Abstract
We have shown previously that a weak 50 Hz magnetic field (MF) invoked the actin-cytoskeleton, and provoked cell migration at the cell level, probably through activating the epidermal growth factor receptor (EGFR) related motility pathways. However, whether the MF also affects the microtubule (MT)-cytoskeleton is still unknown. In this article, we continuously investigate the effects of 0.4 mT, 50 Hz MF on the MT, and try to understand if the MT effects are also associated with the EGFR pathway as the actin-cytoskeleton effects were. Our results strongly suggest that the MF effects are similar to that of EGF stimulation on the MT cytoskeleton, showing that 1) the MF suppressed MT in multiple cell types including PC12 and FL; 2) the MF promoted the clustering of the EGFR at the protein and the cell levels, in a similar way of that EGF did but with higher sensitivity to PD153035 inhibition, and triggered EGFR phosphorylation on sites of Y1173 and S1046/1047; 3) these effects were strongly depending on the Ca2+ signaling through the L-type calcium channel (LTCC) phosphorylation and elevation of the intracellular Ca2+ level. Strong associations were observed between EGFR and the Ca2+ signaling to regulate the MF-induced-reorganization of the cytoskeleton network, via phosphorylating the signaling proteins in the two pathways, including a significant MT protein, tau. These results strongly suggest that the MF activates the overall cytoskeleton in the absence of EGF, through a mechanism related to both the EGFR and the LTCC/Ca2+ signaling pathways.
Highlights
The cell motility depends on the transformation and reorganization of the cytoskeleton network, which mainly consists of actin filaments (F-actin), microtubules (MT), and intermediate filaments
The MT turned into an unstable and typically migrating status [60], with microtubuleorganizing center (MTOC) turning into half-ring shape and reoriented to face the migration leading edge, the MT intensity decayed in cell leading edge, and fewer MT fibers reaching cell periphery (Fig 1A, magnetic field (MF))
When simultaneously blocking the activations of both epithelial growth factor receptors (EGFRs) by PD and L-type Ca2+ channel (LTCC) by NIF, we found the MTOC ring was retained in FL after MF exposure (PNM, Fig 1A), and the “black hollows” (PNM, Fig 1B) and redistribution of focal adhesions (FA) (PNM, Fig 2) induced by MF disappeared in PC12, while the average content of MT per cell was recovered to the sham control level in both cell lines (Fig 1C and 1D)
Summary
The cell motility depends on the transformation and reorganization of the cytoskeleton network, which mainly consists of actin filaments (F-actin), microtubules (MT), and intermediate filaments. The findings that MF activated EGFR reminisced our previous results that MF induced cell migration and F-actin reorganization through up-regulating the F-actin cytoskeleton signal proteins of fascin, MLCK, and Arp2/3, which were all under the modulation of the EGFR pathway [13].
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