Targeted Quantitative Proteomics Revealed Arsenite-induced Proteasomal Degradation of RhoB in Fibroblast Cells

Arsenic
is a toxicant widely present in the environment. Previous
epidemiological and animal studies support that arsenic exposure is
associated with elevated incidences of lung and skin cancers. Therefore,
it is important to understand the molecular mechanisms through which
arsenite initiates malignant transformation of lung and skin tissues.
Ras superfamily of small GTPases assumes a crucial role in many cellular
processes including transcription, protein synthesis, and trafficking.
In addition, small GTPase signaling is known to be altered in many
types of cancer. By employing a multiple-reaction monitoring (MRM)-based
targeted proteomic method, we found that the protein level of RhoB
was substantially decreased in IMR90 human lung fibroblast cells upon
a 12-h exposure to 5 μM NaAsO2. In addition, the
protein level of ectopically expressed RhoB was found to decline in
a dose-dependent manner upon arsenite exposure in HEK293T, HeLa, and
GM00637 cells as well as that of endogenous RhoB protein in IMR90
cells. Moreover, the arsenite-elicited down-regulation of RhoB was
found to arise from enhanced proteasomal degradation. Taken together,
we demonstrated, for the first time, that exposure to arsenite could
attenuate the protein expression of RhoB through proteasomal degradation.