Chromogranin A Transcription and Gene Expression in Folliculostellate (TtT/GF) Cells Inhibit Cell Growth

Abstract

Folliculostellate (FS) cells are present in the anterior pituitary and have important regulatory functions including controlling hormone release from other anterior pituitary cells. FS cells do not usually express neuroendocrine genes such as chromogranin A (CgA). We analyzed transcriptional regulation and gene expression in the TtT/GF FS cell line to better understand the role of FS cells in anterior pituitary function. After transient transfection with a human (h) CgA promoter sequence linked to a luciferase reporter, there was basal level of transcriptional activity, which was two- to fourfold less than that observed in the anterior pituitary neuroendocrine cell lines HP75 and GH3. The transcriptional activity was decreased in all cell lines when a mutant hCgA promoter cyclic AMP response element (CRE) was used for transfection. Sodium butyrate treatment increased the transcriptional activity in all cell lines, but remained two- to fourfold higher in the HP75 and GH3 cell lines than in the TtT/GF cells. Stable transfection of a plasmid expressing bovine (b) CgA in the TtT/GF cells led to inhibition of cell growth as measured by 3H-thymidine incorporation, Ki-67 labeling index, and growth curve analysis. CgA protein and mRNA could be readily demonstrated in the cloned cells but not in the parental cell line or vector control cells. When the CgA expressing cloned cells were injected into SCID mice, there was a decrease in the rate of tumor growth compared to the vector control in vivo. These results indicate that the TtT/GF FS cells are fibroblast-like compared to the neuroendocrine anterior pituitary secretory cells when analyzed by transcriptional activity with a transiently transfected CgA promoter. In TtT/GF cells with a stably transfected bCgA plasmid, CgA has a direct regulatory effect on tumor cell proliferation.