HMGB3 characterization in gastric cancer.

Gastric cancer is a major health problem worldwide; it is the second most common cause of cancer death in the world. Recent studies indicate that the high-mobility group (HMG) of chromosomal proteins is associated with cancer progression. However, HMGB3 has been little studied. We analyzed the co-expression network between HMGB3 and differentially-expressed genes in the GSE17187 database, identifying the relevant transcription factors, and the conserved domain of HMGB3 to understand the underlying regulation mechanisms involved in gastric cancer. Thirty-one relationships between 11 differentially-expressed genes were included in a co-expression network; many of these genes have been identified as related to cancer, including TBX5 and TFR2. Further analysis identified nine transcription factors, these being GATA3, MZF1, GATA1, GATA2, SRY, REL, NFYB, NFYC, and NFYA, which could interact with HMGB3 to regulate target gene expression and consequently regulate gastric cancer cell proliferation, migration and invasion. The HMG-box domain was very similar in various species, with only a few amino acid changes, indicating conserved functions in HMG-box. This information helps to provide insight into the molecular mechanisms of HMGB3 in human gastric cancer.

Localization and functional analysis of HmgB3p, a novel protein containing high-mobility-group-box domain from Tetrahymena thermophila.

The high-mobility-group (HMG)-box domain represents a very versatile protein domain that mediates the DNA-binding of non-sequence-specific and sequence-specific proteins. HMG-box proteins are involved in various nuclear functions, including modulating chromatin structure and genomic stability. In this study, we identified the gene HMGB3 in Tetrahymena thermophila. The predicted HmgB3p contained a single HMG-box, an SK-rich-repeat domain and a neutral phosphorylated C-terminal. HMGB3 was expressed in the growth and starvation stages. Furthermore, HMGB3 showed a higher expression levels during the conjugation stage. HMGB3 knockout strains showed no obvious cytological defects, although initiation of HMGB3 knockout strain mating was delayed and maximum mating was decreased. HA-HmgB3p localized on the micronucleus (MIC) during the vegetative growth and starvation stages. Furthermore, HA-HmgB3p specially decorated the meiotic and mitotic functional MIC during the conjugation stage. Truncated HMGB3 lacking the HMG box domain disappeared from MICs and diffused in the cytoplasm. Overexpressed HmgB3p was abnormally maintained in newly developing macronuclei and affected the viability of progeny. Taken together, these results show that HmgB3p is a germline micronuclear-specific marker protein. It may bind to micronucleus-specific DNA sequences or structures and is likely to have some function specific to micronuclei of T. thermophila.

Chromosomal high mobility group (HMG) proteins of the HMGB-type occurring in the moss Physcomitrella patens.

High mobility group (HMG) proteins of the HMGB family are chromatin-associated proteins that act as architectural factors in nucleoprotein structures, which regulate DNA-dependent processes including transcription. Members of the HMGB family have been characterised from various mono-and dicot plants, but not from lower plant species. Here, we have identified three candidate HMGB proteins encoded in the genome of the moss Physcomitrella patens. The structurally similar HMGB2 and HMGB3 proteins display the typical overall structure of higher plant HMGB proteins consisting of a central HMG-box DNA-binding domain that is flanked by a basic N-terminal and an acidic C-terminal domain. The HMGB1 protein differs from higher plant HMGB proteins by having a very extensive N-terminal domain and by lacking the acidic C-terminal domain. Like higher plant HMGB proteins, HMGB3 localises to the cell nucleus, but HMGB1 is targeted to plastids. Analysis of the HMG-box domains of HMGB1 and HMGB3 by CD revealed that HMGB1box and the HMGB3box have an alpha-helical structure. While the HMGB3box interacts with DNA comparable to typical higher plant counterparts, the HMGB1box has only a low affinity for DNA. Cotransformation assays in Physcomitrella protoplasts demonstrated that expression of HMGB3 resulted in repression of reporter gene expression. In summary, our data show that functional HMGB-type proteins occur in Physcomitrella and most likely in other lower plant species.

Phosphorylation of maize and Arabidopsis HMGB proteins by protein kinase CK2alpha.

In plants, a variety of chromatin-associated high mobility group (HMG) proteins belonging to the HMGB family have been identified. We have examined the phosphorylation of the HMGB proteins from the monocotyledonous plant maize and the dicotyledonous plant Arabidopsis by protein kinase CK2alpha. Maize CK2alpha phosphorylates the maize HMGB1 and HMGB2/3 proteins and the Arabidopsis HMGB1, HMGB2/3, and HMGB4 proteins. Maize HMGB4 and HMGB5 and Arabidopsis HMGB5 are not phosphorylated by CK2alpha. Depending on the HMGB protein up to five amino acid residues are phosphorylated in the course of the phosphorylation reaction. The HMGB1 proteins from both plants are markedly more slowly phosphorylated by CK2alpha than the other HMGB substrate proteins, indicating that certain HMGB proteins are clearly preferred substrates for CK2alpha. The rate of the phosphorylation reaction appears to be related to the ease of interaction between CK2alpha and the HMGB proteins, as indicated by chemical cross-linking experiments. MALDI/TOF mass spectrometry analyses demonstrate that the HMGB1 and HMGB2/3 proteins occur in various phosphorylation states in immature maize kernels. Thus, HMGB1 exists as monophosphorylated, double-phosphorylated, triple-phosphorylated, and tetraphosphorylated protein in kernel tissue, and the tetraphosphorylated form is the most abundant version. The observed in vivo phosphorylation states indicate that protein kinase(s) other than CK2alpha contribute(s) to the modification of the plant HMGB proteins. The fact that the HMGB proteins are phosphorylated to various extents reveals that the existence of differentially modified forms increases the number of distinct HMGB protein variants in plant chromatin that may be adapted to certain functions.