GROWTH-HORMONE AND PROLACTIN REGULATE THE EXPRESSION OF NERVE GROWTH-FACTOR RECEPTORS IN INS-1 CELLS

We have previously demonstrated that beta-cells express both p75(NGF-R) and Trk-A, the low and high affinity nerve growth factor (NGF) receptors, respectively. In the current study, we provide evidences that in the beta-cell line INS-1, the expression of these receptors is tightly controlled by GH and PRL, two hormones implicated in beta-cell development and function. Within 24 h of treatment of INS-1 cells with human (h) GH, the numbers of low and high affinity NGF-binding sites, calculated after Scatchard analysis, increase 3- and 2.5-fold, respectively. The increase in the concentration of the high affinity NGF-binding sites is paralleled by an increase in Trk-A protein without any change at the mRNA steady state level, suggesting a translational/posttranslational effect. On the other hand, the increase in low affinity binding sites is paralleled by an increase in the p75(NGF-R) mRNA steady state level. The effect requires at least 8 h of treatment, and a dose of 50 ng/ml hGH is sufficient to induce an increase in the p75(NGF-R) mRNA steady state level. The effect of hGH can be mimicked in the same time- and dose-dependent manner by rat PRL and bovine GH, suggesting that the expression of NGF receptors can be transduced by both the somatogenic and lactogenic pathways. Finally, the increase in the p75(NGF-R) mRNA steady state level after PRL treatment is not due to mRNA stabilization, suggesting a transcriptional control, and requires concurrent protein synthesis. GH and PRL could thus be important regulators of the sensitivity of beta-cells to NGF.