High-mobility-group proteins and cancer--an emerging link

Expression levels of HMGA2 and CD9 and its clinicopathological significances in the benign and malignant lesions of the gallbladder

Background

The objective of this study was to investigate CD9 and HMGA2 expression and its clinicopathological significance in benign and malignant lesion tissues of the gallbladder.

Methods

The resected specimens of 108 cases of gallbladder adenocarcinoma, 46 cases of adjacent tissue, 15 cases of polyps and 35 cases of chronic cholecystitis were made into conventional paraffin-embedded sections, using the method of EnVision immunohistochemistry to stain HMGA2 and CD9.

Results

HMGA2 expression of gallbladder adenocarcinoma was significantly higher than that of adenocarcinoma adjacent tissues (= 16.13, P <0.01), polyps (= 8.19, P <0.01) and chronic cholecystitis (= 21.41, P <0.01); but CD9 expression was the opposite (P <0.05 or P <0.01). The positive rate of HMGA2 expression from the cases that had well-differentiated adenocarcinoma, with the largest tumor diameter <2 cm, and without lymph node metastasis, and that did not invade the surrounding tissue was significantly lower than that of HMGA2 expression from the cases that had poorly differentiated adenocarcinoma, with the largest tumor diameter ≥2 cm, lymph node metastasis, and that invaded the surrounding tissues (P <0.05 or P <0.01). The positive rate of CD9 expression from the cases that had well-differentiated adenocarcinoma, with the largest tumor diameter <2 cm, and without lymph node metastasis, and that did not invade the surrounding tissue was significantly higher than that of CD9 expression from the cases that had poorly differentiated adenocarcinoma, with the largest tumor diameter ≥2 cm, lymph node metastasis, and which invaded the surrounding tissues (P <0.05 or P <0.01). The Kaplan-Meier survival analysis showed that after surgery, the survival period of HMGA2 expression-positive cases was significantly lower than that of HMGA2 expression- negative cases (P = 0.020), but the survival period of CD9 expression-positive cases was significantly higher than that of cases with CD9 expression-negative (P = 0.019). Cox multivariate regression analysis showed that the HMGA2 positive expression and/or CD9 negative expression was an important indicator reflecting the poor prognosis of gallbladder cancer.

Conclusion

The expression of HMGA2 and/or CD9 might be closely related to the carcinogenesis, clinical biological behaviors and prognosis of gallbladder adenocarcinoma.

Derepression of HMGA2 gene expression in retinoblastoma is associated with cell proliferation

To assess whether retinoblastoma formation is associated with the expression of high mobility group (HMG) A2 protein, a transcription factor that is highly expressed during embryogenesis and completely repressed in normal adult tissues, we performed Northern and Western blots and RT-PCR analyses, and immunohistochemistry to test for HMGA2 expression. We used established retinoblastoma cell lines in tumors grown in nude mice and clinical retinoblastoma specimens, and contrasted these tumors with normal embryonic and adult retina. Adenoviral-mediated antisense experiments were conducted on the retinoblastoma cell lines to suppress HMGA2 expression and determine if cell proliferation is HMGA2-dependent. We also transfected a retinoblastoma cell line to identify cis-regulatory elements and transcription initiation sites on the HMGA2 gene promoter. HMGA2 gene expression was silenced in terminally differentiated retina of 6-wk-old mice, but it was detected in retina of a 13.5-d postcoitum embryo. Reactivation of HMGA2 gene expression was observed in the retinoblastoma cell lines Y79, WERI-Rb1, and TOTL-1, in tumors derived from some of these cells propagated in nude mice, and in a high frequency of retinoblastomas excised from human patients. This suggests that expression of HMGA2 gene in retinoblastoma cells involves a derepression process. By using an antisense approach to block HMGA2 expression, we observed a decrease in the number of proliferating retinoblastoma cells. As a 1st step toward understanding HMGA2 gene reactivation in retinoblastoma, we mapped the 2 transcription initiation sites and associated positive regulatory elements within the WERI-Rb1 cells. Our discovery of derepression of HMGA2 gene expression in retinoblastoma provides the 1st evidence that this protein might contribute to neoplastic transformation of retina cells.

The HMG I proteins: dynamic roles in gene activation, development, and tumorigenesis

The high mobility group I, Y, and I-C proteins are low-molecular-weight, nonhistone chromosomal proteins that play a general role modulating gene expression during development and the immune response. Consistent with their role in early development, all three proteins are expressed at high levels during embryogenesis, and their expression is markedly diminished in differentiated cells. Exceptions to the general repression of these genes in adult tissues involve (1) A burst of synthesis of the HMG I protein during the immune response (during lymphocyte activation and preceding cytokine/adhesion molecule gene expression), (2) A constitutive expression of the HMG I and Y proteins in photoreceptor cells, and (3) Derepression of HMG I, Y, and often I-C expression in neoplastic cells. Work from several laboratories has now uncovered how these proteins participate in gene activation: (1) By altering the chromatin structure around an inducible gene-and thus influencing accessibility of the locus to regulatory proteins-(2) By facilitating the loading of transcription factors onto the promoters, and (3) By bridging adjacent transcription factors on a promoter via protein/protein interactions. Despite the similar structures and biochemical properties of the three proteins, the work has also provided clues to a division of labor between these proteins. HMG I and Y have demonstrable roles in enhanceosome formation, whereas HMG I-C has a specific role in adipogenesis. C-terminal truncations of HMG I-C and wild-type HMG Y appear to function in a manner analogous to oncogenes, as assessed by cellular transforation assays and transgenic mice. Future work should clearly define the similarities and differences in the biological roles of the three proteins, and should evolve to include attempts at pharmaceutical intervention in disease, based upon structural information concerning HMG I interactions with DNA and with regulatory proteins.

Specific binding of high-mobility-group I (HMGI) protein and histone H1 to the upstream AT-rich region of the murine beta interferon promoter: HMGI protein acts as a potential antirepressor of the promoter

The high-mobility-group I (HMGI) protein is a nonhistone component of active chromatin. In this work, we demonstrate that HMGI protein specifically binds to the AT-rich region of the murine beta interferon (IFN-beta) promoter localized upstream of the murine virus-responsive element (VRE). Contrary to what has been described for the human promoter, HMGI protein did not specifically bind to the VRE of the murine IFN-beta promoter. Stably transfected promoters carrying mutations on this HMGI binding site displayed delayed virus-induced kinetics of transcription. When integrated into chromatin, the mutated promoter remained repressed and never reached normal transcriptional activity. Such a phenomenon was not observed with transiently transfected promoters upon which chromatin was only partially reconstituted. Using UV footprinting, we show that the upstream AT-rich sequences of the murine IFN-beta promoter constitute a preferential binding region for histone H1. Transfection with a plasmid carrying scaffold attachment regions as well as incubation with distamycin led to the derepression of the IFN-beta promoter stably integrated into chromatin. In vitro, HMGI protein was able to displace histone H1 from the upstream AT-rich region of the wild-type promoter but not from the promoter carrying mutations on the upstream high-affinity HMGI binding site. Our results suggest that the binding of histone H1 to the upstream AT-rich region of the promoter might be partly responsible for the constitutive repression of the promoter. The displacement by HMGI protein of histone H1 could help to convert the IFN-beta promoter from a repressed to an active state.