Expression of Functional Nerve Growth Factor Receptors in Pancreatic β-cell Lines and Fetal Rat Islets in Primary Culture

Previous data demonstrated that one rat insulinoma cell line, RINm5F cells, which is a rat β-cell line derived from a pancreatic tumor, express mRNA coding for both the low- and the high-affinity nerve growth factor receptors. Goals of this study were to extend our data to other β-cell lines and fetal islets in primary culture and to study further the binding characteristics of nerve growth factor receptors on β-cells. Northern blot analysis revealed that not only a panel of endocrine β-cell lines (RINm5F, INS-1, β-TC3) but also fetal rat islets in primary culture express mRNA coding for trk-A, which has been proposed to be the neuronal high-affinity nerve growth factor receptors. Reverse polymerase chain reaction followed by sequencing revealed that the sequence of trk-A receptor in RINm5F cells is identical to that of trk-A expressed in PC12 cells. The expression of the low-affinity nerve growth factor receptor was examined by Northern blot analysis that showed low-affinity nerve growth factor receptor to be expressed in RINm5F and INS-1 cell lines, in fetal rat islets in primary culture, but not in β-TC3-cells. Binding experiments revealed the presence of low- and high-affinity nerve growth factor binding sites, identical to those described for PC12 cells, on RINm5F and INS-1 cells and only high-affinity binding sites on β-TC3 cells. Exposure of all three β-cell lines to nerve growth factor increased NGFI-A and c-fos mRNA steady-state levels, showing that these receptors are functional. These data demonstrate that the entire machinery required for nerve growth factor action is present in β-cells in culture.