Figure 6.

Differential interactions of Ecto-COLXVII with the ECM. The integration of the ectodomain into the matrix depends on the culture substrate. A: Immunoblot of the ECM and culture medium of cells expressing the deletion mutants COL3, NC6, and ΔPro⁹⁹⁷-Gly¹¹⁵² cultured on different ECM proteins. Ecto-COLXVII was detected in the ECM by the Ab HK139 and in culture medium by the Ab NC16A-3. Coating with laminin 332 increased binding of the ectodomain of all mutants. In contrast, increased binding to collagen IV was observed only with ΔPro⁹⁹⁷-Gly¹¹⁵². This, together with the result shown in Figure 4A, indicates that binding of collagen XVII to collagen IV is mainly mediated by the carboxyl terminus stretching from Ile¹³⁴¹ to Pro¹⁴⁹⁷. On Matrigel, incorporation of the ectodomain of ΔPro⁹⁹⁷-Gly¹¹⁵² into the ECM was significantly lower than was that of the other mutants, suggesting that the limited region of Pro⁹⁹⁷ to Gly¹¹⁵² is important for binding of collagen XVII to Matrigel. B: Schematic representation of putative interaction sites in the Ecto-ColXVII with different ECM proteins. aa, amino acid; TM, transmembrane.