Light Activates Cdc42-Mediated Needle-Shaped Filopodia Formation via the Integration of Small GTPases

Cdc42 has been linked to multiple human cancers and is implicated in the migration of cancer cells. Cdc42 could be activated via biochemical and biophysical factors in tumor microenvironment, the precise control of Cdc42 was essential to determine its role to cell behaviors. Needle-shaped protrusions (filopodia) could sense the extracellular biochemical cues and pave the path for cell movement, which was a key structure involved in the regulation of cancer cell motility.

We used the photoactivatable Cdc42 to elucidate the breast cancer cell protrusions, the mutation of Cdc42 was to confirm the optogenetic results. We also inhibit the Cdc42, Rac or Rho respectively by the corresponding inhibitors.

We identified that the activation of Cdc42 by light could greatly enhance the formation of filopodia, which was positive for the contribution of cell movement. The expression of Cdc42 active form Cdc42-Q61L in cells resulted in the longer and more filopodia while the Cdc42 inactive form Cdc42-T17N were with the shorter and less filopodia. Moreover, the inhibition of Cdc42, Rac or Rho all significantly reduced the filopodia numbers and length in the co-expression of Cdc42-Q61L, which showed that the integration of small GTPases was necessary in the formation of filopodia. Furthermore, photoactivation of Cdc42 failed to enhance the filopodia formation with the inhibition of Rac or Rho. However, with the inhibition of Cdc42, the photoactivation of Cdc42 could partially recover back the filopodia formations, which indicated that the integration of small GTPases was key for the filopodia formations.

Our work highlights that light activates Cdc42 is sufficient to promote filopodia formation without the destructive structures of small GTPases, it not only points out the novel technique to determine cell structure formations but also provides the experimental basis for the efficient small GTPases-based anti-cancer strategies.