Disassembly of bundled F-actin and cellular remodeling via an interplay of Mical, cofilin, and F-actin crosslinkers.

Cellular form and function are controlled by the assembly and stability of actin cytoskeletal structures-but disassembling/pruning these structures is equally essential for the plasticity and remodeling that underlie behavioral adaptations. Importantly, the mechanisms of actin assembly have been well-defined-including that it is driven by actin's polymerization into filaments (F-actin) and then often bundling by crosslinking proteins into stable higher-order structures. In contrast, it remains less clear how these stable bundled F-actin structures are rapidly disassembled.

Enhanced Production of the Mical Redox Domain for Enzymology and F-actin Disassembly Assays.

To change their behaviors, cells require actin proteins to assemble together into long polymers/filaments-and so a critical goal is to understand the factors that control this actin filament (F-actin) assembly and stability. We have identified a family of unusual actin regulators, the MICALs, which are flavoprotein monooxygenase/hydroxylase enzymes that associate with flavin adenine dinucleotide (FAD) and use the co-enzyme nicotinamide adenine dinucleotide phosphate (NADPH) in Redox reactions. F-actin is a specific substrate for these MICAL Redox enzymes, which oxidize specific amino acids within actin to destabilize actin filaments.

Truncated Adenomatous Polyposis Coli Mutation Induces Asef-Activated Golgi Fragmentation.

Adenomatous polyposis coli (APC) is a key molecule to maintain cellular homeostasis in colonic epithelium by regulating cell-cell adhesion, cell polarity, and cell migration through activating the APC-stimulated guanine nucleotide-exchange factor (Asef). The APC-activated Asef stimulates the small GTPase, which leads to decreased cell-cell adherence and cell polarity, and enhanced cell migration. In colorectal cancers, while truncated APC constitutively activates Asef and promotes cancer initiation and progression, regulation of Asef by full-length APC is still unclear.

Common effects of attractive and repulsive signaling: Further analysis of Mical-mediated F-actin disassembly and regulation by Abl.

To change their size, shape, and connectivity, cells require actin and tubulin proteins to assemble together into long polymers - and numerous extracellular stimuli have now been identified that alter the assembly and organization of these cytoskeletal structures. Yet, there remains a lack of defined signaling pathways from the cell surface to the cytoskeleton for many of these extracellular signals, and so we still know little of how they exert their precise structural effects. These extracellular cues may be soluble or substrate-bound and have historically been classified into two independently acting and antagonistic groups: growth-promoting/attractants (inducing turning toward the source of the factor/positive chemotropism) or growth-preventing/repellents (turning away from the source of the factor/negative chemotropism).

MICAL redox enzymes and actin remodeling: New links to classical tumorigenic and cancer pathways.

MICAL Redox enzymes have recently emerged as direct regulators of cell shape and motility - working through specific reversible post-translational oxidation of actin to disassemble and remodel the cytoskeleton. Links are also now emerging between MICALs and cancer, including our recent results that regulation of MICAL sensitizes cancer cells to the cancer drug Gleevec. Targeting this new actin regulatory enzyme system may thus provide new therapeutic options for cancer treatment.

The MICALs are a Family of F-actin Dismantling Oxidoreductases Conserved from Drosophila to Humans.

Cellular form and function - and thus normal development and physiology - are specified via proteins that control the organization and dynamic properties of the actin cytoskeleton. Using the Drosophila model, we have recently identified an unusual actin regulatory enzyme, Mical, which is directly activated by F-actin to selectively post-translationally oxidize and destabilize filaments - regulating numerous cellular behaviors. Mical proteins are also present in mammals, but their actin regulatory properties, including comparisons among different family members, remain poorly defined.

Amplification of F-Actin Disassembly and Cellular Repulsion by Growth Factor Signaling.

Extracellular cues that regulate cellular shape, motility, and navigation are generally classified as growth promoting (i.e., growth factors/chemoattractants and attractive guidance cues) or growth preventing (i.

Characterizing F-actin Disassembly Induced by the Semaphorin-Signaling Component MICAL.

The MICALs are a family of phylogenetically conserved cytoplasmic proteins that modulate numerous cellular behaviors and play critical roles in semaphorin-plexin signaling. Our recent results have revealed that the MICALs are an unusual family of actin regulatory proteins that use actin filaments (F-actin) as a direct substrate-controlling F-actin dynamics via stereospecific oxidation of conserved methionine (Met44 and Met47) residues within actin. In particular, the MICALs have a highly conserved flavoprotein monooxygenase (redox) enzymatic domain in their N-terminus that directly oxidizes and destabilizes F-actin.

Mical links semaphorins to F-actin disassembly.

How instructive cues present on the cell surface have their precise effects on the actin cytoskeleton is poorly understood. Semaphorins are one of the largest families of these instructive cues and are widely studied for their effects on cell movement, navigation, angiogenesis, immunology and cancer. Semaphorins/collapsins were characterized in part on the basis of their ability to drastically alter actin cytoskeletal dynamics in neuronal processes, but despite considerable progress in the identification of semaphorin receptors and their signalling pathways, the molecules linking them to the precise control of cytoskeletal elements remain unknown.