EXPRESSION OF THE RETINOBLASTOMA (RB) TUMOR-SUPPRESSOR GENE INHIBITS TUMOR-CELL INVASION IN-VITRO

To determine if replacement of the retinoblastoma (RE) tumor suppresso r gene could inhibit invasion of RB-defective tumor cells, the capacit y of tumor cells to migrate or invade was quantitated by the Boyden ch amber assay, The studies were done in a diverse group of stable RE-rec onstituted human tumor cell lines, including those derived from the os teosarcoma and carcinomas of the lung, breast and bladder, The express ion of the exogenous wildtype RE protein in these tumor cell lines was driven by either a constitutively active promoter or an inducible pro moter, It was found that significantly more tumor cells from the paren tal RE-defective cell lines and the RB(-) revertants than from the RE- reconstituted RB(+) cell lines penetrated through the Matrigel (P < 0. 001, two-tailed t-test), although both RB(+) and RB(-) cells migrated at approximately the same rate on uncoated polycarbonate filters in th e Boyden chambers, Of note, the inhibition of invasiveness of various RE-defective tumor cells by RE replacement was apparently web correlat ed with suppression of their tumorigenicity in vivo. In contrast, alth ough either functional RE or p53 re-expression effectively suppressed tumor formation in nude mice of the RB(-)/p53(nuII) osteosarcoma cell line, Saos-2, replacement of the wild-type p53 gene had much less impa ct on their invasiveness as compared to the RE gene, These studies pro vided an insight into the broader biological basis of the RE-mediated tumor suppression in RE-defective tumor cells.