Regulation of Mesangial Cell Hexokinase Activity and Expression by Heparin-binding Epidermal Growth Factor-like Growth Factor

Abstract

Heparin-binding epidermal growth factor -like growth factor (HB-EGF) expression and hexokinase (HK) activity are increased in various pathologic renal conditions. Although the mitogenic properties of HB-EGF have been well characterized, its effects on glucose (Glc) metabolism have not. We therefore examined the possibility that HB-EGF might regulate HK activity and expression in glomerular mesangial cells, which constitute the principal renal cell type affected by a variety of pathologic conditions. Protein kinase C (PKC)-dependent classic mitogenactivated protein kinase (MAPK) pathway activation has been associated with increased HK activity in this cell type, so we also examined dependence upon these signaling intermediates. HB-EGF (>10 nM) increased total HK activity over 50% within 12-24 h, an effect mimicked by other EGF receptor agonists, but not by IGF-1 or elevated Glc. EGF receptor and classic MAPK pathway antagonists prevented this increase, as did general inhibitors of gene transcription and protein synthesis. Both HB-EGF and phorbol esters activated the classic MAPK pathway, albeit via PKC-independent and PKC-dependent mechanisms, respectively. Both stimuli were associated with increased HK activity, selectively increased HKII isoform expression, and increased Glc metabolism via both the glycolytic-tricarboxylic acid cycle route and the pentose phosphate pathway. HB-EGF thus constitutes a novel regulator of mesangial cell HK activity and Glc metabolism. HKII is the principal regulated isoform in these cells, as it is in insulin-sensitive peripheral tissues, such as muscle. However, the uniform requirement for classic MAPK pathway activation distinguishes HKII regulation in mesangial cells from that observed in muscle. These findings suggest a novel mechanism whereby growth factors may couple metabolism to glomerular injury.

LPA is a novel lipid regulator of mesangial cell hexokinase activity and HKII isoform expression

“…LPA-stimulated HK activity requires classic MAPK pathway activation. We have previously demonstrated the involvement of the classic MAPK pathway in the regulation of mesangial cell HK activity by phorbol esters, thrombin, and growth factors (31)(32)(33), and similar regulation has been suggested for proinflammatory cytokines (38). Because this pathway constitutes a known effector pathway for LPA signaling, we examined MEK-selective inhibitors for the ability to prevent LPA-increased HK activity in cultured mesangial cells.…”

“…HK immunoblot analysis. Whole cell lysates were electrophoretically resolved and transferred to nitrocellulose membranes for immunoblotting as described previously (32). Blots were routinely stained with 0.1% (wt/vol) Ponceau S in 5% acetic acid to confirm both the uniformity of gel loading and the efficiency of membrane transfer.…”

“…Exogenous LPA selectively increases HKII isoform abundance. We have previously reported that cultured mesangial cells express all three renal HK isoforms (32). To better understand the relative contributions of individual HK isoforms to LPA-stimulated increases in total HK activity, we examined the corresponding effects on individual isoform abundance.…”

“…Phorbol esters, thrombin, and growth factors increase mesangial cell HK activity via classic MAPK pathway activation (31)(32)(33). A uniform requirement for both ongoing gene transcription and de novo protein synthesis has suggested a role for increased HK expression in these effects (31)(32)(33). Associated increases in HKII isoform abundance (Refs.…”

Hexokinase II: The Integration of Energy Metabolism and Control of Apoptosis

“…Hexokinase III is found at relatively low levels in many tissues, with a higher expression in lung [13]. Expression of hexokinase II is increased in renal mesangial cells by growth factors, such as the Heparinbinding Epidermal Growth Factor-like Growth Factor (HB-EGF) and the lipid mediator lysophosphatidic acid (LPA) [14,15]. Both of these ligands depend on the extracellular signal-regulated kinase (MAPK/ERK) and protein kinase C pathways for upregulating hexokinase II levels.…”