Altered Membrane Mechanics Provides a Receptor-Independent Pathway for Serotonin Action

Serotonin, an important signaling molecule in humans, has an unexpectedly high lipid membrane affinity. The significance of this finding has evoked considerable speculation. Here we show that membrane binding by serotonin can directly modulate membrane properties and cellular function, providing an activity pathway completely independent of serotonin receptors. Atomic force microscopy shows that serotonin makes artificial lipid bilayers softer, and induces nucleation of liquid disordered domains inside the raft‐like liquid‐ordered domains. Solid‐state NMR spectroscopy corroborates this data at the atomic level, revealing a homogeneous decrease in the order parameter of the lipid chains in the presence of serotonin. In the RN46A immortalized serotonergic neuronal cell line, extracellular serotonin enhances transferrin receptor endocytosis, even in the presence of broad‐spectrum serotonin receptor and transporter inhibitors. Similarly, it increases the membrane binding and internalization of oligomeric peptides. Our results uncover a mode of serotonin–membrane interaction that can potentiate key cellular processes in a receptor‐independent fashion.

Chlamydia-induced curvature of the host-cell plasma membrane is required for infection

During invasion of host cells, Chlamydia pneumoniae secretes the effector protein CPn0678, which facilitates internalization of the pathogen by remodeling the target cell's plasma membrane and recruiting sorting nexin 9 (SNX9), a central multifunctional endocytic scaffold protein. We show here that the strongly amphipathic N-terminal helix of CPn0678 mediates binding to phospholipids in both the plasma membrane and synthetic membranes, and is sufficient to induce extensive membrane tubulations. CPn0678 interacts via its conserved C-terminal polyproline sequence with the Src homology 3 domain of SNX9. Thus, SNX9 is found at bacterial entry sites, where C. pneumoniae is internalized via EGFR-mediated endocytosis. Moreover, depletion of human SNX9 significantly reduces internalization, whereas ectopic overexpression of CPn0678-GFP results in a dominant-negative effect on endocytotic processes in general, leading to the uptake of fewer chlamydial elementary bodies and diminished turnover of EGFR. Thus, CPn0678 is an early effector involved in regulating the endocytosis of C. pneumoniae in an EGFR- and SNX9-dependent manner.

Perturbing the Dynamics and Organization of Cell Membrane Components: A New Paradigm for Cancer-Targeted Therapies

Cancer is a multi-process disease where different mechanisms exist in parallel to ensure cell survival and constant adaptation to the extracellular environment. To adapt rapidly, cancer cells re-arrange their plasma membranes to sustain proliferation, avoid apoptosis and resist anticancer drugs. In this review, we discuss novel approaches based on the modifications and manipulations that new classes of molecules can exert in the plasma membrane lateral organization and order of cancer cells, affecting growth factor signaling, invasiveness, and drug resistance. Furthermore, we present azurin, an anticancer protein from bacterial origin, as a new approach in the development of therapeutic strategies that target the cell membrane to improve the existing standard therapies.