Knockdown of MTP18, a novel phosphatidylinositol 3-kinase-dependent protein, affects mitochondrial morphology and induces apoptosis

J Biol Chem. 2004 Jul 23;279(30):31544-55. doi: 10.1074/jbc.M404704200. Epub 2004 May 20.

Abstract

We identified a novel human cDNA encoding a mitochondrial protein, MTP18 (mitochondrial protein, 18 kDa) as a transcriptional downstream target of phosphatidylinositol (PI) 3-kinase signaling. We demonstrate that MTP18 mRNA as well as protein expression is dependent on PI 3-kinase activity. Confocal microscopy and biochemical fractionation revealed a mitochondrial localization of MTP18. Loss-of-function analysis employing antisense molecules revealed that MTP18 is essential for cell viability in PC-3 and HaCaT cells. We show that knockdown of MTP18 protein level results in a cytochrome c release from mitochondria and consequently leads to apoptosis. In addition, HaCaT cells with reduced levels of MTP18 become more sensitive to apoptotic stimuli. This effect is accompanied by dramatic subcellular alterations. Reduction of MTP18 impairs mitochondrial morphology resulting in the formation of a highly interconnected mitochondrial reticulum in COS-7 cells. Conversely, overexpression of MTP18 induces a punctuate morphology of mitochondria suggesting also a functional role of MTP18 in maintaining the mitochondrial integrity. Hence, our data indicate an unexpected connection of PI 3-kinase signaling, apoptosis and the morphology of mammalian mitochondria.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Apoptosis / physiology*
  • Base Sequence
  • COS Cells
  • Cell Division
  • Cell Line
  • DNA, Antisense / genetics
  • DNA, Complementary / genetics
  • HeLa Cells
  • Humans
  • Mitochondria / metabolism*
  • Mitochondria / ultrastructure
  • Mitochondrial Proteins / deficiency
  • Mitochondrial Proteins / genetics
  • Mitochondrial Proteins / metabolism*
  • Molecular Sequence Data
  • Phosphatidylinositol 3-Kinases / metabolism*
  • RNA, Messenger / genetics
  • Sequence Homology, Amino Acid
  • Signal Transduction

Substances

  • DNA, Antisense
  • DNA, Complementary
  • MTFP1 protein, human
  • Mitochondrial Proteins
  • RNA, Messenger