Attenuated expression and function of the RECK tumor suppressor under hypoxic conditions is mediated by the MAPK signaling pathways

Abstract

Downregulation of the tumor suppressor, reversion-inducing cysteine-rich protein with Kazal motifs (RECK) has been reported under hypoxic conditions (Lee et al., 2010); however, the signaling pathways involved in this downregulation have not yet been identified. Hypoxia causes the silencing of RECK mRNA expression, but treatment with inhibitors of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated kinase (MAPK) (PD98059, SP600125, and SB203580 respectively) or their dominant negative mutants recovered RECK suppression induced by hypoxia as analyzed with semiquantitative RT-PCR analysis and a RECK promoter luciferase assay. Hypoxia increased phosphorylation of ERK1/2, JNK and p38 MAPKs. The activities of matrix metalloproteinase (MMP)-9 and MMP-2 were increased under hypoxic conditions but treatment with PD98059, SP600125 and SB203580 inhibited their activation in cancer cells, as seen by zymography. Moreover, treatment with the inhibitors blocked cancer cell migration induced by hypoxia in H-Ras transformed MCF10A mammary cells. RECK suppression under hypoxic conditions was inversely related to HIF-1α expression; however, treatment with PD98059, SP600125 and SB203580 did not influence binding of HIF-1α to the reverse hypoxia responsive element site of the RECK promoter in a DNA precipitation assay. These results suggest that the ERK, JNK and p38 MAPK signaling pathways are indirectly involved in RECK suppression but are not involved in the binding activity of HIF-1α to the reverse hypoxia responsive element site on the RECK promoter under hypoxic conditions.