Microtubules’ Role in Transmitting Cellular Signals Revealed

A wide range of cellular activities—including division, movement, and programmed death—depend on internal signaling proteins that decode commands from outside the cell. These signals are first received by receptors on the cell membrane, then transmitted inward through various pathways until they reach the cytoskeleton. Microtubules, the central structural elements of the cytoskeleton, not only provide shape and transport routes for cellular components but also actively participate in signal transmission.

Once viewed merely as passive recipients of instructions, microtubules are now recognized as active conduits in cellular communication. When specific signaling proteins attach to them, microtubules help direct essential cellular activities such as immune defense and cell division. Without their involvement, many molecular messages would never reach their targets. While their signaling role was identified decades ago, the molecular details of how signals pass through them remained unclear until recently.

A research team at the PSI Center for Life Sciences, led by Sung Choi and Michel Steinmetz, in collaboration with Alfred Zippelius’s group at the University of Basel, has now described this mechanism in detail in a Cell paper. Their work focuses on a signaling protein called GEFH1 (guanine nucleotide exchange factor H1), known for activating the RhoA signalling pathway, which regulates cell division and movement. Using cryo-electron microscopy, biochemical, and cell biological methods, the researchers showed that GEFH1 binds specifically to microtubules through its C1 domain, a defined molecular section rich in amino acids.

Choi explains, “We bioengineered and tested fragments of GEFH1 that are capable of binding to microtubules. We constructed variants of GEFH1 with mutated docking sites and introduced them into cells to see if they would bind. This allowed us to clearly establish that the C1 domain alone is responsible for the binding.” The study revealed that this interaction occurs precisely where four tubulin units meet, fitting together like a plug in a tailored socket. When the microtubule disassembles during its normal cycle, GEFH1 is released, triggering the RhoA pathway to initiate further processes.

According to Steinmetz, “They complete our picture of the signaling cascades triggered in the cell by messenger substances such as hormones and cytokines.” Understanding this mechanism could open medical opportunities to modulate such interactions. Proteins with C1 domains, such as the tumor suppressor RASSF1A, may represent similar targets, highlighting how microtubule-protein interactions influence both normal cellular regulation and disease.