Identification and Functional Validation of Caldesmon as a Potential Gastric Cancer Metastasis-associated Protein

In this study, we aim to identify biomarkers for gastric
cancer
metastasis using a quantitative proteomics approach. The proteins
extracted from a panel of 4 gastric cancer cell lines, two derived
from primary cancer (AGS, FU97) and two from lymph node metastasis
(AZ521, MKN7), were labeled with iTRAQ (8-plex) reagents and analyzed
by 2D-LC–MALDI-TOF/TOF MS. In total, 641 proteins were identified
with at least a 95% confidence. Using cutoff values of >1.5 and
<0.67,
19 proteins were found to be up-regulated and 34 were down-regulated
in the metastatic versus primary gastric cancer cell lines respectively.
Several of these dysregulated proteins, including caldesmon, were
verified using Western blotting. It was found that caldesmon expression
was decreased in the two metastasis-derived cell lines, and this was
confirmed by further analysis of 7 gastric cancer cell lines. Furthermore,
immunohistochemical staining of 9 pairs of primary gastric cancer
and the matched lymph node metastasis tissue also corroborated this
observation. Finally, knockdown of caldesmon using siRNA in AGS and
FU97 gastric cancer cells resulted in an increase in cell migration
and invasion, while the overexpression of caldesmon in AZ521 cells
led to a decrease in cell migration and invasion. This study has thus
established the potential role of caldesmon in gastric cancer metastasis,
and further functional studies are underway to delineate the underlying
mechanism of action of this protein.