Turid Eide

Distinct but overlapping domains of AKAP95 are implicated in chromosome condensation and condensin targeting

A‐kinase (or PKA)‐anchoring protein AKAP95 is a zinc‐finger protein implicated in mitotic chromosome condensation by acting as a targeting molecule for the condensin complex. We have identified determinants of chromatin‐binding, condensin‐targeting and chromosome‐condensation activities of AKAP95. Binding of AKAP95 to chromatin is conferred by residues 387–450 and requires zinc finger ZF1. Residues 525–569 are essential for condensation of AKAP95‐free chromatin and condensin recruitment to chromosomes. Mutation of either zinc finger of AKAP95 abolishes condensation. However, ZF1 is dispensable for condensin targeting, whereas the C‐terminal ZF2 is required. AKAP95 interacts with Xenopus XCAP‐H condensin subunit in vitro and in vivo but not with the human hCAP‐D2 subunit. The data illustrate the involvement of overlapping, but distinct, domains of AKAP95 for condensin recruitment and chromosome condensation and argue for a key role of ZF1 in chromosome condensation and ZF2 in condensin targeting. Moreover, condensin recruitment to chromatin is not sufficient to promote condensation.

Identification, cloning and characterization of a novel nuclear protein, HA95, homologous to A-kinase anchoring protein 95⋆

Summary— Previously, we have identified and characterized nuclear AKAP95 from man which targets cyclic AMP (cAMP)‐dependent protein kinase (PKA)‐type II to the condensed chromatin/spindle region at mitosis. Here we report the cloning of a novel nuclear protein with an apparent molecular mass of 95 kDa that is similar to AKAP95 and is designated HA95 (homologous to AKAP95). HA95 cDNA sequence encodes a protein of 646 amino acids that shows 61% homology to the deduced amino acid sequence of AKAP95. The HA95 gene is located on chromosome 19p13.1 immediately upstream of the AKAP95 gene. Both HA95 and AKAP95 genes contain 14 exons encoding similar regions of the respective proteins, indicating a previous gene duplication event as the origin of the two tandem genes. Despite their apparent similarity, HA95 does not bind RII in vitro. HA95 contains a putative nuclear localization signal in its N‐terminal domain. It is localized exclusively into the nucleus as demonstrated in cells transfected with HA95 fused to either green fluorescence protein or the c‐myc epitope. In the nucleus, the HA95 protein is found as complexes directly associated with each other or indirectly associated via other nuclear proteins. In interphase, HA95 is co‐localized with AKAP95, but the two proteins are not biochemically associated. At metaphase, both proteins co‐localize with condensed chromosomes. The similarity in sequence and localization of HA95 and AKAP95 suggests that the two molecules constitute a novel family of nuclear proteins that may exhibit related functions.

Hormonal regulation of beta(2)-adrenergic receptor level in prostate cancer

Androgen deprivation is the only effective systemic therapy available for patients with prostatic carcinoma, but is associated with a gradual transition to a hormone‐refractory prostate cancer (HRCAP) in which ligand‐independent activation of the androgen receptor has been implicated. The β2‐adrenergic receptor (β2‐AR) is a well‐known activator of the androgen receptor.

TWIST1, A novel androgen-regulated gene, is a target for NKX3-1 in prostate cancer cells.

BackgroundTWIST1 plays a key role in EMT-mediated tumor invasion and metastasis. Since bone metastasis is a hallmark of advanced prostate cancer and is detected in at least 85% of patients who die of this disease, it is of great importance to understand the regulation of the cellular signaling pathways involved in the metastatic process.MethodsProstatic cell lines were analyzed using real time RT-PCR, chromatin immunoprecipitations (ChIP) and transfection of siRNA’s and reporter constructs.ResultsWe report in this paper that TWIST1 is an androgen-regulated gene under tight regulation of NKX3-1. Androgens repress the expression of TWIST1 via NKX3-1, which is a prostate–specific tumor suppressor that is down-regulated in the majority of metastatic prostate tumors. We show that NKX3-1 binds to the TWIST1 promoter and that NKX3-1 over-expression reduces the activity of a TWIST1 promoter reporter construct, whereas NKX3-1 siRNA up-regulates endogenous TWIST1 mRNA in prostate cancer cells.ConclusionOur finding that NKX3-1 represses TWIST1 expression emphasizes the functional importance of NKX3-1 in regulating TWIST1 expression during prostate cancer progression to metastatic disease.