Laminin Isoforms 8 and 10 Are Primary Components of the Subendothelial Basement Membrane Promoting Interaction with Neoplastic Lymphocytes
2001
To determine whether subendothelial laminins (LNs) could be implicated
in the extravasation of neoplastic lymphocytes, we have examined the
distribution of a number of LN isoforms in human vascular structures of
adult individuals and have assayed the ability of the isolated LN
molecules to promote adhesion of lymphoma and leukemic cells in
vitro using a novel cell adhesion assay, CAFCA, Centrifugal
Assay for Fluorescence-based Cell Adhesion (E. Giacomello et
al., Biotechniques, 26: 758–762, 1999; P.
Spessotto et al., Methods Mol. Biol.,
139: 321–343, 2000). The use of previously
characterized LN chain-specific antibodies showed that the vast
majority of the smaller vascular compartments, known to correspond to
sites of lymphocyte transmigration, expressed the subunits involved in
the structuring of 9 of the 12 LN isoforms known to date. Eight LN
isoforms ( i.e., LN-1, -2, -4, -5, -8, -9, -10, and -11)
and four naturally occurring LN complexes were isolated from various
tissues and cultured cells by combined gel filtration, ion exchange,
and immunoaffinity chromatographies, and the identity/composition of
the isolated LNs/LN complexes was asserted by immunochemical means and
amino-acid sequencing. Notwithstanding the widespread colocalization of
LN isoforms, a panel of neoplastic B- and T-cell lines and lymphocytes
isolated from patients affected by chronic lymphocytic B-cell leukemia
attached preferentially and with high avidity to purified LN-8,
purified LN-10, and LN-10-containing protein complexes, whereas
lymphocytes derived from patients diagnosed with acute lymphocytic
leukemia failed to bind to these LNs. All of the tested neoplastic
lymphocytes failed to adhere to the isolated LN-1, LN-4, LN-9, and
LN-11 and attached moderately well to purified LN-2 and LN-5. The
interaction of transformed lymphocytes with LNs was cation-dependent
and interchangeably mediated by the α 3 β 1
and α 6 β 1 integrins. The degree of
engagement of the two LN receptors was dependent upon their relative
levels of cell surface expression, whereas, irrespective of the
phenotype, lymphocytes deprived of either of these receptors were
incapable of LN binding. The findings suggest that LN-8 and LN-10 may
act in an independent or complementary fashion as primary
components of the endothelial basement membrane favoring the
interaction of extravasating neoplastic lymphocytes. Thus, our results
would demonstrate that different LN isoforms may evoke diverse cellular
responses in different cell types and that this divergence may be the
basis for the redundancy of LN distribution in a number of vascular
structures.
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