Stability and Secretion of Acetylcholinesterase Forms in Skeletal Muscle Cells

Abstract

Muscle cells express a distinct splice variant of acetylcholinesterase (AChE(T)), but the specific mechanisms governing this restricted expression remain unclear. In these cells, a fraction of AChE subunits is associated with a triple helical collagen, ColQ, each strand of which can recruit a tetramer of AChE(T). In the present study, we examined the expression of the various splice variants of AChE by transfection in the mouse C2C12 myogenic cells in vitro, as well as in vivo by injecting plasmid DNA directly into tibialis anterior muscles of mice and rats. Surprisingly, we found that transfection with an ACHE(H) cDNA, generating a glycophosphatidylinositol-anchored enzyme species, produced much more activity than transfection with AChE(T) cDNA in both C2C12 cells and in vivo. This indicates that the exclusive expression of AChE(T) in mature muscle is governed by specific splicing. Interaction of AChE(T) subunits with the complete collagen tail ColQ increased enzyme activity in cultured cells, as well as in muscle fibers in vivo. Truncated ColQ subunits, presenting more or less extensive C-terminal deletions, also increased AChE activity and secretion in C2C12 cells, although the triple helix could not form in the case of the larger deletion. This suggests that heteromeric associations are stabilized compared with isolated AChE(T) subunits. Coinjections of AChE(T) and ColQ resulted in the production and secretion of asymmetric forms, indicating that assembly, processing, and externalization of these molecules can occur outside the junctional region of muscle fibers and hence does not require the specialized junctional Golgi apparatus.

Demonstration of Acetylcholinesterase Molecular Forms in a Continuous Tubular Lysosomal System of Rat Pancreatic Acinar Cells

“…The absence of AChE from the different cisternae of the Golgi could be related to the nature of the AChE molecules present in acinar cells. The A 12 asymmetric molecules composed of globular catalytic tetramers and a collagen tail are assembled in the Golgi compartment (Rotundo 1984;Legay et al 1999). Previous studies (Gautron 1974;Gautron and Gisiger 1976;Gisiger et al 1978), as well as the present one, have demonstrated that in the SCG, which contains the A 12 form, AChE cytochemical reaction is present throughout the entire Golgi apparatus.…”

Acetylcholinesterase Expression in Muscle Is Specifically Controlled by a Promoter-Selective Enhancesome in the First Intron

“…The distinct C termini of the three alternatively spliced forms of AChE do not affect catalytic mechanism; they only provide appropriate recognition sequences for oligomerization of the catalytic subunits, either for attaching a glycophospholipid link or facilitating association with distinct proline-rich structural subunits. Details of the splicing mechanisms and patterns have been investigated in several laboratories (Li et al, 1993a;Luo et al, 1998;Legay et al, 1999), and the multiple spliced forms have been found in various tissues and synaptic junctional areas.…”

Examination of intrafascicular muscle fiber terminations: Implications for tension delivery in series-fibered muscles

“…These observations support a structural role for AChE in addition to its enzymatic role and the structure of the AChE molecule is consistent with this. A distinct asymmetric form of AChE, called AChE, is expressed in muscle and associates specifically with a triple helical collagen (Legay et al, 1999). This form of AChE has been identified at both endplates and at muscle fiber terminations where it associates with the basal lamina via its collagen tail (Rossi and Rotundo, 1992;Massoulie et al, 1993).…”