RESUMO
The human renal carcinoma cell (RCC) line ACHN proliferates in the absence of exogenous growth factors and secretes a 178-kilodalton growth-promoting substance (GPS). Complementary DNA (cDNA) was isolated that coded for polypeptides antigenically cross-reactive with GPS. Nucleotide sequencing of the cDNA showed strong homology with human fibronectin (FN). The deletion of an adenine in human FN codon 1482 caused a reading-frame shift that predicted early termination of translation after 1518 amino acid residues. Western immunoblotting human FN and GPS with anti-human FN antibodies showed that GPS was a truncated FN. Previous work found that malignant cells synthesized, bound, and deposited into the extracellular matrix decreased amounts of FN. Addition of this substance to transformed cells changed their morphology but not their rate of growth. By contrast, partial proteolysis of FN resulted in a prominent 180-kilodalton fragment that stimulated DNA synthesis. Similar to this finding, the authors showed that truncation of fibronectin during synthesis appeared to unmask latent DNA synthetic stimulating activity. Polymerase chain reaction methods using genomic DNA from normal kidneys and RCC and primers specific for the GPS-human FN gene showed two products of identical size, indicating that genomic amplification did not cause activation of the human FN gene in RCC to produce GPS. Restriction-fragment length analysis demonstrated identical patterns in DNA extracted from both normal kidneys and RCC, suggesting that chromosomal rearrangements did not activate the GPS-human FN gene. This study showed that genetic changes detectable only by DNA sequencing can explain the activation of the normal human FN gene to produce GPS, a product important for autologous growth stimulation of RCC.
