CXCL12/CXCR4-Mediated Procollagen Secretion Is Coupled to Cullin-RING Ubiquitin Ligase Activation

Tissue fibrosis is mediated by the actions of multiple pro-fibrotic proteins that can induce myofibroblast phenoconversion through diverse signaling pathways coupled predominantly to Smads or MEK/Erk proteins. The TGFβ/TGFβR and CXCL12/CXCR4 axes induce myofibroblast phenoconversion independently through Smads and MEK/Erk proteins, respectively. To investigate these mechanisms at the genetic level, we have now elucidated the TGFβ/TGFβR and CXCL12/CXCR4 transcriptomes in human fibroblasts. These transcriptomes are largely convergent, and up-regulate transcripts encoding proteins known to promote myofibroblast phenoconversion. These studies also revealed a molecular signature unique to CXCL12/CXCR4 axis activation for COPII vesicle formation, ubiquitination, and Golgi/ER localization/targeting. In particular, both CUL3 and KLHL12, key members of the Cullin-RING (CRL) ubiquitin ligase family of proteins involved in procollagen transport from the ER to the Golgi, were highly up-regulated in CXCL12-, but repressed in TGFβ-, treated cells. Up-regulation of CUL3 and KLHL12 was correlated with higher procollagen secretion by CXCL12-treated cells, and this affect was ablated upon treatment with inhibitors specific for CXCR4 or CUL3 and repressed by TGFβ/TGFβR axis activation. The results of these studies show that activation of the CXCL12/CXCR4 axis uniquely facilitates procollagen I secretion through a COPII-vesicle mediated mechanism to promote production of the ECM characteristic of fibrosis.