# Calcineurin Homologous Protein 2 Acts as a Conditional Modulator of Migration and Proliferation in Human Bone Sarcoma Cells

## TL;DR

This study shows that CHP2 helps bone sarcoma cells adapt to stress by supporting NHE1 activity, which promotes their migration and growth.

## Contribution

CHP2 is identified as a conditional modulator of NHE1-dependent migration and proliferation in bone sarcoma cells under metabolic stress.

## Key findings

- Serum deprivation caused sarcoma cells to temporarily reduce then recover migration and proliferation.
- NHE1 inhibition reduced migration and slightly reduced proliferation in sarcoma cells.
- CHP2 silencing under stress conditions significantly reduced NHE1 activity and cell migration/proliferation.

## Abstract

This study investigates how human bone sarcoma cells respond to metabolic stress induced by serum deprivation. In two sarcoma cell lines, migration and proliferation were initially reduced but later recovered, whereas non-malignant osteoblastic cells showed sustained inhibition. Sarcoma cells primarily expressed the Na+/H+ exchanger NHE1, and inhibition of NHE1 decreased migration and moderately reduced proliferation. Although serum deprivation did not change CHP2 protein levels, silencing CHP2 reduced NHE1 activity under stress conditions and significantly decreased both migration and proliferation. Together, these findings indicate that bone sarcoma cells can adapt to serum deprivation through an NHE1-dependent mechanism and that CHP2 contributes to this response under metabolic stress.

Background/Objectives: Sarcomas are malignant bone tumors for which current therapeutic approaches provide limited improvement in patient survival. Cancer-associated extracellular acidosis, driven in part by Na+/H+ exchanger 1 (NHE1) activity, promotes malignant cell migration and proliferation while exerting inhibitory effects on normal bone-forming cells. Calcineurin Homologous Protein 2 (CHP2) is a binding partner and functional regulator of NHE1 that is preferentially expressed in cancer cells; however, its role in bone sarcoma biology remains undefined. Methods: In this study, we examined how serum deprivation, used as a model of metabolic stress, affects migration and proliferation in human bone sarcoma cell lines (143B and SW1353) and investigated the contribution of NHE1 and CHP2 to these behaviors. Results: Serum deprivation induced a time-dependent adaptive response in sarcoma cells, characterized by transient suppression followed by recovery of migratory and proliferative capacity, whereas both migration and proliferation were consistently inhibited in non-malignant osteoblastic (hFOB) cells. Both sarcoma cell lines predominantly expressed NHE1, and pharmacological inhibition of NHE1 activity with zoniporide significantly reduced migration and moderately reduced proliferation. Serum deprivation did not significantly alter CHP1 or CHP2 protein expression; however, silencing of CHP2 reduced NHE1 activity under serum-deprived conditions and significantly decreased migration and proliferation in both sarcoma cell lines. Conclusions: Together, these findings demonstrate that NHE1 activity is a critical determinant of migratory capacity in bone sarcoma cells and that CHP2 supports malignant migration and proliferation. Under stress conditions, CHP2 action is associated with NHE1 activity, supporting CHP2 as a conditional modulator of malignant behavior in human bone sarcoma cells.