Stimulation of cleavage of membrane proteins by calmodulin inhibitors

Abstract

The ectodomain of several membrane-bound proteins can be shed by proteolytic cleavage. The activity of the proteases involved in shedding is highly regulated by several intracellular second messenger pathways, such as protein kinase C (PKC) and intracellular Ca# + . Recently, the shedding of the adhesion molecule L-selectin has been shown to be regulated by the interaction of calmodulin (CaM) with the cytosolic tail of L-selectin. Prevention of CaM-L-selectin interaction by CaM inhibitors or mutation of a CaM binding site in L-selectin induced L-selectin ectodomain shedding. Whether this action of CaM inhibitors also affects other membrane-bound proteins is not known. In the present paper we show that CaM inhibitors also stimulate the cleavage of several other transmembrane proteins, such

Interaction of Calmodulin with l-Selectin at the Membrane Interface: Implication on the Regulation of l-Selectin Shedding

“…The CaM hypothesis has since been extended to other membrane proteins because many proteins contain in their cytoplasmic domain a region rich in basic residues and their shedding can be induced by treatment of CaM inhibitors. 18–23 However, there have been observations that do not seem consistent with the CaM hypothesis. 18; 25 It also remains unclear how CaM binding to the cytoplasmic domain of a shedding substrate can influence its proteolytic cleavage on the other side of the membrane.…”

“…18–23 However, there have been observations that do not seem consistent with the CaM hypothesis. 18; 25 It also remains unclear how CaM binding to the cytoplasmic domain of a shedding substrate can influence its proteolytic cleavage on the other side of the membrane. In this study we have characterized the association of CaM with CLS, a peptide containing both transmembrane and cytoplasmic domains of L-selectin, at the surface of a membrane bilayer.…”

“…17 In addition to shedding of L-selectin, shedding of many other proteins can also be induced by treatment of CaM inhibitors. 18–24 Like L-selectin, many of these proteins contain in their cytoplasmic domain a juxtamembrane region that is rich in basic residues and amenable to CaM association. Thus a general mechanism may underlie the shedding of these proteins induced by CaM inhibitors.…”

“…18 Furthermore, deletion of the entire TrkA cytoplasmic domain except for the juxtamembrane 7 residues, or introducing glutamate residues to a basic-rich putative CaM-binding site, did not prevent CaM inhibitor-induced shedding of TrkA. 18 Similarly, while shedding of the GPIbα subunit in the GPIb-IX receptor complex can be stimulated by CaM inhibitors, a mutation in the cytoplasmic domain of the complex that abolishes CaM association does not lead to elevated shedding of GPIbα. 25 …”

The Shedding of CD62L (L-Selectin) Regulates the Acquisition of Lytic Activity in Human Tumor Reactive T Lymphocytes

“…Specifically, the cytoplasmic tail of CD62L has been reported to interact with at least three different proteins [47] including calmodulin, α-actinin (a member of the ezrin/radixin/moesin (ERM) family of membrane-cytoskeleton cross-linkers), and protein kinase C isoenzymes. Disruption of these interactions may reduce the shedding [48] or inhibit tethering/rolling efficiencies in vitro [49].…”