Résumé :
|
Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase that is transiently expressed in specific regions of the central and peripheral nervous systems, suggesting a role in its normal development and function. The nature of the cognate ligands of ALK in vertebrate is still a matter of debate. We produced a panel of monoclonal antibodies (mAbs) directed against the extracellular domain of the human receptor. Two mAbs induced the differentiation of PC12 cells transiently transfected with ALK. In HEK 293 cells stably expressing ALK, we showed that these two Mabs strongly activated the receptor and subsequently the MAP kinase pathway and a specific activation of STAT3. Interestingly, others mAbs present all the characteristics of blocking antibodies. We also studied the primary events occurring at the plasma membrane triggered by ALK activation and driving MAP-kinase activation and subsequently PC12 cells differentiation. We focused on two adaptor proteins Shc and FRS2, and their specific role in the neuron-like differentiation of PC12 cells. We showed that both adaptors could interact with ALK in an activation dependent manner. We also characterized the functional role of Shc adaptor in the neuron-like differentiation of PC12 cells. Recently, we studied the expression of ALK in DRG (dorsal root ganglia) neurons both in vivo and in culture. Our results on the level of expression showed a maximum reach at P0 (birth) in the rat DRG. Immunofluorescence assay on section of DRG showed a specific localization of ALK in a subtype of neurons. Moreover, our data suggested that ALK could be involved in the relation between neurons and Schwann cells. Thus, in absence of clearly established ligand(s) in vertebrates, the availability of mAbs allowing the activation or the inhibition of the receptor will be essential to better understand the roles of ALK.
|