L-Thyroxine vs. 3,5,3'-triiodo-L-thyronine and cell proliferation: activation of mitogen-activated protein kinase and phosphatidylinositol 3-kinase.
3,5,3'-Triiodo-l-thyronine (T(3)), but not l-thyroxine (T(4)), activated Src kinase and, downstream, phosphatidylinositol 3-kinase (PI3-kinase) by means of an alpha(v)beta(3) integrin receptor on human glioblastoma U-87 MG cells. Although both T(3) and T(4) stimulated extracellular signal-regulated kinase (ERK) 1/2, activated ERK1/2 did not contribute to T(3)-induced Src kinase or PI3-kinase activation, and an inhibitor of PI3-kinase, LY-294002, did not block activation of ERK1/2 by physiological concentrations of T(3) and T(4). Thus the PI3-kinase, Src kinase, and ERK1/2 signaling cascades are parallel pathways in T(3)-treated U-87 MG cells. T(3) and T(4) both caused proliferation of U-87 MG cells; these effects were blocked by the ERK1/2 inhibitor PD-98059 but not by LY-294002. Small-interfering RNA knockdown of PI3-kinase confirmed that PI3-kinase was not involved in the proliferative action of T(3) on U-87 MG cells. PI3-kinase-dependent actions of T(3) in these cells included shuttling of nuclear thyroid hormone receptor-alpha (TRalpha) from cytoplasm to nucleus and accumulation of hypoxia-inducible factor (HIF)-1alpha mRNA; LY-294002 inhibited these actions. Results of studies involving alpha(v)beta(3) receptor antagonists tetraiodothyroacetic acid (tetrac) and Arg-Gly-Asp (RGD) peptide, together with mathematical modeling of the kinetics of displacement of radiolabeled T(3) from the integrin by unlabeled T(3) and by unlabeled T(4), are consistent with the presence of two iodothyronine receptor domains on the integrin. A model proposes that one site binds T(3) exclusively, activates PI3-kinase via Src kinase, and stimulates TRalpha trafficking and HIF-1alpha gene expression. Tetrac and RGD peptide both inhibit T(3) action at this site. The second site binds T(4) and T(3), and, via this receptor, the iodothyronines stimulate ERK1/2-dependent tumor cell proliferation. T(3) action here is inhibited by tetrac alone, but the effect of T(4) is blocked by both tetrac and the RGD peptide.
Lin
Hung-Yun
HY
Ordway Research Institute, Albany, NY 12208, USA.
Sun
Mingzeng
M
Tang
Heng-Yuan
HY
Lin
Cassie
C
Luidens
Mary K
MK
Mousa
Shaker A
SA
Incerpi
Sandra
S
Drusano
George L
GL
Davis
Faith B
FB
Davis
Paul J
PJ
D001932:Brain Neoplasms / Q000378:metabolism* / Q000473:pathology; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D005910:Glioma / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism; D039302:Integrin alphaVbeta3 / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000235:genetics / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000235:genetics / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D037021:Thyroid Hormone Receptors alpha / Q000378:metabolism; D013974:Thyroxine / Q000378:metabolism* / Q000494:pharmacology; D014162:Transfection; D014284:Triiodothyronine / Q000378:metabolism* / Q000494:pharmacology
C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D039302:Integrin alphaVbeta3; D037021:Thyroid Hormone Receptors alpha; D014284:Triiodothyronine; D019869:Phosphatidylinositol 3-Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D013974:Thyroxine