Lactogenic hormones rapidly activate p21 ras /mitogen-activated protein kinase in Nb2-11C rat lymphoma cells

Abstract

Lactogenic hormone-dependent Nb2-11C cells proliferate in response to prolactin (PRL) or human growth hormone (hGH). We have investigated the activation of p21( ras ) and mitogen-activated protein kinase (MAP-kinase) by hGH in lactogen-dependent Nb2-11C and in autonomous hormone-independent Nb2-SP rat lymphoma cells. Exposure of Nb2-11C cells to hGH resulted in a dose-dependent activation of p21( ras ) and of MAP-kinase. Activation occurs at physiological hGH concentration and with a rapid onset (∼1 min) reaching maximal level at 10-20 min. In contrast, in Nb2-SP autonomous lactogen-independent cells, p21( ras ) and MAP-kinase are constitutively activated and a challenge with lactogenic hormone had a modest additional activating effect. TPA, an activator of protein kinase C, enhanced p21( ras ) and MAP-kinase activity in Nb2-11C cells but failed to induce proliferation. The mechanism of activation of p21( ras ) in Nb2-11C cells by lactogenic hormones involves both an increased binding of guanine nucleotides to p21( ras ) as well as an increase in GTP/GDP+GTP ratio. In summary, we have demonstrated here that activation of the p21( ras )/MAP-kinase pathway follows PRL receptor activation but is not sufficient for the lactogenic hormone-dependent mitogenesis.

High Insulin Requirements and Poor Metabolic Control do not Modify the Expression, Regulation and PKC Mediated Activation of the p21ras Pathway in PBMC from Type II Diabetic Patients

“…[1] In this work, we examined for the first time the function and expression of the p21ras pathway in a subset of these patients characterized by high insulin requirements and poor metabolic control to further determine the role of p21ras pathway in mediating the insulin resistance in type II diabetes. Determination of MAP-kinase activity was [13] performed as previously described. We previously reported a normal p21ras pathway expression in the presence of defective lymphocyte activation and proliferation.…”