UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Regulation of early steps in malignant transformation by the surrounding non-transforming population : the role of cellular immortalization and aging Mohamedali, Zeid


Normal cells regulate the progression and growth of adjacent cells that undergo malignant transformation, but the precise nature of these interactions is not understood. This study investigated the role of immortalization and aging of the surrounding population in the regulation of v-Ha-ras infected cells in early stages of transformation. The surrounding population consisted of normal low passage (LP) rat adrenal fibroblasts, spontaneously (NRA-E) or SV40 (LP[sub sv40]) immortalized LP cells, and in vitro (HP) or in vivo (LP[sub old]) aged LP cells. Transforming cells from early (LP) and late (NRA-E) stages in the multistep process of malignant transformation were identified using either neomycin resistance or (β-galactosidase expression and the number of cells and colonies were counted. In the presence of regulating LP cells the number of transforming NRA-E or LP cells was reduced as compared to cultures where regulating immortal cells (either NRA-E or LP[sub sv40]) were added. Furthermore, HP or LP[sub old] aged regulating cells had decreased transformation inhibitory activity compared to regulating LP cells. The inhibitory activity of the regulating cells was mediated by a soluble paracrine factor; furthermore, gap junctional communication was not required for inhibition. The secreted LP cell inhibitory factor (LPIF) reduced the number of transforming cells and subsequent colonies within 48 h of being added and within 4 days of introducing the oncogene. LPIF was purified using both reverse phase C₁₈ and size exclusion 300SW HPLC. LPIF had an apparent molecular mass of approximately 18-20 Kd. SDS-PAGE revealed a single protein band at approximately 20 Kd. This investigation suggests that the latency periods seen in the development of clinical tumors may be influenced by the time needed for a change in the environment surrounding the transforming population and the subsequent response of the transforming cells to this change. This change, which in vitro was represented by immortalization or aging of the regulating cells, would lead to the loss of inhibitory factor(s).

Item Media

Item Citations and Data


For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.