Lysyl hydroxylase 2 mediated collagen post-translational modifications and functional outcomes

Abstract

Lysyl hydroxylase 2 (LH2) is a member of LH family that catalyzes the hydroxylation of lysine (Lys) residues on collagen, and this particular isozyme has been implicated in various diseases. While its function as a telopeptidyl LH is generally accepted, several fundamental questions remain unanswered: 1. Does LH2 catalyze the hydroxylation of all telopeptidyl Lys residues of collagen? 2. Is LH2 involved in the helical Lys hydroxylation? 3. What are the functional consequences when LH2 is completely absent? To answer these questions, we generated LH2-null MC3T3 cells (LH2KO), and extensively characterized the type I collagen phenotypes in comparison with controls. Cross-link analysis demonstrated that the hydroxylysine-aldehyde (Hylald)-derived cross-links were completely absent from LH2KO collagen with concomitant increases in the Lysald-derived cross-links. Mass spectrometric analysis revealed that, in LH2KO type I collagen, telopeptidyl Lys hydroxylation was completely abolished at all sites while helical Lys hydroxylation was slightly diminished in a site-specific manner. Moreover, di-glycosylated Hyl was diminished at the expense of mono-glycosylated Hyl. LH2KO collagen was highly soluble and digestible, fibril diameters were diminished, and mineralization impaired when compared to controls. Together, these data underscore the critical role of LH2-catalyzed collagen modifications in collagen stability, organization and mineralization in MC3T3 cells.

Collagen cross‐linking in oral cancer

“…Importantly, when telopeptidyl Lys hydroxylation is deficient, no Hyl ald -derived cross-links are formed causing collagen to become highly soluble and significantly more susceptible to enzymatic degradation. 27 These data provide clear evidence that driving collagen cross-linking toward the LH2-mediated, Hyl ald -derived pathway makes collagen insoluble and more resistant to enzymatic degradation. This finding may explain, at least partially, why LH2 overexpression seen in various cancer types promotes formation of a stiffened collagen matrix.…”

“…The function of LH2 as a telopeptidyl LH was first proposed by Uzawa et al 35 and was further confirmed in part by Mercer et al, 86 van der Slot et al, 36,89 and Pornprasertsuk et al 37,91 Since LH2-knockout mice die at an early embryonic stage (E10.5), 92 we generated LH2-deficient cells and characterized the molecular phenotypes. 27 The results demonstrated that LH2 is responsible for both N-and C-telopeptidyl Lys hydroxylation of α1 and α2 chains of type I collagen, and showed that other LH family members cannot compensate for this function. Importantly, when telopeptidyl Lys hydroxylation is deficient, no Hyl ald -derived cross-links are formed causing collagen to become highly soluble and significantly more susceptible to enzymatic degradation.…”

“…Lys residues in the helical domain having the sequence motif -X-Lys-Gly-are hydroxylated mainly by LH1, while LH2 specifically acts on Lys residues in telopeptidyl domains in the sequences of -X-Lys-Ala-, -X-Lys-Ser-, -X-Lys-Gly-. 27,[34][35][36][37][38] Specific Hyl residues in a -Gly-X-Hyl-motif in the helical domain can then be O-galactosylated forming galactosyl-Hyl (G-Hyl) catalyzed by glycosyltransferase 25 domains 1 and 2 (GLT25D1/2), and further glucosylated forming glucosylgalactosyl-Hyl (GG-Hyl) by LH3. [39][40][41] LH3 was reported to be a multifunctional enzyme that possesses LH, galactosyltransferase and galactosylhydroxylysyl glucosyltransferase 42,43 activities, but for fibrillar collagens, it mainly glucosylates G-Hyl residues to form GG-Hyl.…”

“…[28][29][30][31]100 Considering that one characteristic of solid tumors is accumulation of stiffened fibrillar collagen (mainly type I), the major contributor to this phenotype is likely LH2 overexpression. 27 Similar to LOX (see below), LH2 expression is coordinately upregulated by hypoxic conditions and is a direct target of HIF-1. 101 The state of LH2 expression is correlated with poor prognosis in several human cancers.…”

“…A key determinant of collagen stiffening is the quantity and quality of covalent intermolecular cross-linking. 26,27 In fact, recent studies have indicated that abnormal collagen cross-linking is associated with cancer growth and metastasis. [28][29][30][31][32] In this review, we provide a biochemical/molecular overview of collagen cross-linking, its role in OSCCs and possible clinical implications.…”