Department of Pharmacology and Therapeutics
Roswell Park Cancer Institute
Elm and Carlton Streets
Buffalo NY USA 14263
Tel: 716 - 845 - 1548
Fax: 716 - 845 - 8857
E-mail: athena.lin@roswellpark.org

Education
PhD, University of Massachusetts, Amherst, 1995
BS, Pharmacy, China Medical College, Taiwan, 1985
Postdoctoral Fellow, Coldspring Harbor Laboratory, Coldspring Harbor, NY

 

Program

Oncogenes, tumor suppressor, Ras signaling, senescence, DNA damaging agents, neoplastic transformation, genetic alterations

During the past decade, extensive studies on tumor suppression have mainly focused on apoptosis. While apoptosis presents an excellent means to eliminate cancer cells, effective cancer therapy remains challenging. Recently, there is an emerging view of cellular senescence as an alternate tumor suppression mechanism to apoptosis. Our previous studies have demonstrated that, by signaling through the MAPK pathway, oncogenic H-ras induced a senescence-like permanent growth arrest in normal cells. This H-ras-induced senescence is preceded by a mitogenic phase and involves the activation of the tumor suppressors p53, p16 and ARF. Moreover, cells derived from gene knockout mice deficient in p53 or ARF tumor suppressors can escape H-ras-induced growth arrest and are rendered tumorigenic. These findings indicate that oncogenic H-ras signaling is coupled to tumor suppressor pathways, whose activation can trigger a senescence-like permanent growth arrest (cellular senescence) in normal cells. Understanding the mechanisms by which oncogenic ras signaling induces senescence may help to develop novel therapeutic interventions.

While the ARF tumor suppressor is essential for oncogenic H-ras-induced senescence in primary mouse cells, oncogenic H-ras-induced senescence in IMR90 normal human fibroblasts does not involve induction of ARF. This observation suggests that, depending on the cellular context, oncogenic H-ras can signal through alternative mechanisms to induce cellular senescence. Therefore, the first research interest in this laboratory is to study the activation mechanisms of oncogenic-ras-induced cellular senescence in human cells. The approaches include retroviral gene transfer, siRNA as well as the proteomic analysis. The long-term goal of this research is to explore the potential role of cellular senescence as a tumor suppression mechanism
The observation that normal cells can undergo senescence in response to oncogenic stimuli is consistent with the notion that normal human cells are refractory to oncogenic transformation. In this regard, oncogenic ras-induced senescence can be viewed as a cellular safeguard mechanism to prevent neoplastic transformation. This cellular safeguard mechanism involves the activation of tumor suppressor pathways. Interruption of this senescence program by viral oncogenes, such as SV40 T or E1A, can lead to immortalization of human cells, presumably by inactivation of the p53 and Rb tumor suppressor pathways. While the combined expression of oncogenic ras and the viral oncogene, E1A, provided one of the first demonstrations of neoplastic transformation by cooperating oncogenes in primary rodent cells, the same gene combination typically initiates immortalization but not transformation of normal human cells. Additional genetic alterations are required to cause neoplastic transformation. In some instances, these involve up-regulation of telomerase activity, while in others, telomerase-independent mechanisms may prevail since it has been shown that combined expression of three oncogenes can cause transformation in human fibroblasts. Neoplastic transformation of normal human cells is an exceedingly rare event in cell culture, and the identification of such cells provides a valuable opportunity to further elucidate the molecular mechanisms involved in neoplastic transformation of normal human cells.

IMR90 normal human fibroblasts immortalized via the introduction of oncogenic ras and E1A have served as a cell model in our numerous studies on senescence and apoptosis. We recently derived a spontaneously transformed tumorigenic cell line from these oncogene-immortalized cells. We hypothesize that characterization of the genetic alterations detected in these unique cells will lend important insights into the nature of neoplastic transformation. Therefore, a second line of research interest in this laboratory is to identify and functionally characterize the genetic changes that are crucial in conferring the transformed phenotype in human cells. The long-term goal of this research is to dissect the mechanism by which oncogenes and tumor suppressor genes cooperate to cause neoplastic transformation in human cells.

