Potentiation of the malignant phenotype of the undifferentiated aro thyroid cell line by insertion of the bcl-2 gene

We have reported that bcl-2 is expressed in normal human thyroid epithelium and that its expression is down-regulated in undifferentiated thyroid tumo rs, Production of IL-6 was concomitantly down-regulated in these forms. Bas ed on these observations, we analyzed whether insertion of bcl-2 would reve rse the highly malignant phenotype of a thyroid cell line (ARO) derived fro m an undifferentiated carcinoma. This cell line fails to produce Bcl-2 and IL-6, By infection with a bcl-2 retroviral vector, ARO cells expressing bcl -2 (ARObcl-2) were obtained, Compared with parental cells, expression of bc l-2 was associated with enhancement of growth potential (DNA synthesis, in vitro proliferation rate, anchorage-independent growth in semi-solid media) . Chemotaxis and invasive potential in Boyden chambers were also increased, bcl-2-expressing cells showed a reduced response to apoptotic stimuli (low -serum conditions or anti-neoplastic drugs), Large branched colonies were f ormed in Matrigel from ARObcl-2 cells but not from parental cells. Finally, ARObcl-2 cells showed a decreased latency of tumor appearance when injecte d into immunodeficient mice. Potentiation of the malignant phenotype of ARO cells by bcl-2 was not ascribed to altered expression of (i) cytokine/grow th factors (IL-4, IL-6, IL-8, IL-10, IL-12, TGF-alpha, TGF-beta), (ii) thyr oid specific transcripts (TG, TPO, TSH-R, PIGF, PAX-8) or (iii) genes influ encing tumor aggressiveness [VEGF, HMGI (Y), HMGI-C], Our data indicate tha t bcl-2 potentiates the malignant phenotype of ARO cells not only by limiti ng the response to apoptotic stimuli but also by enhancing proliferation an d tumor aggressiveness. (C) 1999 Wiley-Liss, Inc.