Tyrosine Kinase Receptor

The neuromuscular junction is made up of the apposition of highly differentiated domains of three types of cell: the motor neuronal ending, the terminal Schwann cell and the muscle postsynaptic membrane. These three components are surrounded by a basal lamina, dedicated to molecular signal exchanges controlling neuromuscular formation, maturation and maintenance. This functional and structural differentiated complex conducts synaptic neurotransmission to the skeletal muscle fiber. Nerve and muscle have distinct roles in synaptic compartment differentiation. The initial steps of this differentiation and the motor endplate formation require several postsynaptic molecular agents including agrin, the tyrosine kinase receptor MuSK. Neuregulin is essentially involved in Schwann cell survival and guidance for axonal growth.

Trastuzumab is a monoclonal antibody targeted against the HER2 tyrosine kinase receptor. The majority of patients with metastatic breast cancer who initially respond to trastuzumab develop resistance within one year of treatment initiation, and in the adjuvant setting 15% of patients still relapse despite trastuzumab-based therapy. In this review, we discuss potential mechanisms of antitumor activity by trastuzumab, and how these mechanisms become altered to promote therapeutic resistance. We also discuss novel therapies that may improve the efficacy of trastuzumab, and that offer hope that the survival of breast cancer patients with HER2-overexpressing tumors can be vastly improved.

The lens epithelium can be separated into two regions, the nondividing central zone and the equator, the site of all division in the normal lens. In the present study, the distribution of epithelial growth factor (EGF)/epithelial growth factor receptor (EGFR) signaling components was investigated and related to mitotic distribution in the lens. Anterior and equatorial regions of the native epithelium were prepared separately from donor lenses. In vitro capsular bags were prepared from donor eyes and cultured. Receptor distribution was determined by immunocytochemistry and RT-PCR. Western blot analysis of phospholipase C (PLC)-gamma and extracellular signal-regulated kinase (ERK; total and active) was performed on cell lysates. Function was determined by calcium imaging of Fura-2-AM-loaded cells and also, in the case of capsular bags, by cell growth. Immunocytochemistry and RT-PCR showed an even distribution of EGFR across the native epithelium. Whole lenses, however, exhibited only ...

Liposomes and Flt3 ligand (Flt3L), a ligand for the fms-like tyrosine kinase receptor Flt3/ FLK2, can augment the immune response to an HIV peptide vaccine. The HGP-30 peptide used in these studies is a synthetic peptide that corresponds to a highly conserved region of HIV-1 p17 gag (amino acids 86-115). Mice were immunized with HGP-30 or HGP-30 conjugated to keyhole limpet hemocyanin (KLH) and delayed-type hypersensitivity (DTH) responses, antibody (IgG) amount and antigen-specific proliferative responses by spleen cells were used to monitor the immune response. Daily injections of Flt3L prior to HGP-30 administration enhanced significantly an antigen-specific lymphocyte proliferation response when compared with Flt3L, HGP-30 alone or HGP-30 containing liposomes. Intravenous administration of HGP-30 was superior to intramuscular (i.m.) immunization for the induction of DTH responses. The HGP-30/KLH containing liposomes enhanced both DTH and antibody responses, while liposomes conta...

To understand how extracellular signals may produce long-term effects in neural cells, we have analyzed the mechanism by which neurotransmitters and growth factors induce phosphorylation of the transcription factor cAMP response element binding protein (CREB) in cortical oligodendrocyte progenitor (OP) cells. Activation of glutamate receptor channels by kainate, as well as stimulation of G-protein-coupled cholinergic receptors by carbachol and tyrosine kinase receptors by basic fibroblast growth factor (bFGF), rapidly leads to mitogen-activated protein kinase (MAPK) phosphorylation and ribosomal S6 kinase (RSK) activation. Kainate and carbachol activation of the MAPK pathway requires extracellular calcium influx and is accompanied by protein kinase C (PKC) induction, with no significant increase in GTP binding to Ras. Conversely, growth factor-stimulated MAPK phosphorylation is independent of extracellular calcium and is accompanied by Ras activation. Both basal and stimulated MAPK ...

