Abstract 107P
Background
Controlling metastasis is the key to improve outcomes for osteosarcoma (OS) patients. Our knowledge of metastasizing mechanisms in OS is still not sufficient. Neurofibromatosis gene 2 (NF2) is a known tumor suppressor in various solid tumors in which we found gene mutations in 15% of OS patient samples in our clinic (Molecular Tumor Board, TUM, 2019-2022) while downregulation of NF2 has been reported to correlate with a declined long-term survival.
Methods
Since NF2 remodels the cytoskeleton through small GTPases and metastasis is a complex process involving cancer cell adhesion, migration and invasion, we examined actin-dependent cell functions. First, we studied alterations in molecular mechanisms of NF2 signaling between non-metastatic human OS cell lines (HOS, HOS-MNNG, U2OS) and the metastatic OS cell line (HOS-143B).
Results
Immunofluorescence revealed a downregulation of NF2 and reduced stress fiber formation in metastatic compared to non-metastatic HOS cell lines. Furthermore, in HOS-143B cells, the activity of a small GTPase was enhanced, accompanied by decreased PAK4. Moreover, HOS-143B cells show dysfunctional autophagy, measured by Cyto-ID and Lamp1/LC3 co-localization. In line with our previous work (Landspersky et al., Blood, 2022), dysfunctional autophagy in HOS-143B cells correlated with a disoriented actin cytoskeleton. To rescue the damaged cytoskeletal changes, we treated HOS-143B with an inhibitor of the small GTPase activity. This treatment revealed not only a restored actin stress fiber formation, but also a significantly reduced growth rate of the metastatic cell line. Cell adhesion, migration as well as cellular invasiveness into Matrigel was additionally reduced upon small GTPase inhibition within the HOS-143B cell line.
Conclusions
Our results show that metastatic processes are in part dependent on F-actin fiber organization and small GTPase activation. Most importantly, our results suggest that treatment of metastatic OS cells with a GTPase inhibitor specifically reduces the growth rate of metastatic cells. Our findings help to dissect and understand mechanisms of actin-dependent metastatic processes and suggest new strategies to reduce the growth rate and possibly also the spread of OS cells to metastatic sites.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.