Expression of tyrosine kinase Etk/Bmx and its relationship with AP-1- and NF-kappaB-associated proteins in hepatocellular carcinoma

Etk/Bmx is a cytoplasmic tyrosine kinase, which was first identified in human bone marrow cells. It has been found to play an important role in the regulation of differentiation and tumorigenicity in some cancers. The aim of this study was to investigate the significance of Etk/Bmx expression in hepatocellular carcinoma (HCC) and the relationship between Etk/Bmx and activated protein-1 (AP-1)- and nuclear factor-kappaB (NF-kappaB)-associated proteins. We used immunohistochemisty to examine 40 cases of human HCC along with corresponding nontumor tissues to assess Etk/Bmx, Jun family (c-Jun, JunB, JunD), Fos family (c-Fos, FosB, Fra-1) and NF-kappaB p65 expression in these samples. Etk/Bmx expression was present in 12 of 40 (30%) HCC specimens, 4 of which among the 25 well-differentiated tumors and 8 among the 15 poorly differentiated tumors, respectively. In contrast, 6 of 40 (15%) cases expressed Etk/Bmx in adjacent nontumor tissues. Expression level and cellular localization of Etk/Bmx were different in cancer cells and nontumor cells. Etk/Bmx expression was correlated with histological differentiation, but not with clinicopathological features including tumor size, HBV infection, cirrhosis, and metastasis. There was a close relationship between Etk/Bmx and c-Fos expression in HCC. Etk/Bmx immunopositivity was independent of c-Jun, JunD, FosB, Fra-1 and NF-kappaB p65. Our results indicated that Etk/Bmx may have different biological roles in tumor and nontumor cells, and may be involved in regulating hepatocyte differentiation by c-Fos activation in HCC.     

Attenuated expression of the serum responsive T1 gene in ras transformed fibroblasts due to the inhibition of c-fos gene activity

The T1 gene encodes a protein, which shares homology with the IL-1 receptors. In fibroblasts, T1 is induced by growth factors and in response to the onset of oncogene expression. The c-fos gene is transiently activated in these situations and was shown to be the major mediator of T1 gene induction. In contrast, the sustained expression of a ras oncogene in NIH3T3 cells resulted in the downregulation of basal T1 gene activity and the attenuation of T1 gene induction in response to mitogenic signals. Likewise, the immediate early genes encoding c-Fos, FosB, and Fra-2 are repressed in these cells. T1 gene repression could be overcome by the forced expression of c-fos in ras transformed fibroblasts. Thus, the lack of c-fos gene expression is the likely cause for ras mediated T1 gene repression. Fra-1, in contrast to the other three members of the Fos family, is permanently synthesized in high amounts in ras transformed NIH3T3 fibroblasts. We show that AP-1, which is abundant in these cells throughout the whole cell cycle, consists predominantly of Fra-1/c-Jun and Fra1/JunD heterodimers. We provide evidence that Fra1/c-Jun heterodimers are responsible for the repression of c-fos gene induction following serum stimulation. The introduction of a dominant negative version of c-Jun into ras transformed fibroblasts was able to rescue c-fos gene induction in response to serum stimulation, further demonstrating that AP-1 is indeed involved in c-fos gene repression. We conclude that oncogenic ras mediates the activation of the fra-1 gene which results in elevated AP-1 activity throughout the cell cycle. Fra-1 containing AP-1 complexes repress the c-fos and possibly other immediate early genes thereby preventing the induction of certain delayed early genes such as the T1 gene in response to mitogenic stimulation.     

Fos-related antigen 1 (Fra-1) pairing with and transactivation of JunB in GBM cells

Fos-related antigen 1 (Fra-1) plays an important role in maintenance/progression of various cancers, including glioblastoma multiforme (GBM). In this study, we used both shRNA and siRNA to examine the effect of fra-1 knockdown in GBM cells over-expressing Fra-1. Furthermore, we analyzed both the expression of JunB and its knockdown, a previously identified target for Fra-1, and also examined its potential association with Fra-1. When using fra-1 shRNA and siRNA, we found that GBM cells has Fra-1 levels diminished together with the levels of JunB, but Fra-1 remains unchanged in cells with junB knockdown. This is accompanied by dramatic changes in cell morphology and significant alteration in their migration. We next uncovered that the expression of JunB increased in response to ectopic Fra-1 and also to EGF-induced signaling, similarly to Fra-1. This was associated with an avid pairing between phosphorylated Fra-1 and JunB. Importantly, we found that Fra-1 paired with JunB binds to an AP-1 site in the junB gene promoter. JunB knockdown did not affect Fra-1 and the changes in cell morphology did not fully replicate that seen with Fra-1 knockdown. Thus, Fra-1 takes part in a control of architecture and migratory nature of GBM cells. Moreover, Fra-1 is a phosphorylated factor that transactivates JunB with which it makes effectively AP-1 pairs in GBM cells.     

AP-1在皮肤肿瘤中的表达及其意义

背景与目的：转录激活蛋白AP-1与细胞的分化、增生、调亡以及肿瘤转化密切相关。本研究探讨AP-1亚单位在皮肤肿瘤及邻近皮肤组织中的表达及其与这些肿瘤发生、发展的关系。方法：采用免疫组织化学卵蛋白-生物素-辣根过氧化物酶法对皮肤基底细胞癌、鳞形细胞癌、原位癌、角化棘皮瘤及相邻皮肤组织中的c-jun，p—c-jun、JunB、JunD，c—fos、Fra-1和Fra-2进行分析。结果：c—jun和p—c-jun在皮肤基底细胞癌、鳞形细胞癌、原位癌和角化棘皮瘤肿瘤中表达明显增强，JunB在皮肤基底细胞癌中表达明显减弱。结论：c-jun是皮肤肿瘤形成及细胞增生的促进因素，JunB则是抑制因素。