Integrin αvβ3 is the membrane receptor for THs in human TCL. (A) Blockade of the TH-mediated proliferative effect by 1 nM RGD peptide, added 10 minutes before 24-hour hormone treatment, was analyzed by Cell Titer Blue assay. (B) CUTLL1 cells were transfected by electroporation with siRNA against ITGAV (si-ITGAV), ITGB3 (si-ITGB3), or noncoding siRNA as control (si-CT). mRNA levels of target genes were analyzed by qRT-PCR 24 and 48 hours posttransfection. (C) Effect of ITGAV and ITGB3 knockdown on CUTLL1 cell growth by Trypan Blue staining. (D-F) Knockdown of ITGAV and/or ITGB3 abrogates the TH proliferative effect as measured by [³H]TdR incorporation (D) and cell proliferation by Cell Titer Blue assay (E) after 24 hours of TH treatment in CUTLL1 cells. Similar results were found in mature TCL, HuT 78, and OCI.Ly12 cells (F). (G) Effect of 250 ng/mL vitronectin ligand and/ or THs on cell proliferation in CUTLL1, HuT 78, and OCI-Ly12 cells measured by [³H]TdR incorporation after 24-hour treatment. (H) Growth of OCI-Ly12 cells cultured in an artificial ECM system that offers an RGD ligand, in the presence or absence of physiological levels of TH and in the presence or absence of the inhibitor of integrin αvβ3 cilengitide. Cell proliferation and clustering was measured by microscopical examination. Representative photographs (scale bar, 100 μm) of 4 replicate experiments are shown.