Osteoblastic protein tyrosine phosphatases inhibition and connexin 43 phosphorylation by alendronate

LEZCANO V; BELLIDO T; PLOTKIN LI; MORELLI S

EXPERIMENTAL CELL RESEARCH

ELSEVIER INC

Año: 2014 vol. 324 p. 30 - 39

0014-4827

Bisphosphonates (BPs), potent inhibitors of bone resorption which inhibit osteoclasts, have alsobeen shown to act on osteocytes and osteoblasts preventing apoptosis via connexin (Cx) 43hemichannels and activating the extracellular signal regulated kinases ERKs. We previouslydemonstrated the presence of a saturable, specific and high affinity binding site for alendronate(ALN) in osteoblastic cells which express Cx43. However, cells lacking Cx43 also bound BPs.Herein we show that bound [3H]-alendronate is displaced by phosphatase substrates. Moreover,similar to Na3VO4, ALN inhibited the activity of transmembrane and cytoplasmic PTPs, pointingout the catalytic domain of phosphatases as a putative BP target. In addition, anti-phosphotyrosineimmunoblot analysis revealed that ALN stimulates tyrosine phosphorylation of severalproteins of whole cell lysates, among which the major targets of the BP could beimmunochemically identified as Cx43. Additionally, the transmembrane receptor-like PTPs,RPTPμ and RPTPα, as well as the cytoplasmic PTP1B, are highly expressed in ROS 17/2.8 cells.Furthermore, we evidenced that Cx43 interacts with RPTPμ in ROS 17/2.8 and ALN decreasestheir association. These results support the hypothesis that BPs bind and inhibit PTPs associated toCx43 or not, which would lead to the activation of signaling pathways in osteoblasts.