Sulforaphane covalently interacts with the transglutaminase 2 cancer maintenance protein to alter its structure and suppress its activity

Abstract Type 2 transglutaminase (TG2) functions as an important cancer cell survival protein in a range of cancers including epidermal squamous cell carcinoma. TG2 exists in open and closed conformations each of which has a distinct and mutually exclusive activity. The closed conformation has GTP‐binding/GTPase activity while the open conformation functions as a transamidase to catalyze protein‐protein crosslinking. GTP‐binding/GTPase activity is required for TG2 maintenance of the aggressive cancer phenotype. Thus, identifying agents that convert TG2 from the closed to the open GTP‐binding/GTPase inactive conformation is an important cancer prevention/treatment strategy. Sulforaphane (SFN) is an important diet‐derived cancer prevention agent that is known to possess a reactive isothiocyanate group and has potent anticancer activity. Using a biotin‐tagged SFN analog (Biotin‐ITC) and kinetic analysis we show that SFN covalently and irreversibly binds to recombinant TG2 to inhibit transamidase activity and shift TG2 to an open/extended conformation, leading to a partial inhibition of GTP binding. We also show that incubation of cancer cells or cancer cell extract with Biotin‐ITC results in formation of a TG2/Biotin‐ITC complex and that SFN treatment of cancer cells inhibits TG2 transamidase activity and shifts TG2 to an open/extended conformation. These findings identify TG2 as a direct SFN anticancer target in epidermal squamous cell carcinoma.