Formation of the 67-kDa laminin receptor by acylation of the precursor.
Even though the involvement of the 67-kDa laminin receptor (67LR) in tumor invasiveness has been clearly demonstrated, its molecular structure remains an open problem, since only a full-length gene encoding a 37-kDa precursor protein (37LRP) has been isolated so far. A pool of recently obtained monoclonal antibodies directed against the recombinant 37LRP molecule was used to investigate the processing that leads to the formation of the 67-kDa molecule. In soluble extracts of A431 human carcinoma cells, these reagents recognize the precursor molecule as well as the mature 67LR and a 120-kDa molecule. The recovery of these proteins was found to be strikingly dependent upon the cell solubilization conditions: the 67LR is soluble in NP-40-lysis buffer whereas the 37LRP is NP-40-insoluble. Inhibition of 67LR formation by cerulenin indicates that acylation is involved in the processing of the receptor. It is likely a palmitoylation process, as indicated by sensitivity of NP-40-soluble extracts to hydroxylamine treatment. Immunoblotting assays performed with a polyclonal serum directed against galectin3 showed that both the 67- and the 120-kDa proteins carry galectin3 epitopes whereas the 37LRP does not. These data suggest that the 67LR is a heterodimer stabilized by strong intramolecular hydrophobic interactions, carried by fatty acids bound to the 37LRP and to a galectin3 cross-reacting molecule.
Butò
S
S
Division of Experimental Oncology E, Istituto Nazionale Tumori, Milan, Italy.
Tagliabue
E
E
Ardini
E
E
Magnifico
A
A
Ghirelli
C
C
van den Brûle
F
F
Castronovo
V
V
Colnaghi
M I
MI
Sobel
M E
ME
Ménard
S
S
D000215:Acylation; D000943:Antigens, Differentiation / Q000737:chemistry; D002460:Cell Line; D002846:Chromatography, Affinity; D019281:Dimerization; D000939:Epitopes / Q000737:chemistry; D005227:Fatty Acids / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D037502:Galectin 3; D006801:Humans; D019811:Hydroxylamine / Q000737:chemistry; D007797:Laminin / Q000378:metabolism; D011498:Protein Precursors / Q000737:chemistry / Q000378:metabolism*; D017474:Receptors, Laminin / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism; D012995:Solubility
D000943:Antigens, Differentiation; D000939:Epitopes; D005227:Fatty Acids; D037502:Galectin 3; D007797:Laminin; D011498:Protein Precursors; D017474:Receptors, Laminin; D019811:Hydroxylamine