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    • Recently the FDA approved the

    2023-03-20

    Recently, the FDA approved the first blood-based test for the detection of EGFR mutations in non-small cell lung cancer patients (http://www.fda.gov) (Voelker, 2016). This allows detection of specific, recurrent mutations, which can help the selection of the patients that could benefit from Erlotinib (Tarceva) therapy.
    Androgen receptor structure and function The direct effects of the androgenic hormones like testosterone (T) and dihydrotestosterone (DHT) are mediated by the AR. The AR gene is located on chromosome X (q11-12) and contains 8 exons. With a length of 90 kb, it is the largest and most complex of all nuclear steroid receptor genes, encoding a protein of 920 Reparixin (Lubahn et al., 1988, Tan et al., 2015). The AR is a multi-domain protein composed of the transactivation domain (NTD), a DNA-binding domain (DBD), a hinge region and a C-terminal ligand-binding domain (LBD). The structure of the AR NTD is believed to be flexible and dependent on its interaction partners (Lavery and Mcewan, 2005, McEwan et al., 2007). The activation function 1 (AF1), which serves as docking station for co-regulators, is located in the NTD (Jenster et al., 1991). This AF1 is composed of two separate but functionally interacting transcription activation units (Tau-1 and Tau-5), each believed to recruit different co-activator complexes (Callewaert et al., 2006, Van Tilborgh et al., 2013). The FQNFL motif, located upstream of Tau-1, can interact with the LBD (see below), and is important for the functional interactions between the NTD and the LBD (A. Brinkmann et al., 1999). The AR DBD recognizes very specific DNA motifs, which occur in promoter or enhancer regions of androgen regulated genes (Denayer et al., 2010). This domain consists of two zinc finger modules that are involved in dimerization as well as in positioning of the DNA-recognition α-helix into the major groove of DNA of the response elements (Shaffer et al., 2004). The LBD of the AR consists of 11 α-helices (H) and 4 β-strands (A. O. Brinkmann et al., 1989, Matias et al., 2000). The ligand binding pocket is buried in the LBD and is surrounded by the N-termini of α-helices 3, 5 and 12. The folding of H12 over the ligand binding pocket forms the core of the activation function 2 (AF2), since this forms a binding groove on the surface of the LBD. This surface is recognized by LxxLL-motifs present on the surface of the co-activators (Estébanez-Perpiñá et al., 2007, Rastinejad et al., 2013, Wurtz et al., 1996) or the FQNLF motif in the NTD (see above). Recently, the dimerization interface of the LBD was reported (Nadal et al., 2017). The unliganded AR is located in the cytoplasm, in a complex with heat shock proteins (Echeverria and Picard, 2010). When the hormone binds, conformational changes in the LBD occur and the interacting proteins dissociate, thus exposing the nuclear localization sequence (NLS) located in the hinge region between the DBD and LBD. Subsequently, intramolecular N/C interactions occur and the receptor is transported to the nucleus where it forms intermolecular N/C interactions (van Royen et al., 2012). Once in the nucleus, the AR homodimer regulates gene expression via binding to androgen response elements (ARE), located in the promoter and enhancer regions of the AR target genes. These AREs are organized as inverted repeats of the 5′-AGAACA-3′ hexameric consensus sequence (Claessens et al., 2001, Wang and Brown, 2009). Even though the AR directly binds AREs in vitro, the in vivo accessibility of these binding sites is determined by many factors that shape the chromatin architecture (extensively reviewed in (Arora et al., 2013)). Once bound to the enhancers, the AR N/C interactions are lost and the AR serves as a scaffold for co-regulator proteins and complexes with diverse activities. Some of these proteins/complexes reshape the surrounding chromatin structure by reading, writing, or modifying the histone code, while other complexes mediate the recruitment of general transcription factors to the promotor regions. In this way, the AR and its co-regulators eventually orchestrate the expression of AR target genes (Claessens et al., 2008). The list of AR co-regulators is large and is still expanding (DePriest et al., 2016). The impact of additional levels of control for instance by miRNAs and lncRNAs under normal and pathological conditions are just starting to be unravelled (see contributions by Spahn and Feng elsewhere in this issue).