Induction and down-regulation of PLK, a humanserine/threonine kinase expressed in proliferating cells andtumors.

Abstract

We have Identified the nucleotide sequence of the cDNA encoding the human counterpart of the moue gene Plk (polo-like kinase). . Activated Ras mediates signal transmission from receptor tyrosine kinases to a cascade of serine/threonine kinases including c-Raf, MEK, MAP kinase, and RSK (9). Many observations suggest that MAP kinase and RSK, which are located in the cytoplasm and in the nucleus, directly influence gene expression by phosphorylation of transcription factors (10, 11). Very recently, a MEK kinase independent ofRaf-1 has been described (12). Still, many components of this mitogenic cascade, such as protein kinases and many of their interactions, remain to be discovered.We and others have cloned cDNAs of novel protein kinases by using degenerate oligonucleotide primers for the PCR amplification of reverse-transcribed mRNA (13)(14)(15)(16)(17). A principal attraction of this approach is that based on conserved motifs of the kinase domain it allows amplification of protein kinases which are expressed at very low frequency. Here, we describe the PCR-based identification of a gene coding for a protein kinase from embryonic tissue. The complete cDNA was subsequently isolated from a cDNA library based on RNA from a squamous-cell lung carcinoma. The cDNA encodes a protein which seems to be the human counterpart of a mouse protein referred to as Plk (polo-like kinase) and contains structural hallmarks of protein-serine/ threonine kinases.t We show that expression of human PLK mRNA is increased in proliferating tissues like human tumors, as well as in cell lines and growth-stimulated primary cells. In quiescent cells, PLK transcripts were not found. These data suggest that PLK mRNA expression is tightly linked to proliferation.

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

“…PCR-based isolation of a Plk-related protein kinase cDNA from human embryonic tissues cDNA from human embryonic tissues was ampli®ed using degenerate primers corresponding to highly conserved aa motifs (WVXKWVDYS and DHTK-XIXC) from the polo-box of human Plk (Holtrich et al, 1994) in order to identify new Plk-related genes. One of the isolated clones (termed U1) representing an unknown gene was chosen for further studies because of its homology to Plk.…”

“…The Drosophila gene polo and the yeast cell cycle genes Cdc5 and plo1 encode related protein kinases which are required for progression through mitosis (Sunkel and Glover, 1988;Llamazares et al, 1991;Fenton and Glover, 1993;Kitada et al, 1993;Ohkura et al, 1995;Toczyski et al, 1997). In recent studies mammalian protein kinases have been identi®ed which are homologous to the Drosophila gene polo (Simmons et al, 1992;Clay et al, 1993;Lake and Jelinek, 1993;Golsteyn et al, 1994;Hamanaka et al, 1994;Holtrich et al, 1994). To date the subfamily of polo-related protein kinases encompasses the murine kinases Snk, Plk, Sak and Fnk (Simmons et al, 1992;Clay et al, 1993;Fode et al, 1994;Donohue et al, 1995) as well as the human orthologues Sak and Plk (Lake and Jelinek, 1993;Golsteyn et al, 1994;Hamanaka et al, 1994;Holtrich et al, 1994;Karn et al, 1997).…”

“…In recent studies mammalian protein kinases have been identi®ed which are homologous to the Drosophila gene polo (Simmons et al, 1992;Clay et al, 1993;Lake and Jelinek, 1993;Golsteyn et al, 1994;Hamanaka et al, 1994;Holtrich et al, 1994). To date the subfamily of polo-related protein kinases encompasses the murine kinases Snk, Plk, Sak and Fnk (Simmons et al, 1992;Clay et al, 1993;Fode et al, 1994;Donohue et al, 1995) as well as the human orthologues Sak and Plk (Lake and Jelinek, 1993;Golsteyn et al, 1994;Hamanaka et al, 1994;Holtrich et al, 1994;Karn et al, 1997). The expression of the Plk gene is tightly linked to cell proliferation and regulated during cell cycle progression (Clay et al, 1993;Lake and Jelinek, 1993;Holtrich et al, 1994).…”

“…To date the subfamily of polo-related protein kinases encompasses the murine kinases Snk, Plk, Sak and Fnk (Simmons et al, 1992;Clay et al, 1993;Fode et al, 1994;Donohue et al, 1995) as well as the human orthologues Sak and Plk (Lake and Jelinek, 1993;Golsteyn et al, 1994;Hamanaka et al, 1994;Holtrich et al, 1994;Karn et al, 1997). The expression of the Plk gene is tightly linked to cell proliferation and regulated during cell cycle progression (Clay et al, 1993;Lake and Jelinek, 1993;Holtrich et al, 1994). Several lines of evidence support an essential role of Plk in the control of cell cycledependent checkpoints during G 2 (Llamazares et al, 1991;Okhura et al, 1995;Kumagai and Dunphy, 1996).…”

RNAi-mediated gene silencing in tumour tissue using replication-competent retroviral vectors

“…[15][16][17][18][19] We show efficient and stable knockdown of marker gene expression in vitro on the fibrosarcoma cell line HT1080 stably expressing GFP or firefly luciferase (luc). We further prove the applicability of this RNAi transfer system for gene function studies of tumour biology by suppressing polo-like kinase-1 (PLK1), which is tightly linked to cell proliferation and has been proposed as a diagnostic marker for several tumours 20 and matrix metalloprotease-14 (MMP14), a key target that promotes tumour cell invasion. 21 Efficient gene silencing in vivo with preestablished subcutanous tumours is demonstrated upon intravenous injection or local administration directly into the target tissue.…”