-Protein tyrosine phosphorylation induced by arachidonic acid (AA), an important lipid second messenger, was investigated in rabbit renal proximal tubule epithelial cells. AA stimulated tyrosine phosphorylation of a number of proteins with estimated molecular weights of 42, 44, 52, 56, 85, and 170/180 kDa. The phosphoproteins pp44 and pp42 were identified as 2 isoforms of mitogen-activated protein kinase (MAPK). Phosphorylation of MAPK in response to AA was transient, dose-dependent, and accompanied by an increase in its activity. The mechanism of AA-induced MAPK activation in RTE cells was protein kinase C-independent and involved tyrosine phosphorylation of adaptor protein Shc and its association with Grb2-Sos complex. Moreover, stimulation of RTE cells with AA resulted in significant phosphorylation of epidermal growth factor (EGF) receptor and its association with Shc. The effect of AA on EGF receptor phosphorylation, its association with Shc, and MAPK activation was similar to the effect of 1 ng/mL EGF. Tyrphostin AG1478, a specific inhibitor of EGF receptor tyrosine kinase activity, completely blocked the effects of AA and EGF but not phorbol ester on MAPK phosphorylation. These data suggest that in renal tubular epithelial cells, the mechanism of AA-induced MAPK activation involves tyrosine phosphorylation of EGF receptor and its association with Shc and Grb2-Sos complex. Given the critical role of AA in signaling linked to G protein-coupled receptors (GPCRs), these observations provide a mechanism for cross talk between GPCRs linked to phospholipases and the tyrosine kinase receptor signaling cascades.

EphA2 (Eck) is a tyrosine kinase receptor that is overexpressed in several human cancers such as breast, colon, lung, prostate, gastric carcinoma, and metastatic melanoma but not in nonmalignant counterparts. To validate EphA2 as a tumor antigen recognized by CD8+ T lymphocytes, we used reverse immunology approach to identify HLA-A*0201-restricted epitopes. Peptides bearing the HLA-A*0201-specific anchor motifs were analyzed for their capacity to bind and stabilize the HLA-A*0201 molecules. Two peptides, EphA2(58) and EphA2(550), with a high affinity for HLA-A*0201 were selected. Both peptides were immunogenic in the HLA-A*0201-transgenic HHD mice. Interestingly, peptide-specific murine CTLs cell lines responded to COS-7 cells coexpressing HLA-A*0201 and EphA2 and to EphA2-positive human tumor cells of various origin (renal cell, lung, and colon carcinoma and sarcoma). This demonstrates that EphA2(58) and EphA2(550) are naturally processed from endogenous EphA2. In addition, EphA2(5...

The paradigm of cell surface proteoglycan function has been centered on the role of the ectoplasmic heparan sulfate (HS) chains as acceptors of a wide array of ligands, including extracellular matrix (ECM) proteins and soluble growth factors. Within this picture, the core proteins were assigned only a passive role of carrying the glycosaminoglycan (GAG) chains without direct participation in mediating outside-in signals generated by the binding of the above ligands. It appears now, however, that, side by side with the integrins and the tyrosine kinase receptors, the core proteins of the syndecan family of transmembrane proteoglycans are involved in signaling. The highly conserved tails of all the four members of the syndecan family contain a carboxy-terminal PDZ (Postsynaptic density 95, Disk large, Zona occludens-1)-binding motif, capable of forming multimolecular complexes through the binding of PDZ adaptor proteins. The cytoplasmic tail of the ubiquitously expressed syndecan-4 is distinct from the other syndecans in its capacity to bind phosphatidylinositol 4,5-bisphosphate (PIP2) and to activate protein kinase C (PKC) alpha. These properties may confer on syndecan-4 specific and unique signaling functions.

