Distinct LIM domains of Hic‐5/ARA55 are required for nuclear matrix targeting and glucocorticoid receptor binding and coactivation

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Abstract
Hydrogen peroxide‐inducible clone‐5 (Hic‐5), belongs to the group III LIM domain protein family and contains four carboxyl‐terminal LIM domains (LIM1–LIM4). In addition to its role in focal adhesion signaling, Hic‐5 acts in the nucleus as a coactivator for some steroid hormone receptors such as the glucocorticoid receptor (GR) and androgen receptor (AR). Based upon its effect on AR transactivation, Hic‐5 has also been designated as ARA55. Here, we report mapping studies of Hic‐5/ARA55 functional domains and establish that LIM3 and LIM4 are necessary for maximal effects on GR transactivation. However, results from yeast two‐hybrid assays demonstrated that these two LIM domains together, while necessary, are not sufficient to interact with the tau2 transactivation domain of GR. LIM4 also functions as a nuclear matrix targeting sequence (NMTS) for Hic‐5/ARA55, as it is both necessary and sufficient to target a heterologous protein to the nuclear matrix. Thus, as suggested from previous analysis of LIM domain‐containing proteins, separate but highly related LIM domains serve distinct functions.