prevented stimulation of SHP-1 activity by the physiological ligand 1. These findings prompted us to further examine the determinants for optimal binding to the N-SH2 domain and for the stimulation and inhibition of SHP-1 activity. Herein we demonstrate that combining the preferred residues in both pY+1 (such as Phe or norleucine, Nle) and pY+3 (such as homophenylalanine, Hfe) leads to highly efficient activating ligands of SHP-1. Particularly in the context of the cyclic peptides 7 (EGLc[K(COCH(2)NH)pYFD]Hfe-NH(2)) and 8 (EGLc[K(COCH(2)NH)pYNleD]HfeL-NH(2)), the incorporation of these residues resulted in high-affinity ligands with a significantly increased ability to stimulate SHP-1 activity. We suggest that different binding modes (according to consensus sequences class I and II) are responsible for obtaining either activating (7 and 8) or nonactivating (2 and 3) ligands. Peptides such as 7 and 8 that bind in the extended fashion of the type II mode activate the phosphatase through complete filling of the cavity for pY+3. In contrast, peptides such as 2 and 3 that bind in the class I mode do not activate the enzyme because they allow more conformational space at pY+3. Therefore, their binding does not force the conformational transition necessary to trigger the dissociation of N-SH2 and the catalytic domain.

Protein-tyrosine phosphatases and cancer

Tyrosine phosphorylation is an important signalling mechanism in eukaryotic cells. In cancer, oncogenic activation of tyrosine kinases is a common feature, and novel anticancer drugs have been introduced that target these enzymes. Tyrosine phosphorylation is also controlled by protein-tyrosine phosphatases (PTPs). Recent evidence has shown that PTPs can function as tumour suppressors. In addition, some PTPs, including SHP2, positively regulate the signalling of growth-factor receptors, and can be oncogenic. An improved understanding of how these enzymes function and how they are regulated might aid the development of new anticancer agents.

Survey of the year 2005 commercial optical biosensor literature

We identified 1113 articles (103 reviews, 1010 primary research articles) published in 2005 that describe experiments performed using commercially available optical biosensors. While this number of publications is impressive, we find that the quality of the biosensor work in these articles is often pretty poor. It is a little disappointing that there appears to be only a small set of researchers who know how to properly perform, analyze, and present biosensor data. To help focus the field, we spotlight work published by 10 research groups that exemplify the quality of data one should expect to see from a biosensor experiment. Also, in an effort to raise awareness of the common problems in the biosensor field, we provide side-by-side examples of good and bad data sets from the 2005 literature.