Arachidonic Acid–Induced Ca2+ Entry Is Involved in Early Steps of Tumor Angiogenesis

Abstract

Growth factor -induced intracellular calcium signals in endothelial cells regulate cytosolic and nuclear events involved in the angiogenic process. Among the intracellular messengers released after proangiogenic stimulation, arachidonic acid (AA) plays a key role and its effects are strictly related to calcium homeostasis and cell proliferation. Here, we studied AA-induced intracellular calcium signals in endothelial cells derived from human breast carcinomas (B-TEC). AA promotes B-TEC proliferation and organization of vessel-like structures in vitro. The effect is directly mediated by the fatty acid without a significant contribution of its metabolites. AA induces Ca 2+ i signals in the entire capillary-like structure during the early phases of tubulogenesis in vitro. No such responses are detectable in B-TECs organized in more structured tubules. In B-TECs growing in monolayer, AA induces two different signals: a Ca 2+ i increase due to Ca 2+ entry and an inhibition of store-dependent Ca 2+ entry induced by thapsigargin or ATP. An inhibitor of Ca 2+ entry and angiogenesis, carboxyamidotriazole, significantly and specifically decreases AA-induced B-TEC tubulogenesis, as well as AA-induced Ca 2+ signals in B-TECs. We conclude that (a) AA-activated Ca 2+ entry is associated with the progression through the early phases of angiogenesis, mainly involving proliferation and tubulogenesis, and it is down-regulated during the reorganization of tumor-derived endothelial cells in capillary-like structures; and (b) inhibition of AA-induced Ca 2+ entry may contribute to the antiangiogenic action of carboxyamidotriazole. (Mol Cancer Res 2008;6(4):535 -45)

Multiple Roles of Protein Kinase A in Arachidonic Acid–Mediated Ca2+ Entry and Tumor-Derived Human Endothelial Cell Migration

“…2C). These data are in agreement with the previously described calcium-dependent tubulogenic action of the fatty acid (5). AA-induced wound healing is also abolished by PKI preincubation, providing a functional link between the cAMP/PKA pathways described above and the biological activities of the fatty acid (Fig.…”

“…In B-TECs, low concentrations of AA activate a store-independent calcium entry with similar properties previously observed in BAECs. This event is involved in tubulogenesis progression and is downregulated in the later phases of tubule formation (5,29). Here, we show that the cAMP/ PKA pathway is involved in AA-induced Ca 2+ entry.…”

“…In particular, we previously reported the ability of AA to trigger a NSOCE in bovine aortic ECs (BAEC), playing a critical role in the control of proliferation (1,2,(5)(6)(7).…”

“…We have recently studied the role of AA-induced cytosolic calcium (Ca c ) signals in the angiogenic process of B-TECs (5). AA induces B-TEC proliferation and increases capillary-like formation in vitro.…”

“…Notably, calcium entry promoted by the fatty acid is specifically detected in the early stages of tubule organization and downregulated in the later phases of capillary-like organization. The use of the antiangiogenic agent carboxyamidotriazole (CAI) reduces AA-induced Ca c signals and completely prevents AA-induced in vitro tubulogenesis (5).…”