Y. Yokosaki et al., THE INTEGRIN-ALPHA-9-BETA-1 MEDIATES CELL ATTACHMENT TO A NON-RGD SITE IN THE 3RD FIBRONECTIN TYPE-III REPEAT OF TENASCIN, The Journal of biological chemistry, 269(43), 1994, pp. 26691-26696
We have previously reported the sequence of the integrin alpha 9 subun
it, a partner of the beta 1 subunit that is expressed in basal keratin
ocytes, hepatocytes, airway epithelial cells, and smooth and skeletal
muscle. In the present study, we have stably expressed alpha 9 beta 1
on the surface of the human embryonic kidney cell line 293 and the hum
an colon carcinoma cell line SW480 and used these transfected cell lin
es to identify ligand(s) for this integrin. Transfected cells did not
appear to utilize alpha 9 beta 1 for attachment to the extracellular m
atrix proteins fibronectin, laminin, vitronectin, fibrinogen, thrombos
pondin, or type I or IV collagen. However, in contrast to mock transfe
ctants, both 293 cells and SW480 cells expressing alpha 9 beta 1 adher
ed to intact chicken tenascin. By utilizing a variety of recombinant f
ragments of tenascin, we were able to localize the binding site for al
pha 9 beta 1 to the third type III repeat. This repeat contains the ar
ginine-glycine-aspartic acid (RGD) tripeptide that has been shown to s
erve as a binding site in tenascin for alpha v-integrins. However, the
RGD site does not appear to be the binding site for alpha 9 beta 1, a
s the attachment of alpha 9 transfectants to this fragment was not inh
ibited by RGD peptide, nor by changing the RGD site to RAD or RAA.