High-grade
glioma cells express subunits of the ENaC/Deg superfamily, including members of ASIC subfamily. Our previous work has shown that
glioma cells exhibit a basally active
cation current, which is not present in low-grade
tumor cells or normal astrocytes, and that can be blocked by
amiloride. When ASIC2 is present within the channel complex in the plasma membrane, the channel is rendered non-functional because of inherent negative effectors that require ASIC2. We have previously shown that high-grade
glioma cells functionally express this current because of the lack of ASIC2 in the plasma membrane. We now hypothesize that ASIC2 trafficking in
glioma cells is regulated by a specific chaperone
protein, namely Hsc70. Our results demonstrated that Hsc70 co-immunoprecipitates with ASIC2 and that it is overexpressed in
glioma cells as compared with normal astrocytes. In contrast, there was no difference in the expression of
calnexin, which also co-immunoprecipitates with ASIC2. In addition,
glycerol and
sodium 4-phenylbutyrate reduced the amount of Hsc70 expressed in
glioma cells to levels found in normal astrocytes. Transfection of Hsc70
siRNA inhibited the constitutively activated
amiloride-sensitive current, decreased migration, and increased ASIC2 surface expression in
glioma cells. These results support an association between Hsc70 and ASIC2 that may underlie the increased retention of ASIC2 in the endoplasmic reticulum of
glioma cells. The data also suggest that decreasing Hsc70 expression promotes reversion of a high-grade
glioma cell to a more normal astrocytic phenotype.