Gubieda, A. G. | bioRxiv Science

bioRxiv2025

Identifying the internalization pathways of magnetotactic bacteria and magnetosomes by cancer cells

Given the need for new tumor treatment strategies, therapies using magnetic nanoparticles and bacteria are gaining momentum. In this context, magnetotactic bacteria and magnetosomes could act as theranostic agents for use in magnetic hyperthermia, targeted drug delivery, and magnetic resonance imaging. Thus, understanding their interaction with target cells is essential to ensure their theranostic efficiency. This study investigates the uptake of magnetotactic bacteria (MSR-1) and magnetosomes by lung carcinoma cells (A549). First, MSR-1 and magnetosomes are imaged inside A549 cells using cryo soft X-ray tomography, revealing the presence of MSR-1 and magnetosomes inside endosomes. Subsequently, the endocytosis pathways involved in the internalization of MSR-1 and magnetosomes by the cells are elucidated. It is observed that MSR-1 mainly enter cells by receptor-mediated endocytosis, as described previously for other intracellular bacteria. However, the endocytosis of magnetosomes occurs mainly via phagocytosis or macropinocytosis, probably due to the large size of the formed magnetosome clusters. These findings fill a key gap in our understanding of the internalization of MSR-1 bacteria and magnetosomes by lung carcinoma cells, and establish a method applicable to studying their internalization by other target cell types. Graphical AbstractMagnetotactic bacteria (Magnetospirillum gryphiswaldense MSR-1) and magnetosomes, which are proposed as cancer theranostic mediators, are imaged inside A549 cancer cells in 3D using cryo soft X-ray tomography. Moreover, the endocytosis pathways that the cells use to internalize MSR-1 and magnetosomes are elucidated. MSR-1 predominantly enter A549 cells via receptor-mediated endocytosis, while magnetosomes are preferentially internalized via receptor-independent endocytosis. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=102 SRC="FIGDIR/small/690460v1_ufig1.gif" ALT="Figure 1"> View larger version (44K): org.highwire.dtl.DTLVardef@bbcac0org.highwire.dtl.DTLVardef@fc33d6org.highwire.dtl.DTLVardef@1af65aeorg.highwire.dtl.DTLVardef@3ca539_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2023

Atypical Protein Kinase C Promotes its own Asymmetric Localisation by Phosphorylating Cdc42 in Polarising Cells

Atypical protein kinase C (aPKC) is a major regulator of cell polarity. Acting in conjunction with Par6, Par3 and the small GTPase Cdc42, aPKC becomes asymmetrically localised and drives the polarisation of cells. aPKC activity is crucial for its own asymmetric localisation, suggesting a hitherto unknown feedback mechanism contributing to polarisation. Here we show in the C. elegans zygote that the feedback relies on aPKC phosphorylation of Cdc42 at serine 71. The turnover of CDC-42 phosphorylation ensures optimal aPKC asymmetry and activity throughout polarisation by tuning Par6/aPKC association with Par3 and Cdc42. Moreover, turnover of Cdc42 phosphorylation regulates actomyosin cortex dynamics that are known to drive aPKC asymmetry. Given the widespread role of aPKC and Cdc42 in cell polarity, this form of self-regulation of aPKC may be vital for the robust control of polarisation in many cell types. Key findings/graphical abstract- Phosphorylation of CDC-42 by aPKC accelerates aPKC dissociation from CDC-42, limiting aPKC activity - CDC-42/aPKC dissociation promotes aPKC association with PAR-3 and, thereby, aPKC asymmetry due to actomyosin flow - Cycling of CDC-42 phosphorylation fuels the exchange of aPKC between anteriorly transported PAR-3 and aPKC-active CDC-42 complexes - Turnover of CDC-42 phosphorylation alternates its association with effectors, aPKC and MRCK-1, ensuring proper actomyosin dynamics O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=136 SRC="FIGDIR/small/563985v2_ufig1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@e0ec65org.highwire.dtl.DTLVardef@c00b8dorg.highwire.dtl.DTLVardef@36565dorg.highwire.dtl.DTLVardef@160149a_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