Rac function is crucial for cell migration but is not required for spreading and focal adhesion formation.

Cell migration is commonly accompanied by protrusion of membrane ruffles and lamellipodia. In two-dimensional migration, protrusion of these thin sheets of cytoplasm is considered relevant to both exploration of new space and initiation of nascent adhesion to the substratum. Lamellipodium formation can be potently stimulated by Rho GTPases of the Rac subfamily, but also by RhoG or Cdc42. Here we describe viable fibroblast cell lines genetically deficient for Rac1 that lack detectable levels of Rac2 and Rac3. Rac-deficient cells were devoid of apparent lamellipodia, but these structures were restored by expression of either Rac subfamily member, but not by Cdc42 or RhoG. Cells deficient in Rac showed strong reduction in wound closure and random cell migration and a notable loss of sensitivity to a chemotactic gradient. Despite these defects, Rac-deficient cells were able to spread, formed filopodia and established focal adhesions. Spreading in these cells was achieved by the extension of filopodia followed by the advancement of cytoplasmic veils between them. The number and size of focal adhesions as well as their intensity were largely unaffected by genetic removal of Rac1. However, Rac deficiency increased the mobility of different components in focal adhesions, potentially explaining how Rac - although not essential - can contribute to focal adhesion assembly. Together, our data demonstrate that Rac signaling is essential for lamellipodium protrusion and for efficient cell migration, but not for spreading or filopodium formation. Our findings also suggest that Rac GTPases are crucial to the establishment or maintenance of polarity in chemotactic migration.

Activated lymphocytes secretome inhibits differentiation and induces proliferation of C2C12 myoblasts.

BACKGROUND/AIMS: ageing is associated with a marked decline in immune function which may contribute to the local environment that can influence the regenerative process of skeletal muscle cells. METHODS: Herein, we focused on determining the effect of an activated immune system secretome on myoblast differentiation and proliferation as possible means to attenuate adverse effects of muscle aging. C2C12 myoblasts were used as model to assess the impact of lymphocyte conditioned media (CM) following anti-CD3/IL-2 activation. RESULTS: Myoblasts cultured with activated lymphocytes CM exhibited reduced morphological and biochemical differentiation (98±20, p<0.005) and increased entry to the S Phase of the cell cycle (61%±7, p<0.001), when compared with myoblasts cultured with non-activated lymphocytes CM. Associated with increased proliferation and reduced differentiation, muscle specific transcription factors MyoD and myogenin were significantly reduced in C2C12 treated with activated lymphocytes CM vs control CM, respectively (myoD: 0.5±0.12 fold reduction P<0.005); myogenin: 0.38±0.08 fold reduction; p<0.005). Moreover, key protein of proliferation pERK1/2 increased (46±11U/ml, p<0.05) whereas mediator of differentiation pAkt decreased (21±12U/ml, p<0.05) in C2C12 treated with activated vs. non-activated CM. CONCLUSION: our data demonstrate that, following activation, secretome of the immune system cells elicit marked regulatory effects on skeletal muscle growth and differentiation; enhancing the former with the loss of the latter.

Phospho-tyrosine phosphatase inhibitor Bpv(Hopic) enhances C2C12 myoblast migration in vitro. Requirement of PI3K/AKT and MAPK/ERK pathways.

Muscle progenitor cell migration is an important step in skeletal muscle myogenesis and regeneration. Migration is required for muscle precursors to reach the site of damage and for the alignment of myoblasts prior to their fusion, which ultimately contributes to muscle regeneration. Limited spreading and migration of donor myoblasts are reported problems of myoblast transfer therapy, a proposed therapeutic strategy for Duchenne Muscular Dystrophy, warranting further investigation into different approaches for improving the motility and homing of these cells. In this article, the effect of protein phospho-tyrosine phosphatase and PTEN inhibitor BpV(Hopic) on C2C12 myoblast migration and differentiation was investigated. Applying a wound healing migration model, it is reported that 1 µM BpV(Hopic) is capable of enhancing the migration of C2C12 myoblasts by approximately 40 % in the presence of myotube conditioned media, without significantly affecting their capacity to differentiate and fuse into multinucleated myotubes. Improved migration of myoblasts treated with 1 µM BpV(Hopic) was associated with activation of PI3K/AKT and MAPK/ERK pathways, while their inhibition with either LY294002 or UO126, respectively, resulted in a reduction of C2C12 migration back to control levels. These results propose that bisperoxovanadium compounds may be considered as potential tools for enhancing the migration of myoblasts, while not reducing their differentiation capacity and underpin the importance of PI3K/AKT and MAPK/ERK signalling for the process of myogenic progenitor migration.