Introduction

As discussed in Chapter 10, insulinomas can be induced in experimental animals by diabetogenic agents such as streptozotocin and alloxan (Lazarow, 1952; Rakieten et al., 1971; Yamagami et al., 1985) and by viruses (Uchida et al., 1979). A unifying concept was proposed for the diabetogenic and oncogenic effects of the B-cytotoxins, in which the principal action of streptozotocin and alloxan was considered to be the induction of lesions in the DNA of B-cells of islets of Langerhans (see Fig. 10.5). To elucidate the molecular mechanisms of B-cell oncogenesis, we have looked for genes whose expression is altered in insulinomas. We identified a novel gene named rig (rat insulinoma gene), which is activated in chemically induced rat insulinomas (Takasawa et al., 1986). The gene was also activated in virus-induced hamster insulinomas and in spontaneously occurring human insulinomas (Inoue et al., 1987).

Isolation of rig from insulinomas

The combined administration of streptozotocin or alloxan with poly(ADP-ribose) synthetase inhibitors such as nicotinamide to rats induces a high incidence of insulinomas (Yamagami et al., 1985). We constructed a cDNA library from poly(A)+ RNA of rat insulinomas induced by the combined administration of streptozotocin and nicotinamide (Takasawa et al., 1986). From this library, independent clones were duplicated on nitrocellulose filters for differential screening. One set of filters was hybridized to 32P-labeled cDNA that was reverse-transcribed from poly(A)+ RNA of insulinomas with [32P]deoxycytidine triphosphate (dCTP) and oligo(dT) as primer. The other set of filters was hybridized to 32P-labeled cDNA synthesized from poly(A)+ RNA of normal islets.