Cyclic AMP-dependent protein kinases and cAMP-binding proteins in human mammary tumor MCF-7 cells

Selective modulation of protein kinase A and protein kinase C activities in epidermal growth factor (EGF)-stimulated MCF-7 breast cancer cells

In human MCF-7 breast cancer cells, both protein kinase A (PKA) and different members of the protein kinase C (PKC) family are stimulated upon binding of epidermal growth factor (EGF) to cell surface receptors. Selective stimulation of calcium-dependent PKCs with 10(-6) to 10(-9) M Thymeleatoxin significantly increased the proliferation rate of MCF-7 cells over 5 days in culture. This stimulation was blocked by the PKC antagonist Chelerythrine. In contrast, selective activation of PKA by addition of 1 mM dibutyryl cyclic AMP (dBcAMP) did not affect the proliferation rate of MCF-7 cells. Similarly, activation of the adenylate cyclase by 1 microM Forskolin and inhibition of PKA by the cyclic AMP analogue Rp-cAMPS did not modulate the proliferation rate of these cells. Activation of PKC stimulated the expression of the immediate early gene c-fos but c-myc expression was not significantly enhanced. On the other hand, PKA activation increased both c-myc and c-fos expression in MCF-7 cells. These results suggest that PKA activation and c-myc expression are not obligatory for proliferation of MCF-7 cells.

Functional beta-adrenergic receptors in breast cancer cells

Using L-[3H]dihydroalprenolol [( 3H]DHA), a potent beta-adrenergic antagonist, we demonstrated in breast cancer cells the presence of beta-adrenergic receptors with high affinity (Kd 1-9 nM) as shown by Scatchard analyses. Natural and synthetic agonists inhibited the [3H]DHA binding in the following order of potency: L-isoproterenol = L epinephrine much much greater L-norepinephrine, identical to the well-established order of potency for these compounds in producing beta-adrenergic responses. We verified that these compounds actually stimulated cAMP production in breast cancer cells. At the present time, the pathophysiological significance of beta-adrenergic receptors remains unclear. In view of the importance of cAMP in lactose production and in tumor growth mechanisms, it seems to be important to characterize the beta-adrenergic receptors in breast cancer cells in more detail and study their possible involvement in breast tumor growth.

Changes in the 32P incorporation in rat mammary tumor after chronic administration of LH-RH analogs

We studied endogenous phosphorylation in rat transplantable MT/W9A hormone-dependent mammary tumors of untreated rats and of animals treated with LH-RH analogs, the agonist D-Trp-6-LH-RH and the antagonist N-Ac-D-p-Cl-Phe1,2,D-Trp3,D-Arg6,D-Ala10-LH-RH. Incorporation of 32P from 32P-ATP was reduced significantly in tumors of rats treated with agonistic and antagonistic analogs of LH-RH or ovariectomized. The inhibition of protein phosphorylation may be related to tumor regression.