Adhesion induced expression of the serine/threonine kinase Fnk in human macrophages

Abstract

Members of the polo subfamily of protein kinases play crucial roles in cell proliferation. To study the function of this family in more detail, we isolated the cDNA of human Fnk (FGF-inducible kinase) which codes for a serine/threonine kinase of 646 aa. Despite the homology to the proliferation-associated polo-like kinase (Plk), tissue distribution of Fnk transcripts and expression kinetics di ered clearly. In contrast to Plk no correlation between cell proliferation and Fnk gene expression was found. Instead high levels of Fnk mRNA were detectable in blood cells undergoing adhesion. The transition of monocytes from peripheral blood to matrix bound macrophages was accompanied by increasing levels of Fnk with time in culture. Neither treatment of monocytes with inducers of di erentiation nor withdrawal of serum did in¯uence Fnk mRNA levels signi®cantly, suggesting that cell attachment triggers the onset of Fnk gene transcription. The idea that Fnk is part of the signalling network controlling cellular adhesion was supported by the analysis of the cytoplasmic distribution of the Fnk protein and the in¯uence of its overexpression on the cellular architecture. Fnk as fusion protein with GFP localized at the cellular membrane in COS cells. Dysregulated Fnk gene expression disrupted the cellular f-actin network and induced a spherical morphology. Furthermore, Fnk binds to the Ca 2+ /integrin-binding protein Cib in two-hybrid-analyses and co-immunoprecipitation in assays. Moreover, both proteins were shown to co-localize in mammalian cells. The homology of Cib with calmodulin and with calcineurin B suggests that Cib might be a regulatory subunit of polo-like kinases.

Polo-like kinase isoform expression is a prognostic factor in ovarian carcinoma

“…It has been reported that PLK3 is overexpressed in adherent vs nonadherent macrophages, and that it interacts with calcium-and integrin-binding protein (CIB), a small protein involved in integrin signalling pathways (Holtrich et al, 2000). As PLK3 is also expressed in irreversible postmitotic cells like neuronal ganglion cells (data not shown), it is intriguing to speculate on the basis of data obtained in neuronal cells (Kauselmann et al, 1999) and in macrophages (Holtrich et al, 2000) that the proposed interaction of PLK3 with CIB might play a role in determining the adhesiveness of tumour cells, albeit functional evidence for such a role of PLK3 in tumours is lacking.…”

Differential regulation of polo-like kinase 1, 2, 3, and 4 gene expression in mammalian cells and tissues

“…Holtrich et al (2000) found that Plk3 transcript levels were higher in adherent primary human monocytes compared to nonadherent cells and these authors suggested that Plk3 could participate in adhesion-related signal transduction pathways. Waelput et al (2000) reported that leptin treatment of a PC12 cell line stably expressing the mouse leptin receptor induced Plk3 mRNA expression.…”

“…Three groups reported that Plk3 mRNA expression was frequently reduced in lung tumor specimens in comparison to adjacent uninvolved tissue harvested from the same patients (Li et al, 1996;Holtrich et al, 2000;Ando et al, 2004). Also, Plk3 mRNA downregulation has been detected in uterus (Ando et al, 2004), bladder (Ando et al, 2004), and head and neck squamous cell carcinoma (Dai et al, 2000) specimens.…”

The Plk3-Cdc25 circuit

“…In addition, Plk3 binds to the Ca 2 þ /integrin-binding protein Cib in two-hybrid analyses and in co-immunoprecipitation assays (Kauselmann et al, 1999), and both proteins colocalize in mammalian cells. The homology of Cib with calmodulin and with calcineurin B suggests that Cib might be a Plk regulatory subunit (Holtrich et al, 2000). Lastly, plk3 is an early inducible gene since plk3 mRNA expression in cultured cell lines is rapidly activated by mitogens (Li et al, 1996).…”

“…In addition to its nuclear functions, Plk3 clearly has cytoplasmic roles given its involvement in Golgi breakdown . Furthermore, Holtrich et al (2000) have shown that deregulated Plk3 expression disrupts the cellular Factin network and induces a spherical morphology. In addition, Plk3 binds to the Ca 2 þ /integrin-binding protein Cib in two-hybrid analyses and in co-immunoprecipitation assays (Kauselmann et al, 1999), and both proteins colocalize in mammalian cells.…”