Zyxin and cCRP: two interactive LIM domain proteins associated with the cytoskeleton.

Abstract

Abstract. Interaction with extraceUular matrix can trigger a variety of responses by cells including changes in specific gene expression and cell differentiation. The mechanism by which cell surface events are coupled to the transcriptional machinery is not understood, however, proteins localized at sites of cell-substratum contact are likely to function as signal transducers. We have recently purified and characterized a low abundance adhesion plaque protein called zyxin (Crawford, A. W., and M. C. Beckerle. 1991. J. Biol. Chem. 266:5847-5853; Crawford, A. W., J. W. Michelsen, and M. C. Beckerle. 1992. J. Cell Biol. 116:1381-1393. We have now isolated and sequenced zyxin cDNA and we report here that zyxin exhibits an unusual proline-rich NH2-terminus followed by three tandemly arrayed LIM domains. LIM domains have previously been identified in proteins that play important roles in transcriptional regulation and cellular differentiation. LIM domains have been proposed to coordinate metal ions and we have demonstrated by atomic absorption spectroscopy that purified zyxin binds zinc, a result consistent with the idea that zyxin has zinc fingers. In addition, we have discovered that zyxin interacts in vitro with a 23-kD protein that also exhibits LIM domains. Microsequence analysis has revealed that the 23-kD protein (or cCRP) is the chicken homologue of the human cysteine-rich protein (hCRP). By double-label indirect immunofluorescence, we found that zyxin and cCRP are extensively colocalized in chicken embryo fibroblasts, consistent with the idea that they interact in vivo. We conclude that LIM domains are zinc-binding sequences that may be involved in protein-protein interactions. The demonstration that two cytoskeletal proteins, zyxin and cCRP, share a sequence motif with proteins important for transcriptional regulation raises the possibility that zyxin and cCRP are components of a signal transduction pathway that mediates adhesion-stimulated changes in gene expression.

Inhibition of activated Ras-induced neuronal differentiation of PC12 cells by the LIM domain of LIM-kinase 1

“…Paxillin binds to cytoskeletal component proteins, such as vinculin, talin and pp125 FAK , and zyxin binds to a-actinin, through the regions outside of the LIM domains Turner and Miller, 1994;Salgia et al, 1995), while zyxin and CRP are associated with each other through LIM ± LIM interactions (Sadler et al, 1992;Schmeichel and Beckerle, 1994). As the LIM domains are thought to function as the interface in proteinprotein interactions, the LIM domains of cytoskeletal LIM proteins are likely involved in their binding to cytoskeletal component proteins or regulatory proteins, and thus may contribute to the regulation of cytoskeletal reorganization.…”

TPO1, a Member of a Novel Protein Family, Is Developmentally Regulated in Cultured Oligodendrocytes

“…Although the zinc-finger motif had originally been thought of as a DNA binding domain, more recent evidence suggests that it also facilitates protein-protein interactions (Sehmeichel and Beekerle, 1994). The LIM domain, for example, occurs in a variety of proteins with diverse functions and subcellular distributions, including transcription factors, protooncogene products, components of adhesion plaques, and the actin-based cytoskeleton (Sadler et al, 1992;Crawford et al, 1994). In a similar manner, the members of the RING-finger family have been reported to function as transforming agents, as facilitators of protein-protein interactions (Freemont, 1993), and as regulators of development and cell differentiation (Cheng et al, 1995;Yoon et al, 1995).…”

Isolation, tissue expression, and chromosomal assignment of a human LIM protein gene, showing homology to rat Enigma homologue (ENH)

“…LIM domain proteins have been implicated in developmental regulation, cellular differentiation, and actin-based cytoskeletal interaction (Sadler et al 1992;Crawford et al 1994;Sanchez-Garcia and Rabbitts 1994). Spectroscopic studies of LIM domains derived from a number of different proteins have revealed that the LIM domain specifically coordinates two zinc ions (Michelsen et al 1993Archer et al 1994;Kosa et al 1994).…”