Monocytic cells synthesize, adhere to, and migrate on laminin-8 (α4β1γ1)

Laminins, a growing family of large heterotrimeric proteins with cell adhesive and signaling properties, are major components of vascular and other basement membranes. Expression, recognition, and use of laminin isoforms by leukocytes are poorly understood. Tn monoblastic THP-1 cells, transcripts for laminin gamma (1)-, beta (1)-, and alpha (4)-chains were detected by RT-PCR. Following immunoaffinity purification on a laminin beta (1) Ab-Sepharose column, laminin beta (1)- (220 kDa), gamma (1)- (200 kDa), and alpha (4)- (180/200 kDa) chains were detected by Western blotting in THP-1 cells and in two other monoblastic cell lines, U-937 and Mono Mac 6. After cell permeabilization, a mAb to laminin gamma (1)-chain reacted with practically all blood monocytes by immunofluorescence flow cytometry, and laminin-8 (alpha (4)beta (1)gamma (1)) could be isolated also from these cells. Monoblastic JOSK-I cells adhered constitutively to immobilized recombinant laminin-8, less than to laminin-10/11 (alpha (5)beta (1)gamma (1)/alpha (5)beta (2)gamma (1)) but to a higher level than to laminin-1 (alpha (1)beta (1)gamma (1)). Compared with the other laminin isoforms, adhesion to laminin-8 was preferentially mediated by alpha (6)beta (1) and beta (2) integrins. Laminin-8 and, to a lower extent, laminin-1 promoted spontaneous and chemokine-induced migration of blood monocytes, whereas laminin-10/11 was inhibitory. Altogether, the results indicate that leukocytes, as other cell types, are able to synthesize complete laminin molecules. Expression, recognition, and use of laminin-8 by leukocytes suggest a major role of this laminin isoform in leukocyte physiology.