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Articles by F. B Davis
Total Records ( 2 ) for F. B Davis
  P. J Davis , F. B Davis , H. Y Lin , S. A Mousa , M Zhou and M. K. Luidens

A thyroid hormone receptor on integrin vβ3 that mediates cell surface-initiated nongenomic actions of thyroid hormone on tumor cell proliferation and on angiogenesis has been described. Transduction of the hormone signal into these recently recognized proliferative effects is by extracellular-regulated kinases 1/2 (ERK1/2). Other nongenomic actions of the hormone may be transduced by phosphatidylinositol 3-kinase (PI3K) and are initiated in cytoplasm or at the cell surface. PI3K-mediated effects are important to angiogenesis or other recently appreciated cell functions but apparently not to tumor cell division. For those actions of thyroid hormone [l-thyroxine (T4) and 3,3'-5-triiodo-l-thyronine (T3)] that begin at the integrin receptor, tetraiodothyroacetic acid (tetrac) is an inhibitor of and probe for the participation of the receptor in downstream intracellular events. In addition, tetrac has actions initiated at the integrin receptor that are unrelated to inhibition of the effects of T4 and T3 but do involve gene transcription in tumor cells. Discussed here are the implications of translating these nongenomic mechanisms of thyroid hormone analogs into clinical cancer cell biology, tumor-related angiogenesis, and modulation of angiogenesis that is not related to cancer.

  S. S Mousa , F. B Davis , P. J Davis and S. A. Mousa

The endogenous thyroid hormones L-thyroxine (T4) and 3,5,3'-triiodo-L-thyronine (T3) induce angiogenesis via an endothelial cell iodothyronine receptor on integrin Vβ3. This receptor also exists on platelets. Diiodothyropropionic acid (DITPA) and GC-1, a noniodinated thyroid hormone analog, also induce angiogenesis. Here we examined the effects of iodothyronines (L-T4 vs L-T3) and analogs DITPA and GC-1 on human platelet function. Subthreshold aggregation of platelets obtained from healthy human donors was induced with collagen. Platelet activation (proaggregation) and adenosine triphosphate (ATP) secretion (degranulation) induced by L-T 4, L-T4-agarose, L-T3, DITPA, or GC-1 were determined simultaneously. Platelet aggregation and ATP secretion induced by a subthreshold level of collagen were enhanced 3-fold by either L-T4 or L-T 4-agarose (0.01 µmol/L) as compared to control, whereas, L-T 3, DITPA, or GC-1 had no effect under the same conditions. The platelet proaggregatory and degranulation effects of L-T4 were blocked by the vβ3 antagonist XT199 (0.1 µmol/ L) and by tetraiodothyroacetic acid (tetrac; 0.1 µmol/L). Tetrac inhibits binding of thyroid hormone analogs to the receptor on vβ3 and lacks thyromimetic activity at this site; thus, the proaggregatory action of L-T4 likely involves the cell surface receptor on integrin vβ3. The thyroid hormone receptor (TR) on human platelets but not endothelial cells distinguishes among iodothyronines, reflecting quantitative differences in integrin sites on endothelial cells and platelets or qualitative differences in the phospholipids/protein microenvironment of endothelial and platelet membranes that can affect integrin function. Additional studies in different populations with larger sample sizes are warranted to determine the impact of the current findings on clinical interventions.

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