PARENT SESSION
1:30 PM to 3:30 PM
Tuesday, April 23, 2002
Poster Session 24 Signal Transduction
Room: Nevada Exhibition Center

(P29-288) Ras-mediated radiation resistance via autocrine pathways.

Grana, Theresa^*,1,2,3, Zhou, Hong^2,3, Sartor, Carolyn^2,3, Cox, Adrienne^1,2,3,4, ¹ Curriculum in Genetics and Molecular Biology, Chapel Hill, NC² Dept. of Radiation Oncology, Chapel Hill, NC³ Lineberger Comprehensive Cancer Center, Chapel Hill, NC⁴ Dept. of Pharmacology, Chapel Hill, NC

ABSTRACT-
Ras-transformed cells survive exposure to ionizing radiation (IR) better than non-transformed cells, but the mechanisms by which the radioresistant phenotype is conferred are currently not well defined. Evidence from our lab and others shows that Ras-mediated PI3-K activity contributes to radioresistance, and that inhibition of PI3-K partially radiosensitizes Ras-transformed cells. On the other hand, ERK, JNK and p38 MAPK activity do not appear to play a role in Ras-mediated radioresistance. These results led us to investigate another downstream effector of Ras, NF-B, whose activity is altered by PI3-K effectors. Inhibition of NF-B activity with the proteasome inhibitor PS-341 or SR-I-B led to radiosensitization. We are also investigating the role of Ras-mediated autocrine loops in radioresistance. Transformation of RIE-1 rat intestinal epithelial cells by oncogenic Ras has been shown to trigger upregulation of an EGFR-family autocrine loop that is required for the transformed phenotype. Upregulation of TGF, amphiregulin, and HB-EGF all contribute to Ras transformation. We asked whether a similar pathway contributes to Ras-mediated radioresistance. We observed that conditioned medium from H-, N- or K-Ras-transformed cells dramatically increased EGFR receptor tyrosine phosphorylation and induced a transformed phenotype in untransformed RIE-1 cells, as demonstrated by morphological alteration, scattering and increased motility. Further, HER-2, -3 and -4 tyrosine phosphorylation was also highly increased by oncogenic Ras. Therefore, we determined the effects on post-IR clonogenic survival of conditioned medium from RIE cells expressing vector only or the three different Ras isoforms. Our results indicate that Ras-transformed cells display a complex interplay of normal and deregulated receptor modulation that is altered by ionizing radiation. Taken together, our results suggest that an autocrine loop downstream of oncogenic Ras participates in Ras-mediated radioresistance. It will be interesting to determine if regulation of this autocrine loop occurs through PI3-K or through another Ras effector.

KEYWORDS: ras, signaling, radioresistance, EGFR family