Septin remodeling is essential for the formation of cell membrane protrusions (microtentacles) in detached tumor cells

Abstract

Microtentacles are mostly microtubule-based cell protrusions that are formed by detached tumor cells. Here, we report that the formation of tumor cell microtentacles depends on the presence and dynamics of guanine nucleotide-binding proteins of the septin family, which are part of the cytoskeleton. In matrix-attached breast, lung, prostate and pancreas cancer cells, septins are associated with the cytosolic actin cytoskeleton. Detachment of cells causes redistribution of septins to the membrane, where microtentacle formation occurs. Forchlorfenuron, which inhibits septin functions, blocks microtentacle formation. The small GTPase Cdc42 and its effector proteins Borgs regulate septins and are essential for microtentacle formation. Dominant active and inactive Cdc42 inhibit microtentacle formation indicating that the free cycling of Cdc42 between its active and inactive state is essential for septin regulation and microtentacle formation. Cell attachment and aggregation models suggest that septins play an essential role in the metastatic behavior of tumor cells.

The phytohormone forchlorfenuron decreases viability and proliferation of malignant mesothelioma cells in vitro and in vivo

“…Cell detachment triggers redistribution of septins to the plasma membrane and formation of microtentacles. This process is inhibited by FCF in breast, lung, prostate and pancreas cancer cells in vitro indicating that septins play an essential role in the metastatic behavior of tumor cells [21].…”

Regulation of microtubule plus end dynamics by septin 9

“…In mammalian cells, septins colocalize with subsets of MTs and are required for MT-dependent functions in mitosis (Estey, Di Ciano-Oliveira, Froese, Bejide, & Trimble, 2010; Menon et al, 2014; Spiliotis, Kinoshita, & Nelson, 2005), vesicle trafficking (Spiliotis, Hunt, Hu, Kinoshita, & Nelson, 2008) and the formation of protrusive structures such as cilia (Ghossoub et al, 2013) and axon branches (Hu et al, 2012). In addition, septins have been implicated in the formation of MT-based nanotube-like protrusions, which are caused by bacterial toxins, and micro-tentacle protrusions that tumor cells develop in the absence of matrix attachments (Nolke et al, 2016; Ostevold et al, 2017). …”

Septins are critical regulators of osteoclastic bone resorption

“…We found that this drug had a pronounced and reproducible inhibitory effect on osteoclastic bone resorption with an IC50 of around 20 µM. FCF has previously been reported to inhibit mitosis, exocytosis, microtubule protrusions and cell migration 12 , 32 , 35 , 46 , 47 . Especially cell migration is interesting because it is known to be important for proper bone resorption.…”

“…The ruffles are supported by an actin and microtubule network that physically supports the protrusion, but also facilitates transport of vesicles for exo- and endocytosis. Septins (including SEPT9), were found to facilitate membrane protrusions 10 , 44 , 47 by guiding microtubule growth at the plus-end 35 towards the bottom of the resorption cavity 51 . Thus, septins may be involved in promoting the dynamics of ruffles and their change in shape and location.…”