The kinase activity of c-Abl but not v-Abl is potentiated by direct interaction with RFXI, a protein that binds the enhancers of several viruses and cell-cycle regulated genes

Abstract

c-Abl, the non-receptor tyrosine kinase is associated with EP, a DNA element found in promoters/enhancers of di erent viruses and cell-cycle regulated genes. EP-DNA binds RFXI, a member of a novel family of DNA-binding proteins that is conserved through evolution and in yeast, it controls di erentiation and exit from the mitotic cycle to G 0 . EP-associated proteins are preferentially tyrosine phosphorylated and the associated c-Abl has strong tyrosine kinase activity. Here we investigated the molecular mechanism underlying this c-Abl kinase activity. We show that RFXI and c-Abl are in direct interaction, in vitro and in cell extracts, through the RFXI proline rich (PxxP) motif and the c-Abl SH3 domain. Remarkably, this interaction signi®cantly potentiates cAbl but not v-Abl auto-kinase activity. Collectively, we describe a novel mechanism of c-Abl recruitment to a de®ned DNA-cis element with its concomitant kinase activation. We propose that this mechanism may act to regulate cell-cycle control genes.

c-Abl Has High Intrinsic Tyrosine Kinase Activity That Is Stimulated by Mutation of the Src Homology 3 Domain and by Autophosphorylation at Two Distinct Regulatory Tyrosines

“…In contrast, the activation of nuclear c-Abl in S phase is through the detachment of the inhibitor Rb protein (3), whereas Abl may be activated by free radicals through dissociation of Pag/Msp23, an antioxidant protein that also inhibits Abl (7). Abl kinase activity can also be stimulated by the binding of several activator proteins, including the transcription factors c-Jun (8) and RFX1 (9), and the adapter protein Nck (10). These observations suggest complex regulation of c-Abl at multiple levels through binding or dissociation of activators and inhibitors and via direct phosphorylation.…”

c-Abl: activation and nuclear targets

“…Furthermore, other SH3 binding proteins, such as Abi 1 and 2, are phosphorylated by c-Abl 7,8 and are therefore unlikely to inhibit it. Also, the adaptor protein Crk 26 and the DNA-binding protein RFX1 13 support and even potentiate c-Abl kinase activity in vitro. These findings lend support to the possibility that the cAbl kinase domain is under repression by an intramolecular mechanism.…”

“…64 RFX1 interacts with the c-Abl SH3 domain and stimulates c-Abl kinase activity. 13 A limited number of RFX1 target genes have so far been identified, and the products of most of them are involved in DNA replication and repair. These include c-MYC, PCNA and the DNA-repair gene XRCC1.…”

“…5,6 This domain determines the interaction of c-Abl with many proteins, such as the Abi family of proteins, 7,8 Pag/MSP23, 9 ATM, 10,11 SHPTP1 12 and RFX1. 13 The SH2 domain, about 100 amino acids long, interacts with tyrosine phosphorylated residues. Although various SH2 domains mediate phosphotyrosine dependent protein-protein interactions, each has distinct binding requirements.…”

Aph2, a Protein with a zf-DHHC Motif, Interacts with c-Abl and Has Pro-apoptotic Activity

“…p53, Rb, 3BP-1/3BP-2, AAP1, ATM and DNA-PK, PAG) (18). Some of the interacting proteins, such as PAG and Rb, were found to negatively regulate c-Abl kinase activity and function, whereas others, such as RFXI, an EP-DNA-binding protein that potentiates the kinase activity when bound to c-Abl, were found to be positive regulators for c-Abl (19).In this study we identified a novel c-Abl-interacting protein, * The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C.…”