title: Modulation of parathyroid hormone-related protein levels (PTHrP) in anaplastic thyroid cancer.
abstract: BACKGROUND
  Studies have demonstrated that manumycin, a farnesyltransferase inhibitor, enhances the cytotoxic effect of paclitaxel in anaplastic thyroid cancer cells and in xenografts, but the mechanism of this effect is unknown. Parathyroid hormone-related protein (PTHrP) may function as an oncoprotein that inhibits apoptosis and enhances cell proliferation, in addition to its role as the mediator of humoral hypercalcemia of malignancy. We hypothesized that this protein might have a novel role in anaplastic thyroid cancer.
  
  
  METHODS
  Five anaplastic thyroid cancer cell lines (ARO, DRO, KAT-4, Hth-74, C-643) were examined for PTHrP expression in vitro by immunohistochemistry (IHC), radioimmunoassay, and Western blot (IP/WB) analyses. PTHrP expression was also examined in an in vivo xenograft model. The effects of manumycin and paclitaxel on PTHrP expression were studied.
  
  
  RESULTS
  All 5 ATC cell lines were found to robustly express PTHrP by IHC of fixed cells and radioimmunoassay of cell lysates and conditioned culture media (range, 468 +/- 55 to 1410 +/- 195 pg/mg cellular protein). Manumycin (54 micromol/L), but not paclitaxel (22 micromol/L), decreased the amount of PTHrP. Further, PTHrP was decreased in KAT-4 xenografts in nude mice that had been treated for 3 weeks with biweekly intraperitoneal injections of manumycin (7.5 mg/kg), compared with control mice by IHC. On Western blot analyses, fractionation of radiolabeled proteins showed that manumycin decreased synthesis of PTHrP in cytoplasm, with the amount of newly synthesized PTHrP in the nucleus and increased ubiquitination of PTHrP suggesting increased degradation of PTHrP through the proteasome pathway.
  
  
  CONCLUSIONS
  Manumycin inhibits cell proliferation and decreases PTHrP levels in anaplastic thyroid cancer cells in vitro and in vivo and decreases the PTHrP level in the nucleus where PTHrP may function as an oncoprotein. These data suggest that PTHrP has a novel role in anaplastic thyroid cancer and that modulation of PTHrP levels may be of therapeutic benefit in this lethal malignancy.
authors.affiliation: Department of Surgery, Division of Endocrine and Oncologic Surgery, Johns Hopkins Hospital, Baltimore, MD 21287, USA. adackiw1@jhmi.edu
authors.forename: Alan
authors.initials: A
authors.lastname: Dackiw
authors.forename: Jingxuan
authors.initials: J
authors.lastname: Pan
authors.forename: Guangpu
authors.initials: G
authors.lastname: Xu
authors.forename: Sai-Ching J
authors.initials: SC
authors.lastname: Yeung
mesh_terms: D002277:Carcinoma / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism / Q000473:pathology; D006727:Hormone Antagonists / Q000494:pharmacology; D006801:Humans; D007150:Immunohistochemistry; D008715:Methionine / Q000378:metabolism; D044162:Parathyroid Hormone-Related Protein / Q000378:metabolism*; D011090:Polyenes / Q000494:pharmacology; D053284:Polyunsaturated Alkamides; D013964:Thyroid Neoplasms / Q000378:metabolism* / Q000473:pathology
chemical_list: D006727:Hormone Antagonists; D044162:Parathyroid Hormone-Related Protein; D011090:Polyenes; D053284:Polyunsaturated Alkamides; D008715:Methionine; C054474:manumycin