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The MGSA/GRO protein is endogenously expressed in almost 70% of the melanoma cell lines and tumors, but not in normal melanocytes. We have previously demonstrated that over-expression of human MGSA/GROα, β or γ in immortalized murine melanocytes (melan-a cells) enables these cells to form tumors in SCID and nude mice. To examine the possibility that the MGSA/GRO effect on melanocyte transformation requires expression of other genes, differential display was performed. One of the mRNA's identified in the screen as overexpressed in MGSA/GRO transformed melan-a clones was the newly described M-Ras or R-Ras3 gene, a member of the Ras gene superfamily. Over-expression of MGSA/GRO upregulates M-Ras expression at both the mRNA and protein levels, and this induction requires an intact glutamine-leucine-arginine (ELR)-motif in the MGSA/GRO protein. Western blot examination of Ras expression revealed that K- and N-Ras proteins are also elevated in MGSA/GRO-expressing melan-a clones, leading to an overall increase in the amount of activated Ras. MGSA/GRO-expressing melan-a clones exhibited enhanced AP-1 activity. The effects of MGSA/GRO on AP-1 activation could be mimicked by over-expression of wild-type M-Ras or a constitutively activated M-Ras mutant in control melan-a cells as monitored by an AP-1-luciferase reporter, while expression of a dominant negative M-Ras blocked AP-1-luciferase activity in MGSA/GRO-transformed melan-a clones. In the in vitro transformation assay, over-expression of M-Ras mimicked the effects of MGSA/GRO by inducing cellular transformation in control melan-a cells, while over-expression of dominant negative M-Ras in MGSA/GROα-expressing melan-a-6 cells blocked transformation. These data suggest that MGSA/GRO-mediated transformation requires Ras activation in melanocytes. Oncogene (2000) 19, 4647–4659 [ABSTRACT FROM AUTHOR]

Oncogenic mutations in ras lead to constitutive activation of downstream signaling pathways that modulate the activities of transcription factors. In turn, these factors control the expression of a subset of genes responsible for neoplastic cell transformation. Recent studies suggest that transcription factor NF-κB contributes to cell transformation by inhibiting the cell death signal activated by oncogenic Ras. In this study, inhibition of NF-κB activity by forced expression of a super-repressor form of IκBα, the major inhibitor of NF-κB, markedly decreased the growth rate, saturation density and tumorigenicity of oncogenic H-Ras transformed rat embryo fibroblasts. Such clonally isolated cells overexpressing IκBα super-repressor not only were viable but also exhibited no sign of spontaneous apoptosis. Inhibition of NF-κB in these cells was functionally demonstrated by both the loss of cytokine induced DNA binding activity and a profoundly increased sensitivity to cell death in response to TNF-α treatment. In contrast, inhibition of NF-κB activity in non-transformed fibroblasts had minimal effect on growth, but rendered the cells resistant to a subsequent transformation by H-ras oncogene. Similar results were also obtained with rat intestinal epithelial cells harboring an inducible ras oncogene. Taken together, these findings suggest that NF-κB activity is essential for abnormal cell proliferation and tumorigenicity activated by the ras oncogene and highlight an alternative functional role for NF-κB in oncogenic Ras-mediated cell transformation that is distinct from its anti-apoptotic activity. Oncogene (2000) 19, 841–849. [ABSTRACT FROM AUTHOR]

Mutations in the ras oncogenes have been linked to many different cancers. In contrast to the extensive body of knowledge related to the genetics of ras activation, relatively little is known of the transcriptional events triggered by ras. In previous work we have used differential display to identify Mob-1, a member of α-chemokine family, as one of the immediate transcriptional targets following Ras activation. Here, we provide additional experimental evidence to support this finding by the use of an inducible H-ras expression system, the treatment of Ras farnesyl transferase inhibitor and activation of endogenous Ras by serum growth factors. We further demonstrate that IP-10, the human homolog of Mob-1, is overexpressed in the majority of colorectal cancers. [ABSTRACT FROM AUTHOR]