title: Kalrn promoter usage and isoform expression respond to chronic cocaine exposure.
abstract: BACKGROUND
  The long-term effects of cocaine on behavior are accompanied by structural changes in excitatory glutamatergic synapses onto the medium spiny neurons of the striatum. The Kalrn gene encodes several functionally distinct isoforms; these multidomain guanine nucleotide exchange factors (GEFs) contain additional domains known to interact with phosphatidylinositides as well as with a number of different proteins. Through their activation of Rho proteins and their interactions with other proteins, the different Kalirin isoforms affect cytoskeletal organization. Chronic exposure of adult male rodents to cocaine increases levels of Kalirin 7 in the striatum. When exposed chronically to cocaine, mice lacking Kalirin 7, the major adult isoform, fail to show an increase in dendritic spine density in the nucleus accumbens, show diminished place preference for cocaine, and exhibit increased locomotor activity in response to cocaine.
  
  
  RESULTS
  The use of alternate promoters and 3'-terminal exons of the mouse Kalrn gene were investigated using real-time quantitative polymerase chain reaction. While the two most distal full-length Kalrn promoters are used equally in the prefrontal cortex, the more proximal of these promoters accounts for most of the transcripts expressed in the nucleus accumbens. The 3'-terminal exon unique to the Kalirin 7 isoform accounts for a greater percentage of the Kalrn transcripts in prefrontal cortex than in nucleus accumbens. Western blot analyses confirmed these differences. Chronic cocaine treatment increases usage of the promoter encoding the Δ-Kalirin isoforms but does not alter full-length Kalirin promoter usage. Usage of the 3'-terminal exon unique to Kalirin 7 increases following chronic cocaine exposure.
  
  
  CONCLUSIONS
  Kalrn promoter and 3'-terminal exon utilization are region-specific. In the nucleus accumbens, cocaine-mediated alterations in promoter usage and 3'-terminal exon usage favor expression of Kalirin 7 and Δ-Kalirin 7. The Δ-isoform, which lacks a Sec14p domain and four of the nine spectrin-like repeats found in full-length Kalirin isoforms, increases spine headsize without increasing dendritic spine numbers. Thus cocaine-mediated changes in alternative splicing of the Kalrn gene may contribute importantly to the behavioral, morphological and biochemical responses observed.
authors.affiliation: Department of Neuroscience, University of Connecticut Health Center, 263 Farmington Ave, Farmington, CT 06030-3401, USA. mains@uchc.edu
authors.forename: Richard E
authors.initials: RE
authors.lastname: Mains
authors.forename: Drew D
authors.initials: DD
authors.lastname: Kiraly
authors.forename: Jodi E
authors.initials: JE
authors.lastname: Eipper-Mains
authors.forename: Xin-Ming
authors.initials: XM
authors.lastname: Ma
authors.forename: Betty A
authors.initials: BA
authors.lastname: Eipper
mesh_terms: D000818:Animals; D003042:Cocaine / Q000008:administration & dosage*; D003342:Corpus Striatum / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D018765:Dopamine Uptake Inhibitors / Q000008:administration & dosage*; D005786:Gene Expression Regulation / Q000187:drug effects*; D049452:Green Fluorescent Proteins / Q000235:genetics; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009154:Mutation / Q000235:genetics; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D017397:Prefrontal Cortex / Q000187:drug effects / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000235:genetics; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism
chemical_list: D018765:Dopamine Uptake Inhibitors; D020662:Guanine Nucleotide Exchange Factors; C548820:KALRN protein, mouse; D020033:Protein Isoforms; D012333:RNA, Messenger; D049452:Green Fluorescent Proteins; D003042:Cocaine