Procollagen Lysyl Hydroxylase 2 Expression Is Regulated by an Alternative Downstream Transforming Growth Factor β-1 Activation Mechanism

PLOD2 (procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2) hydroxylates lysine residues in collagen telopeptides and is essential for collagen pyridinoline cross-link formation. PLOD2 expression and subsequent pyridinoline cross-links are increased in fibrotic pathologies by transforming growth factor beta-1 (TGF beta 1). In this report we examined the molecular processes underlying TGF beta 1-induced PLOD2 expression. We found that binding of the TGF beta 1 pathway related transcription factors SMAD:3 and SP1-mediated TGF beta 1 enhanced PLOD2 expression and could be correlated to an increase of acetylated histone H3 and H4 at the PLOD2 promoter. Interestingly, the classical co-activators of SMAD3 complexes, p300 and CBP, were not responsible for the enhanced H3 and H4 acetylation. Depletion of SMAD3 reduced PLOD2 acetylated H3 and H4, indicating that another as of yet unidentified histone acetyltransferase binds to SMAD 3 at PLOD2. Assessing histone methylation marks at the PLOD2 promoter depicted an increase of the active histone mark H3K79me2, a decrease of the repressive H4K2Ome3 mark, but no role for the generally strong transcription-related modifications: H3K4me3, H3K9me3 and H3K27me3. Collectively, our findings reveal that TGF beta 1 induces a SP1- and SMAD3-dependent recruitment of histone modifying enzymes to the PLOD2 promoter other than the currently known TGF beta 1 downstream co-activators and epigenetic modifications. This also suggests that additional activation strategies are used downstream of the TGF beta 1 pathway, and hence their unraveling could be of great importance to fully understand TGF beta 1 activation of genes.