Chromogranin A binds to αvβ6-integrin and promotes wound healing in mice

Abstract

Chromogranin A (CgA), a secretory protein expressed by many neuroendocrine cells, neurons, cardiomyocytes, and keratinocytes, is the precursor of various peptides that regulate the carbohydrate/lipid metabolism and the cardiovascular system. We have found that CgA, locally administered to injured mice, can accelerate keratinocyte proliferation and wound healing. This biological activity was abolished by the Asp(45)Glu mutation. CgA and its N-terminal fragments, but not the corresponding Asp(45)Glu mutants, could selectively recognize the αvβ6-integrin on keratinocytes (a cell-adhesion receptor that is up-regulated during wound healing) and regulate keratinocyte adhesion, proliferation, and migration. No binding was observed to other integrins such as αvβ3, αvβ5, αvβ8, α5β1, α1β1, α3β1, α6β4, α6β7 and α9β1. Structure-activity studies showed that the entire CgA(39-63) region is crucial for αvβ6 recognition (K(i) = 7 nM). This region contains an RGD site (residues CgA(43-45)) followed by an amphipathic α-helix (residues CgA(47-63)), both crucial for binding affinity and selectivity. These results suggest that the interaction of the RGD/α-helix motif of CgA with αvβ6 regulates keratinocyte physiology in wound healing.

Chromogranin A: a paradoxical player in angiogenesis and vascular biology

“…The first indication of a defined receptor for the fulllength CgA and its N-terminal fragment vasostatin-1 stems from a recent study on wound healing in injured mice [64]. A selective binding of CgA and vasostatin-1 to integrin avb6 was demonstrated in the low nanomolar range.…”

“…No binding has been observed, to other RGD-dependent and -independent integrins, such as avß3, avß5, avß8, a5ß1, a1ß1, a3ß1, a6ß4, a6ß7 and a9ß1, in the low nanomolar range. However, it is noteworthy that various peptides of different length containing the integrin-binding region of vasostatin-1 could recognize, in the low micromolar range, also the integrin avß3 [64]. For example, in competitive binding assays the peptide CgA 39-63 could bind avß3 and avß6 with a Ki of 1.7 lM and 7 nM, respectively.…”

“…This integrin has been shown to modulate cancer cell invasion, inhibit apoptosis, regulate the expression of matrix metalloproteases (MMP) and is involved in TGF-ß1 maturation [65,67]. Integrin avß6 is upregulated in keratinocytes and epithelial cells during tissue repair and in cancer [67] and regulates keratinocyte physiology in wound healing [64,68]. Interestingly, full-length CgA, but not a mutant having RGD replaced with the inactive RGE motif, could regulate keratinocyte physiology and promote wound healing in mice [64], suggesting that the RGD/integrin interaction is important for the physiological functions of CgA in wound healing.…”

“…Integrin avß6 is upregulated in keratinocytes and epithelial cells during tissue repair and in cancer [67] and regulates keratinocyte physiology in wound healing [64,68]. Interestingly, full-length CgA, but not a mutant having RGD replaced with the inactive RGE motif, could regulate keratinocyte physiology and promote wound healing in mice [64], suggesting that the RGD/integrin interaction is important for the physiological functions of CgA in wound healing. The relevance of this interaction for the homeostatic regulation of the cardiovascular system and tumor vessels remains to be investigated.…”

Regulation of tumor growth by circulating full-length chromogranin A

“…CgA is also expressed in lower amounts by granulocytes, cardiomyocytes and, in certain conditions, by keratinocyte [1, 3-5]. An increasing number of studies have shown that CgA and certain CgA-derived peptides, called vasostatin-1, pancreastatin, catestatin and serpinin, can regulate the cardiovascular system and metabolism, suggesting that this protein can exert extra-cellular functions [1].…”