Metabolic control of hyaluronan synthases

Abstract

Hyaluronan (HA) is a glycosaminoglycan composed by repeating units of D-glucuronic acid (GlcUA) and N-acetylglucosamine (GlcNAc) that is ubiquitously present in the extracellular matrix (ECM) where it has a critical role in the physiology and pathology of several mammalian tissues. HA represents a perfect environment in which cells can migrate and proliferate. Moreover, several receptors can interact with HA at cellular level triggering multiple signal transduction responses. The control of the HA synthesis is therefore critical in ECM assembly and cell biology; in this review we address the metabolic regulation of HA synthesis. In contrast with other glycosaminoglycans, which are synthesized in the Golgi apparatus, HA is produced at the plasma membrane by HA synthases (HAS1-3), which use cytoplasmic UDP-glucuronic acid and UDP-N-acetylglucosamine as substrates. UDP-GlcUA and UDP-hexosamine availability is critical for the synthesis of GAGs, which is an energy consuming process. AMP activated protein kinase (AMPK), which is considered a sensor of the energy status of the cell and is activated by low ATP:AMP ratio, leads to the inhibition of HA secretion by HAS2 phosphorylation at threonine 110. However, the most general sensor of cellular nutritional status is the hexosamine biosynthetic pathway that brings to the formation of UDP-GlcNAc and intracellular protein glycosylation by O-linked attachment of the monosaccharide β-N-acetylglucosamine (O-GlcNAcylation) to specific aminoacid residues. Such highly dynamic and ubiquitous protein modification affects serine 221 residue of HAS2 that lead to a dramatic stabilization of the enzyme in the membranes.

Periostin Induces Intracellular Cross-talk between Kinases and Hyaluronan in Atrioventricular Valvulogenesis

“…Furthermore, this study demonstrates for the first time that signaling pathways activated by PN/␤-INTEGRIN interaction in developing valve cells can also stimulate HA synthesis and activation of HAS2 protein at a phosphoserine site. There is increasing evidence that phosphorylation of serine and threonine residues in HAS2 control hya-luronan synthesis whether or not it is activated (59,72). The immunoprecipitates in Fig.…”

“…Cells from PN-null cushions were transfected with PN cDNA expression vector as part of a "rescue" experiment. Immunoprecipitates were prepared from the lysates using monoclonal anti-HAS2 antibodies and analyzed for phosphoserine and phosphothreonine residue(s) within the native HAS2 protein (59). This procedure will determine the extent of Has2 protein phosphorylation at serine/ threonine sites of Has2, which play critical regulatory roles in the activation of Has2 and its potential to secrete HA.…”

“…This procedure will determine the extent of Has2 protein phosphorylation at serine/ threonine sites of Has2, which play critical regulatory roles in the activation of Has2 and its potential to secrete HA. The synthesis of HA is an energy-consuming process where the ratio of ATP/AMP-activated kinase controls the synthesis of HA (59,60). During energy stress, the ratio of AMP/ATP increases with consequent activation of AMP kinase.…”

“…During energy stress, the ratio of AMP/ATP increases with consequent activation of AMP kinase. Activated AMP kinase phosphorylates threonine in HAS2, which inactivates the anabolic process to synthesize HA (59,60). Inhibiting anabolic processes and inducing catabolic pathways to restore ATP levels back to normal would be needed to synthesize the UDP-GlcNAc substrate (61,62).…”

Hyaluronic Acid in the 3^rd Millennium

“…The three HAS isoforms share the 50-71% of their amino acid sequences (55% HAS1/HAS2, 57% HAS1/HAS3, 71% HAS2/HAS3) and, indeed, they are all characterized by seven membrane-spanning regions and a central cytoplasmic domain [50,86,89]. However, HAS gene sequences are located on different chromosomes (hCh19-HAS1, hCh8-HAS2, and hCh16-HAS3) [91,92], and the expression and the activity of HAS isoforms are controlled by growth factors, cytokines and other proteins such as kinases in different fashions which appear cell and tissue specific [50,90,93,94]. Hence, the three HAS genes may respond differently to transcriptional signals: for example, in human fibroblasts like synoviocytes, transforming growth factor ß upregulates HAS1 expression, but down-regulates HAS3 expression [95].…”