Recent studies have demonstrated that H(2)O(2) acts as a second messenger of mitogenic signaling and that catalase is under the regulation of PKA and PKC signaling. Here we examined whether catalase binds any mitogenic signaling molecules. Our results indicated that serum stimulation of HeLa, Caco-2, and LiSa-2 cells, but not BJ-1 and primary human bronchial epithelial cells, resulted in catalase binding to Grb2. Whereas serum deprivation, butyrate, and herbimycin-A negatively regulated the binding, an extended culture of confluent Caco-2 cells resulted in binding of an additional but as yet unidentified molecule to the Grb2-catalase complex. Expression of active catalase nearly 15-fold over control level in Tet-off HeLa cells substantially increased binding to Grb2, and this was sensitive to 3-aminotriazole, a specific catalase inhibitor. Furthermore, fibrinogen, fibronectin, and laminin, but not collagen types I to V, hyaluronic acid, elastin, insulin, EGF, IGF-I, PDGF, or NGF, resulted in binding similar to that of serum. A mutation of tyrosine to phenylalanine at 447 abolished the binding capability of catalase to Grb2 in vitro. These results support the view that catalase (447)Tyr-Val-Asn-Val binds Grb2 upon phosphorylation in tumor cells when stimulated with serum or ligands for integrin receptors. This is the first report demonstrating that catalase binds a SH2 domain of the molecule and participates in integrin signaling.