| Budget Amount *help |
¥14,700,000 (Direct Cost: ¥14,700,000)
Fiscal Year 2006: ¥7,100,000 (Direct Cost: ¥7,100,000)
Fiscal Year 2005: ¥7,600,000 (Direct Cost: ¥7,600,000)
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| Research Abstract |
Autophagy is a highly-conserved membrane trafficking pathway that carries cytoplasmic constituents to the degradative compartments, the lysosomes. This physiological process is maintained at a basal level for the quality control of cellular components in daily life, and is induced by change of environmental conditions such as nutrient-starvation to produce energy and proteins essential for survival. We previously showed that autophagy also serves as a cellular defense mechanism against certain intracellular pathogens. Invasive group A Streptococcus (GAS) is effectively eliminated by autophagy. In this process, intracellular GAS induces formation of unusually-large autophagosomes, termed the GAS-containing autophagosome-like vacuoles (GcAVs); their size is over ten times larger than that of the canonical autophagosomes. In this study, we examined how such a large autophagosome is formed. Multiple isolation membranes emerged close by the cytoplasmic GAS and fused with each other, forming GcAVs. Isolation membranes were formed in response to GAS-infection, and wild-type Rab7 localized to those membranes forming GcAVs; however, overexpression of dominant-negative mutant Rab7 (Rab7T22N) blocked GcAV formation. These results suggest that Rab7 plays a pivotal role in the fusion events required for GcAV formation. After successful completion of the GcAVs, these structures underwent homotypic fusion, resulting in larger GcAVs. Since Rab7 is unnecessary for canonical autophagosome formation, our finding demonstrates the existence of a distinct molecular basis for an autophagy system specialized for bacterial elimination. In addition, we found that the Golgi apparatus is one of membrane source to form large GcAVs rapidly (several ten minutes); lipids and Atg9 are transferred from the Golgi apparatus to GcAVs.
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