title: Promotion of lens epithelial-fiber differentiation by the C-terminus of connexin 45.6 a role independent of gap junction communication.
abstract: We previously reported that, among the three connexins expressed in chick lens, overexpression of connexin (Cx) 45.6, not Cx43 or Cx56, stimulates lens cell differentiation; however, the underlying mechanism responsible for this effect is unclear. Here, we took advantage of naturally occurring loss-of-gap-junction function mutations of Cx50 (ortholog of chick Cx45.6) and generated the corresponding site mutants in Cx45.6: Cx45.6(D47A) and Cx45.6(P88S). In contrast to wild-type Cx45.6, the mutants failed to form functional gap junctions, and Cx45.6(P88S) and, to a lesser degree, Cx45.6(D47A) functioned in a dominant-negative manner. Interestingly, overexpression of both mutants incapable of forming gap junctions significantly increased epithelial-fiber differentiation to a level comparable to that of wild-type Cx45.6. To map the functional domain of Cx45.6, we generated a C-terminus chimera as well as deletion mutants. Overexpression of Cx56(*)45.6C, the mutant in which the C-terminus of Cx56 was replaced with that of Cx45.6, had a stimulatory effect on lens cell differentiation similar to that of Cx45.6. However, cells overexpressing Cx45.6(*)56C, the mutant in which C-terminus of Cx45.6 was replaced with that of Cx56, and Cx45.6(-C), in which the C-terminus was deleted, failed to promote differentiation. Taken together, we conclude that the expression of Cx45.6, but not Cx45.6-dependent gap junction channels, is involved in lens epithelial-fiber cell differentiation, and the C-terminal domain of Cx45.6 plays a predominant role in mediating this process.
authors: Department of Biochemistry, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA.
authors: Eric A
authors: EA
authors: Banks
authors: X Sean
authors: XS
authors: Yu
authors: Qian
authors: Q
authors: Shi
authors: Jean X
authors: JX
authors: Jiang
mesh_terms: D000818:Animals; D002450:Cell Communication; D002454:Cell Differentiation; D002478:Cells, Cultured; D002642:Chick Embryo; D017630:Connexins / Q000235:genetics / Q000378:metabolism*; D004847:Epithelial Cells / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D017629:Gap Junctions / Q000378:metabolism*; D007908:Lens, Crystalline / Q000737:chemistry / Q000166:cytology* / Q000378:metabolism*; D050505:Mutant Proteins / Q000378:metabolism; D017434:Protein Structure, Tertiary
chemical_list: D017630:Connexins; D050505:Mutant Proteins; C082920:connexin 45