Showing papers by "Christoph Lengauer published in 1999"

Disruption of p53 in human cancer cells alters the responses to therapeutic agents

Abstract: We have examined the effects of commonly used chemotherapeutic agents on human colon cancer cell lines in which the p53 pathway has been specifically disrupted by targeted homologous recombination. We found that p53 had profound effects on drug responses, and these effects varied dramatically depending on the drug. The p53-deficient cells were sensitized to the effects of DNA-damaging agents as a result of the failure to induce expression of the cyclin-dependent kinase inhibitor p21. In contrast, p53 disruption rendered cells strikingly resistant to the effects of the antimetabolite 5-fluorouracil (5-FU), the mainstay of adjuvant therapy for colorectal cancer. The effects on 5-FU sensitivity were observed both in vitro and in vivo, were independent of p21, and appeared to be the result of perturbations in RNA, rather than DNA, metabolism. These results have significant implications for future efforts to maximize therapeutic efficacy in patients with defined genetic alterations.

14-3-3σ is required to prevent mitotic catastrophe after DNA damage

Abstract: 14-3-3Sigma is a member of a family of proteins that regulate cellular activity by binding and sequestering phosphorylated proteins. It has been suggested that 14-3-3sigma promotes pre-mitotic cell-cycle arrest following DNA damage, and that its expression can be controlled by the p53 tumour suppressor gene. Here we describe an improved approach to the generation of human somatic-cell knockouts, which we have used to generate human colorectal cancer cells in which both 14-3-3sigma alleles are inactivated. After DNA damage, these cells initially arrested in the G2 phase of the cell cycle, but, unlike cells containing 14-3-3sigma, the 14-3-3sigma-/- cells were unable to maintain cell-cycle arrest. The 14-3-3sigma-/- cells died ('mitotic catastrophe') as they entered mitosis. This process was associated with a failure of the 14-3-3sigma-deficient cells to sequester the proteins (cyclin B1 and cdc2) that initiate mitosis and prevent them from entering the nucleus. These results may indicate a mechanism for maintaining the G2 checkpoint and preventing mitotic death.

Netrin-1: Interaction with Deleted in Colorectal Cancer (DCC) and Alterations in Brain Tumors and Neuroblastomas

Abstract: Netrins, a family of laminin-related secreted proteins, have critical roles in axon guidance and cell migration during development. The deleted in colorectal cancer (DCC) protein has been implicated as a netrin-1 receptor component. The expression and function of netrins in adult tissues remain unknown, and direct interaction of netrin-1 with DCC has not been demonstrated. We cloned the human netrin-1 (NTN1L) gene, mapped it to chromosome 17p12‐13, and found that it encodes a 604 amino acid protein with 98% identity to mouse netrin-1 and 50% identity with the Caenorhabditis elegans UNC-6 protein. NTN1L transcripts were detected in essentially all normal adult tissues studied, and markedly reduced or absent NTN1L expression was seen in ;50% of brain tumors and neuroblastomas. In one neuroblastoma, missense mutations at highly conserved NTN1L codons were found. Netrin-1 protein could be cross-linked to DCC protein on the cell surface, but it did not immunoprecipitate with DCC in the absence of crosslinking and it failed to bind to a soluble fusion protein containing the entire DCC extracellular domain. Our findings demonstrating NTN1L loss of expression and mutations suggest that NTN1L alterations may contribute to the development of some cancers. Furthermore, the binding of netrin-1 to DCC appears to depend on the presence of a coreceptor or accessory proteins.