Expressions of Rac1, Tiam1 and Cdc42 in retinoblastoma

The Rho GTPases are the molecular regulators of the cell motility processes and are involved in cell cycle progression and gene transcription. We studied the expression of Rho-like GTPases molecules, particularly Rac, Tiam1 and cdc42, in retinoblastoma and correlated these with clinicopathological parameters of the tumors. Sixty-seven tumors were included which were divided in to two groups; group A: tumors with optic nerve/choroidal/orbital invasion (n=35) and group B: tumors with no invasion (n=32). Immunohistochemistry was done on paraffin sections for all the proteins and were confirmed by Western blot on fresh tumor samples. In group A tumors, Rac was positive in 10/35 (28%), cdc42 was positive in 12/35 (34%) and Tiam1 was positive in 30/35 (85%) tumors. In group 2 tumors, Rac was positive in 5/32 (15%), cdc42 was positive in 4/32 (12%) and Tiam1 was positive in 30/32 (93%) tumors. Two groups (both invasive and non-invasive tumors) showed decreased expression of Rac1 and cdc42 whereas Tiam1 was significantly expressed in invasive tumors compared to non-invasive tumors (P<0.0001). We observed a 70K cleavage product of Tiam1 along with an 110K product by blotting in RB samples. Caspase-3 was also demonstrated in RB samples, which showed Tiam1 cleavage products. This is the first study that showed the expression patterns of Rac, cdc42 and Tiam1 in retinoblastoma tumors. Thus, further studies are required to prove the involvement of caspase-3 in the cleavage of Tiam1 in vitro in RB cells and to trace out alternative pathways involved in tumor progression.