Final Activity Report Summary - TC-GEPAK (Translational control by the small GTPase effector PAK4 in cell survival and transformation)
Understanding the mechanisms that are at the basis of malignant cell proliferation is one of the main topics of modern biological research and scientific innovation in this field is extremely relevant in the fight against cancer. The aim of this research project is to explore a novel link between two cellular pathways that are key players in many of the steps that control both normal and malignant cell growth. We have found that these pathways are strictly connected, and the molecular details of this novel interaction open new perspectives and suggest novel targets for therapy intervention.
The first pathway that is the object of our studies is the Rho family of GTPases and their effector, the protein kinase PAK4. The Rho GTPase proteins share many features with the Ras proto-oncogene: they act as cellular switches that are strictly regulated. Their on and of states relay the environmental cues and control cellular processes that are subverted during cellular transformation, such as cell division, motility and differentiation. PAK4 is one of the Rho GTPases effector proteins, and transfers their message to target enzymes or regulatory proteins, modifying their structure and activity. The PAK4 protein was found overexpressed in tumour cells and its adequate levels in the cell are fundamental for normal embryonic development, cellular growth and survival, as well as programmed cell death (apoptosis).
The second pathway is the protein synthesis cellular machinery. While it has been studied for a long time as the cellular 'protein factory', recently it has become clear that in many events, such as cell division, embryonic development, response to environmental stress, and viral infection, protein synthesis rates are controlled both globally and specifically. Translation of mRNA into protein is in fact the ultimate step for gene expression regulation and allows producing new protein without the need of novel RNA synthesis.
Growing examples suggest that translational control is involved in GTPase regulated cellular events, one for all being that some mutations associated with the Fragile X Mental Retardation syndrome, disrupt the genes for a PAK4 homolog and Rho GTPase proteins.
With the MC-IRG action we started a new line of research aimed at finding novel evidence that PAK4 also mediates cellular transformation by regulating the translational rates of the cell. During the course of this project, we used biochemical techniques, in vitro studies of the translation reaction, and in vivo approaches in cultured cells, and exploited cellular and viral sequences that allow for specific protein synthesis when the global translation activity is shut down.
We could identify a specific region of PAK4 protein that binds to ribosomal proteins and can modulate translation in vitro. We could also show that a deregulated, active, PAK4 protein can influence both global and specific translational rates. Interesting evidence indicates that PAK4 can repress stress induced synthesis of cellular genes in the cell, while viral sequences are in turn activated, suggesting that PAK4 abnormal activation inhibits apoptosis induced translational control mechanisms, and favours viral replication. We could also show that under stress conditions active PAK4 transformed cell lines display enhanced activation of the translation initiation factor eIF4E, which is typically repressed in normal cell lines.
Our data strongly support that translational control mechanisms are involved in PAK4 induced transformed phenotypes, and our next goal is to find the direct molecular targets of such regulation. The data we obtained during the execution of this project consolidate the new line of research that was established, and strongly suggest further developments in the study the molecular mechanisms of cellular transformation and genetic diseases.
The first pathway that is the object of our studies is the Rho family of GTPases and their effector, the protein kinase PAK4. The Rho GTPase proteins share many features with the Ras proto-oncogene: they act as cellular switches that are strictly regulated. Their on and of states relay the environmental cues and control cellular processes that are subverted during cellular transformation, such as cell division, motility and differentiation. PAK4 is one of the Rho GTPases effector proteins, and transfers their message to target enzymes or regulatory proteins, modifying their structure and activity. The PAK4 protein was found overexpressed in tumour cells and its adequate levels in the cell are fundamental for normal embryonic development, cellular growth and survival, as well as programmed cell death (apoptosis).
The second pathway is the protein synthesis cellular machinery. While it has been studied for a long time as the cellular 'protein factory', recently it has become clear that in many events, such as cell division, embryonic development, response to environmental stress, and viral infection, protein synthesis rates are controlled both globally and specifically. Translation of mRNA into protein is in fact the ultimate step for gene expression regulation and allows producing new protein without the need of novel RNA synthesis.
Growing examples suggest that translational control is involved in GTPase regulated cellular events, one for all being that some mutations associated with the Fragile X Mental Retardation syndrome, disrupt the genes for a PAK4 homolog and Rho GTPase proteins.
With the MC-IRG action we started a new line of research aimed at finding novel evidence that PAK4 also mediates cellular transformation by regulating the translational rates of the cell. During the course of this project, we used biochemical techniques, in vitro studies of the translation reaction, and in vivo approaches in cultured cells, and exploited cellular and viral sequences that allow for specific protein synthesis when the global translation activity is shut down.
We could identify a specific region of PAK4 protein that binds to ribosomal proteins and can modulate translation in vitro. We could also show that a deregulated, active, PAK4 protein can influence both global and specific translational rates. Interesting evidence indicates that PAK4 can repress stress induced synthesis of cellular genes in the cell, while viral sequences are in turn activated, suggesting that PAK4 abnormal activation inhibits apoptosis induced translational control mechanisms, and favours viral replication. We could also show that under stress conditions active PAK4 transformed cell lines display enhanced activation of the translation initiation factor eIF4E, which is typically repressed in normal cell lines.
Our data strongly support that translational control mechanisms are involved in PAK4 induced transformed phenotypes, and our next goal is to find the direct molecular targets of such regulation. The data we obtained during the execution of this project consolidate the new line of research that was established, and strongly suggest further developments in the study the molecular mechanisms of cellular transformation and genetic diseases.