Progesterone receptor (PR), glucocorticoid receptor, and mineralocorticoid receptor belong to a subfamily of nuclear receptor superfamily with similar sequence and structural characteristics. Many reports have documented glucocorticoid-like effects of progesterone in various tissues. This study addresses the issue of cross-talk between corticosteroids and PR using PR-transfected MDA-MB-231 cells ABC28 and vector-transfected control cells CTC15. At physiological concentrations, dexamethasone, cortisol, and aldosterone mimic the effects of progesterone by inducing significant growth inhibition, cell spreading, and focal adhesions in PR-positive ABC28 cells. These hormones also induce progesterone-like effects in increasing the expression of p21(CIP1/WAF1) protein and decreasing the level of phospho-p42/p44 mAPK. Two lines of evidence suggest that these effects are mediated by cross-talk with PR. First, these compounds do not exhibit the same progesterone-like effects in PR-negative CTC15 cells. Second, PR blocker ZK98299 abolishes their effect on cell spreading and focal adhesion in ABC28 cells. The cross-talk is corticosteroid specific because estradiol and thyroid hormone triiodothyronine have no effect on PR-transfected cells ABC28. It is also interesting to note that dexamethasone induces a small but detectable increase of focal adhesions and limited growth stimulation in vector-transfected cells CTC15. In contrast, progesterone exhibits no detectable effect on CTC15 cells. This study provides evidence that glucocorticoid and mineralocorticoid cross-talk with PR to produce progesterone-like effects in breast cancer cells. Glucocorticoid receptor and PR share some overlapping activity in mediating focal adhesion but not in regulating cell proliferation.

Since the effects of progesterone are mediated mainly via estrogen-dependent progesterone receptor (PR), the expression of the effects of progesterone may be masked or overridden by the influence of estrogen under conditions in which priming with estrogens is required. We have established a PR-positive but estrogen receptor-alpha (ER-alpha) negative breast cancer cell model by transfecting PR cDNA into ER-alpha- and PR-negative MDA-MB-231 cells in order that the functions of progesterone can be studied independently of estrogens. We have demonstrated using this model that progesterone markedly inhibited cell growth. We have also discovered that progesterone induced remarkable changes in cell morphology and specific adhesion structures. Progesterone-treated cells became considerably more flattened and well spread than vehicle-treated control cells. This was associated with a striking increase of stress fibers, both in number and diameter, and increased focal contacts as shown by the staining of focal adhesion proteins paxillin and talin. There were also distinct increases in tyrosine phosphorylation of focal adhesion protein paxillin and focal adhesion kinase in association with increased focal adhesion. The staining of tyrosine-phosphorylated proteins was concentrated at focal adhesions in progesterone-treated cells. More interestingly, monoclonal antibody (Ab) to beta1 integrin was able to inhibit progesterone-induced cell spreading and formation of actin cytoskeleton. To our knowledge, this is the first report describing a direct effect of progesterone in inducing spreading and adhesion of breast cancer cells, and beta1-integrin appeared to play an essential role in the effect. It is known that the initial step of tumor metastasis is the breakaway of tumor cells from primary tumor mass when they lose the ability to attach. Hence, progesterone-induced cell spreading and adhesion may have significant implications in tumor metastasis.

Hepatocellular carcinoma (HCC) commonly develops in patients with underlying chronic liver disease. Additionally, the tumorous lesions of HCC patients are consistently characterized by the lack of iron accumulation even when arising in iron-loaded liver. However, the molecular mechanism leading to this observed phenomenon is currently poorly understood. In this study, all tumorous tissues from 24 HCC patients with chronic HBV infection were stained negative for iron when histologically assessed by Perls' Prussian blue stain, whereas excess iron deposits were present in 17 of the 24 adjacent non-tumorous liver tissues. To elucidate the concerted regulation of iron homeostasis in these patients, we studied the gene expression profiling of 42 relevant iron-regulatory genes in the tumorous and adjacent non-tumorous liver tissues of these HCC patients along with 10 normal liver controls. Expression for most of the iron-regulatory genes, including hepcidin, transferrin receptor 2 (TfR2), transferrin (Tf), ceruloplasmin (Cp) and iron regulatory protein 1 (IRP1), were significantly down-regulated in the tumorous tissues of these patients compared to the adjacent non-tumorous liver tissues and normal liver controls. On the other hand, expression of hepcidin, TfR2, ferroportin 1 and DMT1 were significantly up-regulated in iron-loaded non-cirrhotic non-tumorous liver tissues as compared with normal liver controls. Hence, the reduction of hepcidin expression within the iron-depleted tumorous lesions likely reflects the physiological consequence of the obligate demand for iron in the rapidly growing neoplastic cells, whereas the up-regulation of hepcidin expression in the iron-loaded adjacent non-tumorous liver tissues is likely a physiological response.