Summary
Intraalveolar fibrin deposition is commonly observed during acute inflammatory and
chronic interstitial lung diseases and may contribute to impairment of surfactant
function and gas exchange.We recently described a chemically cross-linked chimeric
protein consisting of surfactant protein (SP)-B and urokinase (uPA) for targeting
alveolar fibrin under conditions such as acute respiratory distress syndrome (ARDS)
or lung fibrosis.We now investigated the feasibility of a recombinant production of
a fusion protein encoding mature SP-B and uPA, termed SPUC. Four different SPUC proteins
(N-term SP-B/C-term uPA, N-term uPA/C-term SP-B, each +/− His-tag) were prepared by
cloning the cDNA encoding mature SP-B and low-molecular-weight uPA into the expression
vector pcDNA3.1. CHO-cells were transfected with the constructs and the supernatant
and cell lysates were analyzed for expression of SPUC.Using a chromogenic substrate
assay uPA activity was found in supernatants and lysates of transfected cells with
highest activities related to the N-term uPA/C-term SP-B (+/− His-tag) construct in
supernatants 48h after transfection.Casein enzymography showed an enzymatically active
fusion proteins with a molecular weight of ∼ 42 kDa in the supernatant of cells transfected
with the N-term uPA/C-term SP-B (+/− His-tag) construct,but only a minor activity
with the N-term SP-B/C-term uPA construct. The N-term uPA/C-term SP-B construct was
also shown to possess higher resistance towards inhibition by plasminogen activator
inhibitor-1.We conclude that recombinant production of a fusion protein consisting
of mature SP-B and uPA is feasible, when the SP-B moiety is fused to the C-terminus
of urokinase.
Keywords
Urokinase - pulmonary surfactant - acute lung injury - fusion protein