title: Human SHBG mRNA translation is modulated by alternative 5'-non-coding exons 1A and 1B.
abstract: BACKGROUND
  The human sex hormone-binding globulin (SHBG) gene comprises at least 6 different transcription units (TU-1, -1A, -1B, -1C, -1D and -1E), and is regulated by no less than 6 different promoters. The best characterized are TU-1 and TU-1A: TU-1 is responsible for producing plasma SHBG, while TU-1A is transcribed and translated in the testis. Transcription of the recently described TU-1B, -1C, and -1D has been demonstrated in human prostate tissue and prostate cancer cell lines, as well as in other human cell lines such as HeLa, HepG2, HeK 293, CW 9019 and imr 32. However, there are no reported data demonstrating their translation. In the present study, we aimed to determine whether TU-1A and TU-1B are indeed translated in the human prostate and whether 5' UTR exons 1A and 1B differently regulate SHBG translation.
  
  
  RESULTS
  Cis-regulatory elements that could potentially regulate translation were identified within the 5'UTRs of SHBG TU-1A and TU-1B. Although full-length SHBG TU-1A and TU-1B mRNAs were present in prostate cancer cell lines, the endogenous SHBG protein was not detected by western blot in any of them. LNCaP prostate cancer cells transfected with several SHBG constructs containing exons 2 to 8 but lacking the 5'UTR sequence did show SHBG translation, whereas inclusion of the 5'UTR sequences of either exon 1A or 1B caused a dramatic decrease in SHBG protein levels. The molecular weight of SHBG did not vary between cells transfected with constructs with or without the 5'UTR sequence, thus confirming that the first in-frame ATG of exon 2 is the translation start site of TU-1A and TU-1B.
  
  
  CONCLUSIONS
  The use of alternative SHBG first exons 1A and 1B differentially inhibits translation from the ATG situated in exon 2, which codes for methionine 30 of transcripts that begin with the exon 1 sequence.
authors.affiliation: Institut de Recerca Hospital Universitari Vall d'Hebrón, Barcelona, Spain.
authors.forename: Tomàs
authors.initials: T
authors.lastname: Pinós
authors.forename: Anna
authors.initials: A
authors.lastname: Barbosa-Desongles
authors.forename: Antoni
authors.initials: A
authors.lastname: Hurtado
authors.forename: Albert
authors.initials: A
authors.lastname: Santamaria-Martínez
authors.forename: Inés
authors.initials: I
authors.lastname: de Torres
authors.forename: Jaume
authors.initials: J
authors.lastname: Reventós
authors.forename: Francina
authors.initials: F
authors.lastname: Munell
mesh_terms: D020121:5' Untranslated Regions / Q000235:genetics; D017398:Alternative Splicing; D015153:Blotting, Western; D045744:Cell Line, Tumor; D018387:Codon, Initiator / Q000235:genetics; D005091:Exons / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D056945:Hep G2 Cells; D006801:Humans; D008297:Male; D008715:Methionine / Q000235:genetics; D009690:Nucleic Acid Conformation; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D014176:Protein Biosynthesis / Q000235:genetics*; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics*; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012738:Sex Hormone-Binding Globulin / Q000235:genetics* / Q000378:metabolism
chemical_list: D020121:5' Untranslated Regions; D018387:Codon, Initiator; D012333:RNA, Messenger; D012738:Sex Hormone-Binding Globulin; D008715:Methionine