Rho/ROCK-dependent pseudopodial protrusion and cellular blebbing are regulated by p38 MAPK in tumour cells exhibiting autocrine c-Met activation

Background information. The c-Met-dependent, beta-actin-rich, blebbed pseudopodia of MSV-MDCK-INV (invasive Moloney-sarcoma-virus-transformed Madin-Darby canine kidney) cells are induced by Rho/ROCK (Rho kinase) activation, and are morphologically distinct from flat extended lamellipodia. Results. Microtubules were shown to extend to these actin-rich pseudopodial domains, and microtubule depolymerization by nocodazole treatment resulted in progressive cellular blebbing, initiating in the pseudopodial domains and resulting in transient cellular rounding and blebbing after 30 min. The blebbing response was dependent on autocrine HGF (hepatocyte growth factor) activation of c-Met and prevented by inhibition of RhoA, ROCK and p38 MAPK (p38 mitogen-activated protein kinase), but not ERK (extracellular-signal-regulated kinase) or PI3K (phosphoinositide 3-kinase). Phospho-p38 MAPK was present in pseudopodia, localizing activation of this signalling pathway to this protrusive membrane structure. In serum-starved cells, LPA (lysophosphatidic acid) activation of RhoA induced p38 MAPK-dependent pseudopodial protrusions, and inhibition of p38 MAPK prevented pseudopodial protrusion and displacement of MSV-MDCK-INV cells. MSV-MDCK-INV cells exhibited intermittent blebbing and rounding, which may represent an integral part of their motile behaviour. Conclusions. The localized activation of an autocrine HGF/c-Met loop regulates Rho/ROCK activation of p38 MAPK signalling to stimulate both membrane blebbing and pseudopod formation.