Abstract 745: Mst1 Inhibits PGC-1α via Inhibition of CREB
Mammalian sterile 20-like kinase 1 (Mst1) is a STE20-like family serine-threonine kinase which is activated by stress and heart failure, and which has been shown to activate apoptosis in cardiac myocytes. Transgenic mice with cardiac specific overexpression of Mst1 (Tg-Mst1) displayed dilated cardiomyopathy without compensatory hypertrophy and increased numbers of TUNEL positive cells, accompanied by downregulation of a variety of metabolic factors in the heart, including those involved in mitochondrial function. Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), an important regulator of several metabolic pathways and of mitochondrial biogenesis, was downregulated in the hearts of these mice as well. We have previously shown that Mst1 inhibited both PGC-1α transcription and activity in vitro, as determined by luciferase reporter assay. We, therefore, hypothesized that Mst1 inhibits PGC-1α through transcription factor inhibition. Since the PGC-1α promoter contains a CREB response element (CRE), we examined whether Mst1 inhibits CREB transcriptional activity. Immunoblot analysis showed that phosphorylated CREB levels are significantly decreased in Tg-Mst1 (−55%, n=6, p<0.01). Also, in COS7 cells transfected with a CRE-driven luciferase reporter plasmid, CREB transcriptional activity was significantly inhibited when cells were cotransfected with Mst1 expression plasmid (0.44 ± 0.02 vs 1.00 ± 0.04 with or without Mst1, p<0.0001). To determine whether regulation of PGC-1α transcription by CREB is inhibited by Mst1, we cotransfected COS7 cells with PGC-1α promoter luciferase reporter and CREB expression plasmids. PGC-1α promoter activity doubled in the presence of CREB (2.17 ± 0.15 vs 1.00 ± 0.05 with or without CREB, p<0.001), but this increase was completely abolished when Mst1 was cotransfected as well (1.03 ± 0.05, p<0.001 vs CREB alone). PGC-1α plays an essential role in maintaining cardiac function and energy levels, and its regulation has been linked to the differential responses of the mitochondrial metabolism to physiologic and pathologic cardiac hypertrophy. Our data suggest that PGC-1α is negatively regulated by Mst1 via inhibition of CREB transcriptional regulation.