ARCHIVAL REPORTS The ANKK1 Gene Associated with Addictions Is Expressed in Astroglial Cells and Upregulated by Apomorphine Janet Hoenicka, Adolfo Quiñones-Lombraña, Laura España-Serrano, Ximena Alvira-Botero, Leonor Kremer, Rocío Pérez-González, Roberto Rodríguez-Jiménez, Miguel Ángel Jiménez-Arriero, Guillermo Ponce, and Tomás Palomo Background: TaqIA, the most widely analyzed genetic polymorphism in addictions, has traditionally been considered a gene marker for association with D2 dopamine receptor gene (DRD2). TaqIA is located in the coding region of the ANKK1 gene that overlaps DRD2 and encodes a predicted kinase ANKK1. The ANKK1 protein nonetheless had yet to be identified. This study examined the ANKK1 expression pattern as a first step to uncover the biological bases of TaqIA-associated phenotypes. Methods: Northern blot and quantitative reverse-transcriptase polymerase chain reaction analyses were performed to analyze the ANKK1 mRNA. To study ANKK1 protein expression, we developed two polyclonal antibodies to a synthetic peptides contained in the putative Ser/Thr kinase domain. Results: We demonstrate that ANKK1 mRNA and protein were expressed in the adult central nervous system (CNS) in human and rodents, exclusively in astrocytes. Ankk1 mRNA level in mouse astrocyte cultures was upregulated by apomorphine, suggesting a potential relation- ship with the dopaminergic system. Developmental studies in mice showed that ANKK1 protein was ubiquitously located in radial glia in the CNS, with an mRNA expression pick around embryonic Day 15. This time expression pattern coincided with that of the Drd2 mRNA. On induction of differentiation by retinoic acid, a sequential expression was found in human neuroblastoma, where ANKK1 was expressed first, followed by that of DRD2. An opposite time expression pattern was found in rat glioma. Conclusions: Spatial and temporal regulation of the expression of ANKK1 suggest an involvement of astroglial cells in TaqIA-related neuropsychiatric phenotypes both during development and adult life. Key Words: Addictions, ANKK1, astrocytes, astroglia, DRD2, poly- morphism, radial glia, TaqIA T he Taq IA single-nucleotide polymorphism (SNP; rs1800497), located 10.541 bp downstream of the termination codon of the dopamine D2 receptor gene (DRD2; chromosome 11q22– q23), is the most studied genetic variant in a broad range of psychiatric conditions and personality traits (1). The TaqIA polymorphism consists of a single nucleotide C/T change; the two alleles are referred to as A2 (C) and A1 (T). Blum et al.(2) first reported the association between alcohol- ism and the TaqIA A1 allele and the A1 + genotype (hetero- or homozygous for A1). Numerous other studies have related the A1 allele to alcohol addiction (1,3), although others could not replicate this association (1,4). Two meta-analyses of Caucasian alcoholics and control subjects nonetheless support a link be- tween the A1 allele and alcoholism (5,6). The TaqIA SNP has also been related to a variety of addictions and impulsive disorders (1), pharmacogenetics of addictions (7), psychoses (8), and antisocial traits in alcoholics (9,10). A number of dopamine-related endophenotypes are associ- ated with the A1 allele (1,11,12). Of these, a reduction in striatal dopamine D2 receptors for the A1 allele carriers was reported in several studies (1,13), which could explain the association with several neuropsychiatric disorders and learning processes (1,14). It is now known that the TaqIA SNP is located in exon 9 of the ankyrin repeat and kinase domain-containing 1 (ANKK1) gene, where it produces a Glu713-to-Lys (E713K) substitution (15). A positron emission tomography (PET) study of healthy volunteers associated the functional SNP C957T (rs6277) in DRD2 exon seven with low D2 receptor binding potential, a trait previously associated with the nearby TaqIA SNP (16). ANKK1 variants might nonetheless act in the dopaminergic system, which could provide an alternative explanation for some previously reported TaqIA-associated traits. For example, a TaqIA effect on striatal dopamine synthesis, independent of the C957T DRD2 genotype, was reported in a PET study (17). Extensive genotyping of DRD2 and ANKK1 genes suggests that the association between the locus 11q22– q23 and substance dependence is also due to ANKK1 variants (18 –21). Psychopathic traits in alcoholic patients are related to an epistatic interaction between the ANKK1 TaqIA and DRD2 C957T SNP genotypes (22). ANKK1 belongs to the receptor-interacting protein (RIP) serine/threonine kinase family (23). The RIP kinases are impor- tant regulators of cell proliferation and differentiation and initiate responses to various environmental factors by activating tran- scription factors such as NF-B or AP-1 (23). cDNA sequence data analysis predicted a 765-amino-acid ANKK1 protein very similar to RIP4, sharing not only the N-terminal kinase domain From the Department of Psychiatry (JH, LE-S, XA-B, RP-G, RR-J, MAJ-A, GP, TP), Hospital Universitario 12 de Octubre; Centro de Investigación Bi- omédica en Red de Salud Mental (CIBERSAM) (JH, AQ-L, RR-J, MAJ-A, GP, TP), ISCIII; Protein Tools Unit (LK), Centro Nacional de Biotecnología/ CSIC, Campus de Cantoblanco, Madrid, Spain. Authors LE-S and XA-B contributed equally to this work. Address correspondence to Janet Hoenicka, Ph.D., Laboratory of Neuro- sciences, Department of Psychiatry, Hospital Universitario 12 de Oc- tubre, Avenida Andalucía SN, Madrid 28041, Spain; E-mail: jhoenicka@ gmail.com. Received Feb 18, 2009; revised Jul 31, 2009; accepted Aug 16, 2009. BIOL PSYCHIATRY 2010;67:3–11 0006-3223/10/$36.00 doi:10.1016/j.biopsych.2009.08.012 © 2010 Society of Biological Psychiatry