Large, recursive membrane platforms are associated to Trop-1, Trop-2, and protein kinase signaling for cell growth

The transmembrane glycoproteins Trop-1/EpCAM and Trop-2 independently trigger Ca²⁺ and kinase signals for cell growth and tumor progression. Our findings indicated that Trop-1 and Trop-2 tightly colocalize at macroscopic, ruffle-like protrusions (RLP), that elevate from the cell perimeter, and locally recur over hundreds of seconds. These previously unrecognized elevated membrane regions ≥20-µm-long, up to 1.5 µm high were revealed by Z-stack analysis and three-dimensional reconstruction of signal transducer-hosting plasma membrane regions. Trop-2 stimulates cell growth through a membrane supercomplex that comprises CD9, PKCα, ion pumps, and cytoskeletal components. Our findings indicated that the growth-driving Trop-2 supercomplex assembles at RLP. RLP behaved as sites of clustering of signal transducers, of phosphorylation/activation of growth-driving kinases, as recruitment sites of PKCα and as origin of Ca²⁺ signaling waves, suggesting RLP to be novel signaling platforms in living cells. RLP were induced by growth factors and disappeared upon growth factor deprivation and β-actin depolymerization, candidating RLP to be functional platforms for high-dimensional signaling for cell growth.