Monocyte differentiation elevates biosynthesis of tTG and increases surface expression of tTG and the amounts of integrin-tTG complexes.

Untreated THP-1 cells (−TPA) and THP-1 cells induced to differentiate by plating on Fn for 72 hours in the presence of 150 ng/mL TPA (+TPA) were analyzed. The β₁-, β₂-, and β₃-integrins, tTG, and FXIIIA were immunoprecipitated from RIPA lysates of ³⁵S-labeled (A) or surface-biotinylated (B-D) untreated or TPA-treated cells. (A) Autoradiographs of ³⁵S-labeled immune complexes analyzed by SDS-PAGE and fluorography. (B) Surface-biotinylated proteins were immunoprecipitated, separated by SDS-PAGE, and blots developed with avidin-peroxidase. To detect tTG and FXIIIA in the immunoprecipitates, the same blots as in panel B were developed with mAb TG100 against tTG (C) or polyclonal antibody to FXIIIA (D). Note an up-regulation of tTG biosynthesis and elevated amounts of tTG complexed with β₁- and β₃-integrins during biosynthesis in TPA-treated THP-1 cells (A, arrow). Similarly, there is an increase in surface-expressed tTG and the amounts of β₁-integrin-tTG and β₃-integrin-tTG complexes on the surface of THP-1 cells in response to TPA treatment (B,C, arrows). In contrast, there is a decrease in biosynthesis (A) and surface expression (B) of FXIIIA in TPA-treated THP-1 cells. Arrowhead in panel D points to FXIIIA, which does not associate with integrins. Molecular weight markers in panels A and B are shown to the right of the gels.