Characterization of rat liver malonyl-CoA decarboxylase and the study of its role in regulating fatty acid metabolism

Abstract

In the liver, malonyl-CoA is central to many cellular processes, including both fatty acid biosynthesis and oxidation. MalonylCoA decarboxylase (MCD) is involved in the control of cellular malonyl-CoA levels, and functions to decarboxylate malonylCoA to acetyl-CoA. MCD may play an essential role in regulating energy utilization in the liver by regulating malonyl-CoA levels in response to various nutritional or pathological states. The purpose of the present study was to investigate the role of liver MCD in the regulation of fatty acid oxidation in situations where lipid metabolism is altered. A single MCD enzyme of molecular mass 50.7 kDa was purified from rat liver using a sequential column chromatography procedure and the cDNA was subsequently cloned and sequenced. The liver MCD cDNA was identical to rat pancreatic β-cell MCD cDNA, and contained two potential translational start sites, producing proteins of 50.7 kDa and 54.7 kDa. Western blot analysis using polyclonal antibodies generated against rat liver MCD showed that the 50.7 kDa isoform of MCD is most abundant in heart and liver, and of relatively low abundance in skeletal muscle (despite elevated MCD transcript levels in skeletal muscle). Tissue distribution experiments demonstrated that the pancreas is the only rat tissue so far identified that contains both the 50.7 kDa and 54.7 kDa isoforms of MCD. In addition, transfection of the full-length rat liver MCD cDNA into COS cells produced two isoforms of MCD. This indicated either that both initiating methionines are functionally active, generating two proteins, or that the 54.7 kDa isoform is the only MCD protein translated and removal of the putative mitochondrial targeting pre-sequence generates a protein of approx. 50.7 kDa in size. To address this,

Malonyl‐CoA decarboxylase is present in the cytosolic, mitochondrial and peroxisomal compartments of rat hepatocytes

“…The intermediate species (50-51 kDa) was found only in mitochondria and peroxisomes and the lowest Mw species (48-49 kDa) was present exclusively in the peroxisomes. Other laboratories [25,26] using adenovirally expressed or transfected MCD, have reported the presence of different MCD species; but to our knowledge, this is the first time that the existence of different MCD species and their organelle specificity has been observed in untransfected tissue. Whether the different molecular weight species reflect transcriptionally or post-transcriptionally generated isoforms or proteolytic modification of the enzyme remains to be established.…”

Peroxisomal-proliferator-activated receptor alpha activates transcription of the rat hepatic malonyl-CoA decarboxylase gene: a key regulation of malonyl-CoA level

“…On the other hand, it has been strongly suggested that an increase in MCD activity can be the factor contributing to a decrease in malonyl-CoA and increase in fattyacid oxidation in muscle tissue [34]. Moreover, the activity of MCD is highest in tissues such as heart and liver, which are known as the major organs of fatty-acid oxidation [35]. Also, in pathophysiological states such as diabetes or hyperlipidaemia, where lipid metabolism is altered, MCD has an important role in the regulation of fatty-acid metabolism [36].…”

Malonyl‐CoA decarboxylase (MCD) is differentially regulated in subcellular compartments by 5′AMP‐activated protein kinase (AMPK)

“…MCD was originally identified in the uropygial gland of the goose [11]. We also showed MCD to be highly expressed in mammalian cardiac muscle [12], and provided evidence to suggest that cardiac MCD plays an important role in regulating fatty acid metabolism in the heart [10,13]. Regulation of MCD occurs both at the level of transcription and post‐translation [14,15].…”