Hypoxia and Serum‐Deprivation Impacts Calcineurin B Homologous Protein Isoform 2 Expression and Activity in Non‐Small Cell Lung Cancer

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. The calcineurin B homologous proteins (CHP1 and CHP2) appear to be essential cofactors to support NHE1 function. CHP1 appears to be expressed ubiquitously in healthy tissue, while CHP2 is predominantly expressed in tumor cells. While both CHP isoforms are highly homologous and bind in nearly identical regions on NHE1, each has been identified to have a distinct impact on NHE1 function. Our research has demonstrated an elevation in CHP2 expression in tumor samples from patients with either adenocarcinoma or squamous cell carcinoma of the lung as well as in a broad range of NSCLC cell lines. To evaluate the role of CHP2 in NSCLC cells we used NCI‐H1299, a carcinoma cell line, as the parent cell line and developed two new cell lines. One of these cell lines lacked CHP2 expression (H1299 CHP2KD) and the other lacked NHE1 expression (H1299 NHE1KD). We hypothesized that CHP2 expression enhances cell survival and the tumorigenic potential of these cells. We evaluated the impact of a low serum and hypoxic microenvironment on CHP2 expression and determined CHP2 levels increased when H1299 cells are grown in 0.5% serum and 1% O 2 compared to cells grown in 10% serum and 21% O 2 (normal conditions). This increased CHP2 expression drives changes that support the cells' ability to survive these low serum and hypoxic microenvironments. Proliferation and migration rates in normal conditions for H1299 CHP2KD cells were approximately 50% of H1299 cells. When these experiments were performed in low serum and hypoxic conditions, the proliferation and migration rates of the H1299 cells was reduced to about 50% of that seen in normal conditions, while the rates of proliferation and migration in H1299 CHP2KD was reduced to a rate equivalent to the H1299 NHE1KD cells. Finally, in a soft agar assay, a greater rate of tumor formation occurred for H1299 cells in both 10% and 0.5% serum than either the H1299 CHP2KD or H1299 NHE1KD cells. These data suggest a major role for CHP2 expression in the development and progression of non‐small cell lung cancer.