Distinct roles of mouse laminin beta 1 long arm domains for alpha 1 beta 1 gamma 1 trimer formation

Mouse embryonal carcinoma F9 cells expressing partial mouse laminin beta 1 covering either the C-terminal end (Delta beta 1S) or the whole (Delta beta 1L) of the long arm were established to study the assembly and interchain disulfide-bonding of beta 1 to endogenous laminin alpha 1 and gamma 1. Both Delta beta 1S and Delta beta 1L were disulfide-bonded to gamma 1 but only Delta beta 1L gamma 1 dimer formed a disulfide-bonded alpha 1 Delta beta 1L gamma 1 trimer which was actively secreted into the medium, Meanwhile, in the cells producing Delta beta 1S gamma 1 dimer, the level of endogenous alpha 1 beta 1 gamma 1 was reduced but the level of monomeric alpha 1 was increased, suggesting that alpha 1 was recruited to trimer formation with the Delta beta S gamma 1 dimer without disulfide-bonding, This shows that the Delta beta 1S gamma 1 dimer can associate withal but not support the disulfide-bonding at the N-terminus of the long arm of alpha 1, While control cells secrete neither monomeric alpha 1 nor the beta 1 gamma 1 dimer into the medium, the Delta beta 1S gamma 1 producing cells probably do as alpha 1 Delta beta 1 gamma 1 trimer, We thus propose that the N- and C-termini of the long arm of laminin beta 1 have distinct roles for trimer formation.