Repression of in vivo growth of Myc/Ras transformed tumor cells by Mad1

Abstract

The Myc/Max/Mad network of transcriptional regulatory proteins plays an essential role in cell proliferation, growth, apoptosis, and di erentiation. Whereas Myc proteins a ect cell cycle progression positively, Mad proteins are negative regulators of cell proliferation. It has been shown in several in vitro systems that Mad proteins antagonize c-Myc functions. In this report we describe the inhibition of tumor cell outgrowth in vivo by Mad1 expression. Transformed cell lines were generated by co-transfection of c-myc, c-H-ras, and a chimeric mad1ER construct into primary rat embryo cells (MRMad1ER cells). Activation of Mad1 by 4-Hydroxy-Tamoxifen (OHT) resulted in abrogation of telomerase activity, reduced cloning e ciency, and decreased proportion of cells in S phase. Injection of MRMad1ER cells into syngenic rats induced aggressively growing tumors after a short latency period. This tumor growth was inhibited by OHT-treatment of animals, with the extent of inhibition correlating with the amount of OHT injected. No e ect of OHT on tumor growth was observed with similarly transformed Myc/Ras cell lines which did not express Mad1ER. These data demonstrate that Mad1 is able to suppress Myc/Ras-mediated transformation under in vivo conditions.

Induction of Mxi1-SRα by FOXO3a Contributes to Repression of Myc-Dependent Gene Expression

“…Mxi1-SR␤ has been shown to inhibit proliferation of prostate carcinoma and glioblastoma cell lines when overexpressed (67,73). Similarly, Mad1 overexpression inhibits proliferation in different cell lines (31,57) and blocks Myc/Ras-dependent tumor formation (11).…”

Inhibitor of apoptosis protein (IAP) survivin is upregulated by oncogenic c-H-Ras

“…Since the oncogene-transfected REC cultures were replated at a defined cell number, immediate effects of the survivin-antisense construct on cellular viability did not bias the results. Thus, the proven cooperation of cmyc with c-H-ras in primary REC (Land et al, 1983;Cerni et al, 1995Cerni et al, , 2002Simonitsch et al, 2001) was hampered by reduced amounts of endogenous survivin. We are currently investigating whether survivin is also important for other oncogene cooperation models.…”

“…A rare c-H-ras-only transformed cell line (R-1) was also included in the analysis, and normal, nontransfected rat embryo cells (RECs) served as control. Expression of transgenes was verified by Northern-and Western blot analysis (Cerni et al, 1990(Cerni et al, , 1995(Cerni et al, , 2002; and data not shown).…”

“…Cells were cultured in DMEM, P/S and 10% FCS, in presence of G418 (200 mg/ml). The cell lines, subjected to survivin analysis, were chosen at random from a large collection of established cell clones piled up in the last years, which had been generated as neo-resistant clonal isolates from different preparations of primary REC (Cerni et al, 1990(Cerni et al, , 1995(Cerni et al, , 2002. All cell lines were used at low passage numbers, that is, between transfer 8 and 20 after clonal isolation.…”

In silico whole-genome scanning of cancer-associated nonsynonymous SNPs and molecular characterization of a dynein light chain tumour variant

“…Interestingly, we identified a first nsSNP in mitotic-arrest-deficient MAD-1 protein, a transcriptional repressor of MYC target genes, and another in the product of one of the MYC target genes, namely the translation initiation factor eIF-2. Translation initiation factor IF-2 was shown to be involved in transformation when its function is upregulated (Rosenwald et al, 1993;Rosenwald, 1996), while MYC antagonist MAD-1 acts as a tumour suppressor in a variety of cell lines (Ayer et al, 1993;Roussel et al, 1996;Cerni et al, 2002). Notably, the Arg to His change at position 558 identified in the MAD-1 protein has also been reported as an uncommon polymorphism in a case study of lung cancer (Nomoto et al, 1999).…”