Compartmentalization regulates the interaction between the platelet integrin α_IIbβ₃ and ICln

Abstract

SummaryThe volume-regulating protein, ICln, interacts with the conserved KxGFFKR a-integrin signature motif. ICln is an abundant protein (4455 ± 650 molecules/platelet) found exclusively in the soluble cytosolic fraction of unactivated platelets. In contrast, its binding partner, the platelet integrin a IIb b 3 , is present in detergent-insoluble fractions associated with membrane and cytoskeleton subcellular localizations. This study investigated factors that regulate the interaction of ICln with a IIb b 3 during platelet activation. Histagged recombinant ICln bound equally to purified a IIb b 3 and to integrin from resting or activated platelets. Binding was not affected by direct integrin activation with Mn ++ or by inhibitors of integrin occupancy (abciximab, RGD). However, the capacity for interaction between integrin and recombinant ICln was slowly downregulated following prolonged platelet activation for >300 s. In parallel, ICln redistributed to membrane and cytoskeletal platelet subcellular fractions. The time-course of this redistribution preceded the downregulation of integrin binding capacity and suggests that only a short window of opportunity exists for ICln interaction with a IIb b 3 to occur. Thus, although ICln has the inherent capacity to bind to a IIb b 3 regardless of its activation state, it can only do so following platelet activation. Activation-dependent subcellular redistribution of ICln represents a novel, temporally-regulated mechanism for control of integrin function in platelets.

Palmitoylated peptide, being derived from the carboxyl-terminal sequence of the integrin αIIbcytoplasmic domain, inhibits talin binding to αIIbβ3

“…The above hypothesis is supported by a recent study investigating proteins which can be bound to a IIb , membrane-proximal intracellular tail [37]. ICln was one of them [37,38]. It is important to note that the ICln residue, which is most likely involved in the interaction, is positioned in an acidic domain, a part of a disordered and highly mobile loop of the PHdomain [37].…”

Integrins as therapeutic targets: lessons and opportunities

“…Csrc binds to the C-terminal tip of the β-CT and regulates the capacity of this integrin subunit to be phosphorylated. 195 . Targeting any of these specific interactions has the potential to disrupt integrin activation therapeutically.…”

The C-terminus of ICln is Natively Disordered but Displays Local Structural Preformation

“…ICln is an ubiquitous protein which partakes in essential physiological pathways regulating cell volume [1][2], cell morphology [3], angiogenesis [4], the activation of platelets [5][6], and RNA processing [7][8][9]. In line with the diverse roles of ICln in these vital physiological pathways, knock-out of ICln is lethal [10], and altered expression levels of ICln may contribute to diseases like spinal muscular atrophy [11].…”

“…ICln for example interacts with components of the cytoskeleton like actin [12][13][14] or the protein 4.1 [15][16], while interactions of ICln with RNA processing factors like LSm and Sm proteins or the protein arginine methyltransferase PRMT5 most likely take place in the cytosol [7][8][9][17][18][19]. Furthermore, a fraction of ICln is located at the plasma membrane [6,14,[20][21][22], where it is functionally associated with the swelling dependent anion channel [1][2][23][24] and interacts with HSPC038 [25] or the integrin α IIb β 3 [5][6].…”