Signaling Networks in Cross-Striated Muscle Cells

In this research focus, we systematically delineate phosphorylation-dependent signaling pathways and identify their specific targets in mechanically stressed myocytes. Phospho-signaling networks entail reversible and site-specific phosphorylation reactions controlled by kinases and protein phosphatases to determine cell functions and fate. To delineate such large protein phosphorylation networks, we use global and targeted quantitative phosphoproteomics approaches combined with high-end mass spectrometry technology. Based on our myotube phosphoproteome data, we have identified the myofibrillar Z-disc as a protein phosphorylation hotspot in cross-striated muscle cells. Specifically, we are investigating the complex regulation of the myocyte signaling adaptor and mechanosensitive protein filamin C (FLNC). This large actin-crosslinking protein is essential for the formation, the integrity, and the maintenance of sarcomeres. Notably, FLNC gene mutations cause severe myopathies and cardiomyopathies in humans, thus highlighting the high relevance of our research for human health and disease.

In current work, we want to gain a mechanistic understanding of FLNC’s function and regulation both under basal and acute mechanical stress conditions. So far, we have identified >30 mechanical stress-regulated FLNC phosphosites. Furthermore, we discovered that FLNC’s numerous protein interactions as well as its dynamics and turnover are tightly regulated by different protein kinases and protein phosphatases through site-specific phosphorylation/dephosphorylation reactions. For example, we have revealed that the FLNC-FILIP1 interaction is phospho-regulated: While FLNC is shielded from FILIP1 binding through phosphorylations by AKT and PKCa, it is rapidly dephosphorylated by PP1 under acute mechanical stress to promote FILIP1-mediated FLNC degradation. We propose that precise phospho-regulation of FLNC is key to stabilize and maintain sarcomeres in skeletal muscle cells during acute mechanical stress, which we are currently exploring in detail.