Calcineurin B Homologous Protein Isoform 2 (CHP2) Expression and Activity Impact Cell Migration and Tumor Formation in Non‐small Cell Lung Cancer

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. 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. We hypothesized that elevated CHP2 expression enhances cell survival and the tumorigenic potential of these cells. 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 evaluated the impact of a low serum environment on CHP2 expression and determined that CHP2 levels increased when H1299 cells are grown in 0.5% serum compared to cells grown in 10% serum. This increased CHP2 expression drives changes that support the cells ability to survive these low serum environments. In Electric Cell‐substrate Impedance Sensing (ECIS) migration experiments in 10% serum, H1299 cells reestablished a confluent monolayer within 18 hours of wounding. In contrast, the H1299 CHP2KD cells migrated at approximately 50% of that rate and the H1299 NHE1KD cells showed extremely limited cell migration. When these experiments were performed in 0.5% serum, the migration rate of the H1299 cells was reduced to about 50% of that seen in 10% serum while the rate of migration in H1299 CHP2KD was reduced to a rate equivalent to the H1299 NHE1KD cells. In cell proliferation experiments, H1299 cells in 0.5% serum grow at a rate equivalent to H1299 CHP2KD cells in 10% serum. 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.