Interaction of the τ2 Transcriptional Activation Domain of Glucocorticoid Receptor with a Novel Steroid Receptor Coactivator, Hic-5, Which Localizes to Both Focal Adhesions and the Nuclear Matrix

Abstract

Hic-5 (hydrogen peroxide-inducible clone-5) is a focal adhesion protein that is involved in cellular senescence. In the present study, a yeast two-hybrid screen identified Hic-5 as a protein that interacts with a region of the glucocorticoid receptor that includes a nuclear matrix-targeting signal and the tau2 transcriptional activation domain. In transiently transfected mammalian cells, overexpression of Hic-5 potentiated the activation of reporter genes by all steroid receptors, excluding the estrogen receptor. The activity of the estrogen receptor and the thyroid hormone receptor was stimulated by Hic-5 in the presence but not in the absence of coexpressed coactivator GRIP1. In biochemical fractionations and indirect immunofluorescence assays, a fraction of endogenous Hic-5 in REF-52 cells and transiently expressed Hic-5 in Cos-1 cells was associated with the nuclear matrix. The C-terminal region of Hic-5, which contains seven zinc fingers arranged in four LIM domains, was required for interaction with focal adhesions, the nuclear matrix, steroid receptors, and the tau2 domain of glucocorticoid receptor. The N-terminal region of Hic-5 possesses a transcriptional activation domain and was essential for the coactivator activity of Hic-5. Given the coexisting cytoplasmic and nuclear distributions of Hic-5 and its role in steroid receptor-mediated transcriptional activation, it is proposed that Hic-5 might transmit signals that emanate at cell attachment sites and regulate transcription factors, such as steroid receptors.

Paxillin: Adapting to Change

“…A potential role for PYK2 in the nuclear localization of paxillin and Hic-5 has also been reported (4). The localization of paxillin and Hic-5 to the nucleus in normally growing cells would provide additional assurance for a relevant role for these proteins in this compartment, and in fact, ϳ10% of cellular paxillin and Hic-5 can be recovered in nuclear matrix fractions (121,315). Hic-5 association with the nuclear matrix is mediated through the LIM domains (315), whereas for paxillin, the amino terminus is required in addition to the LIM domains (121).…”

“…How-ever, the capacity of both Hic-5 and paxillin to bind steroid receptors provides a more direct path to nuclear function. They contribute to the transactivation of androgen, glucocorticoid, and progesterone receptors, but not the estrogen receptor (63,121,315). The level of transactivation is approximately fivefold stimulation, with paxillin and Hic-5 capable of additive transactivation.…”

“…The mechanism in which this is accomplished differs between the two molecules. While both paxillin and Hic-5 bind to steroid receptors through their carboxy-terminal LIM domains (121, 315), the paxillin transactivation domain is confined to the carboxy terminus (121), whereas this activity resides solely within the amino terminus of Hic-5 (315). In addition, Hic-5 binding to steroid receptors may be ligand dependent (63) while paxillin binding does not require ligand-bound steroid receptor (121).…”

Leupaxin acts as a mediator in prostate carcinoma progression through deregulation of p120catenin expression

“…How LPXN influences p120CTN expression is currently under thorough investigation. In recent reports an important role for paxillin family members in interaction and activation of a series of transcription factors was established (Fujimoto et al, 1999;Yang et al, 2000;Kasai et al, 2003;Shibanuma et al, 2003Shibanuma et al, , 2004Wang et al, 2005Wang et al, , 2008. Hence, we propose that there could be a direct regulation of p120CTN expression by LPXN itself together with other unknown factors.…”

Competitive Nuclear Export of Cyclin D1 and Hic-5 Regulates Anchorage-Dependence of Cell Growth and Survival

“…In contrast, when Gal, Hic-5, or CRM1 were absent ( Figure 6A, H ϩ CrmV, G ϩ CrmV, and GH ϩ V), luciferase activity was Ͻ10% of that in the GH ϩ CrmV condition, indicating that GH ϩ CrmV activity was largely dependent on the presence and interaction of the Hic-5 and CRM1 moieties. Limited activity was detected for Gal-Hic and VP alone (GH ϩ V) possibly because of the weak transactivational activity occurring in the N-terminal half of Hic-5 (Yang et al, 2000).…”