Effect of Transformation on Rat Prostatic Fibroblasts: Alterations in Extracellular Matrix and Cytoskeleton Gene Expression with Retention of Androgen Responsiveness and Androgen Receptor Expression

Abstract

The NbF-1 fibroblast cell line was derived in our laboratory from normal adult rat ventral prostate (Chung et al., Int. J. Cancer 43:1179,1989). Between the 25th and 30th passage the cell line became transformed spontaneously and late passage cells are capable of forming rapidly growing fibrosarcomas in syngeneic animals. In this communication we present the results of experiments designed to determine the effects of spontaneous transformation on NbF-l cells with regard to karyotypic stability, biochemical properties, gene expression and hormonal sensitivity. Gross chromosomal differences, as assessed by Gbanding analyses, between pre-transformed and tumorigenic NbF-1 cells were minor. Tumorigenic NbF-1 cells maintained a normal modal chromosome number and a trisomic chromosome 4 was the only chromosome abnormality that was acquired with tumorigenicity and persisted in the culture with later passages. Transformation, however, resulted in major phenotypic alterations. Extensive analysis of extracellular matrix (ECM) expression revealed profound changes correlating with the acquisition of tumorigenesis. In comparison with early passage NbF-1 cells, tumorigenic NbF-1 cells expressed decreased levels of mRNAs for fibronectin, collagens I, III, and IV, and laminins Bl and B2. The greatest alternation in mRNA expression, a ca. 20-fold decline in transcript levels, was observed for α2 collagen IV. Similarly, synthesis and expression of chondroitin sulfate proteoglycan and glycosaminoglycan declined markedly (ca. 90%) with transformation. Notably, in contrast to ECM, expression of vimentin and actin cytoskeletal protein mRNAs increased (2-2.5 fold) and androgen receptor (AR) mRNA and high affinity androgen receptor, measured by ligand exchange assay, increased slightly (ca. 1.5-fold increase). Transformed NbF-1 cells remain sensitive to mitogenic stimulation by dihydrotestosterone (DHT) in vitro and tumor growth in vivo is androgen responsive. Mitogenic effects of DHT correspond with a rapid induction of ornithine decarboxylase mRNA expression.

These results indicate that: 1. A prostatic cell type can retain androgen responsiveness, AR expression, and apparent AR function despite substantial transformation-associated pleiomorphic change. 2. A highly tumorigenic phenotype can be acquired rapidly and with minimal genetic alteration. 3. In cbntrast to AR expression, extensive change in ECM and cytoskeletal protein gene expression may occur early in tumorigenic transformation. Inverse changes in ECM and cytoskeletal mRNAs may reflect a regulatory interdependence between the ECM and the cytoskeletal protein systems and is likely to be associated directly with gross cell structure changes that accompany tumorigenicity.