Growth inhibition of cervical cancer cells by the human retinoic acid receptor β gene

Transcription of the retinoic receptor β ( RAR β) gene is activated in a ligand‐dependent manner by the retinoic acid receptor α. Reduced RAR β gene expression and loss of ligand inducibility are frequently observed in human carcinoma cells indicating that such alterations might contribute to carcinogenesis. In this study we have analyzed the influence of RAR β on cervical cancer cell growth. Transfection of HeLa cells with RAR β expression plasmids resulted in reduced clonal cell growth in the presence of retinoic acid (RA). RA‐induced growth inhibition in HeLa × fibroblast hybrid cells was partially relieved by a dominant‐negative RAR β mutant. HeLa clones stably expressing a RAR β transgene under control of the human β‐actin promoter [HeLa(RARβ)] were established and analyzed for transgene‐mediated growth alterations in vitro and in vivo . Anchorage‐independent growth of the HeLa(RARβ) lines was indistinguishable from that of control cells in the absence of RA, but strongly impaired after RA treatment. Reduced tumor growth of HeLa(RARβ) clones was associated with high RARβ protein levels. Somatic cell fusion experiments revealed that the loss of ligand inducibility of RAR β gene expression in HeLa cells cannot be complemented by fusion with other cervical cancer cell lines. Our data indicate, firstly, that RARβ is a negative regulator of tumor cell growth and, secondly, that cancer‐associated defects in RAR β gene expression are caused by stable, non‐complementable silencing mechanisms. Int. J. Cancer 85:289–295, 2000. ©2000 Wiley‐Liss, Inc.