FRK (Fyn-related kinase), also known as PTK5 in humans and RAK in rodents, is a non-receptor tyrosine kinase belonging to the Src family kinase (SFK) group. Discovered in the 1990s, FRK is distinguished from other SFK members by its unique structural features, including an N-terminal SH3 domain, an SH2 domain, and a C-terminal catalytic kinase domain. Unlike many SFKs, FRK lacks a conserved regulatory tyrosine residue in its C-terminal tail, resulting in constitutive activation in certain contexts.
Functionally, FRK is implicated in regulating cell proliferation, differentiation, and adhesion. It acts as a tumor suppressor in multiple cancers, including breast, pancreatic, and colorectal cancers, where its expression is often downregulated due to promoter hypermethylation or genetic alterations. FRK inhibits oncogenic signaling pathways, such as EGFR and STAT3. thereby suppressing tumor growth and metastasis. Conversely, in some contexts, FRK may exhibit pro-survival or pro-migratory roles, highlighting its context-dependent duality.
FRK-specific antibodies are critical tools for studying its expression, localization, and interactions. They enable detection via Western blotting, immunohistochemistry, and immunofluorescence, aiding research on FRK's role in cancer biology, signaling networks, and therapeutic targeting. Commercial antibodies typically target epitopes within its kinase or SH2 domains, with validation emphasizing specificity across human and rodent models.