A chemical genetic approach reveals distinct EphB signaling mechanisms during brain development.

EphB receptor tyrosine kinases control multiple steps in nervous system development. However, it remains unclear whether EphBs regulate these different developmental processes directly or indirectly. In addition, given that EphBs signal through multiple mechanisms, it has been challenging to define which signaling functions of EphBs regulate particular developmental events. To address these issues, we engineered triple knock-in mice in which the kinase activity of three neuronally expressed EphBs can be rapidly, reversibly and specifically blocked. We found that the tyrosine kinase activity of EphBs was required for axon guidance in vivo. In contrast, EphB-mediated synaptogenesis occurred normally when the kinase activity of EphBs was inhibited, suggesting that EphBs mediate synapse development by an EphB tyrosine kinase-independent mechanism. Taken together, our data indicate that EphBs control axon guidance and synaptogenesis by distinct mechanisms and provide a new mouse model for dissecting EphB function in development and disease

A Chemical Genetic Approach Reveals Distinct Mechanisms of EphB Signaling During Brain Development

EphB receptor tyrosine kinases control multiple steps in nervous system development. However, it remains unclear whether EphBs regulate these different developmental processes directly or indirectly. In addition, as EphBs signal through multiple mechanisms, it has been challenging to define which signaling functions of EphBs regulate particular developmental events. To address these issues, we engineered triple knockin mice in which the kinase activity of three neuronally expressed EphBs can be rapidly, reversibly, and specifically blocked. Using these mice we demonstrate that the tyrosine kinase activity of EphBs is required for axon guidance in vivo. By contrast, EphB-mediated synaptogenesis occurs normally when the kinase activity of EphBs is inhibited suggesting that EphBs mediate synapse development by an EphB tyrosine kinase-independent mechanism. Taken together, these experiments reveal that EphBs control axon guidance and synaptogenesis by distinct mechanisms, and provide a new mouse model for dissecting EphB function in development and disease

A chemical genetic approach reveals distinct EphB signaling mechanisms during brain development.

EphB receptor tyrosine kinases control multiple steps in nervous system development. However, it remains unclear whether EphBs regulate these different developmental processes directly or indirectly. In addition, given that EphBs signal through multiple mechanisms, it has been challenging to define which signaling functions of EphBs regulate particular developmental events. To address these issues, we engineered triple knock-in mice in which the kinase activity of three neuronally expressed EphBs can be rapidly, reversibly and specifically blocked. We found that the tyrosine kinase activity of EphBs was required for axon guidance in vivo. In contrast, EphB-mediated synaptogenesis occurred normally when the kinase activity of EphBs was inhibited, suggesting that EphBs mediate synapse development by an EphB tyrosine kinase-independent mechanism. Taken together, our data indicate that EphBs control axon guidance and synaptogenesis by distinct mechanisms and provide a new mouse model for dissecting EphB function in development and disease

Human mitochondrial peptide deformylase, a new anticancer target of actinonin-based antibiotics

Peptide deformylase activity was thought to be limited to ribosomal protein synthesis in prokaryotes, where new peptides are initiated with an N-formylated methionine. We describe here a new human peptide deformylase (Homo sapiens PDF, or HsPDF) that is localized to the mitochondria. HsPDF is capable of removing formyl groups from N-terminal methionines of newly synthesized mitochondrial proteins, an activity previously not thought to be necessary in mammalian cells. We show that actinonin, a peptidomimetic antibiotic that inhibits HsPDF, also inhibits the proliferation of 16 human cancer cell lines. We designed and synthesized 33 chemical analogs of actinonin; all of the molecules with potent activity against HsPDF also inhibited tumor cell growth, and vice versa, confirming target specificity. Small interfering RNA inhibition of HsPDF protein expression was also antiproliferative. Actinonin treatment of cells led to a tumor-specific mitochondrial membrane depolarization and ATP depletion in a time- and dose-dependent manner; removal of actinonin led to a recovery of the membrane potential consistent with indirect effects on the electron transport chain. In animal models, oral or parenteral actinonin was well tolerated and inhibited human prostate cancer and lung cancer growth. We conclude that HsPDF is a new human mitochondrial enzyme that may provide a novel selective target for anticancer therapy by use of actinonin-based antibiotics

Staurosporine-Derived Inhibitors Broaden the Scope of Analog-Sensitive Kinase Technology

Analog-sensitive (AS) kinase technology is a powerful approach for studying phospho-signaling pathways in diverse organisms and physiological processes. The key feature of this technique is that a kinase-of-interest can be mutated to sensitize it to inhibitor analogs that do not target wild-type (WT) kinases. In theory, this enables specific inhibition of any kinase in cells and in mouse models of human disease. Typically these inhibitors are identified from a small library of molecules based on the pyrazolopyrimidine (PP) scaffold. However, we recently identified a subset of native human kinases, including the Ephrin A kinase family, that are sensitive to commonly used PP inhibitors. In an effort to develop a bioorthogonal AS-kinase inhibitor and to extend this technique to PP-sensitive kinases we sought an alternative inhibitor scaffold. Here we report the structure-based design of synthetically tractable, potent, and extremely selective AS-kinase inhibitors based on the natural product staurosporine. We demonstrate that these molecules, termed staralogs, potently target AS kinases in cells and we employ X-ray crystallography to elucidate their mechanism of efficacy. Finally, we demonstrate that staralogs target AS mutants of PP-sensitive kinases at concentrations where there is little to no inhibition of native human kinases. Thus, staralogs represent a new class of AS-kinase inhibitors and a core component of the chemical genetic tool kit for probing kinase-signaling pathways

Structure-Guided Inhibitor Design Expands the Scope of Analog-Sensitive Kinase Technology

Engineered analog-sensitive (AS) protein kinases have emerged as powerful tools for dissecting phospho-signaling pathways, for elucidating the cellular function of individual kinases, and for deciphering unanticipated effects of clinical therapeutics. A crucial and necessary feature of this technology is a bioorthogonal small molecule that is innocuous towards native cellular systems but can potently inhibit the engineered kinase. In order to generalize this method we sought a molecule capable of targeting divergent AS-kinases. Here we employ X-ray crystallography and medicinal chemistry to unravel the mechanism of current inhibitors and use these insights to design the most potent, selective and general AS-kinase inhibitors reported to date. We use large-scale kinase inhibitor profiling to characterize the selectivity of these molecules as well as examine the consequences of potential off-target effects in chemical genetic experiments. The molecules reported here will serve as powerful tools in efforts to extend AS-kinase technology to the entire kinome and the principles discovered may help in the design of other engineered enzyme/ligand pairs