The activation sequence of thrombospondin-1 interacts with the latency-associated peptide to regulate activation of latent transforming growth factor-beta
Smf. Ribeiro et al., The activation sequence of thrombospondin-1 interacts with the latency-associated peptide to regulate activation of latent transforming growth factor-beta, J BIOL CHEM, 274(19), 1999, pp. 13586-13593
One of the primary points of regulation of transforming growth factor-beta
(TGF-beta) activity is control of its conversion from the latent precursor
to the biologically active form. We have identified thrombospondin-l as a m
ajor physiological regulator of latent TGF-beta activation. Activation is d
ependent on the interaction of a specific sequence in thrombospondin-l ((KR
FK415)-R-412) with the latent TGF-beta complex. Platelet thrombospondin-1 h
as TGF-beta activity and immunoreactive mature TGF-beta associated with it.
We now report that the latency-associated peptide (LAP) of the latent TGF-
beta complex also interacts with thrombospondin-l as part of a biologically
active complex. Thrombospondin LAP complex formation involves the activati
on sequence of thrombospondin-l (KRFK) and a sequence (LSKL) near the amino
terminus of LAP that is conserved in TGF-beta(1-5). The interactions of LA
P with thrombospondin-l through the LSKL and KRFK sequences are important f
or thrombospondin-mediated activation of latent TGF-beta since LSKL peptide
s can competitively inhibit latent TGF-beta activation by thrombospondin or
KRFK-containing peptides. In addition, the association of LAP with thrombo
spondin-1 may function to prevent the reformation of an inactive LAP TGF-be
ta complex since thrombospondin-bound LAP no longer confers latency on acti
ve TGF-beta. The mechanism of TGF-beta activation by thrombospondin-1 appea
rs to be conserved among TGF-beta isoforms as latent TGF-beta(2) can also b
e activated by thrombospondin-1 or KRFK peptides in a manner that is sensit
ive to inhibition by LSKL peptides.