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Ras1CA-Upregulated bcpi Inhibits Cathepsin Activity to Prevent Tissue Destruction of the Bombyx Posterior Silk Gland
journal contribution
posted on 2016-02-19, 13:52 authored by Li Ma, Shumin Liu, Min Shi, Xue-xin Chen, Sheng LiUsing
the GAL4/UAS transgenic system established in the silkworm, Bombyx mori, we have previously reported that overexpression
of the Ras1CA oncogene specifically in
the posterior silk gland (PSG) resulted in improved fibroin synthesis,
silk yield, and other phenotypic effects. However, the detailed molecular
mechanism remains to be fully elucidated. Using 2D-DIGE-MS/MS analyses,
we compared the proteomic profiles of PSGs from the wild type (WT)
and Ras1CA-overexpressed silkworms. Among
the 24 Ras1CA-enhanced proteins, the Bombyx cysteine protease inhibitor (BCPI) was increased
2.4-fold at the protein level and 3.4-fold at the mRNA level. Consistent
with the developmental profiles, injection of recombinant BCPI into
the WT silkworms at the early wandering stage inhibited cathepsin
activity, prevented tissue destruction of the PSG, and delayed pupation.
Moreover, injection of small-molecule inhibitors of cathepsin into
the WT silkworms prevented PSG destruction and delayed pupation, confirming
the role of BCPI in inhibiting cathepsin activity. Furthermore, injection
of chemical inhibitors of the Ras downstream effectors into the Ras1CA-overexpressed and WT silkworms revealed
that both Raf-MAPK and PI3K-TORC1 pathways were required for Ras1
to induce bcpi expression. Taken together, we conclude
that via the downstream Raf-MAPK and PI3K-TORC1 pathways, Ras1CA upregulates bcpi, which
inhibits cathepsin activity thus preventing PSG destruction in Bombyx.