An Essential Domain of the c-Myc Protein Interacts with a Nuclear Factor That Is Also Required for E1A-Mediated Transformation

Abstract

Cell transformation by nuclear oncogenes such as c-myc presumably involves the transcriptional activation of a set of target genes that participate in the control of cell division. The function of a small evolutionarily conserved domain of the c-myc gene encompassing amino acids 129 to 145 was analyzed to explore the relationship between cell transformation and transcriptional activation. Deletion of this domain inactivated the c-myc oncogene for cell transformation while retaining the ability to activate transcription of either myc consensus binding sites or a GAL4-dependent promoter when the c-myc N-terminus was fused to the GAL4 DNA-binding domain. Point mutations that altered a conserved tryptophan (amino acid 136) within this domain had similar effects. Expression of the wt c-Myc N terminus (amino acids 1 to 262) as a GAL4 fusion was a dominant inhibitor of cell transformation by the c-myc oncogene, and this same domain also inhibited transformation by the adenovirus E1A gene. Surprisingly, deletion of amino acids 129 to 145 eliminated the dominant negative activity of GAL4-Myc on both c-myc and E1A transformation. Expression of the GAL4-Myc protein in Cos cells led to the formation of a specific complex between the Myc N terminus and a nuclear factor, and this complex was absent with the dl129-145 mutant. These results suggest that an essential domain of the c-Myc protein interacts with a specific nuclear factor that is also required for E1A transformation.

Myc represses the growth arrest gene gadd45

“…The identi®cation of Myc-suppressed target genes is of fundamental importance, as recent studies have linked Myc repression of gene transcription with Myc induced transformation (Brough et al, 1995;Lee et al, 1996;Li et al, 1994). Indeed, we show that the region of the human cMyc protein, amino acids 106 to 143, required for Myc-suppression of gadd45, is also required for Myc-induced cell cycle progression, and cellular transformation Freytag et al, 1990;Garte, 1993;Penn et al, 1990b;Stone et al, 1987).…”

“…Recent structure-function analysis of the aminoterminus of the c-Myc protein shows Myc repression and Myc transactivation are separable, with Myc repression being more closely associated with neoplastic transformation (Brough et al, 1995;Lee et al, 1996;Li et al, 1994;Penn et al, 1990b). Myc can repress C/EBPa (Antonson et al, 1995;Li et al, 1994), cyclin D1 (Philipp et al, 1994), the adenovirus 5 major-late promoter (AdMLP) (Li et al, 1994), and cmyc (Facchini et al, 1997) promoter activities.…”

Genetic dissection of c-myc apoptotic pathways

“…(*) indicates that the TAD requirements for proper ODC regulation were determined from assays performed on cellular enzyme levels shown in Figure 4 MBI, although cooperativity in the double mutant D2 ± 42/70 ± 130 was seen. Interestingly, none of the apoptotic responses studied here required MBII which is otherwise essential for transformation and for the restoration of normal growth in c-myc-de®cient ®broblasts (Brough et al, 1995;MacGregor et al, 1996;Cole and McMahon, 1999). Furthermore, MBII deletion has been reported not to a ect the ability of c-myc to up-regulate synthetic reporters containing c-myc E-box elements.…”

“…A number of studies have identi®ed proteins which interact with some of these regions and which can alter various cmyc activities (Facchini and Penn, 1998). Other work has shown that deletion of MBII leaves intact the ability of c-myc to activate at least some c-myc-responsive promoters but impairs its ability to down-regulate others and to transform primary rat embryo ®broblasts in association with an activated ras oncogene (Stone et al, 1987;Li et al, 1994;Brough et al, 1995;MacGregor et al, 1996). However, although MBII may be necessary for c-myc-mediated transformation, it is clearly not su cient as certain deletions in more N-terminal segments of the TAD can profoundly a ect transforming activity (Stone et al, 1987).…”

MYC oncogenes and human neoplastic disease

“…It was originally proposed that this was due to L-myc possessing a weaker TAD than either cmyc or N-myc (Barrett et al, 1992). However, it is now known that the so-called`Myc Box II' domain of cmyc is required for transformation but not for transactivation (Li et al, 1994;Brough et al, 1995;MacGregor et al, 1996). It would therefore appear that di erences in TAD strength are not directly responsible for the di erences in cooperativity with ras.…”