Research lines

• New strategies to inhibit oncogenic K-Ras

  Ras proteins are GTPases that regulate signal transduction pathways, which control cell proliferation, differentiation, survival and apoptosis. K-Ras oncogenic mutations (one of the Ras isoforms) are highly frequent in colorectal, pancreas and lung cancers. Unfortunately, at this moment we do not have suitable K-Ras inhibitors for therapy. In order to better understand the regulation of K-Ras and look for strategies to inhibit its oncogenic action, our group is analyzing new proteins that might be interacting with K-Ras and regulate its function. We have shown that calmodulin and hnRNPA2 proteins bind specifically to K-Ras: Calmodulin inhibits K-Ras phosphorylation at ser181, thus modulating the functionality of non-oncogenic and oncogenic K-Ras forms; and the hnRNPA2 protein promotes signaling of K-Ras in pancreatic adenocarcinoma cells. 

• Signaling, cytoskeleton and cellular migration

  Our group is studying the signaling and trafficking of the epidermal growth factor receptor (EGFR) and the small GTPases K-Ras and Rac1. The signaling elicited by these proteins controls various important cellular processes such as proliferation, cell migration and mobility. EGFR signaling is initiated at the plasma membrane and remains in the endosomes, these signaling platforms can move to different cellular locations, thereby restricting spatial signaling and controlling different processes in the cell. Accordingly, many signaling proteins of EGFR have been detected in endosomes, among them K-Ras and Rac1. The main objective of this research line is to study the involvement of the endocytic compartment on EGFR, K-Ras and Rac1 functionality. 

• Replicative stress: response of untransformed cells versus tumor cells

  Genomic instability is a hallmark of tumor cells, resulting from errors in mitotic progression such as prolonged mitosis, DNA damage on bridged chromosomes or misaligned chromosomes. A better understanding of the upstream triggers of CIN are a long-standing objective in cancer research. Our laboratory is specifically interested in the interconnection between replicative stress, autophagy and CIN biomarkers. We showed that after severe replicative stress, untransformed cells enter into senescence, while most tumor cells are capable to recover and continue to proliferate while acquiring alterations in the genome. Interestingly, reinitiating DNA synthesis in tumor cells depends on new replication origin firing, making this event a possible target for cancer therapy upon replication stress induction. In addition, our findings uncovered a protective role for autophagy and lysosomes in mitosis, thus opening new avenues for CIN-targeted therapy in cancer.   

• Intracellular cholesterol transport and membrane repair in lysosomal diseases: role of AnxA6 and StARD3.

  Cholesterol accumulation in late endosomes is an established phenotype of the lysosomal disorder Niemann-Pick type C1 (NPC1). We demonstrated that annexin A6 (AnxA6) overexpression induces a phenotype reminiscent of NPC1 mutant cells and recently have validated that this cellular cholesterol imbalance is due to AnxA6 promoting Rab7 inactivation via TBC1D15, a Rab7-GAP. In NPC1 mutant cells, AnxA6 depletion and eventual Rab7 activation was associated with peripheral distribution and increased mobility of late endosomes. This was accompanied by an enhanced lipid accumulation in lipid droplets in an acyl-CoA:cholesterol acyltransferase (ACAT)-dependent manner. In addition, in AnxA6-deficient NPC1 mutant cells, Rab7-mediated rescue of late endosome-cholesterol export required the StAR-related lipid transfer domain-3 (StARD3) protein. Electron microscopy revealed a significant increase of membrane contact sites (MCS) between late endosomes and ER in NPC1 mutant cells lacking AnxA6, suggesting late endosome-cholesterol transfer to the ER via Rab7 and StARD3-dependent MCS formation. Thus, we identify AnxA6 as a novel gatekeeper that controls cellular distribution of late endosome-cholesterol via regulation of a Rab7-GAP and MCS formation. However, annexins, including AnxA1, A2, A6, A7, are crucial molecules for plasma membrane and lysosomal repair and it is now believed that accumulation of lipids as well as alterations of Ca2+ dynamics in lysosomes of NPC or Gaucher mutant cells lead to lysosomal damage. The study of AnxA6 and StARD3 interactomes and the relationship with other cell compartments such as mitochondria, ER and peroxisomes will provide insights to better understand the complex mechanistic molecular machinery involved in the cholesterol and lipid homeostasis.