FIF [Fibroblast Growth Factor-2 (FGF-2)-Interacting-Factor], a Nuclear Putatively Antiapoptotic Factor, Interacts Specifically with FGF-2

Abstract

Numerous evidence indicates that some of the activities of fibroblast growth factor 2 (FGF-2) depend on an intracrine mode of action. Recently, we showed that three high molecular mass (HMM) nuclear forms of FGF-2 are part of a 320-kDa protein complex while the cytoplasmic AUG-initiated form is included in a 130-kDa complex. Consequently, the characterization of FGF endogenous targets has become crucial to allow the elucidation of their endogenous activities. Through the screening of GAL4-based yeast two-hybrid expression libraries, we have isolated a gene encoding a nuclear protein of 55 kDa, FIF (FGF-2-interacting-factor), which interacts specifically with FGF-2 but not with FGF-1, FGF-3, or FGF-6. In this system, FIF interacts equally well with the NH2-extended 24-kDa FGF form as with the 18-kDa form, indicating that the FIF-binding motif is located in the last 155 amino acids of FGF-2. Nevertheless, coimmunoprecipitation experiments showed an exclusive association with HMM FGF-2. The predicted protein contains a canonical leucine zipper domain and three overlapping hydrophobic heptad repeats. The region spanning these repeats is, together with a region located in the N-terminal part of the FIF protein, implicated in the binding to FGF-2. In contrast to the full-length FIF protein, several deletion constructs were able to transactivate a lac-Z reporter gene. Furthermore, the COOH-terminal part, but not the full-length FIF protein, has previously been shown to exhibit antiapoptotic properties. Thus we discuss the possibility that these activities could reflect a physiological function of FIF through its interaction with FGF-2.

Helical Repeat Structure of Apoptosis Inhibitor 5 Reveals Protein-Protein Interaction Modules

“…4A). This finding is consistent with a previous report indicating that the replacement of these conserved leucine residues does not abolish FGF-2 binding (16).…”

“…1B). Although hydrophobic interactions may also be important for binding, we predict that the positively charged high molecular mass FGF-2 likely binds to the negatively charged convex surface of API5, as determined from previous immunoprecipitation results and surface electrostatic potential (16).…”

“…It has been reported that high molecular mass FGF-2 interacts with API5 in the nucleus, and immunoprecipitation results suggest that two separate regions corresponding to three helices (␣6 and ␣15-␣16) of API5 are important for FGF-2 binding (16). The ␣6 is exposed to the convex surface of API5, and ␣15-␣16 are exposed on both the concave and convex surfaces.…”

“…Various API5 interaction partners have been identified. API5 interacts with high molecular mass forms of fibroblast growth factor 2 (FGF-2), which are involved in cell proliferation and tumorigenesis (16). API5 also binds to and regulates Acinus, a protein involved in chromatin condensation and DNA fragmentation during apoptosis (23).…”

The fibroblast growth factors in multiple myeloma

“…Four isoforms of FGF2 were detected including high molecular weight (HMW; 22, 22.5 and 24 kDa) FGF2. Correspondingly, the majority of MM cell lines also expressed the intracellular partner of HMW FGF2, FGF2-interacting factor (FIF/AAC-11) 6 (Figure 1c). Among the cell lines used here, the OPM2, KMS11, KMS18, H929 and LP1 cells are known to possess t(4;14)(p16.3;q32) as well as upregulate FGFR3 (Figure 1c).…”