title: Thyroid-stimulating hormone activates phospholipase C in normal and neoplastic thyroid tissue.
abstract: BACKGROUND
  Thyroid-stimulating hormone (TSH) stimulates thyroid growth through two signal transduction pathways: the G protein-adenylate cyclase system and the G protein-phospholipase C (PLC) system. The adenylate cyclase system has been studied extensively, but there is little information available concerning PLC activity in thyroid neoplasms.
  
  
  METHODS
  Human thyroid membranes were incubated for 30 minutes at 37 degrees C in the presence or absence of bovine TSH (300 mU/ml). PLC activity was assayed by liberation of inositol phosphates from the enzymatic hydrolysis of tritiated phosphatidylinositol bisphosphate. Fifty-six tissues were assayed (normal, 23; multinodular goiter, 5; follicular adenoma, 9; and differentiated thyroid cancer, 19 [9 low risk and 10 high risk]).
  
  
  RESULTS
  TSH significantly increased PLC activity in normal, benign, and most malignant thyroid neoplasms. Although there were no differences in basal or TSH-stimulated PLC activity between the groups of normal thyroid, multinodular goiter, follicular adenoma, or the cancers, one half of the high-risk cancers had an aberrant PLC response.
  
  
  CONCLUSIONS
  This is the first demonstration that TSH stimulates PLC activity in normal and neoplastic human thyroid tissue. Aberrant TSH-stimulated PLC activity was present in half of the aggressive thyroid neoplasms.
authors.affiliation: Department of Surgery, Mount Zion Medical Center, University of California, San Francisco 94115.
authors.forename: J K
authors.initials: JK
authors.lastname: Shaver
authors.forename: S
authors.initials: S
authors.lastname: Tezelman
authors.forename: A E
authors.initials: AE
authors.lastname: Siperstein
authors.forename: Q Y
authors.initials: QY
authors.lastname: Duh
authors.forename: O H
authors.initials: OH
authors.lastname: Clark
mesh_terms: D004789:Enzyme Activation / Q000502:physiology; D006042:Goiter / Q000201:enzymology; D006801:Humans; D010282:Parathyroid Neoplasms / Q000201:enzymology; D012016:Reference Values; D013961:Thyroid Gland / Q000201:enzymology*; D013964:Thyroid Neoplasms / Q000201:enzymology*; D013972:Thyrotropin / Q000502:physiology*; D010738:Type C Phospholipases / Q000378:metabolism*
chemical_list: D013972:Thyrotropin; D010738:Type C Phospholipases