EGFR and Calmodulin Signalling group


Functional Regulation of Rac1 and Cdc42 by Calmodulin


On the basis of the preliminary results obtained recently and on the analysis of the aminoacidic sequence of these GTPases, it seems that CaM interacts with Rac1 and cdc42. Therefore, CaM through these small Rho GTPases could regulate cytoskeleton related cellular processes like cellular mobility and/or endocytic compartment functionality.


Calmodulin (CaM) regulates cytoskeleton organization, mitosis and cell cycle, proliferation, signaling, transport of calcium and apoptosis, among others. CaM is also involved in the trafficking of intracellular membranes, in the endocytic and the exocytic pathways. It has been shown that CaM is necessary for transcytosis of IgA receptor and for recycling of transferrin in MDCK cells.


In particular, our group showed that in the presence of W13, a highly specific CaM antagonist, trafficking is blocked in early endosomes, thereby interfering with transport of EGFR toward degradation and recycling pathways. This blockage was associated with a dramatic alteration of the morphology and size of early endosomes.


Furthermore we showed that a crosstalk between CaM and PKCδ is involved in the regulation of the budding from the early endocytic compartment. We have shown that PKCδ activity, through the complex Arp2/3 and cortactin, inhibits the trafficking of the EGF receptor by promoting the formation of an F-actin coat surrounding the endosomes.  It has also been determined the presence of different actin binding proteins on endosomes that could be modulated by CaM and/or PKCδ: α-actinin, MARCKS, annexin A1 and annexin A2.


Actually, the results indicate that the GTPases of the Rho family, cdc42 and Rac1, are also involved in the perturbation of actin dynamics on endosomes. Specifically, we found that Rac1 and Cdc42 interact with CaM. Both proteins, cdc42 and Rac1, are present on enlarged endosomes produced by inhibition of CaM and the expression of dominant negative mutants of these proteins restore the normal morphology of endosomes.


Proteins of the family of RhoGTPases, Rac1 and Cdc42, induce the formation of lamellipodia, circular ruffles and filopodia by activating actin polymerization at the plasma membrane. It is necessary to emphasize the importance that the location of Rac1 in endosomes has recently acquired in order to explain the regulation of cellular migration. Therefore, the objective of the project is to continue the study of the role exerted by CaM and PKCδ in the regulation of the actin cytoskeleton at the cellular level.

Figure 1
Figure 1. F-ACTIN COAT IN W13-ENDOSOMES. F-actin (phalloidin-TRITC, in red) on early endosomes (EEA1-positive, in green) following treatment with W13 in NRK cells
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