Identifying and Characterizing a Novel Protein Kinase STK35L1 and Deciphering Its Orthologs and Close-Homologs in Vertebrates

Abstract

BackgroundThe human kinome containing 478 eukaryotic protein kinases has over 100 uncharacterized kinases with unknown substrates and biological functions. The Ser/Thr kinase 35 (STK35, Clik1) is a member of the NKF 4 (New Kinase Family 4 ) in the kinome with unknown substrates and biological functions. Various high throughput studies indicate that STK35 could be involved in various human diseases such as colorectal cancer and malaria.Methodology/Principal FindingsIn this study, we found that the previously published coding sequence of the STK35 gene is incomplete. The newly identified sequence of the STK35 gene codes for a protein of 534 amino acids with a N-terminal elongation of 133 amino acids. It has been designated as STK35L (STK35 long). Since it is the first of further homologous kinases we termed it as STK35L1. The STK35L1 protein (58 kDa on SDS-PAGE), but not STK35 (44 kDa), was found to be expressed in all human cells studied (endothelial cells, HeLa, and HEK cells) and was down-regulated after silencing with specific siRNA. EGFP-STK35L1 was localized in the nucleus and the nucleolus. By combining syntenic and gene structure pattern data and homology searches, two further STK35L1 homologs, STK35L2 (previously known as PDIK1L) and STK35L3, were found. All these protein kinase homologs were conserved throughout the vertebrates. The STK35L3 gene was specifically lost during placental mammalian evolution. Using comparative genomics, we have identified orthologous sets of these three protein kinases genes and their possible ancestor gene in two sea squirt genomes.Conclusions/SignificanceWe found the full-length coding sequence of the STK35 gene and termed it as STK35L1. We identified a new third STK35-like gene, STK35L3, in vertebrates and a possible ancestor gene in sea squirt genome. This study will provide a comprehensive platform to explore the role of STK35L kinases in cell functions and human diseases.

STK35L1 Associates with Nuclear Actin and Regulates Cell Cycle and Migration of Endothelial Cells

“…We found that the mutant EGFP-STK35L1Δ1-133 (aa 1–133 were deleted) was excluded from the nucleolus but mainly localized in the nucleus (Figure 1C). This mutant corresponds to the protein previously described as STK35 [18]. Our data indicate that the N-terminal aa 1–133 contains a functional nucleolar localization signal (NoLS) in STK35L1 that is absent in STK35.…”

“…We have previously shown that STK35L1 is mainly localized in the nucleolus and the nucleus [18]. To predict a functional nuclear localization signal (NLS) in STK35L1, the basic amino acid-rich motifs of STK35L1 were analyzed by manual comparison with known NLSs of different proteins.…”

“…Recently we identified the full length coding sequence of the STK35L1 gene which codes for a protein of 534 amino acids [18]. The biological function of STK35L1 is not known.…”

Nuclear retention of importin α coordinates cell fate through changes in gene expression

“…Full-length STK35L1 was obtained using a multistep cloning strategy as previously described (Goyal et al, 2009). Primers were 5 0 -GACAGATCTATGGGCCACCAGGAGTCTCC-3 0 (F-1), 5 0 -GGGC CTCGGCCGCCACCGGATC-3 0 (R-520), 5 0 -ATGGAAACGGGGAAGGAC GGCGCCCGC-3 0 (F-400) and 5 0 -CAAGTCGACTTAAGCAGCACATGTG ACCTG-3 0 (R-1605).…”

Serine/Threonine Kinase 35, a Target Gene of STAT3, Regulates the Proliferation and Apoptosis of Osteosarcoma Cells

“…Serine/threonine kinase 35 (STK35) is a member of the serine/threonine protein kinase family [9]. A few studies have investigated the biological function of STK35.…”