HNRNPK (heterogeneous nuclear ribonucleoprotein K)

	Fig.1 HnRNPK structure. The rectangles represent K homology domains (KH1, 2, 3), the K interactive region (KI), the nuclear localization signal (NLS) and the nuclear shuttling domain (KNS).
Description	The hnRNPK protein (65kDa) is structurally related to four other poly(C)-binding proteins (PCBP) which contain three K homology (KH) domains that enable RNA and DNA binding with a high affinity towards polycytosine tracts. The KH domain is about 70 amino acids in length and is found in a variety of proteins from archaea through higher eukaryotes. hnRNPK also carries a nuclear localisation signal (NLS) and a nuclear shuttling domain (KNS) together which allow it to translocate between the cytoplasm and nucleus. It also contains a segment called the K protein interactive (KI) region, located between the KH2 and KH3 domain, which has an intrinsically disordered structure. This domain is not found in the other PCBP proteins and is responsible for many of the known hnRNPK protein-protein interactions (Bomsztyk et al., 2004).
Expression	K protein is an abundant factor.
	Fig.2 HnRNPK expression patterns in normal and cancer tissues based on human EST sequence abundance derived from the GeneHub-GEPIS database.
Localisation	Predominantly in the nucleus and cytoplasm; also found in mitochondria and plasma membrane.
Function	The functions of hnRNPK are defined by its modular structure that allows it to interact with both nucleic acids and proteins. It has been suggested that hnRNPK serves as a docking platform that facilitates the interaction between the molecular partners involved in the processes that compose gene expression, such as transcription and translation regulation, mRNA processing and chromatin remodeling (Bomsztyk et al., 2004). With regard to the factors implicated in the process of tumorgenesis, hnRNPK acts as a transcription activator for the CT element in the human c-myc promoter (Michelotti et al., 1996), the BRCA1 promoter (Thakur et al., 2003) and the basal promoter of the Eukaryotic translation initiation factor 4E - eIF-4E (Lynch et al., 2005). In response to DNA damage, hnRNPK is transiently recruited to the promoters of p53-responsive genes (p21) where it acts as a cofactor of TP53 protein and is required for triggering transcriptional activation (Moumen et al., 2005). A recent study identified K protein as a regulator of androgen receptor (AR) expression levels; it represses AR expression and androgen-induced prostate cancer cell growth through translational regulation of AR mRNA (Mukhopadhyay et al., 2009). In a loss-of-function screening system based on intracellular expression of single domain antibodies, hnRNPK was found as a potential target for cell migration and metastasis of human cancerous cells (Inoue et al., 2007).
Homology	Shares homology with four other PCBP proteins which contain three KH domains.

Search in all EBI   NCBI

For comments and suggestions or contributions, please contact us