Elsevier

Cell Calcium

Volume 25, Issue 2, February 1999, Pages 93-106
Cell Calcium

Research
Replicating myoblasts and fused myotubes express the calcium-regulated proteins S100A1 and S100B

https://doi.org/10.1054/ceca.1998.0012Get rights and content

Abstract

We investigated the expression and the subcellular localization of S100A1 and S100B, two Ca2+-binding proteins of the EF-hand type, in replicating myoblasts and fused myotubes. Northern blot and reverse transcriptase-polymerase chain reaction analyses revealed the presence of S100A1 mRNA and S100B mRNA respectively, in myoblasts. Immunofluorescence and immunogold electron microscopy were used to localize individual proteins in myoblasts and myotubes. In the present report we document that: (1) in replicating myoblasts S100B is localized to intracellular membranes, including Golgi membranes, vimentin intermediate filaments (IFs) and microtubule (MT) structures; (2) in the same cells S100A1 is found associated with intracellular membranes; (3) following treatment of replicating myoblasts with colchicine, a fraction of S100B remains colocalized with bundled and collapsed vimentin IFs, whereas another fraction follows the destiny of endoplasmic membranes; (4) under the same conditions S100A1, like a fraction of S100B, follows the collapse of the endoplasmic reticulum around the nucleus; and (5) in fused myotubes S100A1 is found diffusely in the cytoplasm, whereas S100B is mostly found associated with vimentin IFs. These data suggest that in the skeletal myogenic cell line used in the present study S100A1 and S100B might share binding sites on or close to intracellular membranes, but display a significant degree of target specificity with respect to IFs and MTs. The results of these analyses suggest that expression of S100B in skeletal muscle cells may be developmentally regulated and lend support to the possibility that S100B might regulate the MT and IF dynamics.

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    We have reported that administration of S100B to myoblasts in differentiation medium (DM) results in inhibition of differentiation, stimulation of proliferation, and protection against apoptosis via inactivation of the promyogenic p38 MAPK and activation of the mitogenic ERK1/2 [21,22]. However, S100B is expressed in myoblast cell lines [23] and in muscle satellite cells in situ [24], raising the possibility that intracellular S100B might have a role in myoblast proliferation/survival and/or differentiation. Indeed, increasing intracellular S100B levels resulted in a dramatically reduced myogenic differentiation via IKKβ/NF-κB-dependent inhibition of the expression of the myogenic transcription factor, MyoD, and its downstream effectors, myogenin and p21WAF1, while inhibition of S100B expression resulted in a significant acceleration of differentiation as a result of reduction of NF-κB activity and consequent upregulation of MyoD [24].

  • S100B's double life: Intracellular regulator and extracellular signal

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    S100B is a member of a family of Ca2+-binding proteins of the EF-hand type comprising some 25 members (see Refs. [1–5] for reviews). S100B is expressed in varying abundance in a restricted number of cell types such as astrocytes, maturing oligodendrocytes, kidney epithelial cells, neural progenitor cells, pituicytes, ependymocytes, certain neuronal populations, chondrocytes, adipocytes, melanocytes, Langerhans cells, dendritic cells, certain lymphocyte subpopulations, skeletal myofibers, myoblasts [1,3,6–12], and muscle satellite cells.1 Also, S100B expression is enhanced in several tumors arising from cell types normally expressing the protein as well as in the aging brain and in the brain of patients affected by Alzheimer's disease, chronic epilepsy or HIV infection and other brain pathological conditions [1,2,13–15].

  • S100B increases proliferation in PC12 neuronal cells and reduces their responsiveness to nerve growth factor via Akt activation

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    As a positive control, S100B– PC12 cells were cultivated in the presence of 500 nm S100B as described previously (18) to document the neurite extension activity of S100B. Immunofluorescence—For indirect immunofluorescence, PC12 cells cultivated as described for the proliferation assay were fixed and processed as described previously (21). S100B and p53 were detected using a monoclonal anti-S100B antibody (1:20; Sigma) and a polyclonal anti-p53 antibody (1:50; Santa Cruz Biotechnology), respectively.

  • Capping protein binding to S100B: Implications for the "tentacle" model for capping the actin filament barbed end

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    Therefore, it remains possible that some environment in the cell has a similar effect, enabling CP to bind S100B and be inhibited from binding actin. In skeletal muscle, CP(α/β1) (CapZ) is concentrated at the Z-disc, but S100B is not found at the Z-disc (3, 36). High Ca2+ concentrations (∼2 mm) are required for binding of S100B to the αC28 and TRTK-12 peptides, which also suggests that an interaction between S100B and CP is unlikely to occur in cells.

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