Abstract 4141: Hypoxia-induced transition from collective to amoeboid single cell dissemination in epithelial cancer cells

Tumor hypoxia, by elevating hypoxia-inducible factors (HIFs), is an established inducer of epithelial-to-mesenchymal transition (EMT) and subsequent cancer cell invasion and metastasis. Using epithelial carcinoma spheroids in 3D fibrillar collagen, we characterized the invasion patterns as well as cellular and molecular mechanisms of hypoxia-induced cancer cell migration modes. While epithelial cancer cells show collective invasion under normoxic conditions, hypoxia or pharmacological stabilization of HIF-1 using the prolyl hydroxylase inhibitor dimethyloxalylglycine (DMOG) induced EMT-like detachment and migration of single cells. Besides mesenchymal movement, most epithelial cells converted to amoeboid migration with characteristic actin-rich filopodal or distinctive blebby protrusions towards the direction of migration. Whereas mesenchymal migrating cells moved with low velocities in a directionally persistent manner, amoeboid migrating cells generated a broad spectrum of low to high velocities, but with less persistent invasion paths. Sub-cellular molecular analysis showed typical amoeboid features particularly in hypoxic blebby single cell migration, including low to lacking collagen degradation along the migration path and insensitivity to broad-spectrum matrix metalloproteinase (MMP)-inhibitor GM6001, non-focalized cortical actin cytoskeleton within blebs that interacted with collagen structures and low-beta1 integrin expression with lack of integrin focalization. Thus, tumor hypoxia induces a diversity of single-cancer cell invasion modes, including blebby amoeboid migration, thereby enhancing predominantly MMP- and integrin-independent amoeboid dissemination in parallel to EMT induction.

Citation Format: Steffi Lehmann, Veronika A M te Boekhorst, Julia Odenthal, Liying Jiang, Sjoerd van Helvert, Peter Friedl. Hypoxia-induced transition from collective to amoeboid single cell dissemination in epithelial cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4141. doi:10.1158/1538-7445.AM2015-4141

Role of the transient receptor potential vanilloid 5 (TRPV5) protein N terminus in channel activity, tetramerization, and trafficking

The epithelial Ca(2+) channel transient receptor potential vanilloid 5 (TRPV5) constitutes the apical entry site for active Ca(2+) reabsorption in the kidney. The TRPV5 channel is a member of the TRP family of cation channels, which are composed of four subunits together forming a central pore. Regulation of channel activity is tightly controlled by the intracellular N and C termini. The TRPV5 C terminus regulates channel activity by various mechanisms, but knowledge regarding the role of the N terminus remains scarce. To study the role of the N terminus in TRPV5 regulation, we generated different N-terminal deletion constructs. We found that deletion of the first 32 residues did not affect TRPV5-mediated (45)Ca(2+) uptake, whereas deletion up to residue 34 and 75 abolished channel function. Immunocytochemistry demonstrated that these mutant channels were retained in the endoplasmic reticulum and in contrast to wild-type TRPV5 did not reach the Golgi apparatus, explaining the lack of complex glycosylation of the mutants. A limited amount of mutant channels escaped the endoplasmic reticulum and reached the plasma membrane, as shown by cell surface biotinylation. These channels did not internalize, explaining the reduced but significant amount of these mutant channels at the plasma membrane. Wild-type TRPV5 channels, despite significant plasma membrane internalization, showed higher plasma membrane levels compared with the mutant channels. The assembly into tetramers was not affected by the N-terminal deletions. Thus, the N-terminal residues 34-75 are critical in the formation of a functional TRPV5 channel because the deletion mutants were present at the plasma membrane as tetramers, but lacked channel activity.