Magnetic Cellular Switches

Abstract

This paper focuses on the development of magnetic cellular switches to enable magnetic control of intracellular functions in living mammalian cells, including receptor signal transduction and gene transcription. Our approach takes advantage of the mechanosensitivity of adenosine 3′,5′-monophosphate (cAMP) induction and downstream transcription controlled by the cAMP regulatory element (CRE) to engineer gene constructs that optically report gene expression in living cells. We activate transcription of these gene reporters by applying magnetic (mechanical) stress to magnetic microbeads bound to cell surface integrin receptors. In these gene reporter constructs, CRE motifs drive the expression of fluorescent proteins or enzymes that produce fluorescent products, such as DsRed and β-lactamase (BLA), respectively. We demonstrate that a chemical inducer of cAMP (forskolin) increases expression of CRE-DsRed in living cells. More importantly, a threefold increase in CRE-BLA expression is induced by application of mechanical stress to magnetic microbeads (4.5 µm) bound to cell surface integrin receptors. Induction of cAMP could be detected within 5 min using a protein fragment complementation assay involving interactions between the KID and KIX domains of the CRE binding protein linked to complementary halves of the BLA enzyme. These studies confirm that application of magnetic stress to integrins induces gene transcription by activating the cAMP-dependent transcription factor CREB. Ongoing studies focus on optimizing sensitivity and reducing signal-to-noise by establishing stable cell lines that express these gene reporters. These studies collectively demonstrate the feasibility of using magnetic technologies to control function in living mammalian cells and, hence, support the possibility of developing magnetically-actuated cellular components for use in future micro-and nanotechnologies.

Mechanical control of cAMP signaling through integrins is mediated by the heterotrimeric Gαs protein

“…5A). To further confirm these results, we used NIH‐3T3 cells that stably express a KID/KIX‐based fluorescent (FRET‐based) cAMP reporter, which reads out cAMP signaling within minutes after cell activation [Overby et al, 2004; Spotts et al, 2002]. We similarly found that mechanical strain significantly increased cAMP activity measured by KID/KIX activation, and this response was again inhibited by melittin(Fig.…”

Analysis of driven nanorod transport through a biopolymer matrix

“…Magnetic micro- and nanoscale particles have proven useful in a variety of applications, including microfluidics [1], gene transfection [2], hyperthermia [3], drug delivery [4]–[7], and mechanically induced gene activation [8]. Magnetic fields have been used to achieve translational [9]–[12] and rotational manipulation [13] [15] of nanoparticles in a variety of environments and to various ends, and some groups have achieved elaborate control over particles with many degrees of freedom [16].…”