Biomedical subjects

S D Costa

Publications and source records attributed to S D Costa.

39 records · Page 3Linked to original sources

PubMed1986

Protein kinase C desensitization by phorbol esters and its impact on growth of human breast cancer cells.

Active phorbol esters such as TPA (12-0-tetra-decanoylphorbol-13-acetate) inhibited growth of mammary carcinoma cells (MCF-7 greater than BT-20 greater than MDA-MB-231 greater than = ZR-75-1 greater than HBL-100) with the exception of T-47-D cells presumably by interacting with the phospholipid/Ca2+-dependent protein kinase (PKC). The nonresponsive T-47-D cells exhibited the lowest PKC activity. A rapid (30 min) TPA-dependent translocation of cytosolic PKC to membranes was found in the five TPA-sensitive cell without affecting cell growth. However, TPA-treatment of more than 10 hours inhibited reversibly the growth of TPA-responsive cells. This effect coincided with the complete loss of cellular PKC activity due to the proteolysis of the translocated membrane-bound PKC holoenzyme (75K) into 60K and 50K PKC fragments. Resumption of cell growth after TPA-removal was closely related to the specific reappearance of the PKC holoenzyme activity (75K) in the TPA-responsive human mammary tumor cell lines suggesting an involvement of PKC in growth regulation.

Breast Neoplasms↗

PubMed1986

Correlation between hormone dependency and the regulation of epidermal growth factor receptor by tumor promoters in human mammary carcinoma cells.

The effects of the tumor promoter phorbol 12-tetradecanoate 13-acetate (TPA) on the epidermal growth factor (EGF) receptor levels were investigated in hormone-dependent (MCF-7, T-47-D, and ZR-75-1) and hormone-independent (MDA-MB-231, HBL-100, and BT-20) human mammary carcinoma cell lines. In the absence of TPA, hormone-independent cell lines contained high concentrations of low-affinity EGF receptors (apparent Kd = 8 X 10(-10) M), whereas hormone-dependent cell lines exhibited low concentrations of high-affinity receptors (apparent Kd = 1 X 10(-10) M). TPA causes a change of the receptor from a high- to the low-affinity state in hormone-dependent cell lines (MCF-7, T-47-D, and ZR-75-1), as well as in the hormone-independent HBL-100, whereas the affinity remained unchanged in MDA-MB-231 and BT-20 cells. In addition, progesterone receptor levels are decreased after TPA treatment in the hormone-dependent cell lines MCF-7, T-47-D, and ZR-75-1, whereas the estrogen receptor levels remained unchanged. Tumor promoters such as TPA or teleocidin inhibited the proliferation of these cell lines at concentrations above 10 microM with the exception of the T-47-D cells. The most sensitive cell line towards growth inhibition by tumor promoter was the hormone-dependent MCF-7 cell line. Evaluation of different TPA analogs indicated a positive correlation between the growth-inhibitory effects and their ability to stimulate the subcellular redistribution of protein kinase C activity in MCF-7 cells. These data suggest a protein kinase C-mediated down-regulation of the progesterone receptor concentration and of the EGF receptor affinity, which is supposed to mediate the mitogenic response. Furthermore, these results support the hypothesis that the tumor-derived growth factors induced by estradiol act via the EGF receptor in hormone-dependent mammary carcinoma cells.

Breast Neoplasms↗

PubMed1985

The cytosolic phorboid receptor correlates with hormone dependency in six mammary carcinoma cell lines.

Potent, structurally different tumor promoters inhibited growth of 6 human mammary carcinoma cell lines (ROOS et al, PNAS in press). This growth inhibition was investigated by measuring the phorboid receptor binding using [3H] PDBu (4 beta-phorbol 12, 13 dibutyrate). Specific, high affinity receptors were found in all six cell lines. [3H] PDBu binding affinities were higher in the cytosolic fractions than in the corresponding intact cells (K alpha = app. 1nM vs K alpha = app. 15nM). The hormone-independent cell lines (BT-20, HBL-100 and MDA-MB-231) exhibited significantly higher levels of cytosolic [3H] PDBu receptors than the hormone-dependent cells (MCF-7, T-47-D and ZR-75-1). The subcellular distribution of the [3H] PDBu binding correlated well with the distribution of the protein kinase C activity (r = 0.95).

Breast Neoplasms↗