Ras proteins are small GTPase functioning as molecular switches that, in 
response to particular extracellular signalling, as growth factors, activate a 
diverse array of intracellular effector cascades regulating cell proliferation, 
differentiation and apoptosis. Human tumours frequently express Ras proteins 
(Ha-, Ki-, N-Ras) activated by point mutations which contribute to malignant 
phenotype, including invasiveness and angiogenesis. Despite the common 
signalling pathways leading to similar cellular responses, studies clearly 
demonstrate unique roles of the Ras family members in normal and pathological 
conditions and the lack of functional redundancy seems to be explainable, at 
least in part, by the ability of Ras isoforms to localize in different 
microdomains to plasma membrane and intracellular organelles. This different 
intracellular compartmentalization could help Ras isoforms to contact different 
downstream effectors finally leading to different biological outcomes. 
Interestingly, it has also been shown that Ha- and Ki-Ras exert an opposite role 
in regulating intracellular redox status. In this regard we suggest that H-Ras 
specific induction of ROS (reactive oxygen species) production could be one of 
the main determinants of the invasive phenotype which characterize cancer cells 
harbouring H-Ras mutations. In our hypothesis then, while K-Ras (not able to 
promote oxidative stress) could mainly contribute to cancer progression and 
invasiveness through activation of MAPK and PI3K, H-Ras-mediated oxidative 
stress could play a unique role in modulation of intercellular contacts leading 
to a loss of cell adhesion and eventually also to a metastatic spread.