Is chromosome radiosensitivity and apoptotic response to irradiation correlated with cancer susceptibility?

PURPOSE: Individuals who have been treated for breast cancer have been reported to have increased lymphocyte chromosomal sensitivity to ionizing radiation and a significantly lower apoptotic response to irradiation compared to controls. We set out to test these findings using a substantial number of cases sampled before treatment (which could alter the parameters measured), compared to age-matched controls with normal mammograms. MATERIAL AND METHODS: We used the G2 chromosome breakage, and apoptotic response assays of peripheral blood lymphocytes to ionizing radiation to compare 211 unselected newly diagnosed and untreated breast cancer patients, with 170 age, sex and ethnically matched controls. RESULTS: We found no significant differences between breast cancer patients and their matched controls in the G2 assay or apoptotic response. However, there was some evidence that both cases and controls with a strong family history of breast cancer had higher radiosensitivity than those without. CONCLUSIONS: This is the largest and best controlled study of its kind, but it has not replicated previous reports of differences between chromosome breakage or apoptotic response in breast cancer cases vs. controls. However there was a suggestion of increased radiosensitivity in patients with a strong family history, which may indicate a heritable cancer susceptibility trait, warranting further study.

Reduction of TSG101 protein has a negative impact on tumor cell growth.

TSG101 was defined originally as a tumor-suppressor gene, raising the expectation that absence of the encoded protein should lead to increased tumor cell growth and, perhaps, increased tumor cell aggressiveness. We have used the RNA interference (RNAi) technique to downregulate TSG101 in PC3 (prostate cancer) and MDA-MB-231 (breast cancer) cells. An approximately 85% selective downregulation at the protein level was achieved in both cell lines over a period of 12 days as detected by Western blotting. This treatment resulted in inhibition of tumor cell growth, with a decreased level of TSG101 causing partial cell cycle arrest at the G(1)/S boundary and a reduction in the rate at which cells passed from G(2) through mitosis and back into G(1). In both cell lines, the percentage of cells in S-phase was reduced significantly at day 4 after the TSG101 siRNA transfection (27% vs. 41% in MDA-MB-231 cells; 22% vs. 39% in PC3 cells). Additionally, RNAi-mediated downregulation of TSG101 reduced the colony formation capacities of both cancer cell lines. Rather more surprisingly, TSG101 downregulation affected the migratory activity of the MDA-MB-231 cells, independent of any effect on proliferation. Thus, in a Transwell assay, after 4-hr incubation, 36.0% of control MDA-MB-231 cells had migrated to the lower chamber vs. 7.3% of TSG101-downregulated cells (p < 0.001; scrambled control, 36.5%). These results show that the TSG101 gene does not comply with the usual characteristics of a tumor-suppressor gene; rather, its expression may be necessary for activities associated with aspects of tumor progression.

Site-directed perturbation of protein kinase C- integrin interaction blocks carcinoma cell chemotaxis.

Polarized cell movement is an essential requisite for cancer metastasis; thus, interference with the tumor cell motility machinery would significantly modify its metastatic behavior. Protein kinase C alpha (PKC alpha) has been implicated in the promotion of a migratory cell phenotype. We report that the phorbol ester-induced cell polarization and directional motility in breast carcinoma cells is determined by a 12-amino-acid motif (amino acids 313 to 325) within the PKC alpha V3 hinge domain. This motif is also required for a direct association between PKC alpha and beta 1 integrin. Efficient binding of beta 1 integrin to PKC alpha requires the presence of both NPXY motifs (Cyto-2 and Cyto-3) in the integrin distal cytoplasmic domains. A cell-permeant inhibitor based on the PKC-binding sequence of beta 1 integrin was shown to block both PKC alpha-driven and epidermal growth factor (EGF)-induced chemotaxis. When introduced as a minigene by retroviral transduction into human breast carcinoma cells, this inhibitor caused a striking reduction in chemotaxis towards an EGF gradient. Taken together, these findings identify a direct link between PKC alpha and beta 1 integrin that is critical for directed tumor cell migration. Importantly, our findings outline a new concept as to how carcinoma cell chemotaxis is enhanced and provide a conceptual basis for interfering with tumor cell dissemination.