Differential requirement of the last C-terminal tail of Met receptor for cell transformation and invasiveness

Imaging strategies for receptor tyrosine kinase dimers in living cells

Receptor tyrosine kinases (RTKs) are the essential regulators of cell signal transduction pathways and play important roles in biological processes. RTK dimerization is generally considered the first step in receptor activation and cell communication. And the abnormal expression of RTK dimers is closely related to the occurrence and development of many diseases. Therefore, the visualization of RTK dimerization is of great significance for monitoring physiological processes. The genetic and nongenetic imaging strategies have attracted widespread attention due to their high efficiency and high sensitivity. In this review, the RTKs and their dimers as well as the advances in strategies for imaging RTK dimers are introduced. Furthermore, we analyze the limitations of existing imaging strategies and put forward suggestions for the future development of imaging probes. We expect that this review will inspire more in-depth investigation of RTK dimers, which will also broaden the application of strategies of RTK dimers in biomedical areas.

State of the structure address on MET receptor activation by HGF

The MET receptor tyrosine kinase (RTK) and its cognate ligand hepatocyte growth factor (HGF) comprise a signaling axis essential for development, wound healing and tissue homeostasis. Aberrant HGF/MET signaling is a driver of many cancers and contributes to drug resistance to several approved therapeutics targeting other RTKs, making MET itself an important drug target. In RTKs, homeostatic receptor signaling is dependent on autoinhibition in the absence of ligand binding and orchestrated set of conformational changes induced by ligand-mediated receptor dimerization that result in activation of the intracellular kinase domains. A fundamental understanding of these mechanisms in the MET receptor remains incomplete, despite decades of research. This is due in part to the complex structure of the HGF ligand, which remains unknown in its full-length form, and a lack of high-resolution structures of the complete MET extracellular portion in an apo or ligand-bound state. A current view of HGF-dependent MET activation has evolved from biochemical and structural studies of HGF and MET fragments and here we review what these findings have thus far revealed.

Enhanced prediction of Src homology 2 (SH2) domain binding potentials using a fluorescence polarization-derived c-Met, c-Kit, ErbB, and androgen receptor interactome

Many human diseases are associated with aberrant regulation of phosphoprotein signaling networks. Src homology 2 (SH2) domains represent the major class of protein domains in metazoans that interact with proteins phosphorylated on the amino acid residue tyrosine. Although current SH2 domain prediction algorithms perform well at predicting the sequences of phosphorylated peptides that are likely to result in the highest possible interaction affinity in the context of random peptide library screens, these algorithms do poorly at predicting the interaction potential of SH2 domains with physiologically derived protein sequences. We employed a high throughput interaction assay system to empirically determine the affinity between 93 human SH2 domains and phosphopeptides abstracted from several receptor tyrosine kinases and signaling proteins. The resulting interaction experiments revealed over 1000 novel peptide-protein interactions and provided a glimpse into the common and specific interaction potentials of c-Met, c-Kit, GAB1, and the human androgen receptor. We used these data to build a permutation-based logistic regression classifier that performed considerably better than existing algorithms for predicting the interaction potential of several SH2 domains.

Refined anatomical isolation of functional sleep circuits exhibits distinctive regional and circadian gene transcriptional profiles

Powerful new approaches to study molecular variation in distinct neuronal populations have recently been developed enabling a more precise investigation of the control of neural circuits involved in complex behaviors such as wake and sleep. We applied laser capture microdissection (LCM) to isolate precise brain nuclei from rat CNS at opposing circadian time points associated with wake and sleep. Discrete anatomical and temporal analysis was performed to examine the extent of variation in the transcriptional control associated with both identifiable anatomical nuclei and with light/dark cycle. Precise isolation of specific brain nuclei regulating sleep and arousal, including the LC, SCN, TMN, VTA, and VLPO, demonstrated robust changes in gene expression. Many of these differences were not observed in previous studies where whole brain lysates or gross dissections were used to probe for changes in gene expression. The robust and differential profiles of genomic data obtained from the approaches used herein underscore the requirement for careful anatomical refinement in CNS gene expression studies designed to understand genomic control within behaviorally-linked, but functionally isolated brain nuclei.

RET/Papillary Thyroid Carcinoma Oncogenic Signaling through the Rap1 Small GTPase

RET/papillary thyroid carcinoma (PTC) oncoproteins result from the in-frame fusion of the RET receptor tyrosine kinase with protein dimerization motifs encoded by heterologous genes. Here, we show that RET/PTC1 activates the Rap1 small GTPase. The activation of Rap1 was dependent on the phosphorylation of RET Tyr(1062). RET/PTC1 recruited a complex containing growth factor receptor binding protein 2-associated binding protein 1 (Gab1), CrkII (v-crk sarcoma virus CT10 oncogene homologue II), and C3G (Rap guanine nucleotide exchange factor 1). By using dominant-negative and small interfering duplex (small interfering RNA) oligonucleotides, we show that RET/PTC1-mediated Rap1 activation was dependent on CrkII, C3G, and Gab1. Activation of Rap1 was involved in the RET/PTC1-mediated stimulation of the BRAF kinase and the p42/p44 mitogen-activated protein kinases. Proliferation and stress fiber formation of RET/PTC1-expressing PC Cl 3 thyroid follicular cells were inhibited by the dominant-negative Rap1(N17) and by Rap1-specific GTPase-activating protein. Thus, Rap1 is a downstream effector of RET/PTC and may contribute to the transformed phenotype of RET/PTC-expressing thyrocytes.

Redundant roles for Met docking site tyrosines and the Gab1 pleckstrin homology domain in InlB-mediated entry of Listeria monocytogenes

The bacterial pathogen Listeria monocytogenes causes food-borne illnesses leading to gastroenteritis, meningitis, or abortion. Listeria induces its internalization into some mammalian cells through interaction of the bacterial surface protein InlB with host Met receptor tyrosine kinase. Binding of InlB leads to phosphorylation of Met and the adapter Gab1 and to activation of host phosphoinositide (PI) 3-kinase. The mammalian ligand of Met, hepatocyte growth factor, promotes cell motility and morphogenesis in a manner dependent on phosphorylation of two docking site tyrosines at positions 1349 and 1356 in the receptor's cytoplasmic tail. Here we determined if these tyrosines were essential for Listeria entry. A derivative of the human cell line T47D stably expressing a truncated Met lacking most of its cytoplasmic domain was unable to support InlB-mediated signaling or entry. Surprisingly, cells expressing mutant Met containing phenylalanine substitutions in both tyrosines 1349 and 1356 (MetYF) allowed entry and InlB-induced Gab1 phosphorylation. However, in contrast to the situation in cells expressing wild-type Met, Gab1 phosphorylation in MetYF cells required PI 3-kinase activity. The Gab1 pleckstrin homology (PH) domain was constitutively associated with the plasma membrane of cells in a PI 3-kinase-dependent manner. Overexpression of the PH domain blocked entry of Listeria into cells expressing MetYF but not into cells expressing wild-type Met. Taken together, these results indicate that the docking site tyrosines are dispensable for internalization when membrane localization of Gab1 is constitutive. Distinct pathways of recruitment by phosphorylated tyrosines in Met and PH domain ligands in the membrane are redundant for bacterial entry.