In vivo processing of CXCL12α/SDF-1α after intravenous and subcutaneous administration to mice.

CXCL12α has been shown to be selectively processed at the N- and C-termini in blood and plasma in vitro. In order to study the processing in vivo, several versions of CXCL12α were expressed and purified. The protein was administered either iv or sc to mice, and at different time points postadministration plasma was collected and analyzed. To detect modifications of the CXCL12α molecule in crude plasma a SELDI TOF-MS-based method was developed. Anti-CXCL12 antibodies were immobilized on the SELDI chip and CXCL12α binding to the antibodies was detected by SELDI-TOF-MS. The protein was found to be processed both at the C- and N-termini. The same processed CXCL12α forms as detected in vitro were found; however, in addition further processing was detected at the N-terminus, where altogether seven amino acids were removed. At the C-terminus the lysine was removed as has been seen in vitro, and no further processing was detected. The full-length CXCL12α disappeared within minutes after administration, whereas the processed forms of the protein were detectable for up to 6-8 h postadministration. The same processed forms appeared after iv and sc administration, only the kinetics was different. When the shortest processed form detected in plasma, 7ΔN1ΔC-CXCL12α, was administered directly, no further processed forms were detected. Interestingly, a version of CXCL12α containing a N-terminal methionine was protected against N-terminal processing in plasma in vitro; however, in vivo no protection was seen, the protein was processed in the same way as full-length CXCL12α.