Several lines of evidence indicate that calreticulin has lectin-like properties. As a molecular chaperone, calreticulin binds preferentially to nascent glycoproteins via their immature carbohydrates; this property closely resembles that seen for calnexin, a chaperone with extensive molecular identity to calreticulin. A cell surface form of calreticulin also exhibits lectin-like properties, binding specific oligomannosides including those covalently linked to laminin. In the present study we examined the interaction between calreticulin and laminin by means of surface plasmon resonance. The results show that calreticulin specifically binds to glycosylated laminin but fails to specifically bind tunicamycin-derived unglycosylated laminin or bovine serum albumin. Calreticulin binding to glycosylated laminin requires calcium and is abolished in the presence of EDTA. Scatchard analysis of binding yields an apparent association constant, Ka, of 2.1 +/- 0.9 x 10(6) m-1 while kinetic analysis yields an estimate of the association on rate, (Kassoc), as 2 x 10(5) m-1 s-1. The composite results support calreticulin's lectin-like properties as well as its proposed role in laminin recognition, both in the cell interior and on the cell surface.
"Cell adhesion (Opas et al., 1996), integrin-dependent calcium signaling (Coppolino et al., 1997), and steroid-sensitive gene expression (Burns et al., 1994; Michalak et al., 1996) are some of the functions ascribed to the CRT residing outside endoplasmic reticulum . Cell surface localized CRT has been reported to have a lectin-like function and mediate cell spreading on glycosylated laminin (McDonnell et al., 1996). Cells lacking or under-expressing CRT are also deficient in adhesion (Szabo et al., 2009), which is consistent with previous findings of reduced CRT expression during the uterine receptive phase in non-pregnant and higher expression during the embryo-attachment stage in pregnant bonnet monkeys (Parmar et al., 2009) and of implantation failure in rodents carrying antisense oligonucleotides against CRT (Cheng et al., 2009). "
"Results from several laboratories suggest involvement of extracellular calreticulin in cell contact phenomena (White et al. 1995; McDonnell et al. 1996) and focal contact turnover (Goicoechea et al. 2000). The sources and roles of extracellular calreticulin are not clear. "
[Show abstract][Hide abstract] ABSTRACT: Cell adhesion is regulated by a variety of Ca2+-regulated pathways that depend on Ca2+-binding proteins. One such protein is calreticulin, an ER-resident protein. Calreticulin signalling from within the ER can affect processes outside the ER, such as expression of several adhesion-related genes, most notably vinculin and fibronectin. In addition, changes in the expression level of calreticulin strongly affect tyrosine phosphorylation of cellular proteins, which is known to affect many adhesion-related functions. While calreticulin has been localized to cellular compartments other than the ER, it appears that only the ER-resident calreticulin affects focal-contact-dependent adhesion. In contrast, calreticulin residing outside the ER may be involved in contact disassembly and other adhesion phenomena. Here, we review the role of calreticulin in focal contact initiation, stabilization, and turnover. We propose that calreticulin may regulate cell-substratum adhesion by participating in an "ER-to-nucleus" signalling and in parallel "ER-to-cell surface" signalling based on posttranslational events.
"In fact, CRT is considered to be a cell surface receptor for thrombspondin-1 (TSP-1) on bovine arterial endothelial cells (Goicoechea et al., 2000) and for complement component C1q (McGreal and Gasque, 2002; Ghiran et al., 2003). Further, cell surface CRT binds to the carbohydrate constituent (mannose) of the cell adhesion and basement membrane protein, laminin, important in cell migration through integrin binding (White et al., 1995; McDonnell et al., 1996). Importantly, a series of studies has shown that cell surface CRT interacts with the heparin-binding domain I of TSP-1 to mediate focal adhesion disassembly, for migration. "
[Show abstract][Hide abstract] ABSTRACT: Calreticulin (CRT), an intracellular chaperone protein crucial for the proper folding and transport of proteins through the endoplasmic reticulum, has more recent acclaim as a critical regulator of extracellular functions, particularly in mediating cellular migration and as a requirement for phagocytosis of apoptotic cells. Consistent with these functions, we show that the topical application of CRT has profound effects on the process of wound healing by causing a dose-dependent increase in epithelial migration and granulation tissue formation in both murine and porcine normal and impaired animal models of skin injury. These effects of CRTare substantiated, in vitro, as we show that CRT strongly induces cell migration/wound closure of human keratinocytes and fibroblasts, using a wound/scratch plate assay, and stimulates cellular proliferation of human keratinocytes, fibroblasts, and vascular endothelial cells, providing mechanistic insight into how CRT functions in repair. Similarly, in both animal models, the histology of the wounds show marked proliferation of basal keratinocytes and dermal fibroblasts, dense cellularity of the dermis with notably increased numbers of macrophages and well-organized collagen fibril deposition. Thus, CRT profoundly affects the wound healing process by recruiting cells essential for repair into the wound, stimulating cell growth, and increasing extracellular matrix production.
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