Abstract
Semaphorins and plexins are implicated in the progression of various types of cancer, although the molecular basis has not been fully elucidated. Here, we report the expression of plexin-B3 in glioma cells, which upon stimulation by its ligand Sema5A results in significant inhibition of cell migration and invasion. A search for the underlying mechanism revealed direct interaction of plexin-B3 with RhoGDP dissociation inhibitor α (RhoGDIα), a negative regulator of RhoGTPases that blocks guanine nucleotide exchange and sequesters them away from the plasma membrane. Glioma cells challenged with Sema5A indeed showed a marked reduction in Rac1-GTP levels by 60%, with a concomitant disruption of lamellipodia. The inactivation of Rac1 was corroborated to contribute to the impediment of glioma cell invasion by Sema5A, as supported by the abolishment of effect upon forced expression of a constitutively active Rac1 mutant. Furthermore, silencing the endogenous expression of RhoGDIα in glioma cells was found to be sufficient in abrogating the down-regulation of Rac1-GTP and the ensuing suppression of glioma cell motility induced by Sema5A. Mechanistically, we provide evidence that Sema5A promotes Rac1 recruitment to RhoGDIα and reduces its membrane localization in a plexin-B3-dependent manner, thereby preventing Rac1 activation. This represents a novel signaling of semaphorin and plexin in the control of cell motility by indirect inactivation of Rac1 through RhoGDIα.
Highlights
32436 JOURNAL OF BIOLOGICAL CHEMISTRY the expression of semaphorins and plexins in various types of cancer [3,4,5], suggesting their emerging roles in cancer progression
The results showed that RhoGDI␣ co-precipitated with plexin-B3CD but not with glutathione S-transferase (GST) protein alone (Fig. 2A)
It can be argued that an overexpression of active Rac1 promotes cell invasion in Fc-treated cells by 30%, the percentage increase in the Sema5A-Fc group is well beyond that and reaches over 70%. These findings suggest that the impairment of C6 glioma cell motility by Sema5A and plexin-B3 is mediated through Rac1 inactivation
Summary
32436 JOURNAL OF BIOLOGICAL CHEMISTRY the expression of semaphorins and plexins in various types of cancer [3,4,5], suggesting their emerging roles in cancer progression. Immunoprecipitation—To assay for the binding between RhoGDI␣ and Rac1, glioma cells at 50 –70% confluence were treated with Sema5A-Fc or Fc control protein for 30 min. To ascertain the inactivation of Rac1 by Sema5A is mediated through plexin-B3, the experiments were repeated in glioma cells in which the expression of endogenous plexin-B3 was silenced by RNAi. a significant reduction in Rac1GTP levels was still observed in the siRNA control and mock transfection groups, the negative effect induced by Sema5A-Fc was abrogated when plexin-B3 expression in the cells was down-regulated (Fig. 3B).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
