Alternative titles; symbols
HGNC Approved Gene Symbol: PKNOX2
Cytogenetic location: 11q24.2 Genomic coordinates (GRCh38) : 11:125,164,751-125,433,389 (from NCBI)
Homeodomain proteins are sequence-specific transcription factors that share a highly conserved DNA-binding domain and play fundamental roles in cell proliferation, differentiation, and death. PKNOX2 belongs to the TALE (3-amino acid loop extension) class of homeodomain proteins characterized by a 3-amino acid extension between alpha helices 1 and 2 within the homeodomain (Imoto et al., 2001).
By searching databases for sequences similar to PKNOX1 (602100), followed by RT-PCR of human brain mRNA, Imoto et al. (2001) cloned PKNOX2. The deduced 460-amino acid protein has a calculated molecular mass of 50.8 kD. PKNOX2 contains 2 N-terminal regions, HR1 and HR2, homologous to regions in PKNOX1 and MEIS proteins (see 601739), followed by an atypical homeodomain characteristic of TALE family members and a C-terminal lysine-rich nuclear localization signal. The homeodomains of PKNOX1 and PKNOX2 share 94% identity. Northern blot analysis detected a 4.6-kb PKNOX2 transcript. Expression was highest in brain and skeletal muscle, moderate in pancreas, lung, heart, kidney, small intestine, thymus, spleen, and kidney, and very low in colon, liver, and peripheral blood leukocytes. The expression pattern of PKNOX2 differed from that of PKNOX1, suggesting that the proteins have distinct roles. Epitope-tagged PKNOX2 was expressed in the nucleus, but not in nucleoli, of transfected COS-7 cells.
By RT-PCR of human fetal mRNA, Fognani et al. (2002) cloned PKNOX2, which they called PREP2. The deduced protein contains 461 amino acids. Northern blot analysis showed highest expression of a 4-kb PREP2 transcript in heart, brain, skeletal muscle, and ovary. Lower expression was detected in placenta, lung, pancreas, prostate, testis, and small intestine, and no expression was detected in liver, kidney, spleen, thymus, colon, and peripheral blood leukocytes. A transcript of 7 to 8 kb was also detected in testis. In vitro synthesized PREP2 had an apparent molecular mass of 70 kD. In the absence of PBX1 (176310), epitope-tagged PREP2 was expressed predominantly in the cytoplasm of transfected mouse fibroblasts and insect cells.
Haller et al. (2004) cloned multiple splice variants of mouse Prep2, and the encoded isoforms differed at their N- and C-terminal ends. Western blot and immunohistochemical analyses of mouse embryos and several mammalian cell lines using antibodies that recognized either the N- or C-terminal halves of full-length Prep2 detected proteins with the N terminus in the cytoplasm and proteins with the C terminus in the nucleus.
Fognani et al. (2002) showed that PREP2 bound a synthetic DNA sequence containing a binding site for PREP1-PBX complexes when coexpressed with either of 2 PBX1 isoforms, PBX1a or PBX1b. Similarly, PREP2 bound an oligonucleotide from the Hoxb2 (142967) gene enhancer when coexpressed with HOXB1 (142968) and PBX1a. PREP2 could also form a ternary complex with HOXB1 and PBX1b. However, unlike PREP1, coexpression of PREP2 reduced reporter activity of the HOXB1-PBX1 complex. Fognani et al. (2002) concluded that PREP2, like PREP1, recognizes the sequence TGACAG and can bind this sequence in a ternary complex with PBX1 and HOXB1.
Using mouse fibroblasts transfected with epitope-tagged constructs, Haller et al. (2004) showed that the N-terminal domain of mouse Prep2 interacted with cytoskeletal elements, including microtubules at all stages of mitosis. Coimmunoprecipitation analysis showed that the N terminus of Prep2 also interacted with F-actin and G-actin (see 102610). Disruption of actin or microtubule cytoskeletal elements resulted in dose-dependent relocalization of epitope-tagged Prep2 to the nucleus, including nucleoli, under certain conditions.
Imoto et al. (2001) determined that the PKNOX2 gene contains at least 10 exons. Fognani et al. (2002) reported that the PKNOX2 gene spans about 50.7 kb.
Using FISH, Imoto et al. (2001) mapped the PKNOX2 gene to chromosome 11q24-q25.
Fognani, C., Kilstrup-Nielsen, C., Berthelsen, J., Ferretti, E., Zappavigna, V., Blasi, F. Characterization of PREP2, a paralog of PREP1, which defines a novel sub-family of the MEINOX TALE homeodomain transcription factors. Nucleic Acids Res. 30: 2043-2051, 2002. [PubMed: 11972344] [Full Text: https://doi.org/10.1093/nar/30.9.2043]
Haller, K., Rambaldi, I., Daniels, E., Featherstone, M. Subcellular localization of multiple PREP2 isoforms is regulated by actin, tubulin, and nuclear export. J. Biol. Chem. 279: 49384-49394, 2004. [PubMed: 15339927] [Full Text: https://doi.org/10.1074/jbc.M406046200]
Imoto, I., Sonoda, I., Yuki, Y., Inazawa, J. Identification and characterization of human PKNOX2, a novel homeobox-containing gene. Biochem. Biophys. Res. Commun. 287: 270-276, 2001. [PubMed: 11549286] [Full Text: https://doi.org/10.1006/bbrc.2001.5578]