Cloning and expression of secretagogin, a novel neuroendocrine-and pancreatic islet of Langerhans-specific Ca2+-binding protein

We have cloned a novel pancreatic beta cell and neuroendocrine cell-specifi c calcium-binding protein termed secretagogin. The cDNA obtained by immunos creening a human pancreatic cDNA library using the recently described murin e monoclonal antibody D24 contains an open reading frame of 828 base pairs. This codes for a cytoplasmic protein with six putative EF finger hand calc ium-binding motifs, The gene could be localized to chromosome 6 by alignmen t with GenBanb genomic sequence data, Northern blot analysis demonstrated a bundant expression of this protein in the pancreas and to a lesser extent i n the thyroid, adrenal medulla, and cortex. In addition it was expressed in scant quantity in the gastrointestinal tract (stomach, small intestine, an d colon). Thyroid tissue expression of secretagogin was restricted to C-cel ls, Using a sandwich capture enzyme-linked immunosorbent assay with a detec tion limit of 6.5 pg/ml, considerable amounts of constitutively secreted pr otein could be measured in tissue culture supernatants of stably transfecte d RIN-BF and dog insulinoma (INS-H1) cell clones; however, in stably transf ected Jurkat cells, the protein was only secreted upon CD3 stimulation. Fun ctional analysis of transfected cell lines expressing secretagogin revealed an influence on calcium flux and cell proliferation. In RIN-5F cells, the antiproliferative effect is possibly due to secretagogin-triggered down-reg ulation of substance P transcription.