Critical Role of Integrin-Linked Kinase in Granule Cell Precursor Proliferation and Cerebellar Development

Abstract

Integrin-linked kinase (ILK) is a serine/threonine protein kinase that plays an important role in integrin signaling and cell proliferation. We used Cre recombinase (Cre)-loxP technology to study CNS restricted knock-out of the ilk gene by either Nestin-driven or gfap-driven Cre-mediated recombination. Developmental changes in ilk-excised brain regions are similar to those observed in mice lacking the integrin ␤1 subunit in the CNS, including defective laminin deposition, abnormal glial morphology, and alterations in granule cell migration. Decreases in 6-bromodeoxyuridine (BrdU) pulse labeling and proliferating cell nuclear antigen expression in the external granule cell layer of the cerebellum demonstrated that proliferation is disrupted in granule cells lacking ILK. Previous studies have shown that laminin-sonic hedgehog (Shh)-induced granule cell precursor (GCP) proliferation is dependent on ␤1 integrins, several of which bind laminin and interact with ILK through the ␤1 cytoplasmic domain. Both ex vivo deletion of ilk and a small molecule inhibitor of ILK kinase activity decreased laminin-Shh-induced BrdU labeling in cultured GCPs. Together, these results implicate ILK as a critical effector in a signaling pathway necessary for granule cell proliferation and cerebellar development.

SPARC from Olfactory Ensheathing Cells Stimulates Schwann Cells to Promote Neurite Outgrowth and Enhances Spinal Cord Repair

“…Schwann cells and astrocytes are normally segregated to opposite sides of the laminin-rich basal lamina of the PNS-CNS boundary, yet transplanted OECs help to reestablish a laminin-rich perilesion boundary in the CNS within which SCs and astrocyte freely interact, thus facilitating axon entry to the lesion site (Richter et al, 2005). Intracellular SPARC can regulate cell morphology and motility via a direct interaction with integrin-linked kinase, which has been implicated in the autoregulation of glial laminin production and migration in the CNS (Mills et al, 2006). OEC-produced SPARC at the lesion core could also regulate local laminin-1 production, glial migration, and axonal responsiveness and shift the normally inhibitory ECM environment of the glial scar into one that permits the endogenous astrocytes and Schwann cells to interact and collectively enhance repair (Barker et al, 2005).…”

Integrin-linked kinase – essential roles in physiology and cancer biology

“…Although studies of CNSrestricted ILK-knockout mice failed to detect differential phosphorylation of Akt or GSK3 compared with wild-type mice (Niewmierzycka et al, 2005), these analyses were carried out using western blots of whole brain extracts. Data indicate that ILK is preferentially expressed in particular regions of the brain (Mills et al, 2006), and detailed immunohistochemical analysis of specific areas of the brain for phosphorylated Akt and GSK3 might reveal ILK-mediated regulation of these substrates.…”

“…Although ILK is apparently dispensable for the formation of adhesion complexes in the zebrafish, its kinase activity is required for strengthening the muscle-fiber-ECM interaction (Postel et al, 2008). These data indicate that, in contrast to the dispensable nature of ILK kinase activity in invertebrate muscle function (Mackinnon Adhesion; migration and polarity; proliferation; survival Cobblestone lissencephaly (Belvindrah et al, 2006;Gary et al, 2003;Guo et al, 2006;Guo et al, 2007;Mills et al, 2003;Mills et al, 2006;Naska et al, 2006;Niewmierzycka et al, 2005;Oinuma et al, 2007;Zhou et al, 2004) Immune system (T cells, macrophages)…”

“…The deletion of ILK from the mouse brain using a series of CNS-specific promoters resulted in cortical-lamination defects resembling cobblestone lissencephaly, in neuronal-cellmigration abnormalities, in fragmentation of the basal lamina and in dysregulation of the glial-cell network; often, these mice died prematurely (Belvindrah et al, 2006;Mills et al, 2006;Niewmierzycka et al, 2005). Interestingly, the deletion of ILK did not impact directly on cell survival (Mills et al, 2006;Niewmierzycka et al, 2005), although there was reduced proliferation of granule-cell precursors (GCPs) (Belvindrah et al, 2006;Mills et al, 2006) and the deletion of ILK in primary GCPs inhibited proliferation induced by sonic hedgehog (Shh), a 1-integrin-dependent GCP mitogen that interacts directly with laminin (Blaess et al, 2004;Mills et al, 2006). There was less guanine triphosphate (GTP)-bound Cdc42 in the cerebellum of ILK-deficient mice, and ILK and Cdc42 were required for the 1-integrindependent outgrowth of glial processes (Belvindrah et al, 2006).…”

Basement membrane attachment is dispensable for radial glial cell fate and for proliferation, but affects positioning of neuronal subtypes

“…Colognato and ffrench-Constant, 2004;Mott and Werb, 2004). Integrins integrate signalling via components of the ECM as well as via growth factors (Colognato and ffrench-Constant, 2004); targeted deletion of either ␤1 or ␣6 integrin or the ␤1 integrin cytoplasmic tail binding protein integrin-linked kinase (ILK) abolishes the attachment of radial glial endfeet to the BM and thereby also disrupts the maintenance of BM integrity (Beggs et al, 2003;Georges-Labouesse et al, 1998;Graus-Porta et al, 2001;Halfter et al, 2002;Mills et al, 2006;Niewmierzycka et al, 2005). Thus, radial glia and later astrocyte endfeet contribute to the formation and maintenance of the BM by integrin-mediated binding.…”