Abstract
The development of novel small molecule inhibitors of the cancer-associated tropomyosin 3.1 (Tpm3.1) provides the ability to examine the metabolic function of specific actin filament populations. We have determined the ability of these anti-Tpm (ATM) compounds to regulate glucose metabolism in mice. Acute treatment (1 h) of wild-type (WT) mice with the compounds (TR100 and ATM1001) led to a decrease in glucose clearance due mainly to suppression of glucose-stimulated insulin secretion (GSIS) from the pancreatic islets. The impact of the drugs on GSIS was significantly less in Tpm3.1 knock out (KO) mice indicating that the drug action is on-target. Experiments in MIN6 β-cells indicated that the inhibition of GSIS by the drugs was due to disruption to the cortical actin cytoskeleton. The impact of the drugs on insulin-stimulated glucose uptake (ISGU) was also examined in skeletal muscle ex vivo. In the absence of drug, ISGU was decreased in KO compared to WT muscle, confirming a role of Tpm3.1 in glucose uptake. Both compounds suppressed ISGU in WT muscle, but in the KO muscle there was little impact of the drugs. Collectively, this data indicates that the ATM drugs affect glucose metabolism in vivo by inhibiting Tpm3.1’s function with few off-target effects.
Highlights
As well as forming part of the striated muscle contractile apparatus, the actin cytoskeleton is involved in many fundamental processes in all eukaryotic cells including cell proliferation, cell migration, cell adhesion and intracellular trafficking
Insulin stimulation of Akt resulted in phosphorylation of Tmod[3], capping Tpm3.1-containing actin filaments that are involved in actin reorganization at the cell periphery and increased incorporation of the GLUT4 glucose transporter into the plasma membrane (PM)[24]
We show that the ATM compounds impacted two processes known to be regulated by the actin cytoskeleton, insulin-stimulated glucose uptake and insulin secretion[27,28]
Summary
As well as forming part of the striated muscle contractile apparatus, the actin cytoskeleton is involved in many fundamental processes in all eukaryotic cells including cell proliferation, cell migration, cell adhesion and intracellular trafficking. Tpms are viewed as the ‘gate keepers of the actin cytoskeleton’[17], regulating the interaction of other actin regulatory proteins with the actin filament This provides a means to independently regulate the cytoskeleton at different sites within the cell and to tailor the function of actin filaments at these different sites. This provides the opportunity to target distinct actin filament populations in cells based on Tpm composition. Tpm3.1-containing actin filaments have been shown to regulate glucose uptake in mice in an isoform-specific manner[23,24]. Comparison of the effect of the compounds in wild-type (WT) versus Tpm3.1 knock-out (KO) mice indicate that the compounds are operating by inhibiting Tpm3.1 function
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