title: Feasibility of a novel positive feedback effect of 131I-promoted Bac-Egr1-hNIS expression in malignant glioma via baculovirus.
abstract: OBJECTIVE
  As intracellular iodine is released rapidly, increased expression of sodium/iodide symporter (NIS) is required for effective radioiodine treatment of tumor. As Egr1 promoter is activated by ¹³¹I and may promote human NIS (hNIS) expression, hNIS also induces ¹³¹I uptake and activates Egr1, so the existence of a positive feedback effect of ¹³¹I-promoted Egr1-hNIS expression is possible. Our purpose was to investigate the possible existence of this positive feedback effect through a series of in vitro pioneer studies.
  
  
  METHODS
  Recombinant baculovirus (Bac-Egr1-hNIS) encoding the hNIS gene under the control of a radiation-inducible Egrl promoter was constructed. To test ¹³¹I-promoted hNIS expression, human malignant glioma U87 cells were transfected with Bac-Egr1-hNIS, stimulated with or without ¹³¹I; the expression of hNIS protein was detected by immunofluorescence and flow cytometry test. In addition, the uptake and efflux of ¹³¹I were determined after the incubation of Bac-Egr1-hNIS-transfected U87 cells with or without ¹³¹I.
  
  
  RESULTS
  Immunocytochemical staining and flow cytometry test showed a higher hNIS protein expression in Bac-Egr1-hNIS-transfected U87 cells with ¹³¹I stimulation than in cells without stimulation. Bac-Egr1-hNIS-transfected U87 cells accumulated up to about 4.05 times of ¹³¹I after ¹³¹I stimulation. The amount of ¹³¹I uptake in both groups showed a baculovirus dose-dependent manner. However, rapid efflux of radioactivity was observed in both groups, with 50% lost during the first 2 min after the ¹³¹I-containing medium had been replaced by a nonradioactive medium.
  
  
  CONCLUSIONS
  Our results indicated that an improved transgene expression of ¹³¹I-stimulated hNIS in U87 cells using a baculovirus vector containing the Egr1 promoter is possible, and the increased expression of hNIS is responsible for a higher ¹³¹I uptake. It might provide a reference for the existence of a positive feedback effect in ¹³¹I-promoted Bac-Egr1-hNIS expression in malignant glioma and is an interesting aspect of NIS-related studies.
authors.affiliation: Department of Nuclear Medicine, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, 200025, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Guo
authors.forename: Lipeng
authors.initials: L
authors.lastname: Tian
authors.forename: Bing
authors.initials: B
authors.lastname: Han
authors.forename: Haoping
authors.initials: H
authors.lastname: Xu
authors.forename: Miao
authors.initials: M
authors.lastname: Zhang
authors.forename: Biao
authors.initials: B
authors.lastname: Li
mesh_terms: D016367:Baculoviridae / Q000235:genetics*; D001692:Biological Transport; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D051766:Early Growth Response Protein 1 / Q000235:genetics*; D005240:Feasibility Studies; D025461:Feedback, Physiological / Q000187:drug effects*; D015870:Gene Expression / Q000187:drug effects; D005822:Genetic Vectors / Q000235:genetics; D005910:Glioma / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology; D006801:Humans; D007457:Iodine Radioisotopes / Q000378:metabolism / Q000494:pharmacology; D011401:Promoter Regions, Genetic / Q000235:genetics; D027981:Symporters / Q000235:genetics*; D014162:Transfection; D019076:Transgenes / Q000235:genetics; D000099209:Sodium-Iodide Symporters
chemical_list: D051766:Early Growth Response Protein 1; D007457:Iodine Radioisotopes; D027981:Symporters; D000099209:Sodium-Iodide Symporters