MYC Abrogates p53-Mediated Cell Cycle Arrest in N-(Phosphonacetyl)-l-Aspartate-Treated Cells, Permitting CAD Gene Amplification

摘要: Normal mammalian cells have complex growth controls which prevent them from progressing through the cell cycle when conditions are unfavorable or their DNA has been damaged. In tumor cells, loss of these allows various chromosomal abnormalities, including gene amplification, to accumulate. The suppressor protein p53 mediates arrest apoptosis in response damage (reviewed references 9, 28, and 31). also reversible, protective normal starvation for RNA precursors (32). This G1 occurs without replicative synthesis detectable thus contrasts with (15, 32). is involved G2/M (1, 57), ensuring that mitosis complete before next S phase begins (10), (59). protein, induced activated by stress, stimulates transcription a set genes regulate Ko Prives [28] Cox Lane [9]). large part inducing cyclin-dependent kinase inhibitor p21waf1 (16, 69) gadd45, thought mediate its interactions p21 proliferating-cell nuclear antigen (27, 53). can induce expression bax (36) fas (40) reduce bcl-2 (36), promoting apoptosis. These activities help account connection between genesis aneuploidy, aberrations, amplification tumors lines. Inactivation deletion, mutation, action viral oncogenes required allow tolerate aberrations such as Chernova et al. [8]). We now understand mechanisms well enough appreciate breakage chromosomes an important initial step (44, 63). very sensitive broken DNA, arresting few double-strand breaks gaps present (24); this helps explain why not detected (62, 68) make permissive (33, 71). contrast, frequent mechanism overexpressing mediating drug resistance lines lost (3, 56). Most immortal lines, especially those rodent origin, develop N-(phosphonacetyl)-l-aspartate (PALA) methotrexate (MTX) target carbamyl-P synthetase, aspartate transcarbamylase, dihydro-orotase (cad), dihydrofolate reductase (dhfr) (48, Inactivation deletion 71) mutation (26) inactivation oncoproteins (42, 66) achieve PALA cad cells. The REF52 line unusual because no resistant colonies formed upon selection MTX (the frequency less than 10−9 [42]). Therefore, useful identifying regulating permissivity amplification. For example, ras plus adenovirus E1A simian virus 40 (SV40) T-antigen alone converts state (42), does dominant negative mutant (26). c-MYC regulator cellular proliferation, differentiation, Grandori Eisenman [20], Packham Cleveland [41], Amati Land [4]), it frequently overexpressed tumors. Deregulated c-myc induces progression quiescent and, absence survival factors, p53-mediated (17, 22). diverse yet understood. C-MYC functions transcriptional activator complexed MAX reference 4), progression, 20). plays role repressor cyclinD1 (43), gadd45 (35), itself (18). Fewer data available regarding N-MYC, neuroblastomas (49), retinoblastomas (30), rhabdomyosarcomas (14). Since there evidence overexpression increases frequencies established (12, 34), we decided study whether deregulated MYC might different function overcoming lack introduced N-myc into selected resulting MTX. reveal exogenous abrogates PALA-induced, facilitates Using protocol involving pretreatment low concentration PALA, shown two distinct events form PALA-resistant cells: greatly increased endogenous coamplification cad.