Sorbonne Université (Pierre & Marie Curie, Paris VI), Faculty of Sciences. N° national de thèse: 2006PA066115 https://www.worldcat.org/search?q=no%3A494198160 During development of the nervous system, Receptors with Tyrosine Kinase (RTK) activity play essential roles in a wide variety of fundamental physiological cellular processes such as proliferation, survival, or differentiation. In the RTK family, Alk has been one of the last to be identified. It remains, to date, considered as orphan, as no ligand has been yet attributed in vertebrates. It is essentially expressed in specific regions of the central and peripheral nervous system, and transiently during development. This expression strongly suggests therefore that it could play a fundamental role in the development and functioning of the nervous system. This role still remains however to be clearly identified. Thus, the studies I conducted these last years participate to the general understanding of the role of ALK in neuronal development. My thesis works focused therefore on the study of its function and mechanisms of action, in the frame of the neuronal differentiation of PC12 cells. These works also attempted, more generally, to bring matter to the current thoughts concerning the biochemical/cellular factors and parameters that can determine the specificity of biological responses and their cellular mechanisms of action. Specifically, they focused on the study of the role of the subcellular localization of a Tyrosine Kinase domain (of ALK, in particular) in the orchestration of the signals that determine neuronal development. Therefore, the results I obtained during this thesis, in their whole, have allowed not only to better understand the signalling pathways and the biological effects induced by the activation of the receptor ALK, but they further strongly support that membrane attachment of the ALK Tyrosine Kinase domain is crucial for the control and specificity of the signalling and biological pathways engaged by ALK. Thus, these works, more generally, underline the fundamental importance of the subcellular localization of a Tyrosine Kinase domain in the decision of the fate in which the cell will be engaged, and in particular the immature neuronal cell during the development of the nervous system.

Gastrointestinal stromal tumors (GIST) arising from interstitial cells of Cajal, represent the first type of solid tumor, which is very sensitive to a specific molecularly targeted tyrosine kinase receptor blocker (i. e., imatinib). On CT, which is considered as the reference technique, GISTs typically present as large, well-delineated, heterogeneous and sometimes exophytic masses. In contrast with the absence of lymph

Cancer is a genetic disease and this concept is now widely exploited by both scientists and clinicians to design new targeted molecules. Indeed many data have already allowed us to ameliorate not only our knowledge about cancer onset, but also about patients treatment. Correlation between mutations in cancer alleles and drug response is a key point to identify drugs that match the genetic profile of each individual tumors. On the other hand, experience derived from inhibition of tyrosine kinase receptors has pointed out that targeted treatment is really successful only in a small subset of tumors. The latter are eventually addicted to those genetic alterations which are responsible for receptors activation and for the continued expression of their signalling. Overall these observations provide a strong rationale for a molecular-based diagnosis and patients selection for targeted therapies. This review analyses the current state of the art of molecularly-tailored pharmacological approach to lung cancer, one of the biggest killers among human solid tumors. Main relevance is addressed to genetic lesions activating the EGFR pathway transducers, focusing on their role as markers of targeted drug response.

Gangliosides have long been implicated in cell growth regulation and play an important role as modulators in protein phosphorylation. In order to better understand how glycosphingolipids and growth factors interact, we examined the modulation of epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) effects on retinal Müller glial cells (RMG), following modification of their GG composition. Treatment of MG cells with GG (GM1, GT1b) and asialoGM1 resulted in modifications of several aspects of cellular responses to EGF- and FGF-receptor (R) activation: mitogenesis, cell migration, tyrosine phosphorylation of the EGF-R and FGF-R and even their cellular substrates were particularly influenced by GG. Indeed GG caused modifications of EGF-R and FGF-R autophosphorylation kinetics. GG long term effects (mitogenesis and migration) correlate with short term effects (tyrosine phosphorylation) and differences in receptor tyrosine kinase signalling could explain the specificity...