PROTEIN EXPRESSION CHANGES ASSOCIATED WITH RADIATION-INDUCED NEOPLASTIC PROGRESSION OF HUMAN PROSTATE EPITHELIAL-CELLS

Carcinogenic progression in most epithelial systems is a multistep pro cess and presents as numerous (un)stable intermediate stages prior to the development of a fully malignant phenotype. Recently, we reported the neoplastic transformation of an SV40 immortalized, neonatal human prostate epithelial cell line (267B1) by multiple exposures to X-rays [1, 2]. The parental 267B1 cells acquired anchorage-independence and e xhibited morphological transformation following exposure to two consec utive doses of 2 Gy. Exposure of either the parental 267B1 cells or th e anchorage-independent derivatives (F3-SAC) to a total dose of 30 Gy of X-rays yielded tumorigenic transformants (267B1-XR and 267B1-SXR, r espectively). All of these radiation-treated derivatives (F3-SAC, 267B 1-XR, and 267B1-SXR) were characterized by reduced cell size and poorl y organized actin stress fibers [2, 3]. The present study examines the protein expression changes associated with cytoskeletal alterations d uring the different steps of neoplastic progression induced by X-rays in the in vitro human prostate cell system. This analysis was achieved by using the high resolving power of two-dimensional polyacrylamide g el electrophoresis (2-D PAGE) in the 267B1, F3-SAC, 267B1-XR, and 267B 1-SXR cells. We report changes in the expression of gelsolin in the pa rtially transformed, anchorage-independent, nontumorigenic (F3-SAC) ce lls and a progressive loss of expression of tropomyosin isoforms (TM-1 and TM-3), and myosin light chain-2 (MLC-2) in the tumorigenic (267B1 -XR; 267B1-SXR) cells, respectively. In contrast, our results demonstr ate that the levels of the small GTP-binding protein Rho-A, an active participant in the actin stress fiber organization, are not altered du ring neoplastic progression of these 267B1 cells. Thus the changes in synthesis of gelsolin, tropomyosins, and MLC-2 provide a rationale for the alterations in the actin stress fiber formation and reduction in cell size during the exposure of prostate epithelial cells to multiple doses of X-rays.