RAC1 and melanoma: Another possible explanation for the morphological changes exhibited by B16 melanoma cells exposed to narrow-band UVB radiation is the up- or downregulation of these small GTPases, which is based on the findings of previous studies, according to which Rac1 activation and RhoA inhibition induce elongation of the dendrites and the activated RhoA stimulates dendrite retraction (5,22–24).