A2B5-reactive ganglioside expression determines the differentiation stage and capacity of rat insulinoma (RIN) sublines

We have generated rat insulinoma (RIN) sublines AlGh, m5F, A12, A13 and AhGh with increasing surface expression of the A2B5 ganglioside, a marker of differentiation. We asked whether the capacity of the sublines to differentiate was related to their stage of differentiation, as is characteristic of cells within the normal β-cell lineage. The answer this, we measured the effect of the differentiation inducer sodium butyrate (NaB, 1 mM) on proliferation, insulin content, secretion and biosynthesis, and the expression of A2B5 and 3G5 gangliosides by the sublines. Six days after exposure to NaB, cell numbers/dish ranged from (1–3) × 10⁶ compared to (4–6) × 10⁶ in control cultures. By day 2, AlGh, m5F, A12, A13 and AhGh cells exposed to NaB contained 1.5-, 1.4-, 1.4-, 1.2- and 1.0-fold higher amounts of insulin, respectively, and by day 6, 3.6-, 2.3- and 1.0-fold higher, and 1.2- and 2.4-fold lower, amounts of insulin, respectively, than control cells. After 2 days, insulin secretion from AlGh, m5F, A12, A13 and AhGh cells was 1.7-, 1.0-, 1.5-, 1.0- and 1.0-fold higher, respectively, and the rate of (pro)insulin biosynthesis 1.7-, 2.3-, 1.3-, 1.0- and 1.0-fold higher, respectively, than control cells. After 6 days, A2B5 ganglioside expression was increased 3-, 1.9- and 2-fold on m5F, A12 and A13 cells, respectively, but was not significantly altered on AlGh and AhGh cells. 3G5 ganglioside expression was increased 1.5- and 8.4-fold, respectively, on AlGh and m5F cells, but was unaltered on A12, A13 and AhGh cells. These results support the concept that the degree of RIN subline differentiation as induced by NaB reflects the pre-existing level of A2B5 ganglioside expression and therefore the stage of differentiation.