Expression of retinoic acid receptor beta mediates retinoic acid-induced growth arrest and apoptosis in breast cancer cells.

The expression of the retinoic acid receptor 1�(RAR�) mRNA is absent or down-regulated in most human breast cancer cell lines. To investigate the role RARIJ may have in regulating the proliferation of breast cancer cells, we used retroviral vector-mediated gene transdudion to introduce the human RARI3 gene into two RARg3-negativebreast tumor cell lines, MCF-7 and MDA-MB-231 .RAR�-transduced clones underwent growth inhibition associated with G1 arrest when treated with 1 �M all-trans-retinoic acid (RA). Moreover, the MCF7-RARf3 transduced clones also underwent apoptosis after 4 to 6 days of RA treatment. The RA-induced growth arrest in MDA231 -RARI3 transduced cells is associated with c-myc mRNA down-regulation, whereas the RA-mediated apoptosis of MCF7-RAR�3 transduced cells is not associated with c-myc down-regulation.