Reduced migration, altered matrix and enhanced TGF1 signaling are signatures of mouse keratinocytes lacking Sdc1

We have reported previously that syndecan-1 (Sdc1)-null mice show delayed re-epithelialization after skin and corneal wounding. Here, we show that primary keratinocytes obtained from Sdc1-null mice and grown for 3-5 days in culture are more proliferative, more adherent and migrate more slowly than wt keratinocytes. However, the migration rates of Sdc1-null keratinocytes can be restored to wild-type levels by replating Sdc1-null keratinocytes onto tissue culture plates coated with fibronectin and collagen I, laminin (LN)-332 or onto the matrices produced by wild-type cells. Migration rates can also be restored by treating Sdc1-null keratinocytes with antibodies that block 6 or v integrin function, or with TGF1. Antagonizing either 1 integrin function using a function-blocking antibody or TGF1 using a neutralizing antibody reduced wild-type keratinocyte migration more than Sdc1-null keratinocyte migration. Cultures of Sdc1-null keratinocytes accumulated less collagen than wild-type cultures but their matrices contained the same amount of LN-332. The Sdc1-null keratinocytes expressed similar total amounts of eight different integrin subunits but showed increased surface expression of v6, v8, and 64 integrins compared with wild-type keratinocytes. Whereas wild-type keratinocytes increased their surface expression of 21, v6, v8, and 64 after treatment with TGF1, Sdc1-null keratinocytes did not. Additional data from a dual-reporter assay and quantification of phosphorylated Smad2 show that TGF1 signaling is constitutively elevated in Sdc1-null keratinocytes. Thus, our results identify TGF1 signaling and Sdc1 expression as important factors regulating integrin surface expression, activity and migration in keratinocyte and provide new insight into the functions regulated by Sdc1.