Embryonal Fyn-associated substrate (EFS)

Embryonal Fyn-associated substrate (EFS) is a member of the CAS (Crk-associated substrate) family of adaptor/scaffolding proteins, characterized by an SH3 domain and several tyrosine phosphorylation sites that serve as docking modules for kinases (such as FYN, SRC) and signaling molecules (CRK, YES, FAK). EFS integrates signals downstream of integrin and receptor tyrosine kinase activation, orchestrating actin cytoskeletal remodeling—crucial for cell adhesion, spreading, migration, and neurite outgrowth. In the immune system, EFS is highly expressed in the thymus, where it regulates T cell maturation, self-tolerance, and helps prevent autoimmunity. EFS dysregulation has been associated with cancer progression (including resistance to trastuzumab in breast cancer and methylation in metastatic uveal melanoma), and genetic variation in EFS is linked to immune-mediated disorders such as Crohn’s disease. While not a classical drug target, it is a key signaling hub whose expression and phosphorylation status can influence response to targeted therapies.

Other names

CASS3hEFSEFS2EFS1HEFSSINCas scaffolding protein family member 3CAS3signal transduction protein (SH3 containing)

Not a direct drug target but implicated in modulation of cellular response to therapies via signal transduction network changes (e.g., EFS knockdown restores trastuzumab sensitivity; EFS phosphorylation status correlates with response to vemurafenib in melanoma)