Cross talks between heregulin and progesterone receptor signaling pathways in T47D cells

LETICIA LABRIOLA, MARIANA SALATINO, CECILIA PROIETTI, OMAR COSO, ADALI PECCI, ALBERTO KORNBLIHTT, EDUARDO CHARREAU AND PATRICIA ELIZALDE.

San Francisco, CA, USA.

Congreso; Annual meeting of the American Association of Cancer Research.; 2002

1)               Activation of the progesterone receptor (PR) by heregulin was studied in human breast cancer cells T47D.  We have previously demonstrated that HRG stimulates growth of primary cultures of the progestin-dependent C4HD epithelial cells, potentiates MPA mitogenic effects (Oncogene 18: 6370-6379, 1999) and transcriptionally activates PR. In the present study, we found that HRG (20ng/ml) treatment of T47D cells induced a decrease of protein level of PR A and B isoforms and down-regulation of progesterone-binding sites. HRG also promoted a significant increase in the percentage of PR localized in the nucleus. DNA mobility shift assay showed that HRG was able to induce PR binding to a progesterone response element (PRE). When T47D cells were transiently transfected with a plasmid containing a PRE upstream of a chloranfenicol acetyltransferase (CAT) gene, HRG induce a significant increase in CAT activity. In order to assess molecular mechanisms underlying PR transactivation by HRG, we pretreated T47D cells with the selective MEK 1 inhibitor PD98059 (10uM). We found that PD 98059 blocked HRG capacity to inducePR binding to a PRE and CAT activity.We next studied the ability of MAPK to phosphorylate PR. In vitro phosphorylation assays showed that active MAPKs isolated from HRG treated cells were able to induce PR phosphorylation which was inhibited after PD 98059 treatment. As control for PR activation, in all experiments described, T47D cells were treated with MPA demonstrating that HRG effects on PR activation were comparable to those exerted by MPA. These results provide the first evidence that in the absence of progestins, HRG activates PR in human breast cancer cells by a mechanism that involves PR phosphorylation and requires a functional ErbB-