Aberrant Rac pathway signalling in glioblastoma.

Glioblastoma is an aggressive and incurable form of brain cancer. Both mutation analysis in human glioblastoma and mouse modelling studies have shown that aberrant activation of the PI 3-kinase pathway is a central driver of glioblastoma malignancy. The small GTPase Rac is activated downstream of this pathway, mediating a subset of the effects of aberrant PI 3-kinase pathway activation. Here I discuss the current state of our knowledge on Rac activation mechanisms in glioblastoma. Current knowledge on roles for specific PI 3-kinase pathway responsive Rac guanine nucleotide exchange factors in glioblastoma is reviewed. Rac is best known for its role in promoting cell motility and invasion, but there is also evidence for roles in multiple other cellular processes with cancer relevance, including proliferation, differentiation, apoptosis, DNA damage responses, metabolism, angiogenesis and immunosuppression. I review what is known about the role of Rac in these processes in glioblastoma. Finally, I assess possible strategies to inhibit this pathway in glioblastoma through either direct inhibition of Rac or inhibition of upstream activators or downstream mediators of Rac signalling.