Del-1–αvβ5 interactions induce Hox D3 expression. (a) ECs were plated in monolayers (–BM) or on tissue-culture plates coated with thin layers of basement membrane (+BM) prior to cell lysis and Western blot analysis for cyclin D1, p21^cip, and integrins β3 and β5. (b) RT-PCR was performed for Hox D3, integrins β3 and β5, and GADPH (not shown). Relative levels of each PCR product were determined by densitometry in comparison with GADPH expression levels for each treatment. Asterisks indicate statistical significance relative to monolayer culture (–BM) (P < 0.02). (c) ECs were plated on endothelial monolayers in serum culture, BM + Del-1 (Del), or on BM + Del-1 with anti-αvβ5 function-blocking Ab’s (Del + P1F6), or control Ab’s (Del + cIgG). Integrin β5 and β5 protein expression levels were determined by Western blot analysis. Average expression levels for each integrin were determined in three experiments by densitometry. (d) RT-PCR was performed on RNA isolated from cells treated as in c for Hox D3, integrins β3 and β5, and GADPH. Relative levels of each PCR product were determined by densitometry in comparison with GADPH expression levels for each treatment. Asterisks indicate statistical significance relative to Del-1 stimulation (P < 0.02).