Functional analysis of subcellular localization of oncogene products in Drosophila

ショウジョウバエにおけるがん遺伝子産物の細胞内局在の機能解析

2017-03-24

2017-03-24

I investigate subcellular localization of two oncogene products. 1. Investigation of endoplasmic reticulum (ER) –targeting mechanism of oncogene yorkie mRNA yorkie (yki), the Drosophila homolog of human Yes-associated protein 1 (YAP1), is a oncogene conserved from Drosophila to humans. In multiple human cancers, elevated YAP1 expression has been observed and shown to promote tumor formation. Here I show that the amount of Yki protein is regulated by two novel regulatory mechanisms. I found that yki mRNA are associated with the ER and forms foci that partially colocalize to processing bodies in the vicinity of the ER. This localization is dependent on a stem-loop (SL2) structure in the 3’ untranslated region of yki mRNA. Surprisingly, the deletion of SL2 increases the amount of Yki protein and results in severe overgrowth phenotypes in eye imaginal discs. When the localization to the P-bodies is disrupted, Yki protein level increases without a significant effect on mRNA level. When the SL is completely removed, protein levels drastically increase, but in this case, due to increased RNA stability. In the latter case, we show that the increased RNA accumulation is due to removal of a putative miR-8 seed sequence in the SL2. These data demonstrate two novel regulatory mechanisms, both controlled by the yki SL2 element, that are essential for proper tissue growth regulation. 2. Functional analysis of nucleolus-localization of Rpd3 protein in starvation Epigenetic regulation in starvation is important but not fully understood yet. Recent studies have shown that epigenetic regulation is required for acquiring starvation stress resistance in cancer cell proliferation. Here I identified the Rpd3 gene, a Drosophila homolog of histone deacetylase 1, as a critical epigenetic regulator for acquiring starvation stress resistance. In response to starvation stress, the level of Rpd3 rapidly increased, and it accumulated in the nucleolus. I revealed that Rpd3 binds to the genomic region containing the rRNA promoters and activates rRNA synthesis in response to starvation stress. Polysome analyses revealed that the amount of polysomes was decreased in Rpd3 knockdown flies under starvation stress. Since the autophagy-related proteins are known to be starvation stress tolerance proteins, I examined autophagy activity and found that it was reduced in Rpd3 knockdown flies. Taken together, I conclude that Rpd3 accumulates in the nucleolus in the early stage of starvation, upregulates rRNA synthesis, maintains the polysome amount for translation, and finally increases stress tolerance proteins, such as autophagy-related proteins, to acquire starvation stress resistance.

博士（学術）

京都工芸繊維大学

14303甲第822号

http://hdl.handle.net/10212/2380

eng

ETD

Thesis or Dissertation

Thesis