Granins

Granins are a family of soluble, acidic proteins localized to the secretory granules of neuroendocrine and some endocrine cells. The family includes chromogranin A (CgA) and chromogranin B (CgB) and the secretogranins I–III (SCG1/SCG2/SCG3), collectively referred to as the granin family. They are co-secreted with peptide hormones and amines into secretory granules, where they participate in granule biogenesis and cargo sorting.

Functionally, granins contribute to the packaging and storage of peptide hormones by promoting aggregation under acidic conditions with high calcium, aiding the selective concentration of granule contents. They also serve as precursors to multiple bioactive peptides that are generated by proteolytic processing during or after granule formation.

Bioactive peptides derived from granins include vasostatin and pancreastatin from chromogranin A, as well as secretoneurin from secretogranin II, among others. These peptides are involved in various regulatory roles, including modulation of vascular tone, immune signaling, and neuronal communication, illustrating the diverse functions linked to the granin family.

Clinical relevance is most often associated with chromogranin A as a biomarker for neuroendocrine differentiation and neuroendocrine tumors. Elevated levels can also occur in renal failure, inflammatory states, and during glucocorticoid therapy, among other conditions. Interpreting granin levels typically requires consideration of assay type, renal function, and the broader clinical context. Granins remain a focus of research in endocrinology and oncology due to their roles in hormone processing and as sources of bioactive peptides.