Adrenomedullin as an Autocrine/Paracrine Apoptosis Survival Factor for Rat Endothelial Cells*

Abstract

Adrenomedullin is a potent vasorelaxant/hypotensive peptide recently isolated from human pheochromocytoma. We demonstrate here a novel role of this peptide as an apoptosis survival factor for rat endothelial cells. When rendered quiescent by serum deprivation, a fraction of endothelial cell cultures showed morphological and biochemical features characteristic of apoptosis. Adrenomedullin significantly suppressed apoptosis without inducing cell proliferation. Rat endothelial cells that contained high affinity binding sites for adrenomedullin expressed adrenomedullin gene and released the peptide into culture media. Addition of preimmune rabbit serum prevented apoptosis, whereas rabbit antiadrenomedullin antiserum partially, but significantly, abrogated the protective effect of the preimmune serum, suggesting its autocrine/paracrine role. Although adrenomedullin induced intracellular cAMP formation, other cAMP-elevating agonists, such as prostaglandin I2 and forskolin, did not affect apoptosis. Furthermore, adenosine 3',5'-cyclicmonophosphothioate Rp-isomer, a cAMP antagonist, did not block the cell survival effect of adrenomedullin. Adrenomedullin neither increased intracellular Ca2+ concentrations nor inositol-1,4,5-trisphosphate levels in rat endothelial cells. These results demonstrate that adrenomedullin suppresses serum deprivation-induced apoptosis of rat endothelial cells via cAMP-independent mechanism.

Adrenomedullin inhibits hypoxic cell death by upregulation of Bcl-2 in endometrial cancer cells: a possible promotion mechanism for tumour growth

“…Although our study is the ®rst to describe the antiapoptotic e ect of ADM under hypoxia, prior observations have shown ADM to antagonize serum deprivation-induced apoptosis in endothelial cells (Kato et al, 1997). Interestingly, in glomerular mesangial cells ADM was shown to evoke a contrary e ect by increasing apoptosis during serum starvation (Parameswaran et al, 1999).…”

“…Peptides in the culture medium were extracted according to a previously published method using Sep-Pak C18 cartridges (Waters, Milford, USA) (Kato et al, 1997). Human ADM (1-52) was quanti®ed by a competitive RIA (Peninsula Laboratories, Merseyside, UK) using rabbit-antiserum.…”

Adrenomedullin antagonist suppresses in vivo growth of human pancreatic cancer cells in SCID mice by suppressing angiogenesis

“…Also, we have recently identified 38 genes as hypoxia-inducible genes with the use of a DNA microarray system (Niizeki et al, 2002); in those, we found adrenomedullin (AM), which has been reported to be induced by hypoxia and to promote vasodilation (Nuki et al, 1993;Zhao et al, 1996;Cormier-Regard et al, 1998;Nakayama et al, 1998;Hayakawa et al, 1999;Garayoa et al, 2000). Recent reports further demonstrated that AM acted as a growth factor for several cancer cells besides vasodilator, and that AM acted as a survival factor for several cancer and endothelial cells (Miller et al, 1996;Kato et al, 1997;Oehler et al, 2001;Rocchi et al, 2001). However, the function of AM in pancreatic cancer cells has not been determined.…”

“…Whereas previous reports demonstrated that AM suppressed the apoptosis of endothelial cells and that it was protumorigenic either by stimulating angiogenesis alone or both angiogenesis and carcinoma cell growth directly (Kato et al, 1997;Oehler et al, 2002), the precise mechanism of AM in angiogenesis is yet to be determined. Angiogenesis is a morphogenetic process, which consists of a number of steps including endothelial cell invasion and capillary lumen formation controlled by various factors (Carmeliet, 2000).…”

“…Intratumoral injection of AMA, but not AM N-terminal fragment, AM(1-25) (Watanabe et al, 1996), from day 8 to day 17 completely abrogated the tumor formation (Figure 1a), suggesting that AM is essential for the in vivo tumor formation of pancreatic cancer cells. As recent reports demonstrated that AM acted as a growth factor for several cancer cells (Miller et al, 1996;Kato et al, 1997;Oehler et al, 2001;Rocchi et al, 2001), we then examined the expressions of AM and AM receptors and the effects of AMA on the growth of pancreatic cancer cells in vitro. All the pancreatic cancer cell lines expressed higher levels of AM mRNA under hypoxia than under normoxia (Figure 1b).…”