Progress

We have recently characterized the gene expression profiles of oncogenic H-ras-induced senescent IMR90 normal human fibroblasts, using the Affymetrix GeneChip Array Technology. This time course analysis successfully revealed numerous candidate genes whose expressions were significantly altered in oncogenic H-ras-induced senescent IMR90 cells. Many of these identified genes play important roles in replication, transcription, cell cycle progression, and nuclear organization. We have verified the expression of many of the candidate genes and several of them are being functionally characterized for their roles in mediating cellular senescence.

The notion that senescence can be activated through alternative pathways is intriguing. We have recently observed that tumor cells can also undergo a senescence-like permanent growth arrest in response to DNA damaging agents or oncogenic ras signaling. These observations suggest that tumor cells may harbor a senescence-like program that can be activated. Because many of the tumor suppressor pathways involved in senescence are inactivated in tumor cells, we are currently dissecting the mechanisms by which DNA damaging agents or oncogenic ras signaling trigger a senescence-like permanent growth arrest in these tumor cells.

To identify the genetic alterations that confer tumorigenicity in human cells, we have performed genomic analysis (CGH BAC array), molecular cytogenetic analysis (SKY) and biochemical analysis of the spontaneously transformed tumorigenic cells and their parental immortalized cells. We have identified chromosomal changes that are specific in the spontaneously transformed tumorigenic cells. Current study focuses on the identification of the crucial genes involved in conferring the transformed phenotype in these cells.

Select Publications

• Serrano M, Lin AW, McCurrach ME, Beach D, Lowe SW. Oncogenic ras provokes premature senescence associated with accumulation of p53 and p16ink4a. Cell 88:593-602, 1997
• Lin AW, Barradas M, Stone J, van Aelst L, Serrano M, Lowe SW. Premature senescence involving p53 and p16 is activated in response to constitutive MEK/MAPK mitogenic signaling. Genes & Development 12(19):3008-3019, 1998
• Lowe SW, Lin AW. Apoptosis in cancer (review article). Carcinogenesis 21(3):485-495, 2000
• Lin AW, Lowe SW. Oncogenic ras activates the ARF-p53 pathway to suppress epithelial cell transformation. PNAS 98(9):5025-5030, 2001
• Ferbeyre G, de Stanchina E, Lin AW, Querido E, McCurrach M, Hannon GJ, Lowe SW. Oncogenic ras converts tumor suppressor p53 to activate a senescence program. MCB 22(10):3497-3508, 2002
• Kondo S, Lu Y, Debbad M, Lin AW, Sarosi I, Itie A, Wakeham A, Tuan J, Saris C, Elliott G, Ma W, Benchimol S, Low SW, Mak TW, Thurkral SK. Characterization of cells and gene-targetd mice deficient for the p53-binding kinase HIPK1. PNAS 100:5431-5436, 2003
• Narita M, Nunez S, Heard E, Narita M, Lin AW, Hearn S, Spector DL, Hannon GJ, Lowe SW. Rb-mediated heterochromatin formation and silencing of E2F target genes during cellular senescence. Cell 113:703-71, 2003
• Bihani T, Mason DX, Jackson TJ, Chen CS, Bottner B, Lin AW. Differential Oncogenic ras signaling and senescence in tumor Cells. Cell Cycle. 3(9): 1201-1207, 2004
• Mason DX, Jackson TJ, Lin AW. Molecular signature of oncogenic ras-induced senescence. Oncogene.23: 9238-9246, 2004.
• Weebadda WK, Jackson TJ, Lin AW. Expression of p16 variants in senescent fibroblasts independent of protein phosphorylation. J. Cellular Biochem Jan 24, 2005 Epub ahead of print
• Mason DX, Zhang J, Keppler D, Jackson TJ, Seger YR, Matsui S, Cowell J, Hannon GJ, Lowe SW, Lin AW. Defined genetic events associated with the spontaneous in vitro transformation of ElA/Ras-expressing human IMR90 fibroblasts. Submitted