PREX1 integrates G protein-coupled receptor and phosphoinositide 3-kinase signaling to promote glioblastoma invasion

Abstract

A defining feature of the brain cancer glioblastoma is its highly invasive nature. When glioblastoma cells are isolated from patients using serum free conditions, they accurately recapitulate this invasive behaviour in animal models. The Rac subclass of Rho GTPases has been shown to promote invasive behaviour in glioblastoma cells isolated in this manner. However the guanine nucleotide exchange factors responsible for activating Rac in this context have not been characterized previously. PREX1 is a Rac guanine nucleotide exchange factor that is synergistically activated by binding of G protein αγ subunits and the phosphoinositide 3-kinase pathway second messenger phosphatidylinositol 3,4,5 trisphosphate. This makes it of particular interest in glioblastoma, as the phosphoinositide 3-kinase pathway is aberrantly activated by mutation in almost all cases. We show that PREX1 is expressed in glioblastoma cells isolated under serum-free conditions and in patient biopsies. PREX1 promotes the motility and invasion of glioblastoma cells, promoting Rac-mediated activation of p21-associated kinases and atypical PKC, which have established roles in cell motility. Glioblastoma cell motility was inhibited by either inhibition of phosphoinositide 3-kinase or inhibition of G protein βγ subunits. Motility was also inhibited by the generic dopamine receptor inhibitor haloperidol or a combination of the selective dopamine receptor D2 and D4 inhibitors L-741,626 and L-745,870. This establishes a role for dopamine receptor signaling via G protein βγ subunits in glioblastoma invasion and shows that phosphoinositide 3-kinase mutations in glioblastoma require a context of basal G protein–coupled receptor activity in order to promote this invasion.

P-Rex1 is dispensable for Erk activation and mitogenesis in breast cancer

“…Moreover, P-Rex1 controls the expression of genes involved in invasiveness in breast cancer cells [ 41 ]. Similar effects of P-Rex1 in cell motility and invasion have been observed in other cancers, including prostate and ovarian cancer, melanoma, and glioblastoma [ 21 – 24 ]. The involvement of P-Rex1 in cancer cell migration in vivo has been demonstrated using a mouse model for melanoma metastasis (Lindsay et al , Ref.…”

“…Rather, their findings revealed that in melanoma cells, Erk activity is required for maintaining the expression of P-Rex1 via transcriptional and post-transcriptional mechanisms [ 30 ]. A recent study also showed that P-Rex1 siRNA in glioblastoma cells did not affect growth, whereas it markedly affected motility and invasion [ 24 ]. These results align with ours in luminal breast cancer models, and support a specific role for P-Rex1 in cell motility rather than in cell growth.…”

“…P-Rex1 up-regulation in luminal breast cancer has been associated with deregulated epigenetic mechanisms that lead to PREX1 gene promoter demethylation [ 20 ]. P-Rex1 expression has been also reported in prostate cancer, ovarian cancer, melanoma, and glioblastoma [ 21 – 24 ].…”

A phase 2 study of the first imipridone ONC201, a selective DRD2 antagonist for oncology, administered every three weeks in recurrent glioblastoma

“…Growth factor signaling is also dysregulated in most glioblastoma tumors, with alterations in EGFR, PIK3CA, PTEN, or FGFRA commonly observed. DRD2 is a G protein-coupled receptor that is overexpressed in glioblastoma and controls growth factor signaling through cross-talk mechanisms involving beta-arrestin and scaffold proteins [ 5 , 6 ]. DRD2 blockade is sufficient to inactivate growth factor signaling and induce tumor cell death in preclinical models of glioblastoma and other malignancies [ 6 , 7 ].…”

The role of Rac in tumor susceptibility and disease progression: from biochemistry to the clinic

“…This epigenetic modification in the PREX1 promoter turned out to be a prognostic marker of poor patient survival (61). In melanoma cells, P-Rex1 amplification is primarily driven by augmented gene transcription and protein stability, and it causally associates with invasiveness rather than proliferative capacity, as also described in prostate and glioblastoma models (62–64). …”