Protein expression changes associated with radiation‐induced neoplastic progression of human prostate epithelial cells

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Abstract
Carcinogenic progression in most epithelial systems is a multistep process 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 exhibited morphological transformation following exposure to two consecutive doses of 2 Gy. Exposure of either the parental 267B1 cells or the anchorage‐independent derivatives (F3‐SAC) to a total dose of 30 Gy of X‐rays yielded tumorigenic transformants (267B1‐XR and 267B1‐SXR, respectively). All of these radiation‐treated derivatives (F3‐SAC, 267B1‐XR, and 267B1‐SXR) were characterized by reduced cell size and poorly organized actin stress fibers [2, 3]. The present study examines the protein expression changes associated with cytoskeletal alterations during 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 gel electrophoresis (2‐D PAGE) in the 267B1, F3‐SAC, 267B1‐XR, and 267B1‐SXR cells. We report changes in the expression of gelsolin in the partially transformed, anchorage‐independent, nontumorigenic (F3‐SAC) cells 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 demonstrate that the levels of the small GTP‐binding protein Rho‐A, an active participant in the actin stress fiber organization, are not altered during 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.