Calcineurin B Homologous Protein Isoform 2 Expression and Function in Low Serum Conditions in Non‐Small Cell Lung Cancer Cells

Abstract

The Na+‐H+ exchanger isoform 1 (NHE1) is a key regulator of cell proliferation, migration and invasion in cells from a variety of solid tumors including non‐small cell lung cancer (NSCLC). The Calcineurin B Homologous Proteins (CHP1 and CHP2) appear to be essential cofactors to support NHE1 function. CHP2 expression is elevated in tumor cells. This elevated expression supports cell proliferation and tumor formation. To evaluate the role of CHP2 and NHE1 in NSCLC progression we use three cell lines. H1299 cells are a human NSCLC carcinoma cell line. H1299 CHP2KD is a modified H1299 cell line that lacks CHP2 expression and H1299 NHE1KD which lacks NHE1 expression. We have assessed the expression of CHP1, CHP2 and NHE1 in normal (10%) and low (0.5%) serum conditions through western blot analysis. While CHP1 and NHE1 expression does not change over 48 hours of low serum exposure in any cell line, CHP2 expression increases in both H1299 and H1299 NHE1KD cells. To investigate functionality, we evaluated in vitro tumor formation using a soft agar assay. H1299 cells formed a significant number of large tumors (> 500 µm diameter) in both high and low serum conditions. H1299 NHE1KD cells formed a very low number of tumors in 10% serum and no tumors in 0.5% serum. H1299 CHP2KD cells formed no large tumors under either serum condition. These data suggest a critical role for CHP2 expression in cell migration and tumor formation which allows NSCLC cells to maintain a more aggressive phenotype even in low serum conditions.