Munro, A. | bioRxiv Science

bioRxiv2021

Essential elements of radical pair magnetosensitivity in Drosophila

Many animals use the Earths magnetic field (geoMF) for navigation1. The favored mechanism for magnetosensitivity involves a blue-light (BL) activated electron transfer reaction between flavin adenine dinucleotide (FAD) and a chain of tryptophan (Trp) residues within the photoreceptor protein, CRYPTOCHROME (CRY). The spin-state of the resultant radical pair (RP), and hence the concentration of CRY in its active state, is influenced by the geoMF2. The canonical CRY-centric radical pair mechanism (RPM) does not, however, explain many physiological and behavioural observations2-8. Here, using electrophysiology and behavioural analyses, we assay magnetic field (MF) responses at single neuron and organismal level. We show that the 52 C-terminal (CT) amino acids of CRY, which are missing the canonical FAD binding domain and Trp chain, are sufficient to facilitate magnetoreception. We also show that increasing intracellular FAD potentiates both BL-induced and MF-dependent effects on the activity mediated by the CT. Additionally, high levels of FAD alone are sufficient to cause BL neuronal sensitivity and, remarkably, potentiation of this response in the co-presence of a MF. These unexpected results reveal the essential components of a primary magnetoreceptor in flies, providing strong evidence that non-canonical (i.e., non-CRY-dependent) RPs can elicit MF responses in cells.

physiology↗

bioRxiv2021

Pathway profiling of a novel SRC inhibitor, AZD0424, in combination with MEK inhibitors.

A more comprehensive understanding of how cells respond to drug intervention, the likely immediate signalling responses and how resistance may develop within different microenvironments allows us anticipate how cells adapt to targeted therapy enabling more informed prediction of rational drug combinations. The non-receptor tyrosine kinase SRC regulates many cellular signalling processes and pharmacological inhibition has long been a target of drug discovery projects for the treatment of cancer. Here we describe the in vitro and in vivo characterisation of the small molecule SRC inhibitor, AZD0424. We show that AZD0424 potently inhibits the phosphorylation of tyrosine-416 of SRC (IC50 [~] 100 nM) in many cancer cell lines; however inhibition of cell viability, via a G1 cell cycle arrest, was observed only in a sub-set of cancer cell lines in the low (on target) micromolar range. We profiled the changes in intracellular pathway signalling in cancer cells following exposure to AZD0424 and other targeted therapies using Reverse Phase Protein Array analysis. We demonstrate that SRC is activated in response to MEK inhibitor (trametinib or AZD6244)-treatment of KRAS mutant colorectal cell lines (HCT116 and DLD1) and that AZD0424 abrogates this. Cell lines treated with trametinib or AZD6244 in combination with AZD0424 revealed reduction of EGFR, FAK and SRC compensatory activation, and, synergistically inhibits cell viability in vitro. In vivo, trametinib-treatment of mice bearing HCT116 tumours increased phosphorylation of SRC on Tyr416, and when combined with AZD0424, inhibition of tumour growth is greater than trametinib alone. We also demonstrate that drug-induced resistance to trametinib is not re-sensitised by AZD0424 treatment in vitro, likely as a result of multiple compensatory signalling mechanisms; however inhibition of SRC remains an effective way to block invasion of trametinib resistant tumour cells. These data imply that inhibiting SRC may offer a useful addition to MEK inhibitor combination strategies.

cancer biology↗