Megalencephalic leukoencephalopathy with subcortical cysts protein-1 regulates epidermal growth factor receptor signaling in astrocytes

Abstract

Mutations in the MLC1 gene, which encodes a protein expressed in brain astrocytes, are the leading cause of MLC, a rare leukodystrophy characterized by macrocephaly, brain edema, subcortical cysts, myelin and astrocyte vacuolation. Although recent studies indicate that MLC1 protein is implicated in the regulation of cell volume changes, the exact role of MLC1 in brain physiology and in the pathogenesis of MLC disease remains to be clarified. In preliminary experiments, we observed that MLC1 was poorly expressed in highly proliferating astrocytoma cells when compared with primary astrocytes, and that modulation of MLC1 expression influenced astrocyte growth. Because volume changes are key events in cell proliferation and during brain development MLC1 expression is inversely correlated to astrocyte progenitor proliferation levels, we investigated the possible role for MLC1 in the control of astrocyte proliferation. We found that overexpression of wild type but not mutant MLC1 in human astrocytoma cells hampered cell growth by favoring epidermal growth factor receptor (EGFR) degradation and by inhibiting EGF-induced Ca(+) entry, ERK1/2 and PLCγ1 activation, and calcium-activated KCa3.1 potassium channel function, all molecular pathways involved in astrocyte proliferation stimulation. Interestingly, MLC1 did not influence AKT, an EGFR-stimulated kinase involved in cell survival. Moreover, EGFR expression was higher in macrophages derived from MLC patients than from healthy individuals. Since reactive astrocytes proliferate and re-express EGFR in response to different pathological stimuli, the present findings provide new information on MLC pathogenesis and unravel an important role for MLC1 in other brain pathological conditions where astrocyte activation occurs.

Megalencephalic leukoencephalopathy with cysts: theGlialcam‐null mouse model

“…Cell properties related to in vitro experimental manipulation probably account for the discrepancy between previous in vitro and our in vivo results. Recent in vitro findings suggest specific roles for MLC1 in astrocyte proliferation and maturation and in down‐regulating astrocyte response to injury 51. Notably, however we found no evidence for delayed astrocyte maturation or astrogliosis in both Mlc1 ‐null18 and Glialcam ‐null mice (not shown).…”

“…A similar redistribution of aquaporin4 has been described in a rat model of hydrocephalus, also interpreted as a compensatory phenomenon 50. Recent work suggests that MLC1 could also be involved in regulation of blood–brain barrier permeability, implying that alteration of this astrocytic function could contribute to development of edema 51. The severer white matter vacuolization in Glialcam ‐null than in Mlc1 ‐null mice could explain the difference in aquaporin4 expression between the two MLC mouse models.…”

Transformation Foci in IDH1-mutated Gliomas Show STAT3 Phosphorylation and Downregulate the Metabolic Enzyme ETNPPL, a Negative Regulator of Glioma Growth

“…The reduction of SFRP2 gene expression is particularly significant as this Wnt pathway inhibitor is often reduced by DNA hypermethylation in the progression of various cancers 33 . Regarding EGFR signaling, reduction of MLC1, a gene which favors EGFR degradation 34 , may leads to the higher EGFR expression we previously observed by IHC in foci 9 . The cytoskeleton might also be affected in foci as gene coding for ezrin (EZR) a linker protein between plasma membrane and actin cytoskeleton, is reduced.…”

“…The fact that the downregulated genes in foci are also decreased in high-grade tumours (Table S3) suggests that foci are cells undergoing transformation. In addition, for 3 of these genes, namely MLC1, CST3 and GJA1, it has been demonstrated that they oppose tumorigenesis when overexpressed in glioma lines 34,36,37 and thus they present tumour suppressor activity. Similarly, the reduction of expression of these 3 genes might promote foci expansion and transformation.…”

Leukodystrophies: a proposed classification system based on pathological changes and pathogenetic mechanisms

“…Functional interaction of MLC1 with other protein (β1 subunit of Na,K-ATPase, TRPV4, agrin and ZO-1) has been advocated in vitro [ 22 , 26 , 49 , 100 , 118 , 130 ], but not confirmed in vivo [ 50 ]. Recent in vitro findings also suggest specific roles for MLC1 in astrocyte proliferation and maturation and in down-regulating astrocyte response to injury [ 119 ] via regulation of the epidermal growth factor receptor signaling.…”