V DeGroff | PubMed Health

PubMed2001

Responsiveness to transforming growth factor-beta (TGF-beta)-mediated growth inhibition is a function of membrane-bound TGF-beta type II receptor in human breast cancer cells.

Transforming growth factor-beta (TGF-beta) is a potent inhibitor of growth and proliferation of breast epithelial cells, and loss of sensitivity to its effects has been associated with malignant transformation and tumorigenesis. The biological effects of TGF-beta are mediated by the TGF-beta receptor complex, a multimer composed of TGF-beta receptor type I (TbetaR-I) and TGF-beta receptor type II (TbetaR-II) subunits. Evidence suggests that loss of expression of Tbeta3R-II is implicated in the loss of sensitivity of tumorigenic breast cell lines to TGF-beta-mediated growth inhibition. A panel of human breast cell lines, including the immortalized MCF-10F and tumorigenic MCF-7, ZR75-1, BT474, T47-D, MDA-MB231, BT20, and SKBR-3 cell lines, was characterized for responsiveness to TGF-beta-induced G1 growth arrest. Only the nontumorigenic MCF-10F and the tumorigenic MDA-MB231 cell lines demonstrated a significant inhibitory response to TGF-beta1 and a significant binding of 125I-labeled TGF-beta ligand. While expression of TbetaR-I mRNA was similar across the panel of cell lines, TbetaR-II mRNA expression was decreased significantly in all seven tumorigenic cell lines in comparison with the nontumorigenic MCF- 10F cell line. When total cellular protein was fractionated by centrifugation, TbetaR-I protein was observed in both the cytosolic and membrane fractions at similar levels in all cell lines; however, TbetaR-II protein was present in the cytosolic fraction in all cell lines, but was observed in the membrane fraction of only the TGF-beta-responsive MCF-10F and MDA-MB231 cells. Thus, lack of membrane-bound TbetaR-II protein appears to be an important determinant of resistance to TGF-beta-mediated growth inhibition in this group of breast cell lines.

Blotting, Western↗

PubMed1982

Competition by estrogens for catecholamine receptor binding in vitro.

We have examined the ability of various steroids to compete for high-affinity binding of 3H-labeled ligands to catecholamine receptors in membranes prepared from rat cerebral cortex, striatum, and anterior pituitary. Ligands employed were: [3H]WB4101, [3H]prazosin, [3H]yohimbine, and [3H]clonidine (alpha-noradrenergic); [3H]dihydroalprenolol (beta-noradrenergic); [3H]spiperone and [3H]ADTN (dopaminergic). Only the 17 beta estrogens were effective and only binding of [3H]spiperone and [3H]ADTN in striatum and [3H]WB4101 and [3H]prazosin in cerebral cortex was reduced. Thus putative dopaminergic and alpha 1-noradrenergic sites alone appear to recognize estrogens. A slight competitive effect on [3H]spiperone binding to anterior pituitary membranes was also observed. Among the 17 beta estrogens tested, the most effective in all cases was the catechol estrogen 2-hydroxyestradiol (2-OHE2). The ability of 2-OHE2 (IC50 = 20-30 micro M) to inhibit ligand binding to alpha 1 receptors was comparable to that of norepinephrine (IC50 = 10-20 micro M), whereas for dopamine receptors in striatum and pituitary 2-OHE2 was an order of magnitude less effective than dopamine (IC50 = 12 micro M) in reducing binding of 3H ligands. Estradiol-17 beta and 2-hydroxyestrone were also able to inhibit binding, but the order of steroid potency was different for alpha 1 and dopaminergic receptors. Progesterone, testosterone, and corticosterone were without effect in all cases. These results show that there is specificity of steroid interactions with catecholamine receptors in the brain, both in terms of steroid structure and receptor type. The possible relevance of these interactions to neuroendocrine function is discussed.

Animals↗