Nonmuscle Myosin II and Upstream and Downstream Signaling

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Ligand-induced internalization of the epidermal growth factor receptor (EGFR) is an important process for regulating signal transduction, cellular dynamics, and cell-cell communication. However, until now, the molecular functions of nonmuscle myosin II (NM II) in the internalization of the EGFR have not been fully explored. We demonstrated that NM II is required for the internalization of the EGFR to trigger the EGFR-dependent activation of ERK and AKT. The EGFR was identified as a protein that interacts with NM II-B as determined by mass spectrometry analysis. This interaction requires both the regulatory light chain 20 (RLC20) of NM II and the kinase domain of the EGFR in a caveolin-enriched membrane (CEM). Loss of nonmuscle myosin heavy chain II (NMHC II) attenuates the internalization of the EGFR as determined by Alex 488-EGF internalization, biotinylation, and 125I-EGF labeling. Regulation of the internalization of the EGFR by silencing of NMHC II paralogs is distinct in COS-7 cells and A431 cells which show different expression patterns of these paralogs. Inhibition or loss of either NM II-A or NM II-B impairs the EGFR-dependent activation of ERK and AKT. Blebbistatin, an inhibitor of NM II ATPase activity, decreases the internalization of the EGFR as well as EGFR-dependent activation of ERK and AKT. In NMHC II siRNA treated A431 cells, restoration of the expression of NM II with motor impaired paralogs of NM II-A or II-B unlike wild type NM II failed to rescue EGFR-dependent activation of ERK and AKT. Taken together, these results suggest NM II is required for the internalization of the EGFR and EGFR-mediated signaling pathways.