Histone modifications reflect gene activity, but the relationship between cause and consequence of transcriptional control is heavily debated. Recent developments in rewriting local histone codes of endogenous genes elucidated instructiveness of certain marks in regulating gene expression. Maintenance of such repressive epigenome editing is controversial, while stable reactivation is still largely unexplored. Here we demonstrate sustained gene re-expression using two types of engineered DNA-binding domains fused to a H3K4 methyltransferase. Local induction of H3K4me3 is sufficient to allow re-expression of silenced target genes in various cell types. Maintenance of the re-expression is achieved, but strongly depends on the chromatin microenvironment (that is, DNA methylation status). We further identify H3K79me to be essential in allowing stable gene re-expression, confirming its role in epigenetic crosstalk for stable reactivation. Our approach uncovers potent epigenetic modifications to be directly written onto genomic loci to stably activate any given gene.

Collagen is a macromolecule that has versatile roles in physiology, ranging from structural support to mediating cell signaling. Formation of mature collagen fibrils out of procollagen α-chains requires a variety of enzymes and chaperones in a complex process spanning both intracellular and extracellular post-translational modifications. These processes include modifications of amino acids, folding of procollagen α-chains into a triple-helical configuration and subsequent stabilization, facilitation of transportation out of the cell, cleavage of propeptides, aggregation, cross-link formation, and finally the formation of mature fibrils. Disruption of any of the proteins involved in these biosynthesis steps potentially result in a variety of connective tissue diseases because of a destabilized extracellular matrix. In this review, we give a revised overview of the enzymes and chaperones currently known to be relevant to the conversion of lysine and proline into hydroxyproline and hydroxylysine, respectively, and the O-glycosylation of hydroxylysine and give insights into the consequences when these steps are disrupted.

Collagens are subjected to extensive posttranslational modifications, such as lysine hydroxylation. Bruck syndrome (BS) is a connective tissue disorder characterized at the molecular level by a loss of telopeptide lysine hydroxylation, resulting in reduced collagen pyridinoline cross-linking. BS results from mutations in the genes coding for lysyl hydroxylase (LH) 2 or peptidyl-prolyl cis-trans isomerase (PPIase) FKBP65. Given that the immunophilin FKBP65 does not exhibit LH activity, it is likely that LH2 activity is somehow dependent on FKPB65. In this report, we provide insights regarding the interplay between LH2 and FKBP65. We found that FKBP65 forms complexes with LH2 splice variants LH2A and LH2B but not with LH1 and LH3. Ablating the catalytic activity of FKBP65 or LH2 did not affect complex formation. Both depletion of FKBP65 and inhibition of FKBP65 PPIase activity reduced the dimeric (active) form of LH2 but did not affect the binding of monomeric (inactive) LH2 to procollagen Iα1. Furthermore, we show that LH2A and LH2B cannot form heterodimers with each other but are able to form heterodimers with LH1 and LH3. Collectively, our results indicate that FKBP65 is linked to pyridinoline cross-linking by specifically mediating the dimerization of LH2. Moreover, FKBP65 does not interact with LH1 and LH3, explaining why in BS triple-helical hydroxylysines are not affected. Our results provide a mechanistic link between FKBP65 and the loss of pyridinolines and may hold the key to future treatments for diseases related to collagen cross-linking anomalies, such as fibrosis and cancer.collagen cross-linking | lysyl hydroxylase | FKBP65 | Bruck syndrome | fibrosis C ollagen I is an essential component of the extracellular matrix (ECM) of tissues such as bone and skin, and is involved in a wide variety of biological processes. A deregulated synthesis of collagen type I results in pathologies ranging from severe bone and skin anomalies to fibrosis (1-5). Hydroxylation of specific lysine (Lys) residues into 5-hydroxylysine (Hyl) is performed by lysyl hydroxylases (LHs), also known as the procollagen-lysine, 2-oxoglutarate 5-dioxygenase (PLOD) family. Collagens deposited in the ECM are stabilized by the formation of intermolecular crosslinks by members of the lysyl oxidase family, LOX and LOXL (6). Two collagen cross-linking pathways have been identified, the allysine route and the hydroxyallysine route (7). In the allysine route, a telopeptide Lys is oxidized by lysyl oxidases into an aldehyde; in the hydroxyallysine route, this occurs with a telopeptide Hyl. In turn, the reactive aldehydes interact with the Lys or Hyl residues in the helical part of collagen to form difunctional and finally trifunctional cross-links (8-10). The trifunctional cross-links derived from the hydroxyallysine route are referred to as pyridinolines. Collagens cross-linked by means of pyridinolines are difficult to degrade (11-13).The LH family consists of three individual members, designated LH1, LH2, and LH3. Hydroxylation of Lys present...