title: Dual regulation of P-glycoprotein expression by trichostatin A in cancer cell lines.
abstract: BACKGROUND
  It has been reported that the histone deacetylase inhibitor (iHDAc) trichostatin A (TSA) induces an increase in MDR1 gene transcription (ABCB1). This result would compromise the use of iHDACs in combination with other cytotoxic agents that are substrates of P-glycoprotein (Pgp). It has also been reported the use of alternative promoters by the ABCB1 gene and the existence of a translational control of Pgp protein. Finally, the ABCB1 gene is located in a genetic locus with the nested gene RUNDC3B in the complementary DNA strand, raising the possibility that RUNDC3B expression could interfere with ABCB1 alternative promoter regulation.
  
  
  METHODS
  A combination of RT-PCR, real time RT-PCR, Western blot and drug accumulation assays by flow cytometry has been used in this study.
  
  
  RESULTS
  The iHDACs-induced increase in MDR1 mRNA levels is not followed by a subsequent increase in Pgp protein levels or activity in several pancreatic and colon carcinoma cell lines, suggesting a translational control of Pgp in these cell lines. In addition, the MDR1 mRNA produced in these cell lines is shorter in its 5' end that the Pgp mRNA produced in cell lines expressing Pgp protein. The different size of the Pgp mRNA is due to the use of alternative promoters. We also demonstrate that these promoters are differentially regulated by TSA. The translational blockade of Pgp mRNA in the pancreatic carcinoma cell lines could be related to alterations in the 5' end of the MDR1 mRNA in the Pgp protein expressing cell lines. In addition, we demonstrate that the ABCB1 nested gene RUNDC3B expression although upregulated by TSA is independent of the ABCB1 alternative promoter used.
  
  
  CONCLUSIONS
  The results show that the increase in MDR1 mRNA expression after iHDACs treatment is clinically irrelevant since this mRNA does not render an active Pgp protein, at least in colon and pancreatic cancer cell lines. Furthermore, we demonstrate that TSA in fact, regulates differentially both ABCB1 promoters, downregulating the upstream promoter that is responsible for active P-glycoprotein expression. These results suggest that iHDACs such as TSA may in fact potentiate the effects of antitumour drugs that are substrates of Pgp. Finally, we also demonstrate that TSA upregulates RUNDC3B mRNA independently of the ABCB1 promoter in use.
authors: Fundación para la Investigación Biomédica del Hospital Universitario de Elche, Elche, Alicante, 03203, Spain.
authors: Trinidad Mata
authors: TM
authors: Balaguer
authors: Angeles
authors: A
authors: Gómez-Martínez
authors: Pilar
authors: P
authors: García-Morales
authors: Javier
authors: J
authors: Lacueva
authors: Rafael
authors: R
authors: Calpena
authors: Lourdes Rocamora
authors: LR
authors: Reverte
authors: Natividad Lopez
authors: NL
authors: Riquelme
authors: Isabel
authors: I
authors: Martinez-Lacaci
authors: José A
authors: JA
authors: Ferragut
authors: Miguel
authors: M
authors: Saceda
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D017931:DNA Primers / Q000235:genetics; D005434:Flow Cytometry; D005786:Gene Expression Regulation / Q000502:physiology*; D056572:Histone Deacetylase Inhibitors / Q000378:metabolism*; D006801:Humans; D006877:Hydroxamic Acids / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D017931:DNA Primers; D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids; C012589:trichostatin A