Retinoic acid increases tyrosine phosphorylation of focal adhesion kinase and paxillin in MCF-7 human breast cancer cells

Treatment of estrogen receptor (ER)-positive MCF-7 human breast cancer cell s with retinoic acid (RA) inhibited cell growth and increased cell adhesion to fibronectin. In contrast, ER- MDA-MB-231 cells failed to respond. Weste rn blot analysis showed that tyrosine phosphorylation of two major bands at M-r 125,000 and M-r 68,000 was induced by RA in ER+ MCF-7 human breast car cinoma cells. However, this induction was a late phenomenon detectable at 1 2 and 24 h, but not within 3 h, A similar increase of tyrosine phosphorylat ion by RA was observed in ER+ human breast cancer cell lines T-47D and ZR-7 5-1, but not in the ER- cell lines MDA-MB-231, MDA-MB-453, and MDA-MB-468. Focal adhesion kinase and paxillin, which localize in focal adhesion plaque s and may play important roles in the integrin signaling pathway, were iden tified as the major proteins showing IU-induced tyrosine phosphorylation. T he retinoid X receptor-selective compound SR11237 failed to induce tyrosine phosphorylation, indicating that retinoid X receptor activation is not inv olved in this phenomenon. In contrast, stable overexpression of a truncated RA receptor (RAR) alpha cDNA, RAR alpha 403, with strong RAR dominant nega tive activity prevented the increase in tyrosine phosphate, suggesting that RAR signaling is involved in RA-induced tyrosine phosphorylation. Tyrosine phosphorylation was induced the most by the RAR-alpha (193836), followed b y RAR-gamma (194433), but was not significantly induced by RAR-beta (193174 )-selective retinoids, This study demonstrates a coordinated albeit relativ ely late effect of RA on cell adhesion and tyrosine phosphorylation in ERhuman breast cancer cells and suggests RAR-alpha as the major responsible r etinoid receptor.