Leucine-rich repeat-containing
G-protein coupled receptor 5 (LGR5) has been reported to play critical roles in the proliferation of various
cancer cells. However, the roles of LGR5 in
brain tumors and the specific
intracellular signaling proteins directly associated with it remain unknown. Expression of LGR5 was first measured in normal brain tissue,
meningioma, and
pituitary adenoma of humans. To identify the downstream signaling pathways of LGR5,
siRNA-mediated knockdown of LGR5 was performed in SH-SY5Y
neuroblastoma cells followed by proteomics analysis with 2-dimensional
polyacrylamide gel electrophoresis (2D-PAGE). In addition, the expression of LGR5-associated
proteins was evaluated in LGR5-inhibited
neuroblastoma cells and in human normal brain,
meningioma, and
pituitary adenoma tissue. Proteomics analysis showed 12
protein spots were significantly different in expression level (more than two-fold change) and subsequently identified by
peptide mass fingerprinting. A
protein association network was constructed from the 12 identified
proteins altered by LGR5 knockdown. Direct and indirect interactions were identified among the 12
proteins. HSP 90-beta was one of the
proteins whose expression was altered by LGR5 knockdown. Likewise, we observed decreased expression of
proteins in the
hnRNP subfamily following LGR5 knockdown. In addition, we have for the first time identified significantly higher
hnRNP family expression in
meningioma and
pituitary adenoma compared to normal brain tissue. Taken together, LGR5 and its downstream signaling play critical roles in
neuroblastoma and
brain tumors such as
meningioma and
pituitary adenoma.