passages.id: split_5_test_550_passage
passages.type: progene_text
passages.text: Transient transfection studies showed that competition between activin A and OP-1 also occurred at the type I receptor ( ActR-1 ) level ; constitutively active ( CA ) - ActR-I inhibited CA - ActR-IB - mediated p3TP - Lux reporter induction .