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15-Deoxy-Δ<sup>12,14</sup>-prostaglandin-J<inf>2</inf> reveals a new pVHL-independent, lysosomal-dependent mechanism of HIF-1α degradation

Abstract:

Hypoxia-inducible factor-1α (HIF-1α) protein is degraded under normoxia by its association to von Hippel-Lindau protein (pVHL) and further proteasomal digestion. However, human renal cells HK-2 treated with 15-deoxy-Δ12,14-prostaglandin-J2 (15d-PGJ 2) accumulate HIF-1α in normoxic conditions. Thus, we aimed to investigate the mechanism involved in this accumulation. We found that 15d-PGJ2 induced an over-accumulation of HIF-1α in RCC4 cells, which lack pVHL and in HK-2 cells treated with inhibitors of the pVHL-proteasome pathway. These results indicated that pVHL-proteasome-independent mechanisms are involved, and therefore we aimed to ascertain them. We have identified a new lysosomal-dependent mechanism of HIF-1α degradation as a target for 15d-PGJ2 based on: (1) HIF-1α colocalized with the specific lysosomal marker Lamp-2a, (2) 15d-PGJ2 inhibited the activity of cathepsin B, a lysosomal protease, and (3) inhibition of lysosomal activity did not result in over-accumulation of HIF-1α in 15d-PGJ2-treated cells. Therefore, expression of HIF-1α is also modulated by lysosomal degradation. © 2009 Birkhäuser Verlag, Basel/Switzerland.