Nuclear onco-protein targets of signal transduction pathways

Basic fibroblast growth factor-induced neuronal differentiation of mouse bone marrow stromal cells requires FGFR-1, MAPK/ERK, and transcription factor AP-1

It has been reported recently that bone marrow stromal cells (BMSCs) are able to differentiate into various neural cells both in vivo and in vitro (Egusa, H., Schweizer, F. E., Wang, C. C., Matsuka, Y., and Nishimura, I. (2005) J. Biol. Chem. 280, 23691-23697). However, the underlying mechanisms remain largely unknown. In this report, we have demonstrated that basic fibroblast growth factor (bFGF) alone effectively induces mouse BMSC neuronal differentiation. These differentiated neuronal cells exhibit characteristic electrophysiological properties and elevated levels of the neuronal differentiation marker, growth-associated protein-43 (GAP-43). To explore possible signaling pathways, we first analyzed the expression of various FGF receptors in mouse BMSCs. FGF receptor-1, -2, and -3 were detected, but only FGFR-1 was shown to be activated by bFGF. Small interfering RNA knock down of FGFR-1 in BMSCs significantly inhibited neuronal differentiation. Moreover, we have shown that the mitogen-activated protein kinase (ERK1/2) is persistently activated and blockage of ERK activity with the ERK-specific inhibitor U0126 prevents neuronal differentiation. It appears that activation of ERK cascade and neuronal differentiation of BMSCs induced by bFGF are independent of Ras activity but require functions of phospholipase C-gamma pathway. Lastly, we examined the role of the immediate-early transcription factors AP-1 and NF-kappaB and have found that phospholipase C-gamma-dependent c-Jun and ERK-dependent c-fos, but not the NF-kappaB, are strongly activated by bFGF, which in turn regulates the neuronal differentiation of BMSCs.

An association of a simultaneous nuclear and cytoplasmic localization of Fra-1 with breast malignancy

Background

Overexpression of Fra-1 in fibroblasts causes anchorage-independent cell growth and oncogenic transformation. A high level of Fra-1 expression is found in various tumors and tumorigenic cell lines, suggesting that Fra-1 may be involved in malignant progression. This study aimed to investigate the significance of Fra-1 expression in breast carcinogenesis.

Methods

The expression of Fra-1 was investigated by immunohistochemistry in neoplastic breast diseases ranging from benign fibroadenoma to very aggressive undifferentiated carcinoma. The correlations of Fra-1 expression with other indicators of breast carcinoma prognosis (ER, PR and ErbB2 receptors) were analyzed.

Results

All neoplastic breast tissues, either benign or malignant breast tissues, were nuclear immunoreactive for Fra-1-recognizing antibody. The pattern of Fra-1 expression by benign neoplastic cells was predominantly nuclear. However, the nuclear/cytoplasmic concomitant immunoreactivity was observed in all types of breast carcinomas. A clear shift in Fra-1 immunoreactivity, from an exclusively nuclear to a simultaneous nuclear and cytoplasmic localization was noticed in ~90% of breast carcinomas.

Conclusion

The overall expression, pattern and intensity of Fra-1 proteins were correlated with breast oncogenesis. Overexpression of Fra-1, leading to a persistent high cytoplasmic accumulation, may play a role in the process of breast carcinogenesis.

Intracellular oxidation/reduction status in the regulation of transcription factors NF-kappaB and AP-1

The eukaryotic cell contains a multitude of pathways coupling environmental stimuli to the specific regulation of gene expression. Two early response transcriptional complexes, NF-kappaB and AP-1, appear to respond to environmental stressors by inducing the expression of response specific downstream genes. Both are well-characterized transcriptional regulatory factors that are induced by a wide variety of seemingly unrelated exogenous and endogenous agents and serve important roles in cell growth and differentiation, immunity, inflammation, and other preprogrammed cellular genetic processes. The activities of NF-kappaB and AP-1 are also affected following exposure to chemicals, drugs, or other agents that appear to alter the cellular oxidation/reduction (redox) status. From these observations, it has been suggested that changes in cellular oxidation/reduction status, communicated via a series of cellular redox-sensitive signaling circuitry employing metal- and thiol-containing proteins, serve as common mechanisms linking environmental stressors to adaptive cellular responses. As such, these transcription factors are ideal paradigms to study the mechanism and possible physiological significance of early response genes in the cellular response to changes in cellular redox status. In this article we summarize the evidence suggesting that cellular redox regulates these transcription factors.