title: Cytoplasmic localization of the androgen receptor is independent of calreticulin.
abstract: Identification and characterization of factors regulating intracellular localization of the androgen receptor (AR) are fundamentally important because nucleocytoplasmic trafficking of AR is a critical step in AR regulation by androgen manipulation. Normally, AR is localized to the cytoplasm in the absence of androgen. Upon ligand binding, AR translocates to the nucleus, where it can modulate transcription of AR-responsive genes. The withdrawal of androgen results in the export of unliganded AR from the nucleus to the cytoplasm, where it is transcriptionally inactive. Calreticulin has been implicated as a possible nuclear export factor for AR because the two proteins form a complex. In this study, we assessed whether the cytoplasmic localization of AR requires binding to calreticulin. To test this we substituted the calreticulin binding sequence (CBS) KVFFKR (residues 579-584) with the amino acids RLAARK in AR and monitored the cellular localization of a GFP-AR fusion protein in the absence of androgen. We also determined if knockdown or knockout of calreticulin expression affected the cytoplasmic localization of the AR. We found that a mutated CBS did not affect the localization of AR and that in the absence of androgen, AR is localized to the cytoplasm regardless of its ability to interact with calreticulin. Also, a reduction in the levels or loss of calreticulin did not affect the localization of AR. These data argue that calreticulin is not required for the cytoplasmic localization of AR.
authors.affiliation: Department of Urology, University of Pittsburgh Cancer Institute, School of Medicine, Pittsburgh, PA 15232, United States.
authors.forename: Minh M
authors.initials: MM
authors.lastname: Nguyen
authors.forename: Zehra
authors.initials: Z
authors.lastname: Dincer
authors.forename: James R
authors.initials: JR
authors.lastname: Wade
authors.forename: Mahesh
authors.initials: M
authors.lastname: Alur
authors.forename: Marek
authors.initials: M
authors.lastname: Michalak
authors.forename: Donald B
authors.initials: DB
authors.lastname: Defranco
authors.forename: Zhou
authors.initials: Z
authors.lastname: Wang
mesh_terms: D001665:Binding Sites; D037282:Calreticulin / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D003593:Cytoplasm / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D006801:Humans; D008297:Male; D022022:Nuclear Pore / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D011944:Receptors, Androgen / Q000378:metabolism*
chemical_list: D037282:Calreticulin; D009687:Nuclear Proteins; D011944:Receptors, Androgen