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Mutated N-ras upregulates Bcl-2 in human melanoma in vitro and in SCID mice
C Borner1, H Schlagbauer Wadl, I Fellay
1Institute of Biochemistry, University of Fribourg, Switzerland.
Abstract:
Activation of the N-ras gene by point mutation occurs in about 15% of all human melanomas. In recently established severe combined immunodeficiency (SCID) mouse xenotransplantation models for human melanoma, we demonstrated that mutated N-ras not only contributes to tumour growth by enhancing cellular proliferation, but also by blocking apoptosis. Mutated N-ras overexpression protected human melanomas from naturally occurring apoptosis and, in a more pronounced way, from chemotherapy-induced apoptosis in vitro and in vivo. Given the potential clinical importance of these findings we sought to determine the underlying mechanism. We found that mutated N-ras specifically upregulates the expression of the anti-apoptosis gene bcl-2 in two human melanoma cell lines in vitro and in SCID mice. Neither the expression of the anti-apoptotic protein Bcl-xL nor that of the pro-apoptotic proteins Bax and Bak were altered in cells expressing mutated N-Ras. The increase in Bcl-2 expression mediated by mutated ras therefore qualifies as a rational explanation for the enhanced chemoresistance of human melanoma expressing mutated N-Ras.
Insights
Mutated N-ras in melanoma enhances tumor growth by blocking apoptosis and increasing chemoresistance. This occurs by upregulating the anti-apoptosis gene BCL-2, explaining resistance in human melanoma.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- Point mutations in the N-ras gene are found in approximately 15% of human melanomas.
- Mutated N-ras promotes tumor growth by increasing cellular proliferation and inhibiting apoptosis.
Purpose of the Study:
- To investigate the underlying mechanism by which mutated N-ras confers chemoresistance in human melanoma.
- To determine if mutated N-ras affects the expression of apoptosis-regulating genes.
Main Methods:
- Utilized severe combined immunodeficiency (SCID) mouse xenotransplantation models for human melanoma.
- Assessed gene expression changes in human melanoma cell lines and xenografts in vitro and in vivo.
- Quantified the expression of anti-apoptotic (BCL-2, BCL-xL) and pro-apoptotic (Bax, Bak) genes.
Main Results:
- Mutated N-ras overexpression protected human melanomas from apoptosis, both spontaneous and chemotherapy-induced.
- Mutated N-ras specifically upregulated the expression of the anti-apoptosis gene BCL-2.
- Expression of Bcl-xL, Bax, and Bak remained unaltered by mutated N-ras expression.
Conclusions:
- Upregulation of BCL-2 by mutated N-ras is a key mechanism driving chemoresistance in human melanoma.
- Targeting the N-ras/BCL-2 pathway may offer therapeutic strategies for overcoming chemoresistance in melanoma.