Title

Cell-cell adhesion and cadherin expression in the GH$\sb3$ somatolactotrope cell line: Implications for prolactin gene expression

Date of Completion

January 1997

Keywords

Biology, Molecular|Biology, Cell

Degree

Ph.D.

Abstract

Expression of the prolactin gene by lactotropes of the anterior pituitary is modulated by interactions with other lactotropes, with gonadotropes, and with folliculo-stellate cells. However, little is known about which cell-cell adhesion molecules mediate these interactions. We utilized the GH$\sb3$ rat anterior pituitary cell line as a model system in which to examine the expression and function of anterior pituitary cell-cell adhesion molecules. Extracellular CaCl$\sb2$ induces prolactin mRNA levels by 5-10 fold in GH$\sb3$ cells and causes a striking induction of cell-cell adhesion, raising the possibility that the two events are causally linked. Time course experiments indicated the onset of prolactin mRNA always occurred after the onset of cell-cell adhesion and required voltage sensitive calcium channels. Both heparin and trypsin blocked cell-cell adhesion and the prolactin mRNA induction without affecting the levels of other mRNAs. Based on these data we propose a role for both voltage-sensitive calcium channels and calcium-dependent cell-cell adhesion in the CaCl$\sb2$ induction of prolactin gene expression. Cadherins may mediate GH$\sb3$ cell-cell adhesion based on the observation of adherens junctions between GH$\sb3$ cells. Experiments were inconclusive which used cadherin-specific blocking agents such as N-cadherin antisense oligonucleotides and an N-cadherin blocking antibody in attempts to block the calcium-dependent induction of cell-cell adhesion and prolactin mRNA. This raised the possibility that multiple cadherins and/or other cell-cell adhesion molecules were expressed in GH$\sb3$ cells and contributed to calcium-dependent cell-cell adhesion as well. Studies supporting this hypothesis indicated that N-cadherin, R-cadherin, and cadherin-9 were expressed in GH3 cells. All three mRNAs were induced by cycloheximide, indicating that they may be regulated at the level of mRNA stability. N-cadherin transcripts were detected in male and cycling female adult rat anterior pituitaries, but were downregulated in anterior pituitaries from pregnant rats. These studies raise the possibility that cell-cell adhesion and cadherin expression plays a functional role in the regulation of the lactotrope phenotype. ^